Density and Mass If a CME hits Earth, how much mass does it actually carry? Although the complete cloud carries over one billion tons of gas, it is so spread out across millions of kilometers that what actually blows by Earth is very dilute. By the time it reaches Earth, the density of the gas is only 50 atoms per cubic centimeter. Imagine that the cloud is 20 million kilometers thick, and that the area over which it impacts Earth is 50,000 kilometers in radius. Lets calculate how much gas we actually intercept. 1...The volume of a cylinder is equal to the area of the circular base times the height of the cylinder. If the area of the cylinder is p r2 = 7.8 billion square kilometers, the volume will be 7.8 billion square kilometers x 20 million km = ................ cubic kilometers or ................. cubic centimeters   2... The density of the gas is 50 atoms/cubic centimeter. How many atoms are in the cylinder?   3...If the mass of each atom is 1.6 x 10-24 grams, how many grams of matter are in the cylinder?     4...How many tons of gas are in the cylinder?