This Echo is READ ONLY !   NO Un-Authorized Messages Please!
 ~~~~~~~~~~~~~~~~~~~~~~~~   ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

Early Mars: Warm Enough to Melt Water?
======================================
Pennsylvania State University
February 14, 2003

Denver - While some researchers believe that only asteroid collisions 
made Mars warm enough to have running rivers, a Penn State researcher 
believes the planet had to be continuously warmer to form Mars' deep 
valleys, but he does not know how the planet warmed up.

Some recent research suggests that early Mars was cold most of the 
time and warmed up only when objects impacted the planet. The impacts 
would warm the atmosphere and melt water trapped in underground and 
surface ice, causing rivers to flow and cutting the valleys that rival 
Arizona's Grand Canyon.

"I do not think this is right," said Dr. James F. Kasting, 
distinguished professor of geosciences and meteorology. "I do not 
think there was enough time involved to form the types of features 
that we see on the Martian landscape."

Kasting believes that a greenhouse effect warmed the planet. However, 
he has calculated that a carbon dioxide and water greenhouse would not 
have warmed the planet above the freezing point of water. On Mars, 
before enough carbon dioxide accumulated in the atmosphere to warm 
things up, the carbon dioxide would condense into dry ice clouds and 
eventually there would be ice caps.

"It does not seem possible to get above freezing with gaseous carbon 
dioxide and water," he told attendees at the annual meeting of the 
American Association for the Advancement of Science today (Feb. 14) in 
Denver.

Which is why some researchers think the planet was never warm. But,
according to Kasting, features like Nanedi Vallis, which is a 
half-mile to over a mile wide in places and over a half mile deep, 
could not be made during the short time rivers would run after an 
impact.

"The channel at the bottom of Nanedi Vallis is only about 100 feet 
across," says Kasting. "It took millions of years of constant running 
water to carve the Grand Canyon. It would take a similar time on 
Mars."

One possible solution is that other greenhouse gases were in play in 
the Martian atmosphere. Methane would be a good candidate, but most 
sources of methane on Earth are biological. Today's sources of methane 
are methanogenic bacteria in ruminant animals and rice paddies, but in 
the pre-oxygen atmosphere of the past, methanobacteria could have 
lived in many places.

"Hillary Justh, a graduate student in geosciences, ran a model of Mars 
with three atmospheres of carbon dioxide and a tenth of a percent of 
methane in the atmosphere," adds the Penn State researcher. "Because 
3.8 billion years ago the solar luminosity was only 75 percent of what 
it is today, the model returned an average temperature of minus 13 
degrees Fahrenheit."

This by itself would not have been enough to allow widespread liquid 
water.  However, the Martian surface could have received 20-30 degrees 
Fahrenheit additional warming from the greenhouse effect of carbon 
dioxide ice clouds.  This might have allowed at least the tropics to 
remain above freezing.

One problem with methane-producing bacteria is that the ones we know 
here on Earth, both from the fossil record and today, prefer warm 
environments.

Some geologic processes generate methane, but only in small amounts. 
These process require water and ultramafic rocks to form serpentine 
rocks with methane as a by-product. This process occurs at mid-ocean 
ridges on Earth and can also occur during asteroid collisions that 
excavate large amounts of mantle material.

"We do not really know much about how plate tectonics works on Mars, 
and even if we did, it is doubtful that enough methane could be 
generated to create the necessary greenhouse," says Kasting. "Mars 
probably did need a biological source of methane to form a 
planet-warming greenhouse."

Researchers think that Mars has a supply of water, which is required 
for all terrestrial life. They also think that volcanic activity on 
Mars produced a tenth of a percent or so of hydrogen and substantial 
amounts of carbon dioxide, the two compounds that methanobacteria on 
Earth need to produce methane. Evidence of these methanobacteria could 
be found in subsurface fossils or, the bacteria could still be there 
today.

"What we need to do is go and take samples," said Kasting, a member of 
Penn State's NASA-sponsored Astrobiology Research Center.

NASA's Mars Exploration Rover Mission, scheduled to launch later this 
year, will almost do that. Scheduled to have two fully capable robotic 
vehicles like the Sojourner, it will sample soils looking for signs of 
life. However, while the science objectives of the rover missions are 
to determine if water was present on Mars and whether there are 
conditions favorable to the preservation of evidence for ancient life, 
the mission will not return samples to Earth. The first NASA 
sample-return mission is scheduled for 2020 or later.

                           **aem**

EDITORS: EDITORS: Dr. Kasting may is at 814-865-3207 or at
kasting{at}essc.psu.edu by e-mail.
Contacts:A'ndrea Elyse Messer (814) 865-9481 aem1{at}psu.edu
Vicki Fong (814) 865-9481 vfong{at}psu.edu

 - End of File -
================

---