Binary Asteroids

Up until the late 1990's, it was not generally believed that asteroids could have satellites. Since then, through international collaborations between professional and amateur astronomers, many dozens of binary asteroids have been found.  It is now understood that approximately 15% of all Main Belt asteroids have a companions.  Theories propose the YORP effect, the result of solar radiation emitting from the nighttime side of asteroids give it a little kick - speeding up the rotational period over millions of years until the asteroid spins so fast that material lifts from the equator forming into a satellite.  The satellite then provides a breaking effect slowing down the rotational period.  The detection of these binaries provides important facts in confirming the existence of the YORP effect. 

Since 2006, Bob Stephens has contributed to the Photometric Survey for Asynchronous Binary Asteroids program run by Petr Parvec, an astronomer in the Czech Republic.

The asteroid 2074 Shoemaker is thought to be a binary.  Observations by Bob Stephens in 2003 show a characteristic dimming from a probable occulation by a companion satellite.