(5646) 1990 TR

Lore & Background

The asteroid was discovered on 11 October 1990 by Japanese astronomers Seiji Ueda and Hiroshi Kaneda at Kushiro Observatory. Its orbit takes it from 1.2 to 3.1 AU from the Sun, with an eccentricity of 0.44 and an inclination of 8°, completing one orbit every 1,147 days. The observation arc begins with a pre-discovery observation at Siding Spring Observatory five months earlier.

In December 2012, Brian Warner at Palmer Divide Observatory obtained a rotational lightcurve showing a period of 3.1999 hours with a brightness variation of 0.12 magnitude. Photometric observations also indicated a probable asteroid moon with an orbital period of 19.47 hours and a diameter ratio of 0.18±0.02, corresponding to a moon diameter of about 400 meters.

Diameter and albedo measurements vary: Spitzer and NEOWISE surveys give diameters of 2.03 and 2.723 kilometers, with albedos of 0.19 and 0.66. The Collaborative Asteroid Lightcurve Link assumes an albedo of 0.18 and derives a diameter of 2.3 kilometers from an absolute magnitude of 15.67.

Reader's Guide

The significance of (5646) 1990 TR lies in its classification as a probable rare-type binary asteroid, a relatively uncommon configuration among near-Earth objects. The detection of a likely satellite, with a diameter of about 400 meters, provides valuable data on the formation and evolution of binary systems in the inner solar system. The asteroid's membership in the Amor group—a class of near-Earth objects that approach but do not cross Earth's orbit—makes it a target for understanding the population of bodies that may eventually become Earth-crossing. The multiple diameter and albedo measurements from Spitzer and NEOWISE highlight the challenges in characterizing such objects, with values ranging from 2.03 to 2.723 kilometers and albedos from 0.19 to 0.66. The lightcurve work by Brian Warner in 2012 remains the best-rated rotational study, establishing a precise rotation period and supporting the binary hypothesis. This asteroid thus contributes to the broader study of asteroid moons and the physical properties of near-Earth asteroids.

Did You Know?

• It is a probable rare-type binary asteroid with a likely moon about 400 meters in diameter.
• Its rotation period is 3.1999 hours, measured from the best-rated lightcurve in December 2012.
• The asteroid's diameter ranges from 2.03 to 2.723 kilometers depending on the survey used.