S/2015 (136472) 1, nicknamed MK2 by the discovery team, is the only known

moon The Moon is Earth's only natural satellite. It is the fifth largest satellite in the Solar System and the largest and most massive relative to its parent planet, with a diameter about one-quarter that of Earth (comparable to the width of ...

of the trans-Neptunian dwarf planet Makemake. It is estimated to be in diameter (for an assumed albedo of 4%) and has a semi-major axis at least from Makemake. Its orbital period is ≥ 12 days (the minimum values are those for a circular orbit; the actual orbital eccentricity is unknown). Observations leading to its discovery occurred in April 2015, using the ''

Hubble Space Telescope The Hubble Space Telescope (often referred to as HST or Hubble) is a space telescope that was launched into low Earth orbit in 1990 and remains in operation. It was not the first space telescope, but it is one of the largest and most vers ...

'' Wide Field Camera 3, and its discovery was announced on 26 April 2016. Makemake and are the least-well-known of the large trans-Neptunian objects. The discovery of MK2 and follow-up observations in 2018 will enable Makemake's mass to be determined, which will allow an estimate of its density and other characteristics.

Observations

A preliminary examination of the discovery imagery suggests that MK2 has a

reflectivity The reflectance of the surface of a material is its effectiveness in reflecting radiant energy. It is the fraction of incident electromagnetic power that is reflected at the boundary. Reflectance is a component of the response of the electronic ...

similar to

charcoal Charcoal is a lightweight black carbon residue produced by strongly heating wood (or other animal and plant materials) in minimal oxygen to remove all water and volatile constituents. In the traditional version of this pyrolysis process, ...

, making it an extremely dark object. This is somewhat surprising because Makemake is the second-brightest-known object in the

Kuiper belt The Kuiper belt () is a circumstellar disc in the outer Solar System, extending from the orbit of Neptune at 30 astronomical units (AU) to approximately 50 AU from the Sun. It is similar to the asteroid belt, but is far larger—20 tim ...

. 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. Alex Parker, the leader of the team that performed the analysis of the discovery images at the

Southwest Research Institute Southwest Research Institute (SwRI), headquartered in San Antonio, Texas, is an independent and nonprofit applied research and development (R&D) organization. Founded in 1947 by oil businessman Tom Slick, it provides contract research and devel ...

, said that from the discovery images, MK2's orbit appears to be aligned edge-on to Earth-based observatories. This would make it difficult to detect because it would be lost in Makemake's glare much of the time, which, along with its dark surface, would contribute to previous surveys failing to observe it. Observations taken in 2018 and 2019 may be enough to determine whether the orbit is close to circular, which would suggest that MK2 was formed by an ancient impact event, or if it is significantly elliptical, which would suggest that it was captured.

Name

The nickname 'MK2' simply means ''object 2 in the Makemake system''. A permanent name may be chosen from an associated figure in the mythology of Easter Island.

Notes

References

External links

MPEC 2016-H46 : S/2015 (136472) 1

Minor Planet Center The Minor Planet Center (MPC) is the official body for observing and reporting on minor planets under the auspices of the International Astronomical Union (IAU). Founded in 1947, it operates at the Smithsonian Astrophysical Observatory. Function T ...

, 26 April 2016 {{Solar System Makemake Astronomical objects discovered in 2015 Trans-Neptunian satellites Moons of dwarf planets