Planetary scientists have identified Jupiter's icy moon of Europa as one of their top targets for exploration, believing that its warm interior oceans may well harbor life. A new study published just this week, authored by scientists at NASA's Jet Propulsion Laboratory, found that conditions in the oceans on Europa may indeed be Earth-like and capable of harboring life.

Despite the wishes of the planetary science community to further investigate Europa, NASA has been wary of mounting such a mission because of the high cost—well above $1 billion. Additionally, planetary science hasn't been a priority in President Obama's NASA budgets, and the space agency has preferred to focus most of its robotic solar system exploration on Mars. The red planet is easier to reach, and NASA says it wants to explore Mars further to enable future human missions.

Congress has been more interested in planetary science, however. And in particular, the chairman of the House Appropriations subcommittee with jurisdiction over NASA's budget, John Culberson (R-Texas), has fancied Europa. Even when NASA wasn't asking for Europa funds, the congressman was funneling money to the scientists at the California-based Jet Propulsion Laboratory. Between the 2013 and 2016 fiscal years, NASA requested just $45 million in Europa funding, but Congress appropriated $395 million. For fiscal year 2017, NASA requested $49.6 million in Europa funding, but a House appropriations bill released this week by Culberson's committee proposes $260 million for mission planning and development.

As part of the mission to Europa, Culberson would also like to send a lander to the surface of the heaving, ice-encrusted world. This would allow scientists to better characterize the oceans below and, if the lander touches down near a fissure, possibly even sample the ocean. However, there has been some concern that having both an orbital spacecraft and a lander in a single mission would prove too challenging for a single rocket to deliver.

So as part of the new House bill, the Europa mission is broken into two parts: an orbiter and, two years later, a lander. The plan would be for the orbiter spacecraft to swoop down into the harsh radiation environment near Europa (because of the moon's proximity to Jupiter) and out again to relay data back to Earth. The nominal mission would perform at least 45 flybys of Europa at altitudes varying from 2,700km all the way down to 25km above the surface. By assessing this data, scientists on Earth could determine where best to set their lander down on the surface two years later.

"We have increased funding for planetary programs and made sure we are going to complete the incredibly important mission to Europa that the planetary decadal survey mapped out because of the very high likelihood that life will be discovered in those oceans," Culberson said during a hearing Tuesday. "This will be a transformative moment in the history of humanity and the country."

In its documents about the Europa mission, NASA has not formally approved a lander, and it says only that the flyby mission will launch "sometime in the 2020s." The House bill is much more specific, calling for an orbiter launch no later than 2022 and a lander launch no later than 2024. Senior officials at the Jet Propulsion Laboratory have told Culberson that those dates are attainable. Additionally, the bill specifies that NASA's next budget, for fiscal year 2018, includes a five-year funding profile to support those two launches.

NASA last visited the Jupiter system in the 1990s and early 2000s with the Galileo spacecraft. Galileo snapped images of Europa during 11 flybys, but the best of those pictures had a resolution of only about 10 meters per pixel. The spacecraft stored those images on a tape recorder with a capacity of 114 megabytes, but a flawed rewind mode hampered even that modest device. Yet this limited data was enough to tantalize scientists, and Europa has been a target of high interest for planetary scientists ever since.