Answer: Titan

In a survey of the planets and moons across our solar system, surface liquid is a rare find. Outside of the the abundant lakes and oceans found on Earth there is only one other place in the entire system with stable bodies of surface liquids.

Among all the bodies, only Titan–the sixth moon of Saturn–is known to have consistent liquid bodies. For years scientists had theorized about bodies of liquid hydrocarbons on the surface of the large moon but lacked the tools to confirm them. Information gleaned from the Voyager 1 and 2 probes indicated that the atmosphere was suitably dense enough to support surface liquids, observations from the Hubble telescope confirmed liquid methane, and then the Cassini mission confirmed the presence of large lakes of liquid methane near the poles.

Further observations revealed that the lakes are extremely shallow, averaging only a few meters in depth and that the surface of the lakes varies by an average of merely a few millimeters–indicating the liquid is extremely viscous, that there is little surface wind, or both.