But another requirement for life, he adds, is a source of energy, a.k.a. food. The moon's upper crust is rich in compounds that could be a food source, but the potential nutrients would need a system to deliver them to the ocean deep below.
The mechanism that forms the subsurface lakes – involving rising plumes of heat – could provide that service, the team suggests.
If the team is right, "you've moved from a system that checks [off] one of the requirements for life to a system that checks two requirements for life," Dr. Hoehler says.
The results, set for publication in Thursday's issue of the journal Nature, grew out of an attempt to explain two different areas within Europa's "chaos terrain" – a landscape of jumbled surface features visible in images from the Voyager and Galileo spacecraft.
The two areas that have puzzled scientists cover significant large patches of the moon's surface and host icebergs with ground-up ices filling the channels in between – much as jumbled ice chunks fill gaps between icebergs as they calve from ice shelves in polar regions on Earth.
One of the two areas appeared as a depression in the surface. The other appeared as a dome.
"Why are these two features so similar but so different?" says Britney Schmidt, a planetary scientist at the University of Texas at Austin who led the research team.
In trying to solve the puzzle, the team was struck by parallels on Earth. Similar features are apparent in ice that forms above under-ice volcanoes, as well as at ice shelves where warm sea water is thought to be thinning the ice from underneath.
