Large Former Lake, Catastrophic Flood Identified on Mars

Geologists at the Smithsonian’s National Air and Space Museum have
discovered a large former lake in the highlands of Mars that would
cover an area the size of Texas and New Mexico combined, and which
overflowed to carve one of that planet’s largest valleys. The
findings will appear in the June 21 issue of the journal Science.

• A Large Paleolake Basin at the Head of Ma’adim Vallis, Mars, Abstract, Science

The flood channel, Ma’adim Vallis, is more than 550 miles long and
up to 6,900 feet deep, making it larger than Earth’s Grand Canyon.

"Imagine more than five times the volume of water in the Great
Lakes being released in a single flood, and you’ll have a sense of
the scale of this event," said Ross Irwin, a geologist in the
museum’s Center for Earth and Planetary Studies (CEPS) and the
paper’s lead author.

Mars is now a cold desert planet but its many dry valleys could
indicate that water once flowed on its surface. Recent results from
the Mars Odyssey spacecraft have found evidence of water trapped in
the near surface of the polar regions.

"The size of this lake-1,400 miles long-suggests Mars was warmer
and wetter than previously thought," said Robert Craddock, a CEPS
geologist and co-author of the paper.

Former lakes are considered the most likely places to preserve the
record of any past Martian life. Calm water would allow sediments
to be deposited slowly, preventing small organisms from being
destroyed.

The source of water to carve the flood channel had long been a
mystery to scientists, who had known very little about Mars’
topography prior to the Mars Global Surveyor mission, which has
been orbiting Mars since 1997.

Detailed elevation data from the Mars Global Surveyor shows the
large valley originated nearly full-size at a ridge, much like the
spillway of a dam. Late in the lake’s history, rising water levels
overflowed the lake basin rim, releasing the huge flood as the
river cut into this former dividing ridge. What remained was "some
of the best geological evidence for a lake found to date on Mars,
including clear indications of the former shoreline," Irwin says.

Two other smaller lake basins were identified in the region by
paper co-author Alan Howard, a geologist at the University of
Virginia. All three lakes shared the same water level prior to the
flood, indicating the possibility of an ancient water table and
suggesting the locations of other dry lake basins on Mars. Such
information could be important in determining where to land robotic
probes in coming years.

CEPS is the scientific research unit within the Collections and
Research Department of the National Air and Space Museum. CEPS
performs original research and outreach activities on topics
covering planetary science, terrestrial geophysics, and the remote
sensing of environmental change.

Note to editors: To arrange interviews with the CEPS geologists
involved in this project, please call Peter Golkin in the National
Air and Space Museum Office of Public Affairs at (202) 357-1552.

Ma’adim Vallis Region Imagery

(Above) False-color topographic map of the recently discovered former lakes in the cratered highlands of Mars. Lighter colors denote higher elevations in both images. The largest of the three lakes overtopped its basin rim and the resulting outflow toward the north (arrow) carved Ma’adim Vallis, which is larger than the Earth’s Grand Canyon. The basin and valleys are currently dry, but evidence of the former lake shorelines has been preserved. North is at the top. High resolution image (3.2 MB jpg)
(Right) Facing south, a perspective view looking up Ma’adim Vallis. The channel flowed into Gusev Crater (foreground), which is currently being considered as a landing site for one of the 2003 Mars Exploration Rovers. A view across part of the large former lake (background) shows its deep bowl-shaped floor. High resolution image (977 K jpg)
More information about this project at: http://www.nasm.si.edu/ceps/research/mars/irwin_lakes.htm Image credit: R. P. Irwin III and G. A. Franz, National Air and Space Museum, Smithsonian Institution

High resolution image (1.9 MB jpg)
Meduim resolution image (78 K jpg)	(Top and right) Grayscale versions of the color images on previous page, with water not shown. Image credit: R. P. Irwin III and G. A. Franz, National Air and Space Museum, Smithsonian Institution	High resolution image (461 K jpg)
	(Left) Viking Orbiter image of part of Ma’adim Vallis, where it crosscuts an impact crater. The dry valley is 23 km (14 miles) wide at this location, and the former flood channel is 5 km (3 miles) wide. Image credit: NASA/JPL.