Earth’s Other Moons

Earth usually has more than one moon, according to a team of astronomers from the University of Helsinki, the Paris Observatory and the University of Hawaii at Manoa.

It appears that the Earth captures a small asteroid ( or more than one) each year.  Either the asteroid enters the atmosphere and burns up, or it resumes an orbit around the sun.

The article cites this paper, which can be purchased as a pdf.  A quote from the abstract:

The average temporarily-captured orbiter (TCO; an object that makes at least one revolution around the Earth in a co-rotating coordinate system) completes (2.88 ± 0.82) rev around the Earth during a capture event that lasts (286 ± 18) d. We find a small preference for capture events starting in either January or July.

So, I speculated in a previous post about these things being captured and mined.   A certain percentage of them will be class M asteroids, which would be rich in PGM ( platinum group metals).  Also, there would be carbonaceous asteroids, which could also hold water.  In other words, a lot of good, useful stuff could be mined off these things, but not if they burn up in the atmosphere, or go back to a solar orbit.

If you're looking for a economic justification for space, this could be it.  Or cleaning up space junk.  Or both.


h/t Behind the Black