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The Moon Is Not Alone

Wednesday, May 17, 2006 (11:58 pm cdt)

This post originally appeared on Umm… He Said.

NOTE, 1/31/2022: Originally there were 13 external links on this page; most were broken. I’ve updated what I could.

Our familiar Moon is not the only thing orbiting the Earth! In addition to all of the man-made satellites (and there are a lot of them), a few other tiny moons have recently been discovered, and there may be a lot more of them. It appears that these extra moons fall into two categories: space junk and lost asteroids. A cluster of external links, below, tell the story:

Space junk

• New ‘moon’ found around Earth [BBC, 11 September 2002]
  Object known as JOO2E3, captured by Earth in 2002
• Earth’s new ‘moon’ is space junk [BBC, 12 September 2002]
  Follow-up to article cited above

Cruithne (pronounced “croo-EEN-ya”), a near-earth asteroid

Although Cruithne is often said to be “Earth’s second moon”, its orbit is in fact around the Sun, not the Earth. The catch is that it takes nearly the same length of time to orbit the Sun as the Earth does (but not exactly), so it manages a near approach to the Earth about every 770 years. To make matters more complex, its orbit is not in the same plane as the Earth’s.

• Earth Usually Has More than One Moon, Study Suggests [Space.com, 4 April 2012] — discussion of near-Earth asteroids; this replaced the old article which mentioned Cruithne
• Wikipedia’s article on 3753 Cruithne — declares it to be actually in orbit around the Sun
• Near-Earth Asteroid 3753 Cruithne
• Cruithne, Earth’s “second moon” — includes simulations of its orbit

Other lost asteroids

• Wikipedia article on 2002 AA29, a captured asteroid
• Just search for “near Earth objects” or “near Earth asteroids.” There’s a wealth of information out there (this item added 1/31/2022).