From: Andy Soos, ENN
Published March 14, 2013 04:52 PM
Martian Stream Bed
Scientists have identified sulfur, nitrogen, hydrogen, oxygen,
phosphorus and carbon - some of the key chemical ingredients for life -
in the powder Curiosity drilled out of a sedimentary rock near an
ancient stream bed in Gale Crater on the Red Planet last month.
Sedimentary rock means running water once upon a time. Water often means
life and the rock had the right chemistry to do this. Clues to this
habitable environment come from data returned by the rover's Sample
Analysis at Mars (SAM) and Chemistry and Mineralogy (CheMin)
instruments. The data indicate the Yellowknife Bay area the rover is
exploring was the end of an ancient river system or an intermittently
wet lake bed that could have provided chemical energy and other
favorable conditions for microbes. The rock is made up of a fine-grained
mudstone containing clay minerals, sulfate minerals and other chemicals.
This ancient wet environment, unlike some others on Mars, was not
harshly oxidizing, acidic or extremely salty.
The patch of bedrock where Curiosity drilled for its first sample
lies in an ancient network of stream channels descending from the rim of
Gale Crater. The bedrock also is fine-grained mudstone and shows
evidence of multiple periods of wet conditions, including nodules and
veins.
Current conditions on the planet surface do not support the long-term
existence of liquid water. The average atmospheric pressure and
temperature are far too low, leading to immediate freezing and resulting
sublimation. Despite this, research suggests that in the past there was
liquid water flowing on the surface.
Today, it is generally believed that Mars had abundant water very early
in its history during which snow and rain fell on the planet and created
rivers, lakes, and possibly oceans. Large clay deposits were produced.
Life may even have come into existence. Large areas of liquid water have
disappeared, but climate changes have frequently deposited large amounts
of water-rich materials in mid-latitudes. Recent images have also
detected yearly changes on some slopes that may have been caused by
liquid water.
Curiosity's drill collected the sample at a site just a few hundred
yards away from where the rover earlier found an ancient stream bed in
September 2012.
"Clay minerals make up at least 20 percent of the composition of this
sample," said David Blake, principal investigator for the CheMin
instrument at NASA's Ames Research Center in Moffett Field, Calif.
These clay minerals are a product of the reaction of relatively fresh
water with igneous minerals, such as olivine, also present in the
sediment. The reaction could have taken place within the sedimentary
deposit, during transport of the sediment, or in the source region of
the sediment. The presence of calcium sulfate along with the clay
suggests the soil is neutral or mildly alkaline.
Scientists were surprised to find a mixture of oxidized, less-oxidized,
and even non-oxidized chemicals, providing an energy gradient of the
sort many microbes on Earth exploit to live. This partial oxidation was
first hinted at when the drill cuttings were revealed to be gray rather
than red.
"The range of chemical ingredients we have identified in the sample is
impressive, and it suggests pairings such as sulfates and sulfides that
indicate a possible chemical energy source for micro-organisms," said
Paul Mahaffy, principal investigator of the SAM suite of instruments at
NASA's Goddard Space Flight Center in Greenbelt, Md.
"We have characterized a very ancient, but strangely new gray Mars where
conditions once were favorable for life," said John Grotzinger, Mars
Science Laboratory project scientist at the California Institute of
Technology in Pasadena, Calif. "Curiosity is on a mission of discovery
and exploration, and as a team we feel there are many more exciting
discoveries ahead of us in the months and years to come."
Scientists plan to work with Curiosity in the "Yellowknife Bay" area for
many more weeks before beginning a long drive to Gale Crater's central
mound, Mount Sharp. Investigating the stack of layers exposed on Mount
Sharp, where clay minerals and sulfate minerals have been identified
from orbit, may add information about the duration and diversity of
habitable conditions.
For further information see
Martian Stream Bed.
Two Different Aqueous Environments image via NASA
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