It’s pretty perplexing as to why Saturn’s moon, Titan, has such a thick atmosphere but a planet like Mars does not. Since the most widely accepted explanation of why Mars has such a thin atmosphere is it losing its magnetosphere as its core cooled and does not contain nearly as much metallic iron has the Earth’s, it would make sense that Titan would follow the same pattern since it doesn’t have a magnetosphere. The explanation behind this discrepancy is due to the composition of Titan’s atmosphere. Since Titan’s atmosphere is almost entirely nitrogen and nitrogen is able to withstand the lower amounts of solar radiation that Titan receives relative to Mars even without a magnetosphere, Titan is able to maintain an atmosphere of nitrogen. This also explains why Titan wouldn’t have any oxygen, since this is not true for oxygen molecules as they would be broken up by this radiation. This also explains the situation on Mars, since it was believed to once have oxygen, but due to losing its magnetosphere the oxygen was then broken apart and most likely bonded with the iron on the surface, giving it its red tint. The only thing left unexplained is why Mars or the other large Jovian moons lack the nitrogen that Titan and Earth have. Information from this blog and more detailed information on this subject is found in this video.