10:45 AM - 12:15 PM
[PPS07-P15] Mapping the surface brightness temperature on Europa with ALMA
Keywords:Europa, ALMA, aperture synthesis, imaging fidelity
Characterization of the inner oceans of icy moons are important to understand the presence of “non-terrestrial type” habitability in our solar system.There are several observational studies that imply the existence of an inner ocean in Europa, an icy moon of Jupiter. However, definitive evidences of its existence, such as the confirmation of cryovolcanism plume, are not obtained sufficiently. For example, the past observations of limb-detection of the plume’s shadow using HST (Sparks et al., 2016;2017) have been reanalyzed recently and the new result does not support the detection (Giono et al., 2020). There is another search for plumes using the thermal images taken by the Galileo photopolarimeter radiometer (PPR) instrument: a localized warm region was found around the Pwyll crater (Spencer et al., 1999). It was proposed that a higher subsurface heat flux would explain this thermal anomaly. Such a high heat flux, if exists, may lead to the outbreak of plumes. Later, Trumbo et al. (2017) mapped Europa’s brightness temperatures using the ALMA telescope. The diurnal variation of the brightness temperature on Pwyll crater was analyzed with a one-dimensional thermal diffusion model in order to constrain the thermal inertia and endogenic heat flux. The authors concluded that the thermal anomaly seen in the Galileo PPR images is not due to an unusual endogenic heat flux but to an anomalous thermal inertia instead. One caveat in ALMA data analysis is the evaluation of the imaging fidelity. Absolute flux calibration has the uncertainty of ~ 5 - 10 %, and the aperture synthesis procedure often contains imaging errors due to the insufficient correction of side-lobe patterns. In this study, we evaluate the imaging fidelity of ALMA’s Europa observations and discuss the uncertainties in deriving the Europa’s surface thermal properties from ALMA data.