(809875) 2020 BX12
Binary near-Earth asteroid

(809875) 2020 BX12
Radar images of 2020 BX12 reveal a small, elongated satellite orbiting around the spheroidal asteroid.
2020 BX12 and its satellite imaged by the Arecibo Observatory in February 2020
Discovery[1][2]
Discovered byATLAS-MLO
Discovery siteMauna Loa Obs.
Discovery date27 January 2020
Designations
2020 BX12
A10jUnf[3]
Apollo · PHA · NEO
Orbital characteristics[4]
Epoch 31 May 2020 (JD 2459000.5)
Uncertainty parameter 0
Observation arc6.09 yr (2,224 days)
Earliest precovery date5 January 2014
Aphelion2.4437 AU
Perihelion0.7570 AU
1.6004 AU
Eccentricity0.75704
2.02 yr (739.5 d)
34.442°
0° 29m 12.545s / day
Inclination40.067°
132.904°
70.492°
Known satellites1
Earth MOID0.002061 AU
Physical characteristics
205±65 m[5]: 9 
Mass7×108 to 3×1010 kg (system)[a][5]: 12 
2.5±0.5 h[5]: 9 
0.3 (assumed for S-type asteroids)[5]: 7 
Q or Sq[5]: 6 
20.631±0.396[4]

(809875) 2020 BX12 (or simply 2020 BX12) is a sub-kilometer binary asteroid, classified as a near-Earth asteroid and potentially hazardous object of the Apollo group. It was discovered on 27 January 2020 by the Asteroid Terrestrial-impact Last Alert System survey at the Mauna Loa Observatory during its approach to Earth of 0.02915 AU (4.361 million km; 11.34 LD). The Arecibo Observatory took radar images of 2020 BX12 on 4 February 2020, which led to the discovery of a small natural satellite orbiting 360 m (1,180 ft) away from the asteroid.[6][7] With a diameter of around 200 m (660 ft), 2020 BX12 is among the smallest 10% of known binary asteroids.[5] It was the last binary asteroid discovered by the Arecibo Observatory.[5]

Discovery

2020 BX12 was discovered on 27 January 2020 by the Asteroid Terrestrial-impact Last Alert System (ATLAS) survey at the Mauna Loa Observatory in Hawaii. The ATLAS survey was designed for detecting near-Earth asteroids on approach to Earth, particularly those that may be considered potentially hazardous under circumstances where they can approach Earth from close distances.[8] 2020 BX12 was identified by a team of astronomers consisting of Larry Denneau, John Tonry, Aren Heinze, and Henry Weiland, who were chiefly involved in the ATLAS project.[1][8] The asteroid was discovered during its approach to Earth and was at nominal distance of about 0.11 AU (16,000,000 km; 10,000,000 mi) from the planet.[9] At the time of discovery, 2020 BX12 was located in the constellation of Puppis at an apparent magnitude of 17.6.[1][b]

The discovery of 2020 BX12 was subsequently reported to the Minor Planet Center's Near-Earth Object Confirmation Page (NEOCP), where a preliminary orbit was calculated from additional observations conducted at multiple observatories.[10] Follow-up observations of 2020 BX12 spanned three days since its discovery, and the asteroid was formally announced in a Minor Planet Electronic Circular issued by the Minor Planet Center on 30 January 2020.[1]

Nomenclature

Upon discovery, the asteroid was given the temporary internal designation A10jUnf.[3] After follow up observations confirming the object, it was then given the provisional designation 2020 BX12 by the Minor Planet Center on 30 January 2020.[1] The provisional designation signifies the object's discovery date and year.[11] Once 2020 BX12 had a sufficiently long observation arc for its orbit to be accurately determined, the asteroid received the permanent minor planet number 809875 from the Minor Planet Center,[12] making it eligible for naming.[11]

Orbit and classification

2020 BX12 orbits the Sun at an average distance of approximately 1.60 astronomical units (0.239×10^9 km; 0.149×10^9 mi), taking 2.02 years to complete one full orbit. The orbit of 2020 BX12 is highly eccentric and inclined to the ecliptic plane: it has an orbital eccentricity of 0.757 and inclination of 40 degrees, with its orbit extending from 0.76 AU at perihelion to 2.44 AU at aphelion. As it approaches perihelion, 2020 BX12 moves above the ecliptic and comes closer to the Sun than Venus, whereas at aphelion, 2020 BX12 moves below the ecliptic and recedes from the Sun farther out than the orbit of Mars. The orbit of 2020 BX12 crosses that of Earth; thus it can occasionally make close approaches to Earth, making it a near-Earth object. With a semi-major axis (average orbit distance) greater than 1 AU and a perihelion distance within that of Earth, 2020 BX12 is formally classified under the Apollo group of near-Earth asteroids.[4][2]

