[meteorite-list] New Clues Suggest Wet Era on Early Mars Was Global

From: Ron Baalke <baalke_at_meteoritecentral.com>
Date: Thu, 24 Jun 2010 16:37:19 -0700 (PDT)
Message-ID: <201006242337.o5ONbJ6Y016921_at_zagami.jpl.nasa.gov>

http://www.jpl.nasa.gov/news/news.cfm?release=2010-209

New Clues Suggest Wet Era on Early Mars Was Global
Jet Propulsion Laboratory
June 24, 2010

PASADENA, Calif. -- Minerals in northern Mars craters seen by two
orbiters suggest that a phase in Mars' early history with conditions
favorable to life occurred globally, not just in the south.

Southern and northern Mars differ in many ways, so the extent to which
they shared ancient environments has been open to question.

In recent years, the European Space Agency's Mars Express orbiter and
NASA's Mars Reconnaissance Orbiter have found clay minerals that are
signatures of a wet environment at thousands of sites in the southern
highlands of Mars, where rocks on or near the surface are about four
billion years old. Until this week, no sites with those minerals had
been reported in the northern lowlands, where younger volcanic activity
has buried the older surface more deeply.

French and American researchers report in the journal Science this week
that some large craters penetrating younger, overlying rocks in the
northern lowlands expose similar mineral clues to ancient wet conditions.

"We can now say that the planet was altered on a global scale by liquid
water about four billion years ago," said John Carter of the University
of Paris, the report's lead author.

Other types of evidence about liquid water in later epochs on Mars tend
to point to shorter durations of wet conditions or water that was more
acidic or salty.

The researchers used the Compact Reconnaissance Imaging Spectrometer for
Mars (CRISM), an instrument on the Mars Reconnaissance Orbiter, to check
91 craters in the northern lowlands. In at least nine, they found clays
and clay-like minerals called phyllosilicates, or other hydrated
silicates that form in wet environments on the surface or underground.

Earlier observations with the OMEGA spectrometer on Mars Express had
tentatively detected phyllosilicates in a few craters of the northern
plains, but the deposits are small, and CRISM can make focused
observations on smaller areas than OMEGA.

"We needed the better spatial resolution to confirm the
identifications," Carter said. "The two instruments have different
strengths, so there is a great advantage to using both."

CRISM Principal Investigator Scott Murchie of Johns Hopkins University
Applied Physics Laboratory, Laurel, Md., a co-author of the new report,
said that the findings aid interpretation of when the wet environments
on ancient Mars existed relative to some other important steps in the
planet's early history.

The prevailing theory for how the northern part of the planet came to
have a much lower elevation than the southern highlands is that a giant
object slammed obliquely into northern Mars, turning nearly half of the
planet's surface into the solar system's largest impact crater. The new
findings suggest that the formation of water-related minerals, and thus
at least part of the wet period that may have been most favorable to
life, occurred between that early giant impact and the later time when
younger sediments formed an overlying mantle.

"That large impact would have eliminated any evidence for the surface
environment in the north that preceded the impact," Murchie said. "It
must have happened well before the end of the wet period."

The report's other two authors are Francois Poulet and OMEGA Principal
Investigator Jean-Pierre Bibring, both of the University of Paris.

NASA's Jet Propulsion Laboratory, a division of the California Institute
of Technology, Pasadena, manages the Mars Reconnaissance Orbiter for
NASA. Johns Hopkins University Applied Physics Laboratory provided and
operates CRISM, one of six instruments on that orbiter.

For more information about the Mars Reconnaissance Orbiter, visit
http://www.nasa.gov/mro.

Guy Webster (818) 354-6278
Jet Propulsion Laboratory, Pasadena, Calif.
guy.webster at jpl.nasa.gov

2010-209
Received on Thu 24 Jun 2010 07:37:19 PM PDT


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