16 Psyche () is a large asteroid discovered by the Italian astronomer
Annibale de Gasparis Annibale de Gasparis (9 November 1819, Bugnara – 21 March 1892, Naples; ) was an Italy, Italian astronomer, known for discovering asteroids and his contributions to theoretical astronomy. Biography De Gasparis was born in 1819 in Bugnara ...
, working in Naples, on 17 March 1852 and named after the Greek mythological figure
Psyche Psyche (''Psyché'' in French) is the Greek term for "soul" or "spirit" (ψυχή). It may also refer to: Psychology * Psyche (psychology), the totality of the human mind, conscious and unconscious * Psyche (book), ''Psyche'' (book), an 1846 boo ...
. It is one of the dozen most massive asteroids, containing about one percent of the mass of the
asteroid belt The asteroid belt is a torus-shaped region in the Solar System The Solar SystemCapitalization of the name varies. The International Astronomical Union, the authoritative body regarding astronomical nomenclature, specifies capitalizin ...

asteroid belt
, and is over in diameter. Psyche is thought to be the exposed
core Core or cores may refer to: Science and technology * Core (anatomy) In common parlance, the core of the body is broadly considered to be the torso. Functional movements are highly dependent on this part of the body, and lack of core muscular dev ...
of a
protoplanet A protoplanet is a large planetary embryo that originated within a protoplanetary disc and has undergone internal melting to produce a differentiated interior. Protoplanets are thought to form out of kilometer-sized planetesimal Planetesimals ...
, and is the most massive of the metal-rich
M-type asteroid Definition M-type (aka M-class) asteroids are a Asteroid spectral types, spectral class of asteroids which appear to contain higher concentrations of metal phases (e.g. iron-nickel) than other asteroid classes, and are widely thought to be the s ...
s. Its composition and density match
mesosiderite Mesosiderites are a class of stony–iron meteorites consisting of about equal parts of metallic nickel-iron and silicate In chemistry Chemistry is the scientific discipline involved with Chemical element, elements and chemical compound, co ...
meteorites and it is likely their parent body. Psyche is scheduled for space exploration, targeted for January 2026. The prefix "16" signifies that it was the sixteenth minor planet in order of discovery.


Astronomers created icon-like symbols for the first fifteen asteroids to be discovered, as a type of shorthand notation consistent with older notation for the
classical planets In classical antiquity, the seven classical planets or seven sacred luminaries are the seven moving astronomical object In astronomy, an astronomical object or celestial object is a naturally occurring physical entity, association, or st ...
. Psyche was given an iconic symbol, as were a few other asteroids discovered after 16 Psyche. The symbol , a semicircle topped by a star, represents a butterfly's wing, symbol of the soul (''psyche'' is the Greek word for "soul"), and a star. However the iconic symbols for all asteroids were superseded and Psyche's symbol never came into use. With more than a dozen asteroids discovered, remembering all their individual emblems became increasingly unwieldy, and in 1851, German astronomer Johann Franz Encke, J.F. Encke suggested using a circled number instead: . The first new asteroid that was designated in 1852 using this new scheme was 16 Psyche, when American astronomer James Ferguson (American astronomer), James Ferguson published his observations.


Mass, size and shape

Psyche is massive enough that its gravitational perturbations on other asteroids can be observed, which enables a mass measurement. The values for the mass of and the density of obtained from a 2002 analysis by Kuzmanoski and Kovačević, of a close encounter with asteroid . The new, high density estimate suggests that 16 Psyche must be composed mostly of metals. As of 2019, the best mass estimate is , with a derived bulk density of . The first size estimate of Psyche came from IRAS thermal infrared emission observations. They showed that it had a diameter of about , although it was likely an overestimate as Psyche was viewed pole-on at that time. Lightcurve, Light curve analysis indicates Psyche appears somewhat irregular in shape. There is a pronounced mass deficit near the equator at about 90° longitude comparable to Rheasilvia (crater), Rheasilvia basin on 4 Vesta. There are also two additional smaller (50–70 km in diameter) crater-like depressions near the south pole. Psyche's north pole points towards the ecliptic coordinate system, ecliptic coordinates , , with a 4° uncertainty. This gives an axial tilt of 95°. Observations of two Chord (astronomy), multi-chord stellar occultations of 2010 and 2014 allow the matching of light curve inversions DAMIT model 1806 that give an equivalent-volume mean diameter of  km, and an equivalent surface mean diameter of  km. The density of Psyche derived from these estimates, , is consistent with that of other M-type asteroid, metallic asteroids.


