Oljato revisited.

Oljato revisited

In December 1979, when Lucy A. McFadden first examined a mysterious, sun-orbiting object -- now called 2201 Oljato -- she could not discern whether it was a bare, rocky asteroid or a "dying" comet that had lost most of its ice. Ultraviolet observations of the celestial body by McFadden, a physicist at the University of California, San Diego, proved inconclusive, and measurements by other astronomers provided evidence for both possibilities. Now, after re-reviewing her own and other researchers' analyses of the object, McFadden remains uncertain of its origin, but she says the best available evidence argues that "we perhaps should now call [it] a comet."

The object's brightness, which astronomers have measured at different wavelenghts, is "not characteristic of asteroids," she says. Moreover, radar beams bounced off 2201 Oljato's surface do not yield continuous echoes, she notes, thereby indicating that something -- such as an irregular covering of ice -- is absorbing part of the radar's energy. Finally, if Oljato were a comet, vaporization of its ice as it neared the sun would liberate water. McFadden's new calculations of its optical properties fit with the release of 40 kilograms of water per second.