not a moon, something richer and stranger

[redbird]

Herein I correct the BBC, just to be polite:

Cruithne is very cool, but it's not a moon. The people who figured out what it's doing are very clear on this, but the BBC messed up, and lots of people are now quoting their error.

Cruithne doesn't orbit Earth--it orbits the Sun, doing weird horseshoes around Earth's orbit. This is one of the weirder known solutions to the three-body problem, one spotted mathematically long before it was observed out there in the real world. Now that they know what to look for, they've found two more asteroids in similar resonant orbits, but haven't published details yet.

See http://www.astro.queensu.ca/~wiegert/3753/3753.html for more information.

Comments

[holyoutlaw.livejournal.com]

Dang! I am disappointed. I spent a fair amount of time on the website the BBC linked to with all the animations of Cruithne's orbits.

I know, you say, something richer and stranger, but still. I got a chuckle out of the earth having up to three moons. Oh well.

Particularly interesting...

[purpletigron.livejournal.com]

From the link above (see there for far more information and further links):
`What does "Cruithne" mean? The Dalriada Celtic Heritage Trust inform us the Cruithne were "the first Celtic racio-tribal group to come to the British Isles, appearing between about 800 and 500 B.C., and coming from the European continent. They were also known as the Picts. The correct pronunciation for 'Cruithne' is 'croo-een-ya'. The emphasis should be on the -een-". (Thanks BQ!) Note: It was the privilege of the discoverers of the asteroid, D. Waldron et al., to name their prize, a process which is regulated by the International Astronomical Union. For information see the FAQ or the IAU's Minor Planet Center naming conventions.'

`Does asteroid 3753 Cruithne orbit the Earth like a moon or satellite? No. The asteroid's behaviour is more complicated than that: it doesn't orbit the Earth, but rather it shares the Earth's orbit. The relationship of a moon to its planet is called a two-body because there are only two important players (ie. the moon and the planet). However, in the case of Cruithne, the Earth and the asteroid both share the same orbit about the Sun, but are choreographed in such a away as to remain stable and avoid colliding with each other. This is called a three-body relationship as there are three main players: the Earth, the asteroid and the Sun. Please see the 3753 Cruithne main page for more details on the asteroid's motion.'