New Discovery - Evidence of Subsurface Water on Mars
PASADENA, Calif. -- The ground where NASA's
Mars Exploration Rover Spirit became stuck last year holds
evidence that water, perhaps as snow melt, trickled into the subsurface
fairly recently and on a continuing basis.
Stratified soil layers with different compositions close to the surface
led the rover science team to propose that thin films of water may have
entered the ground from frost or snow. The seepage could have happened
during cyclical climate changes during periods when Mars tilted farther
on its axis. The water may have moved down into the sand, carrying
soluble minerals deeper than less-soluble ones. Spin-axis tilt varies
over timescales of hundreds of thousands of years.
The relatively insoluble minerals near the surface include what is
thought to be hematite, silica and gypsum. Ferric sulfates, which are
more soluble, appear to have been dissolved and carried down by water.
None of these minerals is exposed at the surface, which is covered by
wind-blown sand and dust.
"The lack of exposures at the surface indicates the preferential
dissolution of ferric sulfates must be a relatively recent and ongoing
process since wind has been systematically stripping soil and altering
landscapes in the region Spirit has been examining," said Ray Arvidson
of Washington University in St. Louis, deputy principal investigator
for the twin rovers Spirit and Opportunity.
Analysis of these findings appears in a report in the Journal of
Geophysical Research published by Arvidson and 36 co-authors about
Spirit's operations from late 2007 until just before the rover stopped
communicating in March.
The twin Mars rovers finished their three-month prime missions in April
2004, then kept exploring in bonus missions. One of Spirit's six wheels
quit working in 2006.
In April 2009, Spirit's left wheels broke through a crust at a site
called "Troy" and churned into soft sand. A second wheel stopped
working seven months later. Spirit could not obtain a position slanting
its solar panels toward the sun for the winter, as it had for previous
winters. Engineers anticipated it would enter a low-power, silent
hibernation mode, and the rover stopped communicating March 22. Spring
begins next month at Spirit's site, and NASA is using the Deep Space
Network and the Mars Odyssey orbiter to listen if the rover reawakens.
Researchers took advantage of Spirit's months at Troy last year to
examine in great detail soil layers the wheels had exposed, and also
neighboring surfaces. Spirit made 13 inches of progress in its last 10
backward drives before energy levels fell too low for further driving
in February. Those drives exposed a new area of soil for possible
examination if Spirit does awaken and its robotic arm is still usable.
"With insufficient solar energy during the winter, Spirit goes into a
deep-sleep hibernation mode where all rover systems are turned off,
including the radio and survival heaters," said John Callas, project
manager for Spirit and Opportunity at NASA's Jet Propulsion Laboratory,
in Pasadena, Calif. "All available solar array energy goes into
charging the batteries and keeping the mission clock running."
The rover is expected to have experienced temperatures colder than it
has ever before, and it may not survive. If Spirit does get back to
work, the top priority is a multi-month study that can be done without
driving the rover. The study would measure the rotation of Mars through
the Doppler signature of the stationary rover's radio signal with
enough precision to gain new information about the planet's core. The
rover Opportunity has been making steady progress toward a large
crater, Endeavour, which is now approximately 5 miles away.
Spirit, Opportunity, and other NASA Mars missions have found evidence
of wet Martian environments billions of years ago that were possibly
favorable for life. The Phoenix Mars Lander in 2008 and observations by
orbiters since 2002 have identified buried layers of water ice at high
and middle latitudes and frozen water in polar ice caps. These newest
Spirit findings contribute to an accumulating set of clues that Mars
may still have small amounts of liquid water at some periods during
ongoing climate cycles.
NASA's Jet Propulsion Laboratory manages the rovers for the agency's
Science Mission Directorate in Washington.
For more about the rovers, see:
Exploration Rover Spirit