How Is Mars' Atmosphere Different From Earth's?

PS1.A: Structure and Properties of Matter
  • Gases and liquids are made of molecules or inert atoms that are moving about relative to each other. (MS-PS1-4)
  • In a liquid, the molecules are constantly in contact with others; in a gas, they are widely spaced except when they happen to collide. In a solid, atoms are closely spaced and may vibrate in position but do not change relative locations. (MS-PS1-4)
Atmosphere is the collection of gases around us. Earth's atmosphere is a relatively small layer of gas on the outside of our planet. It is what we breath. It is where our weather occurs. Because the energy that these molecules have is able to overpower earth's gravitational field enough to not be stuck to the ground, but not enough to fly off into space, life is capable of existing on our planet.

Air pressure exists on planet Earth. If we were to measure a column of air 1 m2 into the air to the edge of the atmosphere it would have in it 104 kg of air. Because air is made up of particles it has mass. All that mass causes weight, 1 × 105 N. Therefore Earth's massive atmosphere causes us to feel 1 × 105 N/m2 of pressure here on Earth. We usually do some math on that to make it easier to read and call it 100 kN/m2 or 100 kPa. This is an approximate calculation, the exact number is 101.325 kPa (1 atm) of pressure at sea level. The atmosphere on Mars is only 600 Pascal (0.006 atm) or 0.6% of Earth's air pressure.

On Earth gasses are usually nonmetal elements, or compounds of nonmetals. Earth's atmosphere is made up primarily of Nitrogen (N2), Oxygen (O2), and Argon (Ar). The vast majority of our atmosphere is Nitrogen. According to NASA, the atmosphere of Mars is mostly Carbon Dioxide (CO2), Argon (Ar), Nitrogen (N2), Oxygen (O2), and Carbon Monoxide (CO).

From a physical standpoint there is a limited difference between how different gasses would feel. Avogadro's Law states that equal volumes of different gasses have the same volume at the same temperature and pressure. Therefore, we could weigh the difference in gasses, but they would behave quite similar physically. Chemically, they would be very different, though. Elemental oxygen like Earth has is necessary for cellular respiration, what keeps human’s alive. Carbon Dioxide would have to be reacted and converted to some form of Carbon and Oxygen before humans could live on Mars, since NASA has found only 0.14 % of Mars’ atmosphere to be Oxygen.

The behavior of gases when not reacting is explained by the Ideal Gas Law. Over a more than 100 year period, from the 1600s into the 1800s, scientists like Robert Boyle, Jacques Charles, and William Thomas (or Lord Kelvin), observed gases and made individual laws to describe their behavior under different conditions. Several of these laws can be put together into one powerful equation that describes the behavior of an &ldquoa;ideal gas.” No gas is exactly like an ideal gas, but they behave similarly, making the Ideal Gas Law a close approximation and a powerful tool.

An ideal gas follows the following laws of the kinetic molecular model:
  1. Gasses are made up of a large number of particles all moving very fast in random directions.
  2. The space that each gas particle takes up is negligible.
  3. Attractive and repulsive forces between gas particles is negligible.
  4. Collisions are perfectly elastic.
  5. Average kinetic energy of the gas particles is proportional to the temperature.
For the law, Pressure is represented by P. Temperature (in Kelvin) is T. The number of moles of gas is represented as n. Volume is represented as V. Lastly the equation has a constant R, which is only a number used to make the units work out. It is similar to a power adaptor for electronic devices. If different units for Pressure or Volume are used, a different R is applied. For our purposes, we will be working with atmospheres, and Liters, so R will be 0.08206 L×atm / mol×K.

Ideal Gas Law: PV=nRT

For example if I know the Pressure under which a gas is kept is 2.4 atm, and it fills a 3.4 L container, at a temperature of 250 K, then I can calculate the amount of moles of gas I have.

n = PV/(RT) = (2.4 atm)(3.4 L) /((0.08206 L×atm / mol×K)(250K)) = 0.03978 moles of gas

CCSS.ELA-Literacy.RST.9-10.3 Follow precisely a complex multistep procedure when carrying out experiments, taking measurements, or performing technical tasks, attending to special cases or exceptions defined in the text.
1. In what unit is pressure measured?
2. What is the most abundant gas in Earth's atmosphere?
3. If 7.81 moles of a gas was kept in a 3.2 L container, with a temperature of 201 K, what pressure will the gas exert on the container?

4. If 12.2 L of gas are kept under 4.6 atm of pressure and at 150 K. How many moles of gas are in the container?

NASA currently has machines on Mars carrying out experiments controlled by scientist on Earth. One of the things they are trying to find out about is the atmosphere.. Read the article at NASA's website and answer the questions below.
CCSS.ELA-Literacy.RST.6-8.10 By the end of grade 8, read and comprehend science/technical texts in the grades 6–8 text complexity band independently and proficiently.


5. What previous sources of information about Argon in Mars' atmosphere did the article site?

6. What evidence do scientists look for as an indication that a whirlwind has occurred on Mars?
7. Every other year there is a one month period when Mars appears to be behind the Sun. What is this time called?
Visit our minilab on gasses. See how a change in temperature, volume, or quantity of particles can change the pressure that a gas exerts on its container. After experimenting with the minilab, answer the questions below.

CCSS.ELA-Literacy.RST.9-10.7 Translate quantitative or technical information expressed in words in a text into visual form (e.g., a table or chart) and translate information expressed visually or mathematically (e.g., in an equation) into words.
8. Does pressure increase or decrease when more gas is added to a container?

9. Does pressure increase or decrease when temperature is increased?
10. Does pressure increase or decrease when volume of a gas is increased?
11. Do all the molecules at a given temperature have the same amount of kinetic energy? Defend your claim.