The Martian - Part II -
As we began our next day of catching scenes from “The Martian” the director of NASA makes the worst mistake a person can make in any movie; to paraphrase he said, “This will work out, as long as nothing goes wrong …”
Soon after this scene, the Hab breaks and exposes Watney’s potato crops to the Martian atmosphere.
Unpacking this one scene there are several reasons plants would die on Mars;
First, the extreme cold. The average surface temperature on Mars is -40 degrees Celsius. Side note; negative forty degrees is the point at which the Fahrenheit and Celsius temperature scales “meet.” It’s the same temperature.
The atmosphere on Mars is composed, mainly, of Carbon Dioxide. While that sounds like it might be a wonderful environment for plants - as PHOTOSYNTHESIS converts carbon dioxide and water into sugar and oxygen - the atmospheric pressure is so low that any water would boil away - and then freeze - on Mars. Think about boiling water on Earth. The cooking instructions always call for more boiling time at higher altitudes as water boils at a lower temperature the higher you go. You can think of it as there being less atmosphere to hold in the water. As the average kinetic energy for the water molecules rises high enough, the water molecules can escape the mutual attraction they have with the other water molecules.
The second half of The Martian, and especially the last act, are excellent illustrations of Newton’s Three Laws of Motion.
When the mission to resupply Watney with food, until the next mission can reach Mars, fails the Chinese Space Agency offers a rocket to help with another attempt. However, the flight director - “Mitch Henderson” played by Sean Bean - knows how close this crew is and he defies orders and gives an alternative plan to the Hermes crew. A plan that illustrates how space travel really works in that the Hermes uses the gravity of Earth to “slingshot” back to Mars in order to pick up Watney. Our spaceships would not have nearly enough fuel to simply turn around and go back. Our probes reach other planets after being launched in rockets the size of buildings. Once they have an initial “push” they often carry only a small amount of fuel or gas to maneuver and make small adjustments to their trajectory. (Direction and speed.)This is a wonderful illustration of Newton’s First Law - INERTIA.
Newton’s Second Law - F=MA - is wonderfully illustrated when Watney is asked to make the Mars Assent Vehicle (MAV) as light as possible in order to rendezvous with his returning crew mates. As thrust is a CONSTANT the MAV will have the best chance of achieving a high velocity (speed) with as little weight (mass) as possible. Watney removes as much of the ship as possible; even going to the extreme of taking the front of the ship off. The front, on Earth, is mentioned as weighing close to one thousand pounds. However, as Mars has far less mass than Earth, it would only weigh about 300 pounds on Mars. Still heavy; but manageable. This cycles back to why Earth has been able to maintain an atmosphere and internal heat while Mars has no Plate Tectonics, a very thin atmosphere, and very little in the way of resources to maintain life.
Finally, when we wrap up The Martian, Newton’s Third Law is on display when the Hermes - the ship carrying his crew mates - has to find a way to slow the ship so it can intercept the MAV with Watney aboard. The crew opens a hatch and releases some air in their direction of travel. Newton’s Third Law - Action / Reaction. As the gas (air from the ship) is released in one direction the ship feels a push in the opposite direction.
Whatney, as well, uses air as thrust when he deliberately breaches his own space suit in an attempt to reach his friends and the safety of the Hermes.
The movie does stretch some science about what might be possible in terms of surviving on Mars, but the story does a wonderful job of not only illustrating physical laws and chemistry - but the incredible planet we live on and the importance of cherishing and maintaining the ONE place in the entire universe where life is known to thrive; EARTH.
