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Posted by on November 17, 2008, 3:18 pm
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FROM: Lori Stiles (520-626-4402; lstiles@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@hwr.arizona.edu)
Victor R. Baker (520-621-7875; baker@hwr.arizona.edu)
William V. Boynton (520-621-6941; wboynton@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.
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