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Pluto’s ‘heart’ sheds light on a possible buried ocean

Pluto's famous "heart," half of which was created by an ancient impact, offers clues about a possible subsurface ocean. NASA/APL/SwRI

Pluto’s famous “heart,” half of which was created by an ancient impact, offers clues about a possible subsurface ocean. NASA/APL/SwRI

Ever since NASA’s New Horizons spacecraft flew by Pluto last year, evidence has been mounting that the dwarf planet may have a liquid ocean beneath its icy shell. Now, by modeling the impact dynamics that created a massive crater on Pluto’s surface, a team of researchers has made a new estimate of how thick that liquid layer might be.

The study, led by Brown University geologist Brandon Johnson and published in Geophysical Research Letters, finds a high likelihood that there’s more than 100 kilometers of liquid water beneath Pluto’s surface. The research also offers a clue about the composition of that ocean, suggesting that it likely has a salt content similar to that of the Dead Sea.

“Thermal models of Pluto’s interior and tectonic evidence found on the surface suggest that an ocean may exist, but it’s not easy to infer its size or anything else about it,” said Johnson, who is an assistant professor in Brown’s Department of Earth, Environmental and Planetary Sciences. “We’ve been able to put some constraints on its thickness and get some clues about composition.”

The research focused on Sputnik Planum, a basin 900 kilometers across that makes up the western lobe the famous heart-shaped feature revealed during the New Horizons flyby. The basin appears to have been created by an impact, likely by an object 200 kilometers across or larger.

The story of how the basin relates to Pluto’s putative ocean starts with its position on the planet relative to Pluto’s largest moon, Charon. Pluto and Charon are tidally locked with each other, meaning they always show each other the same face as they rotate. Sputnik Planum sits directly on the tidal axis linking the two worlds. That position suggests that the basin has what’s called a positive mass anomaly — it has more mass than average for Pluto’s icy crust. As Charon’s gravity pulls on Pluto, it would pull proportionally more on areas of higher mass, which would tilt the planet until Sputnik Planum became aligned with the tidal axis.

But a positive mass anomaly would make Sputnik Planum a bit of an odd duck as craters go.

“An impact crater is basically a hole in the ground,” Johnson said. “You’re taking a bunch of material and blasting it out, so you expect it to have negative mass anomaly, but that’s not what we see with Sputnik Planum. That got people thinking about how you could get this positive mass anomaly.”

Part of the answer is that, after it formed, the basin has been partially filled in by nitrogen ice. That ice layer adds some mass to the basin, but it isn’t thick enough on its own to make Sputnik Planum have positive mass, Johnson says.

The rest of that mass may be generated by a liquid lurking beneath the surface.

Like a bowling ball dropped on a trampoline, a large impact creates a dent on a planet’s surface, followed by a rebound. That rebound pulls material upward from deep in the planet’s interior. If that upwelled material is denser than what was blasted away by the impact, the crater ends up with the same mass as it had before the impact happened. This is a phenomenon geologists refer to as isostatic compensation.

Water is denser than ice. So if there were a layer of liquid water beneath Pluto’s ice shell, it may have welled up following the Sputnik Planum impact, evening out the crater’s mass. If the basin started out with neutral mass, then the nitrogen layer deposited later would be enough to create a positive mass anomaly.

“This scenario requires a liquid ocean,” Johnson said. “We wanted to run computer models of the impact to see if this is something that would actually happen. What we found is that the production of a positive mass anomaly is actually quite sensitive to how thick the ocean layer is. It’s also sensitive to how salty the ocean is, because the salt content affects the density of the water.”

The models simulated the impact of an object large enough to create a basin of Sputnik Planum’s size hitting Pluto at a speed expected for that part in the solar system. The simulation assumed various thicknesses of the water layer beneath the crust, from no water at all to a layer 200 kilometers thick.

The scenario that best reconstructed Sputnik Planum’s observed size depth, while also producing a crater with compensated mass, was one in which Pluto has an ocean layer more than 100 kilometers thick, with a salinity of around 30 percent.

“What this tells us is that if Sputnik Planum is indeed a positive mass anomaly —and it appears as though it is — this ocean layer of at least 100 kilometers has to be there,” Johnson said. “It’s pretty amazing to me that you have this body so far out in the solar system that still may have liquid water.”

As researchers continue to look at the data sent by New Horizons, Johnson is hopeful that a clearer picture of Pluto’s possible ocean will emerge.

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Hubble Finds Planet Orbiting Pair of Stars

Credit: NASA, ESA, and G. Bacon (STScI)

This artist’s illustration shows a gas giant planet circling a pair of red dwarf stars. Credit: NASA, ESA, and G. Bacon (STScI)

Two’s company, but three might not always be a crowd — at least in space.

Astronomers using NASA’s Hubble Space Telescope, and a trick of nature, have confirmed the existence of a planet orbiting two stars in the system OGLE-2007-BLG-349, located 8,000 light-years away towards the center of our galaxy.

The planet orbits roughly 300 million miles from the stellar duo, about the distance from the asteroid belt to our sun. It completes an orbit around both stars roughly every seven years. The two red dwarf stars are a mere 7 million miles apart, or 14 times the diameter of the moon’s orbit around Earth.

The Hubble observations represent the first time such a three-body system has been confirmed using the gravitational microlensing technique. Gravitational microlensing occurs when the gravity of a foreground star bends and amplifies the light of a background star that momentarily aligns with it. The particular character of the light magnification can reveal clues to the nature of the foreground star and any associated planets.

The three objects were discovered in 2007 by an international collaboration of five different groups: Microlensing Observations in Astrophysics (MOA), the Optical Gravitational Lensing Experiment (OGLE), the Microlensing Follow-up Network (MicroFUN), the Probing Lensing Anomalies Network (PLANET), and the Robonet Collaboration. These ground-based observations uncovered a star and a planet, but a detailed analysis also revealed a third body that astronomers could not definitively identify.

“The ground-based observations suggested two possible scenarios for the three-body system: a Saturn-mass planet orbiting a close binary star pair or a Saturn-mass and an Earth-mass planet orbiting a single star,” explained David Bennett of the NASA Goddard Space Flight Center in Greenbelt, Maryland, the paper’s first author.

The sharpness of the Hubble images allowed the research team to separate the background source star and the lensing star from their neighbors in the very crowded star field. The Hubble observations revealed that the starlight from the foreground lens system was too faint to be a single star, but it had the brightness expected for two closely orbiting red dwarf stars, which are fainter and less massive than our sun. “So, the model with two stars and one planet is the only one consistent with the Hubble data,” Bennett said.

Bennett’s team conducted the follow-up observations with Hubble’s Wide Field Planetary Camera 2. “We were helped in the analysis by the almost perfect alignment of the foreground binary stars with the background star, which greatly magnified the light and allowed us to see the signal of the two stars,” Bennett explained.

Kepler has discovered 10 other planets orbiting tight binary stars, but these are all much closer to their stars than the one studied by Hubble.

Now that the team has shown that microlensing can successfully detect planets orbiting double-star systems, Hubble could provide an essential role in this new realm in the continued search for exoplanets.

The team’s results have been accepted for publication in The Astronomical Journal.

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New theory proposes explanation for how vertebrates evolved

Image: Wikipedia

Image: Wikipedia

A new theory aims to explain how the complex vertebrate body, with its skeleton, muscles, nervous and cardiovascular systems, arises from a single cell during development and how these systems evolved over time. The theory, called embryo geometry, is the culmination of nearly 20 years of work by a team of researchers and science illustrators.

The new theory is published along with illustrations – or “blueprints” – depicting how it applies to different vertebrate organ systems in Progress in Biophysics & Molecular Biology.

