Orbital detectability of thermal signatures associated with active formation of 'chaos terrain' on Europa

Jovian satellite Europa has one of the youngest surfaces in the solar system and displays a variety of geologically recent resurfacing features, including regions of disrupted crust termed 'chaos terrains.' A new study by Schmidt et al. [2011] suggests that chaos terrains form above liquid water lenses perched within an ice shell as shallow as 3 km, and that one of these chaos regions, Thera Macula, is currently actively resurfacing over a lens comparable in volume to the Great Lakes in North America. This process may produce thermal anomalies detectable by a future Europa orbiter mission, allowing for a direct verification of this finding. These new results provide an opportunity to apply an existing thermal model to a likely actively forming chaos region on Europa, with established constraints on latitude, ice and water thickness, and initial temperatures, and with the overall goal of estimating whether the thermal anomaly associated with Thera Macula could be detected (and therefore confirmed) by a future Europa orbiter mission. We present results from a set of models that quantitatively assess the surface and subsurface temperatures associated with the Thera Macula region as a function of time. In particular, we estimate surface temperature over an actively forming chaos, taking sublimation cooling into account, as well as estimate the amount of time a surface thermal anomaly remains detectable after the active phase of formation ceases. The results of this numerical study suggest that the equilibrium surface temperature at Thera Macula can be as high as ~200 K, and, once active formation ceases, the associated hotspot can remain detectable from orbit for ~10³ to ~10⁵ years, depending on detection criteria. The presence of a thin insulating surface layer or a warm (272 K) upper ice crust can each extend detectable thermal lifetimes by up to a factor of two. The time required for a 3-km liquid water lens underneath Thera Macula to freeze completely is 2.9 x 10⁵ years after cessation of the underlying warm ice plume. (a) Surface temperatures above the Thera Macula hotspot following the cessation of the plume and the end of active chaos formation. (b) Temperature profiles showing the subsurface thermal evolution of Thera Macula following the cessation of the plume and the end of active chaos formation.