[meteorite-list] Mars Express Probes Red Planet's Unusual Deposits

From: Ron Baalke <baalke_at_meteoritecentral.com>
Date: Thu, 1 Nov 2007 16:57:13 -0700 (PDT)
Message-ID: <200711012357.QAA16355_at_zagami.jpl.nasa.gov>

http://www.jpl.nasa.gov/news/news.cfm?release=2007-126

Mars Express Probes Red Planet's Unusual Deposits
Jet Propulsion Laboratory
November 01, 2007

The radar system on the European Space Agency's Mars Express orbiter has
uncovered new details about some of the most mysterious deposits on
Mars: the Medusae Fossae Formation. It has provided the first direct
measurement of the depth and electrical properties of these materials,
providing new clues about their origin.

The Medusae Fossae Formation consists of enigmatic deposits. Found near
the Martian equator along a divide between highlands and lowlands, they
may represent some of the youngest deposits on the surface of the
planet. This is implied because there is a marked lack of impact craters
dotting these deposits.

NASA's Jet Propulsion Laboratory, Pasadena, Calif., manages NASA's roles
in the Mars Express mission. Mars Express has been collecting data on
the Medusae Fossae Formation deposits using its Mars Advanced Radar for
Subsurface and Ionospheric Sounding (Marsis). Between March 2006 and
April 2007, Mars Express flew over the Medusae Fossae Formation deposits
many times, taking radar soundings as it went.

"This is the first direct measurement of the depth of these deposits,"
said Thomas Watters of the Smithsonian Institution, Washington, D.C.,
lead author of a new report on the findings in the journal Science. "We
didn't know whether they were just a thin veneer or much thicker." The
radar observations found the Medusae Fossae Formation to be massive
deposits more than 2.5 kilometers (1.4 miles) thick in places. The
instrument reveals the depth based on the time it takes for the radar
beam to pass through the layers and bounce off the plains material
underneath.

The Medusae Fossae deposits intrigue scientists because they are
associated with regions that absorb certain wavelengths of Earth-based
radar. This had led to them being called "stealth" regions, because they
give no radar echo. However, the radar instrument on Mars Express uses
longer wavelengths than Earth-based radar experiments. At these
wavelengths, the radar waves mostly pass through the deposits, creating
subsurface echoes when the radar signal reflects off the plains material
beneath.

A variety of scenarios has been proposed for the origin and composition
of these deposits. Firstly, they could be volcanic ash deposits from
now-buried vents or nearby volcanoes. Secondly, they could be deposits
of wind-blown materials eroded from Martian rocks. Thirdly, they could
be ice-rich deposits, somewhat similar to the layered ice deposits at
the poles of the planet, but formed when the spin axis of Mars tilts
over, making the equatorial region colder.

Deciding among these scenarios is not easy, even with the new data. The
Marsis data reveal the electrical properties of the layers. These
suggest that the layers could be poorly packed, fluffy, dusty material.
However it is difficult to understand how porous material from
wind-blown dust can be more than two kilometers (more than a mile) thick
and yet not be compacted under the weight of the overlying material.

On the other hand, although the electrical properties are consistent
with water-ice layers, there is no other strong evidence for the
presence of ice today in the equatorial regions of Mars. "If there is
water ice at the equator of Mars, it must be buried at least several
meters below the surface," said co-author Jeffrey Plaut of JPL. This is
because the water vapor pressure on Mars is so low that any ice near the
surface would quickly evaporate.

So, the mystery of Mars's Medusae Fossae Formation continues. "It is
still early in the game. We may get cleverer with our analysis and
interpretation, or we may only know when we go there with a drill and
see for ourselves," Plaut said.

Giovanni Picardi at the University of Rome "La Sapienza," Italy,
principal investigator of the radar experiment, said "Not only is Marsis
providing excellent scientific results, but the team is also working on
the processing techniques that will allow for more accurate evaluation
of the characteristics of the subsurface layers and their constituent
material. Hence, the possible extension of the mission will be very
important to increase the number of observations over the regions of
interest and improve the accuracy of the evaluations."

The Mars Advanced Radar for Subsurface and Ionospheric Sounding was
funded by NASA and the Italian Space Agency and developed by the
University of Rome in partnership with JPL. Italy provided the
instrument's digital processing system and integrated the parts. The
University of Iowa, Iowa City, built the transmitter for the instrument,
JPL built the receiver, and Astro Aerospace, Carpinteria, Calif., built
the antenna. JPL is a division of the California Institute of Technology
in Pasadena.

For additional information about Mars Express, see
http://sci.esa.int/marsexpress . For additional information about NASA's
Mars exploration, see http://www.nasa.gov/mars .

------------------------------------------------------------------------

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

Dwayne Brown 202-358-1726
NASA Headquarters, Washington
dwayne.c.brown at nasa.gov

ESA Media Relations Office 33-1-53-69-7155
European Space Agency, Paris

2007-126
Received on Thu 01 Nov 2007 07:57:13 PM PDT