|Discovered by||Annibale de Gasparis|
|Discovery date||March 17, 1852|
|Minor planet category||Main belt|
|Epoch October 22, 2004 (JD 2453300.5)|
|Aphelion||3.328 AU (497.884 Gm)|
|Perihelion||2.513 AU (375.958 Gm)|
|Semi-major axis||2.921 AU (436.921 Gm)|
|Orbital period||4.99 a (1823.115 d)|
|Average orbital speed||17.34 km/s|
|Longitude of ascending node||150.352°|
|Argument of perihelion||228.047°|
186 km (Geometric mean)
253.2 ± 4 km (IRAS)
6.49 ± 2.94 g/cm³
|Equatorial surface gravity||~0.06 m/s²|
|Escape velocity||~0.13 km/s|
|Rotation period||0.1748 d (4.196 h)|
max: ~280 K (+7 °C)
|Apparent magnitude||9.22 to 12.19|
|Absolute magnitude (H)||5.90|
16 Psyche is one of the ten most massive main-belt asteroids. It is over 200 kilometers in diameter and contains a little less than 1% of the mass of the entire asteroid belt. It is the most massive metallic M-type asteroid. Psyche was discovered by Annibale de Gasparis on March 17, 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. In 1851, however, J. F. Encke suggested using a circled number, and 16 Psyche was the first new asteroid to be discovered that was designated with this scheme (in 1852 by J. Ferguson). However, Psyche was given an iconic symbol as well, as were a few 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.
Radar observations indicate that Psyche has a fairly pure iron–nickel composition. 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. Small amounts of pyroxene appear to be present.
Psyche thus appears to be an exposed metallic core from a larger differentiated 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 does not belong to any asteroid family. One hypothesis is that the collision which 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.
Psyche is massive enough that its perturbations on other asteroids can be measured, which enables a mass measurement. IRAS data shows it to have a diameter of 253 km. Observations of an occultation using five chords suggest an outline of 214×181 km. Recent estimates of Psyche's smaller size has resulted in an increase in its estimated density, which is more appropriate for a metallic asteroid. Psyche appears to have a fairly regular surface and is approximately ellipsoidal in shape. Recent lightcurve analysis indicates that its 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 (from Mexico on March 22, 2002, and another on May 16, 2002). Lightcurve variations indicate a non-spherical body, consistent with the lightcurve and 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 yet visited Psyche. A proposal for an unmanned Psyche orbiter has been made by a team led by Lindy Elkins-Tanton, the director of the Carnegie Institution for Science's Department of Terrestrial Magnetism in Washington, D.C.. This team argues that 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. The team, who have been working on their plan for about one and a half years, plan to submit it in 2015 as a proposal for NASA's Discovery Program, which invites proposals for low-budget robotic space exploration missions.
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