NASA Spacecraft Shows
Diverse, Wet Environments On Ancient Mars
(16 July 2008) Two studies based on
data from NASA's Mars Reconnaissance Orbiter have revealed that the Red Planet
once hosted vast lakes, flowing rivers and a variety of other wet environments
that had the potential to support life.
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 Mars. The data for the
study derives from images taken by the Compact Reconnaissance Imaging
Spectrometer for Mars, or CRISM, and other instruments on the
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 principal investigator at the Johns Hopkins University
Applied Physics Laboratory in Laurel, Md.
The clay-like 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,
approximately 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
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."
Another study, published in
the June 2 issue of Nature Geosciences, finds that the wet conditions on Mars
persisted for a long time. Thousands to millions of years after the clays
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, approximately 25 miles in
diameter.
"The distribution of clays inside the ancient lakebed shows
that standing water must have persisted for thousands of years," says Bethany
Ehlmann, another member of the CRISM team from Brown. Ehlmann is lead author of
the study of an ancient lake within a northern-Mars impact basin called 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 high spatial and spectral resolutions
are better than any previous spectrometer sent to Mars and reveal variations in
the types and composition of the phyllosilicate minerals. By combining data
from CRISM and the orbiter's Context Imager and High Resolution Imaging Science
Experiment, the team identified three principal classes of water-related
minerals dating to the early Noachian period. The classes are
aluminium-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
Murchie.
NASA's Jet Propulsion Laboratory in Pasadena, Calif., manages
the Mars Reconnaissance Orbiter mission for NASA's Science Mission Directorate
in Washington. The Applied Physics Laboratory operates the CRISM instrument in
co-ordination with an international team of researchers from universities,
government and the private sector.
(source: NASA)
