 7968 Elst–Pizarro imaged atLa Silla Observatory in August 1996. The narrow tail is visible. | |
| Discovery | |
|---|---|
| Discovered by | 1979 OW7: M. R. S. Hawkins R. H. McNaught,[1]S. J. Bus[2] 1996 N2: Eric W. Elst,Guido Pizarro |
| Discovery date | 24 July 1979 (1979 OW7)[3] 14 July 1996 (1996 N2) |
| Designations | |
| (7968) Elst–Pizarro | |
| P/1996 N2 1979 OW7 | |
| Main-belt comet[4][5] Main-beltasteroid[6] Themis/ Beagle family[4] | |
| Orbital characteristics[6] | |
| 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) |
| 5.62yr (2051.7d) | |
Averageorbital speed | 16.64 km/s |
| 187.70° (M) | |
| 0° 10m 31.656s / day (n) | |
| Inclination | 1.3873° (i) |
| 160.14° (Ω) | |
| 2024-May-10[7] | |
| 131.97° (ω) | |
| Jupiter MOID | 1.51427 AU (226.532 Gm) |
| TJupiter | 3.185 |
| Physical characteristics | |
| Dimensions | 3.8 ± 0.6 km (2.36 ± 0.37 mi)[8] 3.9+0.4 −0.3 km[9] |
Meandensity | 1.3 g/cm3 (?) (0.047 lb/cu in)[10] |
| 3.471 h (0.1446 d)[6] | |
| 0.074±0.013R | |
| Temperature | 160K[10] |
| 17.24 to 20.71 | |
| 15.7[6] 15.3R (2004)[10] 15.49R (2010)[11] | |
Comet Elst–Pizarro is a body that displays characteristics of bothasteroids andcomets,[12] and is the prototype ofactive asteroids. Its orbit keeps it within theasteroid belt, yet it displayed a dust tail like a comet while nearperihelion in 1996, 2001, and 2007.
Elst–Pizarro was reported in 1979 as minor planet1979 OW7,[13] with its image on a photographic plate being completely stellar in appearance. Its orbit remains entirely within the orbits ofMars andJupiter, witheccentricity 0.165, typical of aminor planet in theasteroid belt. However, the images taken byEric W. Elst and Guido Pizarro in 1996, when it was nearperihelion, clearly show a cometary tail.[13] 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 theESO 1-metre Schmidt telescope atLa Silla Observatory on 7 August 1996.[10][14]
Subsequently, around the next perihelion in November 2001, the cometary activity appeared again, and persisted for 5 months.[10] It again came toperihelion on 8 February 2013.[6] The outgassing was found to happen only on small part of the surface measuring less than 600 metres (2,000 ft) in effective diameter, likely being the relatively recent (younger than 100 million years) impact crater.[9]
At present, seven 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),118401 LINEAR (176P/LINEAR),(323137) 2003 BM80 (282P/2003 BM80),(300163) 2006 VW139 (288P/2006 VW139),(457175) 2008 GO98 (362P/2008 GO98),[15] and(248370) 2005 QN173 (433P/2005 QN173).[16] As a dual status object,astrometric observations of 7968 Elst–Pizarro should be reported under theminor planet designation.[15]
Castalia is a proposed mission concept for a robotic spacecraft to explore Elst–Pizarro and make the firstin situ measurements of water in the asteroid belt, and thus, help solve the mystery of the origin of Earth's water.[17] The lead is Colin Snodgrass, fromThe Open University in the UK.Castalia was proposed in 2015 and 2016 to theEuropean Space Agency within theCosmic Vision programme missions M4 and M5, but it was not selected. The team continues to mature the mission concept and science objectives.[17] Because of the construction time required and orbital dynamics, a launch date of October 2028 was proposed.[17]
Castalia mission scientists are now considering instrument contributions for the ChineseZhengHe comet exploration mission, which will conduct detailed remote sensing and in-situ measurements at Elst–Pizarro in 2032[18] following a proposed launch in 2025.[19]
| Numbered comets | ||
|---|---|---|
| Previous 132P/Helin–Roman–Alu | 7968 Elst–Pizarro | Next 134P/Kowal–Vávrová |
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