Pressure and CO₂ content of the Martian atmosphere: A critical discussion

This article reviews the principal techniques that have been used to estimate the surface pressure on Mars. The basic physics behind each technique is outlined and illustrated with simplified examples. An attempt is made to evaluate the reliability of each technique and its use to date. The problem is outlined in section 1; the older techniques (polarimetry and photometry) are examined in section 2; the spectroscopic method, wherein at least two CO 2 absorption bands are used to derive both the CO 2 abundance and the surface pressure, is reviewed in section 3. The conclusions, summarized in section 4, are principally (1) that the polarimetric and photometric techniques are not nearly so reliable as has been generally supposed, and (2) that, although the spectroscopic method should ultimately settle the problem, the data thus far available do not yield good accuracy in either the CO 2 content or the total pressure.