Titan is the largest moon of Saturn, and it is about 5,150 kilometers (3,200 miles) across. That figure is its mean diameter, measured to its solid surface. Titan is the second-largest moon in the Solar System, and the only moon with a thick atmosphere.

Size

NASA gives Titan's radius as 2,575 kilometers, which makes it about 5,150 kilometers across. NASA's Jet Propulsion Laboratory lists a mean radius of 2,574.76 kilometers, give or take 0.02 kilometers.

That radius is measured to the ground. Titan's hazy atmosphere reaches about 600 kilometers (370 miles) above it, 10 times higher than Earth's atmosphere does. Titan is a little less than twice as dense as water. One model based on data from the Cassini and Huygens spacecraft gives it a rocky core about 4,000 kilometers (2,500 miles) across, covered by layers of ice and salty water.

Size comparisons

• Titan is nearly one and a half times as wide as the Moon, which is 3,475 kilometers (2,159 miles) across.
• Jupiter's moon Ganymede, the next larger object in the explorer, is 5,262 kilometers (3,270 miles) across, about 2% wider than Titan.
• Titan is about 6% wider than the planet Mercury, the next smaller object in the explorer. Mercury, though, has about two and a half times as much mass.
• Earth is about two and a half times as wide as Titan.
• If Saturn, not counting its rings, were shrunk to the size of a basketball, Titan would be a bead about 1 centimeter (0.4 inches) across, circling it about 2.5 meters (8 feet) away.

A thick, hazy atmosphere

Titan's atmosphere is about 95% nitrogen and 5% methane, so like Earth's air, it is mostly nitrogen. At the surface, the pressure is about one and a half times what it is on Earth. A swimmer feels that much pressure about 5 meters (16 feet) under the sea.

High in the atmosphere, sunlight and fast-moving particles split methane and nitrogen apart. The pieces join into other carbon-rich chemicals, forming a thick orange smog that hides the surface. Spacecraft can see through it only with kinds of light that human eyes cannot see.

Lakes, rain and a hidden ocean

Titan is the only world known besides Earth with rivers, lakes and seas on its surface. They hold liquid methane and ethane rather than water. At about −179 °C (−290 °F), water ice takes the place of rock. Methane rains from clouds, flows across the ground and evaporates again, in a cycle like Earth's water cycle.

Titan probably also has an ocean of liquid water under its icy crust. Gravity measurements by NASA's Cassini spacecraft point to it. The European Space Agency's Huygens probe descended to Titan's surface in 2005, and radio signals it recorded suggest the ocean lies 55–80 kilometers (35–50 miles) below the surface.

Discovery and exploration

The Dutch astronomer Christiaan Huygens discovered Titan on March 25, 1655. NASA's next mission there, Dragonfly, is a rotorcraft that will fly from place to place across the surface. As of 2026, it is due to launch no earlier than July 2028, for a planned mission of 3.3 years on Titan.

Sources

• Saturnian Satellite Fact Sheet. NASA, 2025.
• Planetary Satellite Physical Parameters. NASA Jet Propulsion Laboratory.
• Titan: Facts. NASA, 2025.
• Science highlights from Huygens: #1. Profiling the atmosphere of Titan. ESA, 2019.
• Dragonfly. NASA.
• Moon Fact Sheet. NASA, 2024.
• Jovian Satellite Fact Sheet. NASA, 2023.
• Mercury Fact Sheet. NASA, 2024.
• Earth Fact Sheet. NASA, 2024.
• Saturn Fact Sheet. NASA, 2025.
• Official Basketball Rules 2026: Basketball Equipment. FIBA, 2026.