The Asteroid Patrol

ONCE A MONTH, AS THE MOON WANES, GEOLOgist Eugene Shoemaker, 64, and his wife Carolyn, 63, leave their house in Flagstaff, Arizona, load warm clothes into their station wagon and set off to the west on an 800-km (500-mile) trip across the desert. Their destination: Palomar Mountain, site of the mighty Hale telescope, among others. There, using a smaller Schmidt telescope, they begin a seven-night stint of sentry duty.

The intruders they watch for are Earth-crossing asteroids, giant rocks that have strayed from their neighborhood between the orbits of Mars and Jupiter and periodically pass close to Earth -- and sometimes smash into it. The vigil has paid off. Over the years, the couple have discovered more than 300 asteroids, some of which they have named after their children, grandchildren and in-laws. About 10% of their discoveries are ECAs, but none is currently in an orbit that puts it on a collision course with the earth. Still, the Shoemakers keep looking: lurking somewhere out there may be a hulk with bad intentions.

Unlike Gene, who works for the U.S. Geological Survey, Carolyn is unsalaried. "Nepotism rules say that I cannot be employed by the USGS," she explains, "because I work with Gene." But as an amateur astronomer, she has earned a prestigious fringe benefit; while looking for asteroids, she has discovered 28 comets, more than anyone except Jean-Louis Pons, an early 19th century French astronomer, who may have spotted as many as 37.

During their frigid all-nighters on Palomar Mountain, Gene guides the telescope, shooting two pictures, 40 min. apart, of each patch of sky. After developing the film in the observatory darkroom, he turns the negatives over to Carolyn, who scans each set of two under her stereo microscope. If anything has moved against the background of fixed stars during the 40-min. interval, it appears to float in the eyepiece. If so, it is an asteroid or comet and might someday present a threat.

Gene sensed that threat early in his career. Looking at the moon while a graduate student at Princeton, he was convinced that it had been pockmarked not by explosive volcanism, as many geologists then thought, but by asteroid impacts. If that was true, he felt, Earth, a much larger target, must have been heavily bombarded too. For his Ph.D. thesis, Shoemaker prepared a & geologic map of Meteor Crater in Arizona, and in the process confirmed that it had resulted from an impact.

In 1973 Shoemaker, with geologist Eleanor Helin, began the world's first systematic Earth-crossing-asteroid watch. When Helin left in 1982 to launch her own asteroid search, Carolyn, her three children grown, joined Gene. Since then they have been on the alert -- and on the run. Last fall, for example, they went to a conference in Ontario at the site of the 1.8 billion-year-old Sudbury Crater, which is 300 km (188 miles) wide. From there, they flew to Iowa City, Iowa, where Gene examined core samples from the nearby Manson Crater, 35 km (22 miles) across and about 65 million years old and perhaps made by a chunk of the comet that killed the dinosaurs. Then, after a weekend back in Flagstaff, the Shoemakers departed for their annual one-month field trip in the Australian Outback, where the ancient and stable land surface, peppered with craters of all ages, is a happy hunting ground for geologists.

Like the objects he studies, Gene has made an impact. For his pioneering "research on Earth-approaching asteroids and comets" and other accomplishments, he was awarded the National Medal of Science last year. "Nobody believed Chicken Little when he said the sky was falling," Shoemaker says. "But occasionally the sky does fall, and with horrendous effects."