For the first time in astronomical history, an instrumented probe has passed through a comet's tail. From now on, the study of comets will be made in the light of a growing body of knowledge derived from on-site investigation. With its data-transmission tone sounding like an owl's hoot, the International Comet Explorer (ICE) swooped down on comet Giacobini-Zinner at 6:53 a.m. Eastern daylight time Wednesday. Steven P. Maran, a senior scientist here at the Goddard Space Flight Center, pointed out that ICE actually went through the comet's head when it passed within 8,000 kilometers of its nucleus on the side away from the Sun.
NASA Administrator James M. Beggs promptly dubbed it ``one of NASA's prouder moments.''
He explained that, as the ICE data are digested ``we expect the mission . . . to enable us to get better use'' out of the Japanese, European, and Soviet probes that are to intercept Halley's Comet next March.
The part of the comet through which ICE passed turned out to be several times wider than expected. Instead of a four- or five-minute passage, ICE spent 18 minutes in this region, emerging at 7:11 a.m. EDT, giving scientists much more data than they originally hoped to get.
Surprisingly, ICE encountered little or no dust. Flight Director Robert W. Farquhar had warned that cometary dust might severely damage the spacecraft. He was especially concerned that dust would coat ICE's solar cells and rob it of electric power. However, the wavey white line that indicated the solar-cell current on the flight-control monitor screen remained rock-steady.
Obviously pleased that the spacecraft has survived, Dr. Farquahar observed, ``I guess this means we can plan on observing Comet Halley.'' ICE is in an orbit that will position it between the sun and that comet when the Halley's probes arrive next March. It then can provide important information on the solar-wind particles flowing outward from the sun past ICE and Halley's.
Farquhar added that he doesn't know what ICE's survival ``means for my recovery plan.'' He was referring to one of his dream projects to have a space shuttle retrieve ICE when its orbit brings it close to Earth in 2012.
Meanwhile, ICE scientists are ecstatic over the encounter's results. Dr. Edward J. Smith of NASA's Jet Propulsion Laboratory exclaimed, ``Mankind's first encounter with a comet has to be ranked as an unqualified success. The data are full of surprises.''