Gale Crater Methane SGM2010 Dust Frozen CO2 Oceanus BorealisMars Society Switzerland
Geology & Atmosphere
Changes in the atmospheric pressure of Mars.
PIA16912: Seasonal Pressure Curve Peaks at Gale Crater April 8th 2013 Image Credit: NASA/JPL-Caltech/CAB(CSIC-INTA)/FMI/Ashima Research
This graph (from data gathered by the Spanish instrument REMS aboard Curiosity, from the end of August 2012 till the end of February 2013, ie the end of Martian winter till the end of Spring in the Southern hemisphere) shows the strong atmospheric pressure variations on Mars. These pressures do vary along the year, along the day and according to the altitude. It is the lowest during the austral winter. Indeed, with the cold, the carbon dioxide of the atmosphere freezes into ice which accumulates over the Southern polar cap. The cover of such carbonic ice is much thicker during austral winter than during boreal winter on account of the eccentricity of Mars orbit. The reason is that, being much farther from the Sun, Mars is much colder during the southern winter than during the northern winter. The second variable is the time of day. The variation of heat coming from the sun during the circadian cycle has, on another scale, the same effect on the air pressure as the variation of the heat along the seasons’ cycle. The third variable is altitude. On Mars it goes from -8,500 meters at the bottom of the Hellas crater, up to 21,000 meters at the top of Olympus Mons, and the mean pressure ranges from 1,150 to only 30 pascals between these extremes, to stand at 611 pascals (for 0°C) at altitude zero (by definition). At the bottom of Gale the altitude is about -4,200 meters. It is therefore logical that the pressure there be well above the average. The consequences of this variability are obvious for exploration: To undertake the most effective EDL (Entry Descent Landing), we have to look for the atmospheric conditions (altitude, season, time of day) and to choose to go down onto the surface of the planet when and where the atmospheric pressure is the highest (to the extent that the launch window from Earth would allow it). A higher atmospheric pressure results in a more efficient and longer atmospheric braking and a stronger braking effect would allow significant energy savings or the possibility of landing heavier masses on Martian ground. Moreover, when we’ll undertake manned missions, we will have to think of protecting ourselves against solar and galactic radiations and take into account the altitude to choose the landing site. Once on the ground we will have to take into account the time of the day for the EVAs and choose the right season for distant exploration campaigns (not the austral winter, even though the boreal summer is the warmest season on Mars!). Now, be careful! The end of spring in the Southern hemisphere, might be the beginning of a global dust storm, for the same atmospheric pressure reason!
Curiosity 1