Pioneer to Track New-Found Comet on Space Trek

Pioneer 12, which has been orbiting the planet Venus, began a new mission Saturday when NASA officials directed the durable spacecraft to begin tracking the newly discovered Comet Wilson in its dash by Venus on the way to the sun.

Controllers at NASA’s Ames Research Center in Mountain View said they will use Pioneer 12 to track Wilson for seven days, then stop for 10 days when the comet dips beneath the plane of the solar system and the spacecraft’s field of view.

Pioneer 12 will resume observations March 31 and continue until April 30. This period, officials said, includes the comet’s closest approach to the sun on April 20. The comet will be tracked for 20 hours a day.

Wilson was discovered in August by Christine Wilson, a doctoral candidate at Caltech. It is thought to be a “fresh” comet embarking on its first visit to the solar system.

Fresh comets, officials said, are of special interest to researchers because they have not been modified by the sun. These comets, they said, provide a better record of primitive conditions in the solar system.

Pioneer 12’s task will be to measure the rate of water evaporation from the comet’s nucleus and the amount of carbon and oxygen emitted. It will accomplish this by studying the comet in the ultraviolet portion of the electromagnetic spectrum.

The spacecraft’s observations may also indicate the rate of rotation of the comet’s nucleus. Added to Pioneer’s data on other comets of varying ages, the observations will provide information on how comets change over time.

The Wilson observation will mark the fourth time Pioneer 12, which has observed Venus since 1978, has studied a comet. The spacecraft was used to study Halley’s in 1986, Giacobini-Zinner in 1985 and Encke, a comet near the end of its life, in 1984. Pioneer is scheduled to observe Encke again when the comet reenters the inner solar system in June and July.