[meteorite-list] NASA Trapped Mars Rover Finds Evidence of Subsurface Water

[Ron Baalke]

Oct. 28, 2010

Dwayne Brown 
Headquarters, Washington      
202-358-1726 
dwayne.c.brown at nasa.gov 

Guy Webster 
Jet Propulsion Laboratory, Pasadena, Calif. 
818-354-6278 
guy.webster at jpl.nasa.gov 
RELEASE: 10-278

NASA TRAPPED MARS ROVER FINDS EVIDENCE OF SUBSURFACE WATER

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: 

http://www.nasa.gov/rovers 
	
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