The orbit of 2020 BX12 is highly inclined to the ecliptic by 40 degrees.
Side view of 2020 BX12's inclined orbit

The asteroid's minimum orbital intersection distance (MOID) from Earth is approximately 0.002 AU (0.30 million km; 0.19 million mi), or about 0.78 lunar distances.[4] Having such a small Earth MOID, 2020 BX12 is considered a potentially hazardous asteroid (PHA) by the Minor Planet Center, under the definition that PHAs have Earth MOIDs less than 0.05 AU and absolute magnitudes under 22.[2][13] Despite this, 2020 BX12 will not make any close Earth encounters within 15 lunar distances or 0.04 AU (6.0 million km; 3.7 million mi) over the next 200 years,[4][14] and the asteroid has not been listed by the JPL Sentry Risk Table as of 2020[update].[15]

On 12 February 2020, a team of astronomers identified 2020 BX12 in several precovery images taken by the Pan-STARRS 1 survey, with the earliest images dating back to 5 January 2014.[12] The observation arc of these precovery images spanned over six years, long enough for astronomers to refine and calculate 2020 BX12's orbit with accuracy.[2] This greatly reduced uncertainties in the asteroid's orbit, reducing its uncertainty parameter from 8 to 1.[1][12] As of February 2020[update] the observation arc of 2020 BX12 spans 6.09 years or 2,224 days, with an orbit uncertainty parameter of 0 according to the JPL Small-Body Database.[4]

2020 Earth approach

On 3 February 2020 at 18:56 UTC, 2020 BX12 passed 0.02915 AU (4.36 million km; 2.71 million mi), or 11.35 lunar distances, from Earth.[4] During its close approach to Earth, the asteroid approached Earth at a rate of 25.3 km/s (57,000 mph) and its apparent visual brightness peaked around magnitude 15.7, which is too faint to be seen with the naked eye.[4][16] At closest approach the asteroid's apparent motion in the sky was 1.2 degrees per hour, and it was in the constellation of Cetus, with an apparent magnitude of 16 and an angular separation of 20 degrees from the Moon.[16][c]

The February 2020 encounter by 2020 BX12 provided an opportunity for radar observatories to study the asteroid's characteristics in detail. 2020 BX12 was the first radar target observed by the Arecibo Observatory in Puerto Rico since the one-month shutdown of observatory operations due to a series of earthquakes in the southern region of Puerto Rico in December 2019 and January 2020.[17] Radar observations of 2020 BX12 were conducted on 4 February 2020 by a team of astronomers led by Luisa Zambrano-Marín.[18] Over a two-day observation period, astronomers measured the asteroid's size, shape, and rotation, and discovered a small satellite.[7][14]

After the February 2020 encounter, 2020 BX12 passed perihelion on 21 March 2020. During its egress from perihelion, the asteroid made its closest approach to Mars on 28 June 2020, at a distance of 0.042 AU (6.3 million km; 3.9 million mi).[4][14]

Future approaches

Over the course of its orbit in the next 200 years, 2020 BX12 will continue to pass by Earth, though it will not make any approaches as close as the February 2020 encounter that would otherwise warrant attention. The last Earth encounter by 2020 BX12 from a closer distance was on 1 February 1931, when the asteroid approached Earth from a distance of 0.009 AU (1.3 million km; 0.84 million mi), or 3.5 lunar distances.[4][19] An Earth encounter by 2020 BX12 occurred in February 2022 and another occurred in 2024, with approach distances of 0.18 AU and 0.34 AU, respectively.[4]

Physical characteristics

High-resolution delay-Doppler radar imaging by the Arecibo Observatory in February 2020 has shown that 2020 BX12 is a spheroidal object with a diameter of 205 ± 65 m (670 ± 210 ft).[5] This spheroidal shape is commonly seen in other near-Earth objects, such as 2005 YU55 and 101955 Bennu.[18][20] Based on the asteroid's estimated diameter and the bandwidth of radar signals reflected from the asteroid, the rotation period of 2020 BX12 is estimated to be between 2 and 3 hours—close to the 2.2-hour spin barrier at which asteroids tend to break apart due to excessive centrifugal forces.[5]: 2, 11  Like other binary near-Earth asteroids, the rapid rotation of 2020 BX12 suggests that it was sped up by the YORP effect and may have undergone rotational breakup, which led to the formation of its satellite.[5]: 1–2, 12  The axial tilt or direction of 2020 BX12's rotational pole is unknown and could not be constrained by Arecibo's radar observations, however.[5]: 9 

