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Giant Volcano With Glacier On Mars May Have Been A Nice Place For Life

By Amina Khan, Los Angeles Times

If life existed on Mars in the recent past, the best spot for it could have been on a giant volcano once encrusted with a glacier, according to a team of Brown University scientists using data from NASA’s Mars Reconnaissance Orbiter.

Microbial life could potentially have thrived for a time at the foot of Arsia Mons, a giant volcano about twice as tall as Mount Everest, while the dinosaurs were just coming into their own on Earth, according to the study published in the journal Icarus.

Though an active volcano may not sound particularly inviting, this combination of ice and heat would have contained massive, sheltered pockets of water — from melted ice — that could have lasted for hundreds or even a few thousand years.

“I was very excited,” lead author Kathleen Scanlon, a doctoral student and geologist at Brown University, said of the telltale signs left on the Martian surface that led to the team’s conclusions. “It’s all a really nice suite of land forms that together all point to the exact same process. So that was really cool.”

The findings come as NASA and other space agencies send more spacecraft and robots to the Red Planet to better understand how life-friendly Mars was in the past — and whether certain spots were better suited for living things than others.

Recent research has shown that the northwest side of Arsia Mons may have been covered in glacier ice, judging by marks in the terrain that resemble those left by glaciers in Antarctica’s McMurdo Dry Valleys. Around that time, about 210 million years ago, the volcano was active, spewing out lava from beneath the ground and melting some of the thick layer of glacial ice above.

Scanlon looked for certain shapes in the lava that would reveal the conditions under which the lava was coming out. She found a number of striking forms, including pillow-like lava, which extrude into giant rounded globules. On Earth, these pillows form under immense pressure at the bottom of the ocean. On Mars, it could mean the lava was under extreme pressure because it was squeezing out from underneath a glacier.

Two of the liquid bubbles caused by subsequent melting in the solid glacial ice would have held about 40 cubic kilometers of water each, making each of them roughly a third the size of Lake Tahoe. The water in these deposits could have remained liquid for centuries or more, the researchers said.

Microbes trapped in a subglacial lake, in freezing temperatures, total darkness and high pressures may sound extreme, but organisms do it on Earth too. A recent study of ice cores from a subglacial lake in Antarctica found DNA from a variety of microbes living more than 2 miles beneath the ice.

Of course, even a potentially life-friendly zone like Arsia Mons would not have lasted long on geological timescales. At its best, it could have potentially hosted microbes that had already emerged billions of years before, when Mars might have been warmer and wetter.

So the most important thing to understand is whether Mars was habitable more than 3.5 billion years ago, very early in its history, Scanlon noted. If not, then Arsia Mons’ habitability is probably moot. NASA’s Curiosity rover recently dug up some rock in Gale Crater and found some very watery environments rich in chemical building blocks for life. Just before the launch of the atmosphere-testing MAVEN mission last year, NASA released a stunning video of a past Mars, filled with puffy clouds and blue lakes.

But whether much of Mars was so life-friendly, and how long this wet era may have lasted, is up for debate. The less common these life-friendly spots were, and the shorter-lived they were, the less likely that life was able to emerge on the Red Planet. For now, the jury’s out on that mystery.

“If we can confirm that there was life around then, then our next question is, how long was it able to survive, and could there still be dormant microbes lying somewhere around on the surface?” Scanlon said. “I think Arsia Mons would be a good site to answer questions like that — if that does become a question.”

Photo: Luke Bryant via Flickr

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Mercury Is Slowly Shrinking, Scientists Say

By Amina Khan, Los Angeles Times

They say the world is getting smaller — and in Mercury’s case it’s literally true. Though it’s already the tiniest planet in the solar system, scientists say Mercury is still shrinking — and signs of that contraction can be clearly seen in distortions of the planet’s searing surface.

The findings, published in Nature Geoscience, solve a decades-old mystery about the evolution of the little planet’s interior and provide scientists a window into the long-term changes that affect other worlds that don’t have Earth-like plate tectonics.

“Determining the extent to which Mercury contracted is key to understanding the planet’s thermal, tectonic and volcanic history,” the study authors, led by Paul Byrne of the Carnegie Institution of Washington, wrote in the paper.

Mercury is a weird little world. As the solar system’s innermost planet, it sits less than 36 million miles from the sun — less than two-fifths of the Earth-to-sun distance. It’s mostly made up of its heavy iron core, which has about a 1,255-mile radius and leaves a thin rind of just 261 miles for its crust and mantle. Even though it’s unbearably hot, the planet also hosts permanently shadowed regions inside craters that are among the coldest spots in the solar system.

Researchers have long thought that Mercury must be shrinking, because as the planet cools, and the liquid iron core turns solid over time, it contracts. If so, signs of deformation should show up on the planet’s surface — like a plump, smooth-skinned grape that dries up, shrinks and turns into a wrinkly raisin.

Sure enough, when NASA’s Mariner 10 spacecraft flew by the planet in 1974 and 1975, it discovered strange, snaking “lobate scarps” on the surface of the planet. Those scarps, which are Mercury’s version of mountain ranges, were the signs that the planet had shrunk, causing its rocky skin to deform.

But Mariner 10 imaged only 45 percent of the planet, and scientists could account for only about 0.5 to 2 miles of shrinkage in the radius. The models said that Mercury’s radius should have shrunk roughly 3 to 6 miles over the last 4 billion years, since its crust solidified. Were the models wrong? Or was it simply that we hadn’t seen enough of Mercury?

NASA’s MESSENGER spacecraft, which flew by the planet in 2008 and 2009 and entered Mercury’s orbit in 2011, solved the mystery by mapping the remaining 55 percent of the planet that Mariner 10 missed. Scientists found that the lobate scarps covered the whole globe randomly — and that these weren’t the only signs of shrinkage. The scientists found wrinkle ridges all over Mercury’s volcanic plains, and though they’re not as high or as dramatic as those lobate scarps, they’re also a reliable sign that Mercury has been contracting, and can help researchers measure how much volume has been lost.

Based on this new view of Mercury, the researchers found that the planet’s radius had probably shrunk about 3 to 4.3 miles since its crust solidified — safely within range of the theoretical predictions.

“The findings provide a global framework for investigations into Mercury’s surface and interior evolution,” planetary scientist William McKinnon of Washington University in St. Louis wrote in a commentary on the paper.

All planets, Earth included, are cooling down over time — but the findings don’t apply to Earth because our home planet has constantly shifting tectonic plates and Mercury is a one-plate planet. Still, these wrinkly, mountain-like features have also been seen on the moon and on Mars, and Mercury could make it a model for what happens to other single-plate planets.

“Mercury provides an example of what may really happen to a planet that is shrinking,” McKinnon wrote.

Photo: Lunar and Planetary Institute via Flickr