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(614689) 2020 XL5

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2020 XL5
Discovery [1][2]
Discovered byPan-STARRS 1
Discovery siteHaleakala Obs.
Discovery date12 December 2020
Designations
2020 XL5
P11aRcq [3][4]
Earth trojan[5] · NEO
Apollo [6]
Orbital characteristics [6]
Epoch 21 January 2022 (JD 2459600.5)
Uncertainty parameter 2
Observation arc348 days
Earliest precovery date26 November 2020
Aphelion1.389 AU
Perihelion0.6133 AU
1.001 AU
Eccentricity0.38713
1.00 yr (365.77 d)
316.420°
0° 59m 4.269s / day
Inclination13.847°
153.598°
87.981°
Earth MOID0.07571 AU (11,326,000 km)
Venus MOID0.02726 AU (4,078,000 km)[2]
Physical characteristics
320±80 m[7]
22.5 (current)[8]
21.4 (at discovery)[1]
20.18±0.47[6]
20.18[2]

2020 XL5 is a near-Earth asteroid and Earth trojan discovered by the Pan-STARRS 1 survey at Haleakala Observatory, Hawaii on 12 December 2020. It oscillates around the Sun–Earth L4 Lagrangian point (leading 60°), one of the dynamically stable locations where the combined gravitational force acts through the Sun's and Earth's barycenter. Analysis of 2020 XL5's trojan orbit stability suggests it will remain around Earth's L4 point for about 10,000 years until gravitational perturbations from repeated close encounters with Venus destabilize its trojan configuration. It is the second Earth trojan discovered, after 2010 TK7 in 2010.[7]

Discovery

2020 XL5 was discovered by the Pan-STARRS 1 survey at Haleakala Observatory, Hawaii on 12 December 2020. It was first observed in the constellation Crater at an apparent magnitude of 21.4.[1] The asteroid was moving at an on-sky rate of 3.02 arcseconds per minute, from a distance of 0.68 AU (102 million km; 63 million mi) from Earth.[9]

The asteroid was subsequently listed on the Minor Planet Center's Near-Earth Object Confirmation Page (NEOCP) as P11aRcq.[4] Over two days, follow-up observations were carried out by the Višnjan Observatory (L01), ESA Optical Ground Station (J04), and Cerro Tololo Observatory (807). The asteroid was identified in earlier Mount Lemmon Survey (G96) observations from 26 November 2020. The listing was confirmed and publicly announced as 2020 XL5 on 14 December 2020.[1]

Orbit and classification

Heliocentric orbit diagram of 2020 XL5 along with the inner planets

The orbit of 2020 XL5 is well-defined with an uncertainty parameter of 2 and observation arc of 348 days.[6] Additional observations over several oppositions are necessary to constrain its orbit over the long-term.

2020 XL5 orbits the Sun at an average distance of 1.001 AU once every 365.8 days, or approximately 1 Earth year. Its orbit has a high eccentricity of 0.388 and an inclination of 13.8° with respect to the ecliptic plane. Over the course of its orbit, its distance from the Sun ranges from 0.61 AU at perihelion to 1.39 AU at aphelion, crossing the orbits of Venus and Earth. Since its orbit crosses that of Earth's while having a semi-major axis greater than 1 AU (by a small margin), 2020 XL5 is classified as an Apollo asteroid.[6]

Trojan orbit

Effective potential plot showing Earth's Lagrangian points (not to scale); contours around L4 and L5 represent tadpole loop paths
Animation of 2020 XL5's orbit from 1600 to 2500 - relative to Sun and Earth   Sun ·   Earth ·   2020 XL5

Trojan objects are most easily conceived as orbiting at a Lagrangian point, a dynamically stable location (where the combined gravitational force acts through the Sun's and Earth's barycenter) 60 degrees ahead of (L4) or behind (L5) a massive orbiting body, in a type of 1:1 orbital resonance. In reality, they oscillate around such a point.[5]

On 26 January 2021, amateur astronomer Tony Dunn reported that 2020 XL5's nominal trajectory appears to be librating about Earth's leading L4 Lagrangian point, suspecting it to be an Earth trojan.[5] Subsequent analysis confirmed modeling stability for at least several thousand years into the future based on existing orbital parameters.[10][11] This would make 2020 XL5 more stable than the prototype L4 Earth trojan 2010 TK7, which is potentially unstable on timescales of less than 2,000 years.[12] Additional observations from September 2021 confirmed 2020 XL5's trojan nature, and showed that its orbit is unstable on a 10,000 year timescale.[7] Numerical simulations indicate that 2020 XL5 was likely captured into the L4 Langrangian point since the 15th century.[7]

