STARDUST MISSION SET TO BRING BACK A PIECE OF A COMET
NASA's Stardust mission, scheduled for launch February 6, 1999 from Cape
Canaveral, FL, will send a spacecraft flying through the cloud of dust that
surrounds the nucleus of a comet - and, for the first time ever, bring
cometary material back to Earth.
Comets, which periodically grace our sky like celestial bottle rockets, are
thought to hold many of the original ingredients of the recipe that created
the planets and brought plentiful water to Earth. They are also rich in
organic material, which provided our planet with many of the ready-to-mix
molecules that could give rise to life. They may be the oldest, most
primitive bodies in the solar system, a preserved record of the original
nebula that formed the Sun and the planets.
"Scientists have long sought a sample directly from a known comet because of
the unique chemical and physical information these bodies contain about the
earliest history of the solar system," said Dr. Edward Weiler, NASA's
associate administrator for space science. "Locked within comet molecules
and atoms could be the record of the formation of the planets and the
materials from which they were made."
Stardust is the first U.S. mission dedicated solely to a comet and will be
the first to return extraterrestrial material from outside the orbit of the
Moon. Stardust's main objective is to capture a sample from a well-preserved
comet called Wild-2 (pronounced "Vilt-2").
The spacecraft will also collect interstellar dust from a recently
discovered flow of particles that passes through our solar system from
interstellar space. As in the proverbial "from dust to dust," this
interstellar dust represents the ultimate in recycled material; it is the
stuff from which all solid objects in the universe are made, and the state
to which everything eventually returns. Scientists want to discover the
composition of this "stardust" to determine the history, chemistry, physics
and mineralogy of nature's most fundamental building blocks.
Because it would be virtually impossible to equip a spacecraft with the most
sophisticated lab instrumentation needed to analyze such material in space,
the Stardust spacecraft is more of a robotic lab assistant whose job it is
pick up and deliver a sample to scientists back on Earth. The spacecraft
will, however, radio some on-the-spot analytical observations of the comet
and interstellar dust.
"The samples we will collect are extremely small, less than a micron, or
1/25,000th of an inch, in size, and can only be adequately studied in
laboratories with sophisticated analytical instruments," said Dr. Donald C.
Brownlee of the University of Washington, principal investigator for the
"Even if a ton of sample were returned, the main information in the solids
would still be recorded at the micron level, and the analyses would still be
done a single grain at a time." Stardust will meet up with Comet Wild-2 on
January 2, 2004. A gravity assist flyby of Earth will put Stardust on a
trajectory that will allow it to capture cometary dust intact at a low
relative speed of 6.1 kilometers per second (about 13,600 miles per hour).
An onboard camera will aid in navigating the spacecraft as close as about
150 kilometers (100 miles) from the comet's nucleus, permitting the capture
of the freshest samples from the heart of the comet.
Dressed for survival behind armored shields, Stardust will document its
10-hour passage through the hailstorm of comet debris with scientific
instruments and the navigation camera. On approach to the dust cloud, or
"coma," the spacecraft will flip open a tennis-racket-shaped particle
catcher filled with a smoke-colored glass foam called aerogel to capture the
comet particles. Aerogel, the lowest-density material in the world, has
enough "give" in it to slow and stop particles without altering them too
much. After the sample has been collected, the aerogel capturing device will
fold down into a return capsule, which closes like a clamshell to enclose
the sample for its safe delivery to Earth.
In addition, a particle impact mass spectrometer will obtain in-flight data
on the composition of both cometary and interstellar dust, especially very
fine particles. The optical navigation camera should provide excellent
images of the dark mass of the comet's nucleus. Other equipment will reveal
the distribution in both time and space of coma dust, and could give an
estimate of the comet's mass.
On January 15, 2006, a parachute will set the capsule gently onto the salt
flats of the Utah desert for retrieval. The scientifically precious samples
can be studied for decades into the future with ever-improving techniques
and analysis technologies, limited only by the number of atoms and molecules
of the sample material available. Many types of analyses now performed on
lunar samples, for example, were not even conceived at the time of the
Apollo missions to the Moon.
Comets are small, irregularly shaped bodies composed of a mixture of grains
of rock, organic molecules and frozen gases. Most comets are about 50
percent water ice. Typically ranging in size up to about 10 kilometers (6
miles) in diameter, comets have highly elliptical orbits that bring them
close to the Sun and then swing them back out into deep space. They spend
most of their existences in a deep freeze beyond the orbit of Pluto - far
beyond the Sun's dwindling influence, which is why so much of their original
material is well-preserved.
When a comet approaches within about 700 million kilometers (half billion
miles) of the Sun, the surface of the nucleus begins to warm, and material
on the comet's nucleus heats and begins to vaporize. This process, along
with the loss of rocky debris or other particles that fly off the surface,
creates the cloud around the nucleus called the coma. It is the glowing,
fuzzy coma that appears as the head of a comet when one is observed from
Earth. A tail of luminous debris and another, less apparent, tail of gases
flow millions of miles beyond the head in the direction away from the Sun.
Comet Wild-2 is considered an ideal target for study because, until
recently, it was a long-period comet that rarely ventured close to the Sun.
A fateful pass near Jupiter and its enormous gravity field in 1974 pulled
Comet Wild-2 off-course, diverting it onto a tighter orbit that brings it
past the Sun more frequently and also closer to Earth's neighborhood.
Because Wild-2 has only recently changed its orbit, it has lost little of
its original material when compared with other short-period comets, so it
offers some of the best-preserved comet samples that can be obtained.
Stardust was competitively selected in the fall of 1995 under NASA's
Discovery Program of low-cost, highly focused science missions. As a
Discovery mission, Stardust has met a fast development schedule, uses a
small Delta launch vehicle, is cost-capped at less than $200 million, and is
the product of a partnership involving NASA, academia and industry.
Principal investigator Brownlee is well-known for his discovery of cosmic
particles in Earth's stratosphere known as Brownlee particles. Dr. Peter
Tsou of NASA's Jet Propulsion Laboratory, Pasadena, CA, an innovator in
aerogel technology and maker of aerogel, serves as deputy investigator. JPL,
a division of the California Institute of Technology, manages the Stardust
mission for NASA's Office of Space Science, Washington, DC. Dr. Kenneth L.
Atkins of JPL is project manager. The spacecraft is designed, built and
operated by Lockheed Martin Astronautics, Denver, CO. JPL provided the
spacecraft's optical navigation camera, and the Max Planck Institute of
Germany provided the real-time dust composition analyzer.
Last Updated: November 26, 2003