In Martian Rocks, Hints of a Watery Past

By tasting a little bit of the rocks and air on Mars, NASA's robotic Phoenix lander discovered secrets about the history of water on the Red Planet over the last 4 billion years, scientists now reveal.

Phoenix was the most recent spacecraft to land on Mars and spent about five months studying the planet before the dark, icy winter of the Martian arctic damaged its solar panels in 2008. Scientists are still sifting through the wealth of Mars data that was captured by the spacecraft while it was still alive.

From that data mine, researchers discovered that the carbon dioxide in Mars' atmosphere shows evidence of recently interacting with liquid water. [Photos of water ice on Mars.]

"We think of Mars as cold and dry right now, but perhaps these findings suggest there could be things going on that we haven't observed yet, driving a more active system than we see on the face of things," said researcher Paul Niles, a planetary scientist at NASA's Johnson Space Center in Houston.

When combined with studies of 4-billion-year-old Martian meteorites collected on Earth, the results also suggest Mars has experienced substantial interactions between rock and cold water throughout its history.

Unexpected activity

Niles warned that it is hard to judge from the data how much water was involved in the recent interaction — "You could probably get similar results with very little water, just thin films, or with oceans and seas and lakes," he said — and the same uncertainly applies to Mars' past.

"That could be the result of a lot of groundwater flowing, or just thin films of water," Niles told, "but whatever happened, early massive hydrothermal systems were not common on Mars."

The carbon dioxide in the atmosphere of Mars is mostly derived from geologically recent volcanic eruptions, he added.

"All these results suggest that Mars is more active than we have thought," Niles said.

Isotopes tell watery tale

Niles and his colleagues used Phoenix's observations of carbon dioxide isotopes in the atmosphere to study the planet's water history.  During its mission, the lander studied the isotopic composition of carbon dioxide more precisely than any other Mars probe to date.

Isotopes are versions of a chemical element that have differing numbers of neutrons in their nuclei. Carbon dioxide is the major component of Mars' atmosphere, and its isotopic composition can reveal much about the geological processes that liquids and gases on the planet have been involved in, since carbon dioxide reacts readily with water and a variety of rocks there.

Phoenix gathered carbon dioxide from the atmosphere and then compared those samples with a carbon dioxide specimen, one with a known isotopic makeup, brought from Earth. By comparing the two isotopic compositions, scientists can learn more about the Martian atmosphere.

The research is detailed in the Sept. 10 issue of the journal Science.

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