A computer-assisted model of the Mars 2020 rover, which is expected to look for signs of habitable environments on the Red Planet. It also will cache samples for possible return to Earth by another mission. Credit: NASA/JPL-Caltech
Single-celled microbes are considered a living example of the kind of life that might exist elsewhere in the Universe, as they are able to survive some of the extreme conditions that exist on other worlds.
New research on the bacterium Tepidibacillus decaturensis shows that it could be a model organism for what might live on Mars, should any creature inhabit the Red Planet. This microorganism, found in water more than a mile underground in the Illinois Basin in a formation known as Mount Simon Sandstone, has been shown to be moderately tolerant of heat and salt and able to persist in an anoxic environment. Mars itself is believed to harbor similarly briny surface water without the presence of oxygen.
The research was led by Yiran Dong, a research scientist at the Carl R. Woese Institute of Genomic Biology, Robert Sanford, a geomicrobiologist and research associate professor at the University of Illinois, Urbana-Champaign, and Bruce W. Fouke, a professor at the University of Illinois, Urbana-Champaign and was co-funded by the NASA Astrobiology Institute and the National Energy Technology Laboratory.
An image of recurring slope lineae on Mars, which are believed to represent the movement of briny water on the Red Planet’s surface. These areas may be hospitable to microbes. Credit: NASA/JPL-Caltech/Univ. of Arizona
Drilling for CO2 sequestration
The research team piggybacked on drilling activity completed by the Midwest Geological Sequestration Consortium (MGSC), which includes the Illinois State Geological Survey (ISGS) and Archer Daniels Midland (ADM). Supported by the Department of Energy, this project is evaluating locations for storing carbon underground to sequester the enormous volume of CO2 emissions being produced by ADM industrial food production, Sanford explained.
The research team participated in two drill sessions that were completed on the grounds of the ADM facility in Decatur, Illinois. Both wells are within 1,000 feet of one another and clean deep, subsurface groundwater was collected at a variety of depths.The target lithology of the Mount Simon sandstone in this central portion of the Illinois Basin ranges from 1.5 kilometers (0.93 miles) to 2.2 kilometers (1.4 miles) in burial depth. This habitat also happens to have iron oxide minerals coating the sandstone grains, which is also true of much of the surface of Mars.
“There have been some iron-reducers [bacteria] found at deep subsurface environments,” Sanford said. “These organisms have respiratory functions for reducing iron; they are reducing iron like we use oxygen. They use ferric iron to breathe.”
The bacterium they were studying, however, is a fermentative organism. Another example of this kind of organism is yeast, a fungus that converts sugar to alcohol through enzymes. Tepidibacillus decaturensis does not use iron to breathe, but it uses iron to sustain its metabolism in a very similar fashion to how yeast produce ethanol to sustain theirs.
Aqua satellite image of the states of Illinois and Missouri. The Illinois Basin underlies much of the area. Credit: LANCE MODIS Rapid Response
The team is analyzing the genomic composition of Tepidibacillus decaturensis. Luckily, they have found another, separate iron-reducing bacterium from the same geological formation called Orenia metallireducens, the first known bacterial species in genus Orenia that reduces ferric to ferrous iron. (A study based on this finding was recently accepted in the journal Applied and Environmental Microbiology.)
The combination of these two iron-reducing bacteria will allow the scientists to conduct comparative studies of their metabolisms and ecology, permitting them to further explore these novel metal-reducing mechanisms. Two iron-dependent organisms in a similar environment provide valuable comparisons to understand how life behaves in these deep, hostile environments.
“We are trying to see whether there are some new [gene] features to set up experiments to test them, and thus explore for the first time the deep evolutionary history of these organisms on Earth and potentially Mars,” Dong said of the ongoing work.
This illustration represents how hot Jupiters of different temperatures and different cloud compositions might appear to a person flying over the dayside of these planets on a spaceship, based on computer modeling. Credits: NASA/JPL-Caltech/University of Arizona/V. Parmentier
The weather forecast for faraway, blistering planets called “hot Jupiters” might go something like this: Cloudy nights and sunny days, with a high of 2,400 degrees Fahrenheit (about 1,300 degrees Celsius, or 1,600 Kelvin).
These mysterious worlds are too far away for us to see clouds in their atmospheres. But a recent study using NASA’s Kepler space telescope and computer modeling techniques finds clues to where such clouds might gather and what they’re likely made of. The study was published in the Astrophysical Journal and is also available on the arXiv.
Hot Jupiters, among the first of the thousands of exoplanets (planets outside our solar system) discovered in our galaxy so far, orbit their stars so tightly that they are perpetually charbroiled. And while that might discourage galactic vacationers, the study represents a significant advance in understanding the structure of alien atmospheres.
Endless days, endless nights
Hot Jupiters are tidally locked, meaning one side of the planet always faces its sun and the other is in permanent darkness. In most cases, the “dayside” would be largely cloud-free and the “nightside” heavily clouded, leaving partly cloudy skies for the zone in between, the study shows.
“The cloud formation is very different from what we know in the solar system,” said Vivien Parmentier, a NASA Sagan Fellow and postdoctoral researcher at the University of Arizona, Tucson, who was the lead author of the study.
A “year” on such a planet can be only a few Earth days long, the time the planet takes to whip once around its star. On a “cooler” hot Jupiter, temperatures of, say, 2,400 degrees Fahrenheit might prevail.
But the extreme conditions on hot Jupiters worked to the scientists’ advantage.
“The day-night radiation contrast is, in fact, easy to model,” Parmentier said. “[The hot Jupiters] are much easier to model than Jupiter itself.”
An eclipse, then blips
The scientists first created a variety of idealized hot Jupiters using global circulation models — simpler versions of the type of computer models used to simulate Earth’s climate.
Then they compared the models to the light Kepler detected from real hot Jupiters. Kepler, which is now operating in its K2 mission, was designed to register the extremely tiny dip in starlight when a planet passes in front of its star, which is called a “transit.” But in this case, researchers focused on the planets’ “phase curves,” or changes in light as the planet passes through phases, like Earth’s moon.
