Near-Earth asteroid: a far miss.

Improved calculations indicate that the asteroid which grabbed headlines last week has "zero probability" of striking Earth when it passes closest to our planet 30 years from now. Moreover, the asteroid 1997 XF11 will probably come no closer to Earth than 950,000 kilometers, nearly three times the moon's average distance, announced Paul Chodas and Donald K. Yeomans of NASA's Jet Propulsion Laboratory (JPL) in Pasadena, Calif., on March 12.

An estimate reported just a day earlier, based on fewer observations, had placed the 1.6-km-wide body as coming uncomfortably close to Earth -- within 48,000 km -- on Oct. 26, 2028. That's considerably nearer than has been predicted for the orbit of any asteroid of similar size. On the basis of the updated information, the chance of a collision is indeed zero, agrees Brian G. Marsden of the Harvard-Smithsonian Center for Astrophysics in Cambridge, Mass. He reported his initial and revised estimates in the March 11 and 12 circulars of the International Astronomical Union.

The newer calculations take into account recently uncovered images containing the asteroid taken in March 1990 by Eleanor Francis Helin of JPL and her colleagues, well before the asteroid was reported late last year. Shortly after researchers at the University of Arizona's Spacewatch program first spied the body on Dec. 6, 1997, and well before the detailed calculations of its future orbits, the asteroid's relatively large size and near-Earth orbit prompted astronomers to place it on a list of potentially hazardous objects.