When thinking of a comet it is natural to remember Halley's Comet because it is so famous and usually easy to view during regular visits to Earth.

There are many other comets some that are new visitors to our part of the Solar System. One of them is Comet Wild 2, which did not pass close to Earth until 1974, when the power of Jupiter's gravity changed its orbit. It now travels much closer to the sun, between Jupiter and the Earth. Because it has not been exposed to the Sun at close range, its composition has not been altered much from its original condition. By the time Stardust encounters it, Comet Wild 2 will have made only five trips around the sun. By contrast, Comet Halley has passed the sun more than 100 times, coming close enough to have been greatly altered from its original condition.

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

Since Wild 2 has passed the sun only a few times, it still has most of its dust and gases and it is relatively pristine condition. 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 may hold the key to understanding the early development of the Solar System. Comet Wild 2 should contain much of this ancient material, making it an ideal choice for study.

An important aspect of the journey of Comet Wild 2 is the fact that it will be in the right place at the right time for a visit. Particularly helpful for the purposes of the Stardust mission is that scientists were able to plot the spacecraft's flight path to encounter the comet during a period of comparatively low speed. Because of this low velocity meeting, the spacecraft can capture comet dust, rather than having it blow right through the collectors. The dust samples can then be brought back to the Earth to be analyzed.