Dr Chris McKay in California's Mojave Desert. Credit: NASA Ames Imaging Library System (AILS)

What is life? It’s a Tricky, Often Confusing Question.

Dr Chris McKay and Monika Kress, Professor of Astronomy at San Jose State University on a Spaceward Bound event in the Mojave Deser, CA. Credit: NASA Ames Imaging Library System (AILS)

Dr Chris McKay and Monika Kress, Professor of Astronomy at San Jose State University on a Spaceward Bound event in the Mojave Deser, CA. Credit: NASA Ames Imaging Library System (AILS)

What is life? This is a question that is often asked and typically confused.

The confusion starts from the several uses of the word “life” in English. There are at least three usages as exemplified by the following questions:

1) Is there life on Mars?

2) Is there life in this organism?

3) Is life worth living?

The definition of “life” in these three usages is quite different. In the first case, life refers to a collective phenomenon, in the second case it refers to the ability of an individual organism to metabolize and grow, and in the third case life refers to the history of activities that an organism undertakes. The first two usages are of direct relevance to astrobiology.

The usual definition of life, as used in the first case, is that it is a system of material entities that can undergo evolution, which implies reproduction, mutation and selection. This is what we are looking for on Mars and on other worlds. We would be most interested if it represented a second genesis, in other words an independent origin of life. It is often pointed out that the definition of life as a system capable of evolution implies that single, isolated individuals not of child-bearing age are not “life.” This is nonsense and confuses the first and second cases of “life.”

Dr Chris McKay in California's Mojave Desert. Credit: NASA Ames Imaging Library System (AILS)

Dr Chris McKay in California’s Mojave Desert. Credit: NASA Ames Imaging Library System (AILS)

Many commentators hold the view that an effective search for life on other worlds requires that we first have a concise, agreed on, definition of life. This is not the case. Along this line, it has been suggested that once we understand life we will be able to produce a completely mechanistic and predictive theory of life. The example of water is sometimes used. Water is simply defined as two hydrogens joined with one oxygen. However, life is not a simple substance like water, rather it is a process, more like fire than water. There is no simple definition of fire. If life is like fire then even with a complete mechanistic and predictive theory of life we may still not be able to define it in any simple closed form. The search for life on other worlds can be based on what life does rather that its definition. One of the things that life does is build up large specialized molecules, such as DNA and proteins.

Alfonso Davila (l), Denis Lacelle and Chris McKay (r) perform improvised field surgery on drilling equipment during an expedition in Antarctica. The procedure lasted more than an hour but was ultimately successful. Credit: Jen Heldmann

Alfonso Davila (l), Denis Lacelle and Chris McKay (r) perform improvised field surgery on drilling equipment during an expedition in Antarctica. The procedure lasted more than an hour but was ultimately successful. Credit: Jen Heldmann

Viking, the only mission to search for life on another world (that being Mars), focused on the second case. The Viking biology experiments searched for something alive in the sample. The assumption was that if something was alive it would be able to consume organics and release gases; it would have a metabolism. Hence the operational definition of “life” in the Viking biology experiments was the ability to metabolize in the conditions of the experiment.

There are several problems with this operational definition. First, there are many non-biological processes the can consume organics and/or release gases. Second, experience on Earth shows that many micro-organisms are picky eaters and do not grow in laboratory conditions with nutrients added. Perhaps the most severe problem with the Viking approach is that it cannot detect organisms that are dead, which unfortunately is the most likely state of organisms on Mars (or on the surface of Europa, or in the plume of Enceladus). In fact, in the search for life in our solar system what is needed more than a definition of life is a definition of death.

What does it mean to be dead? It means that the organism was once alive and is composed of organic molecules that are specific to life — molecules such as DNA, ATP, and proteins. These are biomarkers that would be compelling evidence that the organism was once alive and is the product of a system of life that has undergone evolution over time. The search for such biomarkers is the basis for life-search methods now being considered. The challenge is to design instruments that can search for biomarkers for Earth-like life and also can detect biomarkers of unknown alien life.


A Planet That Makes Its Star Act Deceptively Old

A planet may be causing the star it orbits to act much older than it actually is, according to new data from NASA’s Chandra X-ray Observatory. This discovery shows how a massive planet can affect the behavior of its parent star.

X-ray: NASA/CXC/SAO/I.Pillitteri et al; Optical: DSS; Illustration: NASA/CXC/M.Weiss

X-ray: NASA/CXC/SAO/I.Pillitteri et al; Optical: DSS; Illustration: NASA/CXC/M.Weiss

The star, WASP-18, and its planet, WASP-18b, are located about 330 light-years from Earth. WASP-18b has a mass about 10 times that of Jupiter and completes one orbit around its star in less than 23 hours, placing WASP-18b in the “hot Jupiter” category of exoplanets, or planets outside our solar system.

WASP-18b is the first known example of an orbiting planet that has apparently caused its star, which is roughly the mass of our sun, to display traits of an older star.

“WASP-18b is an extreme exoplanet,” said Ignazio Pillitteri of the Istituto Nazionale di Astrofisica (INAF)-Osservatorio Astronomico di Palermo in Italy, who led the study. “It is one of the most massive hot Jupiters known and one of the closest to its host star, and these characteristics lead to unexpected behavior. This planet is causing its host star to act old before its time.”

Pillitteri’s team determined – WASP-18 is between 500 million and 2 billion years old, based on theoretical models and other data. While this may sound old, it is considered young by astronomical standards. By comparison, our sun is about 5 billion years old and thought to be about halfway through its lifetime.

Younger stars tend to be more active, exhibiting stronger magnetic fields, larger flares, and more intense X-ray emission than their older counterparts. Magnetic activity, flaring, and X-ray emission are linked to the star’s rotation, which generally declines with age. However, when astronomers took a long look with Chandra at WASP-18 they didn’t detect any X-rays. Using established relations between the magnetic activity and X-ray emission of stars, as well as its actual age, researchers determined WASP-18 is about 100 times less active than it should be.

“We think the planet is aging the star by wreaking havoc on its innards,” said co-author Scott Wolk of the Harvard-Smithsonian Center for Astrophysics in Cambridge, Massachusetts.

The researchers argue that tidal forces created by the gravitational pull of the massive planet – similar to those the moon has on Earth’s tides, but on a much larger scale – may have disrupted the magnetic field of the star.

The strength of the magnetic field depends on the amount of convection in the star, or how intensely hot gas stirs the interior of the star.

“The planet’s gravity may cause motions of gas in the interior of the star that weaken the convection,” said co-author Salvatore Sciortino also of INAF-Osservatorio Astronomico di Palermo in Italy. “This has a domino effect that results in the magnetic field becoming weaker and the star to age prematurely.”

WASP-18 is particularly susceptible to this effect because its convection zone is narrower than most stars. This makes it more vulnerable to the impact of tidal forces that tug at it.

The effect of tidal forces from the planet may also explain an unusually high amount of lithium found in earlier optical studies of WASP-18. Lithium is usually abundant in younger stars, but over time convection carries lithium to the hot inner regions of a star, where it is destroyed by nuclear reactions. If there is less convection, the lithium does not circulate into the interior of the star as much, allowing more lithium to survive.

These results were published in the July issue of Astronomy and Astrophysics and are available online.

Michio Kaku, 2012. Credit: Wikimedia CC

Quão Avançados Eles Podem Ser?: A Física das Civilizações Extraterrestres

This interview with Dr. Michio Kaku was originally published in English on Apr 26, 2004. This translation for the Portuguese edition of Astrobiology Magazine was provided by Bruno Martini. The original article is available here.

Michio Kaku, 2012. Credit: Wikimedia CC

Michio Kaku, 2012. Credit: Wikimedia CC

Para considerar mundos habitáveis, civilizações avançadas, como encontrar e classificá-las, a Astrobiology Magazine teve a chance de descobrir com o Dr. Michio Kaku que as leis da física têm muito a dizer sobre as possibilidades – pelo menos muito mais do que onde você esperaria que a especulação o levasse a partir deste nosso cantinho do Universo.

O Dr. Michio Kaku graduou-se em Harvard em 1968 com as maiores honrarias e como número um em sua turma de física. Ele foi para o Berkeley Radiation Laboratory (Laboratório de Radiação Berkeley) da University of California (Universidade da Califórina) em 1972 e em 1973, Dr. Kaku organizou uma conferência na Princeton University (Universidade de Princeton). Hoje ele ocupa a cadeira Henry Semat de Física Teórica na City University of New York – CUNY (Universidade da Cidade de Nova Iorque), onde ele tem lecionado por mais de 25 anos.

O Dr. Kaku é uma autoriadade internacionalmente reconhecida em física teórica e em meio-ambiente. Seus mais populares e mais vendidos livros incluem “Hiperespaço: Uma Odisseia Científica Através de Universos Paralelos, Empenamentos do Tempo e a Décima Dimensão”, “Visões do Futuro: Como a Ciência Revolucionará o Século XXI”, que vêm sendo amplamente traduzidos em distintos idiomas. Toda semana ele apresenta um programa de uma hora chamado “Explorations in Science” (Explorações na Ciência), que cobre tópicos em ciência, tecnologia, guerra e política.


Astrobiology Magazine (AM): Você pode comentar sobre como a física tem mudado o lugar da Terra de uma posição de raridade (ou Antropomorfismo) para a visão de nossa posição como um cantinho entre possivelmente bilhões de mundos habitáveis disponíveis para a evolução de vida complexa

Michio Kaku (MK): A pergunta não é mais uma questão de especulação inútil. Em breve a humanidade irá encarar um choque existencial quando a atual lista de uma dezena de planetas extrassolares do tamanho de Júpiter se elevar para centenas de planetas do tamanho da Terra, quase irmãos gêmeos de nossa terra natal celeste. Isto pode anunciar uma nova era em nosso relacionamento com o Universo. Nós nunca mais iremos ver o céu noturno da mesma forma novamente, nos dando conta de que os cientistas podem eventualmente compilar uma enciclopédia identificando as precisas coordenadas de talvez centenas de planetas como a Terra.

Hoje em dia, a cada poucas semanas surgem noticias de um novo planeta extrassolar do tamanho de Júpiter sendo descoberto, o último estando a uns 15 anos-luz de distância, orbitando a estrela Gliese 876. A mais espetacular destas descobertas foi fotografado pelo Hubble Space Telescope (Telescópio Espacial Hubble), que capturou fotos de tirar o fôlego de um planeta a 450 anos-luz de distância sendo lançado para o espaço por um sistema estelar duplo.

Mas o melhor ainda está por vir. Logo no início da próxima década, cientistas lançarão um novo tipo de telescópio, o telescópio espacial de interferometria, que usa a interferência dos feixes de luz para ampliar o poder de resolução dos telescópios.

Por exemplo, a Space Interferometry Mission – SIM (Missão de Interferometria Espacial), a ser lançada no final desta década, consiste em múltiplos telescópios posicionados ao longo de uma estrutura de 30 pés (quase 10 m). Com uma resolução sem precedentes que se aproxima dos limites da óptica, a SIM é tão sensível que ela quase desafia nossa crença, já que pode detectar o movimento de uma lanterna sendo agitada por um astronauta em Marte!

