Comet Wild 2 Is Unique Because

• IT IS NEW to the inner solar system.

• IT IS IN PRISTINE CONDITION--By the date of encounter, it will have passed the sun only 5 times.

• IT IS IN THE RIGHT PLACE at the right time.

A FRESH COMET

Periodic comet Wild 2 is new to the inner solar system. Before 1974, the comet was no closer to the sun than Jupiter's orbit. But when Wild 2 flew by Jupiter in 1974, the massive planet's gravitational force changed the comet's orbit . Because of that, it now travels closer to the sun, between Jupiter and the Earth. By the time STARDUST encounters the comet, Wild 2 will have made only five trips around the sun. By contrast, Comet Halley has passed the sun more than 100 times.

5 TIMES A CHARM

When a comet comes close enough to the sun to get heated up, it loses some of its material through the process of sublimation (when a solid becomes a vapor without first melting into a liquid). After about 1,000 trips past the sun, the comet loses most of these volatile materials and no longer generates a coma (the coma is made up of the gases that sublime off the surface). Since it is the escaping gases that drive the dust particles from the nucleus (solid part of the comet), the comet no longer creates the long beautiful dust tail that we can see in the sky.

Since Wild 2 has passed the sun only a few times, it still has most of its dust and gases -- it is "pristine". This is important because comets are made up of material left over from the solar nebula after the planets were formed. Unlike the planets, most comets have not changed very much since the formation of the solar system. Therefore, comets hold the key to understanding the early development of the solar system. Wild 2 should contain much of this ancient material, making it an ideal choice for study.

RIGHT PLACE AT THE RIGHT TIME

Wild 2 presents a unique opportunity -- it is in the right place at the right time. Scientists have found a trajectory (flight path) in which the spacecraft will fly by the comet at a relatively low speed. Because of this "low velocity flyby", comet dust can be captured by collectors on the spacecraft, rather than blowing right through the collectors and out the back side! This comet dust can then be brought back to the Earth to be analyzed.

Ron Baalke, STARDUST Webmaster, ron@jpl.nasa.gov
Last Updated Wednesday, 07-Jun-2000 13:50:34 PDT