Haumea's Shape and Composition

Abstract

We have calculated the figure of equilibrium of a rapidly rotating, differentiated body to determine the shape, structure, and composition of the dwarf planet Haumea. Previous studies of Haumea's light curve have suggested Haumea is a uniform triaxial ellipsoid consistent with a Jacobi ellipsoid with axes $\approx 960\times 774\times 513$ km, and bulk density $\approx 2600\mathrm{kg}{\mathrm{m}}^{-3}$. In contrast, observations of a recent stellar occultation by Haumea indicate its axes are $\approx 1161\times 852\times 523$ km and its bulk density $\approx 1885\mathrm{kg}{\mathrm{m}}^{-3}$; these results suggest that Haumea cannot be a fluid in hydrostatic equilibrium and must be partially supported by interparticle forces. We have written a code to reconcile these contradictory results and to determine if Haumea is in fact a fluid in hydrostatic equilibrium. The code calculates the equilibrium shape, density, and ice crust thickness of a differentiated Haumea after imposing (semi-) axes lengths $a$ and $b$. We find Haumea is consistent with a differentiated triaxial ellipsoid fluid in hydrostatic equilibrium with axes of best fit $a$ = 1050 km, $b$ = 840 km, and $c$ = 537 km. This solution for Haumea has ${\rho }_{\mathrm{avg}}=2018\mathrm{kg}{\mathrm{m}}^{-3}$, ${\rho }_{\mathrm{core}}=2680\mathrm{kg}{\mathrm{m}}^{-3}$, and core axes $a_{\mathrm{c}}=883$ km, $b_{\mathrm{c}}=723$ km, and $c_{\mathrm{c}}=470$ km, which equates to an ice mantle comprising $\sim 17\%$ of Haumea's volume and ranging from 67 to 167 km in thickness. The thick ice crust we infer allows for Haumea's collisional family to represent only a small fraction of Haumea's pre-collisional ice crust. For a wide range of parameters, the core density we calculate for Haumea suggests that today the core is composed of hydrated silicates and likely underwent serpentinization in the past.

15 pages, 3 figures, accepted for publication in ApJ

References in corpus (11)

• The size, shape, density and ring of the dwarf planet Haumea from a stellar occultation
• Photometric Observations Constraining the Size, Shape, and Albedo of 2003 El61, a Rapidly Rotating, Pluto-Sized Object in the Kuiper Belt
• Time-Resolved Photometry of Kuiper Belt Objects: Rotations, Shapes and Phase Functions
• Orbits and Masses of the Satellites of the Dwarf Planet Haumea = 2003 EL61
• Densities of Solar System Objects from their Rotational Lightcurves
• The Surface of 2003EL61 in the Near Infrared
• Study of the Surface of 2003 EL61: the largest carbon-depleted object in the trans-neptunian belt
• High Precision Photometry of Extreme KBO 2003 EL61
• "TNOs are cool": A survey of the trans-neptunian region. II. The thermal lightcurve of (136108) Haumea
• The size and shape of the oblong dwarf planet Haumea
• The effect of orbital evolution on the Haumea (2003 EL61) collisional family

Cited by in corpus (8)

• An advanced multipole model for (216) Kleopatra triple system
• Stellar occultations by Trans-Neptunian Objects
• Beyond Point Masses. III. Detecting Haumea's Nonspherical Gravitational Field
• The visible and thermal light curve of the large Kuiper belt object (50000) Quaoar
• Trans-Neptunian Space and the Post-Pluto Paradigm
• Predictions of Stellar Occultations by Haumea and the Event of 4 May 2026
• Equilibrium figure of Haumea and possible detection by stellar occultation
• A high geometric albedo and small size of the Haumea cluster member (24835) 1995 SM55 from a stellar occultation and photometric observations