SIM com lançamento planejado para 2009, cancelado em 2010. Crédito: NASA/JPL

SIM com lançamento planejado para 2009, cancelado em 2010. Crédito: NASA/JPL

A SIM, por sua vez, irá pavimentar o caminho para o Terrestrial Planet Finder (Buscador de Planetas Terresters), a ser lançado na próxima década, que deverá identificar ainda mais planetas como a Terra. Ele irá escanear as 1.000 estrelas mais luminosas dentro de 50 anos-luz da Terra e irá focar nos 50 a 100 sistemas planetários mais brilhantes.

Tudo isto, por sua vez, estimulará um esforço ativo para determinar se algum deles abriga vida, talvez algum com civilizações mais avançadas que a nossa.

AM: Como se pode começar a considerar este panorama cientificamente?

MK: Apesar de ser impossível prever as características exatas de tais civilizações avançadas, seus esboços gerais podem ser analisados pelas leis da física. Não importa quantos milhões de anos separam nós deles, eles ainda têm de obedecer às leis de ferro da física, que agora são avançadas o suficiente para explicar tudo das partículas sub-atômicas para a estrutura em larga escala do Universo, através de vertiginosas 43 ordens de magnitude.

Especificamente, podemos ranquear as civilizações pelo seu consumo de energia, usando os seguintes princípios:

1) As leis da termodinâmica. Mesmo uma civilização avançada é limitada pelas leis da termodinâmica, especialmente a Segunda Lei, e podem portanto ser ranqueadas pela energia à sua disposição.

2) As leis da matéria estável. Matéria bariônica (Ex: a baseada em prótons e nêutrons) tende a se acumular em três grandes agrupamentos: planetas, estrelas e galáxias (isto é bem definido pelo produto da evolução estelar e galáctica, fusão termonuclear, etc). Então, esta energia também será baseada nestes três tipos distintos e isto coloca limites superiores nas suas taxas de consumo de energia.

3) As leis da evolução planetária. Qualquer civilização avançada tem de crescer em consumo de energia mais rapidamente que a frequência de catástrofes ameaçadoras da vida (Ex: impactos de meteoros, idades do gelo, supernovas, etc). Se elas crescerem mais lentamente, são condenadas à extinção. Isto coloca limites matemáticos inferiores na taxa de crescimento destas civilizações.

Em um artigo pioneiro publicado em 1964 no Journal of Soviet Astronomy, o astrofísico russo Nicolai Kardashev teorizou que civilizações avançadas devem ser então agrupadas em três tipos: Tipo I, II e III, que dominaram formas de energia planetária, estelar e galáctica, respectivamente. Ele calculou que o consumo de energia destes três tipos de civilização seria separado por um fator de muitos bilhões.

AM: Quanto tempo levaria para uma civilização alcançar os patamares de Tipo II e III?

MK: O astrônomo de Berkeley Don Goldsmith nos lembra que a Terra recebe cerca de um bilionésimo da energia do Sol e que humanos utilizam aproximadamente um milionésimo dela. Então nós consumimos aproximadamente um milhão de bilionésimos do total de energia do Sol. No momento, nossa produção total de energia planetária é de uns 10 bilhões de bilhões de ergs por segundo. Mas nosso consumo de energia está crescendo exponencialmente e por isto podemos calcular quanto levará para crescer até os patamares do Tipo II e III.

Freeman Dyson. Image Credit: Trustees of Dartmouth College

Freeman Dyson. Crédito: Trustees of Dartmouth College

Goldsmith diz “veja quão longe chegamos no uso de energia desde que descobrimos como manipular energia, como fazer combustíveis fósseis realmente funcionar, como criar potência elétrica da energia hidráulica e por aí vai. Nós chegamos a usos de energia em uma quantidade extraordinária em apenas uns dois séculos, em comparação com os bilhões de anos em que o nosso planeta está aqui… E este mesmo tipo de coisa pode se aplicar a outras civilizações.

O físico Freeman Dyson do Institute for Advanced Study (Instituto de Estudo Avançado) estima que, dentro de 200 anos ou mais, deveremos alcançar o patamar do Tipo I. De fato, crescendo a uma moderada taxa de 1% por ano, Kardashev estimou que levaria apenas 3.200 anos para alcançar o patamar de Tipo II e 5.800 para chegar ao patamar de Tipo III.

Por exemplo, uma civilização Tipo I, é realmente uma que dominou a maioria das formas de energia planetária. Esta produção de energia pode ser da ordem de bilhões de vezes nossa produção planetária atual. Mark Twain disse uma vez “todos reclamam sobre as condições do tempo, mas ninguém faz nada a respeito.” Isto pode mudar com uma civilização do Tipo I, que tem energia suficiente para modificar a as condições meteorológicas. Eles também possuem energia suficiente para alterar o curso de terremotos, vulcões e construir cidades em seus oceanos.

Atualmente nossa produção de energia nos qualifica para o patamar do Tipo O. Nós não obtemos nossa energia dominando as forças globais, mas queimando plantas mortas (Ex: petróleo e carvão). Mas nós já podemos ver as sementes de uma civilização do Tipo I. Vemos o início de um idioma planetário (inglês), um sistema planetário de comunicação (a internet), uma economia planetária (o surgimento da União Europeia) e mesmo o começo de uma cultura planetária (via as mídias globais, a TV, a música rock e os filmes de Hollywood).

Por definição, uma civilização avançada tem de crescer mais rápido que a frequência de catástrofes ameaçadoras da vida. Uma vez que o impacto de grandes meteoros e cometas ocorre uma vez a cada poucos milhares de anos, uma civilização do Tipo I deve dominar a viagem espacial para desviar detritos espaciais dentro deste intervalo de tempo, o que não deve ser realmente um problema. Eras do gelo podem ocorrer em uma escala de tempo de dezenas de milhares de anos, então uma civilização do Tipo I tem de aprender como modificar as condições meteorológicas dentro de tal intervalo de tempo.

Artist conception of the K/T impact event. Credit: NASA (Oil on canvas panel by Don Davis for NASA HQ)

Artist conception of the K/T impact event. Credit: NASA (Oil on canvas panel by Don Davis for NASA HQ)

AM: Se eu o acompanhei bem até sua conclusão, isto implica que qualquer civilização tecnologicamente avançada que está limitada geograficamente (ou terrestrialmente) deve colapsar após uns poucos milhares de anos bem no auge de sua classificação do Tipo I?

MK: Catástrofes artificiais e internas também devem ser geridas. Mas o problema da poluição global é um risco mortal apenas para uma civilização do Tipo 0; uma civilização Tipo I viveu vários milênios como uma civilização planetária, necessariamente atingindo um equilíbrio ecológico planetário. Problemas internos como guerras impõem sim uma séria ameaça recorrente, mas eles tiveram milhares de anos para resolver conflitos raciais, nacionais e sectários.

Eventualmente, após vários milhares de anos, uma civilização do Tipo I irá exaurir o poder de um planeta e irá obter sua energia consumindo toda a produção de energia de seu sol, ou grosseiramente um bilhão de trilhão de trilhão de ergs por segundo.

Como sua produção de energia comparável com a de uma pequena estrela, eles devem ser visíveis no espaço. Dyson propôs que uma civilização do Tipo II pode eventualmente construir uma gigantesca esfera ao redor de sua estrela para utilizar mais eficientemente sua produção de energia total. Mesmo que eles tentem ocultar sua existência, eles devem, pela Segunda Lei da Termodinâmica, emitir calor como descarte. A partir do espaço exterior, seu planeta pode brilhar como um ornamento em uma árvore de Natal. Dyson até propôs procurar especificamente por emissões em infravermelho (ao invés de rádio e TV) para identificar estas civilizações do Tipo II.

Arecibo: The Largest Telescope. Credit: National Astronomy and Ionosphere Center, Cornell U., NSF

‘[Contatar outras civilizações] é muito caro, é melhor gastar nossos recursos ouvindo.’ – Frank Drake. Imagem: Arecibo Radio Telescope. Crédito da Imagem: National Astronomy and Ionosphere Center, Cornell U., NSF

Talvez a única séria ameaça a uma civilização do Tipo II seja uma explosão de supernova próxima, cuja súbita erupção poderia queimar seu planeta em uma rajada debilitadora de raios-X, matando todas as formas de vida. Então, talvez a mais interessante civilização seja a do Tipo III, por sua verdadeira imortalidade. Eles exauriram o poder de uma estrela individual e alcançaram outros sistemas estelares. Nenhuma catástrofe natural conhecida pela ciência é capaz de destruir uma civilização do Tipo III.

Confrontada como uma supernova vizinha, ela teria diversas alternativas, como alterar a evolução da estrela gigante vermelha que está morrendo e prestes a explodir, ou deixando este sistema estelar em particular e terraformando um sistema planetário próximo.

AM: Frank Drake ao formular a probabilidade para civilizações alcançarem a maturidade para comunicação interestelar, comentou que o fator de sobrevivência é o mais difícil de avaliar ou prever. Você concluiria que esta incerteza é máxima também, ou outra desconhecida domina suas considerações?

MK: Há obstáculos para uma civilização do Tipo III emergente. Eventualmente, ela colide contra outra lei de ferro da física, como a teoria da relatividade. Dyson estima que isto pode atrasar a transição para um Tipo III por talvez milhões de anos.

Mas mesmo com a barreira da luz, há várias maneiras de expandir a velocidades próximas da luz. Por exemplo, a última providência para a capacidade de um foguete é medida por algo chamado “impulso específico” (definido como o produto do impulso com a duração, medido em unidades de segundos). Foguetes químicos podem conseguir impulsos específicos de várias centenas a vários milhares de segundos. Motores de íons podem alcançar dezenas de milhares de segundos. Mas para chegar a velocidades próximas da luz, é preciso alcançar um impulso específico de uns 30 milhões de segundos, o que é bem acima de nossa capacidade atual, mas não de uma civilização do Tipo III. Uma variedade de sistemas de propulsão estariam disponíveis para sondas sub-velocidade da luz (tais como motores de fusão com aríete a jato, motores fotônicos, etc).

AM: Para alcançar a classificação Tipo III, uma civilização tem de cruzar a barreira da luz de alguma forma não compreendida hoje pela física – isto é, se a galáxia é sua ”casa”. Uma vez que a relatividade impõe uma dilatação do tempo em formas que são catastróficas para a maioria das formas de biologia que podemos imaginar, isto implica no inevitável aumento de máquinas assim favorecidas para a exploração espacial no caminho para o patamar do Tipo III?

Frank Drake. Crédito: NASA

Frank Drake. Crédito: NASA

MK: Na ficção científica, a busca por mundos habitados foi imortalizada na TV por heroicos e audaciosos capitães comandando uma nave estelar solitária, ou como os mortíferos Borg, uma civilização que absorve civilizações menores do Tipo II (como a Federação). No entanto, o método matemático mais eficiente para explorar o espaço é bem menos glamoroso: enviar frotas de “sondas de Von Neumann” através da galáxia (nomeada após Von Neumann, que estabeleceu as leis matemáticas de sistemas auto-replicantes).

