Titan is the biggest of the 53 known moons orbiting Saturn. It is a cold world enclosed by a thick, hazy atmosphere impenetrable by telescopes and cameras. With an equatorial radius of 2,575 km (1,600 miles), Titan is the second largest moon in our solar system. It's bigger than our own Moon and even the planet Mercury. Only Jupiter's moon Ganymede is larger than Titan, with a diameter barely 112 km (62 miles) greater. The temperature at Titan's surface is about -289 degrees Fahrenheit (-178 degrees Celsius). Titan orbits Saturn at a distance of about 1.2 million km (745,000 miles), taking almost 16 days to complete a full orbit.