The atmosphere of Mars is the layer of gases surrounding Mars. It is composed mostly of carbon dioxide. The atmospheric pressure on the Martian surface averages pascal (), about 0.6% of Earth's mean sea level pressure of kilopascal (). It ranges from a low of pascal () on Olympus Mons's peak to over pascal () 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 kilometre (mi) versus Earth's kilometre (mi).