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16 Psyche () is a large M-type asteroid discovered by the Italian astronomer Annibale de Gasparis on 17 March 1852 and named after the
Greek goddess A major branch of classical mythology, Greek mythology is the body of myths originally told by the ancient Greeks, and a genre of Ancient Greek folklore. These stories concern the origin and nature of the world, the lives and activities of de ...
Psyche Psyche (''Psyché'' in French) is the Greek term for "soul" (ψυχή). Psyche may also refer to: Psychology * Psyche (psychology), the totality of the human mind, conscious and unconscious * ''Psyche'', an 1846 book about the unconscious by Car ...
. The prefix "16" signifies that it was the sixteenth minor planet in order of discovery. It is the largest and most massive of the M-type asteroids, and one of the dozen most massive asteroids. It has a mean diameter of approximately and contains about one percent of the mass of the
asteroid belt The asteroid belt is a torus-shaped region in the Solar System, located roughly between the orbits of the planets Jupiter and Mars. It contains a great many solid, irregularly shaped bodies, of many sizes, but much smaller than planets, c ...
. Historically, it was hypothesized to be the exposed
core Core or cores may refer to: Science and technology * Core (anatomy), everything except the appendages * Core (manufacturing), used in casting and molding * Core (optical fiber), the signal-carrying portion of an optical fiber * Core, the centra ...
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 planetesimals that gravitation ...
, but numerous recent studies have all but ruled that out. Psyche will be explored by the spacecraft of the same name, with launch planned in 2023 and arrival in 2029.


Symbol

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 planet In classical antiquity, the seven classical planets or seven luminaries are the seven moving astronomical objects in the sky visible to the naked eye: the Moon, Mercury, Venus, the Sun, Mars, Jupiter, and Saturn. The word '' planet'' co ...
s. Psyche was given an iconic symbol, as were a few other asteroids discovered after 16 Psyche. The symbol was a butterfly's wing topped by a star ( or ), as the butterfly was a Greek symbol of the soul (''psyche'' being the Greek word for "soul"). However, the iconic symbols for all asteroids were superseded before Psyche's symbol ever came into use. With more than a dozen asteroids discovered, remembering all their individual emblems became increasingly cumbersome, and in 1851, German astronomer J.F. Encke suggested using a circled number instead: . The first asteroid designated with the new scheme was  Psyche, when American astronomer J. Ferguson published his observations in 1852.


Characteristics


Size

The first size estimate of Psyche was and came from
IRAS The Infrared Astronomical Satellite ( Dutch: ''Infrarood Astronomische Satelliet'') (IRAS) was the first space telescope to perform a survey of the entire night sky at infrared wavelengths. Launched on 25 January 1983, its mission lasted ten ...
thermal
infrared Infrared (IR), sometimes called infrared light, is electromagnetic radiation (EMR) with wavelengths longer than those of Light, visible light. It is therefore invisible to the human eye. IR is generally understood to encompass wavelengths from ...
emission observations. This is 15% larger than the currently accepted mean value, but was later found to be an accurate estimate for the IRAS viewing aspect because Psyche was viewed pole-on at the time of the measurement. Psyche has been observed to
occult The occult, in the broadest sense, is a category of esoteric supernatural beliefs and practices which generally fall outside the scope of religion and science, encompassing phenomena involving otherworldly agency, such as magic and mysticism a ...
a star on nine occasions. Four of these, 2004, 2010, 2014, 2019 generated multi-chord data sets and have been used along with adaptive optics imaging and three-dimensional modeling to estimate Psyche's mean diameter, with recent models all converging to an equivalent-volume mean diameter of  km.


Mass and bulk density

Psyche is massive enough that its
gravitational perturbation In astronomy, perturbation is the complex motion of a massive body subjected to forces other than the gravitational attraction of a single other massive body. The other forces can include a third (fourth, fifth, etc.) body, resistance, as from ...
s on other asteroids can be observed, which enables a
mass Mass is an intrinsic property of a body. It was traditionally believed to be related to the quantity of matter in a physical body, until the discovery of the atom and particle physics. It was found that different atoms and different ele ...
measurement. Historical values for its mass have ranged from to . However, most recent mass estimates have begun to converge to values of . Assuming the mean volume of , this equates to a bulk density of .