Matching the modeled hot Jupiters to phase curves from real hot Jupiters revealed which curves were caused by the planet’s heat, and which by light reflected by clouds in its atmosphere. By combining Kepler data with computer models, scientists were able to infer global cloud patterns on these distant worlds for the first time.
The new cloud view allowed the team to draw conclusions about wind and temperature differences on the hot Jupiters they studied. Just before the hotter planets passed behind their stars — in a kind of eclipse — a blip in the planet’s optical light curve revealed a “hot spot” on the planet’s eastern side.
And on cooler eclipsing planets, a blip was seen just after the planet re-emerged on the other side of the star, this time on the planet’s western side.
The early blip on hotter worlds reveals that powerful winds were pushing the hottest, cloud-free part of the atmosphere, normally found directly beneath its sun, to the east. Meanwhile, on cooler worlds, clouds could bunch up and reflect more light on the “colder,” western side of the planet, causing the post-eclipse blip.
“We’re claiming that the west side of the planet’s dayside is more cloudy than the east side,” Parmentier said.
While the puzzling pattern has been seen before, this research was the first to study all the hot Jupiters showing this behavior.
This led to another first. By figuring out how clouds are distributed, which is intimately tied to the planet’s overall temperature, scientists were able to determine what the clouds were probably made of.
Just add manganese, and stir
Hot Jupiters are far too hot for water-vapor clouds like those on Earth. Instead, clouds on these planets are likely formed as exotic vapors condense to form minerals, chemical compounds like aluminum oxide, or even metals, like iron.
The science team found that manganese sulfide clouds probably dominate on “cooler” hot Jupiters, while silicate clouds prevail at higher temperatures. On these planets, the silicates likely “rain out” into the planet’s interior, vanishing from the observable atmosphere.
In other words, a planet’s average temperature, which depends on its distance from its star, governs the kinds of clouds that can form. That leads to different planets forming different types of clouds.
“Cloud composition changes with planet temperature,” Parmentier said. “The offsetting light curves tell the tale of cloud composition. It’s super interesting, because cloud composition is very hard to get otherwise.”
The new results also show that clouds are not evenly distributed on hot Jupiters, echoing previous findings from NASA’s Spitzer Space Telescope suggesting that different parts of hot Jupiters have vastly different temperatures.
The new findings come as we mark the 21st anniversary of exoplanet hunting. On Oct. 6, 1995, a Swiss team announced the discovery of 51 Pegasi b, a hot Jupiter that was the first planet to be confirmed in orbit around a sun-like star. Parmentier and his team hope their revelations about the clouds on hot Jupiters could bring more detailed understanding of hot Jupiter atmospheres and their chemistry, a major goal of exoplanet atmospheric studies.
After investigating the upper atmosphere of the Red Planet for a full Martian year, NASA’s MAVEN mission has determined that the escaping water does not always go gently into space.
Sophisticated measurements made by a suite of instruments on the Mars Atmosphere and Volatile Evolution, or MAVEN, spacecraft revealed the ups and downs of hydrogen escape – and therefore water loss. The escape rate peaked when Mars was at its closest point to the sun and dropped off when the planet was farthest from the sun. The rate of loss varied dramatically overall, with 10 times more hydrogen escaping at the maximum.
“MAVEN is giving us unprecedented detail about hydrogen escape from the upper atmosphere of Mars, and this is crucial for helping us figure out the total amount of water lost over billions of years,” said Ali Rahmati, a MAVEN team member at the University of California at Berkeley who analyzed data from two of the spacecraft’s instruments.
Hydrogen in Mars’ upper atmosphere comes from water vapor in the lower atmosphere. An atmospheric water molecule can be broken apart by sunlight, releasing the two hydrogen atoms from the oxygen atom that they had been bound to. Several processes at work in Mars’ upper atmosphere may then act on the hydrogen, leading to its escape.
This loss had long been assumed to be more-or-less constant, like a slow leak in a tire. But previous observations made using NASA’s Hubble Space Telescope and ESA’s Mars Express orbiter found unexpected fluctuations. Only a handful of these measurements have been made so far, and most were essentially snapshots, taken months or years apart. MAVEN has been tracking the hydrogen escape without interruption over the course of a Martian year, which lasts nearly two Earth years.
This image shows atomic hydrogen scattering sunlight in the upper atmosphere of Mars, as seen by the Imaging Ultraviolet Spectrograph on NASA’s Mars Atmosphere and Volatile Evolution mission. About 400,000 observations, taken over the course of four days shortly after the spacecraft entered orbit around Mars, were used to create the image. Hydrogen is produced by the breakdown of water, which was once abundant on Mars’ surface. Because hydrogen has low atomic mass and is weakly bound by gravity, it extends far from the planet (the darkened circle) and can readily escape. Credits: NASA/Goddard/University of Colorado
“Now that we know such large changes occur, we think of hydrogen escape from Mars less as a slow and steady leak and more as an episodic flow – rising and falling with season and perhaps punctuated by strong bursts,” said Michael Chaffin, a scientist at the University of Colorado at Boulder who is on the Imaging Ultraviolet Spectrograph (IUVS) team. Chaffin is presenting some IUVS results on Oct. 19 at the joint meeting of the Division for Planetary Sciences and the European Planetary Science Congress in Pasadena, California.
In the most detailed observations of hydrogen loss to date, four of MAVEN’s instruments detected the factor-of-10 change in the rate of escape. Changes in the density of hydrogen in the upper atmosphere were inferred from the flux of hydrogen ions – electrically charged hydrogen atoms – measured by the Solar Wind Ion Analyzer and by the Suprathermal and Thermal Ion Composition instrument. IUVS observed a drop in the amount of sunlight scattered by hydrogen in the upper atmosphere. MAVEN’s magnetometer found a decrease in the occurrence of electromagnetic waves excited by hydrogen ions, indicating a decrease in the amount of hydrogen present.
