A three-dimensional model of 16 Psyche based on its light curve.
|Discovered by||Annibale de Gasparis|
|Discovery date||17 March 1852|
|Epoch JD 2453300.5 (22 October 2004)|
|Aphelion||3.328 AU (497.884 Gm)|
|Perihelion||2.513 AU (375.958 Gm)|
|2.921 AU (436.921 Gm)|
|4.99 yr (1823.115 d)|
Average orbital speed
186 km (Geometric mean)
253.2 ± 4 km (IRAS)
6.73 ± 3.05 g/cm³
|~0.06 m/s²|
|~0.13 km/s|
|0.1748 d (4.196 h)|
±0.11 (radar) 0.29
max: ~280 K (+7 °C)
|9.22 to 12.19|
16 Psyche is one of the ten most-massive asteroids in the asteroid belt. It is over 200 kilometers in diameter and contains a little less than 1% of the mass of the entire asteroid belt. It is thought to be the exposed iron core of a protoplanet. It is the most massive metallic M-type asteroid. Psyche was discovered by the Italian astronomer Annibale de Gasparis on 17 March 1852 from Naples and named after the Greek mythological figure Psyche.
The first fifteen asteroids to be discovered were given symbols by astronomers as a type of shorthand notation. Psyche was given an iconic symbol, as were several other asteroids discovered over the next few years. This 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. In 1851, German astronomer J. F. Encke suggested using a circled number, and 16 Psyche was the first new asteroid to be discovered that was designated using this scheme when American astronomer J. Ferguson published his observations in 1852.
Radar observations indicate that Psyche has a fairly pure iron–nickel composition, consistent with it having the highest radar albedo of any asteroid in the asteroid belt (±0.11). 0.29 Unlike some other M-type asteroids, Psyche shows no sign of the presence of water or water-bearing minerals on its surface, consistent with its interpretation as a metallic body. Psyche seems to have a surface that is 90% metallic (iron), with small amounts of pyroxene.
Psyche thus appears to be an exposed metallic core from a larger differentiated 500 km parent body. If Psyche is indeed the core remnant of a larger, now destroyed, parent body, we might expect to find other asteroids on similar orbits. However, Psyche is not part of any 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 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 mesosiderites, a class of stony–iron meteorites.
Psyche is massive enough that its gravitational perturbations on other asteroids can be observed, which enables a mass measurement. IRAS data shows it to have a diameter of 253 km, whereas observations of an occultation that provided five cross-sectional chords suggest an outline of 214×181 km. Recent[when?] estimates[which?] of Psyche's smaller size has resulted in an increase in its estimated density to one that is more appropriate for a metallic asteroid. Psyche appears to have a fairly regular surface and is approximately ellipsoidal in shape. Light-curve analysis has indicated that Psyche's pole points towards either ecliptic coordinates (β, λ) = (−9°, 35°) or (β, λ) = (−2°, 215°) with a 10° uncertainty. This gives an axial tilt of 95°.
Two stellar occultations by Psyche have been observed (on 22 March 2002 in Mexico and another on 16 May 2002[where?]). Light-curve variations indicate a non-spherical body, consistent with the radar results.
It is possible that at least some examples of enstatite chondrite meteorites originated from this asteroid, based on similar spectral analysis results.
No spacecraft has visited Psyche, but in 2014 a mission to Psyche was proposed to NASA. A proposal for an unmanned Psyche orbiter has been made by a team led by Lindy Elkins-Tanton, the director of the School for Earth and Space Exploration at Arizona State University. This team argues that 16 Psyche would be a valuable object for study because it is the only metallic core-like body discovered so far. The proposed spacecraft would orbit Psyche for six 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 September 30, 2015, the Psyche orbiter mission was one of five Discovery Program semifinalist proposals. If selected for flight in September 2016, the mission would launch in 2020 and arrive in 2026.
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(in a footnote) Herr Professor de Gasparis schreibt mir, in Bezug auf den von ihm März 17 entdeckten neuen Planeten: "J'ai proposé, avec l'approbation de Mr. Hind, le nom de Psyché pour la nouvelle planète, ayant pour symbole une aile de papillon surmontée d'une étoile."
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