6244 Okamoto
A binary asteroid from the inner main belt, discovered in 1990.
6244 Okamoto (1990 QF) is a small binary asteroid located in the inner main belt, roughly 5 km (3 mi) across. It was discovered on 20 August 1990 by Japanese astronomer Tsutomu Seki at the Geisei Observatory in Kōchi, Japan. The asteroid was later named for Hiroshi Okamoto, a Japanese school teacher who sparked Seki’s interest in astronomy. In October 2006, astronomers announced that Okamoto has a moon.
Orbitally, Okamoto belongs to the background population of the main belt, though its osculating elements also place it within the Flora family. It circles the Sun at a distance of 1.8–2.5 AU every 3 years and 2 months (1,160 days), with an eccentricity of 0.15 and an inclination of 5°. The first known observation of the object was a precovery from September 1933 at the Uccle Observatory, nearly 57 years before its official discovery.
The asteroid is assumed to be an S-type, the most common spectral type in the inner belt. Lightcurve observations since 2006 have given a well-defined rotation period of 2.8958 hours, with a brightness amplitude between 0.11 and 0.15 magnitude. The Collaborative Asteroid Lightcurve Link assumes an albedo of 0.24 (based on 8 Flora) and calculates a diameter of 4.59 km from an absolute magnitude of 13.9. Johnston’s archive, using an albedo of 0.14, estimates the primary’s diameter at 6.69 km and the combined system at 6.89 km.
The moon was discovered through photometric observations by David Higgins (Canberra, Australia), Donald Pray (Carbuncle Hill Observatory), and Peter Kušnirák and Petr Pravec (Ondřejov Observatory). It orbits the primary every 20.32 hours at an estimated average distance of 13 km. Mutual occultation events showed the satellite is about 25% the size of the primary, giving it a diameter between 1.15 and 1.67 km, depending on the primary’s size estimate.
The naming citation for Hiroshi Okamoto (born 1915), an entomologist and elementary-school teacher, was published by the Minor Planet Center on 10 June 1998 (M.P.C. 32093).
Quick Facts
- Minorplanet
- yes
- Background
- #D6D6D6
- Discoverer
- T. Seki
- Discovery Site
- Geisei Obs.
- Discovered
- 20 August 1990
- Mpc Name
- (6244) Okamoto
- Named After
- Hiroshi Okamoto / (Japanese school teacher)
- Mp Category
- main-belt(inner) / backgroundFlora
- Epoch
- 23 March 2018 (JD 2458200.5)
- Uncertainty
- 0
- Observation Arc
- 84.58 yr (30,893 d)
- Aphelion
- 2.4888 AU
Facts from the source article.
Lore & Background
6244 Okamoto orbits the Sun in the inner asteroid belt at a distance of 1.8–2.5 AU once every 3 years and 2 months. Its orbit has an eccentricity of 0.15 and an inclination of 5° with respect to the ecliptic. The body's observation arc begins with a precovery taken at the Uccle Observatory in September 1933, nearly 57 years prior to its official discovery. It is a non-family asteroid of the main belt's background population, though based on osculating Keplerian orbital elements it has also been classified as a member of the Flora family.
Physical characteristics include an assumed S-type (stony) spectral type. Several rotational lightcurves have been obtained since 2006, giving a well-defined rotation period of 2.8958 hours with a brightness amplitude between 0.11 and 0.15 magnitude. The Collaborative Asteroid Lightcurve Link assumes an albedo of 0.24 and derives a diameter of 4.59 kilometers, while Johnston's archive estimates a diameter of 6.69 km for the primary and 6.89 km for the combined system based on an assumed albedo of 0.14.
In 2006, photometric observations by David Higgins, Donald Pray, Peter Kušnirák, and Petr Pravec revealed that Okamoto is a synchronous binary asteroid with a minor-planet moon orbiting every 20.32 hours at an estimated average distance of 13 km. The mutual occultation events indicated the satellite is 25% the size of its primary, translating to an estimated diameter of 1.15–1.67 kilometers depending on the underlying size estimate of the primary.
Reader's Guide
6244 Okamoto is significant as a binary asteroid system discovered in the inner main belt, adding to the known population of asteroids with satellites. Its discovery in 2006 via photometric observations by multiple astronomers highlighted the value of collaborative lightcurve analysis in identifying such systems. The asteroid's naming after Hiroshi Okamoto, a Japanese entomologist and school teacher who inspired discoverer Tsutomu Seki, connects the object to a personal legacy of astronomical inspiration. The uncertainty in its diameter estimates—ranging from 4.59 km to 6.89 km depending on assumed albedo—illustrates the challenges in characterizing small asteroids. Its classification as both a background asteroid and a possible Flora family member reflects the complexity of asteroid taxonomy. The precovery observation from 1933 extends its known observation arc by decades, aiding orbital refinement. The binary nature, with a moon about 25% the size of the primary, makes it a target for further study of asteroid formation and dynamics.
Did You Know?
- It is a binary asteroid with a moon that orbits every 20.32 hours at an estimated distance of 13 km.
- The asteroid's rotation period is 2.8958 hours, determined from lightcurve observations since 2006.
- A precovery observation of Okamoto was made at the Uccle Observatory in September 1933, nearly 57 years before its official discovery.
More in Notable Asteroids, Part 3 1-24
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