5474 Gingasen

Lore & Background

5474 Gingasen is a stony S-type asteroid and member of the Vesta family, orbiting the Sun in the inner main-belt at a distance of 2.2–2.5 AU once every 3 years and 8 months (1,344 days). Its orbit has an eccentricity of 0.07 and an inclination of 6° with respect to the ecliptic. First identified as 1955 YK at Alma-Ata (Tian Shan Observatory) in Kazakhstan, its first used observation was taken in 1971, when it was identified as 1971 BO2 at Cerro El Roble Station in Chile, extending the body's observation arc by 17 years prior to its official discovery observation.

According to the survey carried out by NASA's Wide-field Infrared Survey Explorer with its subsequent NEOWISE mission, Gingasen measures 5.05 kilometers in diameter, and its surface has a high albedo of 0.480, while the Collaborative Asteroid Lightcurve Link assumes a standard albedo for stony asteroids of 0.20 and derives a diameter of 6.68 kilometers with an absolute magnitude of 13.28. Four rotational lightcurves of Gingasen were obtained by Petr Pravec, David Higgins and Pedro Sada in 2008, as well as from the Palomar Transient Factory in 2010, giving a well-defined rotation period of 3.624 to 3.628 hours with a brightness variation of 0.11–0.18 in magnitude.

During the photometric observations in 2008, the astronomers came across strong evidence that Gingasen is likely an asynchronous binary asteroid with an asteroid moon orbiting it every 3.1095 hours. However, no mutual occultation/eclipse events were observed. The minor planet was named after a railroad track in Hokkaido; Gingasen means 'Milky Way'. This 150-km public railroad connects the island's eastern cities, and each station along the line is named for a constellation. The approved naming citation was published by the Minor Planet Center on 4 April 1996.

Reader's Guide

5474 Gingasen holds significance as a Vestian asteroid and a suspected binary system, contributing to the study of asteroid moons and the Vesta family. Its discovery by Japanese amateur astronomers highlights the role of non-professional observers in asteroid research. The asteroid's high albedo of 0.480 from NEOWISE data contrasts with the standard assumed albedo of 0.20, illustrating the uncertainty in diameter estimates. The suspected moon, with an orbital period of 3.1095 hours, was inferred from photometric observations but lacks direct confirmation via occultation or eclipse events, leaving its binary nature as strong evidence rather than certainty. The naming after the Gingasen railroad track in Hokkaido, with its constellation-themed stations, ties the asteroid to cultural and astronomical heritage. The extended observation arc from 1971 to its official discovery in 1988 demonstrates the value of archival data in refining asteroid orbits. Overall, Gingasen exemplifies the ongoing exploration of small solar system bodies and the collaborative efforts of amateur and professional astronomers.

Did You Know?

• The asteroid's name 'Gingasen' means 'Milky Way' and refers to a 150-km railroad track in Hokkaido, Japan.
• Its first used observation was taken in 1971 at Cerro El Roble Station in Chile, 17 years before its official discovery.