[meteorite-list] Phoenix Site on Mars May be in Dry Climate Cycle Phase

From: Ron Baalke <baalke_at_meteoritecentral.com>
Date: Mon, 15 Dec 2008 15:27:54 -0800 (PST)
Message-ID: <200812152327.PAA13044_at_zagami.jpl.nasa.gov>

http://www.jpl.nasa.gov/news/news.cfm?release=2008-236

Phoenix Site on Mars May be in Dry Climate Cycle Phase
Jet Propulsion Laboratory
December 15, 2008

PASADENA, Calif. -- The Martian arctic soil that NASA's Phoenix Mars
Lander dug into this year is very cold and very dry. However, when
long-term climate cycles make the site warmer, the soil may get moist
enough to modify the chemistry, producing effects that persist through
the colder times.

Phoenix found clues increasing scientists' confidence in predictive
models about water vapor moving through the soil between the atmosphere
and subsurface water-ice. The models predict the vapor flow can wet the
soil when the tilt of Mars' axis, the obliquity, is greater than it is now.

The robot worked on Mars for three months of prime mission, plus two
months of overtime, after landing on May 25. The Phoenix science team
will be analyzing data and running comparison experiments for months to
come. With some key questions still open, team members at a meeting of
the American Geophysical Union today reported on their progress.

"We have snowfall from the clouds and frost at the surface, with ice
just a few inches below, and dry soil in between," said Phoenix
Principal Investigator Peter Smith of the University of Arizona, Tucson.
"During a warmer climate several million years ago, the ice would have
been deeper, but frost on the surface could have melted and wet the soil."

With no large moon like Earth's to stabilize it, Mars goes through known
periodic cycles when its tilt becomes much greater than Earth's. During
those high-tilt periods, the sun rises higher in the sky above the
Martian poles than it does now, and the arctic plain where Phoenix
worked experiences warmer summers.

"The ice under the soil around Phoenix is not a sealed-off deposit left
from some ancient ocean," said Ray Arvidson of Washington University in
St. Louis, lead scientist for the lander's robotic arm. "It is in
equilibrium with the environment, and the environment changes with the
obliquity cycles on scales from hundreds of thousands of years to a few
million years. There have probably been dozens of times in the past 10
million years when thin films of water were active in the soil, and
probably there will be dozens more times in the next 10 million years."

Cloddy texture of soil scooped up by Phoenix is one clue to effects of
water. The mission's microscopic examination of the soil shows
individual particles characteristic of windblown dust and sand, but
clods of the soil hold together more cohesively than expected for
unaltered dust and sand. Arvidson said, "It's not strongly cemented. It
would break up in your hand, but the cloddiness tells us that something
is taking the windblown material and mildly cementing it."

That cementing effect could result from water molecules adhering to the
surfaces of soil particles. Or it could be from water mobilizing and
redepositing salts that Phoenix identified in the soil, such as
magnesium perchlorate and calcium carbonate.

The Thermal and Electrical Conductivity Probe on Phoenix detected
electrical-property changes consistent with accumulation of water
molecules on surfaces of soil grains during daily cycles of water vapor
moving through the soil, reported Aaron Zent of NASA Ames Research
Center, Moffett Field, Calif., lead scientist for that probe.

"There's exchange between the atmosphere and the subsurface ice," Zent
said. "A film of water molecules accumulates on the surfaces of mineral
particles. It's not enough right now to transform the chemistry, but the
measurements are providing verification that these molecular films are
occurring when you would expect them to, and this gives us more
confidence in predicting the way they would behave in other parts of the
obliquity cycles."

The Phoenix mission is led by Smith at the University of Arizona with
project management at NASA's Jet Propulsion Laboratory, Pasadena,
Calif., and development partnership at Lockheed Martin, Denver.
International contributions come from the Canadian Space Agency; the
University of Neuchatel, Switzerland; the universities of Copenhagen and
Aarhus, Denmark; Max Planck Institute, Germany; and the Finnish
Meteorological Institute; and Imperial College, London. For more about
Phoenix, visit: http://www.nasa.gov/phoenix .

Guy Webster 818-354-6278
Jet Propulsion Laboratory, Pasadena, Calif.
guy.webster at jpl.nasa.gov

Rachel Prucey 650-604-0643
NASA Ames Research Center, Moffett Field, Calif.
rachel.l.prucey at nasa.gov

Lori Stiles 520-626-4402
University of Arizona, Tucson
lstiles at u.arizona.edu

2008-236
Received on Mon 15 Dec 2008 06:27:54 PM PST