(709487) 2013 BL76

Lore & Background

2013 BL76 came to perihelion 8.3 AU from the Sun on 27 October 2012, when it reached an apparent magnitude of about 20. In 1927, when it was 100 AU from the Sun, it had an apparent magnitude of about 30.8; for comparison, the dwarf planet Sedna had an apparent magnitude of 21.7 at the same distance. It comes to opposition at the start of September. It will not be 50 AU from the Sun until 2045. After leaving the planetary region, it will have a barycentric aphelion of 1920 AU with an orbital period of 29900 years.

The orbit of 2013 BL76 currently comes closer to Saturn than any of the other giant planets. In a 10 million year integration of the orbit, the nominal orbit acquires a perihelion point of 0.5 AU (inside the orbit of Venus), and one of the 3-sigma clones acquires a perihelion point of only 0.008 AU (1,200,000 km). It travels in a technically retrograde orbit around the Sun, orbiting in a plane nearly perpendicular to the ecliptic. It has the 55th highest inclination of any known asteroid, after 2010 GW147 and before 2014 HS150.

With an absolute magnitude (H) of 10.8 and an unknown albedo, the object has an estimated diameter of 15–40 km. Since it has not been seen outgassing, it is not known if it is a comet or not. It might also be a damocloid, a type of minor planet that was originally a comet but lost most of its near-surface volatile materials after numerous orbits around the Sun. It also might be a dormant comet that simply has not been seen outgassing.

Reader's Guide

2013 BL76 is significant as one of the most extreme minor planets in terms of its semi-major axis, ranking 5th largest heliocentrically and 3rd largest barycentrically. Its orbit is highly inclined and retrograde, and it currently approaches Saturn more closely than any other giant planet. The object's uncertain nature—whether it is a comet, a damocloid, or a dormant comet—highlights the difficulty in classifying distant bodies that have not been observed outgassing. Its long-term orbital evolution is dramatic: over 10 million years, the nominal orbit can bring it as close as 0.5 AU to the Sun, and one clone even reaches 0.008 AU. This suggests that 2013 BL76 may have originated in the Inner Oort cloud or scattered disk and could eventually become a near-Earth object. Its legacy lies in demonstrating the extreme dynamical pathways available to trans-Neptunian objects and the challenges in predicting their future behavior.

Did You Know?

• 2013 BL76 has the 5th largest heliocentric semi-major axis in the Solar System as of an epoch in February 2017.
• Its barycentric semi-major axis of ~964 AU is the third largest of any minor planet.
• It travels in a retrograde orbit nearly perpendicular to the ecliptic.