Titan has thick hazy skies, rainstorms, lakes, winding river channels, and vast dune fields, all at minus 179 degrees Celsius. The rocks are water ice as hard as granite, the rain is liquid methane, and the sand is dark organic material. This episode explores Saturn’s largest moon, discovered by Christiaan Huygens in 1655, which is 6 percent larger than Mercury but only 40 percent of its mass, a fluffy giant likely made of up to 60 percent water ice around a small rocky core.

The hosts explain the giant impact model behind Titan’s eccentric orbit, why extreme cold lets it hold a nitrogen atmosphere with 1.45 times Earth’s surface pressure, and how UV light shatters methane to create tholin smog and a dual anti-greenhouse and greenhouse climate. They tackle the mystery of why methane still exists when it should have been depleted within 50 million years, pointing to cryovolcanoes and clathrates, then follow the Cassini radar mapping and the January 14, 2005 Huygens landing that revealed ice hills, drainage plains, seas like Kraken Mare and Ligeia Mare, and 100-kilometer dunes. The episode closes with astrobiology, the Dragonfly mission, and Titan’s possible future as a warm water world.

• Why Titan’s stretched orbit is the scar of ancient moons colliding in a cosmic demolition derby
• How a water-and-ammonia slurry could act as lava for ice volcanoes that replenish the atmosphere
• Why some astrobiologists argue liquid methane may be a gentler solvent for early life than water
• How Cornell researchers modeled an azotosome membrane built from nitrogen, carbon, and hydrogen
• What Chris McKay’s 2005 prediction and the 2010 finding of vanishing surface hydrogen might mean