Uma sonda de Von Neumann é um robô desenvolvido para alcançar sistemas estelares distantes e criar fábricas que irão reproduzir cópias deles aos milhares. Uma lua morta, ao invés de um planeta, constitui o destino ideal para sondas de Von Neumann, já que elas podem facilmente pousar e decolar destas luas e também porque estas luas não possuem erosão. Estas sondas viveriam fora no solo, usando depósitos de ocorrência natural de ferro, níquel, etc., para criar a matéria-prima para construir uma fábrica de robôs. Elas criariam milhares de cópias delas mesmas que iriam então dispersar e vasculhar por outros sistemas estelares.

“A luminosidade de estrelas como o Sol muda bem gradualmente, ao longo de milhões de anos. Isto é tempo suficiente para montar um programa tecnológico maciço para se mudar para fora do sistema planetário.” – Frank Drake.Crédito da Imagem: Anima Tek Int.

“A luminosidade de estrelas como o Sol muda bem gradualmente, ao longo de milhões de anos. Isto é tempo suficiente para montar um programa tecnológico maciço para se mudar para fora do sistema planetário.” – Frank Drake.Crédito da Imagem: Anima Tek Int.

Similar a um vírus colonizando um corpo de muitas vezes o seu tamanho, eventualmente haverá uma esfera de trilhões de sondas de Von Neumann expandindo-se em todas as direções, aumentando a uma fração da velocidade da luz. Desta maneira, mesmo uma galáxia de 100.000 anos-luz de diâmetro pode ser completamente analisada dentro de, digamos, meio milhão de anos.

Mesmo se uma sonda de Von Neumann só encontrar evidência de vida primitiva, (como uma instável e selvagem civilização Tipo 0), ela pode simplesmente ficar dormente em uma lua, silenciosamente esperando por vários milênios, podendo ser ativada quando a emergente civilização do Tipo I for avançada o suficiente para estabelecer uma colônia lunar. O físico Paul Davies da University of Adelaide até levantou a possibilidade de haver uma sonda de Von Neumann descansando em nossa própria lua, deixada por uma visita prévia ao nosso sistema éons atrás.

(Se isto soa familiar, é porque foi a base do filme 2001: Uma Odisseia no Espaço. Originalmente Stanley Kubrick começou o filme com uma série de cientistas explicando como sondas como estas poderiam ser o método mais eficiente de explorar o espaço exterior. Infelizmente, no último minuto, Kubrick cortou o segmento inicial do seu filme, e estes monólitos se tornaram quase entidades místicas).

AM: Quando entrevistamos o teórico das supercordas, Brian Greene, ele estava algo filosófico sobre energias danosas na escala de Planck, ou se as fronteiras da física mesmo poderiam oferecer um meio de manipular até o espaço de uma maneira que permita a uma civilização do Tipo III emergir. Assim como a sobrevivência planetária parece um obstáculo para a Tipo I, será a crise da civilização do Tipo III algo comparável a aprender como manipular o espaço em si de formas não imaginadas ainda?

Uma estrela anã-vermelha. Crédito: NASA

Uma estrela anã-vermelha.
Crédito: NASA

MK: Há também a possibilidade de que uma civilização do Tipo II ou do Tipo III possa ser capaz de alcançar a mítica energia de Planck com suas máquinas (1019 bilhões de elétron volts). Esta energia é um quadrilhão de vezes maior que nosso mais potente colisor de átomos. Esta energia, tão fantástica como parece ser, está (por definição) dentro do alcance de uma civilização do Tipo II ou III.

A energia de Planck ocorre apenas no centro de buracos negros e no instante do Big Bang (Grande Explosão). Mas com avanços recentes na gravidade quântica e teoria das supercordas, há um renovado interesse entre os físicos sobre energias tão vastas que os efeitos quânticos rasgam o tecido do espaço e tempo. Apesar de não ser de forma alguma certo que a física quântica permita buracos de minhoca estáveis, isto levanta a possibilidade remota de que civilizações suficientemente avançadas possam ser capazes de se mover via buracos no espaço, como o Espelho da Alice. E se tais civilizações podem navegar por buracos de minhoca estáveis com sucesso, então alcançar um impulso específico de um milhão de segundos não é mais um problema. Elas meramente pegam um atalho através da galáxia. Isto iria reduzir enormemente a transição entre uma civilização do Tipo II para o Tipo III.

Em segundo lugar, a habilidade de abrir buracos no espaço e tempo pode ficar à mão um dia. Astrônomos analisando a luz de supernovas distantes, concluíram recentemente que o Universo pode estar acelerando, ao invés de estar reduzindo sua velocidade. Se isto for verdade, pode haver uma força anti-gravidade (talvez a constante cosmológica de Einstein) que está contra-interagindo com a atração gravitacional de galáxias distantes. Mas isto também significa que o Universo pode expandir para sempre em um Big Chill (Grande Resfriamento), até as temperaturas se aproximarem do zero absoluto. Vários artigos recentemente mostraram como tal universo sinistro se pareceria. Será uma visão lamentável: qualquer civilização que sobreviva estará desesperadamente amontoada próxima das brasas de estrelas de nêutrons enfraquecidas a morrer e buracos negros. Toda vida inteligente morrerá quando o Universo morrer.

AM: Então há algum tipo de final inevitável para a vida inteligente, não importa quão avançada esta civilização em particular possa se tornar?

Uma supernova. Crédito da Imagem: NASA/CXC/Rutgers/J. Hughes

Uma supernova.
Crédito da Imagem: NASA/CXC/Rutgers/J. Hughes

MK: O astrônomo John Barrows da University of Susses escreveu “Suponha que nós estendamos a classificação para cima. Membros destas hipotéticas civilizações do Tipo IV, V, VI… e por aí vai, seriam capazes de manipular as estruturas no Universo em maiores e maiores escalas, envolvendo grupos de galáxias, aglomerados e superaglomerados de galáxias.” Civilizações além do Tipo III podem ter energia suficiente para escapar do nosso universo em falecimento através de buracos no espaço.

Finalmente o físico Alan Guth do MIT, um dos criadores da teoria do universo inflacionário chegou até a computar a energia necessária para criar um universo bebê no laboratório (a temperatura é de 1.000 trilhões de graus, o que é dentro do alcance destas civilizações hipotéticas).

Tradutor: Bruno Martini


Early Earth less hellish than previously thought

Artist's illustration of what a cool early Earth looked like. (Artwork by Don Dixon, cosmographica.com)

Artist’s illustration of what a cool early Earth looked like. (Artwork by Don Dixon, cosmographica.com)

Conditions on Earth for the first 500 million years after it formed may have been surprisingly similar to the present day, complete with oceans, continents and active crustal plates.

This alternate view of Earth’s first geologic eon, called the Hadean, has gained substantial new support from the first detailed comparison of zircon crystals that formed more than 4 billion years ago with those formed contemporaneously in Iceland, which has been proposed as a possible geological analog for early Earth.

The study was conducted by a team of geologists directed by Calvin Miller, the William R. Kenan Jr. Professor of Earth and Environmental Sciences at Vanderbilt University, and published online this weekend by the journal Earth and Planetary Science Letters in a paper titled, “Iceland is not a magmatic analog for the Hadean: Evidence from the zircon record.”

From the early 20th century up through the 1980’s, geologists generally agreed that conditions during the Hadean period were utterly hostile to life. Inability to find rock formations from the period led them to conclude that early Earth was hellishly hot, either entirely molten or subject to such intense asteroid bombardment that any rocks that formed were rapidly remelted. As a result, they pictured the surface of the Earth as covered by a giant “magma ocean.”

Calvin Miller at the Kerlingarfjoll volcano in central Iceland. Some geologists have proposed that the early Earth may have resembled regions like this. (Tamara Carley / Vanderbilt)

Calvin Miller at the Kerlingarfjoll volcano in central Iceland. Some geologists have proposed that the early Earth may have resembled regions like this. (Tamara Carley / Vanderbilt)

This perception began to change about 30 years ago when geologists discovered zircon crystals (a mineral typically associated with granite) with ages exceeding 4 billion years old preserved in younger sandstones. These ancient zircons opened the door for exploration of the Earth’s earliest crust. In addition to the radiometric dating techniques that revealed the ages of these ancient zircons, geologists used other analytical techniques to extract information about the environment in which the crystals formed, including the temperature and whether water was present.

Since then zircon studies have revealed that the Hadean Earth was not the uniformly hellish place previously imagined, but during some periods possessed an established crust cool enough so that surface water could form – possibly on the scale of oceans.

Accepting that the early Earth had a solid crust and liquid water (at least at times), scientists have continued to debate the nature of that crust and the processes that were active at that time: How similar was the Hadean Earth to what we see today?

Two schools of thought have emerged: One argues that Hadean Earth was surprisingly similar to the present day. The other maintains that, although it was less hostile than formerly believed, early Earth was nonetheless a foreign-seeming and formidable place, similar to the hottest, most extreme, geologic environments of today. A popular analog is Iceland, where substantial amounts of crust are forming from basaltic magma that is much hotter than the magmas that built most of Earth’s current continental crust.

“We reasoned that the only concrete evidence for what the Hadean was like came from the only known survivors: zircon crystals – and yet no one had investigated Icelandic zircon to compare their telltale compositions to those that are more than 4 billion years old, or with zircon from other modern environments,” said Miller.

Images of a collection of Icelandic zircons taken with a scanning electron microscope. They range in size from a tenth of a millimeter to a few thousands of a millimeter. (Tamara Carley / Vanderbilt)

Images of a collection of Icelandic zircons taken with a scanning electron microscope. They range in size from a tenth of a millimeter to a few thousands of a millimeter. (Tamara Carley / Vanderbilt)

In 2009, Vanderbilt doctoral student Tamara Carley, who has just accepted the position of assistant professor at Layfayette College, began collecting samples from volcanoes and sands derived from erosion of Icelandic volcanoes. She separated thousands of zircon crystals from the samples, which cover the island’s regional diversity and represent its 18 million year history.

Working with Miller and doctoral student Abraham Padilla at Vanderbilt, Joe Wooden at Stanford University, Axel Schmitt and Rita Economos fromUCLAIlya Bindeman at the University of Oregonand Brennan Jordan at the University of South Dakota, Carley analyzed about 1,000 zircon crystals for their age and elemental and isotopic compositions. She then searched the literature for all comparable analyses of Hadean zircon and for representative analyses of zircon from other modern environments.

“We discovered that Icelandic zircons are quite distinctive from crystals formed in other locations on modern Earth. We also found that they formed in magmas that are remarkably different from those in which the Hadean zircons grew,” said Carley.

Most importantly, their analysis found that Icelandic zircons grew from much hotter magmas than Hadean zircons. Although surface water played an important role in the generation of both Icelandic and Hadean crystals, in the Icelandic case the water was extremely hot when it interacted with the source rocks while the Hadean water-rock interactions were at significantly lower temperatures.

