[meteorite-list] Gamma-Ray Evidence Suggests Ancient Mars Had Oceans

From: Ron Baalke <baalke_at_meteoritecentral.com>
Date: Mon, 17 Nov 2008 12:15:38 -0800 (PST)
Message-ID: <200811172015.MAA03041_at_zagami.jpl.nasa.gov>

FROM: Lori Stiles (520-626-4402; lstiles at u.arizona.edu)
(Editors: Science contact information, image URLs at the end)

Gamma-Ray Evidence Suggests Ancient Mars Had Oceans

An international team of scientists who analyzed data from the Gamma Ray
Spectrometer onboard NASA's Mars Odyssey reports new evidence for the
controversial idea that oceans once covered about a third of ancient Mars.

"We compared Gamma Ray Spectrometer data on potassium, thorium and iron above
and below a shoreline believed to mark an ancient ocean that covered a third of
Mars' surface, and an inner shoreline believed to mark a younger, smaller
ocean," said University of Arizona planetary geologist James M. Dohm, who led
the international investigation.

"Our investigation posed the question, Might we see a greater concentration of
these elements within the ancient shorelines because water and rock containing
the elements moved from the highlands to the lowlands, where they eventually
ponded as large water bodies?" Dohm said.

Mars Odyssey's GRS, or Gamma Ray Spectrometer, led by William Boynton of UA's
Lunar and Planetary Laboratory, has the unique ability to detect elements
buried as much as 1/3 meter, or 13 inches, below the surface by the gamma rays
they emit. That capability led to GRS' dramatic 2002 discovery of water-ice
near the surface throughout much of high-latitude Mars.

Results from Mars Odyssey and other spacecraft suggest that past watery
conditions likely leached, transported and concentrated such elements as
potassium, thorium and iron, Dohm said. "The regions below and above the two
shoreline boundaries are like cookie cutouts that can be compared to the
regions above the boundaries, as well as the total region."

The younger, inner shoreline is evidence that an ocean about 10 times the size
of the Mediterranean Sea, or about the size of North America, existed on the
northern plains of Mars a few billion years ago. The larger, more ancient
shoreline that covered a third of Mars held an ocean about 20 times the size of
the Mediterranean, the researchers estimate.

The potassium-thorium-iron enriched areas occur below the older and younger
paleo-ocean boundaries with respect to the entire region, they said. The
scientists used data from Mars Global Surveyor's laser altimeter for
topographic maps of the regions in their study.

They are reporting their findings in the article, "GRS Evidence and the
Possibility of Paleo-oceans on Mars." The article will be published in a
special edition of Planetary and Space Science, which stems from a June 2007
workshop on Mars and its Earth analogs held in Trento, Italy. UA Regents'
Professor Victor Baker and Boynton, and other scientists from the United
States, Italy, Spain, South Korea and Canada are co-authors.

Scientific debate on the possible existence of ancient Martian oceans marked by
shorelines was sparked by several studies almost 20 years ago. One such study,
by Baker and colleagues at the UA Lunar and Planetary Laboratory, proposed that
a few billion years ago, erupting magma unleashed floods far greater than
Brazil's Amazon River. The floods ponded in the northern lowlands of Mars,
forming seas and lakes that triggered relatively warmer and wetter conditions
that lasted tens of thousands of years.

Scientists are driven to understand how and when water existed on Mars because
water is critical to life.

Spacecraft images going back to Mariner 9 in the early 1970s and the Viking
orbiters and landers later in the 1970s showed widespread evidence for a watery
past for Mars. Images and other information from a flotilla of U.S. and European
Mars orbiters have sharpened the details in the past decade, they added. Results
from Mars Global Surveyor, Mars Odyssey, Mars Express and Mars Reconnaissance
Orbiter highlight a water-and-ice-sculpted Martian landscape.

Scientists studying spacecraft images have a hard time confirming "shoreline"
landforms, the researchers said, because Mars shorelines would look different
from Earth's shorelines. Earth's coastal shorelines are largely a direct result
of powerful tides caused by gravitational interaction between Earth and the
moon, but Mars lacks a sizable moon. Another difference is that lakes or seas
on Mars could have formed largely from giant debris flows and liquefied
sediments. Still another difference is that Mars oceans may have been
ice-covered, which would prevent wave action.

"The GRS adds key information to the long-standing oceans-on-Mars controversy,"
Dohm said. "But the debate is likely to continue well into the future, perhaps
even when scientists can finally walk the Martian surface with instruments in
hand, with a network of smarter spaceborne, airborne and ground-based robotic
systems in their midst."

SCIENCE CONTACTS:
James M. Dohm (520-626-8454; jmd at hwr.arizona.edu)
Victor R. Baker (520-621-7875; baker at hwr.arizona.edu)
William V. Boynton (520-621-6941; wboynton at lpl.arizona.edu)

IMAGES FOR DOWNLOAD:
http://images.uanews.org/dohm_fig1.jpg
http://images.uanews.org/dohm_fig2.jpg

CAPTIONS:

dohm_fig1.jpg
This 3D map superimposes gamma-ray data from Mars Odyssey's Gamma-Ray
Spectrometer onto topographic data from the laser altimeter onboard the Mars
Global Surveyor. The red arrow indicates the shield volcanoes of Elysium rise
in northern Mars, seen obliquely to the southeast. Blue-to-violet colors at the
Elysium rise and highlands stretching to the foreground of the map mark areas
poor in potassium. Red-to-yellow colors mark potassium-rich sedimentary
deposits in lowlands below the Mars Pathfinder landing site (PF) and Viking 1
landing site (V1).

dohm_fig2.jpg
This top illustration shows the location of theTharsis volcanic region and
Valles Marineris in the context of the hypothesized larger, ancient ocean and
smaller, more recent ocean in Mars' northern lowland planes. Victor Baker and
others from The University of Arizona have long argued that Tharsis volcanism
unleashed great floods that carved large outflow channels and deposited
sediment carried from the southern cratered highlands to the northern lowland
plains, where water formed lakes and oceans and changed climate for thousands
of years. The lower part of the illustration explains the mechanism.
Received on Mon 17 Nov 2008 03:15:38 PM PST


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