At any given time, astronomers now estimate our moon has at least one companion—a much smaller second moon in orbit around Earth.
Only one of these moons has thus far been detected, but theoretical astronomy suggests that asteroids slip into Earth orbit comparatively frequently, but then spin back into space as the complex gravities of the Sun, the Moon and Earth jerk it this way and that.
(Image: The line drawing is the simulated orbit of a mini-moon. The photo is an asteroid that shows what such a moon might look like—oddly shaped with pockmarks from impacts with other objects. Credit: K. Teramura, University of Hawai`i Institute for Astronomy.)
Researchers from the University of Hawai`i Institute for Astronomy, the University of Helsinki and the Paris Observatory recently published their work, “The population of natural Earth satellites,” in the journal “Icarus.” The authors are Mikael Granvik, Jeremie Vaubaillon, and Robert Jedicke.
A news release on the report is here.
Each off these temporary moons is thought to be not much more than three feet across, and they may stay in orbit for on average less than a year, although some could remain in orbit around the Earth for much longer, perhaps even decades.
Only one has ever been actually detected. That was in 2006, when the University of Arizona’s Catalina Sky Survey discovered one it called 2006 RH120. The asteroid was about the size of an automobile and it returned to solar orbit after spinning around our planet for several months.
The scientists used a supercomputer to do a massive calculation of the orbits of 10 million asteroids that pass near the Earth, and concluded that at any given time, at least one of them would be in Earth orbit, generally following a wildly twisting path, caused by the competing gravities of the larger objects in our solar system.
© Jan TenBruggencate 2011
