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Surface Pressure
In Figure 1 of this summary information,
the column labeled Po gives
the surface pressure for each of the bodies. Note that Mars, the
smallest of the planets listed and having an escape velocity of only
about 5 km/s, has almost no atmosphere. Most of the atmospheric gases
from Mars have been able to escape, with the predominant remaining gas
being carbon dioxide. Earth, on the other hand, has a CO2
concentration of only 3.60 x 10-4, or about 360 molecules per million
total atmospheric molecules (parts per million by volume, or ppmv).
It is noteworthy that the earth is unusual because it is the only
planet that has a substantial amount of oxygen in its atmosphere. Venus
and Mars have trace amounts, but Earth has a remarkable amount of
oxygen and nitrogen.
NEXT: Four Stages of the Earth's Atmosphere
