Results from NASA’s Hubble Space Telescope played a major role in
preparing ESA’s ambitious Rosetta mission for its new target, comet
67P/Churyumov-Gerasimenko (67P/C-G). For the first time in history,
Rosetta will land a probe on a comet and study its origin. Hubble
precisely measured the size, shape, and rotational period of comet
67P/C-G.

Hubble’s observations revealed that comet 67P/C-G is approximately a
three-by-two mile, football-shaped object on which it is possible to
land. Mission scientists were concerned that the solid nucleus could be
nearly 3.6 miles (6 km) across. The higher gravity on a comet that size
might make a soft landing more difficult. “Although 67P/C-G is roughly
three times larger than the original Rosetta target, its elongated shape
should make landing on its nucleus feasible, now that measures are in
place to adapt the lander package to the new configuration before next
year’s launch,” says Dr. Philippe Lamy of the Laboratoire d’Astronomie
Spatiale in France. Lamy is presenting the Hubble results on comet
67P/C-G on Sept. 5, 2003 at the annual meeting of the Division of
Planetary Sciences of the American Astronomical Society in Monterey,
Calif.

Mission scientists began considering the new target when the Rosetta
mission’s launch date was postponed. The delay made the original target
comet, 46P/Wirtanen, no longer easily reachable. But scientists did not
have enough information on the new target, comet 67P/C-G, and sought
data from the largest telescopes. Using a technique developed over the
past decade by Lamy, Imre Toth (Konkoly Observatory, Hungary), and
Harold Weaver (Johns Hopkins University Applied Physics Laboratory,
Laurel, Md.), the team snapped 61 Hubble images of comet 67P/C-G over an
interval of 21 hours between March 11 and 12, 2003. Hubble’s Wide Field
Planetary Camera 2 isolated the comet’s nucleus from the coma, the
diffuse cloud of dust and gas surrounding the nucleus, and quickly
provided the missing figures. The telescope showed that the nucleus has
an ellipsoidal shape. Hubble also measured its rotation rate of
approximately 12 hours. Rosetta’s launch is currently planned for
February 2004, with a rendezvous with the comet about 10 years later.

The Hubble observing team members are P.L. Lamy and L. Jorda
(Laboratoire d’Astronomie Spatiale, France), I. Toth (Konkoly
Observatory, Hungary), and H.A. Weaver (Johns Hopkins University Applied
Physics Laboratory). The movie simulation of the Hubble results is
provided by Mikko Kaasalainen (University of Helsinki, Finland) and
Pedro Gutierrez (Laboratoire d’Astronomie Spatiale, France). The
observations were made possible through a special program approved by
the Director of the Space Telescope Science Institute, S. Beckwith.

Electronic images, a movie, and additional information are available at

The Space Telescope Science Institute (STScI) is operated by the
Association of Universities for Research in Astronomy, Inc. (AURA), for
NASA, under contract with the Goddard Space Flight Center, Greenbelt,
MD. The Hubble Space Telescope is a project of international cooperation
between NASA and the European Space Agency (ESA).