Astronomical spectroscopy by the 10.4-metre (34 ft) Gran Telescopio Canarias in February 2024 has shown that the visible and near-infrared spectrum of 2020 BX12 most closely matches those of Q- and Sq-type asteroids,[5]: 5–6  indicating that it is predominantly made of silicate minerals.[5]: 12  In particular, 2020 BX12 appears reddish in the visible spectrum until the wavelength of 0.7 μm, and exhibits a spectral absorption band from wavelengths of 0.75 to 1.05 μm, indicating the presence of olivine and pyroxene.[5]: 7, 12  The silicaceous composition and spectral type of 2020 BX12 is commonly seen in near-Earth asteroids.[5]: 12  The geometric albedo of 2020 BX12 has not been directly measured, but is inferred to be around 0.3 based on its spectral type.[5]: 7 

Satellite

Satellite
The satellite of 2020 BX12 appears as a small, elongated object separate from the asteroid in radar images.
Two radar images of 2020 BX12 and its satellite taken by the Arecibo Observatory in February 2020
Discovery[7]
Discovered byLuisa F. Zambrano-Marín et al.
Planetary Radar Science Group[d]
Discovery siteArecibo Obs.
Discovery date4 February 2020
Orbital characteristics[5]: 9 
>400 m (lower limit)
>40 h (lower limit)
Satellite of(809875) 2020 BX12
Physical characteristics[5]: 9 
50±25 m
(likely synchronous)
>6 h (lower limit)
Spectral type
Q or Sq[5]: 9 

The satellite of 2020 BX12 was discovered in Arecibo radar observations conducted by a team of astronomers consisting of Luisa Zambrano-Marín along with other members of the Planetary Radar Science Group.[7][d] With the discovery of a satellite around 2020 BX12, the mass and density of the primary body can be determined from the satellite's orbit.[18] The satellite may have formed as a result of rotational fission or mass ejection of the primary body, since 2020 BX12 along with other binary near-Earth asteroids have been observed to have rapid rotation periods and spheroidal shapes.[19][21]

Physical characteristics

With a diameter of 50 ± 25 m (164 ± 82 ft), the satellite is less than one third of 2020 BX12's diameter.[5]: 12  The satellite's shape is unknown as it was not resolved in Arecibo's radar imagery.[5]: 12 

Orbit and rotation

From radar images taken on 5 February 2020, the separation distance between the satellite and the primary body is estimated to be about 360 m (1,180 ft),[7][14] or 4.4 times the radius of the 2020 BX12 primary.[6] The orbital period of the satellite is thought to be around 45–50 hours, with the best-fit period being 47 hours.[7][6] However, another possible orbital period of 15–16 hours has not been yet been ruled out, due to projection effects of radar images.[7] Radar observations by Arecibo suggest the satellite is likely tidally locked to the primary body, with its rotation period being synchronous with its orbital period.[7][18] However, uncertainties remain in measurements of the satellite's rotation period, thus an upper limit to its period was placed at 49 hours.[7][6]

Notes

  1. ^ Combined mass of 2020 BX12 and its satellite
  2. ^ The celestial coordinates of 2020 BX12 at the time of discovery were 07h 34m 48.39s −38° 14′ 23.2″.[1] See Puppis for constellation coordinates.
  3. ^ The celestial coordinates of 2020 BX12 at 19:00 UTC are 03h 08m 29.788s +05° 03′ 41.65″.[16] See Cetus for constellation coordinates.
  4. ^ a b The Planetary Radar Science Group's press release page credits the satellite's discovery to Luisa Fernanda Zambrano-Marín, Sean Marshall, Anne Virkki, Dylan Hickson, Anna McGilvray, Johbany Lebron, and Israel Cabrera of the Arecibo Observatory.[7]

