Baku, March 18 (AZERTAC). 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."

In December scientists announced that the Hubble Space Telescope had spotted geysers of water vapour shooting from Europa's surface, most likely originating from a liquid water ocean thought to exist under the moon's icy surface (see 'Hubble spots water spurting from Europa'). This theorized ocean has long been the focal point for hopes that Europa could host microbial life, but scientists assumed that a lander would be required to drill down into the ice to reach the liquid water for sampling. The geysers may make the water more accessible, however. "If that’s the case, maybe we don’t have to go to the ocean — the ocean will come to us," says astrobiologist Chris McKay of NASA Ames Research Center at Moffett Field, California.

The discovery of the geysers may have been the push that Europa needed to attain must-explore status. "The big question that ultimately drives us to study Europa is 'Does life exist there?'" says Kurt Retherford of the Southwest Research Institute (SwRI) in San Antonio, Texas, one of the co-discoverers of the water vapour plumes. "I think most of us had imagined that two or three large and expensive Europa missions would be needed before we find a clear answer to this compelling question, including future landers and deep-drilling devices."

Sending a probe to fly through the geysers would be cheaper but Retherford cautions against designing a Europa mission completely around the plumes. For one thing, the water vapour appears to be time-variable, and scientists cannot yet predict when the plumes will be active. "Until we are able to more firmly confirm our discovery of Europa’s water vapour plumes with additional observations in the next few years, it would seem inappropriate to focus a mission to exclusively study geysers at this time," Retherford says.