Haumea's thermal emission revisited in the light of the occultation results

Abstract

A recent occultation measurement of the dwarf planet Haumea (Ortiz et al. 2017) revealed an elongated shape with the longest axis comparable to Pluto's mean diameter. The chords also indicate a ring around Haumea's equatorial plane, where its largest moon, Hi'iaka, is also located. The Haumea occultation size estimate (equivalent diameter 1595 km) is larger than previous radiometric solutions (in the range between 1150 and 1350 km), which lowers the object's density to about 1.8 gcm-3, a value closer to the densities of other large TNOs. We present unpublished and also reprocessed Herschel and Spitzer MIR and FIR measurements. We compare 100 and 160um thermal lightcurve amplitudes - originating from Haumea itself - with models of the total measured system fluxes (ring, satellite, Haumea) from 24-350um. The combination with results derived from the occultation measurements show that Haumea's crystalline water ice surface must have a thermal inertia of ~5 SIu. We also have indications that the satellites (at least Hi'iaka) must have high geometric albedos >=0.5, otherwise the derived thermal amplitude would be inconsistent with the total measured system fluxes at 24, 70, 100, 160, 250, and 350um. The high albedos imply sizes of about 300 and 150 km for Hi'iaka and Namaka, respectively, indicating unexpectedly high densities >1.0 gcm-3 for TNOs this small, and the assumed collisional formation from Haumea's icy crust. We also estimated the thermal emission of the ring for the time period 1980-2030, showing that the contribution during the Spitzer and Herschel epochs was small, but not negligible. Due to the progressive opening of the ring plane, the ring emission will be increasing in the next decade when JWST is operational. In the MIRI 25.5um band it will also be possible to obtain a very high-quality thermal lightcurve to test the derived Haumea properties.

arXiv comment13 pages, 5 figures, 9 tables, accepted for publication in Icarus in November 2018; abstract has been shortened with respect to the original one

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• "TNOs are Cool": A survey of the trans-Neptunian region X. Analysis of classical Kuiper belt objects from Herschel and Spitzer observations
• Trans-Neptunian objects and Centaurs at thermal wavelengths
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• Beyond Point Masses. III. Detecting Haumea's Nonspherical Gravitational Field
• The visible and thermal light curve of the large Kuiper belt object (50000) Quaoar
• The Moon at thermal infrared wavelengths: A benchmark for asteroid thermal models
• A Dearth of Small Members in the Haumea Family Revealed by the OSSOS Survey
• The Case for a Large-Scale Occultation Network
• Herschel-PACS photometry of Uranus' five major moons
• TNOs are Cool! A Survey of the transneptunian Region XV. Physical characteristics of 23 resonant transneptunian and scattered disk objects