4179 Toutatis


4179 Toutatis is one of the largest near-Earth asteroids and potentially one of the most dangerous (see potentially hazardous asteroids. A member of the Apollo group, it was discovered in 1989 by French astronomers and named (somewhat inappropriately) after a Celtic god that was the protector of the tribe in ancient Gaul. Its eccentric, four-year orbit extends from just inside Earth's orbit to the main asteroid belt; the danger comes from the fact that the plane of Toutatis's orbit is closer to the plane of Earth's orbit than any known Earth-crossing asteroid. In December 1992, Toutatis came within about 4 million km of Earth enabling radar images to be acquired using the Goldstone Deep Space Communications Complex in California's Mojave desert. These images revealed two irregularly shaped, cratered objects about 4 and 2.5 kilometers in average diameter which are probably in contact with each other. Such contact binaries may be fairly common since another one, Castalia, was observed in 1989. Numerous surface features on Toutatis, including a pair of large craters, side by side, and a series of three prominent ridges – a type of asteroid mountain range - are presumed to result from a complex history of impacts.


Toutatis shows an extraordinarily complex rotation. Whereas the vast majority of asteroids, and all the planets, spin about a single axis, Toutatis tumbles around two axes with different periods, of 5.4 and 7.3 Earth days, that combine in such a way that Toutatis's orientation with respect to the Solar System never repeats.


On September 29, 2004, Toutatis passed by Earth at a range of just four times the distance between the Earth and the Moon. One consequence of the asteroid's frequent close approaches to Earth is that its trajectory more than several centuries from now cannot be predicted accurately. In fact, of all the Earth-crossing asteroids, the orbit of Toutatis is thought to be one of the most chaotic.


size 4.5 × 2.4 × 1.9 km
density 2.1 g/cm³
spectral class S
rotational periods 5.41 and 7.35 days
semimajor axis 2.516 AU
perihelion 0.92 AU
aphelion 4.11 AU
inclination 0.5°
period 4 years