By investigating hydrogen escape in multiple ways, the MAVEN team will be able to work out which factors drive the escape. Scientists already know that Mars’ elliptical orbit causes the intensity of the sunlight reaching Mars to vary by 40 percent during a Martian year. There also is a seasonal effect that controls how much water vapor is present in the lower atmosphere, as well as variations in how much water makes it into the upper atmosphere. The 11-year cycle of the sun’s activity is another likely factor.
“In addition, when Mars is closest to the sun, the atmosphere becomes turbulent, resulting in global dust storms and other activity. This could allow the water in the lower atmosphere to rise to very high altitudes, providing an intermittent source of hydrogen that can then escape,” said John Clarke, a Boston University scientist on the IUVS team. Clarke will present IUVS measurements of hydrogen and deuterium – a form of hydrogen that contains a neutron and is heavier – on Oct. 19 at the planetary conference.
By making observations for a second Mars year and during different parts of the solar cycle, the scientists will be better able to distinguish among these effects. MAVEN is continuing these observations in its extended mission, which has been approved until at least September 2018.
“MAVEN’s findings reveal what is happening in Mars’ atmosphere now, but over time this type of loss contributed to the global change from a wetter environment to the dry planet we see today,” said Rahmati.
Artist’s impression of NASA’s New Horizons spacecraft encountering a Kuiper Belt object, as part of an extended mission after the spacecraft’s July 2015 Pluto flyby. New Horizons is set to fly past 2014 MU69 – a KBO currently about a billion miles (1.6 billion kilometers) beyond Pluto – on Jan. 1, 2019. Recent data from the Hubble Space Telescope suggests 2014 MU69 has a reddish hue, even redder than Pluto. The object is the smallest KBO to have its surface properties measured. Credits: NASA/JHUAPL/SwRI
The next target for NASA’s New Horizons mission – which made a historic flight past Pluto in July 2015 –– apparently bears a colorful resemblance to its famous, main destination.
Hubble Space Telescope data suggests that 2014 MU69, a small Kuiper Belt object (KBO) about a billion miles (1.6 billion kilometers) beyond Pluto, is as red, if not redder, than Pluto. This is the first hint at the surface properties of the far flung object that New Horizons will survey on Jan. 1, 2019.
Mission scientists are discussing this and other Pluto and Kuiper Belt findings this week at the American Astronomical Society Division for Planetary Sciences (DPS) and European Planetary Science Congress (EPSC) in Pasadena, California.
“We’re excited about the exploration ahead for New Horizons, and also about what we are still discovering from Pluto flyby data,” said Alan Stern, principal investigator from Southwest Research Institute in Boulder, Colorado. “Now, with our spacecraft transmitting the last of its data from last summer’s flight through the Pluto system, we know that the next great exploration of Pluto will require another mission to be sent there.”
Partly Cloudy on Pluto? Pluto’s present, hazy atmosphere is almost entirely free of clouds, though scientists from NASA’s New Horizons mission have identified some cloud candidates after examining images taken by the New Horizons Long Range Reconnaissance Imager and Multispectral Visible Imaging Camera, during the spacecraft’s July 2015 flight through the Pluto system. All are low-lying, isolated small features—no broad cloud decks or fields – and while none of the features can be confirmed with stereo imaging, scientists say they are suggestive of possible, rare condensation clouds. Credits: NASA/JHUAPL/SwRI
Stern said that Pluto’s complex, layered atmosphere is hazy and appears to be mostly free of clouds, but the team has spied a handful of potential clouds in images taken with New Horizons’ cameras. “If there are clouds, it would mean the weather on Pluto is even more complex than we imagined,” Stern said.
Scientists already knew from telescope observations that Pluto’s icy surface below that atmosphere varied widely in brightness. Data from the flyby not only confirms that, it also shows the brightest areas (such as sections of Pluto’s large heart-shaped region) are among the most reflective in the solar system. “That brightness indicates surface activity,” said Bonnie Buratti, a science team co-investigator from NASA’s Jet Propulsion Laboratory in Pasadena. “Because we see a pattern of high surface reflectivity equating to activity, we can infer that the dwarf planet Eris, which is known to be highly reflective, is also likely to be active.”
While Pluto shows many kinds of activity, one surface process apparently missing is landslides. Surprisingly, though, they have been spotted on Pluto’s largest moon, Charon, itself some 750 miles (1,200 kilometers) across. “We’ve seen similar landslides on other rocky and icy planets, such as Mars and Saturn’s moon Iapetus, but these are the first landslides we’ve seen this far from the sun, in the Kuiper Belt,” said Ross Beyer, a science team researcher from Sagan Center at the SETI Institute and NASA Ames Research Center, California. “The big question is will they be detected elsewhere in the Kuiper Belt?”
Both Hubble and cameras on the New Horizons spacecraft have been aimed at KBOs over the past two years, with New Horizons taking advantage of its unique vantage point in the Kuiper Belt to observe nearly a dozen small worlds in this barely explored region. MU69 is actually the smallest KBO to have its color measured – and scientists have used that data to confirm the object is part of the so-called cold classical region of the Kuiper Belt, which is believed to contain some of the oldest, most prehistoric material in the solar system.
Scientists from NASA’s New Horizons mission have spotted signs of long run-out landslides on Pluto’s largest moon, Charon. This image of Charon’s informally named Serenity Chasma was taken by New Horizons’ Long Range Reconnaissance Imager (LORRI) on July 14, 2015, from a distance of 48,912 miles (78,717 kilometers). Arrows mark indications of landslide activity. Credits: NASA/JHUAPL/SwRI
“The reddish color tells us the type of Kuiper Belt object 2014 MU69 is,” said Amanda Zangari, a New Horizons post-doctoral researcher from Southwest Research Institute. “The data confirms that on New Year’s Day 2019, New Horizons will be looking at one of the ancient building blocks of the planets.”
