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Life on Mars? "Missing Mineral" Find Boosts Chances

Victoria Jaggard in San Francisco
National Geographic News
December 19, 2008
 
The possibility that life took hold on early Mars got a boost this week with the announcement of the discovery of a previously "missing" mineral on the red planet.

New images from NASA's Mars Reconnaissance Orbiter show areas fo Mars where magnesium carbonate is exposed in 3.6-billion-year-old bedrock in Mars's Nili Fossae region.

Carbonate minerals contain carbon and oxygen and need liquid water to form. Common carbonates on Earth include limestone and chalk.

Previous missions had seen small percentages of carbonates in Martian dust. More recently the Mars Phoenix Lander found the minerals in the planet's arctic soils.

But until now, evidence for the source of these carbonates in Martian bedrock had been elusive, supporting theories that even if Mars once had bodies of water, they were too acidic to support life as we know it.

"Carbonate, like the baking soda in your refrigerator, dissolves quickly when exposed to acid," said study leader and Brown University professor Bethany Ehlmann yesterday at an American Geophysical Union meeting in San Francisco.

"So the fact that … carbonate is still present means that the waters flowing through [Nili Fossae] must not have been acid" and could therefore have been conducive to life.

Signs of CO2

Scientists had long expected to find carbonates on Mars, because the planet's carbon dioxide (CO2) atmosphere likely would have supported their formation.

Mars currently has a thin atmosphere, leaving the planet dry and frigid. But some experts think that billions of years ago the atmosphere was thicker, capturing enough heat from the sun to support liquid water on the surface.

Carbon dioxide gas should have reacted with Mars's volcanic rock, and that reaction should have produce carbonate, said Richard Zurek, a project scientist for the Mars orbiter based at NASA's Jet Propulsion Laboratory in Pasadena, California.

The newfound carbonate bedrock deposits are relatively small—some just under four square miles (ten square kilometers)—but large enough to hint at early Mars water sources.

Ehlmann and colleagues published their work today in the journal Science.

For now the exposed mineral layers don't reveal enough carbonate to confirm or deny the theory that early Mars had a thick, carbon dioxide-rich atmosphere, noted Scott Murchie, a researcher on the Mars orbiter team based at Johns Hopkins University in Maryland.

However, further study of the Martian minerals could "help us understand whether what's preserved on the surface today is possible evidence of past life," Murchie said.

Study leader Ehlmann agreed. The carbonate-containing regions of Mars "would have been a pretty clement, benign environment for early Martian life, and I think it is a great area to look in future investigations of Mars's habitability," she said.

The Whole Elephant

Earlier this year Andrew Knoll, of Harvard University, co-authored a study based on mineral data from the Mars rover Opportunity.

Early Mars likely supported a salty, toxic stew—waters that would have been inhospitable to known forms of life—the earlier study said.

Knoll, who was not involved in the new study, said that if the carbonates found are definitely from early Mars, they would indicate that—at least locally—the waters would have been neutral enough for life.

But, he said, "there are probably a hundred different criteria by which we would assess the habitability of Mars."

Finding carbonates is not enough to say with any certainty that Mars would have supported life in its past.

"There's a whole history of papers where people look at features on the elephant and try to describe the whole elephant," Knoll said.

"We've been very fortunate in recent years with the rovers and orbiters on Mars to make observations that have changed the way we think about the planet," he continued.

"Nonetheless, there's still a lot we don't know, especially about the origins of life."
 

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