Mars may seem like an Earthlike planet with photos of rolling hills, mesas, boulders, sand dunes, ravines, and distant mountains under clear pink skies brushed with icy white clouds. The beautiful sunlit scenery appears very much like the U.S. Southwest and prompts an urge to put on hiking boots and take a nice, long stroll. Such an act would turn out to be deadly without proper protection. The scenery may look like a warm, inviting desert, but it is harsher than the coldest parts of Antarctica with air that is not breathable. Mars can kill in more ways than those innocent Earthlike photos depict.

Mars has a very thin atmosphere that is clear, dry, and often very dusty. The air pressure is only 1% Earth’s and is composed of 95% carbon dioxide with traces of nitrogen, argon, water vapor, and oxygen. Most of the oxygen is produced from the breakdown of carbon dioxide by the intense ultraviolet radiation that blasts the surface since there is no protective ozone layer. Mars orbits around 50% farther from the Sun than Earth, so it is colder, but the extremes in temperature are more severe than Antarctica. It can get as warm as 50ºF or even warmer during the peak of summer at the equator, but most of the time a pleasant summer day has a high approaching 30ºF after an overnight low of -130ºF. The rest of the year is downright frigid with highs hovering around 0º and lows around -150ºF. Winter is truly brutal with daily highs struggling to -20ºF after lows around -160ºF. This weather data is from landers and rovers near the equator, but it is even more severe towards the poles where temperatures approach -190ºF. The thin air makes it interesting to measure the temperature when standing on the surface. It may be a balmy 30ºF at the feet but a frigid -30ºF at the head. The poles are cold enough for carbon dioxide to snow out of the atmosphere forming dry ice on the surface as deep as several feet. In fact, the snow/ice accumulated heavily enough that it collapsed the solar panels on the Phoenix lander shortly after it ceased functioning due to the lengthening polar nights.

Mars has seasons like Earth’s since its axis is tipped 25.2º and Earth’s 23.5º. The tilt determines how directly sunlight strikes the hemisphere. Mars has long winter nights and long summer days like Earth, but with a twist. Mars is further from the Sun than Earth taking longer to orbit, 687 days versus Earth’s 365 days, making seasons last about twice as long. The stronger summer sun heats up the surface enough to trigger storms familiar to Earth: cold fronts with ice clouds, dust devils, and dust storms. Mars has a high orbital eccentricity which truly makes for some dramatic weather. The orbit is more elongated than Earth’s. While Earth orbits between 91.5 and 94.5 million miles from the Sun for a 3 million miles difference, Mars orbits between 128 to 154 million miles from the Sun for a dramatic 26 million miles difference. Mars receives 45% more sunlight when closest to the Sun compared to 7% for Earth. The elongated orbit means that summer in Mars’ southern hemisphere when it is closest to the Sun and moving fastest in its orbit is shorter than winter, 154 Martian days versus 178 for winter, where a Martian day, or sol, lasts 24 hours and 39 minutes. The increase in solar energy during the summer creates stronger winds that fuels more storms.

Mars is famous for storms ranging from small, solar panel-cleaning dust devils to global, rover-killing dust storms. The global dust storms dramatically affect the surface, atmospheric temperature, and the weather. Storms have been monitored in fine precision daily since 1997 with an armada of orbiters, landers, and rovers. Dust storms have been observed from Earth with telescopes for over a century. Martian dust storms are a different beast. Movies portray them as true howlers destroying bases and killing astronauts with blinding sand and debris. Dust storms can become large and thick enough to block out the Sun enough to turn day into night. The lack of sunlight ended up killing the solar powered Opportunity Rover after more than 14 years of successful exploration. The lack of sunlight rendered the solar panels ineffective in charging the rover, causing it to die. The Curiosity and Perseverance rovers, however, use nuclear power, so they are not threatened by dust storms proven by the survival of Curiosity during the 2018 global dust storm. The dark and disorientating nature of dust storms are the only similar characteristics to those on Earth. The wind speed and force are what make it a different beast.

The force of the winds on Mars is much weaker because the atmosphere is so thin. A 100-mph wind on Mars would feel like a gentle breeze of 10-15 mph on Earth. Martian dust storms may look like ferocious storms, and indeed they are dangerous, but the force does not compare to a Category 5 hurricane. The rovers and landers do get hit by dust devils, often as large and terrifying as a tornado, but they remain upright, intact, and actually benefit from a cleaning off of the nuisance red dust. The arid, dusty nature of the surface along with the weaker gravity makes it easier for the dust to become airborne, reach great heights, and stay airborne longer. This gives Mars its perpetual pinkish skies that would otherwise be deep blue or nearly black. The dust also gives Mars bluish sunrises and sunsets. When the Sun is low in the sky, its light passes through more atmosphere. The red component of sunlight is scattered leaving the blue, therefore the dustier the atmosphere, the bluer the sunrise and sunset. This is the complete opposite to Earth’s blue sky during the day and ruddy sunrises and sunsets.

The winds can have a significant effect on the weather and the surface. The weather patterns are more regular and predictable on a daily and seasonal basis and probably persisted for hundreds of millions of years that the atmosphere has been in its current condition. Orbiting spacecraft have discovered specific storm tracks on Mars for fronts and weather systems. The most common track begins in the north polar region and extends southward along a dark, lowland region known as Acidalia Planitia, near the Mars Pathfinder landing site. Another common storm track runs through the lowland plain known as Utopia, not far from the Viking 2 landing site. The winds are created by temperature differences between the bright, frigid polar ice caps and darker, warmer ice-free regions. Topography is also a factor where storms travel towards the equator and fan out. There is a predictable seasonal rhythm with dust storms forming within the Valles Marineris canyon and Hellas basin at almost precisely the same time each year. Polar storms also behave predictably and while there are tornado and hurricane seasons on Earth, there is no such thing as a storm starting at the same place on Earth on the same day, every year.

There may seem to be a dust storm season, but that is not true for smaller storms. They occur nearly every day somewhere on Mars. Before the Space Age, Mars was best seen when closest to Earth making it easier to see dust storms, but only the larger storms. Many smaller storms start when colder air flows off the polar ice caps or across hills and valleys creating turbulence. These smaller storms frequently merge into larger regional storms. It is not fully understood what occasionally causes them to merge into global storms. The most memorable global dust storms occurred in 1971, 2001 and 2018. The larger storms occur during the heat of the southern hemisphere summer when Mars is closest to the Sun. Fortunately, these do not occur regularly during that time with proof being the historic 2003 opposition when Mars was at its closest to Earth in nearly 60,000 years and it was summer in the southern hemisphere. There were no dust storms and Mars was seen in crisp detail with some of the best full-phase images to this day with special credit to the Hubble Space Telescope.

Mars may have had a thicker atmosphere long ago where rain fell, filling canyons and basins with water, but now it is a cold, dry world with a thin atmosphere. The weather and climate will not change much in the near future. Astronauts will someday explore the rusty deserts swept by the winds and take an evening stroll under the dusty pink skies adorned with two tiny moons.