133P/Elst-Pizarro

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7968 Elst-Pizarro
133P/Elst-Pizarro
Discovery
Discovered by M. R. S. Hawkins and R. H. McNaught[1] and/or S. J. Bus [2]
(as 1979 OW7)
as well as Eric W. Elst and Guido Pizarro (as 1996 N2)
Discovery date 24 July 1979 (as 1979 OW7) [3] and 14 July 1996 (as 1996 N2)
Designations
Alternative names 1996 N2, 1979 OW7
Minor planet
category		 Main-belt comet
Epoch 22 September 2006 (JD 2454000.5)
Aphelion 550.548 Gm (3.680 AU)
Perihelion 395.073 Gm (2.641 AU)
Semi-major axis 472.811 Gm (3.161 AU)
Eccentricity 0.1644
Orbital period 2052.262 d (5.62 a)
Average orbital speed 16.64 km/s
Mean anomaly 310.762°
Inclination 1.386°
Longitude of ascending node 160.220°
Argument of perihelion 132.138°
Physical characteristics
Rotation period 0.1446 d (3.471 h) [4]
Absolute magnitude 14

Comet Elst-Pizarro is a remarkable body in that it displays characteristics of both asteroids and comets [5], 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 [6].

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 [7].

[edit] References

  1. ^ MPEC 1996-R07
  2. ^ IAUC 6473
  3. ^ IAUC 6457
  4. ^ Planetary Data System (PDS) lightcurve data
  5. ^ Main-Belt Comets May Have Been Source Of Earths Water, Space Daily, Mar 23, (2006).
  6. ^ Main Belt Comets page by Henry Hsieh
  7. ^ The Geminid Meteor Shower (html). NASA (2004-12-06). Retrieved on 2007-11-08.
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