1995 SN55


, is a minor planet and likely centaur that orbits in the outer Solar System beyond the orbit of Jupiter. With an estimated diameter of approximately, it would be one of the largest centaurs. First observed by Spacewatch in 1995, it became a lost minor planet with an insufficiently defined orbit after only 7 weeks of observations, and has not been observed since.

Observations

First observation and loss

was about 39 AU from the Sun when it was first observed in 1995, by astronomer Arianna Gleason of the Spacewatch survey at Kitt Peak Observatory in Arizona, United States. It was only observed 14 times over 36 days, from 20 September to 26 October 1995.

Recovery attempts

There have been numerous failed attempts to recover, the most recent in 2018. The failure at recovery indicates it is either dimmer than expected, or on a different orbit than calculated., the uncertainty in the heliocentric distance is ±3.0 billion km.

Classification and orbit

Centaurs have a perihelion greater than Jupiter and a semi-major axis less than that of Neptune. orbits the Sun at a distance of 7.9–39.2 AU once every 114 years and 5 months. Its orbit has an eccentricity of 0.66 and an inclination of 5° with respect to the ecliptic. Due to this short observation arc, the object has a very poorly known orbit with the highest possible uncertainty parameter value of 9 and is considered a lost minor planet.
JPL's small body data base shows this object having an aphelion distance of 39.2 AU, whereas the Deep Ecliptic Survey finds an aphelion distance of 91 AU, which would make it a trans-Neptunian object by JPL's orbital classification.

Physical characteristics

If confirmed to be a centaur, would be one of the largest centaurs known with an diameter estimate of 280 and 290 kilometers. Based on a generic magnitude-to-diameter conversion, could measure 300 kilometers, using an observed absolute magnitude of 6.0, and an albedo of 0.08, which is typically assumed for centaurs. The two largest known centaurs are 10199 Chariklo and 2060 Chiron. These two bodies have an absolute magnitude of 7.40 and 6.2, as well as an albedo of 0.035 and 0.07, respectively. The body's rotation period, shape and spin axes remain unknown.

Numbering and naming

Due to its uncertain orbit, this minor planet has not been numbered. A numbering and subsequent naming will only be considered upon its rediscovery.