The Martian atmosphere is extremely thin, possessing less than one percent of Earth’s density and primarily composed of carbon dioxide. Mars’s weather is not driven by the liquid water cycle that produces rain, snow, and lightning on our planet. Instead, the weather is dominated by the movement of fine, planet-wide dust, which can remain suspended for long periods due to the planet’s lower gravity.
The Dominant Weather Phenomenon
The most powerful and frequent atmospheric disturbance on the Red Planet is the dust storm. Unlike Earth’s storms, which are fueled by condensing water vapor, Martian storms are purely atmospheric phenomena driven by wind lofting fine particulates from the surface. The dust is rich in iron oxides, which imparts the planet’s reddish hue, along with silicates, sulfur, and chlorine. Because of the low atmospheric pressure, even a relatively slow wind speed, around 70 miles per hour, can lift this fine, powdery material into the air and transport it globally.
Anatomy of a Martian Dust Storm
Martian dust storms form when solar heating causes significant temperature differences between the surface and the atmosphere, generating strong thermal gradients that drive winds. These storms are categorized into three distinct scales based on their size and duration.
Local and Regional Storms
The smallest are local dust storms, comparable in size to a major Earth state, such as Arizona, and generally last for a few days. Regional dust storms are much larger, covering areas the size of a continent and persisting for weeks at a time.
Global Storms
The largest scale is the global or planet-encircling dust storm, which can engulf the entire planet and last for months. These massive events typically occur during the southern hemisphere’s spring and summer, when Mars is closest to the Sun, leading to greater solar heating. When fully developed, the thick dust veil poses a serious challenge to solar-powered missions. For example, the 2018 global storm blocked so much sunlight that the Opportunity rover could not recharge its batteries, ultimately ending its operational life.
Other Martian Weather Systems
Beyond the major dust storms, Mars hosts other significant atmospheric phenomena. Small, localized convective vortices known as dust devils are a common sight, forming when superheated air near the surface rises rapidly. These miniature whirlwinds play a role in lofting dust and sometimes help rovers by clearing solar panels of accumulated debris.
Higher in the atmosphere, clouds composed of ice crystals are regularly observed. Most clouds consist of water ice, similar to high-altitude cirrus clouds on Earth, but clouds of frozen carbon dioxide, or dry ice, can also form in the colder upper reaches. These carbon dioxide clouds are sometimes seen after sunset as noctilucent, or “night-shining,” clouds because they catch the last rays of the sun. Seasonal weather changes are driven by the planet’s highly elliptical orbit, which causes atmospheric carbon dioxide to freeze out at the poles during winter. This massive migration of frozen gas causes the atmospheric pressure to fluctuate by as much as 30% over the Martian year, resulting in widespread seasonal frost and dry ice snowfall.