 2020 BX12 and its satellite imaged by theArecibo Observatory in February 2020 | |
| Discovery[1][2] | |
|---|---|
| Discovered by | ATLAS-MLO |
| Discovery site | Mauna Loa Obs. |
| Discovery date | 27 January 2020 |
| Designations | |
| 2020 BX12 | |
| A10jUnf[3] | |
| Apollo · PHA · NEO | |
| Orbital characteristics[4] | |
| Epoch 31 May 2020 (JD 2459000.5) | |
| Uncertainty parameter 0 | |
| Observation arc | 6.09 yr (2,224 days) |
| Earliestprecovery date | 5 January 2014 |
| Aphelion | 2.4437AU |
| Perihelion | 0.7570 AU |
| 1.6004 AU | |
| Eccentricity | 0.75704 |
| 2.02 yr (739.5 d) | |
| 34.442° | |
| 0° 29m 12.545s / day | |
| Inclination | 40.067° |
| 132.904° | |
| 70.492° | |
| Knownsatellites | 1 |
| Earth MOID | 0.002061 AU |
| Physical characteristics | |
| 205±65 m[5]: 9 | |
| Mass | 7×108 to3×1010 kg (system)[a][5]: 12 |
| 2.5±0.5 h[5]: 9 | |
| 0.3 (assumed forS-type asteroids)[5]: 7 | |
| Q orSq[5]: 6 | |
| 20.631±0.396[4] | |
 | This article needs to beupdated. The reason given is:New physical and orbital parameters are given in a new paper byFernanda Zambrano-Marin et al. (2025). Please help update this article to reflect recent events or newly available information.(April 2025) |
(809875) 2020 BX12 (or simply2020 BX12) is a sub-kilometerbinary asteroid, classified as anear-Earth asteroid andpotentially hazardous object of theApollo group. It was discovered on 27 January 2020 by theAsteroid Terrestrial-impact Last Alert System survey at theMauna Loa Observatory during its approach to Earth of 0.02915 AU (4.361 million km; 11.34 LD). TheArecibo Observatory tookradar images of2020 BX12 on 4 February 2020, which led to the discovery of a smallnatural 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]
2020 BX12 was discovered on 27 January 2020 by theAsteroid Terrestrial-impact Last Alert System (ATLAS) survey at theMauna Loa Observatory inHawaii. The ATLAS survey was designed for detectingnear-Earth asteroids on approach to Earth, particularly those that may be consideredpotentially 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 theconstellation ofPuppis at anapparent magnitude of 17.6.[1][b]
The discovery of2020 BX12 was subsequently reported to theMinor Planet Center'sNear-Earth Object Confirmation Page (NEOCP), where a preliminary orbit was calculated from additional observations conducted at multiple observatories.[10] Follow-up observations of2020 BX12 spanned three days since its discovery, and the asteroid was formally announced in aMinor Planet Electronic Circular issued by the Minor Planet Center on 30 January 2020.[1]
Upon discovery, the asteroid was given the temporary internal designation A10jUnf.[3] After follow up observations confirming the object, it was then given theprovisional designation2020 BX12 by the Minor Planet Center on 30 January 2020.[1] The provisional designation signifies the object's discovery date and year.[11] Once2020 BX12 had a sufficiently longobservation arc for its orbit to be accurately determined, the asteroid received the permanentminor planet number 809875 from the Minor Planet Center,[12] making it eligible for naming.[11]
2020 BX12 orbits theSun at an average distance of approximately 1.60astronomical units (0.239×10^9 km; 0.149×10^9 mi), taking 2.02 years to complete one full orbit. The orbit of2020 BX12 is highly eccentric and inclined to theecliptic plane: it has anorbital eccentricity of 0.757 andinclination of 40 degrees, with its orbit extending from 0.76 AU atperihelion to 2.44 AU ataphelion. As it approaches perihelion,2020 BX12 moves above the ecliptic and comes closer to the Sun thanVenus, whereas at aphelion,2020 BX12 moves below the ecliptic and recedes from the Sun farther out than the orbit ofMars. The orbit of2020 BX12 crosses that of Earth; thus it can occasionally make close approaches to Earth, making it anear-Earth object. With asemi-major axis (average orbit distance) greater than 1 AU and a perihelion distance within that of Earth,2020 BX12 is formally classified under theApollo group of near-Earth asteroids.[4][2]
