GeminiFocus July 2018 - Page 16

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