December 4, 2000
RELEASE:  00-190

EVIDENCE OF MARTIAN LAND OF LAKES DISCOVERED

     In what ultimately may be their most significant discovery 
yet, Mars scientists say high-resolution pictures showing layers of 
sedimentary rock paint a portrait of an ancient Mars that long ago 
may have featured numerous lakes and shallow seas.

"We see distinct, thick layers of rock within craters and other 
depressions for which a number of lines of evidence indicate that 
they may have formed in lakes or shallow seas. We have never before 
had this type of irrefutable evidence that sedimentary rocks are 
widespread on Mars," said Dr. Michael Malin, principal investigator 
for the Mars Orbiter Camera on NASA's Mars Global Surveyor 
spacecraft at Malin Space Science Systems (MSSS), San Diego, CA. 
"These images tell us that early Mars was very dynamic and may have 
been a lot more like Earth than many of us had been thinking."

Such layered rock structures where there were once lakes are common 
on Earth. The pancake-like layers of sediment compressed and 
cemented to form a rock record of the planet's history.

The regions of sedimentary layers on Mars are spread out and 
scattered around the planet. They are most common within impact 
craters of Western Arabia Terra, the inter-crater plains of 
northern Terra Meridiani, the chasms of the Valles Marineris, and 
parts of the northeastern Hellas Basin rim. The scientists compare 
the rock layers on Mars to features seen in the American Southwest, 
such as the Grand Canyon and the Painted Desert of Arizona.

"We caution that the Mars images tell us that the story is actually 
quite complicated and yet the implications are tremendous. Mars has 
preserved for us, in its sedimentary rocks, a record of events 
unlike any that occur on the planet today," said Dr. Ken Edgett, 
staff scientist at MSSS. "This is changing the way we think about 
the early history of Mars -- a time perhaps more than 3.5 billion 
years ago."

"On Earth, sedimentary rocks preserve the surface history of our 
planet, and within that history, the fossil record of life. It is 
reasonable to look for evidence of past life on Mars in these 
remarkably similar sedimentary layers," said Malin. "What is new in 
our work is that Mars has shown us that there are many more places 
in which to look, and that these materials may date back to the 
earliest times of Martian history."

Malin added, "I have not previously been a vocal advocate of the 
theory that Mars was wet and warm in its early history. But my 
earlier view of Mars was really shaken when I saw our first high-
resolution pictures of Candor Chasma. The nearly identically thick 
layers would be almost impossible to create without water."

As an alternative to lakes, Malin and Edgett suggest that a denser 
atmosphere on early Mars could have allowed greater amounts of 
windborne dust to settle out on the surface in ways that would have 
created the sedimentary rock.

"We have only solved one little piece of a tremendous puzzle," 
Malin said. "There is no illustration on the box to show us what it 
is supposed to look like when it is completed and we are sure most 
of the pieces are missing."

"These latest findings from the Mars Global Surveyor tell us that 
more study both from orbit and at the surface is needed to decipher 
the tantalizing history of water on Mars," said Dr. Jim Garvin, 
Mars Exploration Program Scientist at NASA Headquarters. "Our 
scientific strategy of following the water by seeking, conducting 
in situ studies, and ultimately sampling will follow up on these 
latest discoveries about Mars, and adapt to the new understanding."

"Mars seems to continually amaze us with unexpected discoveries," 
said Dr. Edward Weiler, Associate Administrator for Space Science 
at NASA Headquarters. "This finding just might be the key to 
solving some of the biggest mysteries on Mars, and it also tells us 
that our new Mars exploration program needs the flexibility to 
follow up in a carefully thought-out manner."

"The finding of layered sedimentary deposits is something that 
biologists have been hoping for," said Dr. Ken Nealson, director of 
the Center for Life Detection at NASA's Jet Propulsion Laboratory 
(JPL), Pasadena, CA. "Perhaps the favorite sites for biologists to 
search for fossils or evidence of past life on Earth are layered 
lake or oceanic sediments such as in these sites Malin and Edgett 
describe."

The Mars Global Surveyor mission is managed by JPL for NASA's 
Office of Space Science, Washington, DC. Malin Space Science 
Systems built and operates the camera system. Lockheed Martin 
Astronautics, Denver, CO, developed and operates the spacecraft. 

Images for this release are available at:

      http://www.msss.com/mars_images/moc/dec00_seds/

Information on the Mars Global Surveyor is available at: 

                 http://mars.jpl.nasa.gov/mgs

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