(357439) 2004 BL86

(357439) 2004 BL₈₆ is a bright sub-kilometer asteroid and binary system, classified as near-Earth object and potentially hazardous asteroid of the Apollo group, approximately 300 meters (980 ft) in diameter. It was discovered on 30 January 2004 by astronomers of the Lincoln Near-Earth Asteroid Research at Lincoln Laboratory's Experimental Test Site near Socorro, New Mexico.^[3] Its 70-meter (200 ft) moon was discovered during the asteroid's close approach to the Earth in January 2015.^[4][5]

(357439) 2004 BL₈₆

Goldstone radar image of 2004 BL86 and its minor-planet moon
Discovery[1][2]
Discovered by	LINEAR
Discovery site	Lincoln Lab's ETS
Discovery date	30 January 2004
Designations
MPC designation	(357439) 2004 BL86
Minor planet category	NEO · PHA · Apollo[1][3]
Orbital characteristics[1]
Epoch 4 September 2017 (JD 2458000.5)
Uncertainty parameter 0
Observation arc	4,863 d (13.31 yr)
Aphelion	2.1070 AU
Perihelion	0.8974 AU
Semi-major axis	1.5022 AU
Eccentricity	0.4026
Orbital period (sidereal)	673 d (1.84 yr)
Mean anomaly	169.27°
Mean motion	0° 32m 7.08s / day
Inclination	23.775°
Longitude of ascending node	126.69°
Argument of perihelion	311.45°
Known satellites	1[4][5]
Earth MOID	0.0092 AU (3.6 LD)
Physical characteristics
Mean diameter	0.263±0.026 km[6] 0.290±0.030 km[7] 0.325±0.025 km[5][a]
Synodic rotation period	2.620±0.001 h[6] 2.6205±0.0003 h[8] 2.637±0.024 h[7]
Geometric albedo	0.40[7] 0.40±0.08[6]
Spectral type	V[7][9][10]
Absolute magnitude (H)	19.05[9] 19.3[1][7] 19.51±0.02[6]

2015 Earth approach

On 26 January 2015 at 16:20 UTC, 2004 BL₈₆ passed 1,199,600 km (745,400 mi), or 3.1 lunar distances, from Earth.^[11] The asteroid briefly peaked around apparent magnitude 9 and was near the celestial equator.^[12] The asteroid was visible in telescopes with objectives of 100 mm (4 in) or larger; high-end binoculars under a dark sky may also have worked.^[13] Near closest approach the asteroid was moving about 2.5 degrees per hour (2.5 arcseconds per second).^[12][14] The asteroid came to opposition (furthest elongation in the sky from the Sun) on 27 January 2015 at 04:37 UTC.^[12] Around 5:00 UTC, the asteroid was near M44 (the Beehive Cluster).^[14]

The 26 January 2015 approach of 3.1 lunar distances was the closest approach of 2004 BL₈₆ for at least the next 200 years.^[11][15] For comparison, 2015 TB145, about twice the size of 2004 BL₈₆, passed 486,800 km (302,500 mi), or 1.3 lunar distances, from Earth on 31 October 2015.^[16]

Satellite

A minor-planet moon orbiting (357439) 2004 BL₈₆ was first detected by ground-based telescopes by Joe Pollock and Petr Pravec.^[8][17] Observations by the Goldstone Deep Space Communications Complex and Green Bank Telescope confirmed that it is a binary asteroid with a secondary roughly 70 meters (200 ft) across.^[5] The secondary is estimated to orbit at least 500 meters (1,600 ft) from the primary.^[4] About 16% of asteroids over 200 meters (660 ft) in diameter are thought to be binaries.^[5]

Numbering and naming

This minor planet was numbered on 27 March 2013 (M.P.C. 83151).^[18] As of 2020, it has not been named.^[3]

Gallery

• 
  Animation of 2004 BL86's orbit
     Sun ·    Earth  ·   2004 BL86
• 
  2004 BL₈₆ safely passes Earth on 26 January 2015
• 
  Trajectory of 2004 BL₈₆ during Earth close approach
• 
  2004 BL₈₆ (star trail on left) near Xi Puppis

Notes

1. Radar Team 2015a: diameter primary 0.325±0.025 km. Diameter secondary 0.070 km. The satellites discovery is credited to Pollock et al.^[8] Summary figures for (357439) 2004 BL₈₆ at LCDB