Main-belt comet

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Main-belt comets are bodies orbiting within the (main) asteroid belt which show cometary activity during a part of their orbit.

Orbits

Unlike most comets which spend most of their orbit at Jupiter-like or greater distances from the Sun, main-belt comets follow near-circular orbits within the asteroid belt that are undistinguishable from the orbits of many standard asteroids. While quite a few short period comets have semimajor axes well within Jupiter's orbit, main-belt comets differ in having small eccentricities and inclinations just like main-belt asteroids. The three known main-belt comets all orbit within the outer part of the main belt .

It is not known how an outer solar system body like the other comets could have made its way into a low-eccentricity orbit typical of the asteroid belt which is only weakly perturbed by the planets. Hence, it is assumed that unlike other comets, the main-belt comets formed in an inner solar system orbit close to their present positions .

Cometary activity

Main belt comets display a cometary dust tail only for a part of their orbit near perihelion. The activity persists for a month or several out of each 5-6 year orbit.

Composition

It has been hypothesised that they may have been the source of Earth's water.

Members

Presently there are three identified members:

• 133P/Elst-Pizarro
• 176P/LINEAR
• P/2005 U1

External links

• Henry Hsieh's Main-Belt Comets page has extensive details on Main-belt comets
• Planetary Society article on MBCs
• Discussion of possible differences in characteristics of the water in MBCs and other comets

References

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Last updated on Sunday February 03, 2008 at 15:08:16 PST (GMT -0800)
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