6244 Okamoto, provisional designation , is a background

asteroid An asteroid is a minor planet of the inner Solar System. Sizes and shapes of asteroids vary significantly, ranging from 1-meter rocks to a dwarf planet almost 1000 km in diameter; they are rocky, metallic or icy bodies with no atmosphere. ...

and binary system from the inner regions of the asteroid belt, approximately in diameter. It was discovered on 20 August 1990, by Japanese astronomer

Tsutomu Seki is a Japanese astronomer and discoverer of minor planets and comets, born in Kōchi, Japan. Career Tsutomu Seki is the Director of the Geisei Observatory in Kōchi, and in charge of the Comet Section of the Oriental Astronomical Association. ...

at the

Geisei Observatory The list of asteroid-discovering observatories contains a section for each observatory which has discovered one or more asteroids, along with a list of those asteroids. For each numbered asteroid, the Minor Planet Center lists one or more dis ...

in Kōchi, Japan, and later named after Japanese school teacher

Hiroshi Okamoto is a Japanese voice actor. He began acting in 2003 and is affiliated with Aoni Production. He graduated from Momoyama Gakuin University, a private university. Filmography Major roles are highlighted in bold. Television Anime *2003 ** ''Sonic ...

. The presumed

S-type asteroid S-type asteroids are asteroids with a spectral type that is indicative of a siliceous (i.e. stony) mineralogical composition, hence the name. They have relatively high density. Approximately 17% of asteroids are of this type, making it the second ...

has a short

rotation period The rotation period of a celestial object (e.g., star, gas giant, planet, moon, asteroid) may refer to its sidereal rotation period, i.e. the time that the object takes to complete a single revolution around its axis of rotation relative to the ...

of 2.9 hours. The discovery of its minor-planet moon was announced in October 2006.

Orbit and classification

''Okamoto'' is a non-

family Family (from la, familia) is a Social group, group of people related either by consanguinity (by recognized birth) or Affinity (law), affinity (by marriage or other relationship). The purpose of the family is to maintain the well-being of its ...

asteroid of the main belt's background population when applying the hierarchical clustering method to its

proper orbital elements __NOTOC__ The proper orbital elements or proper elements of an orbit are constants of motion of an object in space that remain practically unchanged over an astronomically long timescale. The term is usually used to describe the three quantitie ...

. Based on osculating Keplerian

orbital elements Orbital elements are the parameters required to uniquely identify a specific orbit. In celestial mechanics these elements are considered in two-body systems using a Kepler orbit. There are many different ways to mathematically describe the same ...

, the asteroid has also been classified as a member of the Flora family (), a giant

asteroid family An asteroid family is a population of asteroids that share similar proper orbital elements, such as semimajor axis, eccentricity, and orbital inclination. The members of the families are thought to be fragments of past asteroid collisions. An a ...

and the largest family of stony asteroids in the main-belt. It orbits the Sun in the

inner Interior may refer to: Arts and media * ''Interior'' (Degas) (also known as ''The Rape''), painting by Edgar Degas * ''Interior'' (play), 1895 play by Belgian playwright Maurice Maeterlinck * ''The Interior'' (novel), by Lisa See * Interior de ...

asteroid belt at a distance of 1.8–2.5 AU once every 3 years and 2 months (1,160 days;

semi-major axis In geometry, the major axis of an ellipse is its longest diameter: a line segment that runs through the center and both foci, with ends at the two most widely separated points of the perimeter. The semi-major axis (major semiaxis) is the long ...

of 2.16 AU). Its orbit has an eccentricity of 0.15 and an

inclination Orbital inclination measures the tilt of an object's orbit around a celestial body. It is expressed as the angle between a Plane of reference, reference plane and the orbital plane or Axis of rotation, axis of direction of the orbiting object ...

of 5 ° with respect to the ecliptic. The body's

observation arc In observational astronomy, the observation arc (or arc length) of a Solar System body is the time period between its earliest and latest observations, used for tracing the body's path. It is usually given in days or years. The term is mostly use ...

begins with a

precovery In astronomy, precovery (short for pre-discovery recovery) is the process of finding the image of an object in images or photographic plates predating its discovery, typically for the purpose of calculating a more accurate orbit. This happens mos ...

taken at the

Uccle Observatory The Royal Observatory of Belgium (french: link=no, Observatoire Royal de Belgique, nl, Koninklijke Sterrenwacht van België), has been situated in the Uccle municipality of Brussels (Belgium) since 1890. It was first established in Saint-Josse ...

in September 1933, nearly 57 years prior to its official discovery observation at Geisei.

