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Mile-wide Asteroid to Pass Closer than Moon's Orbit in 2028 Recent orbit computations on an asteroid discovered last December indicate it is virtually certain that it will pass within the moon's distance of the earth a little more than 30 years from now. The chance of an actual collision is small, but one is not entirely out of the question. The asteroid, known as 1997 XF11, was discovered by Jim Scotti in the course of the Spacewatch program at the University of Arizona. This program utilizes modern electronic technology on a 36-inch telescope at Kitt Peak that was built 77 years ago. After the discovery observations on December 6, observations made by two Japanese amateur astronomers during the following two weeks showed that the minimum distance between the orbits of 1997 XF11 and the earth was very small. Given also that the object was quite large as earth-approaching asteroids go, perhaps one mile across, it was added to the list of "potentially hazardous objects" (PHAs) that need to be monitored, lest they are destined to come dangerously close to the earth over the course of the next several centuries. There are currently 108 PHAs. As astronomers continued to gather data on 1997 XF11, it slowly began to become apparent that there would be a particularly close approach to the earth in October 2028. A computation from observations spanning 60 days suggested that the miss distance would be 500 thousand miles. This distance may seem large in human terms, but it was less than had previously been predicted in advance for any other known asteroid during the foreseeable future. Observations made on March 3 and 4 by Peter Shelus with a 30-inch telescope at the McDonald Observatory in western Texas extended the observed arc of 1997 XF11 to 88 days. This time, the orbit computation indicated a miss distance of only 30 thousand miles from the center of the earth; the earth's radius is about 4 thousand miles. The time of encounter would be around 1:30 p.m. Eastern Daylight Time on Thursday, October 26, 2028. That evening the object should be visible with the naked eye. In Europe, where it would be dark by that time, the object should be a splendid sight as it moves from northwest to southeast across the sky over a couple of hours. There is still some uncertainty to the computation. On the one hand, it is possible that 1997 XF11 will come scarcely closer than the moon. On the other hand, the object could come significantly closer than 30 thousand miles. Further observations are necessary in order to refine the figures. It is also possible that prediscovery observations of 1997 XF11 can be located on archival photographs. Particularly favorable opportunities for recording the object would have occurred in 1990, 1983, 1976, 1971 and 1957. Ephemerides for these times are available. It is hoped that continuing observations will be made during the next few months. The object is starting to move into the dusk and to fade week by week. Nevertheless, it should be quite accessible for a while with large telescopes, which in addition to helping establish whether a collision in 2028 is possible, could usefully provide more definite information about the object's size. Further observations of 1997 XF11 should be possible with moderate-sized telescopes equipped with electronic sensors early in the year 2000. A better opportunity will occur in late 2002, when the object should be detectable with quite modest telescopes. On that occasion the closest approach will be on Halloween, but the miss distance will be a safe 6 million miles.
Jet Propulsion Laboratory Aateroid Will Miss Earth by "Comfortable Distance" in 2028 Asteroid 1997 XF11 will pass well beyond the Moon's distance from Earth in October 2028 with a zero probability of impacting the planet, according to astronomers at NASA's Jet Propulsion Laboratory, Pasadena, CA. The asteroid "is predicted to pass at a rather comforable distance of about 600,000 miles (about 960,000 kilometers) in 2028," reported Dr. Donald K. Yeomans and Dr. Paul W. Chodas, JPL scientists who specialize in computing the predicted orbits of comets, asteroids, planets and other bodies in the solar system. Data on the asteroid from March 1990 (well before its discovery in December 1997) was integrated into the orbit calculations by Yeomans and Chodas to arrive at the distance the asteroid will pass Earth. The 1990 observations of the object were found today in the Palomar Planet Crossing Asteroid Survey conducted at Caltech's Palomar Observatory, by JPL's Eleanor Helin and Ken Lawrence and by Brian Roman, formerly of JPL. Even prior to the discovery of the earlier Palomar observations, however, Yeomans and Chodas had determined that the impact probability would be zero. The new calculations further underscore that conclusion, they said. For more information, please visit the Asteroid 1997 XF11 web page at: http://ssd.jpl.nasa.gov/ca_97xf11.html
JPL is a division of the California Institute of Technology.
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