|Discovered by||R. Luther|
|Discovery site||Bilk Obs.|
|Discovery date||12 March 1871|
|main-belt · Flora|
|Epoch 31 July 2016 (JD 2457600.5)|
|Uncertainty parameter 0|
|Observation arc||144.90 yr (52926 d)|
|Aphelion||2.5819 AU (386.25 Gm)|
|Perihelion||2.17010 AU (324.642 Gm)|
|2.37598 AU (355.442 Gm)|
|3.66 yr (1337.7 d)|
|0° 16m 8.832s / day|
|9.950 h (0.4146 d)|
113 Amalthea // is a stony Florian asteroid and binary system from the inner regions of the asteroid belt, approximately 50 kilometers (31 miles) in diameter. It was discovered on 12 March 1871, by German astronomer Robert Luther at the Bilk Observatory in Düsseldorf, Germany. The elongated S-type asteroid has a rotation period of 9.95 hours. It was named after Amalthea from Greek mythology. The discovery of its 5-kilometer satellite was announced in July 2017.
Amalthea is thought to be a fragment from the mantle of a Vesta-sized, 300–600 km diameter parent body that broke up around one billion years ago, with the other major remnant being 9 Metis. The spectrum of Amalthea reveals the presence of the mineral olivine, a relative rarity in the asteroid belt.
Based on observations made during a stellar occultation by Amalthea of a 10th-magnitude star on 14 March 2017, it was announced in July 2017 that the asteroid has a small, 5-kilometer-sized satellite, provisionally designated S/2017 (113) 1. The observations also indicated that Amalthea has a distinctly elongated shape.