2020 SO[lower-alpha 1] is a near-Earth object identified to be the Surveyor 2 Centaur rocket booster launched on 20 September 1966. The object was discovered by the Pan-STARRS 1 survey at the Haleakala Observatory on 17 September 2020. It was initially suspected to be an artificial object due to its low velocity relative to Earth and later on the noticeable effects of solar radiation pressure on its orbit. Spectroscopic observations by NASA's Infrared Telescope Facility in December 2020 found that the object's spectrum is similar to that of stainless steel, confirming the object's artificial nature.[8] Following the object's confirmation as space debris, the object was removed from the Minor Planet Center's database on 19 February 2021.[9]

2020 SO

The orbit of 2020 SO around Earth and Sun from Nov. 2020 to Mar. 2021
Discovery [1][2]
Discovered by	Pan-STARRS 1
Discovery site	Haleakalā Obs.
Discovery date	17 September 2020
Designations
MPC designation	2020 SO
Alternative designations	P116rK2 [3]
Minor planet category	NEO · Apollo (May 2020)[4] Atira (Dec 2020)[2]
Orbital characteristics [2]
Epoch 17 December 2020 (JD 2459200.5)
Uncertainty parameter 2
Observation arc	167 days
Earliest precovery date	19 August 2020
Aphelion	0.988 AU
Perihelion	0.985 AU
Semi-major axis	0.986 AU
Eccentricity	0.00181
Orbital period (sidereal)	0.98 yr (357.9 d)
Mean anomaly	276.388°
Mean motion	1° 0m 21.877s / day
Inclination	0.1389°
Longitude of ascending node	216.656°
Argument of perihelion	311.989°
Earth MOID	0.01628 AU (May 2020)[4] 0.00106 AU (Dec 2020)
Physical characteristics
Mean diameter	6–12 m (assumed)[5]
Synodic rotation period	0.0026080±0.0000001 h[6] or 9.39 s
Apparent magnitude	22.4 (at discovery)[1] 14.1 (1 Dec 2020)[7]
Absolute magnitude (H)	27.66±0.34[4] 28.43[2]

Overview

As it approached Earth, the trajectory indicated the geocentric orbital eccentricity was less than 1 by 15 October 2020,[10][lower-alpha 2] 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 the 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][lower-alpha 2]

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 will make bistatic observations 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 of 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][lower-alpha 4]

See also

• 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

Notes

References

External links

• "Pseudo-MPEC" for 2020 SO = Surveyor 2 Centaur, Bill Gray, Project Pluto, 31 January 2021
• Earth May Have Recaptured a 1960s-Era Rocket Booster, Tony Greicius, NASA, 12 November 2020
• Animation of the Line of Variation (via clone orbits) stretching out from December 2020 to May 2021
• 01 Dec 2020 image and rotation – Virtual Telescope Project / G. Masi
• 01 Dec 2020 time-lapse and photometry – Virtual Telescope Project / G. Masi
• 2020 SO at NeoDyS-2, Near Earth Objects—Dynamic Site
  • Ephemerides · Observation prediction · Orbital info · MOID · Proper elements · Observational info · Close approaches · Physical info · Orbit animation

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