NASA has given the first Mercury orbiter mission the go-ahead
to move into full-scale spacecraft development — setting up the
first trip to the Sun’s closest neighbor in more than a

MESSENGER, short for MErcury Surface, Space ENvironment,
GEochemistry, and Ranging, will launch in March 2004 and orbit
Mercury for one Earth-year beginning in April 2009.

“MESSENGER is the most complex and challenging Discovery-class
mission we have ever attempted, and our goal is to do something
never before attempted,” said Dr. Jay Bergstralh, chief scientist
for NASA’s Solar System Exploration Division in NASA’s Office of
Space Science in Washington, D.C. “Conducting a year-long mission
to orbit a planet only 36 million miles from the Sun for
relatively low cost is an amazing concept, and we have selected a
top-flight team to build and fly this mission.”

Dr. Sean C. Solomon of the Carnegie Institution of Washington
(D.C.) is the mission’s principal investigator and lead scientist.
The Johns Hopkins University Applied Physics Laboratory (APL) in
Laurel, MD, manages the mission for NASA’s Office of Space Science
and will design, build and operate the MESSENGER spacecraft.
Preliminary work on the mission began 18 months ago.

MESSENGER will be only the second spacecraft to visit Mercury.
Mariner 10 flew past it three times in 1974 and 1975 but gathered
data on less than half the planet.

MESSENGER’s seven scientific instruments — including a camera,
laser altimeter, magnetometer and several spectrometers — will
globally image Mercury for the first time. It also will collect
unprecedented information on the composition and structure of
Mercury’s crust, its geologic history, the nature of its thin
atmosphere and active magnetosphere, and the makeup of its core
and polar materials.

“This is an opportunity to complete the detailed exploration of
the inner solar system, on a planet where we’ve never even seen
half the surface,” Solomon said. “We’ve had many exciting missions
to Mars and Venus that yielded new theories about the processes
that shaped the inner planets, and for 25 years now Mercury has
clearly stood out as a place where major questions remain to be
answered. Mercury is that last piece of the puzzle.”

Among questions MESSENGER’s science team will investigate: Why is
Mercury — the densest planet in the solar system — mostly made
of iron metal? Why is it the only inner planet besides Earth with
a global magnetic field? How can the planet closest to the sun,
with daytime temperatures soaring past 850 degrees Fahrenheit at
its equator, have what appears to be ice in its polar craters?
Solomon said unlocking Mercury’s secrets will help us understand
the forces that shaped Earth and the other terrestrial (rocky)

MESSENGER’s five-year voyage includes two flybys of Venus and two
flybys of Mercury, “gravity assists” that will help the spacecraft
tune its path and match Mercury’s quick, elliptical orbit around
the sun. The mission team will also use pictures and data from the
Mercury flybys to refine the orbit study.

Once in orbit MESSENGER has to deal with the intense heat at
Mercury, where the sun is up to 11 times brighter than on Earth.
But MESSENGER’s instruments will operate at room temperature
behind a sunshield made of the same ceramic material that protects
parts of the space shuttle. The spacecraft will also pass only
briefly over the hottest parts of the planet’s surface, limiting
the instruments’ exposure to reflected heat.

The $256 million MESSENGER mission is the seventh in NASA’s
Discovery Program of lower-cost, scientifically focused space
flights and the third Discovery project managed by APL. The
mission cost figure does not include the launch vehicle and
mission operations. Information about the Discovery program is
available at:

The MESSENGER science team taps expertise from APL; University of
Colorado, Boulder; University of Arizona, Tucson; Southwest
Research Institute, Boulder, CO; NASA’s Goddard Space Flight
Center, Greenbelt, MD; University of Michigan, Ann Arbor;
Washington University, St. Louis, MO; University of California,
Santa Barbara; Brown University, Providence, RI; Northwestern
University, Evanston, IL; and Massachusetts Institute of
Technology, Cambridge. GenCorp Aerojet, Sacramento, CA, and
Composite Optics Inc., San Diego, CA, are working with APL to
build the spacecraft. NASA’s Jet Propulsion Laboratory, Pasadena,
CA, will provide navigation support for the mission.

More information on MESSENGER is available at:

Animation of MESSENGER’s journey to Mercury is available at: