Figure 4.
Orientation during
each observation
shown in Figure 3 of
the best-fitting triaxial
model derived from the
full set of deconvolved
AO images. The south
pole and equator are
visible in all cases. The
sub-Earth and sub-Sun
points are labeled as m
and b , respectively.
(Figure reproduced
from Drummond, et al.,
2018; Icarus, 305: 174.)
interior much more silicate-rich than its sur-
face, but such an inverted structure would be
difficult to understand.
The study also derives an improved determi-
nation for the asteroid’s rotational pole, with
an uncertainty radius of 3 degrees. This is
useful in operations planning for the Psyche
Mission, but the precision is currently limited
by the restricted range of orientations avail-
able for the modeling. Remarkably, Psyche
has an orbital period of 5.00 years, which
means that only four distinct geometries
are possible at opposition. Improving the
shape and orientation measurements for
this unique asteroid will require further AO
14
GeminiFocus
observations at oppositions with geome-
tries not represented in Figure 4, as well as at
times when it is challengingly away from op-
position. The upcoming robotic rendezvous
will provide an exciting opportunity to test
the analysis methods used for the AO data
and will measure the object’s moment of
inertia, finally revealing the secret structure
beneath Psyche’s shiny surface.
John Blakeslee is the Chief Scientist at Gemini Ob-
servatory and located at Gemini South in Chile.
He can be reached at: [email protected]
July 2018