ScienceShot: Looking for Life on Mars? Dig Deeper

BOSTONCuriosity’s newly drilled hole on the surface of Mars, completed last week, is our first peek at what’s under the surface of the red planet. And even as scientists start their analyses, a martian meteorite that arrived on Earth 12,000 years ago is yielding its own clues to life on Mars, strengthening the idea that we’ll have to go deeper to find life, if it’s there at all. The meteorite, found in 1979, has long been known to contain small amounts of the chemicals nitrate and perchlorate, which could be good or bad for life: To some modern life forms on Earth, perchlorate is toxic, but to others in oxygen-free conditions, and to those in the early days of Earth, it was a source of energy for microbes. But whether those chemicals originated on Mars or crept in during the meteorite’s 12,000-year tenure on Earth was uncertain. Now that question, at least, has been solved: They’re definitely from Mars, scientists reported here today at the annual meeting of AAAS (which publishes ScienceNOW). What’s more, new analyses of data from Curiosity’s predecessor, Phoenix, suggest that the red planet’s surface also contains highly reactive chemicals called oxychlorines, intermediaries between perchlorates and chlorines. With just a little water, oxychlorines react speedily with any organic matter in soils. So if scientists find any organics on Mars, that means the planet is very, very dryat least nowadayswhich, paradoxically isn’t good news for life. But that doesn’t preclude the possibility that life is buried deep, said lead author and planetary scientist Sam Kounaves of Tufts University in Medford, Massachusetts. In just the last 10 years, life has been found in all sorts of surprisingdeep, dark, inhospitablespots on Earth, he said. "We had to go pretty far down. So if Earth is any guide, we’ve got a long way to go."

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*Correction, 1:08 p.m., 19 February: The text has been changed to reflect that the data was collected by the Phoenix lander, not the Opportunity rover. Also, the chemicals found on Mars's surface were oxychlorines, not oxychlorate.