It's ice, Jim, but not as we know it...
Today I went to THE most interesting seminar I've ever attended, without exception, given by this chap. It was close enough to my PhD topic that I could understand the hard-going bits (I use different radar frequencies) but because I'm a sci-fi nut I find Jupiter's moons far more interesting than Greenland or Antarctica.
He'd been involved in doing the feasibility and instrument design for the proposed JIMO mission to 3 of Jupiter's moons. Jupiter has 4 large moons (from inside outwards): Io, Europa, Ganymede and Callisto. Due to the presence of Jupiter and other moons, the inner moons of these moons especially experience huge tidal forces. Io is the innermost and the most volcanic object in the solar system. Europa is ice-covered but due to tidal forces is believed to have an ocean under an ice crust because of the geothermal heat generated from below. This makes it one of most promising sites for LIFE in our solar system. The best evidence for this ocean is the fact that gravity measurements have shown that the outer part of this moon has a density of 1 (water). Europa is pretty structural differentiated and has a silicate mantle. Although Ganymede and Callisto are progressively less differentiated (substance is the same right down), it's also believed they have oceans but buried far deeper.
There are lots of theories about how thick the ice crust is and how the ice moves about. For example, there is the chaos regions where the ice crust seems to disappear and then there are the ridges where material is injected and ice crust seems to be being formed. Blankenship and others (inc. Keith Raney who designed one of the radar altimeters I'm working on) were testing the feasibility of using a ground-penetrating radar to look a the internal structures of Europa and consider the success of these theories. They had to estimate the penetration depth of the radar considering things like grain size, impurities and the radar noise from Jupiter on the side that faced the planet.
Anyway, the JIMO launch is supposed to be 2013 and the instrument should be collecting data in 2027 provided the money isn't taken out of the space program. Space travel is expensive - putting a coffee can into orbit around Jupiter apparently costs $1bn. The feasibility study was promising and the technology has come on since they did the feasibility assessment in 1999. The JIMO mission is using ion fission propulsion which can carry a larger payload. The spacecraft has to be quite long in order to protect the radar from the radiation from the propulsion system. It also has a tennis court's worth of heat dissipating fins and a special cone for deflecting the radiation. However, the ion acceleration plates are at the back. The picture is under the JIMO link.
I'm shocked I can remember all of this. However, the lecture was at 10am and I DID think I had just found my postdoc topic [wink].