The more we learn about Europa, the greater its allure. Galileo Galilei discovered Jupiter’s four largest moons in 1610, and in the intervening centuries Europa, the smallest of them, has revealed itself as a likely harbor for liquid water — and maybe even life. Last week NASA took tentative steps toward sending a robotic mission there — a goal long lauded by planetary scientists. But exploring Europa presents some serious technological, financial and political challenges.
For the last few year's NASA's planetary-science budget has seen a major crunch, and the lion's share of its remaining funds have gone to Mars missions. Despite the high priority given to Europa exploration in the US National Research Council’s last decadal survey, an overview of the most pressing goals in planetary science, NASA has not requested any money for planning a Europa mission in recent years. Nevertheless, Europa fans in Congress have allocated funding for it, granting $43 million in 2013 and $80 million in 2014. Proponents of the mission were therefore heartened last week to see the White House's 2015 NASA budget request include a line item of $15 million for Europa exploration planning, although the amount is far less than many would hope for. "If nothing else, we're excited to see NASA and the White House put it into budget lines and acknowledge it’s an important destination," says Casey Dreier, director of advocacy at the Planetary Society, a nonprofit organization devoted to solar system science and exploration. The size of the request — $15 million out of NASA's total budget request of $17.5 billion — is "a very small amount of money" but the symbolism of the move is significant, he says. "The fact that it's in there is a big, big shift, and I think a big part of that is the discovery of those plumes."