[meteorite-list] Young Clays on Mars Could Have Been Habitable Regions for Life

[Ron Baalke]

NEWS RELEASE FROM THE PLANETARY SCIENCE INSTITUTE

FROM: 
Alan Fischer
Public Information Officer
Planetary Science Institute
520-382-0411
520-622-6300
fischer at psi.edu

Young Clays on Mars Could Have Been Habitable Regions for Life 

Sept. 19, 2011, Tucson, Ariz. -- Two small depressions on Mars found
to be rich in minerals that formed by water could have been places for
life relatively recently in the planet's history, according to a new
paper in the journal Geology.

"We discovered locations at Noctis Labyrinthus that show many kinds of
minerals that formed by water activity," said Catherine Weitz, lead
author and senior scientist at the Planetary Science Institute. "The
clays we found, called iron/magnesium (Fe/Mg)-smectites, are much
younger at Noctis Labyrinthus relative to those found in the ancient
rocks on Mars, which indicates a different water environment in these
depressions relative to what was happening elsewhere on Mars."

Smectites are a specific type of clay mineral that readily expands and
contracts with adsorbed water. They contain Silica, plus Aluminum, Iron
or Magnesium in their structures. They form by the alteration of other
silicate minerals in the presence of non-acidic water.

Weitz and her co-authors studied approximately 300 meters of vertically
exposed layered rocks within two 30 to 40 kilometer depressions, called
troughs, near the western end of the Valles Marineris canyon system.
Using high-resolution images from the High Resolution Imaging Science
Experiment (HiRISE) camera and hyperspectral data from the Compact
Reconnaissance Imaging Spectrometer for Mars (CRISM) on the Mars
Reconnaissance Orbiter (MRO) spacecraft, combined with Digital Terrain
Models (DTMs) to determine elevations and view geometric relationships
between units, the team was able to map hydrated minerals and understand
how the water chemistry varied with time within each trough, said Weitz,
a HiRISE team member.

Each trough probably experienced multiple episodes where water partially
filled in low-lying regions and deposited minerals. As each trough
continued to enlarge and experience collapse over time, older minerals
became buried and separated, followed by deposition of younger minerals,
then finally erosion to re-expose buried units. Volcanism from the
Tharsis volcanoes to the west may have created subsurface water that was
subsequently transported through the ground and into the troughs.
Localized volcanism that produced ash and gases, hydrothermal activity,
and melting snow/ice within the troughs could have also produced some of
the minerals. The observed minerals indicate water varied in pH levels
over time, in one trough from acidic to neutral, and in the other trough
from neutral to acidic and back to neutral.

Other occurrences of Fe/Mg-smectites have been found on Mars but almost
exclusively in association with older, Noachian-age (more than 3.6
billion years ago) rocks, or produced by younger impact events.
Following the deposition of Fe/Mg-smectites in the Noachian period, the
climate on Mars is believed to have changed during the Hesperian time to
favor formation of minerals under more acidic conditions, such as salts
rich in sulfur (sulfates).

Weitz and her co-authors identified the same sulfates and
Fe/Mg-smectites in the Noctis Labyrinthus troughs found elsewhere on
Mars, but the progression of minerals over time, from sulfates to
Fe/Mg-smectites, indicates a reverse order relative to what happened
globally across Mars.

"These clays formed from persistent water in neutral to basic conditions
around 2 to 3 billion years ago, indicating these two troughs are unique
and could have been a more habitable region on Mars at a time when drier
conditions dominated the surface," said co-author and CRISM team member
Janice Bishop from the SETI Institute and NASA AMES Research Center.

"These troughs would be fantastic places to send a rover, but
unfortunately the rugged terrain makes it unsafe both for landing and
for driving," Weitz said.

The study was funded by grants to PSI from NASA, the Jet Propulsion
Laboratory and the University of Arizona.
 

CONTACT:

Catherine M. Weitz
Senior Scientist
520-622-6300, x310
weitz at psi.edu