(118378) 1999 HT11

(118378) 1999 HT11, provisional designation: 1999 HT11, is a trans-Neptunian object from the outermost region of the Solar System, locked in a 4:7 orbital resonance with Neptune. It was discovered on 17 April 1999, by astronomers at the Kitt Peak Observatory, Arizona, in the United States.[2] The very red object measures approximately 134 kilometers (83 miles) in diameter. As of 2021, it has not been named.

(118378) 1999 HT11
Discovery[1][2]
Discovered byKitt Peak National Obs.
Discovery siteKitt Peak National Obs.
Discovery date17 April 1999
Designations
(118378) 1999 HT11
1999 HT11
TNO[3] · res (4:7)[4][5]
Orbital characteristics[3]
Epoch 1 July 2021 (JD 2459396.5)
Uncertainty parameter 3[2][3]
Observation arc20.78 yr (7,589 d)
Aphelion49.001 AU
Perihelion38.734 AU
43.868 AU
Eccentricity0.1170
290.55 yr (106,124 d)
328.33°
0° 0m 12.24s / day
Inclination5.0489°
87.954°
189.27°
Physical characteristics
Mean diameter
134 km (est. at 0.09)[4]
23.42[8]
7.6[2][3]

    Discovery

    1999 HT11 was first observed on the night of 17 April 1999, by astronomers using the 4-meter Nicholas U. Mayall Telescope at Kitt Peak National Observatory in Arizona. Five additional objects were discovered on the same weekend: 1999 HR11, 1999 HS11, 1999 HU11 (Deucalion), 1999 HV11 and 1999 HW11. The observing astronomers were Robert Millis, James Elliot, Matthew Holman, Mark Wagner as well as Kim Falinski. Follow-up observations with the Nordic Optical Telescope at the Roque de los Muchachos Observatory, La Palma, Spain, were made three weeks later. The body's observation arc begins with its official discovery observation at Kitt Peak on 17 April 1999.[1][2]

    Orbit and classification

    This minor planet orbits the Sun at a distance of 38.7–49.0 AU once every 290 years and 7 months (106,124 days; semi-major axis of 43.87 AU). Its orbit has an eccentricity of 0.12 and an inclination of 5° with respect to the ecliptic.[3] As of 2021, it is at 39.7 AU from the Sun with an apparent magnitude of 23.42,[8] and will come to perihelion in 2047.[3]

    1999 HT11 is a resonant trans-Neptunian object that stays in a 4:7 mean-motion orbital resonance with Neptune, orbiting exactly four times the Sun for every seven orbits Neptune does and are therefore protected from the planets scattering effect. The classification is deemed secure.[4][5] The 4:7 resonance is located in the midst of the classical objects of the Kuiper belt, a circumstellar disc of otherwise non-resonant bodies, contrary to the more prominent resonant plutinos (2:3) and twotinos (1:2) which form the inner and outer rim of the Kuiper belt, respectively.

    Numbering and naming

    This minor planet was numbered by the Minor Planet Center on 16 November 2005, receiving the number (118378) in the minor planet catalog (M.P.C. 55526).[9] As of 2021, it has not been named.[2] According to the established naming conventions, it will be given a mythological name associated with the underworld or with creation.[10]

    Physical characteristics

    1999 HT11 has a very red surface color (RR) in the visible part of the spectrum, with B−V and V–R color indices of 1.150±0.064 and 0.670±0.040, respectively, for a combined B−R magnitude of 1.820±0.050.[4][6][7] A red surface color is typically associated with the presence of tholins, polymer-like organic compounds, formed by long exposures to solar and cosmic radiation.

    Based on a generic magnitude-to-diameter conversion, 1999 HT11 measures approximately 134 kilometers (83 miles) in diameter, for an assumed albedo of 0.9 and an magnitude of 7.6.[4][11] According to Mike Brown, who estimates a mean-diameter of 137 km (85 mi), the object is too small for being considered a dwarf planet candidate ("probably not").[12] As of 2021, no rotational lightcurve for this body has been obtained from photometric observations. Its rotation period, pole and shape remain unknown.[3]

    References
    1. "MPEC 1999-K12 : SIX TNOs (including J99H11T)". Minor Planet Electronic Circular. Minor Planet Center. 19 May 1999. Retrieved 9 September 2021.
    2. "118378 (1999 HT11)". Minor Planet Center. Retrieved 11 September 2021.
    3. "JPL Small-Body Database Browser: 118378 (1999 HT11)" (2020-01-26 last obs.). Jet Propulsion Laboratory. Retrieved 11 September 2021.
    4. "List of Known Trans-Neptunian Objects". Johnston's Archive. 18 August 2020. Retrieved 11 September 2021.
    5. "Orbit Fit and Astrometric record for 118378". Southwest Research Institute. Retrieved 11 September 2021. (The Deep Ecliptic Survey Object Classifications)
    6. Sheppard, Scott S. (December 2012). "The Color Differences of Kuiper Belt Objects in Resonance with Neptune". The Astronomical Journal. 144 (6): 169. arXiv:1210.0537. Bibcode:2012AJ....144..169S. doi:10.1088/0004-6256/144/6/169. ISSN 0004-6256. S2CID 53746049.
    7. "LCDB Data for (118378)". Asteroid Lightcurve Database (LCDB). Retrieved 11 September 2021.
    8. "Asteroid (118378) 1999 HT11 – Ephemerides". AstDyS-2, Asteroids – Dynamic Site. Retrieved 11 September 2021.
    9. "MPC/MPO/MPS Archive". Minor Planet Center. Retrieved 11 September 2021.
    10. "Naming of Astronomical Objects – Minor planets". IAU – International Astronomical Union. Retrieved 11 September 2021.
    11. "Asteroid Size Estimator". CNEOS NASA/JPL. Retrieved 11 September 2021.
    12. Brown, Michael E. "How many dwarf planets are there in the outer solar system?". California Institute of Technology. Retrieved 11 September 2021.
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