The International Space Station orbits the Earth at an altitude of about 250 miles. Very accurate temperature measurements place the temperature of the thermosphere (high earth atmosphere) from about 50 to 300 miles up at up to 2,000 degrees F. At 2,000 degrees, the Space Station should burn up and disintegrate along with orbiting satellites and humans. So why don’t they?
In the movie “The Martian,” which has gotten good marks for being realistic and science based, the hero is left stranded on Mars when a dust storm literally blows him off his feet and topples equipment. His comrades, thinking he has been killed, abandon any hope of finding him alive and blast off Mars for Earth without him. But he survives the storm and then finds ingenious ways to remain alive until he can be rescued many months later.
“The Martian” is a good movie in a lot of ways, including promoting not succumbing to a defeatist attitude and using science to find ways to solve seemingly insurmountable problems. The astronomical, navigational, and technical aspects are sound. But some “creative license” had to be taken to make it an interesting story.
Mars is considerably smaller than the Earth and so has less gravity. The force of gravity determines how much you and inanimate objects “weigh.” For instance, if you weigh 180 pounds on Earth, you would only weigh about 30 pounds on the moon because the moon is far smaller. That is why the movements of the astronauts that walked on the moon seem so peculiar. On planets with a lot more gravity, a person would weigh more. On Jupiter, the largest planet in the solar system, a 180-pound person would weigh in at 450 pounds. On Mars, the same person would weigh about 70 pounds.
The amount of gravity an astronomical body has in part determines the “thickness” or density of the atmosphere. The moon has almost no atmosphere because it cannot “hold on to” air molecules and those that are produced or have been produced there are lost to space. Jupiter and the other gas planets are mostly atmosphere because of their massive size. While Mars almost certainly had a thicker atmosphere probably comparable to Earth’s early atmosphere when it formed over four billion years ago, most of that early atmosphere has been lost to space because of Mars’ low gravity. What’s left produces only about 1% of the surface pressure that is present on Earth. Composed primarily of carbon dioxide, it is incredibly thin.
What are the consequences of that thin atmosphere? Well, conventional airplanes could not fly there because the air is not dense enough to create the lift required to get them off the ground, and there is almost no molecular oxygen to support combustion. Standing water exposed to the atmosphere cannot exist in liquid form for any length of time because the low surface pressure would immediately change it into a gas. It is also incredibly cold on Mars with a global climate similar to the innermost regions of Antarctica.
The atmosphere on Mars is so thin, in fact, it is highly unlikely a dust storm on Mars could blow over a human being and certainly not heavy equipment. Wind speeds in Mars dust storms have been measured at 60mph, but with atmospheric surface pressure of only 1% of Earth’s, they could not create the force depicted in the movie. The pressure created by that 60mph wind on Mars would be about the same as a moderate breeze on Earth.
Back to Earth again, it is the very low density of Earth’s atmosphere at 250 miles up that saves the International Space Station from being fried. Heat is the “vibration” of atoms. The greater the vibration, the greater the heat. But the number of atoms floating around in the vicinity of the Space Station is so few that even though they are individually “hot,” there are far too few of them to create a threat to humans or electronics.
Email Terry Mejdrich at firstname.lastname@example.org.