Titan is Saturn’s giant - larger than the planet Mercury - and the only moon with a thick atmosphere, an orange nitrogen haze so opaque that its surface was a mystery until Cassini arrived. Beneath the haze lies astonishingly Earth-like scenery: dunes, river valleys, rain-carved channels and glossy seas near the north pole.
Open the 3D Solar SystemEarth’s weather runs on water evaporating, condensing and raining back down. Titan runs the identical cycle at -179 °C with methane in every role: methane clouds, methane drizzle, methane rivers draining into seas of liquid methane and ethane. It is the only world besides Earth known to keep standing liquid on its surface.
| Diameter | 5,150 km |
| Mass | 1.350e+23 kg |
| Surface gravity | 1.35 m/s² |
| Density | 1.88 g/cm³ |
| Rotation period | 382.7 h |
| Tidally locked | Yes |
| Mean temperature | -179 °C |
| Geometric albedo | 0.2 |
| Atmosphere | Dense nitrogen with a few percent methane; surface pressure is 1.5× Earth’s - the only thick atmosphere on any moon. |
| Composition | Water-ice shell over a probable internal water ocean and a rocky core. |
How we know: Cassini measured how Titan flexes in Saturn’s tides - far too much for a solid interior. The ocean is inferred from that flex plus the electric field Huygens measured.
| Discovered by | Christiaan Huygens |
| Year | 1655 |
| How | A telescope he built with his brother Constantijn |