“Our conclusion is counterintuitive,” said Miller. “Hadean zircons grew from magmas rather similar to those formed in modern subduction zones, but apparently even ‘cooler’ and ‘wetter’ than those being produced today.”


Martian meteorite yields more evidence of the possibility of life on Mars

A tiny fragment of Martian meteorite 1.3 billion years old is helping to make the case for the possibility of life on Mars, say scientists.

Credit: NASA/JPL-Caltech/MSSS

Credit: NASA/JPL-Caltech/MSSS

The finding of a ‘cell-like’ structure, which investigators now know once held water, came about as a result of collaboration between scientists in the UK and Greece.  Their findings are published in the latest edition of the journal Astrobiology.

While investigating the Martian meteorite, known as Nakhla, Dr Elias Chatzitheodoridis of the National Technical University of Athens found an unusual feature embedded deep within the rock.  In a bid to understand what it might be, he teamed up with long-time friend and collaborator Professor Ian Lyon at the University of Manchester.

Professor Lyon, based in Manchester’s School of Earth, Atmospheric and Environmental Sciences, said: “In many ways it resembled a fossilised biological cell from Earth but it was intriguing because it was undoubtedly from Mars. Our research found that it probably wasn’t a cell but that it did once hold water – water that had been heated, probably as a result of an asteroid impact.”

These findings are significant because they add to increasing evidence that beneath the surface, Mars does provide all the conditions for life to have formed and evolved.  It also adds to a body of evidence suggesting that large asteroids hit Mars in the past and produce long-lasting hydrothermal fields that could sustain life on Mars, even in later epochs, if life ever emerged there.

As part of the research, the feature was imaged in unprecedented detail by Dr Sarah Haigh of The University of Manchester whose work usually involves high resolution imaging for next generation electronic devices ,which are made by stacking together single atomic layers of graphene and other materials with the aim of making faster, lighter and bendable mobile phones and tablets. A similar imaging approach was able to reveal the atomic layers of materials inside the meteorite.

Together their combined experimental approach has revealed new insights into the geological origins of this fascinating structure.

Professor Lyon said: “We have been able to show the setting is there to provide life. It’s not too cold, it’s not too harsh.  Life as we know it, in the form of bacteria, for example, could be there, although we haven’t found it yet.  It’s about piecing together the case for life on Mars – it may have existed and in some form could exist still.”

Now the team is using these and other state-of-the-art techniques to investigate new secondary materials in this meteorite and search for possible bio signatures which provide scientific evidence of life, past or present. Professor Lyon concluded: “Before we return samples from Mars, we must examine them further, but in more delicate ways.  We must carefully search for further evidence.”


Microscopic Diamonds Suggest Cosmic Impact Responsible for Major Period of Climate Change

A new study published in The Journal of Geology provides support for the theory that a cosmic impact event over North America some 13,000 years ago caused a major period of climate change known as the Younger Dryas stadial, or “Big Freeze.”

Credit: iStockphoto/Trevor Hunt

Credit: iStockphoto/Trevor Hunt

Around 12,800 years ago, a sudden, catastrophic event plunged much of the Earth into a period of cold climatic conditions and drought. This drastic climate change—the Younger Dryas—coincided with the extinction of Pleistocene megafauna, such as the saber-tooth cats and the mastodon, and resulted in major declines in prehistoric human populations, including the termination of the Clovis culture.

With limited evidence, several rival theories have been proposed about the event that sparked this period, such as a collapse of the North American ice sheets, a major volcanic eruption, or a solar flare.

However, in a study published in The Journal of Geology, an international group of scientists analyzing existing and new evidence have determined a cosmic impact event, such as a comet or meteorite, to be the only plausible hypothesis to explain all the unusual occurrences at the onset of the Younger Dryas period.

Researchers from 21 universities in 6 countries believe the key to the mystery of the Big Freeze lies in nanodiamonds scattered across Europe, North America, and portions of South America, in a 50-million-square-kilometer area known as the Younger Dryas Boundary (YDB) field.

Microscopic nanodiamonds, melt-glass, carbon spherules, and other high-temperature materials are found in abundance throughout the YDB field, in a thin layer located only meters from the Earth’s surface. Because these materials formed at temperatures in excess of 2200 degrees Celsius, the fact they are present together so near to the surface suggests they were likely created by a major extraterrestrial impact event.

In addition to providing support for the cosmic impact event hypothesis, the study also offers evidence to reject alternate hypotheses for the formation of the YDB nanodiamonds, such as by wildfires, volcanism, or meteoric flux.

The team’s findings serve to settle the debate about the presence of nanodiamonds in the YDB field and challenge existing paradigms across multiple disciplines, including impact dynamics, archaeology, paleontology, limnology, and palynology.

Phoebe Cohen, Assistant Professor of Geosciences at Williams College. Credit: Williams College

Q&A with Dr. Phoebe Cohen

Phoebe Cohen, Assistant Professor of Geosciences at Williams College. Credit: Williams College

Phoebe Cohen, Assistant Professor of Geosciences at Williams College. Credit: Williams College

Dr. Phoebe A. Cohen is a Professor of Geosciences at Williams College and is involved in numerous research projects with the NASA Astrobiology Program. Cohen studies the fossil record to uncover clues about the evolution of complex life on Earth. In her work, she studies interactions between life and our planet and how these interactions influenced the origin of animals.  This can help astrobiologists better understand where complex life might arise in the Universe.

Cohen recently took part in a panel discussion at NASA Headquarters entitled “Ancient Earth, Alien Earths,” where she talked about how studying the early Earth could help scientists identify similarly habitable planets around distant stars.

Recently, Astrobiology Magazine’s gURLs in Space spoke to Cohen about how she became interested in astrobiology and the path that led her to professional success in science.

Panelists discuss how research on early Earth could help guide our search for habitable planets orbiting other stars. Photo Credit: (NASA/Aubrey Gemignani)

Panelists discuss how research on early Earth could help guide our search for habitable planets orbiting other stars. Photo Credit: (NASA/Aubrey Gemignani)

Astrobiology Magazine (AM): What or who inspired you to follow a career in science?

I was always interested in science and nature when I was young. My dad was a biologist when I was growing up, so I’m sure that had a big role in my interests. As a kid, I wanted to live in the woods and study wolves and foxes! As I grew older, my interests broadened and for a while I wanted to be a National Geographic photographer. But when I got to college, I took a few really wonderful courses that cemented my love of science — one on conservation biology, and one on the history of the earth. At that point I was hooked, but it took some support from mentors and my parents, as well as a lot of work, to help me move from being a student to having a career in science.

AM: How did you become interested in Astrobiology?

Cohen: I was always interested in space, and for a while used to say I wanted to be the first woman on Mars! When we got the internet way back in the early 90’s I used to go to the NASA website, which at the time was all text — no pictures!! I discovered I was too short to be an astronaut, which was disappointing, but didn’t dampen my interest too much.

When the Pathfinder Mars rover landed, I was a senior in high school and that really captivated my attention. It blew my mind to think that as I went to class and did my homework on Earth there was a little robot driving around on Mars looking for signs of life.

As a research scientist, my interest in Astrobiology returned when I was finishing up my graduate work and had the opportunity to be a part of a NASA Astrobiology funded research team. I began to see how my work studying early life and earth had a lot of applications for the search for life elsewhere.

AM: What scientific questions do you hope to answer with your work?

Cohen: I want to know how and when complex life evolved — eukaryotic cells like the ones all animals, plants, and protists have. I’m trying to piece together events that happened over 700 million years ago which is exciting but also hard work! How did life go from being single celled to multi-celled? Why did it happen when it did, and what role did changes in the Earth’s environment play in that transition? Figuring this out helps us reconstruct how earth and life evolved together over time, and how a similar story might play out on another planet.

AM: What was your educational path? And were there any informal education opportunities or opportunities like internships that were important along the way?

Phoebe Cohen kneeling on some stromatolites in Australia, working on a 'virtual field trip' on the evolution of complex life. Credit: Phoebe Cohen

Phoebe Cohen kneeling on some stromatolites in Australia, working on a ‘virtual field trip’ on the evolution of complex life. Credit: Phoebe Cohen

Cohen: I went to Cornell University as an undergraduate and was an Earth Systems Science major, which gave me a broad background in both the geosciences and biology and ecology. After that, I worked at a natural history museum for two years, which was a really important time in my life. I wasn’t a student anymore, but discovered I still loved learning and wanted to be involved in science. I also got to explore my love of education, which continues to today. After my time at the museum, I did my PhD at Harvard University, which was a very challenging but rewarding experience. When I completed my PhD, I went to MIT as a postdoctoral fellow funded by MIT’s NASA Astrobiology team, where I did research and also headed up the team’s education and outreach work. That was an unusual move for someone like me — to spend so much time doing outreach — but I love it, and it paid off in the end. I got a great job at Williams College three years ago where I get to do both of the things I love – research and teaching!

AM: What advice might you have for young students interested in a career in Astrobiology?

Cohen: Most importantly, I would say be curious! Explore your world, and seek out opportunities to learn. Also, a strong educational foundation is really important. The great thing about Astrobiology is that foundation can be in many fields – chemistry, biology, geosciences, engineering, and other areas. I would say much of my success comes from working hard, being willing to fail, and asking other people for help and guidance. Find mentors and use them!

AM: Do you have any particular advice for young women in science?

Cohen: Science is not a boy thing or a girl thing, it’s a human thing, and we are all humans. If you don’t have support at home or from your teachers, try to seek out a mentor elsewhere. There are many more women in the sciences now than there were even when I started college, but there are still some challenges women face. You have to face those challenges head on, keep a strong sense of confidence in your own abilities, and again, ask for help or guidance if a situation is making you feel discouraged or uncomfortable. In addition, there are many women-specific opportunities in science now, so seek those out. Some internships, summer programs, and scholarships are set aside just for you, so go out and take advantage of them!



Rosetta’s lander Philae will target Site J, an intriguing region on Comet 67P/Churyumov–Gerasimenko that offers unique scientific potential, with hints of activity nearby, and minimum risk to the lander compared to the other candidate sites.

Philae’s primary landing site

Philae’s primary landing site

Site J is on the ‘head’ of the comet, an irregular shaped world that is just over 4 km across at its widest point. The decision to select Site J as the primary site was unanimous. The backup, Site C, is located on the ‘body’ of the comet.

The 100 kg lander is planned to reach the surface on 11 November, where it will perform indepth measurements to characterise the nucleus in situ, in a totally unprecedented way.

But choosing a suitable landing site has not been an easy task.

Philae’s primary landing site in context

Philae’s primary landing site in context

“As we have seen from recent close-up images, the comet is a beautiful but dramatic world – it is scientifically exciting, but its shape makes it operationally challenging,” says Stephan Ulamec, Philae Lander Manager at the DLR German Aerospace Center.

“None of the candidate landing sites met all of the operational criteria at the 100% level, but Site J is clearly the best solution.”

