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WASHINGTON -- A team of researchers studying photographs of
Mars has found teardrop features that they say were sculpted by
flowing water as recently as 10 million years ago.
Evidence for water-carved channels on the Red Planet dates back to
the 1970s Viking missions. More recently, the orbiting Mars Global
Surveyor (MGS) probe has provided pictures that reveal what may be
ancient river beds and sedimentary layers associated with lakes or
oceans. Controversial evidence has emerged indicating more recent
bursts of water flowing down ravines and crater walls.
The newest study involves MGS images studied by scientists at NASA
and the University of Arizona. The researchers examined a series of
fissures that stretch more than 600 miles across the lava-covered
Cerberus Plains, just north of the Martian equator.
The images show geologic evidence for catastrophic floods, the
scientists said in a press statement. Their work is detailed in the
journal Geophysical Research Letters.
The evidence centers on flat-topped, teardrop-shaped mesas that
rise some 330 feet from the channels in which they sit. The
researchers say the features are similar to structures in the
Channeled Scabland in the northwestern United States.
The amount of water needed to carve the structures is estimated to
be 600 cubic kilometers, four times what's in Lake Tahoe.
"What's different here is that this is very recent, and the water
source is nothing like we have on Earth," said Devon Burr, a doctoral
candidate in geosciences at the University of Arizona. "The water
here gushed from volcano-tectonic fissures. While the fissures
themselves may be older, the latest eruption of water was probably
only about 10 million years ago."
The study adds to other evidence suggesting that Mars may still be
geothermally active and might still have the ability to push
groundwater to the surface by a process called flood volcanism. Other
studies have hinted that such subsurface reservoirs may exist. The
heat and water provided by geothermal activity would be good news for
biologists who would search for possible life on Mars.
"Flood volcanism on Earth occurs about every tens of millions of
years," said Alfred McEwen, a university of Arizona planetary
scientist who worked on the study. "The last such event was 10
million years ago. But that doesn't mean it's over. It will happen
again. The same is probably true on Mars -- geologically speaking,
it's still active."
Susan Sakimoto of the NASA Goddard Space Flight Center also worked
on the study.
Other scientists have been cautious or critical of the claims over
photographic evidence of water on Mars. Most researchers agree the
case won't be decided until actual water is found by a surface robot
or human explorers. The possibility exists, however, that the Mars
Odyssey spacecraft, which just recently began its science mission at
Mars, could detect water from its orbital position above the planet.
For Martian geography buffs, the new study involved photos of the
Athabasca Valles channel system that branches south and southwest
from the Cerberus Fossae.
"Athabasca Valles is an almost new component in the Martian
hydrological cycle," Burr said.
The fissures from which the water is thought to have emanated were
likely created by tectonic forces, or a combination of tectonic and
magmatic forces, the scientists say.
In the images, a broad channel floor is often lined with grooves
and ridges running parallel to the streamlined mesas or to the
channel walls. The grooves, about 330 feet wide and 30 feet deep, are
similar to Channeled Scabland grooving on Earth, the study concludes.
Other streamlined forms poking up from the channel floor are also
layered but not flat-topped. These likely formed by erosion during
floods over pre-existing layered terrain, Burr said.
The research team speculates that the area studied may harbor
water ice near the surface, which would have been left behind during
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