According to Neo-Darwinian theory, major evolutionary changes occur as a result of the selection of random, fortuitous genetic mutations over time. However, some researchers say this theory does not satisfactorily account for the appearance of radically different life forms and their rich complexity, particularly that observed in vertebrates like humans.

Embryo geometry, developed by a team from the University of San Diego, Mount Holyoke College, Evergreen State College, and Chem-Tainer Industries, Inc.. in the USA, looks at animal complexity generally and the vertebrate body in particular as more the products of mechanical forces and the laws of geometry than solely the outcome of random genetic mutation.

“Embryo Geometry represents a major game changer, in that it challenges the bottom-up dogma of evolutionary biology by suggesting that, in fact, top-down mechanical forces and geometric principles play a central role in determining animal shape,” said study co-author David Edelman.

Anatomists have long postulated that animal complexity arises during development of the embryo – called embryogenesis – but despite detailed descriptions of the embryonic stages of all major types of animal, the evolution of organismal complexity and its expression during individual development have remained mysterious processes – until now.

The researchers behind embryo geometry have shown that the vertebrate embryo could conceivably arise from mechanical deformation of the blastula, a ball of cells formed when the fertilized egg divides. As these cells proliferate, the ball increases in volume and surface area, altering its geometry. The theory posits that the blastula retains the geometry of the original eight cells produced by the first three divisions of the egg, which themselves determine the three axes of the vertebrate body.

In their new paper, they present 24 schematic figures – or “blueprints” – showing how the musculoskeletal, cardiovascular, nervous, and reproductive systems form through mechanical deformation of geometric patterns. These illustrations explain how the vertebrate body might plausibly arise from a single cell, both over evolutionary time, and during individual embryogenesis.

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New Research Collaboration Explores Microbiome of the Space Station

A petri dish contains colonies of fungi grown from a sample collected aboard the International Space Station during Microbial Tracking-1, a research investigation that looks at the types of microbes present on the surfaces and in the air of the space station. Credits: NASA / JPL

A petri dish contains colonies of fungi grown from a sample collected aboard the International Space Station during Microbial Tracking-1, a research investigation that looks at the types of microbes present on the surfaces and in the air of the space station. Credits: NASA / JPL

More than 200 people have crossed the airlock threshold to the International Space Station to conduct research that benefits people on Earth and the agency’s Journey to Mars. The microbes they brought with them—and left behind—are the focus of a new collaborative research opportunity from NASA and the non-profit Alfred P. Sloan Foundation.

Humans bring microbes everywhere they go—some of which reside inside the body, such as the intestinal tract. Others are outside the body on skin and clothes, for example. When these collective microbial communities enter a human-made environment like the International Space Station they create their own microbial ecosystem known as the Microbiome of Built Environments (MoBE).

NASA is seeking proposals from postdoctoral fellows to analyze the microbial communities inside the space station to determine how the communities colonize, adapt and evolve. The researchers will have access to a collection of space station microbial samples gathered over a decade or more, and archived at NASA’s Johnson Space Center in Houston.

“NASA is incredibly excited to partner with the Sloan Foundation through a Space Act Agreement to look at the microbiome of the space station to better understand how to control the microbial environment in future human exploration spacecraft,” says David Tomko, Ph.D., space biology program scientist at NASA.

NASA and the Sloan Foundation have a shared interest in promoting microbiology research that will enhance scientific understanding of the microbiome of built environments. Sloan funds an extensive research program dedicated to the topic, and has established an online network where researchers in the field can share information, apply for grants and plan meetings and conferences.

Microbiome research on the space station is an important area of research for NASA as it prepares astronauts for future long duration spaceflight. The agency will upload resulting data and analysis onto the open science GeneLab platform to allow for further review from the research community.  Sloan and NASA plan to use results in GeneLab to allow for further development of experiments by the research community.

“We are proud to be partnering with NASA to fund groundbreaking research on the microbial ecosystem of the space station,” says Paula J. Olsiewski, Ph.D., director of Sloan’s Microbiology of the Built Environment program. “The opportunities for discovery are truly unique.”

Proposals are welcome from graduate students in the final year of a doctor of philosophy or equivalent doctoral degree program, from postdoctoral fellows or from applicants who received a doctoral degree within the past two years. The Sloan Foundation anticipates funding an additional two awards through a solicitation of its own with similar goals.

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NASA Scientists Find ‘Impossible’ Cloud on Titan — Again

The hazy globe of Titan hangs in front of Saturn and its rings in this natural color view from NASA's Cassini spacecraft. Image credit: NASA/JPL-Caltech/Space Science Institute

The hazy globe of Titan hangs in front of Saturn and its rings in this natural color view from NASA’s Cassini spacecraft. Image credit: NASA/JPL-Caltech/Space Science Institute

The puzzling appearance of an ice cloud seemingly out of thin air has prompted NASA scientists to suggest that a different process than previously thought — possibly similar to one seen over Earth’s poles — could be forming clouds on Saturn’s moon Titan.

Located in Titan’s stratosphere, the cloud is made of a compound of carbon and nitrogen known as dicyanoacetylene (C4N2), an ingredient in the chemical cocktail that colors the giant moon’s hazy, brownish-orange atmosphere.

Decades ago, the infrared instrument on NASA’s Voyager 1 spacecraft spotted an ice cloud just like this one on Titan. What has puzzled scientists ever since is this: they detected less than 1 percent of the dicyanoacetylene gas needed for the cloud to condense.

Recent observations from NASA’s Cassini mission yielded a similar result. Using Cassini’s composite infrared spectrometer, or CIRS — which can identify the spectral fingerprints of individual chemicals in the atmospheric brew — researchers found a large, high-altitude cloud made of the same frozen chemical. Yet, just as Voyager found, when it comes to the vapor form of this chemical, CIRS reported that Titan’s stratosphere is as dry as a desert.

“The appearance of this ice cloud goes against everything we know about the way clouds form on Titan,” said Carrie Anderson, a CIRS co-investigator at NASA’s Goddard Space Flight Center in Greenbelt, Maryland, and lead author of the study.

The typical process for forming clouds involves condensation. On Earth, we’re familiar with the cycle of evaporation and condensation of water. The same kind of cycle takes place in Titan’s troposphere — the weather-forming layer of Titan’s atmosphere — but with methane instead of water.

A different condensation process takes place in the stratosphere — the region above the troposphere — at Titan’s north and south winter poles. In this case, layers of clouds condense as the global circulation pattern forces warm gases downward at the pole. The gases then condense as they sink through cooler and cooler layers of the polar stratosphere.

Either way, a cloud forms when the air temperature and pressure are favorable for the vapor to condense into ice. The vapor and the ice reach a balance point — an equilibrium — that is determined by the air temperature and pressure. Because of this equilibrium, scientists can calculate the amount of vapor where ice is present.

“For clouds that condense, this equilibrium is mandatory, like the law of gravity,” said Robert Samuelson, an emeritus scientist at Goddard and a co-author of the paper.

But the numbers don’t compute for the cloud made from dicyanoacetylene. The scientists determined that they would need at least 100 times more vapor to form an ice cloud where the cloud top was observed by Cassini’s CIRS.

This graphic illustrates how scientists think "solid state" chemistry may be taking place in ice particles that form clouds in the atmosphere of Saturn's moon Titan. Image credit: NASA/JPL-Caltech/GSFC

This graphic illustrates how scientists think “solid state” chemistry may be taking place in ice particles that form clouds in the atmosphere of Saturn’s moon Titan. Image credit: NASA/JPL-Caltech/GSFC

One explanation suggested early on was that the vapor might be present, but Voyager’s instrument wasn’t sensitive enough in the critical wavelength range needed to detect it. But when CIRS also didn’t find the vapor, Anderson and her Goddard and Caltech colleagues proposed an altogether different explanation. Instead of the cloud forming by condensation, they think the C4N2 ice forms because of reactions taking place on other kinds of ice particles. The researchers call this “solid-state chemistry,” because the reactions involve the ice, or solid, form of the chemical.

