Apparently, there is going to be only one major mission to the outer solar system in the next 30 years or so, and NASA are deciding this month whether to visit Jupiter's moon Europa, or Saturn's Titan.
Of course we all want both, and as soon as possible, but looking at the prospects laid out in a special report in this week's Nature (p366), the choice is clear. Europa would get an orbiter, possibly combined with an ESA-sponsored Ganymede orbiter, which is exciting for the physical investigation of the subsurface ocean, but if there is life in that ocean, we won't see it from the orbiter. Plus, can you get the general public excited about orbiters? Earth has hundreds of them! While the Titan proposals include an orbiter along with ESA's contributions, a splasher (i.e. a lander targeted at the hydrocarbon lakes) and a "hot" air balloon that could sail around Titan's atmosphere for six months or longer. (Considering the temperatures on Titan, the air in the balloon would still be way below freezing.)
Now these two elements would be completely new and at least as cool as the Mars Rovers, so, if we have to choose, it's got to be Titan. Mind you, I'll be a pensioner by the time that balloon sails around Titan in 2030.
But can't we have the Europa mission a couple of years after that ? I know it costs three billion dollars, but hey, that's only a week or so operation in Iraq (I'm guessing, so don't start nitpicking over the number), so if the US managed to avoid foreign policy disasters for a while, the money saved could pay for the exploration of the entire outer solar system in our lifetimes. Alternatively, it's 10 bucks a head for the US population(similar calculation holds for the European contribution and the EU population), that's surely affordable if we as a civilisation decide we want to afford it ? It's surely a lot less than people spend on entertainment involving space-travelling civilisations ...