Design Filter

Visible images - that's pictures taken at wavelengths of light our eyes would detect - show Ganymede's surface to be a mixture of darker and brighter patches. The brighter areas are younger and colder. Juno's radiometer reveals these zonal differences are not just surface phenomena but are related to structures that have deep roots.

At Europa, the temperatures are lower but vary less from place to place. And interestingly, they become very uniform at depth.

"That may be a hint that you're getting near the liquid," said Dr Bolton. "Because when I get to the liquid, it's going to be completely uniform, because it's going to be like a mirror. It's not crazy to think the water might be just a few kilometres down - six, eight, something like that. I'm not ready to say that's the ocean, but it's conceivable that water is playing a role there."