8306 Shoko

Lore & Background

8306 Shoko was discovered on 24 February 1995 by Japanese astronomer Akimasa Nakamura at the Kuma Kogen Astronomical Observatory in southern Japan. It is a member of the Flora family (402), a giant asteroid family of stony asteroids in the main-belt. Its orbit has a semi-major axis of 2.24 AU, eccentricity of 0.22, and inclination of 5°, taking 1,225 days to orbit the Sun. The body's observation arc begins with a first observation as 1986 QA6 at Siding Spring Observatory in August 1986, nearly 9 years before its official discovery.

Shoko is an assumed stony S-type asteroid, consistent with the Florian family. Its absolute magnitude ranges from 14.83 to 15.28. Lightcurve analysis in September and October 2013 by Petr Pravec and David Polishook gave a rotation period of 3.3503 and 3.604 hours, with low brightness amplitudes of 0.11 and 0.10 magnitude. The Collaborative Asteroid Lightcurve Link assumes an albedo of 0.24 and calculates a diameter of 2.38 kilometers, while Johnston's Archive estimates 3.21 kilometers.

In October 2013, photometric observations by Petr Pravec and a large international collaboration revealed Shoko is a synchronous binary asteroid with a moon orbiting every 36.20 hours at an estimated average distance of 9.4 km. The discovery was announced in December 2013. The mutual occultation events suggest a satellite diameter of 1.28 km, more than 40% the size of the primary. The discoverers also suspect a possible third body, making it a rare triple asteroid, but as of 2018 no follow-up observations have been conducted.

Reader's Guide

8306 Shoko is significant as a synchronous binary asteroid within the Flora family, one of the largest asteroid families in the main belt. Its discovery as a binary system in December 2013, based on photometric observations from October 2013, adds to the understanding of asteroid satellite systems. The moon, with a diameter of 1.28 km, is notably large relative to the primary, at over 40% its size. The possibility of a third body, though unconfirmed as of 2018, highlights the potential for complex multi-body systems among small asteroids. The asteroid's naming after Japanese singer-songwriter Shoko Sawada, published by the Minor Planet Center on 10 June 1998, reflects the tradition of honoring cultural figures. The low brightness amplitude of its lightcurves suggests a nearly spheroidal shape. The discrepancy in diameter estimates (2.38 km vs. 3.21 km) underscores the uncertainty in physical characterization without direct observation. Its legacy lies in being a well-studied binary asteroid with a suspected triple nature, awaiting further investigation.

Did You Know?

• 8306 Shoko is a synchronous binary asteroid with a moon that orbits every 36.20 hours.
• The satellite is 1.28 km in diameter, more than 40% the size of the primary.
• The asteroid was named after Japanese singer-songwriter Shoko Sawada, who debuted in 1979.
• The discovery of its moon was announced in December 2013, based on October 2013 observations.