The New Horizons spacecraft is currently 3.4 billion miles (5.5 billion kilometers) from Earth and about 340 million miles (540 million kilometers) beyond Pluto, speeding away from the sun at about nine miles (14 kilometers) every second. About 99 percent of the data New Horizons gathered and stored on its digital recorders during the Pluto encounter has now been transmitted back to Earth, with that transmission set to be completed Oct. 23. New Horizons has covered about one-third of the distance from Pluto to its next flyby target, which is now about 600 million miles (nearly 1 billion kilometers) ahead.
This artistic rendering shows the distant view from Planet Nine back towards the sun. The planet is thought to be gaseous, similar to Uranus and Neptune. Hypothetical lightning lights up the night side. Credit: Caltech/R. Hurt (IPAC)
The large and distant planet may be adding a wobble to the solar system, giving the appearance that the sun is tilted slightly.
“Because Planet Nine is so massive and has an orbit tilted compared to the other planets, the solar system has no choice but to slowly twist out of alignment,” says Elizabeth Bailey, a graduate student at Caltech and lead author of a study announcing the discovery.
All of the planets orbit in a flat plane with respect to the sun, roughly within a couple degrees of each other. That plane, however, rotates at a six-degree tilt with respect to the sun—giving the appearance that the sun itself is cocked off at an angle. Until now, no one had found a compelling explanation to produce such an effect. “It’s such a deep-rooted mystery and so difficult to explain that people just don’t talk about it,” says Brown, the Richard and Barbara Rosenberg Professor of Planetary Astronomy.
Brown and Batygin’s discovery of evidence that the sun is orbited by an as-yet-unseen planet—that is about 10 times the size of Earth with an orbit that is about 20 times farther from the sun on average than Neptune’s—changes the physics. Planet Nine, based on their calculations, appears to orbit at about 30 degrees off from the other planets’ orbital plane—in the process, influencing the orbit of a large population of objects in the Kuiper Belt, which is how Brown and Batygin came to suspect a planet existed there in the first place.
“It continues to amaze us; every time we look carefully we continue to find that Planet Nine explains something about the solar system that had long been a mystery,” says Batygin, an assistant professor of planetary science.
Their findings have been accepted for publication in an upcoming issue of the Astrophysical Journal, and will be presented on October 18 at the American Astronomical Society’s Division for Planetary Sciences annual meeting, held in Pasadena.
The tilt of the solar system’s orbital plane has long befuddled astronomers because of the way the planets formed: as a spinning cloud slowly collapsing first into a disk and then into objects orbiting a central star.
Planet Nine’s angular momentum is having an outsized impact on the solar system based on its location and size. A planet’s angular momentum equals the mass of an object multiplied by its distance from the sun, and corresponds with the force that the planet exerts on the overall system’s spin. Because the other planets in the solar system all exist along a flat plane, their angular momentum works to keep the whole disk spinning smoothly.
Planet Nine’s unusual orbit, however, adds a multi-billion-year wobble to that system. Mathematically, given the hypothesized size and distance of Planet Nine, a six-degree tilt fits perfectly, Brown says.
The next question, then, is how did Planet Nine achieve its unusual orbit? Though that remains to be determined, Batygin suggests that the planet may have been ejected from the neighborhood of the gas giants by Jupiter, or perhaps may have been influenced by the gravitational pull of other stellar bodies in the solar system’s extreme past.
For now, Brown and Batygin continue to work with colleagues throughout the world to search the night sky for signs of Planet Nine along the path they predicted in January. That search, Brown says, may take three years or more.
MAVEN’s Imaging UltraViolet Spectrograph obtained images of rapid cloud formation on Mars on July 9-10, 2016. The ultraviolet colors of the planet have been rendered in false color, to show what we would see with ultraviolet-sensitive eyes. Mars’ tallest volcano, Olympus Mons, appears as a prominent dark region near the top of the image, with a small white cloud at the summit that grows during the day. Three more volcanoes appear in a diagonal row, with their cloud cover (white areas near center) merging to span up to a thousand miles by the end of the day. Credits: NASA/MAVEN/University of Colorado
New global images of Mars from the MAVEN mission show the ultraviolet glow from the Martian atmosphere in unprecedented detail, revealing dynamic, previously invisible behavior. They include the first images of “nightglow” that can be used to show how winds circulate at high altitudes. Additionally, dayside ultraviolet imagery from the spacecraft shows how ozone amounts change over the seasons and how afternoon clouds form over giant Martian volcanoes. The images were taken by the Imaging UltraViolet Spectrograph (IUVS) on the Mars Atmosphere and Volatile Evolution mission (MAVEN).
“MAVEN obtained hundreds of such images in recent months, giving some of the best high-resolution ultraviolet coverage of Mars ever obtained,” said Nick Schneider of the Laboratory for Atmospheric and Space Physics at the University of Colorado, Boulder. Schneider is presenting these results Oct. 19 at the American Astronomical Society Division for Planetary Sciences meeting in Pasadena, California, which is being held jointly with the European Planetary Science Congress.
Nightside images show ultraviolet (UV) “nightglow” emission from nitric oxide (abbreviated NO). Nightglow is a common planetary phenomenon in which the sky faintly glows even in the complete absence of external light. Mars’ nightside atmosphere emits light in the ultraviolet due to chemical reactions that start on Mars’ dayside. Ultraviolet light from the sun breaks down molecules of carbon dioxide and nitrogen, and the resulting atoms are carried around the planet by high-altitude wind patterns that encircle the planet. On the nightside, these winds bring the atoms down to lower altitudes where nitrogen and oxygen atoms collide to form nitric oxide molecules. The recombination releases extra energy, which comes out as ultraviolet light.
This image of the Mars night side shows ultraviolet emission from nitric oxide (abbreviated NO). The emission is shown in false color with black as low values, green as medium, and white as high. These emissions track the recombination of atomic nitrogen and oxygen produced on the dayside, and reveal the circulation patterns of the atmosphere. The splotches, streaks and other irregularities in the image are indications that atmospheric patterns are extremely variable on Mars’ nightside. The inset shows the viewing geometry on the planet. MAVEN’s Imaging UltraViolet Spectrograph obtained this image of Mars on May 4, 2016 during late winter in Mars Southern Hemisphere. Credits: NASA/MAVEN/University of Colorado
Scientists predicted NO nightglow at Mars, and prior missions detected its presence, but MAVEN has returned the first images of this phenomenon in the Martian atmosphere. Splotches and streaks appearing in these images occur where NO recombination is enhanced by winds. Such concentrations are clear evidence of strong irregularities in Mars’ high altitude winds and circulation patterns. These winds control how Mars’ atmosphere responds to its very strong seasonal cycles. These first images will lead to an improved determination of the circulation patterns that control the behavior of the atmosphere from approximately 37 to 62 miles (about 60 to 100 kilometers) high.
