NASA Rover Finds Clue To Mars' Past And Environment For Life

PASADENA, Calif. -- Rocks examined by NASA's Spirit Mars Rover hold
evidence of a wet, non-acidic ancient environment that may have been
favorable for life. Confirming this mineral clue took four years of
analysis by several scientists.

An outcrop that Spirit examined in late 2005 revealed high
concentrations of carbonate, which originates in wet, near-neutral
conditions, but dissolves in acid. The ancient water indicated by
this find was not acidic.

NASA's rovers have found other evidence of formerly wet Martian
environments. However the data for those environments indicate
conditions that may have been acidic. In other cases, the conditions
were definitely acidic, and therefore less favorable as habitats for
life.

Laboratory tests helped confirm the carbonate identification. The
findings were published online Thursday, June 3 by the journal
Science.

"This is one of the most significant findings by the rovers," said
Steve Squyres of Cornell University in Ithaca, N.Y. Squyres is
principal investigator for the Mars twin rovers, Spirit and
Opportunity, and a co-author of the new report. "A substantial
carbonate deposit in a Mars outcrop tells us that conditions that
could have been quite favorable for life were present at one time in
that place. "

Spirit inspected rock outcrops, including one scientists called
Comanche, along the rover's route from the top of Husband Hill to the
vicinity of the Home Plate plateau which Spirit has studied since
2006. Magnesium iron carbonate makes up about one-fourth of the
measured volume in Comanche. That is a tenfold higher concentration
than any previously identified for carbonate in a Martian rock.

"We used detective work combining results from three spectrometers to
lock this down," said Dick Morris, lead author of the report and a
member of a rover science team at NASA's Johnson Space Center in
Houston."The instruments gave us multiple, interlocking ways of
confirming the magnesium iron carbonate, with a good handle on how
much there is."

Massive carbonate deposits on Mars have been sought for years without
much success. Numerous channels apparently carved by flows of liquid
water on ancient Mars suggest the planet was formerly warmer, thanks
to greenhouse warming from a thicker atmosphere than exists now. The
ancient, dense Martian atmosphere was probably rich in carbon
dioxide, because that gas makes up nearly all the modern, very thin
atmosphere.

It is important to determine where most of the carbon dioxide went.
Some theorize it departed to space. Others hypothesize that it left
the atmosphere by the mixing of carbon dioxide with water under
conditions that led to forming carbonate minerals. That possibility,
plus finding small amounts of carbonate in meteorites that originated
from Mars, led to expectations in the 1990s that carbonate would be
abundant on Mars. However, mineral-mapping spectrometers on orbiters
since then have found evidence of localized carbonate deposits in
only one area, plus small amounts distributed globally in Martian
dust.

Morris suspected iron-bearing carbonate at Comanche years ago from
inspection of the rock with Spirit's Moessbauer Spectrometer, which
provides information about iron-containing minerals. Confirming
evidence from other instruments emerged slowly. The instrument with
the best capability for detecting carbonates, the Miniature Thermal
Emission Spectrometer, had its mirror contaminated with dust earlier
in 2005, during a wind event that also cleaned Spirit's solar panels.

"It was like looking through dirty glasses," said Steve Ruff of
Arizona State University in Tempe, Ariz., another co-author of the
report. "We could tell there was something very different about
Comanche compared with other outcrops we had seen, but we couldn't
tell what it was until we developed a correction method to account
for the dust on the mirror."

Spirit's Alpha Particle X-ray Spectrometer instrument detected a high
concentration of light elements, a group including carbon and oxygen,
that helped quantify the carbonate content.

The rovers landed on Mars in January 2004 for missions originally
planned to last three months. Spirit has been out of communication
since March 22 and is in a low-power hibernation status during
Martian winter. Opportunity is making steady progress toward a large
crater, Endeavour, which is about seven miles away.

NASA's Jet Propulsion Laboratory, Pasadena, manages the Mars
Exploration Rovers for the agency's Science Mission Directorate in
Washington. For more information about the rovers, visit:

http://www.nasa.gov/rovers

Source: NASA