16 Psyche

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16 Psyche 16 Psyche symbol.svg
16Psyche (Lightcurve Inversion).png
A three-dimensional model of 16 Psyche based on its light curve.
Discovered by Annibale de Gasparis
Discovery date 17 March 1852
Pronunciation /ˈsk/ SY-kee
Named after
Main belt
Orbital characteristics[1]
Epoch JD 2453300.5 (22 October 2004)
Aphelion 3.328 AU (497.884 Gm)
Perihelion 2.513 AU (375.958 Gm)
2.921 AU (436.921 Gm)
Eccentricity 0.140
4.99 yr (1823.115 d)
17.34 km/s
Inclination 3.095°
Physical characteristics
Dimensions 240×185×145 km[2]
186 km (Geometric mean)
253.2 ± 4 km (IRAS)[1]
Mass 2.27×1019 kg[2]
Mean density

6.73 ± 3.05 g/cm³[2]

3.3 ± 0.7 g/cm³[3]
~0.06 m/s²[citation needed]
~0.13 km/s[citation needed]
0.1748 d (4.196 h)[1][4]
Albedo 0.120 (geometric)[1]
0.29±0.11 (radar)
Temperature ~160 K
max: ~280 K (+7 °C)[citation needed]
Spectral type
9.22 to 12.19

16 Psyche is one of the ten most-massive asteroids in the asteroid belt. It is over 200 kilometers in diameter and contains a little less than 1% of the mass of the entire asteroid belt. It is thought to be the exposed iron core of a protoplanet.[5] It is the most massive metallic M-type asteroid. Psyche was discovered by the Italian astronomer Annibale de Gasparis on 17 March 1852 from Naples and named after the Greek mythological figure Psyche.[6]


The first fifteen asteroids to be discovered were given symbols by astronomers as a type of shorthand notation. Psyche was given an iconic symbol, as were several other asteroids discovered over the next few years. This symbol, a semicircle topped by a star, represents a butterfly's wing, symbol of the soul (psyche is the Greek word for 'soul'), and a star.[7] In 1851, German astronomer J. F. Encke suggested using a circled number, and 16 Psyche was the first new asteroid to be discovered that was designated using this scheme when American astronomer J. Ferguson published his observations in 1852.[8]


Radar observations indicate that Psyche has a fairly pure ironnickel composition,[9][10] consistent with it having the highest radar albedo of any asteroid in the asteroid belt (0.29±0.11).[11] 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] Psyche seems to have a surface that is 90% metallic (iron),[13] with small amounts of pyroxene.[14]

Psyche thus appears to be an exposed metallic core from a larger differentiated 500 km parent body. If Psyche is indeed the core remnant of a larger, now destroyed, parent body, we might expect to find other asteroids on similar orbits. However, Psyche is not part of any asteroid family.[15] One hypothesis is that the collision that formed Psyche 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. However, this scenario is considered to have a probability of just 1%. An alternative is that Psyche was broken by impacts, but not catastrophically torn apart. In this case, it may be a candidate for the parent body of the mesosiderites, a class of stony–iron meteorites.[15]

Psyche is massive enough that its gravitational perturbations on other asteroids can be observed, which enables a mass measurement. IRAS data shows it to have a diameter of 253 km,[1] whereas observations of an occultation that provided five cross-sectional chords suggest an outline of 214×181 km.[16] Recent[when?] estimates[which?] of Psyche's smaller size has resulted in an increase in its estimated density to one that is more appropriate for a metallic asteroid.[2][3] Psyche appears to have a fairly regular surface and is approximately ellipsoidal in shape. Light-curve analysis has indicated that Psyche's pole points towards either ecliptic coordinates (β, λ) = (−9°, 35°) or (β, λ) = (−2°, 215°) with a 10° uncertainty.[17] This gives an axial tilt of 95°.

Two stellar occultations by Psyche have been observed (on 22 March 2002 in Mexico and another on 16 May 2002[where?]). Light-curve variations indicate a non-spherical body, consistent with the radar results.[citation needed]

It is possible that at least some examples of enstatite chondrite meteorites originated from this asteroid, based on similar spectral analysis results.


