Astronomers have announced that a large asteroid on a trajectory heading toward the vicinity of Earth will, in fact, pass no closer to the planet than about 600,000 miles (about 966,000 kilometers). The announcement brought sighs of relief to the general public and scientific community, both of which had been in a frenzy since an earlier announcement suggested the space rock would pass much closer and possibly collide with the Earth. Such an impact would have catastrophic implications for the planet. Much evidence exists to indicate that ancient bombardment of the Earth by asteroids and comets may have precipitated mass extinctions of dinosaurs and other species.

An announcement on March 11 that the asteroid would pass within about 30,000 miles (48,280 kilometers) of the Earth in the year 2028 sparked fear among the public and debate within the scientific community. While the general public learned about the degree of devastation the impact of such an object would cause-including tidal waves, dust clouds that would cause significant global cooling, and disruption of agriculture-astronomers debated the probability of an earthly impact, while other scientists began to discuss the possibility of intercepting and destroying the space rock before it could cause damage.

The initial announcement, made by Brian G. Marsden, director of the Central Bureau for Astronomical Telegrams in Cambridge, Mass., sparked a debate with a colleague at the Jet Propulsion Laboratory in Pasadena, Calif. Marsden, who is regarded as one of the leading authorities on the movement of asteroids, announced that the asteroid-which is called 1997 XF11-would come within 30,000 miles (48,280 kilometers) of the Earth on Oct. 26, 2028. It was further suggested that there was a strong risk of the asteroid hitting the Earth. His views were challenged by Donald Yeomans at the Jet Propulsion Laboratory, who claimed that his analysis of the path of the object indicated that it would pass no closer than about 54,000 miles (86,900 kilometers); Yeomans later recalculated the path of the object and announced an approach of no closer than about 600,000 miles (966,000 kilometers) from Earth.

By the end of the week, photos of the asteroid that had been taken by a camera at the Palomar Observatory in 1990 helped both groups of astronomers to refine their estimates of the trajectory of the asteroid. By measuring the movement of the space rock between four points, they reached an agreement regarding the future behavior of the object, concluding that the asteroid would not come closer to the Earth than about 600,000 miles. This distance is more than twice the distance between the Earth and the moon.

Scientists planned to continue to study the asteroid, but the next chance to measure it was not expected to take place until the year 2000, after the asteroid completed a 21-month orbit around the sun. The interim was to be spent studying the data already available, as well as debating strategies to possibly intercept the object if it does range too close for comfort.