2015 RX245

 is an extreme trans-Neptunian object, detached, on a highly eccentric orbit in the outermost region of the Solar System. It measures approximately 250 km in diameter and is "possibly" a dwarf planet. It was first observed on 8 September 2015, by astronomers with Outer Solar System Origins Survey using the 3.6-meter Canada–France–Hawaii Telescope at Mauna Kea Observatories, Hawaii, in the United States.

Orbit and classification


 belongs to a small group of detached objects with perihelion distances of 30 AU or more, and semi-major axes of 150 AU or more. These extreme trans-Neptunian objects (ETNOs) can not reach such orbits without some perturbing object, which lead to the speculation of Planet Nine. It is also denoted at extended detached disc object or extreme distant detached object (EDDO).

It orbits the Sun at a distance of 45.6–788 AU once every 8512 years (3,109,107 days; semi-major axis of 417 AU). Its orbit has an exceptionally high eccentricity of 0.89 and an inclination of 12° with respect to the ecliptic.

The body's observation arc begins with a precovery taken at Mauna Kea on 23 June 2015, or 11 weeks prior to its official first observation. It has a minimum orbital intersection distance with Neptune of 17.5 AU.  has a similar size and orbit as, as well as close positions to each other at the moment, both about 60 AU from the Sun (see adjunct diagram, in the middle bottom).

Numbering and naming
As of 2018, this minor planet has neither been numbered nor named by the Minor Planet Center. The official discoverers will be defined when the object is numbered.

Physical characteristics
According to American astronomer Michael Brown and to the Johnston's archive,  measures 128 and 130 kilometers in diameter based on an assumed albedo of 0.09 and 0.08, respectively. On his website, Michael Brown lists this object as "possibly" a dwarf planet (200–400 km) which is the least certain category in his 5-class taxonomic system. As of 2018, no rotational lightcurve has been obtained from photometric observations. The body's rotation period, pole and shape remain unknown.