Scientists have discovered another pair of asteroids locked in orbit around each other. Scientists believe there are many paired asteroids in our solar system. Orbital observations will allow astronomers to determine the mass, density, composition, and porosity of each member of the pair.

The spacecraft Galileo discovered the first binary asteroids Ida 243 and its tiny moon Dactyl in 1993 while on its way to Jupiter. Another seven pairs are suspected but haven’t been confirmed.

Some of the pairs are nearly twins in size. Some are more lopsided and probably formed from the larger asteroid being chipped in a collision. Some may be remnants of extinct comets.

Observations of paired craters on the Earth and other bodies led astronomers to suspect that binary asteroids existed. On Earth, the craters are of equal age and are too large and too far apart to have been formed by a single asteroid breaking up in the atmosphere.

Czech astronomer Petr Pravec believes the importance of studying the binary asteroids is increasing. Scientists need to devise ways to protect the Earth from catastrophic collisions from space. Comets and asteroids can be on collision courses with Earth. Now scientists have to plan for the possibility of two asteroids arriving at the same time. Pairs would be harder to divert from a collision course than a single body, making pairs a new threat.