2020 SO
The orbit of 2020 SO around Earth and Sun from Nov. 2020 to Mar. 2021
Discovery [1][2]
Discovered byPan-STARRS 1
Discovery siteHaleakalā Obs.
Discovery date17 September 2020
Designations
2020 SO
P116rK2 [3]
NEO · Apollo (May 2020)[4]
Atira (Dec 2020)[2]
Orbital characteristics [2]
Epoch 17 December 2020 (JD 2459200.5)
Uncertainty parameter 2
Observation arc167 days
Earliest precovery date19 August 2020
Aphelion0.988 AU
Perihelion0.985 AU
0.986 AU
Eccentricity0.00181
0.98 yr (357.9 d)
276.388°
1° 0m 21.877s / day
Inclination0.1389°
216.656°
311.989°
Earth MOID0.01628 AU (May 2020)[4]
0.00106 AU (Dec 2020)
Physical characteristics
Mean diameter
6–12 m (assumed)[5]
0.0026080±0.0000001 h[6]
or 9.39 s
22.4 (at discovery)[1]
14.1 (1 Dec 2020)[7]
27.66±0.34[4]
28.43[2]

    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]

    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 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]

    Photograph of the Surveyor 2 Centaur rocket booster at launch in 1966

    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. 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]

    Orbital Elements for May and December 2020
    Parameter Epoch Orbit
    type    		 Period
    (p)    		 Aphelion
    (Q)    		 Perihelion
    (q)    		 Semi-major
    axis
    (a)    		 Inclination
    (i)    		 Heliocentric
    eccentricity
    (e)    		 Geocentric
    eccentricity
    (e)[10][lower-alpha 3]
    Units (years) AU (°)
    2020-May-31[4] Apollo 1.056 1.0722 1.0020 1.0371 0.14061° 0.03389 737
    2020-Dec-17[2] Atira 0.980 0.9882 0.9847 0.9865 0.13842° 0.00180 0.89934
    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][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

    1. ↑ This was the 14th object ("O") discovered in the first half (period "S") of September 2020. See Provisional designation in astronomy § New-style provisional designation.
    2. 1 2 The JPL Horizons On-Line Ephemeris System shows the geocentric orbital eccentricity dropping below 1 by 15 October 2020. But a second condition for capture is that the object is within Earth's Hill sphere which has a radius of roughly 0.01 AU (1.5 million km). Meeting both conditions is when the object is in a temporary satellite capture around Earth.
    3. ↑ Orbital eccentricity must be below 1 to be orbiting the central body.
    4. ↑ An object needs to be within Earth's Hill sphere to truly be in orbit. An object 1AU from Earth could have a geocentric e<1 if the relative velocities are small, but we would not say it is orbiting Earth.

    References

    1. 1 2 3 "MPEC 2020-S78 : 2020 SO". Minor Planet Electronic Circular. Minor Planet Center. 19 September 2020. Retrieved 20 September 2020.
    2. 1 2 3 4 5 "2020 SO". Minor Planet Center. International Astronomical Union. Archived from the original on 11 February 2021. Retrieved 20 September 2020.
    3. ↑ "2020 SO". NEO Exchange. Las Cumbres Observatory. 18 September 2020. Retrieved 20 September 2020.
    4. 1 2 3 4 5 6 7 8 "JPL Small-Body Database Browser: 2020 SO" (2020-12-01 last obs.). Jet Propulsion Laboratory. Archived from the original on 26 January 2021. Retrieved 20 September 2020.
    5. ↑ "NEO Earth Close Approaches". Center for Near Earth Object Studies. Jet Propulsion Laboratory. Retrieved 10 October 2020.
    6. 1 2 Peter Birtwhistle (Great Shefford Observatory). "Light curve".
    7. 1 2 "2020SO Ephemerides for 1 December 2020". NEODyS (Near Earth Objects – Dynamic Site). Archived from the original on 26 September 2020. Retrieved 26 September 2020.
    8. ↑ Talbert, Tricia (2 December 2020). "New Data Confirm 2020 SO to be the Upper Centaur Rocket Booster from the 1960's". NASA. Retrieved 2 December 2020.
    9. ↑ "MPEC 2021-D62 : DELETION OF 2020 SO". Minor Planet Electronic Circular. Minor Planet Center. 19 February 2020. Retrieved 19 February 2020.
    10. 1 2 3 4 Horizons output. "Geocentric Orbital Elements for Asteroid (2020 SO)". Retrieved 27 September 2020. ("Ephemeris Type" select "Orbital Elements"  · "Center" select 500 for Geocentric. Output lists Eccentricity as "EC".)
    11. 1 2 Greicius, Tony (12 November 2020). "Earth May Have Recaptured a 1960s-Era Rocket Booster". NASA. Retrieved 12 November 2020.
    12. 1 2 Dunn, Marcia (11 October 2020). "Fake asteroid? NASA expert IDs mystery object as old rocket". phys.org. Retrieved 12 October 2020.
    13. ↑ Harris, Alan (20 September 2020). "Re: another natural satellite of Earth... again". groups.io. Retrieved 20 September 2020.
    14. ↑ B., Mark (12 October 2020). "NASA Expert Believes New "Asteroid" is a Discarded Rocket Part". The Science Times. Retrieved 3 November 2020. Spectroscopy on the surface of 2020 SO can also determine whether it has titanium dioxide - the paint material used on space rockets.
    15. ↑ "Goldstone Radar Observations Planning: 2020 SO". Asteroid Radar Research. Retrieved 30 November 2020.
    16. 1 2 "2020 SO · IAA RAS". iaaras.ru. Retrieved 10 December 2020.
    17. ↑ "Limiting Magnitude". The Wilderness Center Astronomy Club. Archived from the original on 17 November 2020. Retrieved 26 September 2020.
    18. ↑ Masi, Gianluca (2 December 2020). "Near-Earth object 2020 SO: rotation and time-lapse – 01 Dec. 2020". Virtual Telescope Project. Retrieved 2 December 2020.
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