| Discovery A | |
|---|---|
| Discoverer | LINEAR |
| Discovery date | September 7, 1999 |
| Alternate designations B |
1999 RE70 |
| Category | Main belt (Themis), Comet |
| Orbital elements C | |
|
|
|
| Eccentricity (e) | 0.192 |
| Semi-major axis (a) | 478.120 Gm (3.196 AU) |
| Perihelion (q) | 386.104 Gm (2.581 AU) |
| Aphelion (Q) | 570.136 Gm (3.811 AU) |
| Orbital period (P) | 2086.967 d (5.71 a) |
| Mean orbital speed | 16.51 km/s |
| Inclination (i) | 0.238° |
| Longitude of the ascending node (Ω) |
346.572° |
| Argument of perihelion (ω) |
36.141° |
| Mean anomaly (M) | 41.182° |
| Physical characteristics D | |
| Diameter | <6.0 km |
| Mass | <2.3 × 1014 kg |
| Density | 2.0? g/cm³ |
| Surface gravity | <0.0017 m/s² |
| Escape velocity | <0.0032 km/s |
| Rotation period | ? d |
| Spectral class | ? |
| Absolute magnitude | 15.1 |
| Albedo (geometric) | 0.10? |
| Mean surface temperature |
~156 K |
| Discovery | |
|---|---|
| Discovered by: | LINEAR |
| Discovery date: | October 18, 2005 |
| Alternate designations: | P/1999 RE70 |
| Orbital characteristics A | |
| Epoch: | November 6, 2005 (JD 2453680.5) |
| Aphelion distance: | 3.811678 AU |
| Perihelion distance: | 2.5811186 AU |
| Semi-major axis: | 3.19640 AU |
| Eccentricity: | 0.1924908 |
| Orbital period: | 5.714 a |
| Inclination: | 0.23795° |
| Last perihelion: | October 18, 2005 |
| Next perihelion: | June 30, 2011 |
118401 LINEAR (provisional designation 1999 RE70) is an asteroid and main-belt comet (176P/LINEAR) 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 6 km[1] in diameter.
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. 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
- New Class of Comets
- Main-Belt Comets
- orbital simulation from JPL (Java)
- 118401 on November 13, 2011
- LINEAR home page
- Seiichi Yoshida's comet list
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| Periodic Comets (by number) | ||
|---|---|---|
| Previous 175P/Hergenrother |
176P/LINEAR | Next 177P/Barnard |
| List of periodic comets | ||
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