 Full image of Donaldjohanson photographed by theLucy spacecraft on 20 April 2025 | |
| Discovery[1] | |
|---|---|
| Discovered by | S. J. Bus |
| Discovery site | Siding Spring Obs. |
| Discovery date | 2 March 1981 |
| Designations | |
| (52246) Donaldjohanson | |
Named after | Donald Johanson[1] (paleoanthropologist) |
| 1981 EQ5 · 1998 YF26 | |
| main-belt[1][2] · (inner) Erigone[3][4] | |
| Orbital characteristics[2] | |
| Epoch 25 February 2023 (JD 2460000.5) | |
| Uncertainty parameter 0 | |
| Earliestprecovery date | 14 February 1981[1] |
| Aphelion | 2.830AU |
| Perihelion | 1.936 AU |
| 2.383 AU | |
| Eccentricity | 0.1876 |
| 3.68 yr (1,343 d) | |
| 186.269° | |
| 0° 16m 4.79s / day | |
| Inclination | 4.424° |
| 262.809° | |
| 213.016° | |
| Physical characteristics | |
| Dimensions | 8.8 km × 4.4 km × 3.1 km[5] |
| 3.895±0.013 km[6] | |
| 251.09 hr[5] | |
North poleright ascension | 324.66115°[5] |
North poledeclination | 50.95721°[5] |
| 0.103±0.019[6] | |
| C[3] | |
| 15.69[2] | |
52246 Donaldjohanson (provisional designation1981 EQ5) is a carbonaceousasteroid from the inner regions of theasteroid belt, approximately 8 kilometers (5.0 miles) long and 3.5 kilometers (2.2 miles) at its widest point. It was discovered on 2 March 1981, by American astronomerSchelte Bus at theSiding Spring Observatory in Australia.
TheC-type asteroid was the second target of theLucy mission, with the spacecraft flying 960 km (600 mi) from the surface on 20 April 2025, revealing the asteroid to be acontact binary.[7] It was named after American paleoanthropologistDonald Johanson, the discoverer of the"Lucy" hominid fossil.[1]
Donaldjohanson is a member of theErigone family (406),[3][4] a large carbonaceousasteroid family of nearly 2,000 known members, which is named after itsparent body163 Erigone.[8] The Erigone family is a relatively old family that was created by an asteroid collision approximately 150 million years ago. Since Donaldjohanson belongs to this family, it likely has the same age of 150 million years.[9]
It orbits the Sun in theinner asteroid belt at a distance of 1.9–2.8 AU once every 3 years and 8 months (1,345 days;semi-major axis of 2.38 AU). Its orbit has aneccentricity of 0.19 and aninclination of 4° with respect to theecliptic.[2] A firstprecovery was taken at the discovering observatory in February 1981, extending the body'sobservation arc by 2 weeks prior to its official discovery observation.[1]
Donaldjohanson has been characterized as a carbonaceousC-type asteroid,[3] in-line with the C andX overallspectral type for Erigonian asteroids.[8]: 23 It has anabsolute magnitude of 15.5.[2]
Photometric observations of Donaldjohanson in August 2020 revealed that it is aslow rotator with an exceptionally highlightcurve amplitude of 1.0[9] to 1.7magnitude.[10][11] The lightcurve suggested that Donaldjohanson must either be highly elongated in shape, or possibly a synchronousbinary system.[10] Extensive photometric observations by the twoTRAPPIST telescopes from November 2020 to February 2021 determined the rotation period of Donaldjohanson to be approximately 252 hours.[12]
According to the survey carried out by NASA'sWide-field Infrared Survey Explorer with its subsequentNEOWISE mission, Donaldjohanson measures 3.895 kilometers in diameter and its surface has analbedo of 0.103.[6] The Lucy spacecraft found the asteroid to be larger than predicted, measuring around 8 kilometers long and 3.5 kilometers wide at its largest point.[13]
On 27 August 2025, the International Astronomical Union announced 11 official names for geological features on Donaldjohanson, which follow the naming theme of archeological sites and hominin fossils.[14] The smaller lobe of Donaldjohanson is named Afar Lobus, after theAfar Triangle in Ethiopia, and the larger lobe is named Olduvai Lobus, afterOlduvai Gorge inTanzania.[14] The neck connecting the two lobes is named Windover Collum, after theWindover Archeological Site in Florida, United States.[14] The middle of Windover Collum is encircled by aridge named Luzia Dorsum (named after theLuzia Woman), which divides the neck into Hadar Regio and Minatogawa Regio (named afterHadar, Ethiopia and theMinatogawa Man, respectively).[14] Several craters and large boulders (saxa) on Olduvai Lobus have been named as well.[14]
Donaldjohanson was visited by theLucy spacecraft that was launched on 16 October 2021. The flyby took place on 20 April 2025, with a closest approach distance of 960 kilometers (600 mi) at a relative velocity of 13.4 kilometers (8.3 mi) per second.[7]
The Lucy probe is named after the"Lucy" hominid fossil, while Donaldjohanson is named for that fossil's co-discovererDonald Johanson (born 1943), an Americanpaleoanthropologist. The approved naming citation was published by theMinor Planet Center on 25 December 2015 (M.P.C. 97569).[1][15]
In 2021, Donald Johanson was quoted as being "enormously excited" to watch the launch of the probe, and said that the naming was "something that was utterly and totally unanticipated in my life".[16] In April 2025, Johanson was at theSouthwest Research Institute in Colorado to watch the flyby of Donaldjohanson live.[17]
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