Before the Viking spacecraft landed on Mars in 1976, it was thought that the atmospheric pressure of Mars was somewhere between 0.4 PSI and 4.4 PSI. When the Viking spacecraft landed, the pressure sensor appeared to indicate that the atmospheric pressure on the surface of Mars was 0.09 PSI.
There was a software error in the conversion of pressure sensor data, where Pa and hPa were not considered as different units, although they differ by a factor of 100. This implies that Mars has an atmospheric pressure of 9 PSI. This has rather large implications for our understanding of physics ... Read even more
