16 Psyche (pronounced /ˈsaɪkiː/ SYE-kee, or as in Greek: Ψυχή) 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 main asteroid belt. It is the most massive of the metallic M-type asteroids.

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 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).[5]

Characteristics

Radar[6][7] 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.[8] Small amounts of pyroxene appear to be present.[9]

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.[10] 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. IRAS data shows Psyche to have a diameter of 253 km.[1] Observations of an occultation using five chords suggest an outline of 214×181 km.[11] Recent estimates of Psyche's smaller size has resulted in an increase in the estimated density which is more appropriate for a metallic asteroid.[2][3] 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.[12] 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.

References

1. ^ a b c d e f g "JPL Small-Body Database Browser: 16 Psyche". 2008-09-19 last obs. http://ssd.jpl.nasa.gov/sbdb.cgi?sstr=16. Retrieved 2008-12-04.
2. ^ a b c d Jim Baer (2008). "Recent Asteroid Mass Determinations". Personal Website. http://home.earthlink.net/~jimbaer1/astmass.txt. Retrieved 2008-12-04.
3. ^ a b Lupishko, D. F. (2006). "On the bulk density and porosity of M-type asteroid 16 Psyche". Solar System Research 40 (3): 214–218. doi:10.1134/S0038094606030051. http://adsabs.harvard.edu/abs/2006SoSyR..40..214L. Retrieved 2007-02-04.
4. ^ PDS lightcurve data
5. ^ Hilton, J. (2001-09-17). "When Did the Asteroids Become Minor Planets?". U.S. Naval Observatory. http://aa.usno.navy.mil/faq/docs/minorplanets.php. Retrieved 2007-04-03.
6. ^ S.J. Ostro (1985). "Radar observations of asteroids and comets". Astronomical Society of the Pacific, Publications 97: 877. doi:10.1086/131619. http://articles.adsabs.harvard.edu/cgi-bin/nph-iarticle_query?1985PASP...97..877O&data_type=PDF_HIGH&type=PRINTER&filetype=.pdf.
7. ^ C. Magri et al. (1999). "Mainbelt Asteroids: Results of Arecibo and Goldstone Radar Observations of 37 Objects during 1980-1995". Icarus 140: 379. doi:10.1006/icar.1999.6130.
8. ^ E. Merényi et al. (1997). "Prediction of Water in Asteroids from Spectral Data Shortward of 3 µm". Icarus 129: 421. doi:10.1006/icar.1997.5796.
9. ^ P.S. Hardersen, M.J. Gaffey, and P.A. Abell (2005). "Near-IR spectral evidence for the presence of iron-poor orthopyroxenes on the surfaces of six M-type asteroids". Icarus 175: 141. doi:10.1016/j.icarus.2004.10.017. http://adsabs.harvard.edu/cgi-bin/nph-bib_query?bibcode=2005Icar..175..141H&db_key=AST&data_type=HTML&format=&high=444b66a47d07948.
10. ^ D.R. Davis, P. Farinella, & M. Francesco (1999). "The Missing Psyche Family: Collisionally Eroded or Never Formed?". Icarus 137: 140. doi:10.1006/icar.1998.6037.
11. ^ "Occultation of TYC 5783-01228-1 by (16) Psyche 2004 May 16". Royal Astronomical Society of New Zealand. http://occsec.wellington.net.nz/planet/2004/results/040516_psyche.htm. Retrieved 2008-12-04.
12. ^ M. Kaasalainen et al. (2002). "Models of Twenty Asteroids from Photometric Data". Icarus 159: 369. doi:10.1006/icar.2002.6907. http://www.rni.helsinki.fi/~mjk/IcarPIII.pdf.

External links

* Shape model deduced from lightcurve (PDF)
* Occultation of TYC 5783-1228 by 16 Psyche (Video)
* Orbital simulation from JPL (Java) / Ephemeris