“We will make the first ever in situ analysis of a comet at this site, giving us an unparalleled insight into the composition, structure and evolution of a comet,” says Jean-Pierre Bibring, a lead lander scientist and principal investigator of the CIVA instrument at the IAS in Orsay, France.

“Site J in particular offers us the chance to analyse pristine material, characterise the properties of the nucleus, and study the processes that drive its activity.”

Philae’s primary landing site close-up

Philae’s primary landing site close-up

The race to find the landing site could only begin once Rosetta arrived at the comet on 6 August, when the comet was seen close-up for the first time. By 24 August, using data collected when Rosetta was still about 100 km from the comet five candidate regions had been identified for further analysis.

Since then, the spacecraft has moved to within 30 km of the comet, affording more detailed scientific measurements of the candidate sites. In parallel, the operations and flight dynamics teams have been exploring options for delivering the lander to all five candidate landing sites.

Over the weekend, the Landing Site Selection Group of engineers and scientists from Philae’s Science, Operations and Navigation Centre at France’s CNES space agency, the Lander Control Centre at DLR, scientists representing the Philae Lander instruments and ESA’s Rosetta team met at CNES, Toulouse, France, to consider the available data and to choose the primary and backup sites.

Philae’s primary landing site in 3D

Philae’s primary landing site in 3D

A number of critical aspects had to be considered, not least that it had to be possible to identify a safe trajectory for deploying Philae to the surface and that the density of visible hazards in the landing zone should be minimal. Once on the surface, other factors come into play, including the balance of daylight and nighttime hours, and the frequency of communications passes with the orbiter.

The descent to the comet is passive and it is only possible to predict that the landing point will place within a ‘landing ellipse’ typically a few hundred metres in size.

A one square kilometre area was assessed for each candidate site. At Site J, the majority of slopes are less than 30º relative to the local vertical, reducing the chances of Philae toppling over during touchdown. Site J also appears to have relatively few boulders, and receives sufficient daily illumination to recharge Philae and continue science operations on the surface beyond the initial battery-powered phase.

Provisional assessment of the trajectory to Site J found that the descent time of Philae to the surface would be about seven hours, a length that does not compromise the on-comet observations by using up too much of the battery during the descent.

Philae landing site context

Philae landing site context

Both Sites B and C were considered as the backup, but C was preferred because of a higher illumination profile and fewer boulders. Sites A and I had seemed attractive during first rounds of discussion, but were dismissed at the second round because they did not satisfy a number of the key criteria.

A detailed operational timeline will now be prepared to determine the precise approach trajectory of Rosetta in order to deliver Philae to Site J. The landing must take place before mid-November, as the comet is predicted to grow more active as it moves closer to the Sun.

“There’s no time to lose, but now that we’re closer to the comet, continued science and mapping operations will help us improve the analysis of the primary and backup landing sites,” says ESA Rosetta flight director Andrea Accomazzo.

“Of course, we cannot predict the activity of the comet between now and landing, and on landing day itself. A sudden increase in activity could affect the position of Rosetta in its orbit at the moment of deployment and in turn the exact location where Philae will land, and that’s what makes this a risky operation.”

Philae’s backup landing site

Philae’s backup landing site

Once deployed from Rosetta, Philae’s descent will be autonomous, with commands having been prepared by the Lander Control Centre at DLR, and uploaded via Rosetta mission control before separation.

During the descent, images will be taken and other observations of the comet’s environment will be made.

Once the lander touches down, at the equivalent of walking pace, it will use harpoons and ice screws to fix it onto the surface. It will then make a 360° panoramic image of the landing site to help determine where and in what orientation it has landed.

The initial science phase will then begin, with other instruments analysing the plasma and magnetic environment, and the surface and subsurface temperature. The lander will also drill and collect samples from beneath the surface, delivering them to the onboard laboratory for analysis. The interior structure of the comet will also be explored by sending radio waves through the surface towards Rosetta.

“No one has ever attempted to land on a comet before, so it is a real challenge,” says Fred Jansen, ESA Rosetta mission manager. “The complicated ‘double’ structure of the comet has had a considerable impact on the overall risks related to landing, but they are risks worth taking to have the chance of making the first ever soft landing on a comet.”

The landing date should be confirmed on 26 September after further trajectory analysis and the final Go/No Go for a landing at the primary site will follow a comprehensive readiness review on 14 October.


NASA Research Helps Unravel Mysteries Of The Venusian Atmosphere

Earth and Venus – worlds apart. Credits: Earth: NASA; Venus: Magellan Project/NASA/JPL

Earth and Venus – worlds apart. Credits: Earth: NASA; Venus: Magellan Project/NASA/JPL

Underscoring the vast differences between Earth and its neighbor Venus, new research shows a glimpse of giant holes in the electrically charged layer of the Venusian atmosphere, called the ionosphere. The observations point to a more complicated magnetic environment than previously thought – which in turn helps us better understand this neighboring, rocky planet.

Planet Venus, with its thick atmosphere made of carbon dioxide, its parched surface, and pressures so high that landers are crushed within a few hours, offers scientists a chance to study a planet very foreign to our own. These mysterious holes provide additional clues to understanding Venus’s atmosphere, how the planet interacts with the constant onslaught of solar wind from the sun, and perhaps even what’s lurking deep in its core.

“This work all started with a mystery from 1978,” said Glyn Collinson, a space scientist at NASA’s Goddard Space Flight Center in Greenbelt, Maryland, who is first author of a paper on this work in the Journal of Geophysical Research. “When Pioneer Venus Orbiter moved into orbit around Venus, it noticed something very, very weird – a hole in the planet’s ionosphere. It was a region where the density just dropped out, and no one has seen another one of these things for 30 years.”

Until now.

New research shows giant holes in Venus’ atmosphere – which serve as extra clues for understanding this planet so different from our own. Image Credit: NASA’s Goddard Space Flight Center/G. Duberstein

Collinson set out to search for signatures of these holes in data from the European Space Agency’s Venus Express. Venus Express, launched in 2006, is currently in a 24-hour orbit around the poles of Venus. This orbit places it in much higher altitudes than that of the Pioneer Venus Orbiter, so Collinson wasn’t sure whether he’d spot any markers of these mysterious holes. But even at those heights the same holes were spotted, thus showing that the holes extended much further into the atmosphere than had been previously known.

The observations also suggested the holes are more common than realized. Pioneer Venus Orbiter only saw the holes at a time of great solar activity, known as solar maximum. The Venus Express data, however, shows the holes can form during solar minimum as well.

Interpreting what is happening in Venus’s ionosphere requires understanding how Venus interacts with its environment in space. This environment is dominated by a stream of electrons and protons – a charged, heated gas called plasma — which zoom out from the sun. As this solar wind travels it carries along embedded magnetic fields, which can affect charged particles and other magnetic fields they encounter along the way. Earth is largely protected from this radiation by its own strong magnetic field, but Venus has no such protection.

What Venus does have, however, is an ionosphere, a layer of the atmosphere filled with charged particles. The Venusian ionosphere is bombarded on the sun-side of the planet by the solar wind. Consequently, the ionosphere, like air flowing past a golf ball in flight, is shaped to be a thin boundary in front of the planet and to extend into a long comet-like tail behind. As the solar wind plows into the ionosphere, it piles up like a big plasma traffic jam, creating a thin magnetosphere around Venus – a much smaller magnetic environment than the one around Earth.

Venus Express aerobraking. Credit: ESA

Venus Express aerobraking. Credit: ESA

Venus Express is equipped to measure this slight magnetic field. As it flew through the ionospheric holes it recorded a jump in the field strength, while also spotting very cold particles flowing in and out of the holes, though at a much lower density than generally seen in the ionosphere.

The Venus Express observations suggest that instead of two holes behind Venus, there are in fact two long, fat cylinders of lower density material stretching from the planet’s surface to way out in space. Collinson said that some magnetic structure probably causes the charged particles to be squeezed out of these areas, like toothpaste squeezed out of a tube.

The next question is what magnetic structure can create this effect? Imagine Venus standing in the middle of the constant solar wind like a lighthouse erected in the water just off shore. Magnetic field lines from the sun move toward Venus like waves of water approaching the lighthouse. The far sides of these lines then wrap around the planet leading to two long straight magnetic field lines trailing out directly behind Venus. These lines could create the magnetic forces to squeeze the plasma out of the holes.

But such a scenario would place the bottom of these tubes on the sides of the planet, not as if they were coming straight up out of the surface. What could cause magnetic fields to go directly in and out of the planet? Without additional data, it’s hard to know for sure, but Collinson’s team devised two possible models that can match these observations.

In one scenario, the magnetic fields do not stop at the edge of the ionosphere to wrap around the outside of the planet, but instead continue further.

“We think some of these field lines can sink right through the ionosphere, cutting through it like cheese wire,” said Collinson. “The ionosphere can conduct electricity, which makes it basically transparent to the field lines. The lines go right through down to the planet’s surface and some ways into the planet.”

Venus cloud tops. Credit: ESA/MPS/DLR/IDA

Venus cloud tops. Credit: ESA/MPS/DLR/IDA

In this scenario, the magnetic field travels unhindered directly into the upper layers of Venus. Eventually, the magnetic field hits Venus’ rocky mantle – assuming, of course, that the inside of Venus is like the inside of Earth. A reasonable assumption given that the two planets are the same mass, size and density, but by no means a proven fact.

A similar phenomenon does happen on the moon, said Collinson. The moon is mostly made up of mantle and has little to no atmosphere. The magnetic field lines from the sun go through the moon’s mantle and then hit what is thought to be an iron core.

In the second scenario, the magnetic fields from the solar system do drape themselves around the ionosphere, but they collide with a pile up of plasma already at the back of the planet. As the two sets of charged material jostle for place, it causes the required magnetic squeeze in the perfect spot.

Either way, areas of increased magnetism would stream out on either side of the tail, pointing directly in and out of the sides of the planet. Those areas of increased magnetic force could be what squeezes out the plasma and creates these long ionospheric holes.

Scientists will continue to explore just what causes these holes. Confirming one theory or the other will, in turn, help us understand this planet, so similar and yet so different from our own.

Planets such as Mercury likely are close to the primordial state of mineral formation, since little was available to alter the surface in terms of "wet" processes (such as ice) or plate tectonics. Credit: NASA/Johns Hopkins University Applied Physics Laboratory/Carnegie Institution of Washington

Planets with Oddball Orbits Like Mercury Could Host Life

On Mercury a solar day is about 176 Earth days long. During its first Mercury solar day in orbit the MESSENGER spacecraft imaged nearly the entire surface of Mercury to generate a global monochrome map at 250 meters per pixel resolution and a 1 kilometer per pixel resolution color map. Credit: NASA/JHU APL/CIW

On Mercury a solar day is about 176 Earth days long. During its first Mercury solar day in orbit the MESSENGER spacecraft imaged nearly the entire surface of Mercury to generate a global monochrome map at 250 meters per pixel resolution and a 1 kilometer per pixel resolution color map. Credit: NASA/JHU APL/CIW

Mercury has an oddball orbit — it takes longer for it to rotate on its axis and complete a day than it takes to orbit the sun and complete a year. Now, researchers suggest photosynthesis could take place on an alien planet with a similarly bizarre orbit, potentially helping support complex life.

