P/2019 LD₂ (ATLAS)

P/2019 LD2 (ATLAS) imaged by the Hubble Space Telescope in April 2020
Discovery  [1]
Discovered by	ATLAS-MLO
Discovery site	Mauna Loa Obs.
Discovery date	10 June 2019 (first observed)
Designations
MPC designation	2019 LD2
Minor planet category	Jupiter-family comet [1] periodic  [2] centaur  [3]
Orbital characteristics  [1] [4]
Epoch 27 July 2019 ( JD 2458691.5)
Uncertainty parameter 4
Observation arc	2.00 yr (729 d)
Earliest precovery date	21 May 2018
Aphelion	6.0774 AU
Perihelion	4.5784 AU
Semi-major axis	5.3279 AU
Eccentricity	0.14068
Orbital period (sidereal)	12.3 yr
Mean anomaly	339.529 °
Mean motion	0° 4m 48.518s / day
Inclination	11.517°
Longitude of ascending node	180.217°
Argument of perihelion	122.688°
Jupiter  MOID	0.0334843 AU
TJupiter	2.940
Physical characteristics
Mean diameter	~14 km (assuming albedo of 0.12) [5]
Apparent magnitude	19.0 [4]
Absolute magnitude (H)	12.20±0.83 (M1=6.9±0.8) [1] 12.1 [4]

P/2019 LD₂ (ATLAS) is a Jupiter-family comet discovered by the Asteroid Terrestrial-impact Last Alert System on 10 June 2019. ^{[6] [7]} It was initially reported as the first known Jupiter trojan asteroid to display cometary activity, ^[8] but its classification as a Jupiter trojan was retracted after closer examination and a longer observation arc revealed its orbit to be unstable like a typical Jupiter family comet and implied that its position near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] [9]}

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. ^[8]

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. ^[8] 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. ^{[9] [10]} 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] [10]} Unlike the Jupiter trojans, P/2019 LD₂ is 21 degrees ahead of Jupiter, and will continue drifting 30 degrees ahead before returning to Jupiter and making close approaches. ^[10] P/2019 LD₂ is now following what looks like a short arc of a quasi-satellite cycle with respect to Jupiter that started in 2017 and will end in 2028. ^[11]

^[12] On 2063 January 23, it will have a very close encounter with Jupiter at 0.016 AU; orbital predictions after this flyby are rather uncertain. ^[12]

Physical characteristics

Based on a generic magnitude-to-diameter conversion, ^[13] 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 ^[update], 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] [14]} The visible spectrum does not exhibit any evidence of CN, C2, or C3 emission. ^{[11] [12]}

During the approach to perihelion in 2020, the comet shed large-grained (0.1 mm typical) dust grains rich with water ice. ^[15]

See also

• 6478 Gault
• 7968 Elst–Pizarro
• 118401 LINEAR
• (300163) 2006 VW139

References

External links

• UPDATE: Astronomers recategorize asteroid-like comet detected by ATLAS telescope, NASA Solar System Exploration, 28 May 2020
• Jupiter Has Trapped a Comet in a Bizarre Orbit, Jeff Hect, Sky & Telescope, 28 May 2020
• Astronomers recategorize asteroid-like comet detected by UH ATLAS telescope, University of Hawaiʻi News, 26 May 2020
• UH ATLAS telescope discovers first-of-its-kind asteroid, University of Hawaiʻi Institute for Astronomy, 20 May 2020
• P/2019 LD2 (ATLAS) at AstDyS-2, Asteroids—Dynamic Site
  • Ephemeris · Observation prediction · Orbital info · Proper elements · Observational info
• P/2019 LD2 at the JPL Small-Body Database
  • Close approach · Discovery · Ephemeris · Orbit diagram · Orbital elements · Physical parameters