The craft did not report in after a critical engine burn this morning designed to send it out of Earth orbit and on toward close encounters with two or possibly three comets.

Among CONTOUR's goals is to examine the diversity of comets, objects that experts say are still highly mysterious. One question astronomers have regards the range of compositions in these frozen objects. The answers would open windows to how the solar system evolved.

"It's hard to find two more diverse comets" than Encke and Schwassmann-Wachmann 3, CONTOUR's two primary targets, said comet expert Donald Yeomans of NASA's Jet Propulsion Laboratory.

"It would be pretty sad" if the craft does not complete its mission," Yeomans said in a telephone interview today. "If we had to go without it we would be losing a significant amount of comet science."

CONTOUR (short for Comet Nucleus Tour) is a $159 million NASA-led project built and operated by the Applied Physics Laboratory (APL) at Johns Hopkins University.

APL is similar to JPL -- it employs both astronomers and engineers and can run nearly all aspects of an entire mission from start to finish. However, APL is much smaller and not directly affiliated with NASA. The loss of even one spacecraft would involve a much larger missing chunk out of APL's space program compared to JPL.

If CONTOUR continues its mission, it would pass within 62 miles (100 km) of comet Encke and take pictures as sharp as 13 feet (4 meter) per pixel in November 2003. This is 10 times sharper than images produced by Deep Space 1, which passed within about 1,400 miles (2,200 km) of comet Borrelly last year. The Borrelly images are said to be the best comet photos ever.

Astronomers have very few close-up pictures of comets, and theories about comet composition are based on thin data. A nucleus of a comet is thought to harbor material that hasn't changed since the solar system's birth.

CONTOUR carries a sophisticated dust analyzer that would investigate what kind of carbon-based molecules are in the two comets.

If the craft were lost, it would not likely be replaced soon. Mission proposals can take years, even a decade or more just to wind through the NASA approval process.

Yeomans said if it became necessary to mount a replacement mission, other comets might have to be chosen because CONTOUR's targets are moving and might not be in favorable locations five or ten years from now.

CONTOUR was still silent as of 2:30 p.m. EDT today, but its fate is not yet known. Officials at APL and NASA were still working to find the spacecraft, whose signals would be picked up by the Deep Space Network if the craft sends any.

More Comet News | Astronotes