118401 LINEAR, provisional designation 1999 RE70, is an asteroid and main-belt comet (176P/LINEAR) that 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. Observations using the Spitzer Space Telescope have resulted in an estimate of 4.0±0.4 km for the diameter of (118401) LINEAR.
|Discovery date||7 September 1999|
|MPC designation||(118401) LINEAR|
|176P/LINEAR · 1999 RE70|
|main-belt  · Themis|
|Epoch 13 January 2016 (JD 2457400.5)|
T_jup = 3.166
|Uncertainty parameter 0|
|Observation arc||5808 days (15.90 yr)|
|Aphelion||3.8110 AU (570.12 Gm)|
|Perihelion||2.5793 AU (385.86 Gm)|
|3.1951 AU (477.98 Gm)|
|5.71 yr (2086.1 d)|
Average orbital speed
|Earth MOID||1.58057 AU (236.450 Gm)|
|Jupiter MOID||1.6475 AU (246.46 Gm)|
|Dimensions||4.0±0.4 km (Spitzer)|
|1.3? g/cm³ (assumed)|
Equatorial surface gravity
Equatorial escape velocity
|18.19 to 21.91|
|Orbital characteristics A|
|Epoch||November 6, 2005 (JD 2453680.5)|
|Semi-major axis||3.19640 AU|
|Orbital period||5.714 a|
|Last perihelion||2017 March 12|
June 30, 2011
October 18, 2005
The main-belt comets are unique in that they have flat (within the plane of the planets' orbits), approximately circular (small eccentricity), asteroid-like orbits, and not the elongated, often tilted orbits characteristic of all other comets. Because (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 (see extinct comet).
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.
Seven 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), 60558 Echeclus (174P/Echeclus), (323137) 2003 BM80 (282P/2003 BM80), (300163) 2006 VW139 (288P/2006 VW139), and (457175) 2008 GO98 (362P/2008 GO98). As a dual-status object, astrometric observations of 118401 LINEAR should be reported under the minor planet designation.
- "JPL Small-Body Database Browser: 118401 LINEAR (1999 RE70)" (2010-11-02 last obs). Retrieved 26 March 2016.
- Henry H. Hsieh (May 2010). "Main Belt Comets". Hawaii. Archived from the original on 2011-08-06. Retrieved 2010-12-15. (older 2010 site) Archived 2009-08-10 at the Wayback Machine
- David Jewitt. "Main Belt Comets". UCLA, Department of Earth and Space Sciences. Retrieved 2010-12-15.
- 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.
- Using a spherical radius of 2 km; volume of a sphere * an assumed density of 1.3 g/cm³ yields a mass (m=d*v) of 4.3E+13 kg
- "176P/LINEAR Orbit". Minor Planet Center. Retrieved 2017-04-09.
- Syuichi Nakano (2006-10-29). "176P/LINEAR = (118401) 1999 RE70 (NK 1373)". OAA Computing and Minor Planet Sections. Retrieved 2012-02-25.
- "Dual-Status Objects". Minor Planet Center. 2008-03-06. Retrieved 2018-02-13.
- 118401 on November 13, 2011
- LINEAR home page
- Seiichi Yoshida's comet list
- New Class of Comets
- 118401 LINEAR at AstDyS-2, Asteroids—Dynamic Site
- 118401 LINEAR at the JPL Small-Body Database