2020 SO

As it approached Earth, the trajectory indicated the geocentric orbital eccentricity was less than 1 by 15 October 2020,^[10][b] and the object became temporarily captured on 8 November when it entered Earth's Hill sphere.^[11] It entered via the outer Lagrange point L₂ and will exit via Lagrange point L₁. During its geocentric orbit around Earth, 2020 SO made a close approach to Earth on 1 December 2020 at a perigee distance of approximately 0.13 lunar distances (50,000 km; 31,000 mi).^[4] It also made another close approach on 2 February 2021, at a perigee distance of approximately 0.58 LD (220,000 km; 140,000 mi).^[4] Since discovery the time of uncertainty for February 2021 closest approach to Earth was reduced from ±3 days to less than 1 minute.^[4] It left Earth's Hill sphere at around 8 March 2021.^[12][b]

Paul Chodas of the Jet Propulsion Laboratory suspects 2020 SO of being the Surveyor 2 Centaur rocket booster, launched on 20 September 1966.^[11][12][13] The Earth-like orbit and low relative velocity suggest a possible artificial object. Spectroscopy may help determine if it is covered in white titanium dioxide paint.^[14] Goldstone radar produced bistatic observations on 30 November 2020 transmitting from the 70-meter DSS-14 and receiving at the 34-meter DSS-13.^[15] As a result of the bistatic DSS-14/RT-32 radar observations, a rotation period of about 9.5 seconds was obtained,^[16] which corresponds to the photometric observations.^[6] Obtained range-Doppler radar images^[16] confirm that the object has an elongated shape with a length of about 10 meters and a width of about 3 meters.

Around the time of closest approach on 1 December 2020, the object was only brightened to about apparent magnitude 14.1,^[7] and required a telescope with roughly a 150mm (6") objective lens to be seen visually.^[17] It displays a large light curve amplitude of 2.5 magnitudes, signifying a highly elongated shape or albedo variations on its surface. It has a rotation period of approximately 9 seconds.^[18]

At the time of its discovery, 2020 SO had unremarkable motion typical of a main-belt asteroid.^{[citation needed]} However, the four observations that Pan-STARRS obtained over the course of 1.4 hours showed non-linear motion due to the rotation of the observer around Earth's axis, which is a signature of a nearby object.^[1][10]

Animation of 2020 SO's orbit

Around the Sun

Around the Earth

  Sun ·    Earth ·    2020 SO ·    Moon

In January and February 2036, it will again approach Earth with a geocentric eccentricity less than 1 since the relative velocities will be small,^[10] but will not be within Earth's Hill sphere of 0.01 AU (1.5 million km).^[4][d]

• J002E3 – a near-Earth object discovered in 2002 that was identified as the S-IVB third stage of the Apollo 12 Saturn V rocket
• WT1190F – temporarily orbiting space debris that entered Earth's atmosphere in 2015
• 2018 AV2 – an artificial object discovered in a temporary orbit around Earth in 2018, now suspected to be the Snoopy module from Apollo 10
• 6Q0B44E – another artificial object discovered in orbit around Earth in 2018
• Space debris
• Temporary satellite