7968 Elst–Pizarro

7968 Elst–Pizarro
133P/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,[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
MPC designation (7968) Elst–Pizarro
P/1996 N2
1979 OW7
Main-belt comet [4][5]
Main-belt asteroid [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)
5.62 yr (2051.7 d)
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) [7]
Mean density
 1.3(?) g/cm³ [8]
3.471 h (0.1446 d)[6]
0.05±0.02R [7]
Temperature 160 K [8]
17.24 to 20.71
15.7[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.

    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]

    References

    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. 1 2 Henry H. Hsieh (May 2010). "Main Belt Comets". Hawaii. Retrieved 2010-12-15. (older 2010 site) Archived August 10, 2009, at the Wayback Machine.
    5. ↑ David Jewitt. "Main Belt Comets". UCLA, Department of Earth and Space Sciences. Retrieved 2010-12-15.
    6. 1 2 3 4 5 "JPL Small-Body Database Browser: 7968 Elst–Pizarro (1996 N2)" (2012-06-06 last obs). Archived from the original on 9 August 2012. Retrieved 13 April 2016. from the original on 2012-08-08
    7. 1 2 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. Bibcode:2009ApJ...694L.111H. arXiv:0902.3682 Freely accessible. doi:10.1088/0004-637X/694/2/L111. Retrieved 2010-12-17.
    8. 1 2 3 4 5 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. Bibcode:2010MNRAS.403..363H. arXiv:0911.5522 Freely accessible. 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. 1 2 "Dual-Status Objects". Minor Planet Center. 2008-03-06. Retrieved 2010-12-17.
    Numbered comets
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