133P/Elst-Pizarro

Infobox Planet | discovery=yes | physical_characteristics = yes | bgcolour=#FFFFC0
name=7968 Elst-Pizarro
133P/Elst-Pizarro
discoverer=M. R. S. Hawkins and R. H. McNaught [http://www.cfa.harvard.edu/iau/mpec/J96/J96R07.html MPEC 1996-R07] ] and/or S. J. Bus [http://www.cfa.harvard.edu/iauc/06400/06473.html#Item2 IAUC 6473] ]
"(as mp|1979 OW|7)"
as well as Eric W. Elst and Guido Pizarro "(as mp|1996 N|2)"
discovered=24 July, 1979 "(as mp|1979 OW|7)" [http://www.cfa.harvard.edu/iauc/06400/06457.html#Item1 IAUC 6457] ] and 14 July, 1996 "(as mp|1996 N|2)"
alt_names=mp|1996 N|2, mp|1979 OW|7
mp_category=Main-belt comet
epoch=22 September, 2006 (JD 2454000.5)
semimajor=472.811 Gm (3.161 AU)
perihelion=395.073 Gm (2.641 AU)
aphelion=550.548 Gm (3.680 AU)
eccentricity=0.1644
period=2052.262 d (5.62 a)
inclination=1.386°
asc_node=160.220°
arg_peri=132.138°
mean_anomaly=310.762°
avg_speed=16.64 km/s
dimensions=
mass=
density=
surface_grav=
escape_velocity=
rotation= 0.1446 d (3.471 h) [ [http://www.psi.edu/pds/resource/lc.html Planetary Data System (PDS) lightcurve data] ]
spectral_type=
abs_magnitude=14
albedo=
single_temperature=

Comet Elst-Pizarro is a remarkable body in that it displays characteristics of both asteroids and comets " [http://www.spacedaily.com/reports/Main_Belt_Comets_May_Have_Been_Source_Of_Earths_Water.html Main-Belt Comets May Have Been Source Of Earths Water] ", Space Daily, Mar 23, (2006).] , and is the prototype of main-belt comets. Its orbit keeps it within the asteroid main belt, while it displays a dust tail like a comet while near perihelion.

*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.

Subsequently, around the next perihelion in late 2002, the cometary activity appeared again, and persisted for several months [http://www.ifa.hawaii.edu/~hsieh/mbcs.html Main Belt Comets] page by Henry Hsieh] .

At present, there are only four other objects that are cross-listed as both comets and asteroids: 2060 Chiron (95P/Chiron), Comet 107P/Wilson-Harrington (4015 Wilson-Harrington), 60558 Echeclus (174P/Echeclus), and 118401 LINEAR (176P/LINEAR (LINEAR 52)). 3200 Phaethon could be a member of this group [cite web | url= http://science.nasa.gov/headlines/y2004/06dec_geminids.htm | title= The Geminid Meteor Shower | accessdate= 2007-11-08 | format= html | date=2004-12-06 | publisher = NASA] .

References