Toutatis

Toutatis

Minor planet Toutatis (4179) is captured in a series of 60-second exposures (with a 60-second gap between exposures) on December 12 shortly before reaching its closest distance to Earth (7 million kilometers). Photo copyright 2012 by Fred Espenak

During the second week of December 2012, the minor planet Toutatis (4179) made a close approach to Earth passing within 7 million kilometers (4 million miles (on Dec. 12 at 06:40 UT). This is about 18 times the average Earth-Moon distance which is quite close relative to the scale of the Solar System.

The rapid motion of Toutatis is revealed in a video made from a series of 60-second exposures shot over a 102-minute period on December 13. Photo copyright 2012 by Fred Espenak

Toutatis is an irregular 5-kilometer chunk of rock that makes a close approach to Earth every four years. Its orbit is chaotic because of the large perturbations it undergoes from the gravitational interact with Earth and Jupiter. In fact, Toutatis is in a 3:1 orbital resonance with Jupiter, and a 1:4 orbital resonance with Earth (which is why it passes close to Earth every 4 years).

Toutatis was first sighted in February 1934, but it was then lost. It wasn’t until January 1989 until it was rediscovered by French astronomer Pollas.

According to Minor Planet Circ. 16444: “Named after the Gaulish god, protector of the tribe. This totemic deity is well known because of the cartoon series “Les aventures d’Asterix” by Uderzo and Goscinny. This tells the stories of two almost fearless heroes living in the last village under siege in Roman-occupied Gaul in 50 B.C., and whose only fear is that the sky may fall onto their heads one day. Since this object is the Apollo object with the smallest inclination known, it is a good candidate to fall on our heads one of these days… But as the chief of the village always says: “C’est pas demain la veille…” Citation written by the discoverer and A. Maury and endorsed by J. D. Mulholland, who with Maury obtained the discovery plates.”

I imaged Toutatis on two nights from Bifrost Observatory using the ASA N12 Astrograph. It was quite amazing to see how quickly the minor planet crossed the field of the camera – over 3 degrees per day.

The rapid motion of Toutatis is revealed in a video made from a series of 60-second exposures shot over a 102-minute period on December 13. Photo copyright 2012 by Fred Espenak on Vimeo.

Because of its close proximity to Earth, astronomers of NASA’s Goldstone dish were able to obtain radar images of Toutatis with unprecedented resolution.

According to Michael Busch (NRAO): “Toutatis appears to have a complicated internal structure. Our radar measurements are consistent with the asteroid’s little lobe being ~15% denser than the big lobe; and they indicate 20% to 30% over-dense cores inside the two lobes.” This suggests that Toutatis may be a loose composite of smaller space rocks. “Toutatis could be re-accumulated debris from an asteroid-asteroid collision in the main belt,” says Busch.

Fred Espenak

Radar Image of Toutatis from Goldstone

Radar Image of Toutatis from Goldstone

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