Delta-like Fan on Mars Suggests Ancient Rivers Were Persistent

Newly seen details in a fan-shaped apron of debris on
Mars may help settle a decades-long debate about whether the
planet had long-lasting rivers instead of just brief, intense
floods.

Pictures from NASA’s Mars Global Surveyor orbiter show eroded
ancient deposits of transported sediment long since hardened
into interweaving, curved ridges of layered rock. Scientists
interpret some of the curves as traces of ancient meanders
made in a sedimentary fan as flowing water changed its course
over time.

“Meanders are key, unequivocal evidence that some valleys on
early Mars held persistent flows of water over considerable
periods of time,” said Dr. Michael Malin of Malin Space
Science Systems, San Diego, which supplied and operates the
spacecraft’s Mars Orbiter Camera.

“The shape of the fan and the pattern of inverted channels in
it suggest it may have been a real delta, a deposit made
where a river enters a body of water,” he said. “If so, it
would be the strongest indicator yet Mars once had lakes.”

Malin and Dr. Ken Edgett, also of Malin Space Science
Systems, have published pictures and analysis of the landform
in today’s online edition of Science Express. The images with
captions are available online from the Mars Orbiter Camera
team, at:

http://www.msss.com/mars_images/moc/2003/11/13/
and from JPL at:
http://photojournal.jpl.nasa.gov/catalog/PIA04869

The fan covers an area about 13 kilometers (8 miles) long and
11 kilometers (7 miles) wide in an unnamed southern
hemisphere crater downslope from a large network of channels
that apparently drained into it billions of years ago.

“This latest discovery by the intrepid Mars Global Surveyor
is our first definitive evidence of persistent surface
water,” said Dr. Jim Garvin, NASA’s Lead Scientist for Mars
Exploration, NASA Headquarters, Washington. “It reaffirms we
are on the right pathway for searching the record of Martian
landscapes and eventually rocks for the record of habitats.
Such localities may serve as key landing sites for future
missions, such as the Mars Science Laboratory in 2009,”
continued Garvin. “These astounding findings suggest that
‘following the water’ with Mars Global Surveyor, Mars
Odyssey, and soon with the Mars Exploration Rovers, is a
powerful approach that will ultimately allow us to understand
the history of habitats on the red planet.”

No liquid water has been detected on Mars, although one of
the previous major discoveries from Mars Global Surveyor
pictures suggests some gullies have been cut in geologically
recent times by the flow of ephemeral liquid water. Another
NASA orbiter, Mars Odyssey, discovered extensive deposits of
near-surface ice at high latitudes. Mars’ atmosphere is so
thin, over most of the planet, any liquid water at the
surface would rapidly evaporate or freeze, so evidence of
persistent surface water in the past is also evidence for a
more clement past climate.

Malin and Edgett estimate the volume of material in the
delta-like fan is about one-fourth the volume of what was
removed by the cutting of the upstream channels. Their
analysis draws on information from Mars Global Surveyor’s
laser altimeter and from cameras on Mars Odyssey and NASA’s
Viking Orbiter, as well as images from the Mars Orbiter
Camera.

“Because the debris in this fan is now cemented, it shows
that some sedimentary rocks on Mars were deposited by water,”
Edgett said. “This has been suspected, but never so clearly
demonstrated before.”

The camera on Mars Global Surveyor has returned more than
155,000 pictures since the spacecraft began orbiting Mars
Sept. 12, 1997. Still, its high-resolution images cover only
about three percent of the planet’s surface. Information
about Mars Global Surveyor is available on the Internet at:
http://mars.jpl.nasa.gov/mgs.

JPL, a division of the California Institute of Technology,
Pasadena, manages Mars Global Surveyor for NASA’s Office of
Space Science, Washington. JPL’s industrial partner is
Lockheed Martin Space Systems, Denver, which developed and
operates the spacecraft. Malin Space Science Systems and the
California Institute of Technology built the Mars Orbiter
Camera. Malin Space Science Systems operates the camera from
facilities in San Diego.