[meteorite-list] NASA Reveals New Discoveries From Mercury (MESSENGER)

From: Ron Baalke <baalke_at_meteoritecentral.com>
Date: Sat, 5 Jul 2008 21:48:35 -0700 (PDT)
Message-ID: <200807060448.VAA12979_at_zagami.jpl.nasa.gov>

July 3, 2008

J.D. Harrington
Headquarters, Washington
202-358-5241
j.d.harrington at nasa.gov

Mike Buckley
Johns Hopkins University Applied Physics Laboratory, Laurel, Md.
240-228-7536
mike.buckley at jhuapl.edu

RELEASE: 08-166

NASA REVEALS NEW DISCOVERIES FROM MERCURY

GREENBELT, Md. -- Scientists have argued about the origins of
Mercury's smooth plains and the source of its magnetic field for more
than 30 years. Now, analyses of data from the January 2008 flyby of
the planet by the Mercury Surface, Space Environment, Geochemistry
and Ranging (MESSENGER) spacecraft have shown that volcanoes were
involved in plains formation and suggest that its magnetic field is
actively produced in the planet's core.

Scientists additionally took their first look at the chemical
composition of the planet's surface. The tiny craft probed the
composition of Mercury's thin atmosphere, sampled charged particles
(ions) near the planet, and demonstrated new links between both sets
of observations and materials on Mercury's surface. The results are
reported in a series of 11 papers published in a special section of
Science magazine July 4.

The controversy over the origin of Mercury's smooth plains began with
the 1972 Apollo 16 moon mission, which suggested that some lunar
plains came from material that was ejected by large impacts and then
formed smooth "ponds." When Mariner 10 imaged similar formations on
Mercury in 1975, some scientists believed that the same processes
were at work. Others thought Mercury's plains material came from
erupted lavas, but the absence of volcanic vents or other volcanic
features in images from that mission prevented a consensus.

Six of the papers in Science report on analyses of the planet's
surface through its reflectance and color variation, surface
chemistry, high-resolution imaging at different wavelengths, and
altitude measurements. The researchers found evidence of volcanic
vents along the margins of the Caloris basin, one of the solar
system's youngest impact basins. They also found that Caloris has a
much more complicated geologic history than previously believed.

The first altitude measurements from any spacecraft at Mercury also
found that craters on the planet are about a factor of two shallower
than those on Earth's moon. The measurements also show a complex
geologic history for Mercury.

Mercury's core makes up at least 60 percent of its mass, a figure
twice as large as any other known terrestrial planet. The flyby
revealed that the magnetic field, originating in the outer core and
powered by core cooling, drives very dynamic and complex interactions
among the planet's interior, surface, exosphere and magnetosphere.

Remarking on the importance of the core to surface geological
structures, Principal Investigator Sean Solomon at the Carnegie
Institution of Washington said, "The dominant tectonic landforms on
Mercury, including areas imaged for the first time by MESSENGER, are
features called lobate scarps, huge cliffs that mark the tops of
crustal faults that formed during the contraction of the surrounding
area. They tell us how important the cooling core has been to the
evolution of the surface. After the end of the period of heavy
bombardment, cooling of the planet's core not only fueled the
magnetic dynamo, it also led to contraction of the entire planet. And
the data from the flyby indicate that the total contraction is a
least one-third greater than we previously thought."

The flyby also made the first-ever observations of the ionized
particles in Mercury's unique exosphere. The exosphere is an
ultrathin atmosphere in which the molecules are so far apart they are
more likely to collide with the surface than with each other. The
planet's highly elliptical orbit, its slow rotation and particle
interactions with the magnetosphere, interplanetary medium and solar
wind result in strong seasonal and day-night differences in the way
particles behave.

For more information, visit:

http://www.nasa.gov/messenger

or

http://messenger.jhuapl.edu/mer_flyby1.html

        
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Received on Sun 06 Jul 2008 12:48:35 AM PDT