The first step in the proposed process is the formation of ice particles made from the related chemical cyanoacetylene (HC3N). As these tiny bits of ice move downward through Titan’s stratosphere, they get coated by hydrogen cyanide (HCN). At this stage, the ice particle has a core and a shell comprised of two different chemicals. Occasionally, a photon of ultraviolet light tunnels into the frozen shell and triggers a series of chemical reactions in the ice. These reactions could begin either in the core or within the shell. Both pathways can yield dicyanoacteylene ice and hydrogen as products.

The researchers got the idea of solid-state chemistry from the formation of clouds involved in ozone depletion high above Earth’s poles. Although Earth’s stratosphere has scant moisture, wispy nacreous clouds (also called polar stratospheric clouds) can form under the right conditions. In these clouds, chlorine-bearing chemicals that have entered the atmosphere as pollution stick to crystals of water ice, resulting in chemical reactions that release ozone-destroying chlorine molecules.

“It’s very exciting to think that we may have found examples of similar solid-state chemical processes on both Titan and Earth,” said Anderson.

The researchers suggest that, on Titan, the reactions occur inside the ice particles, sequestered from the atmosphere. In that case, dicyanoacetylene ice wouldn’t make direct contact with the atmosphere, which would explain why the ice and the vapor forms are not in the expected equilibrium.

“The compositions of the polar stratospheres of Titan and Earth could not differ more,” said Michael Flasar, CIRS principal investigator at Goddard. “It is amazing to see how well the underlying physics of both atmospheres has led to analogous cloud chemistry.”

The findings are published in the journal Geophysical Research Letters.

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Cassini Begins Epic Final Year at Saturn

Since NASA's Cassini spacecraft arrived at Saturn, the planet's appearance has changed greatly. This view shows Saturn's northern hemisphere in 2016, as that part of the planet nears its northern hemisphere summer solstice in May 2017. Credits: NASA/JPL-Caltech/Space Science Institute

Since NASA’s Cassini spacecraft arrived at Saturn, the planet’s appearance has changed greatly. This view shows Saturn’s northern hemisphere in 2016, as that part of the planet nears its northern hemisphere summer solstice in May 2017. Credits: NASA/JPL-Caltech/Space Science Institute

After more than 12 years studying Saturn, its rings and moons, NASA’s Cassini spacecraft has entered the final year of its epic voyage. The conclusion of the historic scientific odyssey is planned for September 2017, but not before the spacecraft completes a daring two-part endgame.

Beginning on November 30, Cassini’s orbit will send the spacecraft just past the outer edge of the main rings. These orbits, a series of 20, are called the F-ring orbits. During these weekly orbits, Cassini will approach to within 4,850 miles (7,800 kilometers) of the center of the narrow F ring, with its peculiar kinked and braided structure.

“During the F-ring orbits we expect to see the rings, along with the small moons and other structures embedded in them, as never before,” said Linda Spilker, Cassini project scientist at NASA’s Jet Propulsion Laboratory, Pasadena, California. “The last time we got this close to the rings was during arrival at Saturn in 2004, and we saw only their backlit side. Now we have dozens of opportunities to examine their structure at extremely high resolution on both sides.”

The Last Act: A Grand Finale

Cassini’s final phase — called the Grand Finale — begins in earnest in April 2017. A close flyby of Saturn’s giant moon Titan will reshape the spacecraft’s orbit so that it passes through the gap between Saturn and the rings – an unexplored space only about 1,500 miles (2,400 kilometers) wide. The spacecraft is expected to make 22 plunges through this gap, beginning with its first dive on April 27.

NASA’s Cassini spacecraft stared at Saturn for nearly 44 hours in April 2016 to obtain this movie showing four Saturn days. Cassini will begin a series of dives between the planet and its rings in April 2017, building toward a dramatic end of mission — a final plunge into the planet, six months later.

During the Grand Finale, Cassini will make the closest-ever observations of Saturn, mapping the planet’s magnetic and gravity fields with exquisite precision and returning ultra-close views of the atmosphere. Scientists also hope to gain new insights into Saturn’s interior structure, the precise length of a Saturn day, and the total mass of the rings — which may finally help settle the question of their age. The spacecraft will also directly analyze dust-sized particles in the main rings and sample the outer reaches of Saturn’s atmosphere — both first-time measurements for the mission.

“It’s like getting a whole new mission,” said Spilker. “The scientific value of the F ring and Grand Finale orbits is so compelling that you could imagine a whole mission to Saturn designed around what we’re about to do.”

Getting Into Saturn, Literally

Since the beginning of 2016, mission engineers have been tweaking Cassini’s orbital path around Saturn to position the spacecraft for the mission’s final phase. They have sent the spacecraft on a series of flybys past Titan that are progressively raising the tilt of Cassini’s orbit with respect to Saturn’s equator and rings. This particular orientation enables the spacecraft to leap over the rings with a single (and final) Titan flyby in April, to begin the Grand Finale.

“We’ve used Titan’s gravity throughout the mission to sling Cassini around the Saturn system,” said Earl Maize, Cassini project manager at JPL. “Now Titan is coming through for us once again, providing a way for Cassini to get into these completely unexplored regions so close to the planet.”

The Grand Finale will come to a dramatic end on Sept. 15, 2017, as Cassini dives into Saturn’s atmosphere, returning data about the planet’s chemical composition until its signal is lost. Friction with the atmosphere will cause the spacecraft to burn up like a meteor soon afterward.

To celebrate the beginning of the final year and the adventure ahead, the Cassini team is releasing a new movie of the rotating planet, along with a color mosaic, both taken from high above Saturn’s northern hemisphere. The movie covers 44 hours, or just over four Saturn rotations.

The Cassini spacecraft has logged impressive numbers in the 12 years since it arrived at Saturn on July 1, 2004. This infographic offers a snapshot of just a few of the mission's big numbers on Sept. 15, 2016, as it heads into a final year of science at Saturn. Credits: NASA/JPL-Caltech

The Cassini spacecraft has logged impressive numbers in the 12 years since it arrived at Saturn on July 1, 2004. This infographic offers a snapshot of just a few of the mission’s big numbers on Sept. 15, 2016, as it heads into a final year of science at Saturn. Credits: NASA/JPL-Caltech

‘A Truly Thrilling Ride’

“This is the sort of view Cassini will have as the spacecraft repeatedly climbs high above Saturn’s northern latitudes before plunging past the outer — and later the inner — edges of the rings,” said Spilker.

And so, although the mission’s end is approaching — with a “Cassini Final Plunge” clock already counting down in JPL mission control — an extremely important phase of the mission is still to come.

“We may be counting down, but no one should count Cassini out yet,” said Curt Niebur, Cassini program scientist at NASA Headquarters in Washington. “The journey ahead is going to be a truly thrilling ride.”

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Some Ancient Mars Lakes Came Long After Others

Lakes and snowmelt-fed streams on Mars formed much later than previously thought possible, according to new findings using data primarily from NASA’s Mars Reconnaissance Orbiter.

Valleys much younger than well-known ancient valley networks on Mars are evident near the informally named "Heart Lake" on Mars. This map presents color-coded topographical information overlaid onto a photo mosaic. Lower elevations are indicated with white and purple; higher elevations, yellow. Credits: NASA/JPL-Caltech/ASU

Valleys much younger than well-known ancient valley networks on Mars are evident near the informally named “Heart Lake” on Mars. This map presents color-coded topographical information overlaid onto a photo mosaic. Lower elevations are indicated with white and purple; higher elevations, yellow.
Credits: NASA/JPL-Caltech/ASU

The recently discovered lakes and streams appeared roughly a billion years after a well-documented, earlier era of wet conditions on ancient Mars. These results provide insight into the climate history of the Red Planet and suggest the surface conditions at this later time may also have been suitable for microbial life.

