118401 LINEAR

Minor Planet
name=118401 LINEAR
176P/LINEAR
discoverer=LINEAR
discovery_date=September 7, 1999
designations=mp|1999 RE|70
category=Main belt (Themis), Comet
epoch=June 14, 2006 (JD 2453900.5)
semimajor=478.120 Gm (3.196 AU)
perihelion=386.104 Gm (2.581 AU)
aphelion=570.136 Gm (3.811 AU)
eccentricity=0.192
period=2086.967 d (5.71 a)
inclination=0.238°
asc_node=346.572°
arg_peri=36.141°
mean_anomaly=41.182°
speed=16.51 km/s
dimensions=<6.0 km
mass=<2.3e|14 kg
density=2.0? g/cm³
gravity=<0.0017 m/s²
escape_velocity=<0.0032 km/s
rotation=? d
spectral_class=?
abs_mag=15.1
albedo=0.10?
temperature=~156 KInfobox Comet
name=176P/LINEAR


discoverer=LINEAR
discovery_date=October 18, 2005
designations=mp|1999 RE|70
epoch=November 6, 2005 (JD 2453680.5)
semimajor=3.19640 AU
perihelion=2.5811186 AU
aphelion=3.811678 AU
eccentricity=0.1924908
period=5.714 a
inclination=0.23795°
last_p=October 18, 2005
next_p=June 30, 2011

118401 LINEAR (provisional designation mp|1999 RE|70) is an asteroid and main-belt comet (176P/LINEAR, also known as LINEAR 52) which was discovered by the Lincoln Near-Earth Asteroid Research (LINEAR) 1-metre telescopes in Socorro, New Mexico on September 7, 1999. (118401) LINEAR was discovered to be cometary on November 26, 2005, by Henry H. Hsieh and David C. Jewitt as part of the Hawaii Trails project using the Gemini North 8-m telescope on Mauna Kea and was confirmed by the University of Hawaii's 2.2-m (88-in) telescope on December 24-27, 2005, and Gemini on December 29, 2005. Based on an absolute magnitude (H) of 15.04, (118401) LINEAR is assumed to be smaller than [http://neo.jpl.nasa.gov/glossary/h.html 6 km] in diameter.

The main-belt comets are unique in that they have flat, circular, asteroid-like orbits, and not the elongated, often tilted orbits characteristic of all other comets. Since (118401) LINEAR can generate a coma (produced by vapour boiled off the comet), it must be an icy asteroid. When a typical comet approaches the Sun, its ice heats up and sublimates (changes directly from ice to gas), venting gas and dust into space, creating a tail and giving the object a fuzzy appearance. Far from the Sun, sublimation stops, and the remaining ice stays frozen until the comet's next pass close to the Sun. In contrast, objects in the asteroid belt have essentially circular orbits and are expected to be mostly baked dry of ice by their confinement to the inner solar system.

It is suggested that these main-belt asteroid-comets are evidence of a recent impact exposing an icy interior to solar radiation. A good question is, "How long will current main-belt comets keep generating a coma?" It is estimated short period comets remain active for about 10,000 years before having most of their ice sublimated away and going dormant.

Four other objects are classified as both periodic comets and numbered asteroids: 2060 Chiron (95P/Chiron), 4015 Wilson-Harrington (107P/Wilson-Harrington), 7968 Elst-Pizarro (133P/Elst-Pizarro), and 60558 Echeclus (174P/Echeclus).

References

* [http://www.ifa.hawaii.edu/~hsieh/mbc-release.html New Class of Comets]
* [http://www.ifa.hawaii.edu/~hsieh/mbcs.html Main-Belt Comets]
* [http://ssd.jpl.nasa.gov/sbdb.cgi?sstr=118401;orb=1 orbital simulation] from JPL (Java)
* [http://home.comcast.net/~kpheider/118401_2011.gif118401] on November 13th, 2011
* [http://www.ll.mit.edu/LINEAR LINEAR home page]
* [http://www.aerith.net/comet/catalog/0176P/ Seiichi Yoshida's comet list]