An image of the Martian surface from NASA’s Viking 2

To eke out even the barest subsistence on Mars, a living thing would have to adapt to a formidable set of environmental challenges: an arid, often extremely cold landscape with miniscule amounts of oxygen in the atmosphere and no organic matter to eat. During a recent foray into a similarly inhospitable part of our own planet, scientists have discovered several species of bacteria that hint at what life on Mars, if it exists, might look like. These microbes survive on minerals in the surrounding rocks—minerals also found in the Martian surface.

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A cluster of 3.4 billion-year-old fossilized cells

What’s the News: Geologists have found fossils of microorganisms from 3.4 billion years ago, which may be the oldest fossils ever uncovered. Since these microbes date from a time when Earth’s atmosphere was still oxygen-free, astrobiologists could look for similarly structured microbes when searching for extraterrestrial life.

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Early Earth’s chemical seas are presumed to have given rise to the first life, but how could anything so complex have come from such a disorganized stew of molecules? That’s the question Gerald Joyce of the Scripps Research Institute is exploring with his swarms of self-replicating RNA, which can evolve over time. Along with Steve Benner, Craig Venter, Jack Szostak, and others, he is on the road to creating life in the lab, thus giving us insight into both our origins and what, exactly, “life” is. As Dennis Overbye writes in a look at the field in the New York Times:

The possibilities of a second example of life are as deep as the imagination. It could be based on DNA that uses a different genetic code, with perhaps more or fewer than four letters; it could be based on some complex molecule other than DNA, or more than the 20 amino acids from which our own proteins are made, or even some kind of chemistry based on something other than carbon and the other elements that we take for granted, like phosphorous or iron. Others wonder whether chemistry is necessary at all. Could life manifest itself, for example, in the pattern of electrically charged dust grains in a giant interstellar cloud, as the British astronomer and author Fred Hoyle imagined in his novel “The Black Cloud”?

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What’s the News: On Friday, after five years of deliberation over 100 candidates, NASA announced its choice of landing site for Curiosity, the next Mars rover: Gale crater, a massive pit with a three-mile-high mound in its center.  The mission’s primary goal is to assess whether conditions suitable for microbial life ever existed on the Red Planet; Gale was selected over the three other finalists in part because its mountain promises access to layered sediments extending deep into the Martian past.

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First came the extraterrestrial speculation. Then came the actual answer. Then came the backlash.

NASA’s big astrobiology news last week had nothing to do with E.T., of course—the team behind a study in Science announced the find of a kind of bacteria that appear to thrive in arsenic and can even use it in place of phosphorus in the backbone of its DNA double helix. But after the big announcement finally happened and squelched the more imaginative rumors, scientists started asking some hard questions about the study online.

Over at Slate, DISCOVER blogger Carl Zimmer rounded up expert critiques from biologists, and many didn’t hold back.

Almost unanimously, they think the NASA scientists have failed to make their case. “It would be really cool if such a bug existed,” said San Diego State University’s Forest Rohwer, a microbiologist who looks for new species of bacteria and viruses in coral reefs. But, he added, “none of the arguments are very convincing on their own.” That was about as positive as the critics could get. “This paper should not have been published,” said Shelley Copley of the University of Colorado. [Slate]

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It’s back. ALH 84001, the meteorite of Martian origin that NASA scientists claimed in 1996 contained evidence of life on Mars, has returned to the scene. This time, the team published a paper in the journal Geochimica et Cosmochimica Acta (the journal of the Geochemical and Meteoritic Society). And the scientists say they’re more confident than ever that the meteorite shows signs of martian life.

The NASA team of David McKay, Everett Gibson and Kathie Thomas-Keprta garnered widespread attention and even an announcement by President Bill Clinton when the 1996 paper came out. The NASA claim focused on nano-sized evidence: magnetite crystals embedded in the meteorite, which arrived here on Earth 13,000 years ago. Because some Earth bacteria secrete magnetite, McKay and his team argued that the mineral in the meteorite could be of biological origin, and the ‘biomorphs” in this image (which is from the new study) could be a fossilized colony of tiny bacteria. But the research was widely panned, and the NASA team making claims for life on Mars subsequently retreated [Discovery News].

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With its thick atmosphere, chemical makeup, and an atmospheric pressure not too far from Earth’s, Titan is one of the most likely candidates for finding life elsewhere in our solar system. But at a temperature close to -300 degrees Fahrenheit, the surface of this Saturnian moon in anything but what we humans would call hospitable. Since this frigid place is far too cold for liquid water, any life there would need an alternative survival method. A new study published in Astrophysical Journal Letters suggests that the simple hydrocarbon acetylene, proposed as a possible energy source for life on Titan, could be much more abundant than scientists previously thought.

Titan has previously been shown to be dotted with lakes of liquid hydrocarbons, primarily methane and ethane. An estimate made in 1989 suggested bodies of liquid hydrocarbons on Titan would contain a few parts in 10,000 of acetylene. But an updated estimate based on data from the Cassini-Huygens mission to Saturn now suggests the lakes contain much more food for any hungry alien life-forms that might be present [New Scientist]. Lead researcher Daniel Cordier says the acetylene abundance could be as high as one part in 100, or 1 percent, of the surface lakes on Titan.

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