1578 Kirkwood, provisional designation , is a

Hilda asteroid The Hilda asteroids (adj. ''Hildian'') are a List of minor-planet groups#Other groups out to the orbit of Jupiter, dynamical group of more than 6,000 asteroids located beyond the asteroid belt but within Jupiter's orbit, in a 3:2 orbital resonanc ...

from the outermost 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 52 kilometers in diameter. It was discovered on 10 January 1951, by astronomers of the

Indiana Asteroid Program The Indiana Asteroid Program was a photographic astronomical survey of asteroids during 1949–1967, at the U.S. Goethe Link Observatory near Brooklyn, Indiana, Brooklyn, Indiana. The program was initiated by Frank K. Edmondson of Indiana Universi ...

Goethe Link Observatory The Goethe Link Observatory, observatory code 760, is an astronomical observatory near Brooklyn, Indiana, United States. It is owned by Indiana University and operated by the Indiana Astronomical Society https://iasindy.org/about.html, which eff ...

in Indiana, United States. The asteroid was named after American astronomer

Daniel Kirkwood Daniel Kirkwood (September 27, 1814 – June 11, 1895) was an American astronomer. Kirkwood was born in Harford County, Maryland, to John and Agnes (née Hope) Kirkwood. He graduated in mathematics from the York County Academy in York, Pennsyl ...

Orbit and classification

''Kirkwood'' belongs to the orbital

Hilda group The Hilda asteroids (adj. ''Hildian'') are a dynamical group of more than 6,000 asteroids located beyond the asteroid belt but within Jupiter's orbit, in a 3:2 orbital resonance with Jupiter. The namesake is the asteroid 153 Hilda. Hildas move ...

, which is located outermost part of the main belt. Asteroids in this dynamical group have

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 ...

between 3.7 and 4.2 AU and stay in a 3:2

resonance Resonance is a phenomenon that occurs when an object or system is subjected to an external force or vibration whose frequency matches a resonant frequency (or resonance frequency) of the system, defined as a frequency that generates a maximu ...

with the gas giant

Jupiter Jupiter is the fifth planet from the Sun and the List of Solar System objects by size, largest in the Solar System. It is a gas giant with a Jupiter mass, mass more than 2.5 times that of all the other planets in the Solar System combined a ...

. ''Kirkwood'', however, is a background asteroid and not a member of the (collisional)

Hilda family The Hilda family ( 001) is an ancient collisional asteroid family of at least 409 known asteroids, named for its largest member, the -across asteroid 153 Hilda. It lies within the larger dynamical group of Hilda asteroids, a group of asteroids ...

(). It orbits the Sun at a distance of 3.0–4.9 AU once every 7 years and 9 months (2,839 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 0.24 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 1 ° 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 ...

. The asteroid was first observed as at

Turku Observatory Turku ( ; ; , ) is a city in Finland and the regional capital of Southwest Finland. It is located on the southwestern coast of the country at the mouth of the Aura River (Finland), River Aura. The population of Turku is approximately , while t ...

in February 1944. 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 observation as at

Heidelberg Observatory Heidelberg (; ; ) is the List of cities in Baden-Württemberg by population, fifth-largest city in the States of Germany, German state of Baden-Württemberg, and with a population of about 163,000, of which roughly a quarter consists of studen ...

in October 1949, fifteen months prior to its official discovery observation at Goethe Link.

Physical characteristics

In the

Tholen 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 ...

, ''Kirkwood'' is a dark

D-type asteroid D-type asteroids have a very low albedo and a featureless reddish spectrum. It has been suggested that they have a composition of organic-rich silicates, carbon and anhydrous silicates, possibly with water ice in their interiors. D-type asteroids ...

. It is also characterized as a D-type by

PanSTARRS The Panoramic Survey Telescope and Rapid Response System (Pan-STARRS1; obs. code: F51 and Pan-STARRS2 obs. code: F52) located at Haleakala Observatory, Hawaii, US, consists of astronomical cameras, telescopes and a computing facility that i ...

photometric survey.

Rotation period

In October 2012, a rotational

lightcurve In astronomy, a light curve is a graph (discrete mathematics), graph of the Radiance, light intensity of a celestial object or region as a function of time, typically with the magnitude (astronomy), magnitude of light received on the ''y''-axis ...

of ''Kirkwood'' was obtained from photometric observations at the Etscorn Campus Observatory () in New Mexico, United States. 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 12.518 hours with a brightness variation of 0.05

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 ...

(). Another lightcurve gave a period of 17.9 hours and an amplitude of 0.22 magnitude ().

Diameter and albedo

According to the surveys carried out by the Japanese Akari satellite, the

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 of 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 ...

and the Infrared Astronomical Satellite

IRAS The Infrared Astronomical Satellite (Dutch language, Dutch: ''Infrarood Astronomische Satelliet'') (IRAS) was the first space telescope to perform a astronomical survey, survey of the entire night sky at infrared wavelengths. Launched on 25 Janu ...

, ''Kirkwood'' measures between 47.077 and 57.14 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 ...

between 0.044 and 0.063. The ''Collaborative Asteroid Lightcurve Link'' adopts the results obtained by IRAS, that is, an albedo of 0.0517 and a diameter of 51.88 kilometers based on an absolute magnitude of 10.26.

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 memory of American astronomer

(1814–1895), long-time professor of mathematics at

Indiana University Indiana University (IU) is a state university system, system of Public university, public universities in the U.S. state of Indiana. The system has two core campuses, five regional campuses, and two regional centers under the administration o ...

. He discovered the

Kirkwood gap A Kirkwood gap is a gap or dip in the distribution of the semi-major axes (or equivalently of the orbital periods) of the orbits of main-belt asteroids. They correspond to the locations of orbital resonances with Jupiter. The gaps were first n ...

s, which are gaps in the distribution of the mean distances of the minor planets in the asteroid belt. ''Kirkwood'' was the

's first numbered discovery. The official 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 ...

in March 1952 (). The lunar crater '' Kirkwood'' was also named in the astronomer's honor.

Orbit and classification

Physical characteristics

Rotation period

Diameter and albedo

Naming

Notes

References

External links