Europa has a moderate atmosphere which is not as dense as Ganymede, but because it has quite a large proportion of water vapor in its atmosphere (which is a strong greenhouse gas), in addition to its proximity to the Sun, it is, on average, 15˚F warmer than Ganymedian tempratures if not warmer with average of 28˚C/83˚F. It is also composed primarily Nitrogen, Oxygen and some other gases.