8306 Shoko, provisional designation , is a Florian

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 a synchronous

binary system A binary system is a system of two astronomical bodies which are close enough that their gravitational attraction causes them to orbit each other around a barycenter ''(also see animated examples)''. More restrictive definitions require that thi ...

from the inner regions of the

asteroid belt The asteroid belt is a torus-shaped region in the Solar System, located roughly between the orbits of the planets Jupiter and Mars. It contains a great many solid, irregularly shaped bodies, of many sizes, but much smaller than planets, called ...

, approximately in diameter. It was discovered on 24 February 1995, by Japanese astronomer

Akimasa Nakamura (born 1961) is a Japanese astronomer. He is a prolific observer of asteroids and comets, as well as a discoverer of minor planets. He has worked extensively at the Kuma Kogen Astronomical Observatory near Kuma, Ehime Prefecture, where he rema ...

at the

Kuma Kogen Astronomical Observatory The Kuma Kogen Astronomical Observatory ( Obs. code: 360) is located at Kumakōgen in Ehime Prefecture, Japan. The observatory is in the Furusato Country Open Air Museum that incorporates the Seiten Castle (''sei ten'' means "fine weather" a ...

in southern Japan, who named it after Japanese singer-songwriter

Shoko Sawada is a Japanese singer-songwriter, reporter, and radio personality. Since the start of her professional singing career in 1980, Sawada has recorded over 27 studio albums. Life and career At the age of five, Sawada became a member of the Otowa Bas ...

. The likely

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

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 3.35 hours. The discovery of its 1.3-kilometer

minor-planet moon A minor-planet moon is an astronomical object that orbits a minor planet as its natural satellite. , there are 457 minor planets known or suspected to have moons. Discoveries of minor-planet moons (and binary objects, in general) are important ...

was announced in December 2013.

Orbit and classification

''Shoko'' is a member of the

Flora family The Flora family (''adj. Florian''; ; also known as ''Ariadne family'') is a prominent family of stony asteroids located in the inner region of the asteroid belt. It is one of the largest families with more than 13,000 known members, or approx ...

(), 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 1.7–2.7 AU once every 3 years and 4 months (1,225 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 2.24 AU). Its orbit has an

eccentricity Eccentricity or eccentric may refer to: * Eccentricity (behavior), odd behavior on the part of a person, as opposed to being "normal" Mathematics, science and technology Mathematics * Off-center, in geometry * Eccentricity (graph theory) of a v ...

of 0.22 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 ecliptic or ecliptic plane is the orbital plane of the Earth around the Sun. From the perspective of an observer on Earth, the Sun's movement around the celestial sphere over the course of a year traces out a path along the ecliptic again ...

. 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 its first observation as at the

Siding Spring Observatory Siding Spring Observatory near Coonabarabran, New South Wales, Australia, part of the Research School of Astronomy & Astrophysics (RSAA) at the Australian National University (ANU), incorporates the Anglo-Australian Telescope along with a coll ...

in August 1986, nearly 9 years prior to its official discovery observation at Kuma Kogen.

Physical characteristics

''Shoko'' is an assumed, stony

, which is also the overall

spectral type In astronomy, stellar classification is the classification of stars based on their stellar spectrum, spectral characteristics. Electromagnetic radiation from the star is analyzed by splitting it with a Prism (optics), prism or diffraction grati ...

of the Florian asteroids. It has 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 ...

between 14.83 and 15.28.

Rotation period

In September and October 2013, two rotational

lightcurve In astronomy, a light curve is a graph of light intensity of a celestial object or region as a function of time, typically with the magnitude of light received on the y axis and with time on the x axis. The light is usually in a particular frequ ...

s of ''Shoko'' were obtained from photometric observations by astronomers

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 ...

and David Polishook. Lightcurve analysis gave a well-defined

of 3.3503 and 3.604 hours with a low brightness amplitude of 0.11 and 0.10

magnitude Magnitude may refer to: Mathematics *Euclidean vector, a quantity defined by both its magnitude and its direction *Magnitude (mathematics), the relative size of an object *Norm (mathematics), a term for the size or length of a vector *Order of ...

, respectively ().

Diameter and albedo

The ''Collaborative Asteroid Lightcurve Link'' assumes an

albedo Albedo (; ) is the measure of the diffuse reflection of sunlight, solar radiation out of the total solar radiation and measured on a scale from 0, corresponding to a black body that absorbs all incident radiation, to 1, corresponding to a body ...

of 0.24 – derived 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 of the Flora family – and calculates a diameter of 2.38 kilometers based on an

of 15.28, while the Johnston's Archive estimates a diameter 3.21.

Satellite

In October 2013, photometric observations by

and a large international collaboration, revealed, that ''Shoko'' is an synchronous

binary asteroid A binary asteroid is a system of two asteroids orbiting their common barycenter. The binary nature of 243 Ida was discovered when the Galileo spacecraft flew by the asteroid in 1993. Since then numerous binary asteroids and several triple ast ...

with a

orbiting it every 36.20 hours (1.508 days) at an estimated average distance of . The discovery was announced in December 2013. The mutual occultation events suggest the presence of a satellite with a diameter or more than 40% the size of its primary. The discoverers also suspect that there might be a possible third body, which would make it a rare

trinary asteroid A minor-planet moon is an astronomical object that orbits a minor planet as its natural satellite. , there are 457 minor planets known or suspected to have moons. Discoveries of minor-planet moons (and binary objects, in general) are important ...

. As of 2018, no follow-up observations have been conducted.

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 by the discoverer after Japanese singer-songwriter of ballads and pop songs,

(born 1962), who has recorded a large number of studio albums since her debut in 1979. 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 ().