An assault on comets. (Astronomy).

On July 3, NASA launched a spacecraft that will provide the closest look yet at the core of comets. CONTOUR, which will visit at least two comets during its 4-year mission, is one of three craft that will soon be conducting close-up studies of these icy relics from the birth of the solar system. The craft is set to fly within 100 kilometers of its first target, Comet Encke, on Nov. 12, 2003.

CONTOUR, or Comet Nucleus Tour, is scheduled to dose in on its second target, Comet Schwassman-Wachmann 3, until June 19, 2006. That comet should prove especially interesting to astronomers because in 1995, it broke into several large pieces. CONTOUR will take dose-up pictures and measure the chemical composition of the icy nucleus of both Encke and Schwassman-Wachmann 3, as well as explore their huge shrouds of gas and dust.

In 2004, before CONTOUR's second comet encounter, a spacecraft called Stardust, launched in 1999, will sweep close enough to Comet Wild-2 to collect gas and dust samples and carry them back to Earth. And if all goes according to plan, NASA expects to launch another craft, Deep Impact, in 2004. It will fire projectile into Comet Tempel 1 in 2005 and study debris from the 25-meter-crater it will gouge.--R.C.