Dayside images show the atmosphere and surface near Mars’ south pole in unprecedented ultraviolet detail. They were obtained as spring comes to the southern hemisphere. Ozone is destroyed when water vapor is present, so ozone accumulates in the winter polar region where the water vapor has frozen out of the atmosphere. The images show ozone lasting into spring, indicating that global winds are inhibiting the spread of water vapor from the rest of the planet into winter polar regions. Wave patterns in the images, revealed by UV absorption from ozone concentrations, are critical to understanding the wind patterns, giving scientists an additional means to study the chemistry and global circulation of the atmosphere.
This ultraviolet image near Mars’ South Pole was taken by MAVEN on July 10 2016 and shows the atmosphere and surface during southern spring. The ultraviolet colors of the planet have been rendered in false color, to show what we would see with ultraviolet-sensitive eyes. Darker regions show the planet’s rocky surface and brighter regions are due to clouds, dust and haze. The white region centered on the pole is frozen carbon dioxide (dry ice) on the surface. Pockets of ice are left inside craters as the polar cap recedes in the spring, giving its edge a rough appearance. High concentrations of atmospheric ozone appear magenta in color, and the wavy edge of the enhanced ozone region highlights wind patterns around the pole. Credits: NASA/MAVEN/University of Colorado
MAVEN observations also show afternoon cloud formation over the four giant volcanoes on Mars, much as clouds form over mountain ranges on Earth. IUVS images of cloud formation are among the best ever taken showing the development of clouds throughout the day. Clouds are a key to understanding a planet’s energy balance and water vapor inventory, so these observations will be valuable in understanding the daily and seasonal behavior of the atmosphere.
“MAVEN’s elliptical orbit is just right,” said Justin Deighan of the University of Colorado, Boulder, who led the observations. “It rises high enough to take a global picture, but still orbits fast enough to get multiple views as Mars rotates over the course of a day.”
Comets are travellers in time as well as space. Coming to us from the very beginning of our Solar System — 4-billion-years ago or so — their dark bodies brighten as they approach the Sun, offering us an unparalleled window into our ancient chemical origins.
Thanks to Rosetta, we know for sure that chemicals living in our own DNA, proteins, and cell membranes can be found in the furthest corners of the Solar System. More such discoveries likely lie in store as researchers troll through two years of streaming data — a stream that finally came to an end on September 30th, 2016, as Rosetta dove into comet C-G, reporting on everything it saw, touched, and smelled with its many sensors, right up to when it finally came to rest on the face of that dark, slightly-less-mysterious-than-before, wandering body.
To Catch a Comet by the Tail: Rosetta’s historic meet and greet with Churyumov-Gerasimenko (Originally posted on June 2, 2014)
ESA’s Rosetta spacecraft carries 11 scientific instruments that it will use to examine two asteroids while en route to its final destination, comet 67P Churyumov-Gerasimenko. Credits: ESA/AOES Medialab
The European Space Agency’s Rosetta spacecraft has been traveling for a decade to meet comet 67P/Churyumov-Gerasimenko (C-G). Rosetta is expected to finally catch up with C-G in August. Then in November, Rosetta will eject a lander called Philae onto the comet’s surface: a one-way trip to a totally unknown landscape.
You might be wondering: How does one build a lander for an unknown land?
To start with: prepare for a hard landing and a soft landing at the same time. To that end, Philae’s 100 kilogram (220 lb.) payload includes a spring-tipped landing tripod and two harpoons.
That’s right, harpoons. If the comet has a hard surface, Philae’s harpoons will hopefully keep it from bouncing off the comet and floating away. In case harpoons alone don’t suffice, Philae also has a jet full of cold gas that can fire to keep it pinned to C-G’s surface.
How much dust lies on the surface of a comet is anyone’s guess. It could be a few inches, a few feet or few meters. In case comet 67P/is covered in a thick coat of soft dust, Philae’s three human-sized tripod legs have drills on their tips to keep the lander from sliding around or sinking too far down.
“We’re landing in complete unknown. That’s where the tricky engineering is. There’s a lot of dust on the surface brought up by the gas,” said U.S. project manager Art Chmielewski during a teleconference in March 2014. “It will be pretty exciting to see how deep these [tripod] legs go into the dust.”
After the lander’s release from the orbiter, the rest is up to automation, chance, good luck and incredible engineering, and example of which is its solar panels. Philae has a solar panel on each of its six sides. If it hits the dust and sinks or rolls into a gully, one of the solar panels will hopefully still be able to take in enough energy to continue making observations. For now, we don’t know how long the landing itself will take or where Philae will land. For many of the questions that you would ask before kicking a satellite the size of a dishwasher onto an active comet, the answer is likely, “We don’t know yet, but we will soon.”
Sometimes the best way, or the only way, to learn about what’s going on the Universe is to reach out and touch it.
Comets are fascinating for many reasons.
Scientifically speaking, comets are complex remnants from the very earliest times in our Solar System. They accreted, or grew, out of the same spinning gas cloud that gave rise to the Sun. Comets are believed to be at least as old as the gas giants Jupiter and Saturn, yet were recently discovered to be rich in organic molecules.
Artist Rendition of Rosetta releasing the Philae lander. Credit: NASA JPL and and Art B. Chmielewski
Credible theories maintain that comets may have introduced the basic components of life to Earth. If that’s true, it’s likely that they have introduced life’s building blocks to other bodies in our solar system, such as Mars and the moons Enceladus and Europa. From an astronomer’s perspective, we have many reasons to be chasing after comets.
