Space Junk Moonlets

Q: About all the space junk (old satellites and so on) orbiting the Earth: Will this material ever coalesce into a moon? How long might it take for this to happen?
Eric, Albuquerque, New Mexico

A: Your question — can space junk now orbiting the Earth ever coalesce into a moon — is an interesting idea. But, no, it can't because the space-junk mass is too small to generate enough gravity to draw the mass together. Also, there is such a scattering of junk in orbit that few pieces manage to snuggle up next to each other in close orbits. Moreover, they've got to get that close so gravity can pull the fragments into a larger mass. It just won't work.

To get a rough idea of the amount of junk in orbit around Earth, I checked Space Command's space surveillance site. The fact sheet lists 8,300 man-made space objects (baseball size and larger) in orbit. About 600 of these objects are operational satellites, the rest are inactive satellites, payloads, platforms, rocket bodies, and plain debris: such as, nose-cone shrouds, lenses, or hatch covers.

About 90 percent of the space junk is too close to the Earth (closest point of its orbit within 16,000 km or 10,000 mi) to withstand the effects of tidal gravitational forces. These unfortunate pieces can never collect into a cohesive body because the Earth's tidal forces constantly work at pulling any such body apart. That leaves only 830 hunks of space junk for moonlet candidates. Eight hundred or so pieces are too small in both mass and numbers — by orders of magnitudes — to pull together into another moon.

Further Surfing:

Orbital space debris, SpaceRef.com

(Answered Oct. 4, 2002, updated Sep. 20, 2007)