2011 JY31

 is a binary trans-Neptunian object from the Kuiper belt, located in the outermost region of the Solar System. It is a cold classical Kuiper belt object. was discovered on 4 May 2011, by a team of astronomers using one of the Magellan Telescopes in Chile during the New Horizons KBO Search for a potential flyby target for the New Horizons spacecraft. Distant observations by New Horizons from September 2018 revealed its binary nature, showing two 68 km-wide components in a tight, mutual orbit 200 km apart.

Numbering and naming
This minor planet has not been numbered by the Minor Planet Center and remains unnamed.

Physical parameters
High resolution observation by the New Horizons spacecraft made it possible to estimate the parameters of the binary orbit and the system mass. Assuming that the orbit is circular the period is $54 km$, semimajor axis is $46.62 h$ and the system mass is about $61.4 °$. The components are approximately equal in size and are approximately 68 km in size assuming density of 0.5 kg/cm3.

The discovery adds support to streaming instability as the dominant mechanism in the formation of tight and contact binary planetesimals such as 486958 Arrokoth, which appear to be prevalent in the cold classical Kuiper belt population.