However, the scientists noted that the threat of prolonged periods of darkness and cold on these planets would present significant challenges to life, and could even potentially freeze their atmospheres. They detailed their findings in the International Journal of Astrobiology.

Astronomers have discovered more than 1,700 alien planets in the past two decades, raising the hope that at least some might be home to extraterrestrial life. Scientists mostly focus the search for alien life on exoplanets in the habitable zones of stars. These are regions where worlds would be warm enough to have liquid water on their surfaces, a potential boon to life.

The 3:2 spin orbit resonance of Mercury and the Sun. Credit: Wikicommons

The 3:2 spin orbit resonance of Mercury and the Sun. Credit: Wikicommons

Although many exoplanets are potentially habitable, they may differ from Earth significantly in one or more ways. For instance, habitable planets around dim red dwarf stars orbit much closer than Earth does to the Sun, sometimes even closer than Mercury’s distance. Red dwarfs are of interest as possible habitats for life because they are the most common stars in the universe — if life can exist around red dwarfs, then life might be very common across the cosmos. Recent findings from NASA’s Kepler Space Observatory suggest that at least half of all red dwarfs host rocky planets that are one-half to four times the mass of Earth.

Since a planet in the habitable zone of a red dwarf orbits very near its star, it experiences much stronger gravitational tidal forces than Earth does from the Sun, which slows the rate at which those worlds spin. The most likely result of this slowdown is that the planet enters what is technically called a 1:1 spin orbit resonance, completing one rotation on its axis every time it completes one orbit around its star. This rate of rotation means that one side of that planet will always face toward its star, while the other side will permanently face away, just as the Moon always shows the same side to Earth. One recent study suggests that such “tidally locked” planets may develop strange lobster-shaped oceans basking in the warmth of their stars on their daysides, while the nightsides of such worlds are mostly covered in an icy shell.

However, if a habitable red dwarf planet has a very eccentric orbit — that is, oval-shaped — it could develop what is called a 3:2 spin orbit resonance, meaning that it rotates three times for every two orbits around its star. Mercury has such an unusual orbit, which can lead to strange phenomena. For instance, at certain times on Mercury, an observer could see the Sun rise about halfway and then reverse its course and set, all during the course of one mercurial day. Mercury itself is not habitable, since it lacks an atmosphere and experiences temperatures ranging from 212 to 1,292 degrees Fahrenheit (100 to 700 degrees Celsius).

“If the Sun were less intense, Mercury would be within the habitable zone, and therefore life would have to adapt to strange light cycles,” said lead study author Sarah Brown, an astrobiologist at the United Kingdom Center for Astrobiology in Edinburgh, Scotland.

Light is crucial for photosynthesis, the process by which plants and other photosynthetic organisms use the Sun’s rays to create energy-rich molecules such as sugars. Most life on Earth currently depends on photosynthesis or its byproducts in one way or the other, and while primitive life can exist without photosynthesis, it may be necessary for more complex multi-cellular organisms to emerge because the main source for oxygen on Earth comes from photosynthetic life, and oxygen is thought to be necessary for multi-cellular life to arise.

To see what photosynthetic life might exist on a habitable red dwarf planet with an orbit similar to Mercury’s, scientists calculated the amount of light that reached all points on its surface. Their model involved a planet the same mass and diameter as the Earth with a similar atmosphere and amount of water on its surface. The red dwarf star was 30 percent the Sun’s mass and 1 percent as luminous, giving it a temperature of about 5,840 degrees Fahrenheit (3,225 degrees Celsius) and a habitable zone extending from 10 to 20 percent of an astronomical unit (AU) from the star. (One AU is the average distance between Earth and the Sun.)

The 1:1 spin orbit resonance of Earth and the Moon. Credit: Wikicommons

The 1:1 spin orbit resonance of Earth and the Moon. Credit: Wikicommons

The scientists found that the amount of light the surface of these planets received concentrated on certain bright spots. Surprisingly, the amount of light these planets receive do not just vary over latitude as they do on Earth, where more light reaches equatorial regions than polar regions, but also varied over longitude. Were photosynthetic life to exist on worlds with these types of orbits, “one would expect to find niches that depend on longitude and latitude, rather than just latitude,” said study co-author Alexander Mead, a cosmologist at the Royal Observatory, Edinburgh, in Scotland.

The research team found these planets could experience nights that last for months. This could pose major problems for photosynthetic life, which depends on light. Still, the scientists noted that many plants can store enough energy to last through 180 days of darkness. Moreover, some photosynthetic microbes spend up to decades dormant in the dark, while others are mixotrophic, which means they can survive on photosynthesis when light is abundant and switch to devouring food when light is absent.

Another problem these long spans of darkness pose for life is the cold, which could freeze the atmospheres of these planets. Still, the investigators note that heat can flow from the dayside of such a planet to its nightside and prevent this freezing if that planet’s atmosphere is sufficiently dense and can trap infrared light from the planet’s star. This heat flow could lead to very strong winds, but this does not necessarily make the world uninhabitable, they added.

“Life having to cope with such tidally driven resonances could be common in the universe,” Mead said. “It changes one’s perception of what habitable planets in the Universe would be like. There are many possibilities that are very un-Earth-like.”

It is difficult to form Mercury in solar system simulations, suggesting that some of our assumptions about the small planet's formation might be wrong, a new study suggests. NASA/Johns Hopkins University Applied Physics Laboratory/Carnegie Institution of Washington

It is difficult to form Mercury in solar system simulations, suggesting that some of our assumptions about the small planet’s formation might be wrong, a new study suggests. NASA/Johns Hopkins University Applied Physics Laboratory/Carnegie Institution of Washington

However, the researchers noted that the strength of a world’s magnetic field depends in large part on how quickly it spins, which suggests that planets with orbits like Mercury’s might have relatively weak magnetic fields. This could mean these worlds are not as good at deflecting harmful electrically charged particles streaming from their red dwarfs and other stars that can damage organisms and strip off the atmospheres of these planets.

The investigators suggested that dense atmospheres could help keep such planets habitable in the face of radiation from space. They added that life might be confined to certain spots on the surfaces of those planets that experience relatively safe levels of radiation.

Are astronomers capable of detecting habitable planets with a 3:2 spin orbit resonance?

“Measuring the day length of extrasolar planets is enormously difficult, and the first day length measurements for any extrasolar planets were only published this year,” Mead said. “Such a measurement for the planets we discuss would be much more difficult due to the fact that they are small, rocky planets around faint stars. This means that we are probably a long way from measuring the spin rates of such habitable worlds.”


‘Hot Jupiters’ provoke their own host suns to wobble

Artist conception of a hot Jupiter. (Image credit: NASA/JPL-Caltech)

Artist conception of a hot Jupiter. (NASA/JPL-Caltech)

Blame the “hot Jupiters.”

These large, gaseous exoplanets (planets outside our solar system) can make their suns wobble when they wend their way through their own solar systems to snuggle up against their suns, according to new Cornell University research to be published in Science, Sept. 11.

“Although the planet’s mass is only one-thousandth of the mass of the sun, the stars in these other solar systems are being affected by these planets and making the stars themselves act in a crazy way,” said Dong Lai, Cornell professor of astronomy and senior author on the research, “Chaotic Dynamics of Stellar Spin in Binaries and the Production of Misaligned Hot Jupiters.” Physics graduate student Natalia I. Storch (lead author) and astronomy graduate student Kassandra R. Anderson are co-authors.

In our solar system, the sun’s rotation axis is approximately aligned with the orbital axis of all the planets. The orbital axis is perpendicular to the flat plane in which the planets revolve around the sun. In solar systems with hot Jupiters, recent observations have revealed that the orbital axis of these planets is misaligned with the rotation axis of their host star. In the last few years, astronomers have been puzzled by spin-orbit misalignment between the star and the planets.

Roasting like marshmallows on an open fire, hot Jupiters – large gaseous planets dispensed throughout the universe in other solar systems – wander from distant places to orbit extraordinarily close to their own suns. Partner binary stars, some as far as hundreds of astronomical units (an astronomical unit is 93 million miles, the distance between Earth and the sun,) influence through gravity the giant Jupiter-like planets and cause them to falter into uncommon orbits; that, in turn, causes them to migrate inward close to their sun, Lai said.

Credit: Cornell University

Credit: Cornell University

“When exoplanets were first found in the 1990s, it was large planets like Jupiter that were discovered. It was surprising that such giant planets can be so close to parent star,” Lai said. “Our own planet Mercury is very close to our sun. But these hot Jupiters are much closer to their suns than Mercury.”

By simulating the dynamics of these exotic planetary systems, the Cornell astronomers showed that when the Jupiter-like planet approaches its host star, the planet can force the star’s spin axis to precess (that is, change the orientation of their rotational axis), much like a wobbling, spinning top.

“Also, it can make the star’s spin axis change direction in a rather complex – or even a chaotic – way,” said Lai. “This provides a possible explanation to the observed spin-orbit misalignments, and will be helpful for understanding the origin of these enigmatic planets.”

Another interesting feature of the Cornell work is that the chaotic variation of the star’s spin axis resembles other chaotic phenomena found in nature, such as weather and climate.


NASA Research Gives Guideline for Future Alien Life Search

Astronomers searching the atmospheres of alien worlds for gases that might be produced by life can’t rely on the detection of just one type, such as oxygen, ozone, or methane, because in some cases these gases can be produced non-biologically, according to extensive simulations by researchers in the NASA Astrobiology Institute’s Virtual Planetary Laboratory. 

Left: Ozone molecules in a planet's atmosphere could indicate biological activity, but ozone, carbon dioxide and carbon monoxide -- without methane, is likely a false positive. Right: Ozone, oxygen, carbon dioxide and methane -- without carbon monoxide, indicate a possible true positive. Image Credit: NASA

Left: Ozone molecules in a planet’s atmosphere could indicate biological activity, but ozone, carbon dioxide and carbon monoxide — without methane, is likely a false positive. Right: Ozone, oxygen, carbon dioxide and methane — without carbon monoxide, indicate a possible true positive. Image Credit: NASA

The researchers carefully simulated the atmospheric chemistry of alien worlds devoid of life thousands of times over a period of more than four years, varying the atmospheric compositions and star types.

“When we ran these calculations, we found that in some cases, there was a significant amount of ozone that built up in the atmosphere, despite there not being any oxygen flowing into the atmosphere,” said Shawn Domagal-Goldman of NASA’s Goddard Space Flight Center in Greenbelt, Maryland. “This has important implications for our future plans to look for life beyond Earth.”

Methane is a carbon atom bound to four hydrogen atoms. On Earth, much of it is produced biologically (flatulent cows are a classic example), but it can also be made inorganically; for example, volcanoes at the bottom of the ocean can release the gas after it is produced by reactions of rocks with seawater.

