Toutatis: A Visitor In Our Skies

Toutatis, photographed by Steve Ostro of NASA's JPL labs in 1992

Toutatis passes Earth at a distance of just 962,951 miles on September 29th this year (2004). In astronomical terms, that's pretty much a near-miss.

Toutatis - or 4179 Toutatis, as it's officially known - was discovered in 1989 by Christian Pollas and named after the Celtic God. Fans of Asterix The Gaul may recognise the name from the comic books. Many think Asterix's creators Goscinny and Uderzo made up the oath "by Toutatis", but it was a genuine Gallic oath, recorded around the time of Alexander The Great.

The asteroid has a four-year orbit, and is noted for the extremely low orbital inclination:

The orbit of Toutatis. Image: NASA/JPL

You can watch an animation of how Toutatis' passage relative to the other planets via the NASA-JPL website. [You must have Javascript enaled to see the animation - if you're having problems, check the preferences setting for your browser.]

Radar studies of Toutatis suggest that it is what's known as a "rubble pile" - an object which has been fragmented by a collision and then re-accumulated to form a loosely bound body. The shape of the asteroid resembles two bodies which have gently come together.

Toutatis is both an Apollo Asteroid and an Alinda Asteroid. Apollo asteroids have mean average distances from the Sun of more than 1 AU (the average Earth-Sun distance - find out how to measure the AU). However, their closest approaches to the Sun are less than 1 AU which means they can sometimes pass close by Earth.

Alinda asteroids have eccentric orbits with average distances from the Sun of 2.5 AU. Gravitational interactions with Jupiter cause them to have orbital periods close to 4 years, which can result, as in the case of Toutatis, in them making close approaches to the Earth on repeated occasions.

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