, unofficially designated , and , is a

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

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, ...

in the

classical Kuiper belt 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 ...

, the outermost region of the

Solar System The Solar SystemCapitalization 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 S ...

. It was first observed 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 ...

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 versa ...

on 30 July 2014. Until 2015, when the object 486958 Arrokoth was selected, it was a potential flyby target for the ''

New Horizons ''New Horizons'' is an Interplanetary spaceflight, 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 ...

'' probe. Estimated to be approximately in diameter, the object has a poorly determined orbit as it had been observed for only a few months.

Discovery and designation

was discovered by the New Horizons Search Team with the help of the Hubble Space Telescope because the object has a magnitude of 26.3, which is too faint to be observed by ground-based telescopes. Preliminary observations by the HST searching for KBO flyby targets for the ''New Horizons'' probe started in June 2014, and more intensive observations continued in July and August. was first discovered in observations on July 30, 2014, but it was designated e31007AI at the time, nicknamed e3 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 agency of the US federal government responsible for the civil space program, aeronautics research, and space research. NASA was established in 1958, succeeding t ...

in October 2014 and designated PT2, but the official name was not assigned 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 ...

until March 2015 after better orbit information was available.

Orbit and classification

is a

and likely 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 axe ...

, also known as "cubewano". It orbits the Sun at a distance of 42.5–45.4 AU once every 291 years and 3 months (106,394 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 43.94 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 0.03 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 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 again ...

. As this object has not been observed since October 2014, its orbit remains poorly determined still containing a high

uncertainty Uncertainty refers to epistemic situations involving imperfect or unknown information. It applies to predictions of future events, to physical measurements that are already made, or to the unknown. Uncertainty arises in partially observable or ...

. 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 In astronomy, precovery (short for pre-discovery recovery) is the process of finding the image of an object in images or photographic plates predating its discovery, typically for the purpose of calculating a more accurate orbit. This happens mos ...

taken on 25 June 2014, by the

team using the

Subaru Telescope is the telescope of the National Astronomical Observatory of Japan, located at the Mauna Kea Observatory on Hawaii. It is named after the open star cluster known in English as the Pleiades. It had the largest monolithic primary mirror in the wo ...

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 located ...

on Hawaii.

Binary

After the ''New Horizons'' probe completed its flyby of Arrokoth, the probe began observations of other nearby surrounding Kuiper belt objects, including . Observations of 's brightness variations at high phase angles allowed the ''New Horizons'' probe to make a rough determination of its rotation period as well as its shape. As ''New Horizons'' observed at phase angles near 90°, it displayed large variations in brightness, indicating that its shape is either extremely elongated or could be a

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 ...

of two separated components. appeared to be possibly a separated binary in a few resolved ''New Horizons'' images, but in 2020 this remained inconclusive. Later work by Hal Weaver in 2021 showed that is indeed a binary, with two components about in diameter, about apart.

Exploration

After the ''New Horizons'' probe completed its flyby of

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

, the probe was to be maneuvered to a flyby of at least one Kuiper belt object. Several potential targets were under consideration for the first such flyby. has an estimated mean-diameter between 30 and 55 kilometers, depending on the body's assumed

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 ...

. The potential encounter in 2018–2019 would have been at a distance of 43–44 AU from the Sun. On 28 August 2015, the ''New Horizons'' team announced the selection of (later named

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 ...

) as the next flyby target, eliminating the other possible targets — , , and . The spacecraft passed in January 2019, at a distance of less than 0.1 AU (15 million km, 9.3 million miles). This makes the second closest KBO observed by ''New Horizons'', after Arrokoth.

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 ''minor ...

has not been numbered by the

and remains unnamed.

References

External links

List of Transneptunian Objects
Minor Planet Center * {{DEFAULTSORT:2014 OS393 # Minor planet object articles (unnumbered) # Discoveries by the Hubble Space Telescope New Horizons # 20140730