[meteorite-list] Upcoming Mercury Encounter Presents New Opportunities for Magnetometer

From: Ron Baalke <baalke_at_meteoritecentral.com>
Date: Mon, 14 Sep 2009 13:54:45 -0700 (PDT)
Message-ID: <200909142054.n8EKsj7h012061_at_zagami.jpl.nasa.gov>

http://messenger.jhuapl.edu/news_room/details.php?id=128

MESSENGER Mission News
August 20, 2009

Upcoming Mercury Encounter Presents New Opportunities for Magnetometer

On September 29, the MESSENGER spacecraft will pass by Mercury for the
third time, flying 141.7 miles above the planet's rocky surface for a
final gravity assist that will enable it to enter orbit about Mercury in
2011. This encounter will also provide new observational opportunities
for MESSENGER's Magnetometer, designed to determine the structure and
origin of Mercury's intrinsic magnetic field.

The comparison of magnetosphere observations from MESSENGER's first
flyby in January 2008 with data from the probe's second pass in October
2008 provided key new insight into the nature of the planet's internal
magnetic field and revealed new features of Mercury's magnetosphere,
explains *Brian Anderson*, of the Johns Hopkins University Applied
Physics Laboratory (APL) in Laurel, Md.

"MESSENGER's first flyby of Mercury and Mariner 10's encounters with the
planet provided data only from Mercury's eastern hemisphere," says
Anderson, MESSENGER's Deputy Project Scientist. "The October 2008 flyby
provided the first measurements from Mercury's western hemisphere, and
scientists learned that the planet's magnetic field is highly symmetric.
This finding is significant for the planet's internal field because it
implies that the dipole is even more closely aligned with the planet's
rotation axis than we could conclude before the second flyby."

The probe's third flyby of Mercury next month will take it again over
the planet's western hemisphere, and the observations will be used to
refine the estimate of the planetary magnetic field, Anderson explains.

"The previous flybys yielded significant insight into the dynamics of
Mercury's magnetosphere and its boundaries," Anderson says. "During the
second flyby a plasmoid and a series of traveling compression regions
were observed in Mercury's magnetotail, and a large flux transfer event
was observed at the dayside magnetopause. These observations proved that
the solar wind interaction, under the right circumstances, can drive
intense magnetic reconnection at rates 10 times the rates observed at
Earth."

The behavior during the second flyby was markedly different from that
found in the first flyby, demonstrating the profound influence of the
solar wind environment on Mercury's magnetosphere. "The third flyby is
the last opportunity to survey the magnetotail and magnetopause regions
in the equatorial plane, and the contrast in the system's structure
under different solar wind conditions already observed make it likely
that the third flyby will yield new insights and perhaps more surprises
for the dynamics of this smallest and most highly variable of the solar
system's planetary magnetospheres," Anderson says.

As with the previous two flybys, the Magnetometer will record the
magnetic field at the highest available observation rate of 20 vector
magnetic field samples per second for a period of twelve hours centered
on the time of closest approach. "This observing plan guarantees the
highest possible science return from the encounter and will provide key
observations to guide the magnetic field investigation plan for the
prime orbital phase of the mission," Anderson says.

------------------------------------------------------------------------

*Berkel Leaves Its Mark*

The crater in the lower left corner of this image
<http://messenger.jhuapl.edu/gallery/sciencePhotos/pics/berkel_three_arrows.png>
is Berkel, recently named for Turkish painter and printmaker Sabri Berkel (1909-1993).
The crater contains dark material in its center and in a ring immediately
surrounding it. Moreover, Berkel is surrounded by a blanket of bright
ejecta and a system of bright rays. Other craters on Mercury's surface,
such as Basho
<http://messenger.jhuapl.edu/gallery/sciencePhotos/image.php?page=2&gallery_id=2&image_id=183>,
also exhibit both bright rays and dark halos. In contrast, two
neighboring craters in this image (indicated by white arrows) have
bright rays but lack dark halos. Members of the MESSENGER Science Team
are investigating why some craters contain dark material while others do
not, and what that means for the nature and structure of Mercury's
crust. To view other images released over the summer, go online to
http://messenger.jhuapl.edu/gallery/sciencePhotos/index.php.

------------------------------------------------------------------------

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 Mon 14 Sep 2009 04:54:45 PM PDT