Shape and spin pole

The first published three-dimensional shape model for Psyche was derived from an analysis of numerous light curves. Since then, additional refinements to the shape have been made based on the inversion of lightcurves, adaptive optics observations, radar observations, thermal imaging, and occultations. The most recent models show that Psyche has a shape consistent with a Jacobi ellipsoid and dimensions within a few km of 278 km x 238 km x 171 km. Each shape model provides an estimate of the direction of the north pole (spin axis). All recent models for Psyche suggest it rotates about a pole pointed towards the
ecliptic coordinates The ecliptic coordinate system is a celestial coordinate system commonly used for representing the apparent positions, orbits, and pole orientations of Solar System objects. Because most planets (except Mercury) and many small Solar System bodi ...
(long, lat) , , with a 3° uncertainty. This means that it is essentially tilted toward the ecliptic, with an
axial tilt In astronomy, axial tilt, also known as obliquity, is the angle between an object's rotational axis and its orbital axis, which is the line perpendicular to its orbital plane; equivalently, it is the angle between its equatorial plane and orb ...
of 98°.


Features

Numerous features have been reported on Psyche. The largest of these are regions of mass-deficits relative to its nominal ellipsoid shape and are reminiscent of the
Rheasilvia Rheasilvia is the most prominent surface feature on the asteroid Vesta and is thought to be an impact crater. It is in diameter, which is 90% the diameter of Vesta itself, and is 95% the mean diameter of Vesta, . However, the mean is affect ...
basin on
4 Vesta Vesta ( minor-planet designation: 4 Vesta) is one of the largest objects in the asteroid belt, with a mean diameter of . It was discovered by the German astronomer Heinrich Wilhelm Matthias Olbers on 29 March 1807 and is named after Vesta, t ...
. In addition to the large-scale regions of mass-deficit, several apparent craters have been reported. Observers using the
Very Large Telescope The Very Large Telescope (VLT) is a telescope facility operated by the European Southern Observatory on Cerro Paranal in the Atacama Desert of northern Chile. It consists of four individual telescopes, each with a primary mirror 8.2 m acro ...
's
adaptive optics Adaptive optics (AO) is a technology used to improve the performance of optical systems by reducing the effect of incoming wavefront distortions by deforming a mirror in order to compensate for the distortion. It is used in astronomical tele ...
SPHERE A sphere () is a geometrical object that is a three-dimensional analogue to a two-dimensional circle. A sphere is the set of points that are all at the same distance from a given point in three-dimensional space.. That given point is the c ...
imager reported 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 ''Metamorphoses'' by Apuleius. Observers using the Arecibo Radar Telescope reported craters at the south pole (referred to as Delta), southern midlatitudes (referred to as Eros), and the north pole (referred to as Foxtrot). An analysis of the features present in several independent shape models suggests that craters Panthia and Eros are almost certainly real and Foxtrot is likely to be real. However, there is uncertainty over the existence of Meroe and Delta. Early lightcurve studies suggested that Psyche had large variations in its surface brightness. These variations became more evident when attempts were made to invert lightcurves to generate shape models. The most recent shape models based on lightcurve inversions simultaneously solve for surface albedo variations. Maps made from these inversions show regions where the surface may be up to 20% or more brighter or darker than the mean albedo. The reported Panthia crater coincides with a region considerably brighter than the mean, while the reported Meroe crater coincides with a much darker area. Radar observations with the Arecibo Radar Telescope revealed that Psyche's "background" radar albedo is \hat_=0.26 , comparable to other M-type asteroids like
21 Lutetia ) , mp_category=Main belt , mpc_name=(21) Lutetia , orbit_ref = , epoch=May 31, 2020 ( JD 2459000.5) , semimajor=2.435 AU , perihelion=2.037 AU , aphelion=2.833 AU , eccentricity=0.16339 , period=3.80 yr (1388.1 d) , inclination=3.064� ...
. This value is consistent with a
silicate In chemistry, a silicate is any member of a family of polyatomic anions consisting of silicon and oxygen, usually with the general formula , where . The family includes orthosilicate (), metasilicate (), and pyrosilicate (, ). The name is a ...
(rocky) regolith enriched in metal phases. However, in at least three locations, Psyche's radar albedo is nearly twice this value, suggesting high concentrations of metal phases in these regions. One of these locations corresponds with the optically bright Panthia crater, while the other two correspond with regions that have been reported as optically bright. This apparent correlation between optical and radar albedos on Psyche has led to the hypothesis that there is a link between the process(es) that create regions of high metal content and brighter terrain.


