25 March 1655

Saturn’s largest moon, Titan, is discovered by Christiaan Huygens.

Titan is the largest moon of Saturn and the second-largest moon in the solar system, with a diameter of about 5,150 kilometers (3,200 miles). It is also the only moon in the solar system with a dense atmosphere. Here are some key facts about Titan:

Atmosphere: Titan’s atmosphere is primarily composed of nitrogen (about 95%) with small amounts of methane (about 5%). The methane in the atmosphere gives Titan its orange-brown color. The atmosphere is about 1.5 times denser than Earth’s, which allows for clouds, rain, and other weather phenomena.

Surface features: Titan’s surface is covered in a thick layer of organic-rich, hydrocarbon-based materials, including lakes and seas of liquid methane and ethane. It also has vast sand dunes made of organic compounds. The surface is mostly flat, with some icy mountains and impact craters.

Climate: Because of its distance from the Sun and its thick atmosphere, Titan is very cold, with surface temperatures averaging around -290 degrees Fahrenheit (-179 degrees Celsius). The climate is also affected by the changing seasons caused by Saturn’s orbit around the Sun.

Exploration: The first close-up images of Titan were taken by NASA’s Voyager 1 spacecraft in 1980, and more detailed images were obtained by the Cassini spacecraft, which orbited Saturn from 2004 to 2017. The Huygens probe, which was carried by Cassini, landed on Titan’s surface in 2005 and provided the first direct measurements of Titan’s atmosphere and surface.

Potential for life: While there is no evidence of life on Titan, some scientists believe that its organic-rich environment could potentially support life, perhaps in the form of microbial organisms that use methane as a source of energy.