References

  1. ^ a b c d e f g Denneau, L.; et al. (30 January 2020). "MPEC 2020-B281: 2020 BX12". Minor Planet Electronic Circular. Minor Planet Center. Retrieved 11 February 2020.
  2. ^ a b c d "2020 BX12". Minor Planet Center. International Astronomical Union. Retrieved 11 February 2020.
  3. ^ a b "2020 BX12". NEO Exchange. Las Cumbres Observatory. 27 January 2020. Retrieved 11 February 2020.
  4. ^ a b c d e f g h i j k "JPL Small-Body Database Browser: 2020 BX12" (2020-02-07 last obs.). Jet Propulsion Laboratory. Retrieved 11 February 2020.
  5. ^ a b c d e f g h i j k l m n o p q r s t u Zambrano-Marin, Luisa Fernanda; Marshall, Sean E.; Howell, Ellen S.; de León, Julia; Pinilla-Alonso, Noemi; Virkki, Anne K.; et al. (December 2025). "2020 BX12—The Last Binary Asteroid Discovered at Arecibo". The Planetary Science Journal. 6 (4): 91. Bibcode:2025PSJ.....6...91Z. doi:10.3847/PSJ/adbe39.
  6. ^ a b c d Johnston, Wm. Robert (7 February 2020). "2020 BX12". Johnston's Archive. Retrieved 11 February 2020.
  7. ^ a b c d e f g h i j Virkki, A. K. (10 February 2020). "Discovery Announcement of Binary System 2020 BX12". Planetary Radar Science Group. NAIC-Arecibo Observatory. Archived from the original on 12 February 2020. Retrieved 11 February 2020.
  8. ^ a b Tonry, J. L.; Denneau, L.; Heinze, A. N.; Stalder, B.; Smith, K. W.; Smartt, S. J.; et al. (June 2018). "ATLAS: A High-Cadence All-Sky Survey System". Publications of the Astronomical Society of the Pacific. 130 (988): 26. arXiv:1802.00879. Bibcode:2018PASP..130f4505T. doi:10.1088/1538-3873/aabadf. S2CID 59135328.
  9. ^ "2020BX12 Ephemerides". Near Earth Objects – Dynamic Site (Ephemerides at discovery). Department of Mathematics, University of Pisa, Italy. Retrieved 11 February 2020.
  10. ^ ""Pseudo-MPEC" for A10jUnf". Project Pluto. 30 January 2020. Archived from the original on 16 February 2020. Retrieved 15 February 2020.
  11. ^ a b "How Are Minor Planets Named?". Minor Planet Center. International Astronomical Union. Retrieved 12 February 2020.
  12. ^ a b c Bulger, J.; et al. (12 January 2020). "MPEC 2020-C132: 2020 BX12". Minor Planet Electronic Circular. Minor Planet Center. Retrieved 12 February 2020.
  13. ^ "PHA (Potentially Hazardous Asteroid)". Center for Near Earth Object Studies. Jet Propulsion Laboratory. Retrieved 11 February 2020.
  14. ^ a b c d Starr, Michelle (11 February 2020). "An Asteroid Totally Just Mooned Earth". ScienceAlert. Retrieved 11 February 2020.
  15. ^ "Sentry: Earth Impact Monitoring". Center for Near Earth Object Studies. Jet Propulsion Laboratory. Retrieved 11 February 2020.
  16. ^ a b c "2020BX12 Ephemerides". Near Earth Objects – Dynamic Site (Ephemerides at 3 February 2020 approach). Department of Mathematics, University of Pisa, Italy. Retrieved 11 February 2020.
  17. ^ Bartels, Meghan (13 February 2020). "Scientists just watched a newfound asteroid zoom by Earth. Then they saw its moon". Space.com. Retrieved 13 February 2020.
  18. ^ a b c d Becker, Tracy (12 February 2020). "Arecibo Observatory Discovers Moon Orbiting Near-Earth Asteroid". UCF Today. University of Central Florida. Retrieved 13 February 2020.
  19. ^ a b Guarino, Ben (14 February 2020). "Astronomers spy near-Earth asteroid that has its own moon". Washington Post. Retrieved 17 February 2020.
  20. ^ Taylor, Patrick A.; Howell, Ellen S.; Nolan, Michael C.; Thane, Abby A. (May 2012). The Shape and Spin Distributions of Near-Earth Asteroids Observed with the Arecibo Radar System (PDF). Asteroids, Comets, Meteors. Niigata, Japan: Lunar and Planetary Institute. Bibcode:2012LPICo1667.6340T. 6340.
  21. ^ Margot, J. L.; Nolan, M. C.; Benner, L. A. M.; Ostro, S. J.; Jurgens, R. F.; Giorgini, J. F.; et al. (24 May 2002). "Binary Asteroids in the Near-Earth Object Population". Science. 296 (5572): 1445–1448. Bibcode:2002Sci...296.1445M. doi:10.1126/science.1072094. PMID 11951001. S2CID 8768432.
Wikimedia Commons has media related to 2020 BX12.
  • Arecibo Observatory Discovers Moon Orbiting Near-Earth Asteroid, Tracy Becker, University of Central Florida, 12 Feb 2020
  • An Asteroid Totally Just Mooned Earth, Michelle Starr, ScienceAlert, 11 Feb 2020
  • Discovery Announcement of Binary System 2020 BX12 Archived 12 February 2020 at the Wayback Machine, Planetary Radar Science Group, 10 Feb 2020
  • 2020BX12 – Summary, ESA Space Situational Awareness, 10 Feb 2020
  • (809875) 2020 BX12 at NeoDyS-2, Near Earth Objects—Dynamic Site
    • Ephemerides · Observation prediction · Orbital info · MOID · Proper elements · Observational info · Close approaches · Physical info · Orbit animation
  • (809875) 2020 BX12 at the JPL Small-Body Database
    • Close approach · Discovery · Ephemeris · Orbit viewer · Orbit parameters · Physical parameters
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