“We discovered valleys that carried water into lake basins,” said Sharon Wilson of the Smithsonian Institution, Washington, and the University of Virginia, Charlottesville. “Several lake basins filled and overflowed, indicating there was a considerable amount of water on the landscape during this time.”

Wilson and colleagues found evidence of these features in Mars’ northern Arabia Terra region by analyzing images from the Context Camera and High Resolution Imaging Science Experiment camera on the Mars Reconnaissance Orbiter and additional data from NASA’s Mars Global Surveyor and the European Space Agency’s Mars Express.

“One of the lakes in this region was comparable in volume to Lake Tahoe,” Wilson said, referring to a California-Nevada lake that holds about 45 cubic miles (188 cubic kilometers) of water. “This particular Martian lake was fed by an inlet valley on its southern edge and overflowed along its northern margin, carrying water downstream into a very large, water-filled basin we nicknamed ‘Heart Lake.'”

The chain of lakes and valleys that are part of the Heart Lake valley system extends about 90 miles (about 150 kilometers). Researchers calculate Heart Lake held about 670 cubic miles of water (2,790 cubic kilometers), more than in Lake Ontario of North America’s Great Lakes.

Wilson and co-authors of the report in the Journal of Geophysical Research, Planets, map the extent of stream-flow in “fresh shallow valleys” and their associated former lakes. They suggest that the runoff that formed the valleys may have been seasonal.

To bracket the time period when the fresh shallow valleys in Arabia Terra formed, scientists started with age estimates for 22 impact craters in the area. They assessed whether or not the valleys carved into the blankets of surrounding debris ejected from the craters, as an indicator of whether the valleys are older or younger than the craters. They concluded that this fairly wet period on Mars likely occurred between two and three billion years ago, long after it is generally thought that most of Mars’ original atmosphere had been lost and most of the remaining water on the planet had frozen.

Streamlined forms in this Martian valley resulted from the outflow of a lake hundreds of millions years more recently than an era of Martian lakes previously confirmed. This image from the Context Camera on NASA's Mars Reconnaissance Orbiter covers an area in Arabia Terra about 8 miles wide. Credits: NASA/JPL-Caltech/MSSS

Streamlined forms in this Martian valley resulted from the outflow of a lake hundreds of millions years more recently than an era of Martian lakes previously confirmed. This image from the Context Camera on NASA’s Mars Reconnaissance Orbiter covers an area in Arabia Terra about 8 miles wide. Credits: NASA/JPL-Caltech/MSSS

The characteristics of the valleys support the interpretation that the climate was cold: “The rate at which water flowed through these valleys is consistent with runoff from melting snow,” Wilson said, “These weren’t rushing rivers. They have simple drainage patterns and did not form deep or complex systems like the ancient valley networks from early Mars.”

They note that similar valleys occur elsewhere on Mars between about 35 and 42 degrees latitude, both north and south of the equator. The similar appearance and widespread nature of these fresh, shallow valleys on Mars suggest they formed on a global scale rather than a local or regional scale.

“A key goal for Mars exploration is to understand when and where liquid water was present in sufficient volume to alter the Martian surface and perhaps provide habitable environments,” said Mars Reconnaissance Orbiter Project Scientist Rich Zurek of NASA’s Jet Propulsion Laboratory, Pasadena, California. “This paper presents evidence for episodes of water modifying the surface on early Mars for possibly several hundred million years later than previously thought, with some implication that the water was emplaced by snow, not rain.”

The findings will likely prompt more studies to understand how conditions warmed enough on the frozen planet to allow an interval with flowing water. One possibility could be an extreme change in the planet’s tilt, with more direct illumination of polar ice.

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Pluto ‘Paints’ its Largest Moon Red

NASA's New Horizons spacecraft captured this high-resolution, enhanced color view of Pluto’s largest moon, Charon, just before closest approach on July 14, 2015. Credits: NASA/JHUAPL/SwRI

NASA’s New Horizons spacecraft captured this high-resolution, enhanced color view of Pluto’s largest moon, Charon, just before closest approach on July 14, 2015. Credits: NASA/JHUAPL/SwRI

In June 2015, when the cameras on NASA’s approaching New Horizons spacecraft first spotted the large reddish polar region on Pluto’s largest moon, Charon, mission scientists knew two things: they’d never seen anything like it elsewhere in our solar system, and they couldn’t wait to get the story behind it.

Over the past year, after analyzing the images and other data that New Horizons has sent back from its historic July 2015 flight through the Pluto system, the scientists think they’ve solved the mystery. As they detail this week in the international scientific journal Nature, Charon’s polar coloring comes from Pluto itself – as methane gas that escapes from Pluto’s atmosphere and becomes “trapped” by the moon’s gravity and freezes to the cold, icy surface at Charon’s pole. This is followed by chemical processing by ultraviolet light from the sun that transforms the methane into heavier hydrocarbons and eventually into reddish organic materials called tholins.

“Who would have thought that Pluto is a graffiti artist, spray-painting its companion with a reddish stain that covers an area the size of New Mexico?” asked Will Grundy, a New Horizons co-investigator from Lowell Observatory in Flagstaff, Arizona, and lead author of the paper. “Every time we explore, we find surprises. Nature is amazingly inventive in using the basic laws of physics and chemistry to create spectacular landscapes.”

The team combined analyses from detailed Charon images obtained by New Horizons with computer models of how ice evolves on Charon’s poles. Mission scientists had previously speculated that methane from Pluto’s atmosphere was trapped in Charon’s north pole and slowly converted into the reddish material, but had no models to support that theory.

The New Horizons team dug into the data to determine whether conditions on the Texas-sized moon (with a diameter of 753 miles or 1,212 kilometers) could allow the capture and processing of methane gas. The models using Pluto and Charon’s 248-year orbit around the sun show some extreme weather at Charon’s poles, where 100 years of continuous sunlight alternate with another century of continuous darkness. Surface temperatures during these long winters dip to -430 Fahrenheit (-257 Celsius), cold enough to freeze methane gas into a solid.

“The methane molecules bounce around on Charon’s surface until they either escape back into space or land on the cold pole, where they freeze solid, forming a thin coating of methane ice that lasts until sunlight comes back in the spring,” Grundy said. But while the methane ice quickly sublimates away, the heavier hydrocarbons created from it remain on the surface.

The models also suggested that in Charon’s springtime the returning sunlight triggers conversion of the frozen methane back into gas. But while the methane ice quickly sublimates away, the heavier hydrocarbons created from this evaporative process remain on the surface.

Sunlight further irradiates those leftovers into reddish material – called tholins – that has slowly accumulated on Charon’s poles over millions of years. New Horizons’ observations of Charon’s other pole, currently in winter darkness – and seen by New Horizons only by light reflecting from Pluto, or “Pluto-shine” – confirmed that the same activity was occurring at both poles.

“This study solves one of the greatest mysteries we found on Charon, Pluto’s giant moon,” said Alan Stern, New Horizons principal investigator from the Southwest Research Institute, and a study co-author. “And it opens up the possibility that other small planets in the Kuiper Belt with moons may create similar, or even more extensive ‘atmospheric transfer’ features on their moons.”

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X-ray Detection Sheds New Light on Pluto

Scientists using NASA’s Chandra X-ray Observatory have made the first detections of X-rays from Pluto. These observations offer new insight into the space environment surrounding the largest and best-known object in the solar system’s outermost regions.

