4951 Iwamoto, provisional designation , is a stony, synchronous

binary Binary may refer to: Science and technology Mathematics * Binary number, a representation of numbers using only two values (0 and 1) for each digit * Binary function, a function that takes two arguments * Binary operation, a mathematical op ...

asteroid An asteroid is a minor planet—an object larger than a meteoroid that is neither a planet nor an identified comet—that orbits within the Solar System#Inner Solar System, inner Solar System or is co-orbital with Jupiter (Trojan asteroids). As ...

and slow rotator from the inner regions of the

asteroid belt The asteroid belt is a torus-shaped region in the Solar System, centered on the Sun and roughly spanning the space between the orbits of the planets Jupiter and Mars. It contains a great many solid, irregularly shaped bodies called asteroids ...

, approximately 5.5 kilometers in diameter. It was discovered on 21 January 1990, by Japanese astronomers

Yoshikane Mizuno is a Japanese astronomer and co-discoverer of asteroids. The Minor Planet Center credits him with the discovery of 52 minor planets he made at the Kani Observatory () between 1989 and 1993. The inner main-belt asteroid 4541 Mizuno, discovered ...

and

Toshimasa Furuta is a Japanese astronomer. He is a prolific discoverer of asteroid An asteroid is a minor planet—an object larger than a meteoroid that is neither a planet nor an identified comet—that orbits within the Solar System#Inner Solar System, i ...

at Kani Observatory () in Japan.

Orbit

''Iwamoto'' orbits the Sun in the inner main-belt at a distance of 1.9–2.6 AU once every 3 years and 5 months (1,239 days). 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-Centre (geometry), center, in geometry * Eccentricity (g ...

of 0.17 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 reference plane and the orbital plane or axis of direction of the orbiting object. For a satellite orbiting the Eart ...

of 8 ° with respect to the

ecliptic The ecliptic or ecliptic plane is the orbital plane of Earth's orbit, Earth around the Sun. It was a central concept in a number of ancient sciences, providing the framework for key measurements in astronomy, astrology and calendar-making. Fr ...

. It was first identified as at

Lowell Observatory Lowell Observatory is an astronomical observatory in Flagstaff, Arizona, United States. Lowell Observatory was established in 1894, placing it among the oldest observatories in the United States, and was designated a National Historic Landmark ...

in 1931, extending 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 ...

by 59 years prior to its official discovery observation at Kani.

Physical characteristics

In the

SMASS classification An asteroid spectral type is assigned to asteroids based on their reflectance spectrum, color, and sometimes albedo. These types are thought to correspond to an asteroid's surface composition. For small bodies that are not internally different ...

, ''Iwamoto'' is a common

S-type asteroid S-type (stony-type or silicaceous-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 ...

Diameter and albedo

According to the survey carried out by NASA's

Wide-field Infrared Survey Explorer Wide-field Infrared Survey Explorer (WISE, List of observatory codes, observatory code C51, Explorer 92 and MIDEX-6) was a NASA infrared astronomy Space observatory, space telescope in the Explorers Program launched in December 2009.. . WISE L ...

with its subsequent

NEOWISE Wide-field Infrared Survey Explorer (WISE, observatory code C51, Explorer 92 and MIDEX-6) was a NASA infrared astronomy space telescope in the Explorers Program launched in December 2009.. . WISE discovered thousands of minor planets and nu ...

mission, ''Iwamoto'' measures 5.192 and 5.515 kilometers in diameter, and its surface has an

albedo Albedo ( ; ) is the fraction of sunlight that is Diffuse reflection, diffusely reflected by a body. It is measured on a scale from 0 (corresponding to a black body that absorbs all incident radiation) to 1 (corresponding to a body that reflects ...

of 0.218 and 0.186, respectively. The ''Collaborative Asteroid Lightcurve Link'' adopts

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 ...

's revised WISE-data, that is, an albedo of 0.1844 and a diameter of 5.528 kilometers with on an absolute magnitude of 13.74.

