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Donald Savage
Headquarters, Washington             April 11, 2003
(Phone: 202/358-1547)

Guy Webster
Jet Propulsion Laboratory, Pasadena, Calif.
(Phone: 818/354-6278)

RELEASE: 03-137

NASA ROVERS SLATED TO EXAMINE TWO INTRIGUING SITES ON MARS

     NASA has chosen two scientifically compelling landing 
sites for twin robotic rovers to explore on the surface of 
Mars early next year. The two sites are a giant crater that 
appears to have once held a lake, and a broad outcropping of 
a mineral that usually forms in the presence of liquid 
water. 

Each Mars Exploration Rover (MER) will examine its landing 
site for geological evidence of past liquid water activity 
and past environmental conditions hospitable to life.  

"Landing on Mars is very difficult, and it's harder on some 
parts of the planet than others," said Dr. Ed Weiler, NASA 
associate administrator for space science in Washington. "In 
choosing where to go, we need to balance science value with 
engineering safety considerations at the landing sites. The 
sites we have chosen provide such balance."

The first rover, scheduled for launch May 30, will be 
targeted to land at Gusev Crater, 15 degrees south of Mars' 
equator. The second, scheduled to launch June 25, will be 
targeted to land at Meridiani Planum, an area with deposits 
of an iron oxide mineral (gray hematite) about two degrees 
south of the equator and halfway around the planet from 
Gusev. 

Which rover is targeted to a specific site is still 
considered tentative, while further analyses and simulations 
are conducted. NASA can change the order as late as 
approximately one month after the launch of the first rover. 
The first mission will parachute to an airbag-cushioned 
landing on Jan. 4, 2004, and the second on Jan. 25, 2004.

"A tremendous amount of effort has gone into evaluating 
possible landing sites in the past two years, to maximize 
the probability of mission success" said Peter Theisinger, 
MER project manager at NASA's Jet Propulsion Laboratory 
(JPL), Pasadena, Calif.

Images and measurements from two NASA spacecraft orbiting 
Mars provided scientists and engineers, evaluating potential 
landing sites, with details of candidate site topography, 
composition, rockiness and geological context.

"Meridiani and Gusev both show powerful evidence of past 
liquid water, but in very different ways," said Dr. Steve 
Squyres, principal investigator for the rovers' science 
toolkit and a geologist at Cornell University, Ithaca, N.Y. 
"Meridiani has a chemical signature of past water. Gray 
hematite is usually, but not always, produced in an 
environment where there is liquid water. At Gusev, you've 
got a big hole in the ground with a dry riverbed going right 
into it. There had to have been a lake in Gusev Crater at 
some point. They are fabulous sites, and they complement 
each other because they're so different," he said.

MER site selection began with identifying all areas on Mars 
that fit a set of engineering-driven requirements, said 
JPL's Dr. Matt Golombek, co-chair of a landing-site steering 
committee. To qualify, candidate sites had to be near the 
equator, low in elevation, not too steep, not too rocky and 
not too dusty, among other criteria; 155 potential sites 
were studied. A series of public meetings evaluated the 
merits of potential landing sites. More than 100 Mars 
scientists participated in the meetings. 

"These two landing sites have been studied more than 
anywhere else on Mars. Both sites have specific scientific 
hypotheses that can be tested using the instruments on board 
each rover. It should be a very busy and exciting time after 
landing for the scientists analyzing the wealth of new data 
from the ground," said Dr. Cathy Weitz, MER program 
scientist at NASA Headquarters, Washington. 

"Clearly there is tremendous interest in the science 
community in what these missions can accomplish and 
eagerness to help see that the rovers go to the best 
possible sites," said National Air and Space Museum's Dr. 
John Grant, the steering committee's other co-chair.

Once they reach their landing sites, each rover's prime 
mission will last at least 90 Martian days (92 Earth days). 
The rovers are solar-powered, and in approximately 90 days, 
dust accumulating on the solar arrays likely will be 
diminishing the power supply. 

The twin MER spacecraft are at NASA's Kennedy Space Center, 
Fla., in preparation for launch. JPL manages the MER Project 
for NASA's Office of Space Science, Washington. JPL is a 
division of the California Institute of Technology in 
Pasadena.

Information about the MER project is available online at: 
http://mars.jpl.nasa.gov/mer/

For more information about NASA on the Internet, visit: 
http://www.nasa.gov

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