52246 Donaldjohanson
52246 Donaldjohanson is a carbonaceous asteroid from the inner regions of the asteroid belt, approximately long and at its widest point. It was discovered on 2 March 1981, by American astronomer Schelte Bus at the Siding Spring Observatory in Australia.
The C-type asteroid was the second target of the Lucy mission, with the spacecraft flying 960 km from the surface on 20 April 2025, revealing the asteroid to be a contact binary. It was named after American paleoanthropologist Donald Johanson, the discoverer of the "Lucy" hominid fossil.
Orbit and classification
Donaldjohanson is a member of the Erigone family, a large carbonaceous asteroid family of nearly 2,000 known members, which is named after its parent body 163 Erigone. 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.It orbits the Sun in the inner asteroid belt at a distance of 1.9–2.8 AU once every 3 years and 8 months. Its orbit has an eccentricity of 0.19 and an inclination of 4° with respect to the ecliptic. A first precovery was taken at the discovering observatory in February 1981, extending the body's observation arc by 2 weeks prior to its official discovery observation.
Physical characteristics
Donaldjohanson has been characterized as a carbonaceous C-type asteroid, in-line with the C and X overall spectral type for Erigonian asteroids. It has an absolute magnitude of 15.5.Lightcurve
Photometric observations of Donaldjohanson in August 2020 revealed that it is a slow rotator with an exceptionally high lightcurve amplitude of 1.0 to 1.7 magnitude. The lightcurve suggested that Donaldjohanson must either be highly elongated in shape, or possibly a synchronous binary system. Extensive photometric observations by the two TRAPPIST telescopes from November 2020 to February 2021 determined the rotation period of Donaldjohanson to be approximately 252 hours.Diameter and albedo
According to the survey carried out by NASA's Wide-field Infrared Survey Explorer with its subsequent NEOWISE mission, Donaldjohanson measures 3.895 kilometers in diameter and its surface has an albedo of 0.103. 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.Geology
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. The smaller lobe of Donaldjohanson is named Afar Lobus, after the Afar Triangle in Ethiopia, and the larger lobe is named Olduvai Lobus, after Olduvai Gorge in Tanzania. The neck connecting the two lobes is named Windover Collum, after the Windover Archeological Site in Florida, United States. The middle of Windover Collum is encircled by a ridge named Luzia Dorsum, which divides the neck into Hadar Regio and Minatogawa Regio. Several craters and large boulders on Olduvai Lobus have been named as well.Exploration
Donaldjohanson was visited by the Lucy spacecraft that was launched on 16 October 2021. The flyby took place on 20 April 2025, with a closest approach distance of at a relative velocity of per second.Naming
The Lucy probe is named after the "Lucy" hominid fossil, while Donaldjohanson is named for that fossil's co-discoverer Donald Johanson, an American paleoanthropologist. The approved naming citation was published by the Minor Planet Center on 25 December 2015.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". In April 2025, Johanson was at the Southwest Research Institute in Colorado to watch the flyby of Donaldjohanson live.