Complex sentence: Preliminary results suggest that Xanadu is a higher plateau-like region of highly reflective water ice, contrasting with the somewhat darker lower regions and the very dark maria, which may actually be seas of liquid hydrocarbons.
Split into simpler sentences: Preliminary results suggest that Xanadu is a higher plateau-like region of highly reflective water ice, contrasting somewhat with the darker lower regions. These in turn seem to contrast quite sharply with the very dark maria, which may actually be seas of liquid hydrocarbons.