NASA’s Goddard Space Flight Center is supplying an instrument to
provide key data on the CONTOUR mission, set to explore at least two
comets following its July 1 launch from Cape Canaveral, Fla. The
Goddard instrument will explore the chemical composition of the comet
nucleus, an icy core in the head of the comet.

Goddard’s Neutral Gas and Ion Mass Spectrometer (NGIMS) instrument
will sample ambient gas atoms and molecules in the comet’s atmosphere
(coma) as CONTOUR zips past the nucleus. Sampling the coma gives
information about a comet’s composition because the coma is comprised
of dust and gas evaporated from the nucleus. The coma appears as the
bright “head” of a comet, and it develops if a comet’s orbit takes it
close to the Sun, where solar heat and radiation vaporize the comet’s
ices. (The nucleus is technically part of the head also, but it is
too small to see, and it is obscured by the coma.)

“It’s truly exciting to have the opportunity to fly this close to the
nucleus of a comet for the first time,” said Dr. Paul Mahaffy, a
Goddard Co-Investigator with the CONTOUR mission for NGIMS. “With
NGIMS we’ll sample gases from Comet Encke and at least one more comet
and hope to learn much about the diversity of comets and how these
bodies may have helped shape our own environment in the distant past
through delivery of water and organic molecules. It has been a real
privilege working with a uniquely talented team at Goddard to develop
this measurement capability.”

NGIMS will identify the types and relative amounts of atoms and
molecules in the coma by creating ions (electrically charged atoms
and molecules) from neutral gas and then separating these by their
mass to charge ratio using electromagnetic fields. Since this ratio
is often unique to a particular atom or molecule, this separation, or
mass spectrometry, can be used to identify the atoms and molecules
present in the coma.

Comets are thought to be relics left over from the formation of the
solar system. They are comprised of dust and frozen gasses that were
present in the primordial cloud that became the Sun and planets.
Comets normally inhabit the outer regions of the solar system, far
from the Sun, where frigid temperatures keep their ices completely
frozen. There, a comet is just a nucleus, very small and faint,
without the much larger and brighter coma or tail structure.

Occasionally, however, gravity from another solar system object, or
perhaps a passing star, disrupts a comet’s orbit and sends it
hurtling into the inner solar system, where the coma forms. Sunlight
and a stream of electrified gas that blows constantly from the Sun,
called the solar wind, push dust and gas away from the coma in the
direction opposite from the Sun, giving a comet its familiar
tail-like shape.

“Comets are the solar system’s smallest bodies, but among its biggest
mysteries,” says Dr. Joseph Veverka, CONTOUR’s Principal Investigator
from Cornell University, Ithaca, N.Y. “We believe they hold the most
primitive materials in the solar system and that they played a role
in shaping some of the planets, but we really have more ideas about
comets than facts. CONTOUR will change that by coming closer to a
comet nucleus than any spacecraft ever has before and gathering
detailed, comparative data on these dynamic objects.”

CONTOUR’s flexible four-year mission plan includes encounters with
comets Encke (Nov. 12, 2003) and Schwassmann-Wachmann 3 (June 19,
2006), though it can add a study of a “new” comet from the outer
solar system should one be discovered in time for CONTOUR to catch
it. CONTOUR will examine each comet’s “heart,” or nucleus, which
scientists believe is a chunk of ice and rock, often just a few
kilometers across and hidden from Earth-based telescopes beneath a
dusty atmosphere and long tail.

The 8-sided solar-powered craft will fly as close as 100 kilometers
(62 miles) to each nucleus, at top speeds that could cover the 56
kilometers between Washington and Baltimore in two seconds. A 5-layer
dust shield of heavy Nextel and Kevlar fabric protects the compact
probe from comet dust and debris. CONTOUR’s four scientific
instruments will take pictures and measure the chemical makeup of the
nuclei while analyzing the surrounding gases and dust.

The $159 million CONTOUR is the sixth mission in NASA’s Discovery
Program of lower cost, scientifically focused exploration projects.
The Johns Hopkins University Applied Physics Laboratory (APL),
Laurel, Md., manages the mission, built the spacecraft and its two
cameras, and will operate CONTOUR during flight. NASA’s Goddard Space
Flight Center, Greenbelt, Md., provided CONTOUR’E=”utral gas/ion
mass spectrometer and von Hoerner & Sulger, GmbH, Schwetzingen,
Germany, built the dust analyzer. NASA’s Jet Propulsion Laboratory,
Pasadena, Calif., will provide navigation and Deep Space Network
(DSN) support. Cornell’s Veverka leads a science team of 18
co-investigators from universities, industry, and government agencies
in the U.S. and Europe.

CONTOUR is scheduled to lift off from Cape Canaveral Air Force
Station, Fla., on a three-stage Boeing Delta II rocket during a
25-day launch window that opens July 1 at 2:56 a.m. EDT. The
spacecraft will orbit Earth until Aug. 15, when it should fire its
main engine and enter its comet-chasing orbit around the Sun.

NASA TV will provide live coverage of the launch beginning at 1:30 a.m. EDT.

More information on CONTOUR is available on the Web at: