What future missions are being considered to explore Europa?
Galileo will continue to observe Europa, but beyond that, NASA is developing a Europa Orbiter mission (which could set off in 2003) and perhaps landers a few years later. A Europa Orbiter might be able to definitively answer the ocean question by combining a number of techniques. One approach is to use radar to penetrate the ice and measure its thickness. Another is to use very precise gravity and altimetry measurements to observe the tides raised by Jupiter on Europa (these will be much larger – as great as 40 meters or so – if there is a liquid layer than if the water is all frozen).
