NASA's first trip to Mercury in 30 years — and
the closest look ever at the innermost planet —
starts this month with the launch of the MESSENGER
spacecraft from Cape Canaveral Air Force Station, Fla.
As of press time on Friday, the launch was scheduled
for 2:16 a.m. today, the first day of a 13-day launch
period. (For updates, go to
Johns Hopkins' Applied Physics Laboratory manages the
mission for NASA's Office of Space Science and designed,
built and will operate the spacecraft.
MESSENGER will conduct an in-depth study of the sun's
closest neighbor, the least explored of the terrestrial
("rocky") planets that also include Venus, Earth and Mars.
After a liftoff aboard a Delta II launch vehicle,
MESSENGER's voyage includes three flybys of Mercury in 2008
and 2009 and a yearlong orbit of the planet starting in
"Our missions to Mars and Venus have produced exciting
data and new theories about the processes that formed the
inner planets," said Orlando Figueroa, director of the
Solar System Exploration Division at NASA Headquarters,
Washington. "Yet Mercury still stands out as a planet with
a fascinating story to tell. MESSENGER should complete the
detailed exploration of the inner solar system — our
planetary backyard — and help us to understand the
forces that shaped planets like our own."
MESSENGER — short for MErcury Surface, Space
ENvironment, GEochemistry and Ranging — is only the
second spacecraft to set sights on Mercury; Mariner 10
sailed past it three times in 1974 and 1975 and gathered
detailed data on less than half the surface. Carrying seven
scientific instruments on its compact and durable composite
frame, MESSENGER will provide the first images of the
entire planet. The mission will also collect detailed
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.
MESSENGER's science team will shape its investigation
around several questions, including why is Mercury —
the densest planet in the solar system — made mostly
of iron? 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 near 840 degrees Fahrenheit,
have what appears to be ice in its polar craters?
"For nearly 30 years we've had questions that couldn't
be answered until technology and mission designs caught up
with our desire to go back to Mercury," said MESSENGER
principal investigator Sean C. Solomon, from the Carnegie
Institution of Washington. "Now we are ready. The answers
to these questions will not only tell us more about Mercury
but illuminate processes that affect all the terrestrial
Mercury's proximity to the sun makes it both a
fascinating subject and an unprecedented mission design
challenge. The sun can be up to 11 times brighter than what
we see on Earth, and surface temperatures at Mercury's
equator can reach 450 degrees Celsius (about 840 degrees
Fahrenheit), but MESSENGER will operate at room temperature
behind a sunshade of heat-resistant ceramic fabric. The
1.2-ton spacecraft also features a heat-radiation system
and will pass only briefly over Mercury's hottest regions,
limiting exposure to the intense heat bouncing back from
the broiling surface.
"We're doing something no one has ever tried before,"
said MESSENGER project manager David G. Grant, of APL.
"After launch and a long trip through the inner solar
system, we still face the risky and difficult job of
orbiting the planet next to the sun. The team is confident
that the spacecraft they designed, built and tested is
ready for this journey and its mission to Mercury."
On a 4.9-billion-mile journey that includes 15 loops
around the sun, the solar-powered MESSENGER will fly past
Earth once, Venus twice and Mercury three times before
easing into orbit around its target planet. The Earth
flyby, a year after launch, and the Venus flybys, in
October 2006 and June 2007, use the pull of the planets'
gravity to guide MESSENGER toward Mercury's orbit. The
Mercury flybys in January 2008, October 2008 and September
2009 fine-tune and slow MESSENGER's track while allowing
the spacecraft to gather data critical to planning the
mission's orbit phase.
MESSENGER's science instruments were built by APL;
NASA Goddard Space Flight Center, Greenbelt, Md.;
University of Michigan, Ann Arbor; and University of
Colorado, Boulder. GenCorp Aerojet, Sacramento, Calif., and
Composite Optics, San Diego, provided the spacecraft's
propulsion system and composite structure, respectively.
The MESSENGER science team draws expertise from APL;
Brown University; Carnegie Institution of Washington;
Goddard Space Flight Center; Los Alamos National
Laboratory; MIT; Northwestern University; Southwest
Research Institute; University of Arizona, Tucson;
University of California, Santa Barbara; University of
Colorado, Boulder; University of Michigan, Ann Arbor; and
Washington University in St. Louis.
The MESSENGER project is the seventh in NASA's
Discovery Program of lower cost, scientifically focused