[meteorite-list] Analyses Show Water Stayed On Mars Longer Than Previously Thought

From: Ron Baalke <baalke_at_meteoritecentral.com>
Date: Thu Apr 22 09:47:14 2004
Message-ID: <200111261929.LAA18124_at_zagami.jpl.nasa.gov>


Washington University in St. Louis

Tony Fitzpatrick, (314) 935-5272, tony_fitzpatrick_at_aismail.wustl.edu

Nov. 26, 2001

Analyses show water stayed on Mars longer than previously thought
By Brian Schnall

St. Louis, MO. -- An analysis of high-resolution topographic maps and
photographs, as well as recent studies of Martian meteorites suggest
the presence of water on the Red Planet for a longer time scale than
scientists had previously believed.

Brian M. Hynek, doctoral candidate in earth and planetary sciences in
Arts & Sciences at Washington University in St. Louis, and Roger J.
Phillips, Ph.D., professor of earth and planetary sciences and Director
of Washington University's McDonnell Center for the Space Sciences,
analyzed topographic maps of the planet (accurate to within half a
meter) that are based on data returned from the Mars Orbiter Laser
Altimeter (MOLA) on the Mars Global Surveyor (MGS) mission.

Phillips also used earlier analyses of Martian meteorites to help
constrain models of the ancient climate of Mars. The meteorites contain
weathering deposits produced from liquid water filling cracks and voids
in the rock within the last billion years. This work led to a better
understanding of when, and how much, water was on Mars in the past.

"Certainly water was circulating in the upper part of the Martian
crust within the last billion years," said Hynek. "And even until
today, water seems to be an important agent in some places on the
surface of Mars that would argue for very near surface water on a lot
of the planet."

A recent discovery by the imaging camera team on MGS indicates the
presence of small gullies at high latitudes on Mars that were formed
in the very recent past and may still be active today. Phillips and
his colleague, Michael Mellon, Ph.D., of the University of Colorado,
modeled the properties of Martian soil and concluded that the gullies
were probably formed by liquid water, which may be present only
several hundred feet beneath the surface Mars. This work was published
in the October Journal of Geophysical Research.

The research was presented on Nov. 7 in an invited talk for the 113th
annual meeting of the Geological Society of America. The research is
primarily supported by NASA grants.

Evidence for the ancient presence of water on Mars has existed for many
years. Scientists long have accepted the river valley networks, ancient
lakes, and outflow channels as indicative of surface water flowing at
some time in the planet's four-billion-old plus history.

"There has always been evidence from very ancient valley networks that
water was there at some time extremely early on," Hynek said. "But
new evidence from meteorites, young gullies, and better topographic
resolution is helping to clarify a more precise time frame for water
on the planet."

Hynek and Phillips focused some of their analysis in two predominant
regions of Mars, the Tharsis rise and the Arabia bulge. The Tharsis
rise dominates the western hemisphere of Mars. It is a broad,
elevated region rising up to 10 kilometers above its surroundings and
encompassing over 30 million square kilometers. The rise is the site
of large-scale volcanism and extensive fracturing of the crust. Due
to the extreme pressure of this rise on the planet's surface, the
opposite side of Mars bulges outward, causing a deformation known as
the Arabia bulge.

River valley networks flow all over the Arabia bulge. The prevailing
theory is that these intricate networks represent evidence for water
once flowing on the surface of Mars. Although researchers have known
about these formations for many years, they had no idea of their
greater significance until they looked at the high-resolution
topographic map.

"Most of the valley networks flow downhill from the bulge, and this
argues that the valley networks follow the topography induced by the
massive load of Tharsis," Hynek explained.

According to Hynek, the valley networks came after Tharsis warped the
planet because they are following the topography formed by Tharsis.
The argument is that during emplacement, or formation, of Tharsis
approximately 4 billion years ago, volatiles from volcanoes probably
created an atmosphere that would have led to a hydrogeologic cycle
to help form the valley networks. This work was reported in the
journal Science earlier this year.

"MOLA data are starting to put together a coherent picture of early
Mars that couldn't be done or tested before," Hynek said.

The spacecraft Mars Odyssey, just recently placed in orbit around
Mars, carries a high-resolution thermal emission spectrometer that
will help look for water-related minerals, such as carbonates and
sulfates, on the surface of the planet. If water once existed on
the planet's surface, compositional data should show evidence of
its ancient presence to back up topographic evidence.

The search for definitive evidence of water represents a focus in a
NASA debate over proposed landing sites for the 2003 rover mission
to the planet. Hynek and Phillips are involved in the landing site
selection process for the mission. Their recent research has involved
the analysis of a top candidate landing site that has distinctive
minerals, which may be indicative of extensive water. Geologic
mapping of the deposit, combined with topographic and compositional
analyses, has helped to constrain how and when it formed.

"It is likely that these materials formed in middle Martian history,
possibly from the circulation of groundwater or hydrothermal
springs," Hynek said. This is additional evidence for a long-lived
history of water on Mars.

Hynek noted that this unique region of Mars would almost certainly
be chosen for the 2003 mission. "The battle cry for the upcoming
rover mission is: 'Follow the water'," Hynek said.
Received on Mon 26 Nov 2001 02:29:28 PM PST

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