Concept art for Psyche at Psyche

No spacecraft has visited Psyche, but in 2014 a mission to Psyche was proposed to NASA.[18] A proposal for an unmanned Psyche orbiter has been made by a team led by Lindy Elkins-Tanton,[5] the director of the School for Earth and Space Exploration at Arizona State University. This team argues that 16 Psyche would be a valuable object for study because it is the only metallic core-like body discovered so far.[18] The proposed spacecraft would orbit Psyche for six 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 September 30, 2015, the Psyche orbiter mission was one of five Discovery Program semifinalist proposals.[19] If selected for flight in September 2016, the mission would launch in 2020 and arrive in 2026.[20]


  1. ^ a b c d e f g "JPL Small-Body Database Browser: 16 Psyche" (2008-09-19 last obs). Retrieved 2008-12-04. 
  2. ^ a b c d Baer, Jim (2011). "Recent Asteroid Mass Determinations". Personal Website. Retrieved 2012-04-14. 
  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. Bibcode:2006SoSyR..40..214L. doi:10.1134/S0038094606030051. 
  4. ^ PDS lightcurve data Archived 17 January 2010 at WebCite
  5. ^ a b Elkins-Tanton, L. T.; et al. (March 2014). "Journey to a Metal World: Concept for a Discovery Mission to Psyche" (PDF). LPI Contribution No. 1777. 45th Lunar and Planetary Science Conference. p. 1253. Bibcode:2014LPI....45.1253E. Retrieved 2015-10-05. 
  6. ^ Schmadel, Lutz D. (2012). Dictionary of Minor Planet Names (6th ed.). Springer Science & Business Media. pp. 14−15. ISBN 3642297188. 
  7. ^ Sonntag, A. (1852). "Elemente und Ephemeride der Psyche". Astronomische Nachrichten 34 (20): 283. Bibcode:1852AN.....34..283.. doi:10.1002/asna.18520342010. (in a footnote) Herr Professor de Gasparis schreibt mir, in Bezug auf den von ihm März 17 entdeckten neuen Planeten: "J'ai proposé, avec l'approbation de Mr. Hind, le nom de Psyché pour la nouvelle planète, ayant pour symbole une aile de papillon surmontée d'une étoile." 
  8. ^ Hilton, J. (2001-09-17). "When Did the Asteroids Become Minor Planets?". U.S. Naval Observatory. Archived from the original on 2010-01-18. Retrieved 2007-04-03. 
  9. ^ Ostro, S.J. (1985). "Radar observations of asteroids and comets". Astronomical Society of the Pacific, Publications 97: 877. Bibcode:1985PASP...97..877O. doi:10.1086/131619. 
  10. ^ Magri, C.; et al. (1999). "Mainbelt Asteroids: Results of Arecibo and Goldstone Radar Observations of 37 Objects during 1980–1995". Icarus 140 (2): 379. Bibcode:1999Icar..140..379M. doi:10.1006/icar.1999.6130. 
  11. ^ Ostro, S. J. (October 1985). Radar observations of asteroids and comets. Astronomical Society of the Pacific, Symposium on New Directions in Asteroids and Comet Research, Northern Arizona University 97. Astronomical Society of the Pacific. pp. 877−884. Bibcode:1985PASP...97..877O. doi:10.1086/131619. 
  12. ^ Merényi, E.; et al. (1997). "Prediction of Water in Asteroids from Spectral Data Shortward of 3 µm". Icarus 129 (2): 421. Bibcode:1997Icar..129..421M. doi:10.1006/icar.1997.5796. 
  13. ^ Callahan, Jason (March 30, 2015). "Discovery lives". The Space Review. Retrieved 30 March 2015. 
  14. ^ Hardersen, P.S.; Gaffey, M.J. & Abell, P.A. (2005). "Near-IR spectral evidence for the presence of iron-poor orthopyroxenes on the surfaces of six M-type asteroids". Icarus 175 (1): 141. Bibcode:2005Icar..175..141H. doi:10.1016/j.icarus.2004.10.017. 
  15. ^ a b Davis, D.R.; Farinella, P. & Francesco, M. (1999). "The Missing Psyche Family: Collisionally Eroded or Never Formed?". Icarus 137 (1): 140. Bibcode:1999Icar..137..140D. doi:10.1006/icar.1998.6037. 
  16. ^ "Occultation of TYC 5783-01228-1 by (16) Psyche 2004 May 16". Royal Astronomical Society of New Zealand, Occultation Section. Retrieved 2015-10-05. 
  17. ^ Kaasalainen, M.; et al. (2002). "Models of Twenty Asteroids from Photometric Data" (PDF). Icarus 159 (2): 369. Bibcode:2002Icar..159..369K. doi:10.1006/icar.2002.6907. Retrieved 16 May 2006. 
  18. ^ a b Wall, Mike (15 January 2014). "Strange Metal Asteroid Targeted in Far-Out NASA Mission Concept". Space.com. TechMedia Network. Retrieved 16 January 2014. 
  19. ^ Brown, Dwayne C.; Cantillo, Laurie (September 30, 2015). "NASA Selects Investigations for Future Key Planetary Mission". NASA TV. NASA. Retrieved 2015-10-05. 
  20. ^ Hand, Eric (30 September 2015). "Venus and a bizarre metal asteroid are leading destinations for low-cost NASA missions". Science Insider. American Association for the Advancement of Science. doi:10.1126/science.aad4651. 

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