While NASA’s New Horizons spacecraft was speeding toward and beyond Pluto, Chandra was aimed several times on the dwarf planet and its moons, gathering data on Pluto that the missions could compare after the flyby. Each time Chandra pointed at Pluto – four times in all, from February 2014 through August 2015 – it detected low-energy X-rays from the small planet.

The first detection of Pluto in X-rays has been made using NASA’s Chandra X-ray Observatory in conjunction with observations from NASA’s New Horizon spacecraft. Credits: X-ray: NASA/CXC/JHUAPL/R.McNutt et al; Optical: NASA/JHUAPL

The first detection of Pluto in X-rays has been made using NASA’s Chandra X-ray Observatory in conjunction with observations from NASA’s New Horizon spacecraft.
Credits: X-ray: NASA/CXC/JHUAPL/R.McNutt et al; Optical: NASA/JHUAPL

Pluto is the largest object in the Kuiper Belt, a ring or belt containing a vast population of small bodies orbiting the Sun beyond Neptune.  The Kuiper belt extends from the orbit of Neptune, at 30 times the distance of Earth from the Sun, to about 50 times the Earth-Sun distance.  Pluto’s orbit ranges over the same span as the overall Kupier Belt.

“We’ve just detected, for the first time, X-rays coming from an object in our Kuiper Belt, and learned that Pluto is interacting with the solar wind in an unexpected and energetic fashion,” said Carey Lisse, an astrophysicist at the Johns Hopkins University Applied Physics Laboratory (APL) in Laurel, Maryland, who led the Chandra observation team with APL colleague and New Horizons Co-Investigator Ralph McNutt. “We can expect other large Kuiper Belt objects to be doing the same.”

The team recently published its findings online in the journal Icarus. The report details what Lisse says was a somewhat surprising detection given that Pluto – being cold, rocky and without a magnetic field – has no natural mechanism for emitting X-rays. But Lisse, having also led the team that made the first X-ray detections from a comet two decades ago, knew the interaction between the gases surrounding such planetary bodies and the solar wind – the constant streams of charged particles from the sun that speed throughout the solar system ­– can create X-rays.

New Horizons scientists were particularly interested in learning more about the interaction between the gases in Pluto’s atmosphere and the solar wind. The spacecraft itself carries an instrument designed to measure that activity up-close – the aptly named Solar Wind Around Pluto (SWAP) – and scientists are using that data to craft a picture of Pluto that contains a very mild, close-in bowshock, where the solar wind first “meets” Pluto (similar to a shock wave that forms ahead of a supersonic aircraft) and a small wake or tail behind the planet.

The immediate mystery is that Chandra’s readings on the brightness of the X-rays are much higher than expected from the solar wind interacting with Pluto’s atmosphere.

“Before our observations, scientists thought it was highly unlikely that we’d detect X-rays from Pluto, causing a strong debate as to whether Chandra should observe it at all,” said co-author Scott Wolk, of the Harvard-Smithsonian Center for Astrophysics in Cambridge, Mass. “Prior to Pluto, the most distant solar system body with detected X-ray emission was Saturn’s rings and disk.”

The Chandra detection is especially surprising since New Horizons discovered Pluto’s atmosphere was much more stable than the rapidly escaping, “comet-like” atmosphere that many scientists expected before the spacecraft flew past in July 2015. In fact, New Horizons found that Pluto’s interaction with the solar wind is much more like the interaction of the solar wind with Mars, than with a comet. However, although Pluto is releasing enough gas from its atmosphere to make the observed X-rays, in simple models for the intensity of the solar wind at the distance of Pluto, there isn’t enough solar wind flowing directly at Pluto to make them.

Lisse and his colleagues – who also include SWAP co-investigators David McComas from Princeton University and Heather Elliott from Southwest Research Institute – suggest several possibilities for the enhanced X-ray emission from Pluto.  These include a much wider and longer tail of gases trailing Pluto than New Horizons detected using its SWAP instrument. Other possibilities are that interplanetary magnetic fields are focusing more particles than expected from the solar wind into the region around Pluto, or the low density of the solar wind in the outer solar system at the distance of Pluto could allow for the formation of a doughnut, or torus, of neutral gas centered around Pluto’s orbit.

That the Chandra measurements don’t quite match up with New Horizons up-close observations is the benefit – and beauty – of an opportunity like the New Horizons flyby. “When you have a chance at a once in a lifetime flyby like New Horizons at Pluto, you want to point every piece of glass – every telescope on and around Earth – at the target,” McNutt says. “The measurements come together and give you a much more complete picture you couldn’t get at any other time, from anywhere else.”

New Horizons has an opportunity to test these findings and shed even more light on this distant region – billions of miles from Earth – as part of its recently approved extended mission to survey the Kuiper Belt and encounter another smaller Kuiper Belt object, 2014 MU69, on Jan. 1, 2019. It is unlikely to be feasible to detect X-rays from MU69, but Chandra might detect X-rays from other larger and closer objects that New Horizons will observe as it flies through the Kuiper Belt towards MU69.

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ALMA Spots Possible Formation Site of Icy Giant Planet

Artist's impression of the dust disk and a forming planet around TW Hydrae. Credit: NAOJ

Artist’s impression of the dust disk and a forming planet around TW Hydrae. Credit: NAOJ

Astronomers found signs of a growing planet around TW Hydra, a nearby young star, using the Atacama Large Millimeter/submillimeter Array (ALMA). Based on the distance from the central star and the distribution of tiny dust grains, the baby planet is thought to be an icy giant, similar to Uranus and Neptune in our Solar System. This result is another step towards understanding the origins of various types of planets.

A number of extrasolar planets have been found in the past two decades and now researchers agree that planets can have a wide variety of characteristics. However, it is still unclear how this diversity emerges. Especially, there is still debate about how the icy giant planets, such as Uranus and Neptune, form.

To take a close look at the planet formation site, a research team led by Takashi Tsukagoshi at Ibaraki University, Japan, observed the young star TW Hydrae. This star, estimated to be 10 million years old, is one of the closest young stars to the Earth. Thanks to the proximity and the fact that its axis of rotation points roughly in the Earth’s direction, giving us a face-on-view of the developing planetary system, TW Hydrae is one of the most favorable targets for investigating planet formation.

Past observations have shown that TW Hydrae is surrounded by a disk made of tiny dust particles. This disk is the site of planet formation. Recent ALMA observations revealed multiple gaps in the disk. Some theoretical studies suggest that the gaps are evidence of planet formation.

The team observed the disk around TW Hydrae with ALMA in two radio frequencies. Since the ratio of the radio intensities in different frequencies depends on the size of the dust grains, researchers can estimate the size of dust grains. The ratio indicates that smaller, micrometer-sized, dust particles dominate and larger dust particles are absent in the most prominent gap with a radius of 22 astronomical units.

ALMA image of the disk around the young star TW Hydrae. Several gaps are clearly depicted. Researchers found that the size of the dust particles in the inner 22 au gap is smaller than in the other bright regions and guess that a planet similar to Neptune is located in this gap. Credit: ALMA (ESO/NAOJ/NRAO), Tsukagoshi et al.

ALMA image of the disk around the young star TW Hydrae. Several gaps are clearly depicted. Researchers found that the size of the dust particles in the inner 22 au gap is smaller than in the other bright regions and guess that a planet similar to Neptune is located in this gap. Credit: ALMA (ESO/NAOJ/NRAO), Tsukagoshi et al.

Why are smaller dust particles selectively located in the gap in the disk? Theoretical studies have predicted that a gap in the disk is created by a massive planet, and that gravitational interaction and friction between gas and dust particles push the larger dust out from the gap, while the smaller particles remain in the gap. The current observation results match these theoretical predictions.

Researchers calculated the mass of the unseen planet based on the width and depth of the 22 au gap and found that the planet is probably a little more massive than the Neptune. “Combined with the orbit size and the brightness of TW Hydrae, the planet would be an icy giant planet like Neptune,” said Tsukagoshi.

