(53319) 1999 JM8

(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 kilometers (4 miles) in diameter, making it the largest PHA known to exist.^[12] 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.^[2]

(53319) 1999 JM₈

Radar image of 1999 JM8 taken at Arecibo Observatory
Discovery[1][2]
Discovered by	LINEAR
Discovery site	Lincoln Lab's ETS
Discovery date	13 May 1999
Designations
MPC designation	(53319) 1999 JM8
Alternative designations	1999 JM8 · 1990 HD1
Minor planet category	NEO · PHA · Apollo[1][2] Mars-crosser
Orbital characteristics[1]
Epoch 2022-Aug-09 (JD 2459800.5)
Uncertainty parameter 0
Observation arc	31.03 yr
Aphelion	4.4741 AU
Perihelion	0.9759 AU
Semi-major axis	2.7236 AU
Eccentricity	0.6417
Orbital period (sidereal)	4.49 yr (1,642 days)
Mean anomaly	19.009°
Mean motion	0° 13m 8.4s / day
Inclination	13.842°
Longitude of ascending node	133.62°
Argument of perihelion	166.83°
Earth MOID	0.0258 AU (10.0 LD)
Jupiter MOID	0.85 AU
Physical characteristics
Dimensions	5 km[3] 5.4±1.2 km[4] 6.4 km[5] 7 km[6][7]
Synodic rotation period	136±2 h[8]
Geometric albedo	0.02±0.01[4] 0.03 (derived)[9]
Spectral type	SMASS = X:[1] · C[10] X(Tholen)[9]
Absolute magnitude (H)	15.00[10] · 15.14±0.38[11] · 15.2[1][9] · 16.5[4]

Orbit and classification

1999 JM₈ 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.^[1] This makes it also a Mars-crossing asteroid.

The body's observation arc begins with its first identification as 1990 HD₁ at Palomar Observatory in April 1990, more than 9 years prior to its official discovery observation at Socorro.^[2]

Close approaches

1999 JM₈ has an Earth minimum orbital intersection distance of 0.0258 AU (3,860,000 km; 10.0 LD)^[1] 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 (38,300,000 km; 23,800,000 mi; 100 LD) and in August 2137 at 0.0764 au (11,430,000 km; 7,100,000 mi; 29.7 LD).^[1] For comparison, the planet Venus passed 103 LD (40,000,000 km; 25,000,000 mi) from Earth in 2022.

Physical characteristics

Radar images and computer models of (53319) 1999 JM₈

In the SMASS and Tholen classification, 1999 JM₈ is an X-type asteroid.^[1][9] It has also been characterized as a carbonaceous C-type asteroid, which seems more likely due to its exceptionally low albedo (see below).^[10]

A radar image of (53319) 1999 JM₈, showing two large craters or basins on its surface

Rotation period

Radar imaging by Goldstone and Arecibo observatories revealed that 1999 JM₈ has an unusually slow and possibly chaotic rotation period, similar to that of asteroid 4179 Toutatis.^[9][5]

In July 1999, a rotational lightcurve of 1999 JM₈ was obtained from photometric observations. It gave a period of 136±2 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.^[8]

Diameter and albedo

1999 JM₈ measures between 5 and 7 kilometers in diameter and its surface has an exceptionally low albedo of 0.02.^[3][4][6][7] 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.^[9]

Numbering and naming

This minor planet was numbered by the Minor Planet Center on 16 February 2003.^[13] As of 2018, it has not been named.^[2]