[meteorite-list] MESSENGER's X-Ray Spectrometer Reveals Chemical Diversity on Mercury's Surface

From: Ron Baalke <baalke_at_meteoritecentral.com>
Date: Fri, 21 Sep 2012 13:32:11 -0700 (PDT)
Message-ID: <201209212032.q8LKWB6g001227_at_zagami.jpl.nasa.gov>

http://messenger.jhuapl.edu/news_room/details.php?id=229

MESSENGER Mission News
September 21, 2012

MESSENGER's X-Ray Spectrometer Reveals Chemical Diversity on Mercury's
Surface

New data from the X-Ray Spectrometer (XRS) on the MESSENGER spacecraft
-- one of two instruments designed to measure the abundances of many key
elements on Mercury -- show variations in the composition of surface
material on Mercury that point to changes over time in the
characteristics of volcanic eruptions on the solar system's innermost
planet.

In results to be published in the Journal of Geophysical Research,
scientists report that Mercury's volcanic smooth plains units differ in
composition from older surrounding terrains. The older terrain has
higher ratios of magnesium to silicon, sulfur to silicon, and calcium to
silicon, but lower ratios of aluminum to silicon, suggesting that the
smooth plains material erupted from a magma source that was chemically
different from the source of the material in the older regions, explains
Shoshana Weider of the Carnegie Institution of Washington, the lead
author on the paper.

"The new findings further illuminate the geological history of the
planet,"?? she says. "We now know that these areas are compositionally
distinct, indicating that different parts of Mercury's mantle melted at
different times and temperatures, and through volcanic activity created
the materials in the different terrains."

Weider and her co-authors also report that Mercury's surface is
dominated by minerals high in magnesium and enriched in sulfur.

"None of the other terrestrial planets have such high levels of sulfur.
We are seeing about ten times the amount of sulfur than on Earth and
Mars,"?? Weider says. "In terms of magnesium, we do have some materials
on Earth that are high in magnesium. They tend to be ancient volcanic
rocks that formed from very hot lavas. So this composition on Mercury
tells us that eruptions of high-temperature lavas might have formed
these high-magnesium materials."

These findings stem from the team's analysis of 205 X-ray measurements
of Mercury's surface, focusing on the large expanse of smooth volcanic
plains at high northern latitudes and surrounding areas that are higher
in crater density and therefore older than the northern plains. Weider
says the measurements support what other MESSENGER scientists have
observed from the mission's images. "Now we can correlate their findings
with our data, providing increased confidence in what we are discovering
about the planet," she says.

MESSENGER has been orbiting Mercury since March 2011, and has been
revealing new information about the surface chemistry and geological
history of the innermost planet in the solar system. The XRS measures
elemental abundances on the surface of Mercury by detecting fluorescent
X-ray emissions induced on the planet's surface by the incident solar
X-ray flux. The instrument began orbital observations on March 23, 2011,
and has observed X-ray fluorescence from the surface of the planet
whenever a sunlit portion of Mercury has been within the XRS field of view.

"The X-ray spectrometer focuses on the estimation of elemental
abundances on Mercury; i.e., the amount of magnesium, aluminum, sulfur,
calcium, and iron in surface material,"?? Weider says. "From there we can
start to work out what kinds of minerals are present, then the types of
rocks that were formed, and then we can start to unravel the geological
history."
------------------------------------------------------------------------
MESSENGER (MErcury Surface, Space ENvironment, GEochemistry, and
Ranging) is a NASA-sponsored scientific investigation of the planet
Mercury and the first space mission designed to orbit the planet closest
to the Sun. The MESSENGER spacecraft launched on August 3, 2004, and
after flybys of Earth, Venus, and Mercury will start a yearlong study of
its target planet in March 2011. Dr. Sean C. Solomon, of the Carnegie
Institution of Washington, leads the mission as Principal Investigator.
The Johns Hopkins University Applied Physics Laboratory built and operates
the MESSENGER spacecraft and manages this Discovery-class mission for NASA.
Received on Fri 21 Sep 2012 04:32:11 PM PDT