While almost everyone has their eyes set on Mars as the next destination for Humans in space, the truth is that we should probably not send people there (read why here). Look further and meet Titan, Saturn’s largest moon, which is likely the most inviting place for us beyond Earth.
Titan was discovered in 1655 by the Dutch astronomer Christiaan Huygens who first named it Saturni Luna (or Luna Saturni, Latin for “Saturn’s moon”). The name Titan, and the names of all 7 satellites of Saturn then known (62 known moons now), came from John Herschel in 1847. He suggested the names of the mythological Titans, brothers and sisters of Cronus, the Greek Saturn and patron of the harvest.
Titan has a diameter of 5151 km and is the second largest moon of the Solar System after Jupiter’s Ganymede (5270 km of diameter). It’s actually larger than one of our planets, Mercury (4880 km) and not so much smaller than Mars (6780 km). Titan orbits at 1.2 million km from Saturn, which itself orbits at 1.5 billion km from the Sun. By comparison Earth and Mars orbit respectively at 150 million km and 225 million km from the Sun. Saturn (and Titan) takes 30 years to orbit the Sun, and Titan needs 16 Earth days to complete a full rotation on itself with regards to the Sun, so a year and a day on Titan lasts respectively 30 Earth years and 16 Earth days.
Watch the Titan touchdown by the Huygens lander on Jan. 14, 2005, as the most distant landing ever on another world, and the only landing on a body in the outer solar system. The video below uses actual images taken by the probe during its two-and-a-half hour fall under its parachutes:
Titan’s gravity is 14% of Earth gravity (the Moon is 16.5% and Mars 37.6%), meaning someone weighing 100 kg will feel on Titan what someone hypothetically weighing 14kg would feel on Earth.
It is also the only moon in the Solar System known to have a dense atmosphere, 4.5 denser than Earth’s atmosphere. Its atmospheric pressure is actually the second highest for a body with a surface in the Solar System (excluding the 4 gas giants), after Venus and before Earth! (Warning : one should not confuse density of the air (calculated in kg of matter per cubic meter of air) and atmospheric pressure (calculated in Newton per square meter, as the weight of a column of air exerted on a given surface, at sea level for instance). Next in line is Mars with an atmospheric pressure of a mere 0.6% of Earth’s! (Compared to 145% for Titan and 9200% for Venus). On Titan, you’d feel the same pressure on your skin as when at the bottom of a pool on Earth, below 5 meters of water. We’ll see further below how much of an advantage such a dense atmosphere is when compared to Mars !
The average temperature at the surface is of −179.5 °C. Yes, it’s cold, but it’s not a show-stopper as we’ll see below.
Thanks to its atmosphere, Titan has weather with a methane cycle of evaporation and condensation, leading to clouds, rains, rivers and seas. Titan has long droughts and big storms. And because of the angle between Titan’s rotational axis and the orbital plane, Titan even has seasons!
Titan is indeed the only object in space other than Earth where clear evidence of stable bodies of surface liquid has been found: it has a handful of seas, and hundreds of lakes and rivers of liquid methane and ethane. Its largest sea Kraken Mare located in the northern polar region is 1,170 km long with depths estimated at 300 m and is named after The Kraken, the Norse sea monster. Titan’s crust is made of water ice and near its equator it also has mountains made of water ice, with Mithrim Montes culminating at 3,337 m. At the equator as well, gigantic dunes sit atop ice. Instead of being made of sand, the dunes are likely piles of complex organic compounds called hydrocarbons, more viscous than sand, that were made in the atmosphere due to the reaction of other hydrocarbons and sunlight. Think of it as very small pellets of plastics. These dunes actually cover 20% of Titan’s surface, and can be hundreds of km long, 1-2 km wide, and 150 m high. Titan is even believed to have a global subsurface liquid water ocean, which may be 100 to 200 km thick, located below the surface ice crust estimated to be 50 to 150 km thick.