Washington: In the light of recent news that there may be giant plates of ice shuffling around Jupiter's moon Europa - much as plates of rock do on the Earth - NASA is seeking ideas for instruments that could fly on a mission to Europa.
The possibilities range from a stripped-down probe that would zip past the moon to a carefully designed Jupiter orbiter that would explore Europa over many years.
Active geology suggests that Europa's icy surface is connected to its buried ocean - creating a possible pathway for salts, minerals and maybe even microbes to get from the ocean to the surface and back again, scientific journal Nature reported.
Simon Kattenhorn, a geologist previously at the University of Idaho, and Louise Prockter, a planetary scientist at the Johns Hopkins Applied Physics Laboratory in Laurel, Maryland, made the finding after combing through pictures from NASA's Galileo spacecraft that orbited Jupiter from 1995 to 2003.
"When we moved all the pieces back together, there was a big hole in the reconstruction, a sort of blank space," Kattenhorn said.
The missing portion, the scientists concluded, must have been somehow sucked down into the moon's interior.
Kattenhorn and Prockter proposed a system of plate tectonics which involves a shell of ice a few kilometres thick sliding around on warmer, more fluid ice.
When one plate hits another and begins to dive downwards - or subducts - it melts and becomes incorporated in the underlying ice.
"Places have already been spotted on Europa where fresh ice crust is being born, but the latest research is the first to pinpoint where it might be going to die," Prockter emphasised.
To begin with, NASA has called for ideas that would run at $1 billion. The agency is now reportedly evaluating a handful of suggestions.