Zusammenfassung
Hydrothermal plumes may be responsible for transmitting radiogenic
or tidally generated heat from Europa's rocky interior through a
liquid ocean to the base of its ice shell. This process has been
implicated in the formation of chaos regions and lenticulae by melting
or exciting convection in the ice layer. In contrast to earlier work,
we argue that Europa's ocean should be treated as an unstratified
fluid. We have adapted and expanded upon existing work describing
buoyant plumes in a rotating, unstratified environment. We discuss
the scaling laws governing the flow and geometry of plumes on Europa
and perform a laboratory experiment to obtain scaling constants and
to visualize plume behavior in a Europa-like parameter regime. We
predict that hydrothermal plumes on Europa are of a lateral scale
(at least 25-50 km) comparable to large chaos regions; they are too
broad to be responsible for the formation of individual lenticulae.
Plume heat fluxes (0.1-10 W/m(2)) are too weak to allow complete
melt-through of the ice layer. Current speeds in the plume (3-8 mm/s)
are much slower than indicated by previous studies. The observed
movement of ice blocks in the Conamara Chaos region is unlikely to
be driven by such weak flow.
Nutzer