In terms of the strictly human experience, comets captivate not just our curiosity, but also our attention, in a very unique way.
“Seeing a comet in the sky is a powerfully visceral experience,” said Claudia Alexander, the Rosetta project scientist at NASA’s Jet Propulsion Laboratory. “It appears as something that shouldn’t be there, and if you didn’t know better it’s easy to see them as scary.”
With comets, part of the fear factor is that they come streaking through the darkness seemingly out of nowhere. Most of the time comets slip along unnoticed. We only see them clearly for what amounts to an astronomical split-second as they come charging towards the Sun or go streaking away from it.
Because of their stealth and seeming unpredictability, comets have traditionally invoked terror, suspicion and awe in human kind. In many ways they resemble tigers, not just in their quiet approach and dramatic charge, but also in appearance. The similarity, of course, is their tails. Tails are the feature most people think about first when they think about comets.
Tails add vastly to comets’ mystique and render them unique as astronomical phenomena. Tails mark the approach to the solar apex of a comet’s long orbit, when surface temperature, dust halo thickness and geologic activity all change. Most of these attributes contribute to the production of the tail, which can be observed from Earth with the naked eye over the course of weeks and, in the case of Halley’s comet, from one generation to the next.
Throughout the ages, whenever these bright-tailed visitors have come by Earth we wished we could keep them longer, look at them closer, and understand them better. After millennia of watching in wonder from the ground-and more than 15 years after the Rosetta mission was approved-we are swiftly approaching our long-awaited rendezvous.
Join Claudia Alexander as she provides an overview of the Rosetta mission and its plans to encounter a comet to learn more about the formation of the solar system. Credit: JPL
Whether or not the lander Philae makes it down in one piece, a year from now we will have a whole new world of knowledge about these tigers of space.
Rosetta: Humanity’s first attempt to land on a comet
The European Space Agency named the mission Rosetta after the Rosetta Stone, a key discovery in human history that allowed us to unlock critical components of our own history.
“They chose that name because they wanted the mission to provide a ‘bridge’ to the past of our solar system, the same way that the original Rosetta Stone provided a bridge to an ancient culture that had previously not been understood,” said Alexander.
Previous comet-centered missions have revealed just enough to allow us to unseat prevailing theories, but not enough to firm up new ones.
In 1986, Images of Halley’s comet nucleus showed us a dark, jelly-bean-shaped object very distinct from the traditional “dirty snowball” postulated by astronomer Fred Whipple in the 1950s. In 2005, NASA threw a coffee-table-sized spacecraft at comet Temple. The resulting Deep Impact explosion was shallower than anticipated, but nonetheless implied that comets may be more porous the previously thought and not armored with an icy exterior or shell.
Artist’s impression of the Philae lander with Rosetta in the distance. The CONCERT instrument will pass signals back and forth between the two to determine. Credit: ESA
Then, there’s the “dirty” part of the “dirty snowball” comet theory. Comet surfaces are covered in some inky-colored material, which may be hydrocarbons (the result of interactions between nitrogen, methane and energetic particles) or may be something else entirely. Whatever the dark material is composed of, after examining the aftermath of Deep Impact we discovered that comets may not only be coated in dark material: they may be entirely composed of it.
The Deep Impact and the EPOXI missions also showed us that comets possess distinct geology — ridges, cracks and even cliffs that sprout jets. NASA’s Stardust spacecraft chased down comet Wild 2 and discovered glycine, one of the basic building blocks of life, streaming out of its nucleus.
The list of comet missions goes on. Each revealed an abundance of surprises. None have been as ambitious as Rosetta.
Rosetta is essentially a flying comet laboratory. It carries 16 experiments on 11 instruments jointly managed by the US and Europe. These will measure the volume and contents of the gas in the comet’s coma, bounce radio signals off the comet’s nucleus, measure thermal and electrical properties of the surface, count water, carbon monoxide, ammonia, and methanol molecules, and take high-resolution infrared images. Experimenters will try to figure out what causes the famous jets on comet surfaces by comparing maps of surface temperature to where the jets appear, in the hope of discovering whether or not hot spots create jets.
One Rosetta instrument called COSIMA (Cometary Secondary Ion Mass Analyser) will literally put comet C-G under the microscope by examining the dust from Philae’s landing. Another instrument called CONSERT (Comet Nucleus Sounding Experiment by Radio wave Transmission) lives partly on the orbiter and partly on the lander. By sending and transmitting radio signals back and forth, CONSERT will effectively ultrasound comet C-G’s nucleus.
Philae’s landing could easily end up less than ideal: with two legs in a rut or with the lander lying on its side. But as long as CONSERT arrives in working order, Rosetta should be able to discover whether comet Churyumov-Gerasimenko is loosely packed, made of discrete layers or dense all the way through. Even if Philae crash-lands, or its sensors become coated in sticky, electrically-charged dust, CONSERT will take initial readings of C-G’s surface layer during the descent to the surface.
If Philae lands upright and all systems are a go, we may get answers to many long-standing mysteries, including, to use Whipple’s analogy, what’s making the snowball dirty. Philae’s SD2 instrument is a drill and sample collector with three instruments all its own. Between two gas analyzers, seven micro-cameras, an infrared spectrometer and a light microscope, we may come to learn far more about cometary “dark stuff.”
Approach to comet Churyumov-Gerasimenko. Credit: ESA
Above all, Rosetta’s cameras will watch the C-G come alive in real time at it approaches the Sun.
“The whole idea of the mission is to be close enough to see its changing activity from very nearby, and also to periodically take in particles that are coming off the surface,” said Alexander. “So ‘escorting’ the comet means that we’ll be that close all the time, as the comet comes to life underneath us.”
This transition is important for many reasons, one of which involves the search for life itself. Several experiments are designed to replace long-held speculation with facts about life’s components on comets and in the Solar System at large. For astrobiologists, this is where things get really interesting.
Life in Deep Space
Many of life’s precursors have been found in space, including, some believe, the base pairs that make up our own DNA.
