P/2019 LD2 (ATLAS)

P/2019 LD2 (ATLAS) is a Jupiter-family comet discovered by the Asteroid Terrestrial-impact Last Alert System on 10 June 2019. It was initially reported as the first known Jupiter trojan asteroid to display cometary activity,[6] but its classification as a Jupiter trojan was retracted after closer examination and a longer observation arc revealed its orbit to be unstable like a typical Jupiter family comet and implied that its position near the trojans is temporary.[1][7]

P/2019 LD2 (ATLAS)
P/2019 LD2 (ATLAS) imaged by the Hubble Space Telescope in April 2020
Discovery [1]
Discovered byATLAS-MLO
Discovery siteMauna Loa Obs.
Discovery date10 June 2019 (first observed)
Designations
2019 LD2
Jupiter-family comet[1]
periodic [2]
centaur [3]
Orbital characteristics [1][4]
Epoch 27 July 2019 (JD 2458691.5)
Uncertainty parameter 4
Observation arc2.00 yr (729 d)
Earliest precovery date21 May 2018
Aphelion6.0774 AU
Perihelion4.5784 AU
5.3279 AU
Eccentricity0.14068
12.3 yr
339.529°
0° 4m 48.518s / day
Inclination11.517°
180.217°
122.688°
Jupiter MOID0.0334843 AU
TJupiter2.940
Physical characteristics
Mean diameter
~14 km (assuming albedo of 0.12)[5]
19.0[4]
12.20±0.83 (M1=6.9±0.8)[1]
12.1[4]

    Discovery

    P/2019 LD2 was discovered in images by the Asteroid Terrestrial-impact Last Alert System (ATLAS) at the Mauna Loa Observatory taken on 10 June 2019.[4] Upon discovery, astronomers Alan Fitzsimmons and David Young at Queen's University Belfast suspected a faint coma around P/2019 LD2.[2] Follow-up observations by the Las Cumbres Observatory in 11 and 13 June 2019 confirmed the cometary appearance of P/2019 LD2, which now had a more apparent coma and tail. Later observations by the ATLAS-MLO in April 2020 showed that P/2019 LD2 still retained its cometary appearance, suggesting that it has been continuously active for almost a year.[6]

    The discovery of P/2019 LD2's cometary activity was announced in a press release by the University of Hawaiʻi Institute for Astronomy on 20 May 2020, purporting it as the first known active Jupiter trojan, as it was discovered near Jupiter's L4 Lagrangian point where the Greek camp trojans reside.[6] However, upon closer examination of P/2019 LD2's orbital dynamics by amateur astronomer Sam Deen, P/2019 LD2 was found to be a Jupiter-family comet with a chaotic orbit instead of a Jupiter trojan.[7][8] Subsequently, the comet was reclassified and was given the periodic comet designation P/2019 LD2 (ATLAS) by the Minor Planet Center on 22 May 2020.[2]

    Orbit and classification

    P/2019 LD2 orbits the Sun at a mean distance of 5.29 AU once every 12.18 years. Its orbit has an eccentricity of 0.135 and an inclination of 11.6 degrees with respect to the ecliptic.[1] The body's observation arc begins with a precovery, published by the Pan-STARRS 1 survey and taken at Haleakala Observatory on 21 May 2018, or 11 months prior to its official discovery observation by the ALTAS-MLO survey.[4]

    P/2019 LD2 is a Jupiter-family comet with a Tisserand parameter of 2.94, typical for other Jupiter-family comets.[1] The comet's nominal orbit suggests that it is not in a stable 1:1 resonance with Jupiter as it has made a close approach to the planet on 17 February 2017, at a distance of 0.092 AU (13.8 million km; 8.6 million mi), and will make a similarly close approach in 2028.[1][8] Unlike the Jupiter trojans, P/2019 LD2 is 21 degrees ahead of Jupiter, and will continue drifting 30 degrees ahead before returning back to Jupiter and making close approaches.[8]

    Physical characteristics

    Based on a generic magnitude-to-diameter conversion,[9] P/2019 LD2 measures approximately 14 kilometers in diameter, for an assumed albedo of 0.12 as the median for small Jupiter trojans,[5] and an absolute magnitude of 12.2.[1] As of May 2020, no rotational light curve of P/2019 LD2 has been obtained from photometric observations. The body's rotation period, pole and shape remain unknown.[1][10]

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    See also

    References
    1. "JPL Small-Body Database Browser: (P/2019 LD2)" (2020-05-19 last obs.). Jet Propulsion Laboratory. Retrieved 21 May 2020.
    2. "MPEC 2020-K134 : COMET P/2019 LD2 (ATLAS)". Minor Planet Electronic Circular. Minor Planet Center. 22 May 2020. Retrieved 22 May 2020.
    3. Kareta, Theodore; Volk, Kathryn; Noonan, John W.; Sharkey, Benjamin N. L.; Harris, Walter M.; Reddy, Vishnu (May 2020). "An Extremely Temporary Co-orbital: The Dynamical State of Active Centaur 2019 LD2". Research Notes of the AAS. 4 (5). arXiv:2007.13945. Bibcode:2020RNAAS...4...74K. doi:10.3847/2515-5172/ab963c. 74.
    4. "P/2019 LD2". Minor Planet Center. International Astronomical Union. Retrieved 21 May 2020.
    5. Fernández, Y. R.; Jewitt, D.; Ziffer, J. E. (June 2009). "Albedos of Small Jovian Trojans". The Astronomical Journal. 138 (1): 240–250. arXiv:0906.1786. Bibcode:2009AJ....138..240F. doi:10.1088/0004-6256/138/1/240.
    6. "UH ATLAS telescope discovers first-of-its-kind asteroid". Institute for Astronomy. University of Hawaiʻi. 20 May 2020. Retrieved 21 May 2020.
    7. "Astronomers recategorize asteroid-like comet detected by UH ATLAS telescope". University of Hawaiʻi News. University of Hawaiʻi. 26 May 2020. Retrieved 27 May 2020.
    8. Hecht, Jeff (28 May 2020). "Jupiter Has Trapped a Comet in a Bizarre Orbit". Sky & Telescope. Retrieved 28 May 2020.
    9. Bruton, D. "Conversion of Absolute Magnitude to Diameter for Minor Planets". Department of Physics, Engineering, and Astronomy. Stephen F. Austin State University. Retrieved 21 May 2020.
    10. "LCDB Data for 2019 LD2 – Not in Data Base". Asteroid Lightcurve Database (LCDB). Retrieved 21 May 2020.

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