16 Psyche
16 Psyche
is one of the ten most massive main-belt
Asteroid belt
The asteroid belt is the region of the Solar System located roughly between the orbits of the planets Mars and Jupiter. It is occupied by numerous irregularly shaped bodies called asteroids or minor planets...

Asteroids are a class of small Solar System bodies in orbit around the Sun. They have also been called planetoids, especially the larger ones...

s. 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 of the metallic M-type asteroid
M-type asteroid
M-type asteroids are asteroids of partially known composition; they are moderately bright . Some, but not all, are made of nickel-iron, either pure or mixed with small amounts of stone. These are thought to be pieces of the metallic core of differentiated asteroids that were fragmented by impacts,...


Psyche was discovered by Annibale de Gasparis
Annibale de Gasparis
Annibale de Gasparis was an Italian astronomer. From 1864 to 1889 he was the director of the Astronomical Observatory of Capodimonte in Naples.He won the Gold Medal of the Royal Astronomical Society in 1851....

 on March 17, 1852 from Naples
Naples is a city in Southern Italy, situated on the country's west coast by the Gulf of Naples. Lying between two notable volcanic regions, Mount Vesuvius and the Phlegraean Fields, it is the capital of the region of Campania and of the province of Naples...

 and named after the Greek mythological figure
Greek mythology
Greek mythology is the body of myths and legends belonging to the ancient Greeks, concerning their gods and heroes, the nature of the world, and the origins and significance of their own cult and ritual practices. They were a part of religion in ancient Greece...

 Psyche. The first fifteen asteroids to be discovered were given symbols by astronomers as a type of short-hand notation. In 1851, however, J. F. Encke
Johann Franz Encke
Johann Franz Encke was a German astronomer. Among his activities, he worked on the calculation of the periods of comets and asteroids, measured the distance from the earth to the sun, and made observations on the planet Saturn.-Biography:Encke was born in Hamburg, where his father was a...

 suggested using a circled number. 16 Psyche was the first new asteroid to be discovered that was designated with this scheme (in 1852 by J. Ferguson
James Ferguson (astronomer)
James Ferguson was an American astronomer and engineer born in Scotland who made the first discovery of an asteroid from North America . Starting in 1847, he worked at the U.S...



Radar astronomy
Radar astronomy is a technique of observing nearby astronomical objects by reflecting microwaves off target objects and analyzing the echoes. This research has been conducted for six decades. Radar astronomy differs from radio astronomy in that the latter is a passive observation and the former an...

observations indicate a fairly pure iron
Iron is a chemical element with the symbol Fe and atomic number 26. It is a metal in the first transition series. It is the most common element forming the planet Earth as a whole, forming much of Earth's outer and inner core. It is the fourth most common element in the Earth's crust...

Nickel is a chemical element with the chemical symbol Ni and atomic number 28. It is a silvery-white lustrous metal with a slight golden tinge. Nickel belongs to the transition metals and is hard and ductile...

 composition. Psyche appears to be a genuine case of an exposed metallic core from a larger differentiated parent body. 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
The pyroxenes are a group of important rock-forming inosilicate minerals found in many igneous and metamorphic rocks. They share a common structure consisting of single chains of silica tetrahedra and they crystallize in the monoclinic and orthorhombic systems...

 appear to be present.

If Psyche is the core remnant of a larger parent body, we might expect other asteroids on similar orbits. Psyche does not belong to any asteroid family
Asteroid family
An asteroid family is a population of asteroids that share similar proper orbital elements, such as semimajor axis, eccentricity, and orbital inclination. The members of the families are thought to be fragments of past asteroid collisions...

. One hypothesis is that the collision 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
Mass can be defined as a quantitive measure of the resistance an object has to change in its velocity.In physics, mass commonly refers to any of the following three properties of matter, which have been shown experimentally to be equivalent:...

 measurement. IRAS
The Infrared Astronomical Satellite was the first-ever space-based observatory to perform a survey of the entire sky at infrared wavelengths....

 data shows Psyche to have a diameter of 253 km. Observations of an occultation
An occultation is an event that occurs when one object is hidden by another object that passes between it and the observer. The word is used in astronomy . It can also refer to any situation wherein an object in the foreground blocks from view an object in the background...

 using five chords
Chord (astronomy)
In the field of astronomy the term chord typically refers to a line crossing an object which is formed during an occultation event. By taking accurate measurements of the start and end times of the event, in conjunction with the known location of the observer and the object's orbit, the length of...

 suggest an outline of 214×181 km. Recent estimates of Psyche's smaller size has resulted in an increase in the 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
Ecliptic coordinate system
The ecliptic coordinate system is a celestial coordinate system that uses the ecliptic for its fundamental plane. The ecliptic is the path that the sun appears to follow across the celestial sphere over the course of a year. It is also the intersection of the Earth's orbital plane and the celestial...

 (β, λ) = (-9°, 35°) or (β, λ) = (-2°, 215°) with a 10° uncertainty. This gives an axial tilt
Axial tilt
In astronomy, axial tilt is the angle between an object's rotational axis, and a line perpendicular to its orbital plane...

 of 95°.

Two stellar occultations by Psyche have been observed (from Mexico
The United Mexican States , commonly known as Mexico , is a federal constitutional republic in North America. It is bordered on the north by the United States; on the south and west by the Pacific Ocean; on the southeast by Guatemala, Belize, and the Caribbean Sea; and on the east by the Gulf of...

 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
Enstatite chondrite
Enstatite chondrites are a rare form of meteorite thought to comprise only about 2% of the chondrites that fall on Earth. Only about 200 E-Type chondrites are currently known....

meteorites originated from this asteroid, based on similar spectral analysis results.

External links

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