Observations of Psyche with Very Large Telescope's adaptive optics SPHERE imager revealed two large craters, on the order of 90 km across, which were provisionally named Meroe and Panthia , after the twin witches in the Roman novel The Golden Ass, ''Metamorphoses'' by Apuleius.

Composition and origin

Observations indicate that Psyche has a metal-pyroxene composition, consistent with it having one of the brightest Radar astronomy, radar albedos in the asteroid belt (). Its density, , is compatible with
mesosiderite Mesosiderites are a class of stony–iron meteorites consisting of about equal parts of metallic nickel-iron and silicate In chemistry Chemistry is the scientific discipline involved with Chemical element, elements and chemical compound, co ...
meteorites (≈ ) and the Steinbach meteorite (≈ ). Psyche seems to have a surface that is 90% metallic and 10% silicate rock, with % of orthopyroxene. Scientists think that these metals may be mostly iron and nickel. The NASA Infrared Telescope Facility at the Mauna Kea Observatories reported evidence (~3 μm absorption feature) of Hydroxy group, hydroxyl ions on the asteroid in October 2016 that may suggest water ice. Since Psyche is thought to have formed under dry conditions without the presence of water, the hydroxyl may have reached Psyche via past impacts from smaller Carbonaceous asteroid, carbonaceous asteroids. Psyche appears to be an exposed Planetary core, metallic core or a fragment of a metallic core from a larger Planetary differentiation, differentiated parent body some 500 kilometers in diameter. If Psyche is indeed one, there could be other asteroids on similar orbits. However, Psyche is not part of any identified asteroid family. One hypothesis is that the collision that formed Psyche occurred very early in the Solar System's history, and all the other remnants have since been ground into fragments by subsequent collisions or had their orbits Perturbation (astronomy), perturbed beyond recognition. However, this scenario is considered to have a probability of just 1%. An alternative is that Psyche was broken by impacts, but not catastrophically torn apart. In this case, it may be a candidate for the parent body of the
mesosiderite Mesosiderites are a class of stony–iron meteorites consisting of about equal parts of metallic nickel-iron and silicate In chemistry Chemistry is the scientific discipline involved with Chemical element, elements and chemical compound, co ...
s, a class of stony–iron meteorites. Another possibility is that Psyche may be an endmember of diverse relic bodies left by the Formation and evolution of the Solar System#Terrestrial planets, inner planet formation. The asteroid's Mantle (geology), mantle may have been stripped away not by a single collision but by multiple (more than three) relatively slow sideswipe collisions with bodies of comparable or larger size. What is left is a metallic core covered by a thin layer of silicates, which reveals itself spectrally. In such a case, Psyche would be analogous to Mercury (planet), Mercury but much less massive.


No spacecraft has visited Psyche, but in 2014 a mission to Psyche was proposed to NASA. A team led by Lindy Elkins-Tanton, the director of the School for Earth and Space Exploration at Arizona State University, presented a concept for a robotic Psyche (spacecraft), ''Psyche'' orbiter. This team argued that 16 Psyche would be a valuable object for study because it is the only metallic core-like body discovered so far. The spacecraft would orbit Psyche for 20 months, studying its topography, surface features, gravity, magnetism, and other characteristics and would be based on current technology, avoiding high cost and the necessity to develop new technologies. On 30 September 2015, the ''Psyche'' orbiter mission was one of five Discovery Program semifinalist proposals. The mission was approved by NASA on 4 January 2017 and was originally targeted to launch in October 2023, with an Earth gravity assist maneuver in 2024, a Mars flyby in 2025, and arriving at the asteroid in 2030. In May 2017, the launch date was moved up to target a more efficient trajectory, launching in 2022, with a Mars gravity assist in 2023 and arriving in 2026. On February 28, 2020, NASA awarded SpaceX a US$117 million contract to launch the ''Psyche'' spacecraft, and two smallsat secondary missions, on a Falcon Heavy rocket in July 2022.Falcon Heavy to launch NASA Psyche asteroid mission
Jeff Foust, Space News, February 28, 2020

See also

*List of minor planets and comets visited by spacecraft#Planned visits *List of missions to minor planets *Asteroid mining


External links

* * * * {{DEFAULTSORT:000016 Astronomical objects discovered in 1852, 18520317 Background asteroids Discoveries by Annibale de Gasparis, Psyche M-type asteroids (Tholen) Minor planets named from Greek mythology, Psyche Minor planets to be visited by spacecraft Named minor planets, Psyche X-type asteroids (SMASS)