Mars ~ Atmosphere Temperature and Pressure

Mars is the fourth planet from the Sun and is commonly referred to as the Red Planet. The rocks, soil and sky have a red or pink hue. The distinct red colour was observed by stargazers throughout history. It was given its name by the Romans in honour of their god of war. Other civilizations have had similar names. The ancient Egyptians named the planet Her Descher meaning the red one.

Before space exploration, Mars was considered the best candidate for harbouring extraterrestrial life. Astronomers thought they saw straight lines crisscrossing its surface. This led to the popular belief that irrigation canals on the planet had been constructed by intelligent beings. In 1938, when Orson Welles broadcasted a radio drama based on the science fiction classic War of the Worlds by H.G. Wells, enough people believed in the tale of invading Martians to cause a near panic.

Another reason for scientists to expect life on Mars had to do with the apparent seasonal colour changes on the planet's surface. This phenomenon led to speculation that conditions might support a bloom of Martian vegetation during the warmer months and cause plant life to become dormant during colder periods.

In July of 1965, Mariner 4, transmitted 22 close-up pictures of Mars. All that was revealed was a surface containing many craters and naturally occurring channels but no evidence of artificial canals or flowing water. Finally, in July and September 1976, Viking Landers 1 and 2 touched down on the surface of Mars. The three biology experiments aboard the Landers discovered unexpected and enigmatic chemical activity in the Martian soil, but provided no clear evidence for the presence of living microorganisms in the soil near the landing sites. According to mission biologists, Mars is self-sterilizing. They believe the combination of solar ultraviolet radiation that saturates the surface, the extreme dryness of the soil and the oxidizing nature of the soil chemistry prevent the formation of living organisms in the Martian soil. The question of life on Mars at some time in the distant past remains open.

Other instruments found no sign of organic chemistry at either landing site, but they did provide a precise and definitive analysis of the composition of the Martian atmosphere and found previously undetected trace elements.

Atmosphere

The atmosphere of Mars is quite different from that of Earth. It is composed primarily of carbon dioxide with small amounts of other gases. The six most common components of the atmosphere are:

• Carbon Dioxide (CO2): 95.32%
• Nitrogen (N2): 2.7%
• Argon (Ar): 1.6%
• Oxygen (O2): 0.13%
• Water (H2O): 0.03%
• Neon (Ne): 0.00025 %

Martian air contains only about 1/1,000 as much water as our air, but even this small amount can condense out, forming clouds that ride high in the atmosphere or swirl around the slopes of towering volcanoes. Local patches of early morning fog can form in valleys. At the Viking Lander 2 site, a thin layer of water frost covered the ground each winter.There is evidence that in the past a denser Martian atmosphere may have allowed water to flow on the planet. Physical features closely resembling shorelines, gorges, riverbeds and islands suggest that great rivers once marked the planet.

Temperature and Pressure

The average recorded temperature on Mars is -63° C (-81° F) with a maximum temperature of 20° C (68° F) and a minimum of -140° C (-220° F). Barometric pressure varies at each landing site on a semi-annual basis. Carbon dioxide, the major constituent of the atmosphere, freezes out to form an immense polar cap, alternately at each pole. The carbon dioxide forms a great cover of snow and then evaporates again with the coming of spring in each hemisphere. When the southern cap was largest, the mean daily pressure observed by Viking Lander 1 was as low as 6.8 millibars; at other times of the year it was as high as 9.0 millibars. The pressures at the Vi, the mean daily pressure observed by Viking Lander 1 was as low as 6.8 millibars; at other times of the year it was as high as 9.0 millibars. The pressures at the Viking Lander 2 site were 7.3 and 10.8 millibars. In comparison, the average pressure of the Earth is 1000 millibars.

Mars Statistics:

Time taken to orbit the Sun in Earth years: 1.88
Average orbital velocity in miles/second (km/sec): 15.0 (24.1)
Angle between orbit of planet and orbit of Earth: 1.85º
Time taken to rotate on axis in Earth time: 24hr 37min
Tilt of axis to perpendicular of orbital plane: 24º
Average distance from Sun in astronomical units*: 1.52
Average distance from Sun in miles (km): 142 million (228 million)
Average surface temperature in degrees Celsius: -23º
Density relative to water: 3.9
Equatorial diameter relative to Earth diameter**: 0.53
Equatorial diameter in miles (km): 4200 (6800)
Mass relative to Earth: 0.11
Escape velocity in miles/second (km/sec): 3.12 (5.02)
Number of known moons: 2
Number of known rings: 0
Date of discovery: Mars is visible to the naked eye
* One astronomical unit is 92,956,000 miles (149,598,000km)
** Earth's diameter is 7,926 miles (12,756km)