Gravity measurements are key in addressing the habitability of a subsurface ocean in Jupiter's Moon Europa

Abstract

The habitability of Europa's subsurface ocean increases greatly if there is volcanism occurring at the underlying rock-water interface. The potential for volcanic activity is lowered, however, if Europa's silicate interior only has radiogenic nuclides as a heat source; depths to silicate solidus temperatures would be hundreds of kilometers deep. The addition of tidal heating in the silicate interior increases the chances of volcanism, with its implications for life. Thus, constraining the heat flow from the silicate interior can be used as a proxy for habitability. Here, we show that the structure of the silicate interior's near surface dominates the Bouguer gravity anomalies (measured surface gravity minus the gravity resulting from the ice surface) for global to regional horizontal scales greater than ~200 km. We next use the finite element method to predict the compensation state of topography on the silicate interior, derived from the Moon and assuming the likely possibility of a basaltic crust over a peridotitic mantle. These compensation models are tied to the heat flow from the silicate interior. We then calculate the gravity coming from the silicate interior as a function of heat flow, finding that the magnitude of the anomalies can discriminate heat flow regimes. Gravity anomalies only exceed ~250 mGal for the case of solely radiogenic heating. We then discuss the implications for future missions to Europa, including the discrete gravity sampling of the proposed Europa Clipper mission, and conclude that gravity and topography measurements should be given very high priority in mission planning.