page_title: 16 Psyche
section_title: Mass, size and shape
hierarchical_section_title: 16 Psyche / Characteristics / Mass, size and shape
caption_attribution_description: English: en:16 Psyche orbit between Mars and Jupiter
context_page_description: 16 Psyche is one of the most massive asteroids in the asteroid belt. This object is over 200 km in diameter and contains about 1% of the mass of the entire asteroid belt. It is thought to be the exposed iron core of a protoplanet, and 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. The prefix "16" signifies that it was the sixteenth minor planet in order of discovery.
context_section_description: Psyche is massive enough that its gravitational perturbations on other asteroids can be observed, which enables a mass measurement. The values for the mass of (3.38±0.28)×10⁻¹¹M☉ and the density of 6.98±0.58 g/cm³ obtained from a 2002 analysis by Kuzmanoski and Kovačević, of a close encounter with asteroid (13206) 1997 GC₂₂. The new, high density estimate suggests that 16 Psyche must be composed mostly of metals. As of 2019, the best mass estimate is (2.41±0.32)×10¹⁹ kg, with a derived bulk density of 3.99±0.26 g/cm³.
  The first size estimate of Psyche came from IRAS thermal infrared emission observations. They showed that it had a diameter of about 253 km, although it was likely an overestimate as Psyche was viewed pole-on at that time.
  Light curve analysis indicates Psyche appears somewhat irregular in shape. There is a pronounced mass deficit near the equator at about 90° longitude comparable to Rheasilvia basin on Vesta. There are also two additional smaller (50–70 km in diameter) crater-like depressions near the south pole. Psyche's north pole points towards the ecliptic coordinates β = 28°, λ = −6°, with a 4° uncertainty. This gives an axial tilt of 95°.
  Observations of two multi-chord stellar occultations of 2010 and 2014 allow the matching of light curve inversions DAMIT model 1806 that give an equivalent-volume mean diameter of 216±12 km, and an equivalent surface mean diameter of 227±13 km. The density of Psyche derived from these estimates – 3.7±0.6 g/cm³ – is consistent with that of other metallic asteroids.
  Observations of Psyche with Very Large Telescope's adaptive optics SPHERE imager revealed two large craters, which were informally named Meroe and Panthia, after the twin witches in the Roman novel Metamorphoses by Apuleius.
caption: The orbit of Psyche between Mars and Jupiter is near-circular
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