Mars once hosted vast lakes, flowing rivers and a
variety of other wet environments that had
the potential to support life, according to two new studies
based on data from the Compact
Reconnaissance Imaging Spectrometer for Mars and other
instruments on board NASA's Mars
Reconnaissance Orbiter.
"The big surprise from these new results is how
pervasive and long-lasting Mars' water was, and
how diverse the wet environments were," said Scott Murchie,
CRISM's principal investigator at Johns
Hopkins' Applied Physics Laboratory.
One study, published in the July 17 issue of
Nature, shows that vast regions of the ancient
highlands of Mars — which cover about half the planet
— contain clay minerals, which can form only in
the presence of water. Volcanic lavas buried the clay-rich
regions during subsequent, drier periods of
the planet's history, but impact craters later exposed them
at thousands of locations across the
planet.
The claylike minerals, called phyllosilicates,
preserve a record of the interaction of water with
rocks dating back to what is called the Noachian period of
Mars' history, about 4.6 billion to 3.8 billion
years ago. This period corresponds to the earliest years of
the solar system, when Earth, the moon
and Mars sustained a cosmic bombardment by comets and
asteroids. Rocks of this age have largely
been destroyed on Earth by plate tectonics; they are
preserved on the moon, but were never exposed
to liquid water. The phyllosilicate-containing rocks on
Mars therefore preserve a unique record of
liquid water environments — possibly suitable for
life — in the early solar system.
"The minerals present in Mars' ancient crust show a
variety of wet environments," said John
Mustard, a member of the CRISM team from Brown University
and lead author of the Nature study.
"In most locations the rocks are lightly altered by liquid
water, but in a few locations they have been
so altered that a great deal of water must have flushed
though the rocks and soil. This is really
exciting because we're finding dozens of sites where future
missions can land to understand if Mars
was ever habitable and if so, to look for signs of past
life."
A companion study, published in the June 2 issue of
Nature Geosciences, finds that the wet
conditions persisted for a long time. Thousands to millions
of years after the clays were formed, a
system of river channels eroded them out of the highlands
and concentrated them in a delta where
the river emptied into a crater lake slightly larger than
California's Lake Tahoe, about 25 miles in
diameter. "The distribution of clays inside the ancient
lakebed shows that standing water must have
persisted for thousands of years," said Bethany Ehlmann,
another member of the CRISM team from
Brown and lead author of the study of the ancient lake
within Jezero Crater. "Clays are wonderful at
trapping and preserving organic matter, so if life ever
existed in this region, there's a chance of its
chemistry being preserved in the delta."
CRISM's combination of high spatial and spectral
resolutions — better than any previous imaging
spectrometer sent to Mars — reveals variations in the
types and composition of the phyllosilicate
minerals. By combining data from CRISM and MRO's Context
Imager and High Resolution Imaging
Science Experiment, the team has identified three principal
classes of water-related minerals dating
to the early Noachian period: aluminum-phyllosilicates,
hydrated silica or opal, and the more common
and widespread iron/magnesium-phyllosilicates. The
variations in the minerals suggest that different
processes, or different types of watery environments,
created them.
"Our whole team is turning our findings into a list of
sites where future missions could land to
look for organic chemistry and perhaps determine whether
life ever existed on Mars," said APL's
Murchie.
APL, which has built more than 150 spacecraft
instruments over the past four decades, led the
effort to build CRISM and operates the instrument in
coordination with an international team of
researchers from universities, government and the private
sector. The Jet Propulsion Laboratory of
the California Institute of Technology, Pasadena, manages
the Mars Reconnaissance Orbiter mission
for NASA's Science Mission Directorate. Lockheed Martin
Space Systems, Denver, is the prime
contractor for the project and built the spacecraft.
For more information on CRISM, go to crism.jhuapl.edu.