Constraints on the detection of cryovolcanic plumes on Europa

摘要

Surface venting is a common occurrence on several outer solar system satellites. Spacecraft have observed plumes erupting from the geologically young surfaces of Io,Triton and Enceladus. Europa also has a relatively young surface and previous studies have suggested that cryovolcanic eruptions may be responsible for the production of low-albedo deposits surrounding lenticulae and along triple band margins and lineae. Here,we have used the projected thicknesses of these deposits as constraints to determine the lifetimes of detectable cryovolcanic plumes that may have emplaced them. In an effort to explore the feasibility of detection of the particle component of plumes by spacecraft cameras operating at visible wavelengths,we present a conservative model to estimate plume characteristics such as height,eruption velocity,and optical depth under a variety of conditions. We find that cryovolcanic plumes on Europa are likely to be fairly small in stature with heights between 2.5 and 26 km,and eruption velocities between 81 and 261 m/s,respectively. Under these conditions and assuming that plumes are products of steady eruptions with particle radii of 0.5 μm,our model suggests that easily detectable plumes will have optical depths,τ,greater than or equal to 0.04,and that their lifetimes may be no more than 300,000 years. Plume detection may be possible if high phase angle limb observations and/or stereo imaging of the surface are undertaken in areas where eruptive activity is likely to occur. Cameras with imaging resolutions greater than 50 m/pixel should be used to make all observations. Future missions could employ the results of our model in searches for plume activity at Europa.