Following this result, the team is planning further observations to better understand planet formation. One of their plans is to observe the polarization of the radio waves. Recent theoretical studies have shown that the size of dust grains can be estimated more precisely with polarization observations. The other plan is to measure the amount of gas in the disk. Since gas is the major component of the disk, the researchers hope to attain a better estimation of the mass of the forming planet.

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Know Thy Star, Know Thy Planet

Artist conception. Credit: NASA

Artist conception. Credit: NASA

When it comes to exoplanets, astronomers have realized that they only know the properties of the planets they discover as well as they know the properties of the stars being orbited. For a planet’s size, precisely characterizing the host star can mean the difference in our understanding of whether a distant world is small like Earth or huge like Jupiter.

For astronomers to determine the size of an exoplanet—planets outside the solar system—depends critically on knowing not only the radius of its host star but also whether that star is single or has a close companion. Consider that about half of the stars in the sky are not one but two stars orbiting around each other, this makes knowing the binary property of a star paramount.

One particularly interesting and relatively nearby star, named TRAPPIST-1, recently caught the attention of a team of researchers. They wanted to determine if TRAPPIST-1, which is home to three small, potentially rocky planets—one of which orbits in the temperate habitable zone where liquid water might pool on the surface—was a single star like the sun, or if it had a companion star. If TRAPPIST-1 did have a companion star, the discovered planets will have larger sizes, possibly large enough to be ice giants similar to Neptune.

If an exoplanet orbits a star in a binary system but astronomers believe the starlight captured by the telescope is from a single star, the real radius of the planet will be larger than measured. The difference in the measured size of the exoplanet can be small ranging from 10 percent to more than a factor of two in size, depending on the brightness of the companion star in the system.

To confirm or deny the single star nature of TRAPPIST-1, Steve Howell, senior research scientist at NASA’s Ames Research Center at Moffett Field, California, led an investigation of the star. Using a specially designed camera, called the Differential Speckle Survey Instrument or DSSI, Howell and his team measured the rapid disturbances in the light emitted by the star caused by the Earth’s atmosphere and corrected for them. The resultant high-resolution image revealed that the light coming from the TRAPPIST-1 system is from a single star.

With the confirmation that no other companion star resides in the vicinity of TRAPPIST-1, the research team’s result validates not only that transiting planets are responsible for the periodic dips seen in the star’s brightness but that they are indeed Earth-size and may likely to be rocky worlds.

“Knowing that a terrestrial-size potentially rocky planet orbits in the habitable zone of a star only 40 light-years from the Earth is an awesome finding,” said Howell. “The TRAPPIST-1 system will continue to be studied in great detail as these transiting exoplanets offer one of the best chances to characterize the atmosphere of an alien world.”

Mounted on the 8-meter Gemini Observatory South telescope in Chile, the DSSI provided astronomers with the highest resolution images available today from a single ground-based telescope. The nearness of TRAPPIST-1 allowed astronomers to peer deep into the system, looking closer than Mercury’s orbit to our sun.

The paper the result is based on is published in the September 13th issue of The Astrophysical Journal Letters.

The four-panel graphic illustrates the difference of measured starlight when seen through a ground-based telescope with and without (top left corner) the blurring effects caused by Earth's atmosphere. The technique to neutralize Earth's atmospheric blur is called speckle interferometry. All four images are shown at the same scale. Credits: NASA/Ames/W. Stenzel

The four-panel graphic illustrates the difference of measured starlight when seen through a ground-based telescope with and without (top left corner) the blurring effects caused by Earth’s atmosphere. The technique to neutralize Earth’s atmospheric blur is called speckle interferometry. All four images are shown at the same scale. Credits: NASA/Ames/W. Stenzel

Interest in the recently-discovered TRAPPIST-1 with its three Earth-size planets is high. Astronomically speaking, at 40 light-years from Earth, the system is a hop, skip and a jump away. The star itself is a dim M-type star, which, relative to most stars, is very small and cool, but making transit detection of small planets easier.

Further detailed measurement of the planetary transits seen in TRAPPIST-1 will begin later this year when NASA’s Kepler space telescope in its K2 mission will precisely monitor minute changes in the light emitted from the star for a period of about 75 days.

The space-based observations from the Kepler spacecraft will provide extremely precise measurements of the planet transit shapes allowing for more refined radius and orbital period determination. Noting variations in the mid-time of the transit events can also help astronomers determine the planet masses. Additionally, the new observations will be searched for more transiting planets in the TRAPPIST-1 system.

Speckle interferometry, the imaging technique used by the DSSI, is a powerful asset in the astronomer’s toolkit as it provides a unique capability to characterize the environment around distant stars. The technique provides ultra high-resolution images by taking multiple extremely short (40-60 millisecond) exposures of a star to capture fine detail in the received light and “freeze” the turbulence caused by Earth’s atmosphere.

By combining the many thousands of exposures and using mathematical techniques to remove the momentary distortions caused by Earth’s atmosphere, the final result provides a resolution equal to the theoretical limit of what the 8-meter Gemini telescope would produce if no atmosphere were present.

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Chemistry says moon is proto-Earth’s mantle, relocated

Planetary smackdown: An artist's conception of the giant impact that created Earth's moon. New research suggests the impact was even more violent than this image suggests. (Illustration: Dana Berry/SwRI)

Planetary smackdown: An artist’s conception of the giant impact that created Earth’s moon. New research suggests the impact was even more violent than this image suggests. (Illustration: Dana Berry/SwRI)

Measurements of an element in Earth and moon rocks have just disproved the leading hypotheses for the origin of the moon.

Tiny differences in the segregation of the isotopes of potassium between the moon and Earth were hidden below the detection limits of analytical techniques until recently. But in 2015, Washington University in St. Louis geochemist Kun Wang, then the Harvard Origins of Life Initiative Prize postdoctoral fellow, and Stein Jacobsen, professor of geochemistry at Harvard University, developed a technique for analyzing these isotopes that can hit precisions 10 times better than the best previous method .

Wang and Jacobsen now report isotopic differences between lunar and terrestrial rocks that provide the first experimental evidence that can discriminate between the two leading models for the moon’s origin. In one model, a low-energy impact leaves the proto-Earth and moon shrouded in a silicate atmosphere; in the other, a much more violent impact vaporizes the impactor and most of the proto-Earth, expanding to form an enormous superfluid disk out of which the moon eventually crystallizes.

The isotopic study, which supports the high-energy model, was published Sept. 12 in the advance online edition of Nature. “Our results provide the first hard evidence that the impact really did (largely) vaporize  Earth,” said Wang, assistant professor in Earth and Planetary Sciences in Arts & Sciences.

An isotopic crisis

In the mid-1970s, two groups of astrophysicists independently proposed that the moon was formed by a grazing collision between a Mars-sized body and the proto-Earth. The giant impact hypothesis, which explains many observations, such as the large size of the moon relative to the Earth and the rotation rates of the Earth and moon, eventually became the leading hypothesis for the moon’s origin.

In 2001, however, a team of scientists reported that the isotopic compositions of a variety of elements in terrestrial and lunar rocks are nearly identical. Analyses of samples brought back from the Apollo missions in the 1970s showed that the moon has the same abundances of the three stable isotopes of oxygen as the Earth.

This was very strange. Numerical simulations of the impact predicted that most of the material (60-80 percent) that coalesced into the moon came from the impactor, rather than from Earth. But planetary bodies that formed in different parts of the solar system generally have different isotopic compositions, so different that the isotopic signatures serve as “fingerprints” for planets and meteorites from the same body.

The probability that the impactor just happened to have the same isotopic signature as the Earth was vanishingly small.

