Thermal emission from Kuiper belt object (136108) Haumea was measured with Herschel-PACS at 100 μm and 160 μm for almost a full rotation period. Observations clearly indicate a 100 μm thermal lightcurve with an amplitude of a factor of ~2, which is positively correlated with the optical lightcurve. This confirms that both are primarily due to shape effects. A 160 μm lightcurve is marginally detected. Radiometric fits of the mean Herschel- and Spitzer- fluxes indicate an equivalent diameter D ~ 1300 km and a geometric albedo pv ~0.70-0.75. These values agree with inferences from the optical lightcurve, supporting the hydrostatic equilibrium hypothesis. The large amplitude of the 100 μm lightcurve suggests that the object has a high projected a/b axis ratio (~1.3) and a low thermal inertia as wellas possible variable infrared beaming. This may point to fine regolith on the surface, with a lunar-type photometric behavior. The quality of the thermal data is not sufficient to clearly detect the effects of a surface dark spot. Herschel is an ESA space observatory with science instruments provided by European-led Principal Investigator consortia and with important participation from NASA.
- Kuiper belt objects: individual: (136108) Haumea
- techniques: photometric