16 Psyche

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16 Psyche
Discovery
Discovered by Annibale de Gasparis
Discovery date March 17, 1852
Designations
Alternative names none
Minor planet
category		 Main belt
Epoch October 22, 2004 (JD 2453300.5)
Aphelion 497.884 Gm (3.328 AU)
Perihelion 375.958 Gm (2.513 AU)
Semi-major axis 436.921 Gm (2.921 AU)
Eccentricity 0.140
Orbital period 1823.115 d (4.99 a)
Average orbital speed 17.34 km/s
Mean anomaly 323.379°
Inclination 3.095°
Longitude of ascending node 150.352°
Argument of perihelion 228.047°
Physical characteristics
Dimensions ~280×230×190 km[1][2][3][4][5]
Mass ~1.7×1019 kg [6]
Mean density 3.3 ± 0.7 g/cm³[7]
Equatorial surface gravity ~0.06 m/s²
Escape velocity ~0.13 km/s
Rotation period 0.1748 d (4.196 h) [8]
Albedo 0.120 (geometric)[1]
Temperature ~160 K
max: ~280 K (+7 °C)
Spectral type M
Apparent magnitude 9.26 to 12.23
Absolute magnitude 5.90

16 Psyche (pronounced /ˈsaɪki/, Greek: 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.[6]

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).[9]

[edit] Characteristics

Radar[10][11] 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.[12] Small amounts of pyroxene appear to be present.[13]

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.[14] 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%.[7] 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.[3] 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.


[edit] References

  1. ^ a b Supplemental IRAS Minor Planet Survey
  2. ^ Dunham, D. W. and Herald, D. (2006). Asteroid Occultations. EAR-A-3-RDR-OCCULTATIONS-V4.1. NASA Planetary Data System. Retrieved on 2007-04-03.
  3. ^ a b M. Kaasalainen et al (2002). "Models of Twenty Asteroids from Photometric Data". Icarus 159: 369. doi:10.1006/icar.2002.6907. 
  4. ^ Magnusson, P. and Neese, C.:Asteroid Spin Vectors. EAR-A-5-DDR-ASTEROID-SPIN-VECTORS-V4.2. NASA Planetary Data System (1996). Retrieved on 2007-04-03.
  5. ^ A. Cellino et al (2002). "Speckle interferometry observations of main belt asteroids at TNG". Proceedings of Asteroids, Comets, Meteors - ACM 2002. International Conference: 497. 
  6. ^ a b B. Vitaeau (2000). "Mass and density of asteroids (16) Psyche and (121) Hermione". Astronomy & Astrophysics 354: 725. 
  7. ^ 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. 
  8. ^ PDS lightcurve data
  9. ^ Hilton, J. (September 17, 2001). When Did the Asteroids Become Minor Planets?. U.S. Naval Observatory. Retrieved on 2007-04-03.
  10. ^ S.J. Ostro (1985). "Radar observations of asteroids and comets". Astronomical Society of the Pacific, Publications 97: 877. 
  11. ^ 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. 
  12. ^ 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. 
  13. ^ 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. 
  14. ^ 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. 


[edit] External links


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