7. Which planets have atmospheres? The innermost planet with an atmosphere is Venus. Its atmosphere is composed of 96% carbon dioxide (the same gas which is dissolved in soft drinks). Of course our own planet, Earth, possesses a rich atmosphere, composed mainly of oxygen and nitrogen. Mars' atmosphere is very thin, containing large quantities of carbon dioxide. Jupiter has a thick atmosphere composed mainly of hydrogen gas and helium (about 80% hydrogen, 20% helium), while Jupiter's clouds form from ammonia and water vapour. Despite the appearance of Saturn, its atmosphere's composition is very similar to Jupiter's, containing hydrogen and helium, plus smaller quantities of ammonia and methane. Uranus' atmosphere is similar to that of Jupiter and Saturn containing hydrogen, helium, and small amounts of methane. Methane has been found in Neptune's atmosphere, but it is otherwise thought to be similar to Uranus. Spectroscopic observations have revealed ice water on the surface of Pluto with the possibility of a thin methane atmosphere. |