[meteorite-list] Radar Map of Buried Mars Layers Matches Climate Cycles (MRO)

From: Ron Baalke <baalke_at_meteoritecentral.com>
Date: Wed, 23 Sep 2009 13:14:48 -0700 (PDT)
Message-ID: <200909232014.n8NKEmYV012156_at_zagami.jpl.nasa.gov>

http://www.jpl.nasa.gov/news/news.cfm?release=2009-144

Radar Map of Buried Mars Layers Matches Climate Cycles
Jet Propulsion Laboratory
September 22, 2009

PASADENA, Calif. -- New, three-dimensional imaging of Martian
north-polar ice layers by a radar instrument on NASA's Mars
Reconnaissance Orbiter is consistent with theoretical models of Martian
climate swings during the past few million years.

Alignment of the layering patterns with the modeled climate cycles
provides insight about how the layers accumulated. These ice-rich,
layered deposits cover an area one-third larger than Texas and form a
stack up to 2 kilometers (1.2 miles) thick atop a basal deposit with
additional ice.

"Contrast in electrical properties between layers is what provides the
reflectivity we observe with the radar," said Nathaniel Putzig of
Southwest Research Institute, Boulder, Colo., a member of the science
team for the Shallow Radar instrument on the orbiter. "The pattern of
reflectivity tells us about the pattern of material variations within
the layers."

Earlier radar observations indicated that the Martian north-polar
layered deposits are mostly ice. Radar contrasts between different
layers in the deposits are interpreted as differences in the
concentration of rock material, in the form of dust, mixed with the ice.
These deposits on Mars hold about one-third as much water as Earth's
Greenland ice sheet.

Putzig and nine co-authors report findings from 358 radar observations
in a paper accepted for publication by the journal Icarus and currently
available online.

Their radar results provide a cross-sectional view of the north-polar
layered deposits of Mars, showing that high-reflectivity zones, with
multiple contrasting layers, alternate with more-homogeneous zones of
lower reflectivity. Patterns of how these two types of zones alternate
can be correlated to models of how changes in Mars' tilt on its axis
have produced changes in the planet's climate in the past 4 million
years or so, but only if some possibilities for how the layers form are
ruled out.

"We're not doing the climate modeling here; we are comparing others'
modeling results to what we observe with the radar, and using that
comparison to constrain the possible explanations for how the layers
form," Putzig said.

The most recent 300,000 years of Martian history are a period of less
dramatic swings in the planet's tilt than during the preceding 600,000
years. Since the top zone of the north-polar layered deposits -- the
most recently deposited portion -- is strongly radar-reflective, the
researchers propose that such sections of high-contrast layering
correspond to periods of relatively small swings in the planet's tilt.

They also propose a mechanism for how those contrasting layers would
form. The observed pattern does not fit well with an earlier
interpretation that the dustier layers in those zones are formed during
high-tilt periods when sunshine on the polar region sublimates some of
the top layer's ice and concentrates the dust left behind. Rather, it
fits an alternative interpretation that the dustier layers are simply
deposited during periods when the atmosphere is dustier.

The new radar mapping of the extent and depth of five stacked units in
the north-polar layered deposits reveals that the geographical center of
ice deposition probably shifted by 400 kilometers (250 miles) or more at
least once during the past few million years.

"The radar has been giving us spectacular results," said Jeffrey Plaut
of NASA's Jet Propulsion Laboratory, Pasadena, Calif., a co-author of
the paper. "We have mapped continuous underground layers in three
dimensions across a vast area."

The Italian Space Agency operates the Shallow Radar instrument, which it
provided for NASA's Mars Reconnaissance Orbiter. The orbiter has been
studying Mars with six advanced instruments since 2006. It has returned
more data from the planet than all other past and current missions to
Mars combined. For more information about the mission, visit:
http://www.nasa.gov/mro .

JPL, a division of the California Institute of Technology, Pasadena,
manages the Mars Reconnaissance Orbiter for NASA's Science Mission
Directorate, Washington. Lockheed Martin Space Systems, Denver, is the
prime contractor for the project and built the spacecraft.

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

Maria Martinez 210-522-3305
Southwest Research Institute, San Antonio, Texas
maria.martinez at swri.org

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

2009-144
Received on Wed 23 Sep 2009 04:14:48 PM PDT