Composition

The bulk density of Psyche () places constraints on its overall composition. The iron-nickel found in most
iron meteorites Iron meteorites, also known as siderites, or ferrous meteorites, are a type of meteorite that consist overwhelmingly of an iron–nickel alloy known as meteoric iron that usually consists of two mineral phases: kamacite and taenite. Most iron met ...
has a bulk density of . If Psyche were the remnant
core Core or cores may refer to: Science and technology * Core (anatomy), everything except the appendages * Core (manufacturing), used in casting and molding * Core (optical fiber), the signal-carrying portion of an optical fiber * Core, the centra ...
of an early
planetesimal Planetesimals are solid objects thought to exist in protoplanetary disks and debris disks. Per the Chamberlin–Moulton planetesimal hypothesis, they are believed to form out of cosmic dust grains. Believed to have formed in the Solar System ...
, it would have to have an overall porosity of 50%. Given Psyche's size, this is considered highly improbable. However, there are other metal-rich
meteorite A meteorite is a solid piece of debris from an object, such as a comet, asteroid, or meteoroid, that originates in outer space and survives its passage through the atmosphere to reach the surface of a planet or moon. When the original object ...
types that have been suggested as Psyche analogs, each of which have bulk densities that are similar to Psyche's, including enstatite chondrites, bencubbinites, and mesosiderites. Several observers have reported the presence of
silicate minerals Silicate minerals are rock-forming minerals made up of silicate groups. They are the largest and most important class of minerals and make up approximately 90 percent of Earth's crust. In mineralogy, silica (silicon dioxide, ) is usually con ...
on the surface of Psyche. Spectra taken in October 2016 at the NASA Infrared Telescope Facility at the Mauna Kea Observatories showed evidence (~3 μm absorption feature) of
hydroxyl In chemistry, a hydroxy or hydroxyl group is a functional group with the chemical formula and composed of one oxygen atom covalently bonded to one hydrogen atom. In organic chemistry, alcohols and carboxylic acids contain one or more hydrox ...
ions on the asteroid that may suggest the presence of hydrated silicates. 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 C-type ( carbonaceous) asteroids are the most common variety, forming around 75% of known asteroids. They are volatile-rich and distinguished by a very low albedo because their composition includes a large amount of carbon, in addition to rock ...
s. Psyche's radar albedo varies considerably over the surface, ranging from 0.22 to 0.52, values that are two to four times as high as most main-belt asteroids. Models of radar reflection equate this range of values with regolith bulk densities of 2.6 to 4.7 . This range is consistent with most of the metal-rich
meteorite A meteorite is a solid piece of debris from an object, such as a comet, asteroid, or meteoroid, that originates in outer space and survives its passage through the atmosphere to reach the surface of a planet or moon. When the original object ...
classes noted above and the spectroscopic detection of silicate minerals. It is inconsistent with a pure
iron-nickel Iron meteorites, also known as siderites, or ferrous meteorites, are a type of meteorite that consist overwhelmingly of an iron–nickel alloy known as meteoric iron that usually consists of two mineral phases: kamacite and taenite. Most iron met ...
regolith unless it is highly porous.