So the giant impact hypothesis had a major problem. It could match many physical characteristics of the Earth-moon system but not their geochemistry. The isotopic composition studies had created an “isotopic crisis” for the hypothesis.

At first, scientists thought more precise measurements might resolve the crisis. But more accurate measurements of oxygen isotopes published in 2016 only confirmed that the isotopic compositions are not distinguishable. “These are the most precise measurements we can make, and they’re still identical,” Wang said.

A slap, a slug or a wallop?

“So people decided to change the giant impact hypothesis,” Wang said. “The goal was to find a way to make the moon mostly from the Earth rather than mostly from the impactor. There are many new models — everyone is trying to come up with one — but two have been very influential.”

In the original giant impact model, the impact melted a part of the Earth and the entire impactor, flinging some of the melt outward, like clay from a potter’s wheel.

Two recent models for the formation of the moon, one that allows exchange through a silicate atmosphere (top), and another that creates a more thoroughly mixed sphere of a supercritical fluid (bottom), lead to different predictions for potassium isotope ratios in lunar and terrestrial rocks (right). (Illustration: Kun Wang)

Two recent models for the formation of the moon, one that allows exchange through a silicate atmosphere (top), and another that creates a more thoroughly mixed sphere of a supercritical fluid (bottom), lead to different predictions for potassium isotope ratios in lunar and terrestrial rocks (right). (Illustration: Kun Wang)

A model proposed in 2007 adds a silicate vapor atmosphere around the Earth and the lunar disk (the magma disk that is the residue of the impactor). The idea is that the silicate vapor allows exchange between the Earth, the vapor and the material in the disk, before the moon condenses from the melted disk.

“They’re trying to explain the isotopic similarities by addition of this atmosphere,” Wang said, “but they still start from a low-energy impact like the original model.”

But exchanging material through an atmosphere is really slow, Wang said. You’d never have enough time for the material to mix thoroughly before it started to fall back to Earth.

So another model, proposed in 2015, assumes the impact was extremely violent, so violent that the impactor and Earth’s mantle vaporized and mixed together to form a dense melt/vapor mantle atmosphere that expanded to fill a space more than 500 times bigger than today’s Earth. As this atmosphere cooled, the moon condensed from it.

The thorough mixing of this atmosphere explains the identical isotope composition of the Earth and moon, Wang said. The mantle atmosphere was a “supercritical fluid,” without distinct liquid and gas phases. Supercritical fluids can flow through solids like a gas and dissolve materials like a liquid.

Why potassium is decisive 

The Nature paper reports high-precision potassium isotopic data for a representative sample of  lunar and terrestrial rocks. Potassium has three stable isotopes, but only two of them, potassium-41 and potassium-39, are abundant enough to be measured with sufficient precision for this study.

Wang and Jacobsen examined seven lunar rock samples from different lunar missions and compared their potassium isotope ratios to those  of eight terrestrial rocks representative of Earth’s mantle. They found that  the lunar rocks were enriched by about 0.4 parts per thousand in the heavier isotope of potassium, potassium-41.

The only high-temperature process that could separate the potassium isotopes in this way, said Wang, is incomplete condensation of the potassium from the vapor phase during the moon’s formation. Compared to the lighter isotope, the heavier isotope would preferentially fall out of the vapor and condense.

Calculations show, however, that if this process happened in an absolute vacuum, it  would lead to an enrichment of heavy potassium  isotopes in lunar samples of about 100 parts per thousand, much higher than the value Wang and Jacobsen found. But higher pressure would suppress fractionation, Wang said. For this reason, he and his colleague predict the moon condensed in a pressure of more than 10 bar, or roughly 10 times the sea level atmospheric pressure on Earth.

Their finding that the lunar rocks are enriched in the heavier potassium isotope does not favor the silicate atmosphere model, which predicts lunar rocks will contain less of the heavier isotope than terrestrial rocks, the opposite of what the scientists found.

Instead it supports the mantle atmosphere model that predicts lunar rocks will contain more of the heavier isotope than terrestrial rocks.

Silent for billions of years, the potassium isotopes have finally found a voice, and they have quite a tale to tell.

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First Signs Of Animal Life On Earth May Be From Microbes

A Dickinsonia Costa fossil from the Ediacaran period. Credit: Wikipedia Commons

A Dickinsonia Costa fossil from the Ediacaran period. Credit: Wikipedia Commons

Evidence suggests that microbes existed on Earth as far back as 3.7 billion years ago, a billion years after the planet formed. Animal remains, however, don’t appear in the fossil record until 600 million years ago during the Ediacaran period, though there are indirect signs that animal life may have gotten started much earlier.

Scientists are attempting to put a date on the earliest lifeforms in the kingdom of Animalia, but without an actual cast of a body they’ve had to rely on the credibility of “trace” fossils to show signs of an animal’s presence in the form of footprints, scratches, feeding marks or burrows. Some scientists claim to have found trace fossils made by animals more than a billion years ago, raising controversy over whether animal life could have existed this early. There are also trace fossils from the Ediacaran Period and soft bodied animals were known to exist during this period, so understanding the tracks they made is important for studying the early animals.

Giulio Mariotti, an oceanographer from Louisiana State University, and colleagues, examined supposed animal trace fossils from the Ediacaran Period, and found that it is possible that some of them could be microbial in origin. The results, which were recently published in a paper entitled “Microbial Origin of Early Animal Trace Fossils” in the Journal of Sedimentary Research, raise questions about the reliability of trace fossils as evidence for early animal life.

The research was funded by the Exobiology & Evolutionary Biology element of the NASA Astrobiology Program.

Trace fossils, such as this one caused by a trilobite, are trails or footprints left behind by an animal. The trilobite moved from right to left and then partially buried itself, leaving an impression. Not all trace fossils are as easily identifiable, particularly ones of early life. Credit: Stefano Novello

Trace fossils, such as this one caused by a trilobite, are trails or footprints left behind by an animal. The trilobite moved from right to left and then partially buried itself, leaving an impression. Not all trace fossils are as easily identifiable, particularly ones of early life. Credit: Stefano Novello

Ancient microbial mats

Many of the Ediacaran animal trace fossils are found within “wrinkle” structures, small ridges and pits interpreted as evidence of ancient microbial mats. Microbial mats are comprised of layers of microorganisms, and fossilized mats are among the earliest clear signs of microbial life. Microbial mats were widespread in the Precambrian, the period before animal life became extremely common and diverse. But the mats were no longer able to flourish in certain marine areas when grazing animals became more abundant because the animals destroyed the structures.

Mariotti and colleagues devised an experiment to try to create trails of grooves and pits similar to the trace fossils. They did this by moving microbial aggregates across sand at the bottom of a tank of water by creating waves in the water. Microbial aggregates are small cluster of microbes which are larger than sand but less dense. This low density enables them to be moved across the sand at the bottom of the tank by very low energy waves.

The use of low energy waves is important as waves with higher energy would also erase the trail left in the sand. A wide variety of trails were produced by the aggregates depending on the wave conditions and the size of the aggregate. Some of these trails were strikingly similar to those that are currently deemed to be Ediacaran trace fossils, meaning that it is possible that some trace fossils are actually not fossils at all and are instead caused by the movement of microbial aggregates.

However, not only did the trails produced by the wave tank experiment replicate the supposed animal traces, the experiment also produced a wrinkle structure in the sand. The aggregates caused the wrinkle structure when they were smaller than the amplitude of the wave, where as the trails were formed when the aggregates were larger than the wave amplitude.

