7968 Elst–Pizarro

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7968 Elst–Pizarro
133P/Elst–Pizarro

7968 Elst–Pizarro in August 1996 by ESO. The narrow tail is visible.
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 P/1996 N2, 1979 OW7
Minor planet category 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)
Semi-major axis 3.1609 AU (a)
(472.66 Gm)
Eccentricity 0.16167
Orbital period 5.62 yr
(2052.69 d)
Average orbital speed 16.64 km/s
Mean anomaly 336.84°
Inclination 1.3868°
Longitude of ascending node 160.15°
Argument of perihelion 132.18°
Physical characteristics
Dimensions 3.8±0.6 km (Spitzer)[7]
Mean density 1.3(?) g/cm³[8]
Rotation period 3.471 hr
(0.1446 d)[6]
Albedo 0.05±0.02R[7]
Temperature 160K[8]
Apparent magnitude 17.24 to 20.71
Absolute magnitude (H) 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. 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. The cometary nature of Elst–Pizarro was first discovered on 1996 August 7 when a linear dust feature was observed.[8]

    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).[11] As a dual status object, astrometric observations of 7968 Elst–Pizarro should be reported under the minor planet designation.[11]

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

    References

    1. ↑ MPEC 1996-R07
    2. ↑ IAUC 6473
    3. ↑ IAUC 6457
    4. ↑ 4.0 4.1 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. ↑ 6.0 6.1 6.2 6.3 6.4 "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. ↑ 7.0 7.1 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. 
    8. ↑ 8.0 8.1 8.2 8.3 8.4 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. 
    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. 
    10. ↑ Main-Belt Comets May Have Been Source Of Earths Water, Space Daily, Mar 23, (2006).
    11. ↑ 11.0 11.1 "Dual-Status Objects". Minor Planet Center. 2008-03-06. Retrieved 2010-12-17. 
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