Arizona researchers challenge Mars water
U.S. Water News Online
TUCSON, Ariz. -- Studies by University of Arizona
scientists are challenging theories that water formed gullies found
The Arizona studies suggest the gullies on crater walls probably
were carved by carbon dioxide, not water. Further, they suggest that
features thought to be shorelines were shaped by tectonic forces, not
Don Musselwhite, Tim Swindle, and Jonathan Lunine of the
university's Lunar and Planetary Laboratory published their
hypothesis in the April 1 issue of Geophysical Research
The water theory arose after images from the Mars Surveyor
spacecraft showed what appeared to be young features such as sand
Swindle said the concept bothered him immediately.
``When I saw that, I went, 'Wait a minute,''' Swindle said. ``What
bothered me was that you have the very coldest places on the planet
being touted as the very most recent places with recent liquid
The gullies are found near Mars' south pole, where temperatures
range from about minus 80 to minus 130 degrees Fahrenheit, cold
enough to actually freeze the carbon dioxide that prevails in the
martian atmosphere, he said.
In the winter, it gets so cold that carbon dioxide goes directly
from gas to dry ice and fills up pore spaces in rocks below the
surface. At a depth of about 100 meters below these crater walls,
there is enough pressure that when the temperatures rise in the
spring, the pressure in the pores builds up enough to allow the
frozen carbon dioxide to turn into a liquid.
``Generally, it just evaporates, but as the pressure is building
and the walls are thinning, you have liquid CO2 inside a bottle of
dry ice and eventually it pops the cork,'' Musselwhite said. ``It
vaporizes as it starts to flow and turns to a slurry of rock debris
and dry ice snow.''
On the other side of Mars, in what is the smoothest surface known
in the solar system, an ocean is thought to have formed shorelines.
Paul Withers, a UA doctoral student in planetary sciences, studied
topographic data from the Mars Orbiter Laser Altimeter this summer
with an MIT researcher at NASA's Goddard Space Flight Center.
The features were consistent with a shoreline at first glance.
But Withers said that on further inspection, it became clear the
features had little ridges. That would mean that receding water would
have had to miraculously avoid a ridge while making the area behind
it flat, he said.
Withers and his co-researcher realized the wrinkled features
looked more like they were caused by tectonic shifts resulting from
Return to the
U.S. Water News Archives page
Return to the U.S. Water
Use a comma to separate e-mail addresses:
Hi, I thought you might like to read this article.