They wander two by two across the cosmos
Photo courtesy of NASA

Binary asteroids are a pair of asteroids orbiting each other in a two-body system astronomers are currently developing theories on to explain their formation. Astronomers are presently studying binary asteroids in an effort to both confirm recent theories and develop new ones.

Astronomers recently took a closer look at the relative brightness of 35 binary asteroids, in order to determine the relative sizes, spin rates and shape of each asteroid pair. Backtracking along the orbit of each binary asteroid 1 million miles, they also determined 31 of the asteroid pairs studied came together sometime in the past.

Examining the 31 asteroid pairs they believe came together sometime during the past, astronomers determined that for each asteroid pair the smaller asteroid is consistently 60 percent less than the size of the larger asteroid. Astronomers believe this coincides with rotational fission theory first suggested in 2007 in explain the formation of binary asteroids.

The rotational fission theory postulates that sunlight striking the surface of an asteroid can increase rotational velocity of a smaller stellar body. Astronomers believe that if enough rotational velocity is added this could provide enough force to split an asteroid into two separate pieces orbiting each other.

Computer simulations of binary asteroids seem to indicate that is the asteroid in question breaks into two smaller pieces, with one asteroid being no more than 60 percent of the size of the other, they'll begin orbiting one another. The computer simulations also indicate that if the smaller asteroid is 60 percent less than the size of the larger asteroid in the binary asteroid pair. The asteroid pair created during rotation fission will separate and head off on their own. Astronomers believe this could indicate a range of size required for the formation of binary asteroids in our solar system.