2020 SL₁ is a near-Earth asteroid of the Apollo group, discovered by the Pan-STARRS 1 survey at Haleakala Observatory, Hawaii on 18 September 2020. With an estimated diameter of 0.9–2.0 km (0.56–1.24 mi), it is the largest potentially hazardous asteroid discovered in 2020.^[8]

Discovery

2020 SL₁ was discovered by the Pan-STARRS 1 survey at Haleakala Observatory, Hawaii on 18 September 2020. It was first observed in the constellation Triangulum at an apparent magnitude of 22.3.^[1] The asteroid was moving at an on-sky rate of 0.56 arcseconds per minute, from a distance of 1.94 AU (290 million km; 180 million mi) from Earth.^[9]

The asteroid was subsequently listed on the Minor Planet Center's Near-Earth Object Confirmation Page (NEOCP) as P116Atg.^[4] Follow-up observations were carried out by the Astronomical Research Observatory (H21) and the asteroid was identified in earlier Mount Lemmon Survey (G96) observations from 28 August and 17 September 2020. The listing was confirmed and publicly announced as 2020 SL₁ on 19 September 2020.^[1]

Since discovery, 2020 SL₁ has been identified in several precovery observations from Pan-STARRS 1 between November 2012 and January 2015 as well as October 2012 observations from the Mount Lemmon Survey. The earliest known precovery observations were identified in three Sloan Digital Sky Survey images from 25 October 2008.^[2]

Orbit and classification

2020 SL₁ orbits the Sun at an average distance of 2.52 AU once every 3.99 years. Its orbit has a high eccentricity of 0.64 and an inclination of 14° with respect to the ecliptic plane. Over the course of its orbit, its distance from the Sun ranges from 0.91 AU at perihelion to 4.1 AU at aphelion, crossing the orbits of Earth and Mars.^[5] Since its orbit crosses that of Earth's while having a semi-major axis greater than 1 AU, 2020 SL₁ is classified as an Apollo asteroid.

Having a long observation arc over 12 years, the orbit of 2020 SL₁ is well-defined with a condition code of 1.^[5] Although it is classified as a potentially hazardous asteroid due to its large size combined with its small minimum orbit intersection distance of 0.047 AU (7.0 million km; 4.4 million mi) from Earth's orbital path, the asteroid will not make any close approaches within 0.1 astronomical units (15×10^⁶ km; 9.3×10^⁶ mi) over the next 200 years. The closest Earth encounter by 2020 SL₁ in the last 200 years was on 10 July 1972, when it passed within 0.073 AU (10.9 million km; 6.8 million mi) of Earth at closest approach.^[5]

Physical characteristics

Diameter and albedo

Based on an magnitude-to-diameter conversion and a measured absolute magnitude of 17.35, 2020 SL₁ measures between 0.9 and 2.0 kilometers in diameter for an assumed geometric albedo of 0.25 and 0.05, respectively.^[2][6] It is the largest potentially hazardous asteroid discovered in 2020, followed by 2020 QF6 with an absolute magnitude of 17.8.^[8]