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.
