Titan is unusual in that it is the only body in the solar system, other than Earth, that has a substantial atmosphere and bodies of surface liquids. Titan's surface temperature is -180 degrees Celsius, making it too cold for liquid water on the surface, but adequate for liquid methane and ethane.
These organic compounds evaporate into the atmosphere and rain down to form rivers, lakes and seas. Lakes and rivers only cover about 3% of the surface, so Titan is still much drier than Earth.
Titan's thick orange haze comes from soot particles that form when ultraviolet light from the sun breaks up methane in the atmosphere. This should have used up all the methane on the surface billions of years ago, so Titan must have an underground deposit that is replenishing it, according to a study published in Nature Astronomy.
So far, scientists haven't found any solid evidence that cryovolcanoes may be supplying this methane. Like Callisto, Titan can have an ocean that is kept liquid by the antifreeze effects of dissolved ammonia. It would be equally difficult for life to evolve there, as the liquid ocean is likely sandwiched between solid, impermeable ice sheets.
Life could have evolved in hydrocarbon seas on the surface, according to NASA, but without access to liquid water , it would have a very different chemistry than life on Earth.