Origin

Several possible origins have been proposed for Psyche. The earliest of these was that Psyche is an exposed metallic core resulting from a collision that stripped away the crust and
mantle A mantle is a piece of clothing, a type of cloak. Several other meanings are derived from that. Mantle may refer to: *Mantle (clothing), a cloak-like garment worn mainly by women as fashionable outerwear **Mantle (vesture), an Eastern Orthodox ve ...
of an originally larger differentiated parent body some 500 kilometers in diameter. Other versions of this include the idea that it was not the result of a single large collision but multiple (more than three) relatively slow sideswipe collisions with bodies of comparable or larger size. However, this idea has fallen out of recent favor as mass and density estimates are inconsistent with a remnant core. A second hypothesis is that Psyche was disrupted and gravitationally re-accreted into a mix of metal and silicate. 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. They are breccias with an irregular texture; silicates and metal occur often in lumps or pebbles as well as in fine-grained ...
s, a class of stony–iron meteorites. A third hypothesis is that Psyche may be a differentiated object (like
1 Ceres Ceres (; minor-planet designation: 1 Ceres) is a dwarf planet in the asteroid belt between the orbits of Mars and Jupiter. It was the first asteroid discovered, on 1 January 1801, by Giuseppe Piazzi at Palermo Astronomical Observatory in Sic ...
and
4 Vesta Vesta ( minor-planet designation: 4 Vesta) is one of the largest objects in the asteroid belt, with a mean diameter of . It was discovered by the German astronomer Heinrich Wilhelm Matthias Olbers on 29 March 1807 and is named after Vesta, t ...
) but has experienced a type of iron volcanism, also known as ferrovolcanism, while still cooling. If true, this model predicts that metal would be highly enriched only in those regions containing (relic) volcanic centers. This view has been bolstered by recent radar observations.


Exploration

No spacecraft has visited Psyche, but in 2014 a mission to Psyche was proposed to NASA. A team led by
Lindy Elkins-Tanton Lindy Elkins-Tanton is a planetary scientist and professor; her research concerns terrestrial planetary evolution. She is the Principal Investigator of NASA's '' Psyche'' mission to explore the metallic asteroid 16 Psyche, Arizona State Universit ...
, the director of the School for Earth and Space Exploration at
Arizona State University Arizona State University (Arizona State or ASU) is a public research university in the Phoenix metropolitan area. Founded in 1885 by the 13th Arizona Territorial Legislature, ASU is one of the largest public universities by enrollment in the ...
, presented a concept for a robotic ''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 In orbital mechanics and aerospace engineering, a gravitational slingshot, gravity assist maneuver, or swing-by is the use of the relative movement (e.g. orbit around the Sun) and gravity of a planet or other astronomical object to alter the p ...
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 28 February 2020, NASA awarded
SpaceX Space Exploration Technologies Corp. (SpaceX) is an American spacecraft manufacturer, launcher, and a satellite communications corporation headquartered in Hawthorne, California. It was founded in 2002 by Elon Musk with the stated goal o ...
a US$117 million contract to launch the ''Psyche'' spacecraft, and two smallsat secondary missions, on a
Falcon Heavy Falcon Heavy is a partially reusable heavy-lift launch vehicle that is produced by SpaceX, an American aerospace manufacturer. The rocket consists of two strap-on boosters made from Falcon 9 first stages, a center core also made from a Falc ...
rocket. As of October 2022, the mission is scheduled to launch no earlier than October 2023, reaching the asteroid in August 2029.


See also

* List of minor planets and comets visited by spacecraft * List of missions to minor planets *
Asteroid mining Asteroid mining is the hypothetical exploitation of materials from asteroids and other minor planets, including near-Earth objects. Notable asteroid mining challenges include the high cost of spaceflight, unreliable identification of asteroids ...


References


External links

* * * * {{DEFAULTSORT:000016 18520317 Background asteroids
Psyche Psyche (''Psyché'' in French) is the Greek term for "soul" (ψυχή). Psyche may also refer to: Psychology * Psyche (psychology), the totality of the human mind, conscious and unconscious * ''Psyche'', an 1846 book about the unconscious by Car ...
M-type asteroids (Tholen) Minor planets to be visited by spacecraft
Psyche Psyche (''Psyché'' in French) is the Greek term for "soul" (ψυχή). Psyche may also refer to: Psychology * Psyche (psychology), the totality of the human mind, conscious and unconscious * ''Psyche'', an 1846 book about the unconscious by Car ...
X-type asteroids (SMASS)