Titan

There are 82 known moons of Saturn but only 53 of them are officially named. The most notable of these moons would probably be Titan (pictured above) because it is the only moon in the Solar System with a dense atmosphere.

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Titan's Properties:​

Mass: 1.35*10²³ kg

Radius: 2574.73 km

Semi-major axis: 1221870 km

Orbital Period: 15.95 days

Rotational Period: 15.95 days(synchronous)

Surface Gravity: 1.35 m/(s²)

Etymology: Titan(immortal race from Greek mythology)

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Titan is known to have a noticeably dense atmosphere, a unique aspect that differentiates it from every other moon in the Solar System. Its atmosphere is also nitrogen-rich, a quality that it only shares with Earth's atmosphere. Due to the lower gravity on Titan, the Titan atmosphere is far more spread out and less attracted to the moon's center of mass. Due to traces of methane, sunlight is severely trapped in the upper atmosphere, meaning that Titan has a significant greenhouse effect of its own. However, haze in the upper atmosphere also causes Titan to have an anti-greenhouse effect by reflecting incident sunlight back into outer space. This is why Titan's upper atmosphere is far hotter than the extremely cold surface.

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On the surface of Titan, there are many lakes made up of hydrocarbons(a compound made up of hydrogen and carbon) like ethane and methane. The abundance of these lakes suggests a slight probability of organisms that are suited to different compounds in order to thrive.

Of course, there would be significant differences in Titan-based life than Earth-based life. Titan-based life would inhale molecular hydrogen(H2) instead of molecular oxygen(O2) and exhale methane(CH4) instead of carbon dioxide(CO2). Also, these organisms would metabolize with acetylene(C2H2) instead of glucose(C6H12O6). Earth-based organisms use water as a solvent but these organisms would likely use liquid hydrocarbons like methane instead as a solvent. Water is a stronger solvent than methane so it can break down organic molecules(through hydrolysis) far more easily. This means that if there was hydrocarbon-based life on Titan, it would be at a lesser risk of its biomolecules being broken down. However, given that Titan's surface is very cold, these organisms would have to metabolize and thrive in extremely cold surface conditions of about 94 K(-179.2 C).