(53319) 1999 JM8

 is an asteroid, slow rotator and tumbler, classified as a near-Earth object and potentially hazardous asteroid (PHA) of the Apollo group, approximately 7 km in diameter, making it the largest PHA known to exist. It was discovered on 13 May 1999, by astronomers of the Lincoln Near-Earth Asteroid Research at the Lincoln Laboratory's Experimental Test Site near Socorro, New Mexico.

Orbit and classification
orbits the Sun at a distance of 1.0–4.5 AU once every 4 years and 6 months (1,644 days; semi-major axis of 2.73 AU). Its orbit has an eccentricity of 0.64 and an inclination of 14° with respect to the ecliptic. This makes it also a Mars-crossing asteroid.

The body's observation arc begins with its first identification as at Palomar Observatory in April 1990, more than 9 years prior to its official discovery observation at Socorro.

Close approaches
has an Earth minimum orbital intersection distance of 0.0258 AU It passed closer than 0.20 AU to the Earth five times in the last century (0.033 AU in 1990), but its next closest approach in the 21st century will be in 2075 at 0.256 au and in August 2137 at 0.0764 au. For comparison, the planet Venus passed 103 LD from Earth in 2022.

Physical characteristics


In the SMASS and Tholen classification, is an X-type asteroid. It has also been characterized as a carbonaceous C-type asteroid, which seems more likely due to its exceptionally low albedo (see below).



Rotation period
Radar imaging by Goldstone and Arecibo observatories revealed that has an unusually slow and possibly chaotic rotation period, similar to that of asteroid 4179 Toutatis.

In July 1999, a rotational lightcurve of was obtained from photometric observations. It gave a period of $5 km$ hours with a brightness amplitude of 0.7 magnitude (U=2), and suggested that the body is in a non-principal axis rotation, commonly known as tumbling.

Diameter and albedo
measures between 5 and 7 kilometers in diameter and its surface has an exceptionally low albedo of 0.02. The Collaborative Asteroid Lightcurve Link derives an albedo of 0.03 and adopts a diameter of 7 kilometers based on an absolute magnitude of 15.2.

Numbering and naming
This minor planet was numbered by the Minor Planet Center on 16 February 2003. As of 2018, it has not been named.