The planet Mars has an atmosphere. How and why is the atmosphere of Mars different from Earth’s?

Answer 1

Some excellent replies from a challenge sent by NASA- I think you will find it interesting.

Good luck

http://quest.nasa.gov/mars/events/challenge/23.html

Answer 2

The answer is complex, but the primary difference arises from where Mars and Earth formed during the birth of the solar system. That affected their composition, their size, and how far they were from the sun. Both planets started out with massive atmospheres relative to today. In fact, during my studies in the '90s, scientists were unsure if Earth started out with an atmosphere of 10 times the current mass, 100 times, or even 1000 times. The debate is muddled by what constitutes a young earth. When it was molten? When it was 100 Million years old after solidifying? Etc?
The sun is important because it affects the atmosphere by heating it (and the ground) with light. The solar wind also carries along a small amount of energetic particles that affect the very thinnest top of the atmosphere. Even though the atmosphere thins out to almost nothing on top, enough atoms get up there to get knocked into outer space by these energetic particles. Over a few billion years, that effect can add up and deplete an atmosphere. (Atmospheres also get depleted when gases bind up with rock, as much of Mars' atmosphere and Earth's atmosphere have both done - forming carbonate and silicate rocks from carbon dioxide and oxygen. Likewise, gases can dissolve into the ocean.)

Given enough time (and Mars already had its time), planetary atmospheres can escape into outer space (due to the mechanisms driving something "hydrogen escape"). The time required for atmospheres to disappear varies. Earth, too, will see its atmosphere evaporate but not perhaps for a few billion years. However, unlike for Mars, Earth's atmospheric loss will probably be driven along when the sun swells up and begins to bake the Earth severely.

As for "partial pressure", I don't what that other answerer is trying to get at. If I recall my Master's Level studies in Meteorology well (my studies included "Planetary Atmospheres"), the pressure of Mars' atmosphere is mostly due to CO2 (carbon dioxide). Because a lot of the CO2 freezes, Mars actually has ice caps that have CO2 and water frozen in them. Due to the seasonal variations in frozen CO2, the atmospheric pressure can vary. If I recall, the average pressure is about 6mb (Earth's averages slighlty over 1000mb). Mars' pressure is almost all due to CO2. The Martian atmosphere has very little in other gases.

Answer 3

Mars:
Carbon Dioxide 95%
Nitrogen 2.7%
Argon 1.6%
Oxygen 0.13%

Earth:
Nitrogen 78%
Oxygen 21%
Carbon dioxide, argon, and other trace gases 1%




Mars has a thin atmosphere, with a pressure on the planet's surface that is only about 0.7% of the Earth's atmospheric pressure at sea level.

The air at the surface of Mars is thinner than that found on Earth at an altitude nineteen times higher than Denver, CO.

Liquid water cannot exist on Mars because the thin atmosphere causes melting ice to evaporate directly into vapor, a process called sublimation.

Answer 4

Early in its history, Mars was much more like Earth. As with Earth almost all of its carbon dioxide was used up to form carbonate rocks.

But lacking the Earth's plate tectonics, Mars is unable to recycle any of this carbon dioxide back into its atmosphere and so cannot sustain a significant greenhouse effect.

The surface of Mars is therefore much colder than the Earth would be at that distance from the Sun

Answer 5

Next to no water vapour, and the partial pressure is such that you would need a respirator to breathe (too thin), although it is dense enough that you wouldn't necessarily need a pressure suit to survive.