“That’s part of the purpose of the Rosetta mission — to give us concrete evidence that we can use to replace speculation,” said Alexander. “Some sophisticated molecule fragments found in DNA are seen in asteroid chemistry. We really are at the beginning of understanding how some of this chemistry is related to life’s origins (if at all).”
In a manner reminiscent of a forensics lab, Rosetta will look for the chemicals associated with the comet and with life as we know it. The experimenters are asking basic scientific questions about comets: Do comets, like asteroids, harbor basic amino-acid precursors? Are molecules on comets left or right handed?
All life on Earth uses left-handed amino acids to make proteins. In 2011, left-handed amino acids were discovered on asteroids, but so far not on comets, perhaps because on comets the outer layers are destroyed as they heat up. How a comet’s chemical components change as it becomes active it another major focus of Rosetta research.
Rosetta launched in 2004. Three years ago and 163 million kilometers (101 million miles) from comet C-G, Rosetta was put to sleep to wait out the remaining 31-month journey through deep space. It woke up on Jan 20th, 2014 and is moving 3,000 miles closer to its target every minute.
In the meanwhile, comet C-G has also started to stir, growing a dusty veil that makes it visible against the starfield.
How the environment affects a comet, activating it and creating two tails. Credit: ESA
Rosetta caught first site of C-G on March 20th. Now the navigation camera is actively taking the observations and allowing course corrections that will bring the two objects closer together. A few short months from now, in August 2014, Rosetta will be close enough to the comet to chose a target landing site for Philae. Then in November, Philae is expected to be dropped from 1 kilometer above C-G’s surface, with its drills, solar panels and harpoons at the ready.
The Rosetta orbiter itself bears a striking resemblance to a passenger airplane with the wings cut off. Coincidentally, the plan is to to release the lander onto comet C-G from a cruising altitude similar to an airplane on Earth.
“The lander drops. It just drops, but not like the some landers [Mars Curiosity Rover],” said Chmielewski. “Imagine a sheet of paper. Lift it up over your head and let go of it. That’s a better idea of the kind of speed and connotation of what this landing’s going to look like.”
With Philae perched upon its back waiting to fly, and with all of its experiments, sensors, and other in-case gadgetry, Rosetta is speeding towards a long-awaited date with ancient history. In the coming year, this spacecraft will unveil the shape, structure and contents of a comet. Through its infrared eye we will watch C-G respond to solar radiation as it comes closer and closer to the Sun. In the process, we will discover the many differences between a 4 billion-year-old piece of the Solar System quietly moving through space and a 4 billion-year-old piece of the Solar System evaporating into a visually stunning stream across the sky. Which of life’s chemical constituents comets can carry into the Inner Solar System will be explored, and we may, with a little bit of luck, land upright on the surface, dig in our heels and ride the tiger across the sky.
“Comets… are the travelers,” said Alexander. “They come from a distant place in space, and because of we think they represent pristine, unchanged remnants of the distant past. They come to us as ambassadors, if you like, from a different time. At present, we don’t have the capability to travel to those distant solar system locales or to go backwards in time. So comets present a unique ‘archeological dig’ opportunity, so to speak — and they travel to us.”
Research partially funded by Cardiff Centre for Astrobiology, ESA member states and NASA. Airbus Defense and Space built the Rosetta spacecraft. NASA’s Jet Propulsion Laboratory, Pasadena, California, manages the U.S. contribution of the Rosetta mission for NASA’s Science Mission Directorate in Washington.
This jumble of eroded blocks lies along the distinctive boundary between the Red Planet’s southern highlands and the northern lowlands, with remnants of ancient glaciers flowing around them.
This boundary is one of the oldest and most prominent features on Mars, marking a height difference of several kilometres.
The scene presented here, captured by the high-resolution camera on ESA’s Mars Express on 29 May, is just one example of the terrain found along this ancient boundary, and focuses on part of the Colles Nili region.
‘Colles’ comes from the Latin word for ‘hill’, and indeed this region hosts a swath of such features. They are likely erosional remnants of a former plateau, as suggested with their similarity in height seen in the topography map.
Colles Nili in context. Credit: NASA MGS MOLA Science Team
Zooming in to the main colour image and perspective views shows that some of the mounds are surrounded by smooth, layered deposits gently sloping away from the sides of the hills.
An even closer look reveals other finer features on the channel floors around the mounds and inside some of the impact craters: series of ridges and troughs.
Both the layered deposits and the ridges and troughs are thought to be associated with buried ice that has since been covered over by wind-blown dust and local debris from the eroding plateau, perhaps as an underlying ice sheet retreated.
Similar features are found all along the planet-wide boundary and are thought to represent multiple episodes of glaciation within the past several hundred million years.
Later, volcanic dust has blown in from elsewhere to create the striking streaks of dark material seen in various spots, but particularly dominant in the right-hand side of the main colour image.
Looking inside the large impact crater seen in the top right of the main image, and also in the top left of the perspective view, shows this dark material has been piled up into dunes inside the crater, presumably by prevailing winds.
Mars Express has been orbiting the Red Planet since 2003. Next week it will play an important role in listening for signals from Schiaparelli, the ExoMars entry, descent and landing demonstrator, as the lander makes its six-minute descent through the atmosphere to the surface.
Mars Express, Schiaparelli mothership Trace Gas Orbiter and NASA’s Mars Reconnaissance Orbiter will record signals from Schiaparelli to confirm its safe arrival, and they will subsequently act as data relays from the surface.
A new model of canyon-forming floods from UMass Amherst and CalTech researchers suggests that deep canyons can be formed in bedrock by significantly less water than previously thought. Credit: UMass Amherst/Isaac Larsen
Geomorphologists who study Earth’s surface features and the processes that formed them have long been interested in how floods, in particular catastrophic outbursts that occur when a glacial lake ice dam bursts, for example, can change a planet’s surface, not only on Earth but on Mars.
