Chances are Prof. Sushil Atreya is anticipating Christmas more
than you are. He already knows what he wants: a couple of dust
particles, some gas samples, and, if he has been really good, some
hydrocarbon-chain molecules. The only catch is that these
substances are some 600 million miles away from Earth.

Beth Dykstra
(Photo courtesy of NASA)

On Dec. 25, the Cassini orbiter will release its Huygens probe
for a freefall descent into Titan, the largest of Saturn’s
moons. Then, on board the probe, a crucial component designed by
Atreya, a professor in the University’s Department of
Atmospheric, Oceanic and Space Sciences, will begin collecting

The Cassini-Huygens mission was launched seven years ago —
the result of a collaborative effort between NASA and its European
equivalent, the European Space Agency, composed of 17 different

After more than two billion miles of interplanetary travel and
accelerated by the gravities of Venus, Earth and Jupiter, the
Cassini orbiter shot through a precise gap in Saturn’s rings
and finally sidled into orbit around the planet in July.

Several scientists in AOSS played leading roles in the design
and construction of instruments included on the Cassini orbiter and
Huygens probe.

Prof. Tamas Gombosi, chair of the department, said, “(The
University) has the greatest university involvement in
Cassini.” Over 20 members of AOSS play leadership roles such
as principal investigators, co-investigators and team leaders of
various projects within the mission.

An interdisciplinary scientist in magnetosphere and plasma
physics, Gombosi will study Saturn’s ionosphere, a large
magnetic region around the planet composed of charged particles. He
hopes that studying this region will lead to a greater
understanding of Earth’s own magnetic fields.

AOSS Prof. Andrew Nagy will use radioscientific methods to
determine the composition of Titan and Saturn’s atmospheres.
Radio waves beamed back at Earth will pass through Saturn’s
atmosphere and be altered in a measurable way, which gives the
chemical signature of the compounds present, Nagy said. This may
help explain the presence of five to 10 times more water in
Saturn’s ionosphere than previously expected.

Atreya will have to wait a few more months for the instrument of
his expertise, the gas chromatograph mass spectrometer to come
online. It is part of the Huygens probe that will be released onto
Titan on Christmas Day. During its three weeks of descent onto the
surface of the moon, it will sample gaseous and solid particles in
Titan’s atmosphere.

The thick atmosphere and the presence of
“pre-biotic” carbon molecules on the natural satellite
make it especially interesting to scientists. “Titan has all
the constituents of life that primordial Earth had,” Atreya

The extreme cold of Titan’s surface, however, makes it
unlikely to harbor life. Even the instruments themselves need
thermal blankets and a radioactive heat source to stay operational
in the harsh –300 degree Fahrenheit environment. It also
provides shielding from potentially disastrous impacts with

The payoffs of exploration in such a forbidding environment are
promising, Atreya said. Saturn’s rings of gaseous and solid
material are analogous in structure to the early solar system and
may shed light on the processes of collisions and coalescing that
form planets.

Marking the beginning of NASA’s “faster, better,
cheaper” mission philosophy, Cassini-Huygens still cost a
substantial $3 billion. In addition, the orbiter is larger than
previous solar system explorers — its fuel source alone is
more massive than the Galileo and Voyager spacecrafts combined.

Besides driving technological change, “there are always
several ways to justify costs,” said Gombosi, who goes on to
cite the figure that “for every $1 NASA spends, the national
economy benefits $10.” The University did not contribute
money to the mission, though — “only

Currently, Cassini-Huygens has completed only the first of its
76 planned orbits around Saturn. The orbiter has so far met with
early success: During its flyby of Jupiter, other members of the
AOSS participated in taking measurements of Jupiter.

The release of the Huygens probe into Titan will be the
orbiter’s next great challenge, Atreya said. But he still
keeps it simple. At the end of the day, he said, he’s just
“trying to drop things onto a planet.”

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