Titan

Cassini Image of Titan showing the atmosphere of the moon

Image Credit:

NASA/Cassini

 

Titan is the largest Saturnian moon and the second largest in the Solar System behind Jupiter's moon Ganymede. Like Ganymede, it is also larger than Mercury. Christian Huygens, who discerned the rings of Saturn, also discovered Titan in 1655, making it the fifth satellite discovered with the telescope.

 

It is the only moon known to have a dense atmosphere, where atmospheric pressure is measurable on the surface. Though Europa, Ganymede, and Callisto may have liquid oceans below their outer crusts, Titan is the only body in the Solar System to have surface liquid besides the Earth. However, you wouldn't want to swim in those oceans as they are bodies of methane.

 

Because it has liquid methane oceans and lakes, much like Earth has a water cycle, Titan experiences a methane cycle. Surface methane evaporates and forms clouds in the Titan sky. The rain Titan experiences is methane.

 

Although Titan is smaller than Earth, its atmosphere is dense enough to create higher surface pressure than on Earth, at about 1.45 atmospheres (146.7 kPa). One atmosphere on Earth is the normal pressure at sea level which is 101.5 kPa (kilopascals). As shown in the above image, the atmosphere is extended with a composition of 98.4% Nitrogren (N₂), 1.4% methane (CH₄), and trace other molecules including water in the stratosphere (higher levels) and 95% N₂, 4.9% CH₄, and other molecules in the troposphere. Because of the methane clouds, the sky is very hazy on Titan so would have poor visibility on the surface when we make our first crewed mission to Titan sometime in the future.

 

The gravity on Titan is only 85% of that on the Moon even though it is larger because of its smaller density. If you were to stand on Titan, your weight would only be 15% of that on Earth.

 

Much like the Moon and Earth are tidally locked, Titan is tidally locked to Saturn, so for every orbit around Saturn, which is almost 16 Earth days, it only rotates once on its axis.