Comets are among the most beautiful and least understood nomads of
the night sky. To date, half a dozen of these most heavenly of heavenly
bodies have been visited by spacecraft in an attempt to unlock their
secrets. All these missions have had one thing in common: the high-speed
flyby. Like two ships passing in the night (or one ship and one icy
dirtball), they screamed past each other at hyper velocity -- providing
valuable insight, but fleeting glimpses, into the life of a comet. That
is, until Rosetta.
NASA is participating in the European Space Agency's Rosetta mission,
whose goal is to observe one such space-bound icy dirt ball from up
close -- for months on end. The spacecraft, festooned with 25
instruments between its lander and orbiter (including three from NASA),
is programmed to "wake up" from hibernation on Jan. 20. After a
check-out period, it will monitor comet 67P/Churyumov-Gerasimenko as it
makes its nosedive into, and then climb out of, the inner solar system.
Over 16 months, during which old 67P is expected to transform from a
small, frozen world into a roiling mass of ice and dust, complete with
surface eruptions, mini-earthquakes, basketball-sized, fluffy ice
particles and spewing jets of carbon dioxide and cyanide.
"We are going to be in the cometary catbird seat on this one," said
Claudia Alexander, project scientist for U.S. Rosetta from NASA's Jet
Propulsion Laboratory in Pasadena, Calif. "To have an extended presence
in the neighborhood of a comet as it goes through so many changes
should change our perspective on what it is to be a comet."
Since work began on Rosetta back in 1993, scientists and engineers
from all over Europe and the United States have been combining their
talents to build an orbiter and a lander for this unique expedition.
NASA's contribution includes three of the orbiter's instruments (an
ultraviolet spectrometer called Alice; the Microwave Instrument for
Rosetta Orbiter; and the Ion and Electron Sensor. NASA is also providing
part of the electronics package for an instrument called the Double
Focusing Mass Spectrometer, which is part of the Swiss-built Rosetta
Orbiter Spectrometer for Ion and Neutral Analysis instrument. NASA is
also providing U.S. science investigators for selected non-U.S.
instruments and is involved to a greater or lesser degree in seven of
the mission's 25 instruments. NASA's Deep Space Network provides support
for ESA's Ground Station Network for spacecraft tracking and
navigation.
"All the instruments aboard Rosetta and the Philae lander are
designed to work synergistically," said Sam Gulkis of JPL, the principal
investigator for the Microwave Instrument for Rosetta Orbiter. "They
will all work together to create the most complete picture of a comet to
date, telling us how the comet works, what it is made of, and what it
can tell us about the origins of the solar system."
The three NASA-supplied instruments are part of the orbiter's
scientific payload. Rosetta's Microwave Instrument for Rosetta Orbiter
specializes in the thermal properties. The instrument combines a
spectrometer and radiometer, so it can sense temperature and identify
chemicals located on or near the comet's surface, and even in the dust
and ices jetting out from it. The instrument will also see the gaseous
activity through the dusty cloud of material. Rosetta scientists will
use it to determine how different materials in the comet change from ice
to gas, and to observe how much it changes in temperature as it
approaches the sun.
Like the Microwave for Rosetta Orbiter, the Alice instrument contains
a spectrometer. But Alice looks at the ultraviolet portion of the
spectrum. Alice will analyze gases in the coma and tail and measure the
comet’s production rates of water and carbon monoxide and dioxide. It
will provide information on the surface composition of the nucleus, and
make a potentially key measurement of argon, which will be a big clue
about what the temperature was in the primordial solar system when the
comet's nucleus originally formed (more than 4.6 billion years ago).
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