New observations are now available for asteroid 1999 AN10, which is gradually moving away from the glare of the Sun. The new data allow a considerably improved orbit to be calculated for this potentially hazardous object, and the revised predictions indicate that this kilometer-size asteroid could pass particularly close to the Earth on August 7, 2027. The passage in 2027 could be as close as 37,000 km from the Earth’s center (just 19,000 miles above the Earth’s surface), but no closer. The miss distance is still very uncertain, and the asteroid could easily pass well outside the Moon’s orbit. The probability of a collision in 2027 is essentially zero.
The accompanying diagram shows the uncertainty in the predicted close approach in 2027. The asteroid must pass through the plane of the diagram somewhere within an extremely elongated uncertainty ellipse, which appears simply as a line segment. (To be precise, the ellipse as drawn is a three-sigma linear confidence boundary.) The center of the ellipse is indicated by the plus sign, which is located at a nominal distance of 58,000 km from the center of the Earth. The minimum distance between the ellipse and the Earth center is 37,000 km.
There is still a very remote possibility that asteroid 1999 AN10 could pass by Earth in 2027 in such a way as to return in the year 2039 on an impacting trajectory. First identified by researchers Andrea Milani, Steven R. Chesley and Giovanni B. Valsecchi, this scenario is still exceedingly unlikely, but the probability of collision in 2039 has now increased to about 1 chance in 10 million. The post-2027 (Monte Carlo) analysis of this object’s motion will continue.
Paul W. Chodas
Near Earth Object Program Office
Jet Propulsion Laboratory
May 18, 1999