MAIN-BELT COMET

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

Contents

Orbits

Cometary activity

Composition

Members

External Links

References

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 ^[1].
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 ^[2].

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^[3].

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

1. Diagram from
Henry Hsieh's ''Main Belt Comets'' webpage.
2. Main Belt Comets, webpage written by Henry Hsieh.
3. ''Main-Belt Comets May Have Been Source Of Earths Water'', Space Daily, Mar 23, (2006).