2020 XL5's high orbital eccentricity results in wide, tadpole-shaped oscillation paths in a corotating reference frame with Earth and its Lagrangian points. Although the asteroid crosses Venus's orbit with a minimum orbit intersection distance (MOID) of 0.0273 AU (4.1 million km; 2.5 million mi),[2] perturbations by the planet are currently negligible since its nominal orbit brings it either too high or too low from the plane of Venus's orbit.[13] Venus's influence on 2020 XL5's orbit will become greater over time as their longitudes of the ascending node precess over hundreds of years, lowering 2020 XL5's Venus MOID and eventually destabilizing its trojan orbit by sending it to Earth's L3 point in several thousand years.[13]

Physical characteristics

Based on an magnitude-to-diameter conversion and a measured absolute magnitude of 20.18, 2020 XL5 measures between 250 and 550 meters in diameter for an assumed geometric albedo of 0.25 and 0.05, respectively.[14] Its absolute magnitude is slightly smaller (thus brighter) than that of 2010 TK7 (20.8),[15] implying that 2020 XL5 likely has a slightly larger diameter if both have the same geometric albedos.[5] This makes 2020 XL5 likely the largest known Earth trojan to date.

See also

References

  1. ^ a b c d "MPEC 2020-X171 : 2020 XL5". Minor Planet Electronic Circular. Minor Planet Center. 14 December 2020. Retrieved 5 February 2021.
  2. ^ a b c d "2020 XL5". Minor Planet Center. International Astronomical Union. Retrieved 5 February 2021.
  3. ^ "2020 XL5". NEO Exchange. Las Cumbres Observatory. 14 December 2020. Retrieved 6 February 2021.
  4. ^ a b Gray, Bill (14 December 2020). ""Pseudo-MPEC" for P11aRcq". Project Pluto. Retrieved 6 February 2021.
  5. ^ a b c d Hecht, Jeff (4 February 2021). "Second Earth Trojan Discovered". Sky & Telescope. Retrieved 5 February 2021.
  6. ^ a b c d e "JPL Small-Body Database Browser: 2020 XL5" (2021-11-09 last obs.). Jet Propulsion Laboratory. Retrieved 5 February 2021.
  7. ^ a b c d Hui, Man-To; Wiegert, Paul A.; Tholen, David J.; Föhring, Dora (November 2021). "The Second Earth Trojan 2020 XL5". The Astrophysical Journal Letters. 922 (2): L25. arXiv:2111.05058. Bibcode:2021ApJ...922L..25H. doi:10.3847/2041-8213/ac37bf. S2CID 243860678.{{cite journal}}: CS1 maint: unflagged free DOI (link)
  8. ^ "2020XL5". Near Earth Objects – Dynamic Site. Department of Mathematics, University of Pisa, Italy. Retrieved 5 February 2021.
  9. ^ "2020XL5 Ephemerides". Near Earth Objects – Dynamic Site (Ephemerides at discovery (obs. code F51)). Department of Mathematics, University of Pisa, Italy. Retrieved 6 February 2021.
  10. ^ Vitagliano, Aldo (28 January 2021). "Re: Could newly-discovered 2020 XL5 be an Earth Trojan?". groups.io. Retrieved 6 February 2021.
  11. ^ de la Fuente Marcos, Carlos; de la Fuente Marcos, Raúl (18 February 2021). "Transient Terrestrial Trojans: Comparative Short-term Dynamical Evolution of 2010 TK7 and 2020 XL5". Research Notes of the American Astronomical Society. 5 (2): 29. Bibcode:2021RNAAS...5...29D. doi:10.3847/2515-5172/abe6ad.
  12. ^ Connors, Martin; Wiegert, Paul; Veillet, Christian (July 2011). "Earth's Trojan asteroid". Nature. 475 (7357): 481–483. Bibcode:2011Natur.475..481C. doi:10.1038/nature10233. PMID 21796207. S2CID 205225571.
  13. ^ a b Dunn, Tony (2 January 2021). "Re: Could newly-discovered 2020 XL5 be an Earth Trojan?". groups.io. Retrieved 6 February 2021.
  14. ^ Bruton, Dan. "Conversion of Absolute Magnitude to Diameter for Minor Planets". Department of Physics, Engineering, and Astronomy. Stephen F. Austin State University. Retrieved 5 February 2021.
  15. ^ "JPL Small-Body Database Browser: 2010 TK7" (2017-10-30 last obs.). Jet Propulsion Laboratory. Retrieved 6 February 2021.
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