A mission that will orbit the two largest asteroids in
the solar system is one of a pair of missions chosen by NASA
for the agency’s Discovery program.

The mission, called Dawn, is managed by NASA’s Jet
Propulsion Laboratory, Pasadena, Calif. Led by principal
investigator Dr. Christopher T. Russell of the University of
California, Los Angeles, Dawn is scheduled for launch in 2006.

The second new Discovery mission is Kepler, a spaceborne
telescope, also scheduled for launch in 2006. It will search
for Earth-like planets around stars beyond the solar system.
Kepler is managed by NASA’s Ames Research Center, Moffett
Field, Calif.

"Kepler and Dawn are exactly the kind of missions NASA
should be launching, missions that tackle some of the most
important questions in science yet do it for a very modest
cost," said Dr. Edward Weiler, associate administrator for
space science at NASA Headquarters in Washington D.C. "It’s
an indicator of how far we’ve come in our capability to
explore space when missions with such ambitious goals are
proposed for the Discovery program of lower-cost missions
rather than as major projects costing ten times as much."

The Dawn mission will make a nine-year journey to orbit
the two most massive asteroids known, Vesta and Ceres, two
"baby planets" very different from each other yet both
containing tantalizing clues about the formation of the solar
system. Using the same set of instruments to observe these two
bodies, both located in the main asteroid belt between Mars
and Jupiter, Dawn will improve our understanding of how
planets formed during the earliest epoch of the solar system.

Ceres has quite a primitive surface, water-bearing
minerals, and possibly a very weak atmosphere and frost. Vesta
is a dry body that has been resurfaced by basaltic lava flows,
and may have an early magma ocean like Earth’s Moon. Like the
Moon, it has been hit many times by smaller space rocks, and
these impacts have sent out meteorites at least five times in
the last 50 million years.

The mission will determine these pre-planets’ physical
attributes, such as shape, size, mass, craters and internal
structure, and study more complex properties such as
composition, density and magnetism.

The Dawn mission builds on the highly successful ion-
propulsion technology pioneered by NASA’s Deep Space 1
spacecraft. During its nine-year journey through the asteroid
belt, Dawn will rendezvous with Vesta and Ceres, orbiting from
as high as 800 kilometers (500 miles) to as low as 100
kilometers (about 62 miles) above the surface.

"I’m ecstatic that we’ll have such a great opportunity to
show what ion propulsion can do," said JPL’s Sarah Gavit, Dawn
project manager. "Ceres and Vesta are two of the largest
unexplored worlds in our solar system. We’ll learn about
early planet formation in ways that wouldn’t have been
possible before this mission." She said she looks forward to
working with Orbital Sciences, a new industry partner for
NASA’s interplanetary spacecraft. Orbital Sciences
Corporation, Dulles, Va., will develop the Dawn spacecraft.

"With its cutting-edge capability, Kepler may help us
answer one of the most enduring questions humans have asked
throughout history: are there others like us in the universe?"
said principal investigator William Borucki of NASA’s Ames
research Center, Moffett Field, Calif., leader of the second
selected mission.

The Kepler mission differs from previous ways of looking
for planets orbiting other stars. Kepler will look for the
‘transit’ signature of planets that occurs each time a planet
crosses the line-of-sight between the planet’s parent star and
the observer. When this happens, the planet blocks some of the
light from its star, resulting in a periodic dimming. This
periodic signature is used to detect the planet and to
determine its size and orbit. Kepler will continuously fix its
gaze at a region of space containing 100,000 stars and will be
able to determine if Earth-sized planets make a transit across
any of the stars.

The industrial partner for mission hardware development
is Ball Aerospace & Technologies Corp., Boulder, Colo.
Kepler’s selection involves a delayed start of development of
up to one year due to funding constraints in the Discovery

NASA selected these missions from 26 proposals made in
early 2001. The missions must stay within the Discovery
program’s development cost cap of about $299 million.

The Discovery program emphasizes lower-cost, highly
focused scientific missions. The past Discovery missions are
Near Shoemaker, Mars Pathfinder and Lunar Prospector, all of
which successfully completed their missions. Stardust and
Genesis are in space; both have begun collecting science data,
although Stardust has not yet arrived at its target comet.
Contour is scheduled to launch next summer, Deep Impact in
January 2004 and Messenger in March 2004. Aspera-3 and
NetLander are Discovery Missions-of-Opportunity under

Information about Dawn and images are available
at: http://www-ssc.igpp.ucla.edu/dawn/ . Details about the
Kepler mission are available at:
http://www.kepler.arc.nasa.gov . Kepler images are available
at: http://www.kepler.arc.nasa.gov/downloading.html .
Information about the Discovery program is available at:
http://discovery.nasa.gov/ .

JPL, a division of the California Institute of Technology
in Pasadena, manages Dawn for NASA’s Office of Space Science,
Washington, D.C.