Abstract
Asteroid (16) Psyche was dominantly thought to be a remnant of a core
that is a pure-metallic body because of the higher radar albedo
(~0.37) detected than other main-belt asteroids (0.14 -
0.15). However, there are some features Psyche has incompatible with
this hypothesis. The most inconsistent physical parameter is the bulk
density. The reported bulk density of Psyche (~4.0 g
cm-3) is remarkably lower than that of iron meteorites
(~7.5 g cm-3). Another feature is that
Psyche has radar albedo variations across the surface, indicating
non-uniformly distributed surface compositions. Recent observations and
investigations [1-3] also support the existence of orthopyroxene and
hydrated silicates on the surface. Following this, Psyche is interpreted
as a mixed metal and silicate world.
Given this surface composition, a key issue is Psyche’s internal
structure. The most plausible structure is a metallic core covered with
a silicate-rich layer; however, this structural condition is unsuited to
the detected highest albedo, possibly representing metals on the
surface. Thus, we numerically estimate the internal structure
distribution (i.e., the size of iron core and thickness of the
silicate-rich layer) using our technique, combined with a three-layer
model and FEM approach, and show that this structure condition is still
thin enough to reveal the metallic materials in the iron core onto the
surface. The three-layer model represents Psyche’s possible structural
layout consisting of a spherical iron core and two types of the
silicate-rich layer (compressed and uncompressed one) resulting from the
compaction process in the silicate-rich layer (Fig. 1(a)), while the FEM
accesses the stress field of Psyche with a varying bulk density on each
layer. As a result, we find that Psyche is likely to have an iron core
sized 76 to 103 km in radius (Fig. 1(b)). Given this core size, the
silicate-rich layer, consisting of both compressed and uncompressed
regions, has a thickness ranging between 0 and 64 km. Assumed a
spherical iron core, a very thin silicate-rich layer on the polar region
is still sufficient to expose the metallic components at crater-like
regions and experience ferrovolcanic surface eruptions at localized
regions.
[1] Sanchez et al. (2016) AJ 153
[2] Landsman et al. (2018) Icarus, 304
[3] Shepard et al. (2021) PSJ, 2