25th March: Titan, Saturn's moon

On this date in 1655 Dutch physicist and astronomer Christiaan Huygens discovered Titan, a moon of Saturn. Here are 10 facts about Titan:

1. Huygens, inspired by Galileo's discovery of four of Jupiter's moons, started building telescopes with his brother's help, and, using one of his own Telescopes, was the first to observe a moon orbiting Saturn. He named it simply Saturni Luna (Latin for "Saturn's moon"). As more moons were discovered around Saturn, astronomers began to number them. Titan has been known as Saturn II, Saturn IV and Saturn VI, the latter being its final and official number when the number system was frozen to prevent confusion. John Herschel later suggested the names of the mythological Titans (the brothers and sisters of Cronus, the Greek Saturn) as suitable names for Saturn's largest moons.
2. It is the second-largest moon in the Solar System, after Jupiter's moon Ganymede. Titan is larger than the smallest planet, Mercury. It is 50% bigger than Earth's Moon.
3. It is the only moon to have a dense atmosphere (as far as we know, anyway). Titan's atmosphere is 98.4% nitrogen, 1.4% methane and 0.1–0.2% hydrogen.
4. It used to be thought that Titan was bigger than Ganymede because of Titan's thick, opaque atmosphere. It was only when Voyager I passed close by it in 1980 that we realised this.
5. It is also the only moon where liquid has been observed on its surface. There is only one other object in the Solar system which has liquid on its surface - planet Earth. The liquid on Titan is thought to be liquid methane, and it has weather patterns and surface features similar to those we find on earth, only caused by liquid methane, not Water.
6. The temperature on Titan is about 94 K (−179.2 °C), so it's effing cold up there. Titan only gets 1% as much sunlight as Earth does. It would be even colder if it wasn't for the methane in the atmosphere creating a greenhouse effect.
7. Titan orbits Saturn once every 15 days and 22 hours. Like our own moon, it rotates at the same rate as it orbits, which means if Saturn had inhabitants, they would always see the same side of Titan. Titan has seasons, too - long ones as its year lasts 30 Earth years.
8. In 2004, a spacecraft named Cassini–Huygens (after the discoverers of the various moons) reached the Saturn system and began mapping Titan by radar. The Cassini probe flew by Titan on October 26, 2004, and took the highest-resolution images ever of Titan's surface. On January 14, 2005 Huygens landed on Titan, making Titan the most distant body from Earth to have a space probe land on it.
9. Therefore, scientists have been able to observe, and name, some of the surface features of Titan. These include Xanadu, a large, reflective equatorial area about the size of Australia, which is filled with hills, valleys and chasms. There are also lakes of liquid methane, one of which has a feature called the “magic island,” spotted in images from the Cassini spacecraft taken in 2013 and 2014. It measures about 260 square kilometers (100 square miles) in size – roughly the size of Washington DC. What makes it fascinating is that it was not present in the images taken in 2007 or in later ones taken in 2015. This suggests that Titan’s liquid hydrocarbon seas are active. The predominant theory as to what caused the "magic island" to appear is waves moving slowly on the surface. This theory is supported by the fact that the moon’s Northern Hemisphere, where the sea is located, is entering its summer, and winds are expected to pick up at this time, causing waves.
10. Could there be life on Titan? Dr. Robert Zubrin has pointed out that Titan possesses an abundance of all the elements necessary to support life, and that it might be the most hospitable place in the Solar System for humans to colonise. There may, he says, be liquid water under the surface which could be used to make breathable air, and Nitrogen, methane and ammonia can all be used to produce fertilizer for growing food. The problems would be living in low gravity, and the extreme cold.