Finally: "a virtually unlimited energy source for propulsion"

New fuel-free submarines are doing test dives here on the water planet. Are there implications for exploring Saturn, Jupiter and other gas planets?

Like a sequel to Verne's 20,000 Leagues under the Sea, submarines that can travel thousands of miles without steam, internal combustion or nuclear power sources have been spotted, last year in Antarctic waters, and now tirelessly crisscrossing the Virgin Islands Basin off Saint Thomas.

Rising and falling through the ocean like whales, these robo-subs exploit the thermal variation of different strata of the water column. According to a recent Science Daily article, the new Autonomous Underwater Vehicle:

" draws its energy for propulsion from the differences in temperature--thermal stratification--between warm surface waters and colder, deeper layers of the ocean. The heat content of the ocean warms wax-filled tubes inside the engine. The expansion of the warming wax converts heat to mechanical energy, which is stored and used to push oil from a bladder inside the vehicle's hull to one outside, changing its buoyancy. Cooling of the wax at depth completes the cycle."..........

"Wings generate lift, while a vertical tail fin and rudder allow the vehicles to be steered horizontally. Gliding underwater vehicles trace a saw-tooth profile through the ocean's layers, surfacing periodically to fix their positions via the Global Positioning System and to communicate via Iridium satellite to a shore lab."

Now let's apply this propulsive thinking to exploring other worlds. While Rovers are in use for the solid surface worlds like Mars, may it be possible to develop a "Flipper" class of AUVs, suitably modified for the harsh environments, for use in exploring Saturn, Jupiter, and other liquid planets?
Images courtesy WHOI and Webb Research Corporation