The atmosphere of Mars is the layer of gases surrounding Mars composed mostly of carbon dioxide. The atmospheric pressure on the Martian surface averages , about 0.6% of Earth's mean sea level pressure of . It ranges from a low of on Olympus Mons's peak to over in the depths of Hellas Planitia. This pressure is well below the Armstrong limit for the unprotected human body. Mars's atmospheric mass of 25 teratonnes compares to Earth's 5148 teratonnes with a scale height of about versus Earth's .