133P/Elst-Pizarro

Comet Elst-Pizarro is a remarkable body in that it displays characteristics of both asteroids and comets , and is the prototype of main-belt comets. Its orbit keeps it within the asteroid main belt, while it displays a dust tail like a comet while near perihelion.

• As a comet it is formally designated 133P/Elst-Pizarro.
• As an asteroid it is designated 7968 Elst-Pizarro.

Elst-Pizarro was reported in 1979 as minor planet 1979 OW₇, with its image on a photographic plate being completely stellar in appearance. The orbit remains entirely within the orbits of Mars and Jupiter, with eccentricity 0.165, typical of a minor planet in the asteroid belt. However, the images taken by Eric W. Elst and Guido Pizarro in 1996, when it was near perihelion, clearly show a cometary tail. Since this is not normal behaviour for asteroids, it is suspected that Elst-Pizarro has a different, probably icy, composition.

Subsequently, around the next perihelion in late 2002, the cometary activity appeared again, and persisted for several months .

At present, there are only four other objects that are cross-listed as both comets and asteroids: 2060 Chiron (95P/Chiron), Comet 107P/Wilson-Harrington (4015 Wilson-Harrington), 60558 Echeclus (174P/Echeclus), and 118401 LINEAR (176P/LINEAR (LINEAR 52)). 3200 Phaethon could be a member of this group .

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