(614689) 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 Lagrangian point, one of the dynamically stable locations where the combined gravitational force acts through the Sun's and Earth's barycenter. Analysis of 's trojan orbit stability suggests it will remain around Earth's point for at least four thousand years until gravitational perturbations from repeated close encounters with Venus destabilize its trojan configuration. With a diameter of about, is the second Earth trojan discovered, after, and is the largest of its kind known.
Discovery
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. The asteroid was moving at an on-sky rate of 3.02 arcseconds per minute, from a distance of from Earth.The asteroid was subsequently listed on the Minor Planet Center's Near-Earth Object Confirmation Page as P11aRcq. Over two days, follow-up observations were carried out by the Višnjan Observatory, ESA Optical Ground Station, and Cerro Tololo Observatory. The asteroid was identified in earlier Mount Lemmon Survey observations from 26 November 2020. The listing was confirmed and publicly announced as on 14 December 2020.
Name and numbering
This minor planet was given the permanent number 614689 by the Minor Planet Center on 28 March 2022 and is now eligible for naming. In accordance with the International Astronomical Union's naming conventions for near-Earth objects, will be given a mythological name.Orbit and classification
The orbit of is well known with an uncertainty parameter of 0 and a long observation arc over 8 years. The asteroid has been identified in several precovery observations by various sky surveys, including Pan-STARRS, from dates as far back as December 2012.orbits the Sun at an average distance of 1.001 AU once every 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 Earth's while having a semi-major axis greater than 1 AU, is classified as an Apollo asteroid.
Trojan orbit
Trojan objects are most easily conceived as orbiting at a Lagrangian point, a dynamically stable location 60 degrees ahead of or behind a massive orbiting body, in a type of 1:1 orbital resonance. In reality, they oscillate around such a point.On 26 January 2021, amateur astronomer Tony Dunn reported that 's nominal trajectory appears to be librating about Earth's leading Lagrangian point, suspecting it to be an Earth trojan. Subsequent analysis confirmed modeling stability for at least several thousand years into the future based on existing orbital parameters. This would make more stable than the prototype Earth trojan, which is potentially unstable on timescales of less than 2,000 years. Additional follow-up observations and precoveries confirmed 's trojan nature, and showed that it will leave trojan orbit at least 4,000 years into the future. Numerical simulations indicate that has likely been captured into the Langrangian point since the 15th century.
'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 of, 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. Venus's influence on 's orbit will become greater over time as their longitudes of the ascending node precess over hundreds of years, lowering 's Venus MOID and eventually destabilizing its trojan orbit by sending it past Earth's point in several thousand years.
Physical characteristics
Photometric measurements of optical observations from 2020–2021 show that exhibits a color resembling that of carbonaceous C-type asteroids. Based on 's phase curve being similar to C-type asteroids, its absolute magnitude of 18.6 corresponds to a mean diameter about, calculated from a geometric albedo of 0.06 typical for C-type asteroids. This makes the largest Earth trojan asteroid known to date, being up to three times as large as (706765) whose size is.Because of its fixed position in Earth's sky, relative to the Sun, is only visible low on the horizon, during twilight. Accurate photometry of its light curve by terrestrial observers is made erratic by heavy atmospheric distortion and swamped by scattered light from the recently set Sun. Consequently, no information about its rotation has been determined.