The pressure (i.e. the force per unit area) exerted on the surface of a planet by the weight of gas contained in a column extending vertically upwards to the limit of the ATMOSPHERE. At the surface of the EARTH, the average value of atmospheric pressure is 10330 kg per square metre (kg m_2); this value is equivalent to 1013.25 millibars, and may be referred to as 1 atmosphere. By way of comparison, the atmospheric pressures at the surfaces of VENUS and MARS are, respectively, 100 and 0.008 atmospheres.
