Jan. 10, 2008

Dwayne Brown
Headquarters, Washington

Paulette Campbell
Johns Hopkins University Applied Physics Laboratory, Laurel, Md.

RELEASE: 08-003


LAUREL, Md. - On Monday, Jan. 14, a pioneering NASA spacecraft will
the first to visit Mercury in almost 33 years when it soars over the
planet to explore and snap close-up images of never-before-seen
terrain. These findings could open new theories and answer old
questions in the study of the solar system.

The MErcury Surface, Space ENvironment, GEochemistry, and Ranging
spacecraft, called MESSENGER, is the first mission sent to orbit the
planet closest to our sun. Before that orbit begins in 2011, the
probe will make three flights past the small planet, skimming as
close as 124 miles above Mercury’s cratered, rocky surface.
MESSENGER’s cameras and other sophisticated, high-technology
instruments will collect more than 1,200 images and make other
observations during this approach, encounter and departure. It will
make the first up-close measurements since Mariner 10 spacecraft’s
third and final flyby on March 16, 1975. When Mariner 10 flew by
Mercury in the mid-1970s, it surveyed only one hemisphere.

“This is raw scientific exploration and the suspense is building by
the day,” said Alan Stern, associate administrator for NASA’s Science
Mission Directorate, Washington. “What will MESSENGER see? Monday
will tell the tale.”

This encounter will provide a critical gravity assist needed to keep
the spacecraft on track for its March 2011 orbit insertion, beginning
an unprecedented yearlong study of Mercury. The flyby also will
gather essential data for mission planning.

“During this flyby we will begin to image the hemisphere that has
never been seen by a spacecraft and Mercury at resolutions better
than those acquired by Mariner 10,” said Sean C. Solomon, MESSENGER
principal investigator, Carnegie Institution of Washington. “Images
will be in a number of different color filters so that we can start
to get an idea of the composition of the surface.”

One site of great interest is the Caloris basin, an impact crater
about 800 miles in diameter, which is one of the largest impact
basins in the solar system.

“Caloris is huge, about a quarter of the diameter of Mercury, with
rings of mountains within it that are up to two miles high,” said
Louise Prockter, the instrument scientist for the Mercury Dual
Imaging System at the Johns Hopkins University Applied Physics
Laboratory in Laurel. “Mariner 10 saw a little less than half of the
basin. During this first flyby, we will image the other side.”

MESSENGER’s instruments will provide the first spacecraft
of the mineralogical and chemical composition of Mercury’s surface.
It also will study the global magnetic field and improve our
knowledge of the gravity field from the Mariner 10 flyby. The
long-wavelength components of the gravity field provide key
information about the planet’s internal structure, particularly the
size of Mercury’s core.

The flyby will provide an opportunity to examine Mercury’s
in unique ways, not possible once the spacecraft begins orbiting the
planet. The flyby also will map Mercury’s tenuous atmosphere with
ultraviolet observations and document the energetic particle and
plasma of Mercury’s magnetosphere. In addition, the flyby trajectory
will enable unique particle and plasma measurements of the magnetic
tail that sweeps behind Mercury.

Launched Aug. 3, 2004, MESSENGER is slightly more than halfway
its 4.9-billion mile journey. It already has flown past Earth once
and Venus twice. The spacecraft will use the pull of Mercury’s
gravity during this month’s pass and others in October 2008 and
September 2009 to guide it progressively closer to the planet’s
orbit. Insertion will be accomplished with a fourth Mercury encounter
in 2011.

The MESSENGER project is the seventh in NASA’s Discovery Program of
low-cost, scientifically focused space missions. The Applied Physics
Laboratory designed, built and operates the spacecraft and manages
the mission for NASA.

For more information about MESSENGER, visit: