[meteorite-list] Martian Air Once Had Moisture, New Soil Analysis Says

From: Ron Baalke <baalke_at_meteoritecentral.com>
Date: Sat, 5 Jul 2008 21:41:54 -0700 (PDT)
Message-ID: <200807060441.VAA12087_at_zagami.jpl.nasa.gov>

Media Relations
University of California-Berkeley

Media Contacts:

Sarah Yang, (510) 643-7741

25 June 2008

Martian air once had moisture, new soil analysis says

By Sarah Yang, Media Relations

BERKELEY -- A new analysis of Martian soil data led by University of
California, Berkeley, geoscientists suggests that there was once enough
water in the planet's atmosphere for a light drizzle or dew to hit the
ground, leaving tell-tale signs of its interaction with the planet's
surface.

The study's conclusion breaks from the more dominant view that the liquid
water that once existed during the red planet's infancy came mainly in the
form of upwelling groundwater rather than rain.

To come up with their conclusions, the UC Berkeley-led researchers used
published measurements of soil from Mars that were taken by various NASA
missions: Viking 1, Viking 2, Pathfinder, Spirit and Opportunity. These five
missions provided information on soil from widely distant sites surveyed
between 1976 and 2006.

"By analyzing the chemistry of the planet's soil, we can derive important
information about Mars' climate history," said Ronald Amundson, UC Berkeley
professor of ecosystem sciences and the study's lead author. "The dominant
view, put forward by many now working on the Mars missions, is that the
chemistry of Mars soils is a mix of dust and rock that has accumulated over
the eons, combined with impacts of upwelling groundwater, which is almost
the exact opposite of any common process that forms soil on Earth. In this
paper, we try to steer the discussion back by re-evaluating the Mars data
using geological and hydrological principles that exist on Earth."

The final version of the study will appear online in Geochimica et
Cosmochimica Acta, the journal of the International Geochemical Society, by
the end of June, and in a print issue in August.

Martian soil has made headlines in recent weeks as NASA's Phoenix lander
began sampling soil from the planet's north pole and analyzing its chemical
elements. The goal of the tests is to determine whether Mars was once
capable of supporting life, an idea that got a boost on Friday (June 20)
when Phoenix scientists announced the discovery of ice underneath the
Martian soil.

While the UC Berkeley-led study does not delve directly into evidence of
life on Mars, it does suggest what kind of climate that life, if it existed,
might have encountered.

The planet is currently too cold for water to exist in a liquid state, but
scientists generally agree that during the planet's earliest geological
period, known as the Noachian epoch and dating 4.6 billion to 3.5 billion
years ago, there were enough atmospheric greenhouse gases to warm the air
and support lakes and flowing rivers.

But unlike Earth, Mars does not have plate tectonics to help generate
volcanoes and other terrestrial sources of greenhouse gases to sustain heat,
explained Amundson. He said that many scientists believe that by the time
the planet moved from the Noachian epoch to the Hesperian epoch, dating from
3.5 billion to 1.8 billion years ago, water on Mars had either frozen or
evaporated. (The planet is now in its third geological time period, the
Amazonian epoch, which started about 1.8 billion years ago.)

The new study, however, suggests that liquid water existed in the Martian
atmosphere into the Hesperian era.

To support this view, the team showed that soil at the Viking, Pathfinder
and Spirit landing sites had lost significant fractions of the elements that
make up the rock fragments from which the soil was formed, a sign that water
once moved downward through the dirt, carrying the elements with it.
Amundson also pointed out that the soil records a long period of drying, as
evidenced by surface patterns of the now sulfate-rich land. The distinctive
accumulations of sulfate deposits are characteristic of soil in northern
Chile's Atacama Desert, where rainfall averages approximately 1 millimeter
per year, making it the driest region on Earth.

"The Atacama Desert and the dry valleys of Antarctica are where Earth meets
Mars," said Amundson. "I would argue that Mars has more in common
geochemically with these climate extremes on Earth than these sites have in
common with the rest of our planet."

Amundson noted that sulfate is prevalent in Earth's oceans and atmosphere,
and is incorporated in rainwater. However, it's so soluble that it typically
washes away from the surface of the ground when it rains. The key for the
distinctive accumulation in soil to appear is for there to be enough
moisture to move it downward, but not so much that it is washed away
entirely.

The researchers also noted that the distribution of the chemical elements in
Martian soil, where sulfates accumulate on the surface with layers of
chloride salt underneath, suggest atmospheric moisture.

"Sulfates tend to be less soluble in water than chlorides, so if water is
moving up through evaporation, we would expect to find chlorides at the
surface and sulfates below that," said Amundson. "But when water is moving
downward, there's a complete reversal of that where the chlorides move
downward and sulfates stay closer to the surface. There have been weak but
long-term atmospheric cycles that not only add dust and salt but periodic
liquid water to the soil surface that move the salts downward."

Amundson pointed out that there is still debate among scientists about the
degree to which atmospheric and geological conditions on Earth can be used
as analogs for the environment on Mars. He said the new study suggests that
Martian soil may be a "museum" that records chemical information about the
history of water on the planet, and that our own planet holds the key to
interpreting the record.

"It seems very logical that a dry, arid planet like Mars with the same
bedrock geology as many places on Earth would have some of the same
hydrological and geological processes operating that occur in our deserts
here on Earth," said Amundson. "Our study suggests that Mars isn't a planet
where things have behaved radically different from Earth, and that we should
look to regions like the Atacama Desert for further insight into Martian
climate history."

The study co-authors are Stephanie Ewing, Mendhall Fellow at the U.S.
Geological Survey; William Dietrich, UC Berkeley professor of geomorphology;
Brad Sutter, research scientist at NASA's Johnson Space Center; Justine
Owen, UC Berkeley graduate student of ecosystem sciences; Oliver Chadwick,
professor of geography at UC Santa Barbara; Kunihiko Nishiizumi, Senior
Space Fellow at UC Berkeley's Space Sciences Laboratory; Michelle Walvoord,
research hydrologist at the U.S. Geological Survey; and Christopher McKay,
planetary scientist at the NASA Ames Research Center.

NASA, the National Science Foundation and the UC Agricultural Experiment
Station helped support this research.

IMAGE CAPTIONS:

[IMAGE 1:
http://www.berkeley.edu/news/media/download/2008/06/Mars-Opportunity.jpg
(6MB)]
Cracks caused by the contraction of sulfate are evident in this image of the
surface of Mars' Meridiani Planum site by NASA's Opportunity Rover. Credit:
NASA

[IMAGE 2:
http://www.berkeley.edu/news/media/download/2008/06/Mars-Atacama.jpg (440KB]
In this photo taken at the Atacama Desert in Chile, the ground has similar
sulfate cracks to those seen on the surface of Mars. The researcher in the
foreground is William Dietrich, UC Berkeley professor of geomorphology.
Credit: Ronald Amundson/UC Berkeley
Received on Sun 06 Jul 2008 12:41:54 AM PDT