Ozone and oxygen were previously thought to be stronger biosignatures on their own. Ozone is three atoms of oxygen bound together. On Earth, it is produced when molecular oxygen (two oxygen atoms) and atomic oxygen (a single oxygen atom) combine, after the atomic oxygen is created by other reactions powered by sunlight or lightning. Life is the dominant source of the molecular oxygen on our planet, as the gas is produced by photosynthesis in plants and microscopic, single-cell organisms. Because life dominates the production of oxygen, and oxygen is needed for ozone, both gases were thought to be relatively strong biosignatures.

But this study demonstrated that both molecular oxygen and ozone can be made without life when ultraviolet light breaks apart carbon dioxide (a carbon atom bound to two oxygen atoms). Their research suggests this non-biological process could create enough ozone for it to be detectable across space, so the detection of ozone by itself would not be a definitive sign of life.

“However, our research strengthens the argument that methane and oxygen together, or methane and ozone together, are still strong signatures of life,” said Domagal-Goldman. “We tried really, really hard to make false-positive signals for life, and we did find some, but only for oxygen, ozone, or methane by themselves.”

Credit: NASA Ames/SETI Institute/JPL-Caltech

Credit: NASA Ames/SETI Institute/JPL-Caltech

Domagal-Goldman and Antígona Segura from the Universidad Nacional Autónoma de México in Mexico City are lead authors of a paper about this research, along with astronomer Victoria Meadows, geologist Mark Claire, and Tyler Robison, an expert on what Earth would look like as an extrasolar planet. The paper appeared in the Astrophysical Journal Sept. 10, and is available online.

Methane and oxygen molecules together are a reliable sign of biological activity because methane doesn’t last long in an atmosphere containing oxygen-bearing molecules. “It’s like college students and pizza,” says Domagal-Goldman. “If you see pizza in a room, and there are also college students in that room, chances are the pizza was freshly delivered, because the students will quickly eat the pizza. The same goes for methane and oxygen. If both are seen together in an atmosphere, the methane was freshly delivered because the oxygen will be part of a network of reactions that will consume the methane. You know the methane is being replenished. The best way to replenish methane in the presence of oxygen is with life. The opposite is true, as well. In order to keep the oxygen around in an atmosphere that has a lot of methane, you have to replenish the oxygen, and the best way to do that is with life.”

Scientists have used computer models to simulate the atmospheric chemistry on planets beyond our solar system (exoplanets) before, and the team used a similar model in its research. However, the researchers also developed a program to automatically compute the calculations thousands of times, so they could see the results with a wider range of atmospheric compositions and star types.

In doing these simulations, the team made sure they balanced the reactions that could put oxygen molecules in the atmosphere with the reactions that might remove them from the atmosphere. For example, oxygen can react with iron on the surface of a planet to make iron oxides; this is what gives most red rocks their color. A similar process has colored the dust on Mars, giving the Red Planet its distinctive hue. Calculating the appearance of a balanced atmosphere is important because this balance would allow the atmosphere to persist for geological time scales. Given that planetary lifetimes are measured in billions of years, it’s unlikely astronomers will happen by chance to be observing a planet during a temporary surge of oxygen or methane lasting just thousands or even millions of years.

It was important to make the calculations for a wide variety of cases, because the non-biological production of oxygen is subject to both the atmospheric and stellar environment of the planet. If there are a lot of gases that consume oxygen, such as methane or hydrogen, then any oxygen or ozone produced will be destroyed in the atmosphere.

However, if the amount of oxygen-consuming gases is vanishingly small, the oxygen and the ozone might stick around for a while. Likewise, the production and destruction of oxygen, ozone, and methane is driven by chemical reactions powered by light, making the type of star important to consider as well. Different types of stars produce the majority of their light at specific colors.

For example, massive, hot stars or stars with frequent explosive activity produce more ultraviolet light. “If there is more ultraviolet light hitting the atmosphere, it will drive these photochemical reactions more efficiently,” said Domagal-Goldman. “More specifically, different colors (or wavelengths) of ultraviolet light can affect oxygen and ozone production and destruction in different ways.”

Astronomers detect molecules in exoplanet atmospheres by measuring the colors of light from the star the exoplanet is orbiting. As this light passes through the exoplanet’s atmosphere, some of it is absorbed by atmospheric molecules. Different molecules absorb different colors of light, so astronomers use these absorption features as unique “signatures” of the type and quantity of molecules present.

“One of the main challenges in identifying life signatures is to distinguish between the products of life and those compounds generated by geological processes or chemical reactions in the atmosphere. For that we need to understand not only how life may change a planet but how planets work and the characteristics of the stars that host such worlds”, said Segura.

The team plans to use this research to make recommendations about the requirements for future space telescopes designed to search exoplanet atmospheres for signs of alien life.

“Context is key – we can’t just look for oxygen, ozone, or methane alone,” says Domagal-Goldman. “To confirm life is making oxygen or ozone, you need to expand your wavelength range to include methane absorption features. Ideally, you’d also measure other gases like carbon dioxide and carbon monoxide [a molecule with one carbon atom and one oxygen atom]. So we’re thinking very carefully about the issues that could trip us up and give a false-positive signal, and the good news is by identifying them, we can create a good path to avoid the issues false positives could cause. We now know which measurements we need to make. The next step is figuring out what we need to build and how to build it.”


NASA’s Mars Curiosity Rover Arrives at Martian Mountain

Artist concept features NASA's Mars Science Laboratory Curiosity rover, a mobile robot for investigating Mars' past or present ability to sustain microbial life. Image Credit: NASA/JPL-Caltech

Artist concept features NASA’s Mars Science Laboratory Curiosity rover, a mobile robot for investigating Mars’ past or present ability to sustain microbial life. Image Credit: NASA/JPL-Caltech

NASA’s Mars Curiosity rover has reached the Red Planet’s Mount Sharp, a Mount-Rainier-size mountain at the center of the vast Gale Crater and the rover mission’s long-term prime destination.

“Curiosity now will begin a new chapter from an already outstanding introduction to the world,” said Jim Green, director of NASA’s Planetary Science Division at NASA Headquarters in Washington. “After a historic and innovative landing along with its successful science discoveries, the scientific sequel is upon us.”

Curiosity’s trek up the mountain will begin with an examination of the mountain’s lower slopes. The rover is starting this process at an entry point near an outcrop called Pahrump Hills, rather than continuing on to the previously-planned, further entry point known as Murray Buttes. Both entry points lay along a boundary where the southern base layer of the mountain meets crater-floor deposits washed down from the crater’s northern rim.

This image from NASA's Mars Curiosity rover shows the "Amargosa Valley," on the slopes leading up to Mount Sharp on Mars. This area represents a boundary between the plains of Gale Crater, named Aeolis Palus, and the layered slopes of Mount Sharp, or Aeolis Mons. Curiosity has recently crossed into this terrain and now is on the Mount Sharp side of the transition zone. Image credit: NASA/JPL-Caltech/MSSS

This image from NASA’s Mars Curiosity rover shows the “Amargosa Valley,” on the slopes leading up to Mount Sharp on Mars. This area represents a boundary between the plains of Gale Crater, named Aeolis Palus, and the layered slopes of Mount Sharp, or Aeolis Mons. Curiosity has recently crossed into this terrain and now is on the Mount Sharp side of the transition zone. Image credit: NASA/JPL-Caltech/MSSS

“It has been a long but historic journey to this Martian mountain,” said Curiosity Project Scientist John Grotzinger of the California Institute of Technology in Pasadena. “The nature of the terrain at Pahrump Hills and just beyond it is a better place than Murray Buttes to learn about the significance of this contact. The exposures at the contact are better due to greater topographic relief.”

The decision to head uphill sooner, instead of continuing to Murray Buttes, also draws from improved understanding of the region’s geography provided by the rover’s examinations of several outcrops during the past year.

Curiosity currently is positioned at the base of the mountain along a pale, distinctive geological feature called the Murray Formation. Compared to neighboring crater-floor terrain, the rock of the Murray Formation is softer and does not preserve impact scars, as well. As viewed from orbit, it is not as well-layered as other units at the base of Mount Sharp.

This image shows the old and new routes of NASA's Mars Curiosity rover and is composed of color strips taken by the High Resolution Imaging Science Experiment, or HiRISE, on NASA's Mars Reconnaissance Orbiter. This new route provides excellent access to many features in the Murray Formation. And it will eventually pass by the Murray Formation's namesake, Murray Buttes, previously considered to be the entry point to Mt. Sharp. Image Credit: NASA/JPL-Caltech/Univ. of Arizona

This image shows the old and new routes of NASA’s Mars Curiosity rover and is composed of color strips taken by the High Resolution Imaging Science Experiment, or HiRISE, on NASA’s Mars Reconnaissance Orbiter.  Image Credit: NASA/JPL-Caltech/Univ. of Arizona

Curiosity made its first close-up study last month of two Murray Formation outcrops, both revealing notable differences from the terrain explored by Curiosity during the past year. The first outcrop, called Bonanza King, proved too unstable for drilling, but was examined by the rover’s instruments and determined to have high silicon content. A second outcrop, examined with the rover’s telephoto Mast Camera, revealed a fine-grained, platy surface laced with sulfate-filled veins.

While some of these terrain differences are not apparent in observations made by NASA’s Mars orbiters, the rover team still relies heavily on images taken by the agency’s Mars Reconnaissance Orbiter (MRO) to plan Curiosity’s travel routes and locations for study.

For example, MRO images helped the rover team locate mesas that are over 60 feet (18 meters) tall in an area of terrain shortly beyond Pahrump Hills, which reveal an exposure of the Murray Formation uphill and toward the south. The team plans to use Curiosity’s drill to acquire a sample from this site for analysis by instruments inside the rover. The site lies at the southern end of a valley Curiosity will enter this week from the north.

Though this valley has a sandy floor the length of two football fields, the team expects it will be an easier trek than the sandy-floored Hidden Valley, where last month Curiosity’s wheels slipped too much for safe crossing.

This portion of a color mosaic taken by NASA's Mars Curiosity rover shows strata exposed along the margins of the valleys in the "Pahrump Hills" region on Mars. The scale of layering increases upward, providing what's called a "thickening upward" trend. This is consistent with a variety of ancient environments, in particular those that involved water. Credit: NASA/JPL-Caltech/MSSS

This portion of a color mosaic taken by NASA’s Mars Curiosity rover shows strata exposed along the margins of the valleys in the “Pahrump Hills” region on Mars. The scale of layering increases upward, providing what’s called a “thickening upward” trend. This is consistent with a variety of ancient environments, in particular those that involved water. Credit: NASA/JPL-Caltech/MSSS

Curiosity reached its current location after its route was modified earlier this year in response to excessive wheel wear. In late 2013, the team realized a region of Martian terrain littered with sharp, embedded rocks was poking holes in four of the rover’s six wheels. This damage accelerated the rate of wear and tear beyond that for which the rover team had planned. In response, the team altered the rover’s route to a milder terrain, bringing the rover farther south, toward the base of Mount Sharp.

