Mission to Mars - 03: Atmosphere

LEARNING GOAL: I will be able to compare/contrast the atmosphere on Mars with the atmosphere on Earth during today's class.

OPENING QUESTION: Hopefully you are reading this with a friend online:

Have a conversation with your study friend and have them suggest the weight of the Atmosphere (in pounds or Newtons) that we experience on every square inch of ourselves here on Earth during our day to day life.


  • Sol (The Sun's proper name)
  • Solar System (Everything that orbits Sol, our sun)
  • Mars (The 4th planet from the sun)
  • Magnetic Field (Lines of magnetic force)
  • Atmosphere (Gas surrounding a planet or <on rare occasions, moons>)
  • Atmospheric pressure (the weight of an atmosphere per unit area)


Please do watch "The Martian" if you have access to it.

Also, please watch the first episode of "Mars" if you have streaming on Amazon Prime, Hulu or Netflix (it's FREE there!)


Yesterday's work was ALL about the magnetic field that shields the Earth from NASTY radiation from the sun and sorta kinda barely shields the Martian surface from the same.

Today we're going to talk about another important 'shield' that protects the Earth and sorta kinda barely protects Mars: Atmosphere

Many people are surprised to learn that the Earth's atmosphere (about 78% nitrogen and 20% oxygen and 2% other stuff) weighs down on us with 14.7 pounds of pressure per square inch.

Because the atmosphere can actually be modeled as a liquid, that pressure pushes on us not just from the top, but from the sides and everywhere else....just like ocean water does when we dive down into the depths!

No doubt you've heard the term "psi" and if you've taken chemistry, you've certainly heard of other measurements such as "mm of mercury" or "Pascals" to describe air pressure.

There is actually no physical boundary where we can say:

"Here be atmosphere and there be space".

Out atmosphere just gets thinner and thinner and thinner the higher we go until we finally say "ok, we're in space already!"

The important thing for you to remember is that every single molecule in the Earth's atmosphere has a mass.

Gravity acts on that mass resulting in a force.

That force is measured in units of area (pounds/inch or Newtons/meter) which gives us pressure!


We are MOST thankful for a nice thick atmosphere above our heads (although we can only comfortably breathe (?) up to about 3 km or so. Gonzo mount climbers sometimes go without bottled oxygen up to the top of Mt Everest (29,029 ft or 8.85 km) but they PAY dearly for it in the toll that it takes on their bodies, and many die from the effort.

Moving right along...

Clearly Earth and Mars' atmosphere are vastly different.

We couldn't breathe on Mars... at all.

That's not really the point though... Mars' atmosphere is very, very tenuous (thin). In fact it has only 1% of the atmospheric pressure that the Earth's atmosphere has.

That means Mars' atmosphere doesn't do nearly as good a job shielding the planet's surface from nasty radiation AND flying bits of rocks like meteors.

As with the magnetic field, there is SOME atmosphere so we would get SOME protection. But... day after day, month after month the cumulated effects would be dangerous.

Also as with the magnetic field, if the a nasty storm of particles did happen to rain down on us on the surface, that could be lethal as well.

Ok... now for the good stuff:

Air Pressure Modeling Challenge:



There is a scene in the movie where the airlock fails -- explosively. If you don't want to watch the actual movie and you just want to see that particular scene (boo!) click HERE

  • Physics Students: Please Model that explosion using the following specifications:

    • The airlock door as a rectangular object - you'll need to estimate the area of the airlock door
    • You may need to estimate the mass of the airlock door
    • The atmospheric pressure inside the "habitat" is 1.00 atmosphere or about 14.7 pounds per square inch (psi) just like Earth. You'll need to lookup/convert that into SIUs
    • Estimate the force exerted on the airlock door by the escaping air
    • Estimate the acceleration the airlock door experiences
    • Compare that acceleration with what you see in that scene... does the physics in the movie appear accurate?
    • Bonus challenge: Use the impulse formula to determine the VELOCITY of the airlock door as it is blown away from the habitat
    • Submit your work on our general classroom submission page by scanning/taking a picture of your HAND WRITTEN calculations on our regular classroom submission page HERE

AEROSPACE Students - Please jot some notes, questions and comments about whether that scene is accurate. In other words, is there enough force present to shoot that airlock door across the compound?

If you are comfortable doing some mathematical modeling, by all means please do take a shot at that.

In any case, please be prepared to discuss during our classtime on Friday


Physics Classes: Please submit your calculations HERE

Aerospace Class: Please submit your paragraph HERE