Atmosphere of Mars

[Victoria Liss]

Atmosphere of Mars

Mars, the 4th planet from the Sun, has a very different atmosphere from that of the Earth. There has been much interest[1] in studying its composition since the recent detection of trace amounts of methane,[2] which may indicate the presence of life on Mars; its presence could also be caused by a geochemical process, or it could be the result of volcanic or hydrothermal activity.[3]

The atmosphere of Mars is relatively thin, and the atmospheric pressure on the surface varies from around 30 pascals (0.0044 psi) on Olympus Mons's peak to over 1,155 pascals (0.1675 psi) in the depths of Hellas Planitia, with a mean surface level pressure of 600 pascals (0.087 psi), compared to Earth's sea level average of 101.3 kilopascals (14.69 psi), and a total mass of 25 teratonnes, compared to Earth's 5148 teratonnes. However, the scale height of the atmosphere is about 11 kilometers (6.8 mi), somewhat higher than Earth's 7 kilometers (4.3 mi). The atmosphere on Mars consists of 95% carbon dioxide, 3% nitrogen, 1.6% argon, and contains traces of oxygen, water, and methane, for a mean molecular weight of 43.34 g/mole[4]. The atmosphere is quite dusty, giving the Martian sky a light brown or orange color when seen from the surface; data from the Mars Exploration Rovers indicate that suspended dust particles within the atmosphere are roughly 1.5 micrometers across.[5]

[Victoria Liss]

Carbon dioxide 95.32%
Nitrogen 2.7%
Argon 1.6%
Oxygen 0.13%
Carbon monoxide 0.07%
Water vapor 0.03%
Nitric oxide 0.013%
Neon 2.5 ppm
Krypton 300 ppb
Formaldehyde 130 ppb
Xenon 80 ppb
Ozone 30 ppb
Methane 10.5 ppb

[Victoria Liss]

History
Mars' atmosphere is believed to have changed over the course of the planet's lifetime, with evidence suggesting the possibility that Mars had large oceans a few billion years ago.[6] As stated in the Mars Ocean Hypothesis, atmospheric pressure on the present day Martian surface only exceeds that of the triple point of water (6.11 hectopascals (0.0886 psi)) in the lowest elevations; at higher elevations water can exist only in solid or vapor form. Annual mean temperatures at the surface are currently less than 210 K (−63 °C; −82 °F), significantly less than what is needed to sustain liquid water. However, early in its history Mars may have had conditions more conducive to retaining liquid water at the surface.

Possible causes for the depletion of a previously thicker martian atmosphere include:

Catastrophic collision by a body large enough to blow away a significant percentage of the atmosphere;[7]
Gradual erosion of the atmosphere by solar wind;[8] and
On-going removal of atmosphere due to electromagnetic field and solar wind interaction.[7]

[Victoria Liss]

Structure
Mars' atmosphere is composed of the following major divisions:

Lower Atmosphere: This is a warm region affected by heat from airborne dust and from the ground.
Middle Atmosphere: Mars has a jetstream, which flows in this region.
Upper Atmosphere, or Thermosphere: This region has very high temperatures, caused by heating from the Sun. Atmospheric gases start to separate from each other at these altitudes, rather than forming the even mix found in the lower atmospheric layers.
Exosphere: Typically stated to start at 200 kilometers (120 mi) and higher, this region is where the last wisps of atmosphere merge into the vacuum of space. There is no distinct boundary where the atmosphere ends; it just tapers away.

[Victoria Liss]

[edit] Carbon dioxide
The main component of the atmosphere of Mars is carbon dioxide (CO2). During the Martian winter the poles are in continual darkness and the surface gets so cold that as much as 25% of the atmospheric CO2 condenses at the polar caps into solid CO2 ice (dry ice). When the poles are again exposed to sunlight during the Martian summer, the CO2 ice sublimes back into the atmosphere. This process leads to a significant annual variation in the atmospheric pressure and atmospheric composition around the Martian poles.

[Victoria Liss]

Mars' thin atmosphere, visible on the horizon in this low orbit image.