“The wheels issue contributed to taking the rover farther south sooner than planned, but it is not a factor in the science-driven decision to start ascending here rather than continuing to Murray Buttes first,” said Jennifer Trosper, Curiosity Deputy Project Manager at NASA’s Jet Propulsion Laboratory (JPL) in Pasadena, California.

“We have been driving hard for many months to reach the entry point to Mount Sharp,” Trosper said. “Now that we’ve made it, we’ll be adjusting the operations style from a priority on driving to a priority on conducting the investigations needed at each layer of the mountain.”

A swept Martian rock called "Bonanza King" can be seen in this image take by NASA's Mars Curiosity rover. This rock is located across the boundary that defines the base of Mount Sharp. The rover later partially drilled into and analyzed the rock, representing a first  "taste" of the "Murray Formation” of rocks on the slopes of Mount Sharp, where the rover will continue exploring. Credit: NASA/JPL-Caltech/MSSS

A swept Martian rock called “Bonanza King” can be seen in this image take by NASA’s Mars Curiosity rover. This rock is located across the boundary that defines the base of Mount Sharp. The rover later partially drilled into and analyzed the rock, representing a first “taste” of the “Murray Formation” of rocks on the slopes of Mount Sharp, where the rover will continue exploring. Credit: NASA/JPL-Caltech/MSSS

After landing inside Gale Crater in August 2012, Curiosity fulfilled in its first year of operations its major science goal of determining whether Mars ever offered environmental conditions favorable for microbial life. Clay-bearing sedimentary rocks on the crater floor, in an area called Yellowknife Bay, yielded evidence of a lakebed environment billions of years ago that offered fresh water, all of the key elemental ingredients for life, and a chemical source of energy for microbes.

NASA’s Mars Science Laboratory Project continues to use Curiosity to assess ancient habitable environments and major changes in Martian environmental conditions. The destinations on Mount Sharp offer a series of geological layers that recorded different chapters in the environmental evolution of Mars.


First evidence for water ice clouds found outside solar system

Artists Conception : Credit Rob Gizis, CUNY BMCC

Artists Conception : Credit Rob Gizis, CUNY BMCC

A team of scientists led by Carnegie’s Jacqueline Faherty has discovered the first evidence of water ice clouds on an object outside of our own Solar System. Water ice clouds exist on our own gas giant planets–Jupiter, Saturn, Uranus, and Neptune–but have not been seen outside of the planets orbiting our Sun until now. Their findings are published today by The Astrophysical Journal Letters and are available here.

At the Las Campanas Observatory in Chile, Faherty, along with a team including Carnegie’s Andrew Monson, used the FourStar near infrared camera to detect the coldest brown dwarf ever characterized. Their findings are the result of 151 images taken over three nights and combined. The object, named WISE J085510.83-071442.5, or W0855, was first seen by NASA’s Wide-Field Infrared Explorer mission and published earlier this year. But it was not known if it could be detected by Earth-based facilities.

“This was a battle at the telescope to get the detection,” said Faherty.

Chris Tinney, an Astronomer at the Australian Centre for Astrobiology, UNSW Australia and co-author on the result stated: “This is a great result. This object is so faint and it’s exciting to be the first people to detect it with a telescope on the ground.”

Brown dwarfs aren’t quite very small stars, but they aren’t quite giant planets either. They are too small to sustain the hydrogen fusion process that fuels stars. Their temperatures can range from nearly as hot as a star to as cool as a planet, and their masses also range between star-like and giant planet-like. They are of particular interest to scientists because they offer clues to star-formation processes. They also overlap with the temperatures of planets, but are much easier to study since they are commonly found in isolation.

W0855 is the fourth-closest system to our own Sun, practically a next-door neighbor in astronomical distances. A comparison of the team’s near-infrared images of W0855 with models for predicting the atmospheric content of brown dwarfs showed evidence of frozen clouds of sulfide and water.

“Ice clouds are predicted to be very important in the atmospheres of planets beyond our Solar System, but they’ve never been observed outside of it before now,” Faherty said.

Artist's concept of lightning on Venus. Image credit: ESA

In the Zone. The Venus Zone: Seeking the Twin of our Twin Among the Stars

Artist's concept of lightning on Venus. Image credit: ESA

Artist’s concept of lightning on Venus. Image credit: ESA

What if, in our quest to find another Earth, we happen upon another Venus?

We should celebrate, of course. Venus is often called Earth’s “twin” because it shares of lot of our home planet’s physical characteristics: surface area, composition and density. Also, roughly speaking, both planets inhabit the area around the Sun’s habitable zone – though Venus is near the inner edge, while we on Earth occupy the relative center. Bearing the similarities and differences in mind, scientists Ravi Kumar Kopparapu, Stephen Kane and Shawn Domagal-Goldman explored how distant analogs to Venus might be detected and differentiated from Earth-like planets occupying the same relative space. The paper pinpointing their finding was published in Astrophysical Journal Letters on 9/10/2014.

Successfully detecting analogs of our inner planets out in the Universe, as Kopparapu and colleagues describe, means that at least two important events have taken place.

One says something about us. At present, our ability to identify the existence of other planetary systems is increasing by the day. When it comes to divining which exoplanet is a mini-Neptune and which is a mega-Earth, we still have a ways to go. Gaining the ability to pick out Venus-like planets will imply that we have gotten really good at sorting exoplanets.

The other is a larger statement about the Universe: If Venus-like planets are found in abundance, then Solar Systems like ours may be the rule rather than the exception. Discovering a twin to Venus around another star might well spark our interest in focusing our observations there, both for signs of another Earth and for clues about the dynamics of exoplanetary systems that harbor conditions similar to our own.

In their paper, Kopparapu, Domagal-Goldman and Kane explain how we can determine the distance between a planet and a star from calculations we can make today. They project that in the near future, when the James Webb Space Telescope takes to the skies, measurements of exoplanetary atmospheres will distinguish Venus-like from Earth-like from Mars-like. In the meantime, Kane and colleagues made some important calculations that will assist astronomers in the search for distant Venuses.

Not every planet in or near a habitable zone is habitable. Inhospitable Venus is an excellent example. Credit: NASA/JPL/Caltech

Not every planet in or near a habitable zone is habitable. Inhospitable Venus is an excellent example. Credit: NASA/JPL/Caltech

First, they estimated how close a planet can be to a star and still retain its atmosphere. Those figures pertain to planets like Mercury, with close-in orbits where the Solar Wind strips away nearly all atmospheric particles. Then, they approximated the furthest distance from a star likely to sustain a planet-wide runaway greenhouse effect. Taken together, these parameters describe the Venus zone: a place where we can start looking for planets with characteristics of own second planet from the Sun.

Before we move on to finding planets in other solar systems, we should talk a bit about our own Solar System. Here to do that and then discuss his findings is Dr. Shawn Domagal-Goldman, one of the paper’s authors and the mind behind The Pale Blue Blog at astrobio.net.

Astrobiology Magazine (AM): Shawn, the discovery of just how much Earth and Venus differ is relatively recent. What did it take for us to figure out that our own twin in the Solar System was not just uninhabited, but utterly uninhabitable?

Domagal-Goldman: This is one of the things we’ve learned through telescope and spacecraft observations of Venus over the last century or so. And this highlights two of the things I love about this paper – it leverages what we’ve learned about planets from observations of the ones in our own solar system to inform exoplanet data; and it also reinforces the notion that two planets with fairly Earth-like “astrophysical” properties such as mass/radius can be dramatically different in terms of their habitability.

AM: Where is our own “Venus zone”?

Domagal-Goldman: The outer edge of the “Venus zone” is, by the way we’ve defined it here, the same as the inner edge of the habitable zone. This is roughly the “border” between where we think a planet is more likely to be Venus (closer to the Sun than the border) or more like Earth (further from the Sun than the border). This border therefore is between Earth and Venus. The inner edge of the “Venus zone” is the distance at which Venus would lose it’s atmosphere from all high energy input from the Sun. In our system, this is VERY close to the Sun – about twice as close to the Sun as Mercury is.

AM: We’re just beginning to find rocky planets in so-called habitable zones around other stars. Why is now a good time to start breaking up these habitable zones into discrete bands that reflect Earth and Venus? How will we be able to tell a Venus-zone from an Earth-zone at such tremendous distances?  Will there be a Mars-zone as well, when all is said and done?

In the present-day Solar System with the Sun in its current state, Venus is outside of the habitable zone (HZ) – or rather, it is closer to the Sun than the inner boundary of where water will be found in liquid form. The stability of water as a liquid sets the lines for the traditional habitable zone, outlined here in blue. However, for exoplantary systems with characteristics distinct from ours – where the stars exhibit different luminosity, the planets rotate differently, or the atmosphere conditions vary on those planets vary – the HZ will vary in size and distance from the star. Image Credit: NASA

In the present-day Solar System with the Sun in its current state, Venus is outside of the habitable zone (HZ) – or rather, it is closer to the Sun than the inner boundary of where water will be found in liquid form. The stability of water as a liquid sets the lines for the traditional habitable zone, outlined here in blue. However, for exoplantary systems with characteristics distinct from ours – where the stars exhibit different luminosity, the planets rotate differently, or the atmosphere conditions vary on those planets vary – the HZ will vary in size and distance from the star. Image Credit: NASA

Domagal-Goldman:: There could be a Mars-zone, as well! But getting at that will require us to understand the degree to which Mars was habitable, for how long, and what caused the demise of the red planet’s habitability. These are all questions currently being explored by Curiosity, and we look forward to answers on all those topics.

Ultimately, these sorts of categorizations are going to be done better when we can analyze exoplanets in more detail with bigger future telescopes. The reason we’re doing all this now is for two reasons. First, this gives the community scientific hypotheses for us to test with that sort of mission. Second, it helps us design those missions, and prioritize which objects we would look at first when those missions happen.

AM: The size and location of the Venus zone in each system is going to be dependent on a lot of factors: for example, the luminosity and size of the primary star. A white dwarf star will have a Venus zone much smaller and closer in than our Sun’s. What else will we need to consider in trying to size up Venus zones?

Domagal-Goldman: The other thing that’s really needed now is more simulations of Venus-like atmospheres. This is something that’s very difficult to do, as Venus has been one of the planets that is most difficult to simulate in our computer models. Making advances in that will help us determine the boundaries of both the Venus zone and the habitable zone. Ultimately, we want to define these boundaries with observations from telescopes, but until that happens the best thing we can do will be to improve our simulations and use those results to refine the concept of the Venus zone.

AM: The Kepler Space Telescope has been the workhorse of our planet-hunting mission thus far. When the James Webb takes to the skies, what will change, in terms of finding the Venus Zones, the Venus-analogs, the Earth-analogs and places where we should focus the search for life?

Domagal-Goldman: If we’re lucky, we’ll get a couple Venus-like candidates to study, as the first tests of the hypotheses in this paper. And if we’re extremely lucky, we may get a potentially habitable world or two for us to study, as well. That will be the first mission to move us from studying the “physics” of these planets to being able to study the “chemistry” for a large number of them. Eventually, with a future mission, the goal is to study the biology of such worlds.