Now geoscience researchers Isaac Larsen at the University of Massachusetts Amherst and Michael Lamb at the California Institute of Technology have proposed and tested a new model of canyon-forming floods which suggests that deep canyons can be formed in bedrock by significantly less water than previously thought. They point out that “reconstructing the magnitude of the canyon-forming floods is essential for understanding how floods modify planetary surfaces, the hydrology of early Mars, and abrupt climate change.”
Larsen and Lamb apply their new model to the “channeled scablands” in eastern Washington State, an area that, like some on Mars, has very deep canyons cut into fractured basalt bedrock. The researchers say their results suggest “there may be a rich imprint of both the history and discharge of flooding in the morphology of canyons” such as terraces, valley shapes and slope profiles on Earth and on Mars “that warrant further investigation.” Details appear in the current issue of Nature.
The researchers say channels in the scablands today, which are up to 650 feet (200 meters) deep and 3 miles (5 km) wide, were likely formed by flood discharges five- to tenfold smaller than brimful estimates, that is by “significantly lower megaflood discharges than previously thought. The channeled scablands are a classic landscape in the history of geomorphology and we’re bringing new views of how it was formed.”
Until the 1920s, scientists did not understand what could have formed the tortured landscape of eastern Washington studied for decades by J Harlen Bretz, a giant figure in geosciences, Larsen recalls. Bretz was the first to suggest that they were formed by catastrophic flooding of unknown origin. His views were dismissed for years, but Bretz was later vindicated when glacial Lake Missoula was identified as the floodwater source.
As most scientists came to accept the catastrophic flood explanation for the canyons and then tried to estimate floodwater discharges, they assumed that floods filled canyons to the brim, a huge amount of water. But an alternate hypothesis proposed and now tested by Lamb and and Larsen posits that as floodwater cuts into bedrock, the canyon deepens, meaning less water is required to shape it.
In areas underlain by fractured bedrock, Larsen says, “our general concept is that the channel floor was being cut and lowered as the floods were happening, and you need to account for that when reconstructing the scenario of flood magnitude. This applies to the scablands, to Mars and other areas where there have been catastrophic outburst floods.”
He and Lamb combine numerical flood models with estimates of the force required to erode basalt bedrock to show that for Moses Coulee, a canyon carved by catastrophic Lake Missoula floods in eastern Washington when an ice dam repeatedly broke and reformed around 15,000 years ago, their “threshold shear stress model” explains the shape and depth of currently observed channels better than the brimful model.
“We numerically routed floods through the canyon in different states, from current configuration and at four different past scenarios,” Larsen notes. “We predicted the discharge from two models and tested which one is most reasonable, based on the depositional evidence from the current bars seen today in the canyons. The size of floods our model predicts from the basalt erosion better match locations of depositional flood bars in the canyon than the brimful model predicts.”
Larsen and Lamb’s new model also works better to explain observed canyon-cutting mechanics and outflow channels observed on Mars, they point out, “supporting the notion of a multi-flood or low-magnitude flood origin for the Mars outflow channels. ” Larsen adds, “There are very similar but larger canyons on the surface of Mars. These outflow channels are much bigger than the ones on Earth, but they look very similar and the assumption is they formed by similar processes. We know in most cases there were not canyons before these floods happened. They had to be carved, so the bottoms were getting lower and lower with each flood. We believe in the final phases of floods, they were not filled to the brim.”
Artist view of a planet orbiting two aging stars that exchange material and spiral closer together. Image by Jon Lomberg
Planets that revolve around two suns may surprisingly survive the violent late stages of the stars’ lives, according to new research out of the NASA Goddard Space Flight Centre and York University. The finding is surprising because planets orbiting close to a single sun, like Mercury and Venus in our solar system, would be destroyed when the aging star swells into a red giant.
Led by Veselin Kostov at the NASA Goddard Space Flight Centre, in collaboration with York University master’s student Keavin Moore and Professor Ray Jayawardhana, the study found that planets orbiting two (binary) stars – also referred to as circumbinary planets or “Tatooine worlds” after the iconic planetary home of Luke Skywalker in Star Wars – often escape death and destruction by moving out to wider orbits.
The paper, “Tatooine’s Future: The Eccentric Response of Kepler’s Circumbinary Planets to Common-Envelope Evolution of their Host Stars,” has been accepted for publication in The Astrophysical Journal.
“This is very different from what will happen in our own solar system a few billion years from now, when our Sun starts to evolve and expand to such a tremendous size that it will engulf the inner planets, like Mercury and Venus and possibly Earth too, faster than they can migrate out to larger orbits,” says Kostov. “It seems that if we had a second star in the center of our solar system, things might go differently.”
Binary star systems are ubiquitous in the Universe and consist of two stars that orbit around a common center of gravity. If the two stars are close enough to each other, when one starts evolving and expanding into a giant, they exchange material and spiral towards each other resulting in their sharing a common atmosphere (also called a common envelope). The binary star system ends up losing a large amount of mass, or might be destroyed in a supernova explosion.
“Given the exciting recent discoveries of planets circling binary stars, some with orbits similar in size to that of Mercury around the Sun, we were curious to explore the ultimate fate of these Tatooine worlds,” says Jayawardhana. “We found that many such planets are likely to survive the messy and violent late stages of their stars’ lives by moving farther out.”
The team, which also included Daniel Tamayo of the Canadian Institute for Theoretical Astrophysics and Stephen Rinehart of NASA Goddard, simulated the fate of nine circumbinary planets recently discovered by NASA’s Kepler mission. They found that the planets will predominantly survive the common envelope phase – even those orbiting very close to their stars. In addition, the planets can migrate to farther orbits similar to what it would be like if Venus moved out to where Uranus orbits our Sun. In some cases, planets can even reach more than twice the distance to Pluto.
Interestingly, when there are multiple planets orbiting a binary star, some can be ejected from the system, while others can switch places or even collide with their stars.
“The reconfiguration can be quite dramatic when there are several planets,” says Moore. “Although all of the known circumbinary planets are gas giants, it is possible that somewhere out there is a terrestrial circumbinary planet that migrates to an orbit that now makes the planet potentially habitable for a little while.”