Physical characteristics

''Okamoto'' is an assumed

, the most common spectral type in the inner asteroid belt.

Rotation period

Several rotational lightcurves of ''Okamoto'' have been obtained from photometric observations since 2006. Analysis of the best-rated lightcurve gave a well-defined

of 2.8958 hours with a consolidated brightness amplitude between 0.11 and 0.15 magnitude ().

Diameter and albedo

The ''Collaborative Asteroid Lightcurve Link'' assumes an albedo of 0.24 – taken from

8 Flora Flora (minor planet designation: 8 Flora) is a large, bright main-belt asteroid. It is the innermost ''large'' asteroid: no asteroid closer to the Sun has a diameter above 25 kilometres (20% that of Flora), and not until 20-km 149 Medusa was dis ...

, the

parent body In meteoritics, a parent body is the celestial body from which originates a meteorite or a class of meteorites. Identification The easiest way to correlate a meteorite with a parent body is when the parent body still exists. This is the case fo ...

of the Flora family – and derives a diameter of 4.59 kilometers based on an

absolute magnitude Absolute magnitude () is a measure of the luminosity of a celestial object on an inverse Logarithmic scale, logarithmic Magnitude (astronomy), astronomical magnitude scale. An object's absolute magnitude is defined to be equal to the apparent mag ...

of 13.9. Based on an assumed albedo of 0.14, the Johnston's archive estimates a diameter of 6.69 and 6.89 kilometer for the primary and the combined system, respectively ''(see below)''.

Satellite

In 2006, photometric observations obtained by David Higgins at Canberra, Australia, Donald Pray at Carbuncle Hill Observatory , as well as

Peter Kušnirák Peter Kušnirák (born 1974) is a Slovakia, Slovak astronomer, discoverer of minor planets, and a prolific Photometry (astronomy), photometrist of light-curves at Ondřejov Observatory in the Czech Republic. He was married to Slovak astronomer Ulr ...

and

Petr Pravec Petr Pravec (born September 17, 1967) is a Czech astronomer and a discoverer of minor planets, born in Třinec, Czech Republic. Pravec is a prolific discoverer of binary asteroids, expert in photometric observations and rotational lightcurves a ...

Ondřejov Observatory The Ondřejov Observatory (; cs, Observatoř Ondřejov) is the principal observatory of the Astronomical Institute () of the Academy of Sciences of the Czech Republic. It is located near the village of Ondřejov, southeast of Prague, Czech R ...

revealed that ''Okamoto'' is a synchronous binary asteroid with a minor-planet moon orbiting it every 20.32 hours at an estimated average distance of . The discovery was announced on 19 October 2006. The mutual occultation events indicated the presence of a satellite 25% the size of its primary, which translates into an estimated diameter of kilometers depending on the underlying size estimate of the primary.

Naming

This

minor planet According to the International Astronomical Union (IAU), a minor planet is an astronomical object in direct orbit around the Sun that is exclusively classified as neither a planet nor a comet. Before 2006, the IAU officially used the term ''minor ...

was named after Japanese

Entomologist Entomology () is the scientific study of insects, a branch of zoology. In the past the term "insect" was less specific, and historically the definition of entomology would also include the study of animals in other arthropod groups, such as arach ...

and elementary-school teacher

(born 1915), who inspired the discoverer

with a love of the stars. The official naming citation was published by the

Minor Planet Center The Minor Planet Center (MPC) is the official body for observing and reporting on minor planets under the auspices of the International Astronomical Union (IAU). Founded in 1947, it operates at the Smithsonian Astrophysical Observatory. Function ...

on 10 June 1998 ().