16 Psyche

Infobox Planet | discovery=yes | physical_characteristics = yes | bgcolour=#FFFFC0
name=16 Psyche
discoverer=Annibale de Gasparis
discovered=March 17, 1852
alt_names="none"
mp_category=Main belt
epoch=October 22, 2004 (JD 2453300.5)
semimajor=436.921 Gm (2.921 AU)
perihelion=375.958 Gm (2.513 AU)
aphelion=497.884 Gm (3.328 AU)
eccentricity=0.140
period=1823.115 d (4.99 a)
inclination=3.095°
asc_node=150.352°
arg_peri=228.047°
mean_anomaly=323.379°
avg_speed=17.34 km/s
dimensions=~280×230×190 km [http://www.psi.edu/pds/resource/imps.html Supplemental IRAS Minor Planet Survey] ] cite web
author = Dunham, D. W. and Herald, D.
year = 2006
url = http://www.psi.edu/pds/resource/occ.html
title = Asteroid Occultations
work = EAR-A-3-RDR-OCCULTATIONS-V4.1
publisher = NASA Planetary Data System
accessdate = 2007-04-03] cite journal | author= M. Kaasalainen et al| title= "Models of Twenty Asteroids from Photometric Data"| journal= Icarus| year= 2002| volume= 159| pages= 369| url= http://www.rni.helsinki.fi/~mjk/IcarPIII.pdf | doi = 10.1006/icar.2002.6907 ] cite web
editor = Magnusson, P. and Neese, C.
year = 1996
url = http://www.psi.edu/pds/resource/spin.html
title = Asteroid Spin Vectors
work = EAR-A-5-DDR-ASTEROID-SPIN-VECTORS-V4.2
publisher = NASA Planetary Data System
accessdate = 2007-04-03] cite journal | author= A. Cellino et al| title= "Speckle interferometry observations of main belt asteroids at TNG"| journal= Proceedings of Asteroids, Comets, Meteors - ACM 2002. International Conference| year= 2002| volume= | pages= 497| url= http://articles.adsabs.harvard.edu/cgi-bin/nph-iarticle_query?2002acm..conf..497C&data_type=PDF_HIGH&type=PRINTER&filetype=.pdf]
mass=~1.7×10¹⁹ kg
density=3.3 ± 0.7 g/cm³cite journal
last = Lupishko
first = D. F.
title=On the bulk density and porosity of M-type asteroid 16 Psyche
journal=Solar System Research
year=2006
volume=40
issue=3
pages=214–218
url=http://adsabs.harvard.edu/abs/2006SoSyR..40..214L
accessdate=2007-02-04
doi=10.1134/S0038094606030051 ]
surface_grav=~0.06 m/s²
escape_velocity=~0.13 km/s
rotation=0.1748 d (4.196 h) [http://www.psi.edu/pds/resource/lc.html PDS lightcurve data] ]
spectral_type=M
magnitude = 9.26 to 12.23
abs_magnitude=5.90
albedo=0.120 (geometric)
single_temperature=~160 K
"max:" ~280 K (+7 °C)

16 Psyche (pronEng|ˈsaɪki, _gr. "Ψυχή)" is a very large Main belt asteroid, well over 200 kilometers in diameter, and likely the largest of the metallic M-type asteroids. It is estimated to contain 0.6 percent of the mass of the entire asteroid belt.cite journal | author= B. Vitaeau| title= "Mass and density of asteroids (16) Psyche and (121) Hermione"| journal= Astronomy & Astrophysics| year= 2000| volume= 354| pages= 725| url= http://aa.springer.de/papers/0354002/2300725.pdf]

This asteroid was discovered by Annibale de Gasparis on March 17, 1852 from Naples and named after, the Greek female, 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 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). [cite web
last = Hilton
first = J.
date = 2001-09-17
url = http://aa.usno.navy.mil/hilton/AsteroidHistory/minorplanets.html
title = When Did the Asteroids Become Minor Planets?
publisher = U.S. Naval Observatory
accessdate = 2007-04-03 ]

Characteristics

Radarcite journal | author= S.J. Ostro| title= "Radar observations of asteroids and comets"| journal= Astronomical Society of the Pacific, Publications | year= 1985| volume= 97| pages= 877| url= http://articles.adsabs.harvard.edu/cgi-bin/nph-iarticle_query?1985PASP...97..877O&data_type=PDF_HIGH&type=PRINTER&filetype=.pdf| doi= 10.1086/131619] cite journal | author= C. Magri et al| title= "Mainbelt Asteroids: Results of Arecibo and Goldstone Radar Observations of 37 Objects during 1980-1995"| journal= Icarus| year= 1999| volume= 140| pages= 379 | doi = 10.1006/icar.1999.6130 ] observations indicate a fairly pure iron-nickel 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.cite journal | author= E. Merényi et al| title= "Prediction of Water in Asteroids from Spectral Data Shortward of 3 µm"| journal= Icarus| year= 1997| volume= 129| pages= 421 | doi = 10.1006/icar.1997.5796 ] Small amounts of pyroxene appear to be present.cite journal| author = P.S. Hardersen, M.J. Gaffey, and P.A. Abell | title="Near-IR spectral evidence for the presence of iron-poor orthopyroxenes on the surfaces of six M-type asteroids"| journal= Icarus| volume = 175| page= 141 | year=2005| url=http://adsabs.harvard.edu/cgi-bin/nph-bib_query?bibcode=2005Icar..175..141H&db_key=AST&data_type=HTML&format=&high=444b66a47d07948 | pages = 141 | doi = 10.1016/j.icarus.2004.10.017 ]

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.cite journal | author= D.R. Davis, P. Farinella, & M. Francesco| title= "The Missing Psyche Family: Collisionally Eroded or Never Formed?"| journal= Icarus| year= 1999| volume= 137| pages= 140 | doi = 10.1006/icar.1998.6037 ] 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 measurement. Its density is relatively low for metal (although fairly typical for asteroids as such), indicating a relatively high porosity of 30–40%. The asteroid is probably an enormous rubble pile.

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.

References

External links

* [http://www.rni.helsinki.fi/~mjk/IcarPIII.pdf Shape model deduced from lightcurve] (PDF)
* [http://users.tpg.com.au/users/daveg/astrovideos/videos.htm Occultation of TYC 5783-1228 by 16 Psyche] (Video)
* [http://ssd.jpl.nasa.gov/sbdb.cgi?sstr=16;orb=1 Orbital simulation] from JPL (Java) / [http://ssd.jpl.nasa.gov/horizons.cgi?find_body=1&body_group=sb&sstr=16 Ephemeris]