According to NASA, an asteroid, designated 2004 BL86, will safely pass about three times the distance of Earth to the moon today, Monday, January 26, 2015. The flyby will be the closest by any known space rock this large until 2027. While not a danger to the planet, UMass Dartmouth Physics Professor Alan Hirshfeld discusses this rare instance of an asteroid passing this close to Earth.
How rare of an opportunity is to see an asteroid this close to Earth? How often do asteroids this size come close to Earth?
AH: Asteroids commonly pass close to the earth, but most of them are extremely small -- the size of a house, perhaps -- and pass without notice. Astronomers estimate that maybe several dozen such asteroids pass by Earth each year without being detected. A few of the larger ones are randomly captured on photographs, either as they are heading in toward Earth or heading out away from Earth. The asteroid, called 2004 BL86, that is coming on the night of January 26-27 is relatively large, as Earth-passing asteroids go -- about half a kilometer across. It might be visible through a small telescope if one knows where and when to look. Even at its closest, the asteroid will be three times farther than the moon is from Earth, so it poses no danger of collision with us.
Scientists are eager to study this asteroid as it passes earth. What are they looking to find?
AH: There is probably not much that astronomers can learn about the physical nature of the asteroid as it zips by that they haven't already learned from spacecraft that have visited asteroids. From its brightness as it passes, they will certainly pinpoint its size and have a better handle on the shape of its orbit in the solar system.
How were scientists able to see this coming 10 years ago?
AH: The asteroid was discovered in 2004 as part of MIT's near-earth asteroid survey program. Once discovered, an asteroid is tracked and its orbit in the solar system determined with great accuracy. We certainly want to know whether there are any asteroids that pose a collision danger with Earth. Although exceedingly rare, such collisions can inflict global damage on the environment.
How are we able to predict that another near-Earth asteroid of this size will not arrive until 2027?
AH: The asteroid that will pass close in 2027 had likewise been discovered years ago and its orbit is well known. Of course, there's always a chance that a previously unseen asteroid will pass by before that, but that is a random event that cannot be predicted.
About Alan Hirshfeld
Professor Alan Hirshfeld conducts research in the history of physics and astronomy. He is the author of "Parallax: The Race to Measure the Cosmos," published by Henry Holt & Co. in 2002, "The Electric Life of Michael Faraday," published by Walker & Co. in 2006, the "Astronomy Activity and Laboratory Manual," published by Jones & Bartlett Publishers in 2008, "Eureka Man: The Life and Legacy of Archimedes, published by Walker & Co. in 2009, and "Starlight Detectives: How Astronomers, Inventors, and Eccentrics Discovered the Modern Universe," published by the Bellevue Literary Press in 2014. Hirshfeld is the director of the UMass Dartmouth Observatory and has been named an Associate of the Harvard College Observatory.