7968 Elst–Pizarro
7968 Elst–Pizarro imaged at La Silla Observatory in August 1996. The narrow tail is visible.
|
|
| Discovery | |
|---|---|
| Discovered by |
1979 OW7: M. R. S. Hawkins R. H. McNaught,S. J. Bus 1996 N2: Eric W. Elst, Guido Pizarro |
| Discovery date | 24 July 1979 (1979 OW7) 14 July 1996 (1996 N2) |
| Designations | |
| MPC designation | (7968) Elst–Pizarro |
| P/1996 N2 1979 OW7 |
|
|
Main-belt comet Main-belt asteroid Themis/ Beagle family |
|
| Orbital characteristics | |
| Epoch 13 January 2016 (JD 2457400.5) | |
| Uncertainty parameter 0 | |
| Observation arc | 13350 days (36.55 yr) |
| Aphelion | 3.66751 AU (548.652 Gm) (Q) |
| Perihelion | 2.6524 AU (396.79 Gm) (q) |
| 3.1600 AU (472.73 Gm) (a) | |
| Eccentricity | 0.16062 (e) |
| 5.62 yr (2051.7 d) | |
|
Average orbital speed
|
16.64 km/s |
| 187.70° (M) | |
| 0° 10m 31.656s / day (n) | |
| Inclination | 1.3873° (i) |
| 160.14° (Ω) | |
| 131.97° (ω) | |
| Earth MOID | 1.63474 AU (244.554 Gm) |
| Jupiter MOID | 1.51427 AU (226.532 Gm) |
| Jupiter Tisserand parameter | 3.185 |
| Physical characteristics | |
| Dimensions | 3.8±0.6 km (Spitzer) |
|
Mean density
|
1.3(?) g/cm³ |
| 3.471 h (0.1446 d) | |
| 0.05±0.02R | |
| Temperature | 160 K |
| 17.24 to 20.71 | |
| 15.7 15.3R (2004) 15.49R (2010) |
|
Comet Elst–Pizarro is a body that displays characteristics of both asteroids and comets, and is the prototype of main-belt comets. Its orbit keeps it within the asteroid belt, yet it displayed a dust tail like a comet while near perihelion in 1996, 2001, and 2007.
Elst–Pizarro was reported in 1979 as minor planet 1979 OW7, with its image on a photographic plate being completely stellar in appearance. Its 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. The cometary nature of Elst–Pizarro was first discovered when a linear dust feature was observed with the ESO 1-metre Schmidt telescope at La Silla Observatory on 7 August 1996.
Subsequently, around the next perihelion in November 2001, the cometary activity appeared again, and persisted for 5 months.
At present, there are only four other objects that are cross-listed as both comets and asteroids: 2060 Chiron (95P/Chiron), 4015 Wilson–Harrington (107P/Wilson-Harrington), 60558 Echeclus (174P/Echeclus), and 118401 LINEAR (176P/LINEAR, previously 1999 RE70). As a dual status object, astrometric observations of 7968 Elst–Pizarro should be reported under the minor planet designation.
...
Wikipedia