The images on the left show Ediacaran trace fossils, and the images on the right show the trails produced in the wave tank with the microbial aggregates. The white scale bar is 1 centimeter.  Credit: SEPM/Journal of Sedimentary Research. Used with permission

The images on the left show Ediacaran trace fossils, and the images on the right show the trails produced in the wave tank with the microbial aggregates. The white scale bar is 1 centimeter. Credit: SEPM/Journal of Sedimentary Research. Used with permission

This research does not necessarily mean that all early trace fossils were caused by microbial aggregates, however it does put forward a plausible alternative explanation for those that occur alongside wrinkle structures. Therefore, possible trace fossils from the Ediacaran period or earlier should be looked upon with skepticism until it is possible to rule out microbial aggregates as a cause of the grooves and pits in the rock.

Trails caused by aggregates and those caused by animals can be distinguished in some cases if certain distinctive features exist. For example an animal trail can be “self avoiding,” meaning that the animal didn’t cross back over its own trail as it had already searched for food in that location. Unfortunately, most of the more distinctive signs of animal activity are rare until the very end of the Ediacaran period.

It is much easier to distinguish younger trace fossils from aggregate trails. “There is much more evidence that recent tracks were formed by animals,” explains Mariotti. Trace fossils created in the time since the Ediacaran are more complex because they are three-dimensional, meaning that they go into the sediments such as a tunnel, and cannot be reproduced with the moving aggregates. “It is easier to challenge old trails because they have less ancillary information associated with them,” said Mariotti.

The formation and evolution of Earth’s earliest life is crucial in order to inform us of what types of life might exist on other planets. To do this, we need concrete evidence of what the earliest animals on Earth were like. Mariotti and his team plan to perform further experiments to examine the geometry of aggregate trails and how well animal trails are preserved in sediments that have an abundance of microbes compared to sediments with no microbes. They hope that these experiments will help distinguish real animal fossils from the aggregate trails, and therefore further our understanding of the earliest animal life on Earth.

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Mars Rover Views Spectacular Layered Rock Formations

Curiosity got close to this outcrop on Sept. 9, 2016, which displays finely layered rocks. Image Credit: NASA/JPL-Caltech/MSSS

Curiosity got close to this outcrop on Sept. 9, 2016, which displays finely layered rocks. Image Credit: NASA/JPL-Caltech/MSSS

The layered geologic past of Mars is revealed in stunning detail in new color images returned by NASA’s Curiosity Mars rover, which is currently exploring the “Murray Buttes” region of lower Mount Sharp. The new images arguably rival photos taken in U.S. National Parks.

Curiosity took the images with its Mast Camera (Mastcam) on Sept. 8. The rover team plans to assemble several large, color mosaics from the multitude of images taken at this location in the near future.

“Curiosity’s science team has been just thrilled to go on this road trip through a bit of the American desert Southwest on Mars,” said Curiosity Project Scientist Ashwin Vasavada, of NASA’s Jet Propulsion Laboratory, Pasadena, California.

The rim of Gale Crater is visible in the distance, through the dusty haze, in this Curiosity view of a sloping hillside on Mount Sharp. Image Credit: NASA/JPL-Caltech/MSSS

The rim of Gale Crater is visible in the distance, through the dusty haze, in this Curiosity view of a sloping hillside on Mount Sharp. Image Credit: NASA/JPL-Caltech/MSSS

The Martian buttes and mesas rising above the surface are eroded remnants of ancient sandstone that originated when winds deposited sand after lower Mount Sharp had formed.

“Studying these buttes up close has given us a better understanding of ancient sand dunes that formed and were buried, chemically changed by groundwater, exhumed and eroded to form the landscape that we see today,” Vasavada said.

The new images represent Curiosity’s last stop in the Murray Buttes, where the rover has been driving for just over one month. As of this week, Curiosity has exited these buttes toward the south, driving up to the base of the final butte on its way out. In this location, the rover began its latest drilling campaign (on Sept. 9). After this drilling is completed, Curiosity will continue farther south and higher up Mount Sharp, leaving behind these spectacular formations.

This closeup view from NASA's Curiosity rover shows finely layered rocks, deposited by wind long ago as migrating sand dunes. Image Credit: NASA/JPL-Caltech/MSSS

This closeup view from NASA’s Curiosity rover shows finely layered rocks, deposited by wind long ago as migrating sand dunes. Image Credit: NASA/JPL-Caltech/MSSS

Curiosity landed near Mount Sharp in 2012. It reached the base of the mountain in 2014 after successfully finding evidence on the surrounding plains that ancient Martian lakes offered conditions that would have been favorable for microbes if Mars has ever hosted life. Rock layers forming the base of Mount Sharp accumulated as sediment within ancient lakes billions of years ago.

On Mount Sharp, Curiosity is investigating how and when the habitable ancient conditions known from the mission’s earlier findings evolved into conditions drier and less favorable for life.

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Scientists expect to calculate amount of fuel inside Earth by 2025

By 2022, scientists expect to be able to detect at least 536 antineutrino events per year at these five underground detectors: KamLAND in Japan, Borexino in Italy, SNO+ in Canada, and Jinping and JUNO in China. Credit: Ondrej Sramek

By 2022, scientists expect to be able to detect at least 536 antineutrino events per year at these five underground detectors: KamLAND in Japan, Borexino in Italy, SNO+ in Canada, and Jinping and JUNO in China. Credit: Ondrej Sramek

Earth requires fuel to drive plate tectonics, volcanoes and its magnetic field. Like a hybrid car, Earth taps two sources of energy to run its engine: primordial energy from assembling the planet and nuclear energy from the heat produced during natural radioactive decay. Scientists have developed numerous models to predict how much fuel remains inside Earth to drive its engines — and estimates vary widely — but the true amount remains unknown.

In a new paper, a team of geologists and neutrino physicists boldly claims it will be able to determine by 2025 how much nuclear fuel and radioactive power remain in the Earth’s tank. The study, authored by scientists from the University of Maryland, Charles University in Prague and the Chinese Academy of Geological Sciences, was published on September 9, 2016, in the journal Nature Scientific Reports.

“I am one of those scientists who has created a compositional model of the Earth and predicted the amount of fuel inside Earth today,” said one of the study’s authors William McDonough, a professor of geology at the University of Maryland. “We’re in a field of guesses. At this point in my career, I don’t care if I’m right or wrong, I just want to know the answer.”

To calculate the amount of fuel inside Earth by 2025, the researchers will rely on detecting some of the tiniest subatomic particles known to science — geoneutrinos. These antineutrino particles are byproducts of nuclear reactions within stars (including our sun), supernovae, black holes and human-made nuclear reactors. They also result from radioactive decay processes deep within the Earth.

Detecting antineutrinos requires a huge detector the size of a small office building, housed about a mile underground to shield it from cosmic rays that could yield false positive results. Inside the detector, scientists detect antineutrinos when they crash into a hydrogen atom. The collision produces two characteristic light flashes that unequivocally announce the event. The number of events scientists detect relates directly to the number of atoms of uranium and thorium inside the Earth. And the decay of these elements, along with potassium, fuels the vast majority of the heat in the Earth’s interior.

To date, detecting antineutrinos has been painfully slow, with scientists recording only about 16 events per year from the underground detectors KamLAND in Japan and Borexino in Italy. However, researchers predict that three new detectors expected to come online by 2022–the SNO+ detector in Canada and the Jinping and JUNO detectors in China–will add 520 more events per year to the data stream.

“Once we collect three years of antineutrino data from all five detectors, we are confident that we will have developed an accurate fuel gauge for the Earth and be able to calculate the amount of remaining fuel inside Earth,” said McDonough.

The new Jinping detector, which will be buried under the slopes of the Himalayas, will be four times bigger than existing detectors. The underground JUNO detector near the coast of southern China will be 20 times bigger than existing detectors.

“Knowing exactly how much radioactive power there is in the Earth will tell us about Earth’s consumption rate in the past and its future fuel budget,” said McDonough. “By showing how fast the planet has cooled down since its birth, we can estimate how long this fuel will last.”