The Martian atmosphere, composed of 95% carbon dioxide and characterized by an average pressure of 6.1 millibars at the reference level – or approximately 0.6% of terrestrial atmospheric pressure – presents unique atmospheric dynamics, radically different from our planet.
Even though Mars does not experience extreme events like hurricanes, periodically, gigantic dust storms envelop the entire planet. These atmospheric phenomena, whose scale can reach several million km², sometimes persist for months. Thanks to the analysis of data collected by the Mars Reconnaissance Orbiter probe (which took these photos more than two years ago), we now better understand how they form.
Martian storms: a story of heat and dust
The Mars Climate Sounder instrument, on board the Mars Reconnaissance Orbiter, made it possible to identify a precise causal sequence: the absence of aerosols suspended in the atmosphere creates a window of atmospheric transparency. This phenomenon causes a rapid increase in surface temperature by direct absorption of solar radiation. The data reveals that in 68% of cases, this thermal rise precedes the appearance of these colossal storms.
The thermal gradient thus created between the surface and the upper atmospheric layers triggers an intense thermal convection process. The regolith particles, with an average diameter of three micrometers, are then lifted by the ascending currents, creating a positive feedback loop : their presence in the atmosphere modifies the local albedo (the capacity of a surface to reflect sunlight) and further disrupts the radiative balance.
Implications for space engineering
The Rover Opportunity unfortunately paid the price a few years ago. In 2018, atmospheric opacity reached a tau greater than 10.8 – an extraordinary value characterizing an almost total extinction of direct solar radiation. The progressive accumulation of particles on its photovoltaic panels reduced their energy yield below the critical threshold of 0.4 Wh per Martian soil, leading to the irreversible depletion of its lithium-ion batteries.
Although the Martian atmospheric density (around 0.020 kg/m³ at ground level) does not allow winds to exert mechanical forces greater than a few pascals, the cumulative effect of dust deposition remains a very important constraint for electrical power systems. For future Martian missions, this data will absolutely be considered in order to realize them.
- Dust storms on Mars are triggered by intense surface heating, amplified by the absence of aerosols.
- These global storms kick up particles that disrupt sunlight and fuel a climate feedback cycle.
- Future space missions will need to anticipate the critical impact of dust on energy systems.
