(internally designated , and ) is a

trans-Neptunian object A trans-Neptunian object (TNO), also written transneptunian object, is any minor planet in the Solar System that orbits the Sun at a greater average distance than Neptune, which has a semi-major axis of 30.1 astronomical units (au). Typically ...

from the cold classical Kuiper belt located in the outermost region of the

Solar System The Solar System Capitalization of the name varies. The International Astronomical Union, the authoritative body regarding astronomical nomenclature, specifies capitalizing the names of all individual astronomical objects but uses mixed "Solar ...

. It measures approximately in diameter. The object was first observed by the New Horizons Search Team using the

Hubble Space Telescope The Hubble Space Telescope (often referred to as HST or Hubble) is a space telescope that was launched into low Earth orbit in 1990 and remains in operation. It was not the first space telescope, but it is one of the largest and most vers ...

on 6 August 2014, and was a proposed flyby target for the '' New Horizons'' probe until 2015, when the alternative target

486958 Arrokoth Arrokoth (minor-planet designation 486958 Arrokoth; provisional designation ), formerly nicknamed Ultima Thule, is a trans-Neptunian object located in the Kuiper belt. Arrokoth became the farthest and most primitive object in the Solar System ...

was selected.

Discovery and designations

was discovered by the New Horizons Search Team during an observation campaign intended to search for KBO flyby targets for the ''New Horizons'' probe. The observations started in June 2014, and more intensive ones continued in July and August. They were conducted with the help of the Hubble Space Telescope; the object's

apparent magnitude Apparent magnitude () is a measure of the brightness of a star or other astronomical object observed from Earth. An object's apparent magnitude depends on its intrinsic luminosity, its distance from Earth, and any extinction of the object's ...

of 26.4 is too faint to be observed by ground-based telescopes. was first discovered in observations on August 6, 2014, and it was designated g12000JZ at the time, nicknamed g1 for short. Its existence as a potential target of the ''New Horizons'' probe was revealed by

NASA The National Aeronautics and Space Administration (NASA ) is an independent agencies of the United States government, independent agency of the US federal government responsible for the civil List of government space agencies, space program ...

in October 2014 and it was designated PT3; its official

provisional designation Provisional designation in astronomy is the naming convention applied to astronomical objects immediately following their discovery. The provisional designation is usually superseded by a permanent designation once a reliable orbit has been cal ...

, , was not assigned by the Minor Planet Center until March 2015 after better orbit information was available.

Orbit and classification

is a

. More specifically, it is a non-resonant

classical Kuiper belt object A classical Kuiper belt object, also called a cubewano ( "QB1-o"), is a low-eccentricity Kuiper belt object (KBO) that orbits beyond Neptune and is not controlled by an orbital resonance with Neptune. Cubewanos have orbits with semi-major a ...

, also known as "cubewano". It orbits the Sun at a distance of 42.1–46.6 AU once every 295 years and 4 months (107,886 days; semi-major axis of 44.4 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-Centre (geometry), center, in geometry * Eccentricity (g ...

of 0.05 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 4 ° 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 agains ...

. This makes it a typical member of the "cold population" among the cubewanos in the Kuiper belt. 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 taken by the

New Horizons KBO Search ''New Horizons'' is an interplanetary space probe that was launched as a part of NASA's New Frontiers program. Engineered by the Johns Hopkins University Applied Physics Laboratory (APL) and the Southwest Research Institute (SwRI), with a t ...

team with the Subaru Telescope at

Mauna Kea Observatory The Mauna Kea Observatories (MKO) are a group of independent astronomical research facilities and large telescope observatories that are located at the summit of Mauna Kea on the Big Island of Hawaiʻi, United States. The facilities are locate ...

on Hawaii, six week prior to its official first observation by Hubble.

Numbering and 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 ''mino ...

has not been numbered by the Minor Planet Center and remains unnamed.

Physical characteristics

, has a diameter approximately , based on an estimated

albedo Albedo (; ) is the measure of the diffuse reflection of 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 that refl ...

between 0.04 and 0.10 respectively. Astronomer

Marc Buie Marc William Buie (; born 1958) is an American astronomer and prolific discoverer of minor planets who works at the Southwest Research Institute in Boulder, Colorado in the Space Science Department. Formerly he worked at the Lowell Observatory ...

gives a similar estimate of , and the ''Johnston's archive'' calculated a diameter of 39 km. Based on generic magnitude-to-diameter conversion, the object measures 44 km, for an

absolute magnitude Absolute magnitude () is a measure of the luminosity of a celestial object on an inverse logarithmic astronomical magnitude scale. An object's absolute magnitude is defined to be equal to the apparent magnitude that the object would have if it ...

of 10.3 and an assumed albedo of 0.07. Hubble observations of show that it is very red in color.

Exploration

Having completed its flyby of

Pluto Pluto (minor-planet designation: 134340 Pluto) is a dwarf planet in the Kuiper belt, a ring of bodies beyond the orbit of Neptune. It is the ninth-largest and tenth-most-massive known object to directly orbit the Sun. It is the largest ...

, the '' New Horizons'' space probe was to perform a flyby of at least one Kuiper belt object. Several potential targets were under consideration. (PT3) was considered a second choice after (PT1), because more fuel was required to carry out a flyby. (PT2) was already no longer under consideration as a potential target. On 28 August 2015, the ''New Horizons'' team announced the selection of (later named

) as the next flyby target. is one of the objects that ''New Horizons'' observed from greater distances, as part of its extended Kuiper belt mission. The spacecraft passed in March 2019, at a distance of approximately . This made the third closest KBO observed by ''New Horizons'', after Arrokoth and . ''New Horizons'' made its first observations of on 5 January 2019, from a distance of 92.7 million km. ''New Horizons'' did not come close enough to resolve either or , but the observations should be sufficient to determine the rotation periods and surface properties of these objects and to search for possible satellites. The distant KBO observations provide an important context for the data collected during the close flyby of Arrokoth.

References

External links

OPAG: We Did It!
''p.33'', Presentation to the Outer Planets Assessment Group,

Alan Stern Sol Alan Stern (born November 22, 1957) is an American engineer and planetary scientist. He is the principal investigator of the ''New Horizons'' mission to Pluto and the Chief Scientist at Moon Express. Stern has been involved in 24 suborbita ...

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