7968 Elst–Pizarro

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7968 Elst–Pizarro
7968 Elst–Pizarro Eso9637a.jpg
7968 Elst–Pizarro imaged at La Silla Observatory in August 1996. The narrow tail is visible.
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)
P/1996 N2
1979 OW7
Main-belt comet[4][5]
Main-belt asteroid[6]
Themis/ Beagle family [4]
Orbital characteristics[6]
Epoch 2012-Sep-30 (JD 2456200.5)
T_jup = 3.184
Aphelion 3.67196 AU (Q) (549.45 Gm)
Perihelion 2.6499 AU (q) (395.86 Gm)
3.1609 AU (a) (472.66 Gm)
Eccentricity 0.16167
5.62 yr (2052.69 d)
16.64 km/s
Inclination 1.3868°
Physical characteristics
Dimensions 3.8±0.6 km (Spitzer) [7]
Mean density
1.3(?) g/cm³ [8]
3.471 hr (0.1446 d) [6]
Albedo 0.05±0.02R[7]
Temperature 160 K[8]
17.24 to 20.71
14.0 [6]
15.3R (2004) [8]
15.49R (2010) [9]

Comet Elst–Pizarro is a body that displays characteristics of both asteroids and comets,[10] 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.

  • 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. 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.[8][11]

Subsequently, around the next perihelion in November 2001, the cometary activity appeared again, and persisted for 5 months.[8]

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).[12] As a dual status object, astrometric observations of 7968 Elst–Pizarro should be reported under the minor planet designation.[12]

It most recently came to perihelion on 8 February 2013.[6]


  1. ^ "MPEC 1996-R07 : COMET P/1996 N2 (ELST-PIZARRO)". IAU-Minor Planet Center. 12 September 1996. 
  2. ^ "IAUC 6473". IAU-Central Bureau for Astronomical Telegrams. 12 September 1996. 
  3. ^ "IAUC 6457". IAU-Central Bureau for Astronomical Telegrams. 21 August 1996. 
  4. ^ a b Henry H. Hsieh (May 2010). "Main Belt Comets". Hawaii. Retrieved 2010-12-15.  (older 2010 site)
  5. ^ David Jewitt. "Main Belt Comets". UCLA, Department of Earth and Space Sciences. Retrieved 2010-12-15. 
  6. ^ a b c d e "JPL Small-Body Database Browser: 7968 Elst–Pizarro (1996 N2)" (2012-06-06 last obs). Retrieved 2012-08-08.  Archived from the original on 2012-08-08
  7. ^ a b Hsieh, Henry H.; Jewitt, David C.; Fernández, Yanga R. (2009). "Albedos of Main-Belt Comets 133P/Elst–Pizarro and 176P/LINEAR". The Astrophysical Journal Letters 694 (2): L111–L114. arXiv:0902.3682. Bibcode:2009ApJ...694L.111H. doi:10.1088/0004-637X/694/2/L111. Retrieved 2010-12-17. 
  8. ^ a b c d e Hsieh, Henry H.; Jewitt, David C.; Fernández, Yanga R. (2004). "The Strange Case of 133P/Elst–Pizzarro: A Comet Among the Asteroids". The Astronomical Journal 127 (5): 2997–3017. Bibcode:2004AJ....127.2997H. doi:10.1086/383208. Retrieved 2010-12-17. 
  9. ^ Hsieh, Henry H.; Jewitt, David C.; Lacerda, Pedro; Lowry, Stephen C.; Snodgrass, Colin (2010). "The return of activity in main-belt comet 133P/Elst–Pizarro". Monthly Notices of the Royal Astronomical Society 403 (1): 363–377. arXiv:0911.5522. Bibcode:2010MNRAS.403..363H. doi:10.1111/j.1365-2966.2009.16120.x. Retrieved 2010-12-17. 
  10. ^ "Main-Belt Comets May Have Been Source Of Earths Water". Space Daily. 23 March 2006. 
  11. ^ "Strange Comet Discovered at ESO". ESO. 16 September 1996. 
  12. ^ a b "Dual-Status Objects". Minor Planet Center. 2008-03-06. Retrieved 2010-12-17. 

External links[edit]

Periodic comets (by number)
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