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Those who watched it may remember an episode of QI in which Stephen Fry asked "how many moons does the earth have", and told the panel that there were two - the standard one, and a smaller more distant one called Cruithne.
I just found this article about it, and the truth is far stranger - it is an asteroid, about 5 km in diameter
- it is in orbit around the sun
- its orbit is very close to earth's, so from an earth's-eye view it is zig-zagging without going anywhere much
- it's behind us, and catching up
- it'll reach us around 2292 AD, coming within about 12 million km
- when it gets here, it'll do a little dance around us, lose a bit of energy, and start falling back the other way round the orbit until it reaches us from the other side
- then it'll dance again, gain some energy, and start back
- and so, ad infinitum
Fascinating stuff,
Hugo
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