6478 Gault, provisional designation , is a

Phocaea asteroid The Phocaea family ( ; adj. ''Phocaean''; ) is a collisional family of asteroids located between 2.25 and 2.5 AU in the inner region of the asteroid belt. Phocaea asteroids are of stony S-type composition and have orbits with eccentricities ...

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. 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 ...

was discovered on 12 May 1988, by astronomer couple

Carolyn Carolyn is a female given name, a variant of Caroline. Other spellings include Karolyn, Carolyne, Carolynn or Carolynne. Caroline itself is one of the feminine forms of Charles. List of Notable People *Carolyn Bennett (born 1950), Canadian pol ...

and

Eugene Shoemaker Eugene Merle Shoemaker (April 28, 1928 – July 18, 1997) was an American geologist. He co-discovered Comet Shoemaker–Levy 9 with his wife Carolyn S. Shoemaker and David H. Levy. This comet hit Jupiter in July 1994: the impact was televise ...

at the

Palomar Observatory Palomar Observatory is an astronomical research observatory in San Diego County, California, United States, in the Palomar Mountain Range. It is owned and operated by the California Institute of Technology (Caltech). Research time at the observat ...

in California. It was named in honor of planetary geologist . In January 2019, it was found that ''Gault'' shows cometary activity and that it has multiple tails, making it an

active asteroid Active asteroids are small Solar System bodies that have asteroid-like orbits but show comet-like visual characteristics. That is, they show comae, tails, or other visual evidence of mass-loss (like a comet), but their orbit remains within Jup ...

. It was subsequently realised that it had been active since at least 2013.

Orbit and classification

''Gault'' is a core member of the

Phocaea family The Phocaea family ( ; adj. ''Phocaean''; ) is a collisional family of asteroids located between 2.25 and 2.5 AU in the inner region of the asteroid belt. Phocaea asteroids are of stony S-type composition and have orbits with eccentricities ...

(). The large

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 ...

consists of nearly 2,000 known stony asteroids, and was named after its largest member,

25 Phocaea Phocaea (minor planet designation: 25 Phocaea) is a stony asteroid from the inner regions of the asteroid belt, approximately 75 kilometers in diameter. It is the parent body of the Phocaea family. Discovered by Jean Chacornac in 1853, it was n ...

. The old family formed up to 2.2 billion years ago and has the highest inclination of all families 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. Several of its members are also

Mars-crossing asteroid A Mars-crossing asteroid (MCA, also Mars-crosser, MC) is an asteroid whose orbit crosses that of Mars. Some Mars-crossers Minor planet designation, numbered below 100000 are listed here. They include the two numbered Mars trojans 5261 Eureka and ...

s with high eccentricities. It orbits the Sun at a distance of 1.9–2.8 AU once every 3 years and 6 months (1,278 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 2.31 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 0.19 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 23 ° 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 official discovery observation at Palomar in May 1988. It last came to

perihelion An apsis (; ) is the farthest or nearest point in the orbit of a planetary body about its primary body. For example, the apsides of the Earth are called the aphelion and perihelion. General description There are two apsides in any ellip ...

in January 2020 and will next come to perihelion in July 2023.

Main-belt comet

On January 5, 2019, it was discovered that ''Gault'' possesses a

comet tail A comet tail—and coma—are features visible in comets when they are illuminated by the Sun and may become visible from Earth when a comet passes through the inner Solar System. As a comet approaches the inner Solar System, solar radiation ca ...

, which had not been present in previous images taken during the 2018/19 opposition. The asteroid began to break up as its spin accelerated due to the

YORP effect Yorp or YORP may refer to one of the following: * 54509 YORP, an Earth co-orbital asteroid *Yarkovsky–O'Keefe–Radzievskii–Paddack effect, a second-order variation on the Yarkovsky effect *Yorps, friendly one-eyed Martians from the Commander Ke ...

, and its rotation speed approached two hoursnear the limit of stability for an asteroid. The ejected matter created two dust tails, and the longer one has been estimated at over long. Earlier hypotheses of a collision with another asteroid were ruled out as a source of the tail-forming dust, and its two tails were believed to be a result of sudden dust ejections near October 28 and December 30, 2018. It is also possible that solar heating caused sublimation of ice, perhaps beneath the surface in a "pocket," and the force of the ejection of material (after being exposed to solar heating during the rotation of the asteroid) resulted in the spin rate increase. A prior example of such an occurrence is in the literature. In April 2019, upon analyzing archive images taken in 2013, 2016 and 2017, it was found that ''Gault'' had been perpetually active for at least five years before the discovery, with a tail visible when the asteroid was near its furthest distance from the Sun during the 2013 apparition. If its activity is indeed caused by a rotational breakup, then ''Gault'' has remained active far longer than any other object of this type seen before. This indicates that it may represent a new type of object.

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 planetary geologist (1923–1999), an expert in the field of

impact crater An impact crater is a circular depression in the surface of a solid astronomical object formed by the hypervelocity impact of a smaller object. In contrast to volcanic craters, which result from explosion or internal collapse, impact craters ...

forming processes. Gault conducted field experiments and applied his insight to the interpretation of impact data from the Moon, Earth, Mars and Mercury. 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. Function ...

on 28 July 1999 ().

Physical characteristics

''Gault''

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 ...

resembles that of a stony

, according its membership to the

, but some of the features of the spectrum are more similar to the carbonaceous

C-type asteroid C-type (carbonaceous) asteroids are the most common variety, forming around 75% of known asteroids. They are volatile-rich and distinguished by a very low albedo because their composition includes a large amount of carbon, in addition to rocks ...

class. Based on a generic magnitude-to-diameter conversion, the asteroid measures approximately 3.7 kilometers in diameter, for an assumed family-specific albedo of 0.22, and 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 14.4. Rotational lightcurves of ''Gault'' obtained from photometric observations in 2019 showed a rotation period of either 1.79 or 3.36 hours. The body's

pole Pole may refer to: Astronomy *Celestial pole, the projection of the planet Earth's axis of rotation onto the celestial sphere; also applies to the axis of rotation of other planets *Pole star, a visible star that is approximately aligned with the ...

and shape remain unknown, but based on its lightcurve, its surface likely has irregularities and concavities.

Gallery

File:Heic1906a Asteroid 6478 Gault.jpg, Background stars surrounding asteroid 6478 Gault and its tails. File:The asteroid (6478) Gault on 2019-03-26.jpg, (6478) Gault imaged on 2019-03-26 with iTelescope's T21 File:Orbit Diagram for the Main-belt Asteroid 6478 Gault on 2019-01-01.jpg, JPL Small-Body Database Browser's Orbit Diagram for the Main-belt Asteroid 6478 Gault on 2019-01-01 at 00:00 UTC

References

External links

image of (6478) Gault showing tail
astrobin.com
Dictionary of Minor Planet Names
Google books

– Minor Planet Center * * {{DEFAULTSORT:Gault 006478 006478 Discoveries by Carolyn S. Shoemaker Discoveries by Eugene Merle Shoemaker Named minor planets 19880512