Equilibrium figure of Haumea and possible detection by stellar occultation

Abstract

The equilibrium figure of dwarf planet Haumea is studied to determine if the observed shape is compatible with a differentiated hydrostatic body. Three groups of interior models of Haumea are assumed, all with a rocky core and a volatile-rich outer shell that may contain some porosity. A third layer located between the core and the outer shell has a density suggesting partial differentiation or the presence of a large fraction of organic matter. Using the code BALEINES, which solves for the equilibrium figures of the boundaries between layers, we show that the hydrostatic models closest to the shape derived by stellar occultation approach a state of critical rotation, which translates into a pinched shape with large deviations from an ellipsoid (up to 110~km). The previous stellar occultation and light curves cannot distinguish between the ellipsoid and the pinched shape, but we predict this figure could be observable on the next stellar occultation of Haumea on May 4, 2026, if some chords are obtained in the northern or southern limbs of the shadow.

Figures (5)

• Figure 1: Possible hydrostatic models obtained in this work (pink region) compared with the Jacobi sequence (red line). The models of table \ref{['tab:results']} are plotted with black crosses; "D19" corresponds to the hydrostatic model preferred by ddp19. The best-fit ellipsoid obtained by ortiz17 is reported as well and plotted with 1, 2 or $3\upsigma$ uncertainty regions.
• Figure 2: Hydrostatic shape models for Haumea in the $(x{\rm O}z)$ (left) and $(y{\rm O}z)$ (right) planes, corresponding to the configurations reported in table \ref{['tab:results']}. The dashed lines correspond to the ellipsoids with the same axis lengths as the layers' boundary.
• Figure 3: Projections of the six hydrostatic representative solutions in the sky plane at the epoch of the 2017 occultation. $u$ and $v$ are the celestial East and North, respectively.
• Figure 4: Projections of the hydrostatic shape of configuration C in the sky plane at the time of the 2017 occultation (left) and the future 2026 occultation (right). The projection of the ellipsoidal shape derived by ortiz17 is shown in white dotted line for comparison. The facet colours code the relative irradiance they receive, red being the highest and purple-blue the lowest.
• Figure 5: Comparisons between the light curves of Haumea reported by lacerda2008, lockwood14 and ortiz17 and synthetic light curves obtained with the hydrostatic figures.