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176P/LINEAR
Discovery
Discovered by	LINEAR
Discovery date	October 18, 2005
Designations
Alternative designations	P/1999 RE70
Orbital characteristics
Epoch	November 6, 2005 (JD 2453680.5)
Aphelion	3.811678 AU
Perihelion	2.5811186 AU
Semi-major axis	3.19640 AU
Eccentricity	0.1924908
Orbital period	5.714 a
Inclination	0.23795°
Last perihelion	November 21, 2022; 2017 March 12; June 30, 2011; October 18, 2005
Next perihelion	2028-Aug-05

118401 LINEAR
176P/LINEAR
Discovery
Discovered by	LINEAR
Discovery date	7 September 1999
Designations
MPC designation	(118401) LINEAR
Named after	LINEAR
Alternative designations	176P/LINEAR · 1999 RE70
Minor planet category	main-belt · Themis; MBC
Orbital characteristics
	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)
Semi-major axis	3.1951 AU (477.98 Gm)
Eccentricity	0.19276
Orbital period (sidereal)	5.71 yr (2086.1 d)
Average orbital speed	16.51 km/s
Mean anomaly	286.74°
Mean motion	0.17257°/day
Inclination	0.23477°
Longitude of ascending node	345.96°
Argument of perihelion	35.460°
Earth MOID	1.58057 AU (236.450 Gm)
Jupiter MOID	1.6475 AU (246.46 Gm)
Physical characteristics
Dimensions	4.0±0.4 km (Spitzer)
Mass	4.3×1013? kg
Mean density	1.3? g/cm3 (assumed)
Equatorial surface gravity	<0.0017 m/s2
Equatorial escape velocity	<0.0032 km/s
Synodic rotation period	? d
Geometric albedo	0.06±0.02R
Temperature	~156 K
Spectral type	?
Apparent magnitude	18.19 to 21.91
Absolute magnitude (H)	15.1

118401 LINEAR (provisional designation 1999 RE₇₀, comet designation 176P/LINEAR) is an active asteroid and main-belt comet^[2]^[3] 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.^[4]

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.^[2] It is estimated short-period comets remain active for about 10,000 years before having most of their ice sublimated away and going dormant.

Eight 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), (457175) 2008 GO98 (362P/2008 GO₉₈),^[9] and (248370) 2005 QN173 (433P/2005 QN₁₇₃).^[10] As a dual-status object, astrometric observations of 118401 LINEAR should be reported under the minor planet designation.^[9]

118401 LINEAR last came to perihelion on 2017 March 12.^[6]

References

^ ^a ^b ^c "JPL Small-Body Database Browser: 118401 LINEAR (1999 RE70)" (2010-11-02 last obs). Retrieved 26 March 2016.
^ ^a ^b ^c 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
^ ^a ^b David Jewitt. "Main Belt Comets". UCLA, Department of Earth and Space Sciences. Retrieved 2010-12-15.
^ ^a ^b ^c 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. S2CID 17438376.
^ 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
^ ^a ^b ^c "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.
^ "Horizons Batch for 118401 LINEAR (1999 RE70 on 2028-Aug-05" (Perihelion occurs when rdot flips from negative to positive). JPL Horizons. Retrieved 2023-05-01. (JPL#73/Soln.date: 2023-Apr-27)
^ ^a ^b "Dual-Status Objects". Minor Planet Center. 2008-03-06. Retrieved 2018-02-13.
^ M.P.C. 133823