The asteroid'sminimum orbital intersection distance (MOID) from Earth is approximately 0.002 AU (0.30 million km; 0.19 million mi), or about 0.78lunar distances.[4] Having such a small Earth MOID,2020 BX12 is considered apotentially hazardous asteroid (PHA) by the Minor Planet Center, under the definition that PHAs have Earth MOIDs less than 0.05 AU andabsolute 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 JPLSentry Risk Table as of 2020[update].[15]
On 12 February 2020, a team of astronomers identified2020 BX12 in severalprecovery images taken by thePan-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 calculate2020 BX12's orbit with accuracy.[2] This greatly reduced uncertainties in the asteroid's orbit, reducing itsuncertainty parameter from 8 to 1.[1][12] As of February 2020[update] the observation arc of2020 BX12 spans 6.09 years or 2,224 days, with an orbit uncertainty parameter of 0 according to theJPL Small-Body Database.[4]
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 ofCetus, with an apparent magnitude of 16 and anangular separation of 20 degrees from theMoon.[16][c]
The February 2020 encounter by2020 BX12 provided an opportunity forradar observatories to study the asteroid's characteristics in detail.2020 BX12 was the first radar target observed by theArecibo Observatory inPuerto Rico since the one-month shutdown of observatory operations due to a series ofearthquakes in the southern region of Puerto Rico in December 2019 and January 2020.[17] Radar observations of2020 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]
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 by2020 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 by2020 BX12 occurred in February 2022 and another occurred in 2024, with approach distances of 0.18 AU and 0.34 AU, respectively.[4]
High-resolution delay-Doppler radar imaging by the Arecibo Observatory in February 2020 has shown that2020 BX12 is aspheroidal object with a diameter of 205 ± 65 m (670 ± 210 ft).[5] This spheroidal shape is commonly seen in other near-Earth objects, such as2005 YU55 and101955 Bennu.[18][20] Based on the asteroid's estimated diameter and thebandwidth of radar signals reflected from the asteroid, therotation period of2020 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 excessivecentrifugal forces.[5]: 2, 11 Like other binary near-Earth asteroids, the rapid rotation of2020 BX12 suggests that it was sped up by theYORP effect and may have undergone rotational breakup, which led to the formation of its satellite.[5]: 1–2, 12 Theaxial tilt or direction of2020 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 thevisible andnear-infraredspectrum of2020 BX12 most closely matches those ofQ- andSq-type asteroids,[5]: 5–6 indicating that it is predominantly made ofsilicate minerals.[5]: 12 In particular,2020 BX12 appears reddish in the visible spectrum until thewavelength of0.7 μm, and exhibits a spectralabsorption band from wavelengths of 0.75 to1.05 μm, indicating the presence ofolivine andpyroxene.[5]: 7, 12 The silicaceous composition andspectral type of2020 BX12 is commonly seen in near-Earth asteroids.[5]: 12 Thegeometric albedo of2020 BX12 has not been directly measured, but is inferred to be around 0.3 based on its spectral type.[5]: 7
 Two radar images of2020 BX12 and its satellite taken by theArecibo Observatory in February 2020 | |
| Discovery[7] | |
|---|---|
| Discovered by | Luisa F. Zambrano-Marín et al. Planetary Radar Science Group[d] |
| Discovery site | Arecibo Obs. |
| Discovery date | 4 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 | |
| (likelysynchronous) >6 h (lower limit) | |
Spectral type | Q orSq[5]: 9 |
The satellite of2020 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 around2020 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, since2020 BX12 along with other binary near-Earth asteroids have been observed to have rapid rotation periods and spheroidal shapes.[19][21]
With a diameter of 50 ± 25 m (164 ± 82 ft), the satellite is less than one third of2020 BX12's diameter.[5]: 12 The satellite's shape is unknown as it was not resolved in Arecibo's radar imagery.[5]: 12
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 the2020 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 likelytidally locked to the primary body, with its rotation period beingsynchronous 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]
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