Slow rotator

From 25 December 2006 to 23 March 2007, photometric observations of ''Iwamoto'' were obtained by the international community of photometrists at Badlands Observatory (SD, USA),

Ondřejov Observatory The Ondřejov Observatory (; ) is the principal observatory of the Astronomical Institute of the Czech Academy of Sciences. It is located in the municipality of Ondřejov, southeast of Prague, Czech Republic. It has a wide telescope, which i ...

(Czech Republic),

Modra Observatory The Astronomical Observatory of Modra (), also known as Modra Observatory or the Astronomical and Geophysical observatory in Modra, is an astronomical observatory located in Modra, Slovakia. It is owned and operated by the Comenius University in B ...

(Slovakia), Carbuncle Hill Observatory (RI, USA), Sonoita Research Observatory (AZ, USA), Kharkiv Observatory (Ukraine),

McDonald Observatory McDonald Observatory is an astronomical observatory located near unincorporated community of Fort Davis in Jeff Davis County, Texas, United States. The facility is located on Mount Locke in the Davis Mountains of West Texas, with additional faci ...

(TX, USA), Ironwood Observatory (HI, USA), Leura Observatory (Australia), Skalnaté pleso Observatory (Slovakia), Shed of Science Observatory (MN, USA),

Pic du Midi Observatory The Pic du Midi de Bigorre () or simply the Pic du Midi (elevation ) is a mountain in the French Pyrenees. It is the site of the Pic du Midi Observatory. Pic du Midi Observatory The Pic du Midi Observatory () is an astronomical observator ...

(France). Lightcurve analysis gave a

rotation period In astronomy, the rotation period or spin period of a celestial object (e.g., star, planet, moon, asteroid) has two definitions. The first one corresponds to the '' sidereal rotation period'' (or ''sidereal day''), i.e., the time that the objec ...

of 118 hours with a brightness variation of 0.34

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 ...

(). In May 2011, astronomers Etienne Morelle,

Raoul Behrend This is a list of minor-planet discoverers credited by the Minor Planet Center with the discovery of one or several minor planets (such as near-Earth and main-belt asteroids, Jupiter trojans and distant objects). , the discovery of 612,011 nu ...

obtained another lightcurve with a concurring period of 118 hours and an amplitude of 0.38 magnitude.(). With such a long period, ''Iwamoto'' is also a slow rotator, as the vast majority of asteroids have a much shorter rotation period of 2.2 to 20 hours.

Binary system

During the photometric observations in 2006/7, it was revealed that ''Iwamoto'' ("primary") is a synchronous

binary system A binary system is a system of two astronomical bodies of the same kind that are comparable in size. Definitions vary, but typically require the center of mass to be located outside of either object. (See animated examples.) The most common ki ...

with a

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 ...

("secondary") orbiting it every 4.917 days (or 118 hours, which identical to the primary's rotation). Based on the secondary-to-primary mean-diameter ratio (D_s/D_p) of at least 0.76, it was estimated that ''Iwamoto'' and its moon measure 4.0 and 3.5 kilometers, respectively. The diameter of ''Iwamoto'' has since increased to 5.5 kilometers ''(see above)''. The "Jonstonarchive" estimates that the moon has a

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 longe ...

of 31 kilometers.

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 in honor of Japanese astronomer

Masayuki Iwamoto is a Japanese astronomer from Awa in the Tokushima Prefecture. The Minor Planet Center credits him with the co-discovery of 6 asteroids made together with Japanese astronomer Toshimasa Furuta at the Tokushima-Kainan Astronomical Observatory ...

(born 1954), a

discoverer of minor planets This is a list of minor-planet discoverers credited by the Minor Planet Center with the discovery of one or several minor planets (such as near-Earth and main-belt asteroids, Jupiter trojans and distant objects). , the discovery of 612,011 num ...

at the Tokushima Observatory (). The approved 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. Funct ...

on 5 March 1996 ().

Orbit

Physical characteristics

Diameter and albedo

Slow rotator

Binary system

Naming

Notes

References

External links