S/2015 (136472) 1

S/2015 (136472) 1, nicknamed MK 2 by the discovery team,^[2] is the only known moon of the dwarf planet Makemake.^[1][3][4] It is estimated to be 175 km (110 mi) km in diameter and has a semi-major axis at least 21,000 km (13,000 mi) from Makemake.^[5] Observations leading to its discovery occurred in April 2015, using the Hubble Space Telescope's Wide Field Camera 3 and its discovery was announced on 26 April 2016.^[2]

Observations

A preliminary examination of the imagery suggests that S/2015 (136472) 1 has a reflectivity similar to charcoal, making it an extremely dark object. This is somewhat surprising because Makemake is the second-brightest known object in the Kuiper belt. One hypothesis to explain this is that its gravity is not strong enough to prevent bright but volatile ices from being lost to space when it is heated by the distant Sun.^[6]

Further observations will be needed in order to determine S/2015 (136472) 1's orbit. If it is circular, it would suggest that S/2015 (136472) 1 formed by an ancient impact event, but if it is elliptical, it suggests that it may have been captured.^[6]

Alex Parker, the leader of the team that performed the analysis of the images at the Southwest Research Institute, said that S/2015 (136472) 1's orbit appears to be aligned edge-on to Earth-based observatories. This would make it much more difficult to detect because it would be lost in Makemake's glare much of the time and, along with its dark surface, would contribute to previous surveys failing to observe it.^[6]

References

Natural satellites of the Solar System
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Other satellites	Asteroid moons Plutonian Haumean Eridian Makemakean
Largest satellites (mean radius ≥ 100 km)	size Ganymede largest / 2634 km / 0.413 Earths Titan Callisto Io Moon Europa Triton Titania Rhea Oberon Iapetus Charon Umbriel Ariel Dione Tethys [Dysnomia] Enceladus Miranda Proteus Mimas [Hi'iaka] Nereid Hyperion Phoebe smallest / 106 km / 0.017 Earths abc's Ariel Callisto Charon Dione [Dysnomia] Enceladus Europa Ganymede [Hi'iaka] Hyperion Iapetus Io Mimas Miranda Moon Nereid Oberon Phoebe Proteus Rhea Tethys Titan Titania Triton Umbriel
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