How do scientists determine that Titan has lakes and seas of methane?

Titan’s dense orange haze hides much of its surface in visible light, so scientists rely on radar and infrared instruments to map it. Cassini and the Huygens probe showed that Titan has rivers, lakes, and seas, especially near its poles. Because Titan’s surface temperature is about -179°C, methane and ethane can exist as liquids instead of gases. This makes Titan the only world besides Earth known to have stable liquid bodies on its surface, although the liquid is not water.