Titan

It is the second largest moon in the solar system, just a bit smaller than Ganymede.

Physical and surface stats
When astronomers first discovered it, they thought it was even larger than ganymede because it looked larger as it has a thick and solid-looking atmosphere. In reality, Titan is a few hundred kilometers smaller than ganymede, but still larger than Mercury. Like ganymede, it's roughly 1/3 the mass of mercury.

The average temperature on Titan is 93.7 kelvin or −179.5 °C. Its gravity is around 1.35 m/s and its escape velocity is around 2.64 km/s.

Titan is known for its yellow-orange thick atmosphere. Its atmospheric pressure is 146.7 kPa (1.45 times the pressure of Earth's atmosphere!).

Discovery
Titan was discovered by Christiaan Huygens on March 25, 1655.