Mars' atmosphere is over 100 times thinner than Earth's and is primarily composed of carbon dioxide, nitrogen and argon gases. Oxygized dust particles kicked up from the Martian surface fill the atmosphere turning Mars' skies a rusty tan color, according to NASA (opens in new tab).
Water exists on Mars but the atmosphere is too thin for it to last long on the surface in a liquid state. Instead, water on Mars is found below the surface of the polar regions as water-ice and also as seasonal briny water flows down hillsides and crater walls.
Despite Mars' thin atmosphere, the Red Planet still exhibits a dynamic climate and extreme weather events including impressive dust storms and even snow! But Mars hasn't always been this way. NASA's MAVEN mission scientists reported that Mars once had a thick atmosphere (opens in new tab) that could have supported surface liquid water on the surface for extended periods of time.
Mars atmosphere composition
According to ESA (opens in new tab), Mars' atmosphere is composed of 95.32% carbon dioxide, 2.7% nitrogen, 1.6% argon and 0.13% oxygen. The atmospheric pressure at the surface is 6.35 mbar which is over 100 times less Earth's. Humans therefore cannot breathe Martian air.
For crewed Mars exploration efforts, we need to find a way to generate oxygen from the thin, carbon dioxide atmosphere and an experiment carried out on NASA's Perseverance rover has demonstrated it is possible. On Apr. 20, 2021, the rover used its MOXIE (short for "Mars Oxygen In-Situ Resource Utilization Experiment") to successfully convert carbon dioxide to oxygen on Mars. "MOXIE has more work to do, but the results from this technology demonstration are full of promise as we move toward our goal of one day seeing humans on Mars." Jim Reuter, associate administrator of NASA's Space Technology Mission Directorate, said in a statement (opens in new tab).
Martian climate and weather(opens in new tab)
Early in its history Mars had a thick enough atmosphere for water to run on its surface. According to NASA, some surface features suggest that Mars experienced huge floods about 3.5 billion years ago.
Orbital pictures show vast river plains and possible ocean boundaries, while several Mars rovers have found evidence of water-soaked rocks on the surface (such as hematite or clay). However, for reasons that are still poorly understood, the Martian atmosphere thinned.
Mars is much colder than Earth due to the thin atmosphere and the fact it is farther from the sun. The average temperature on Mars is about minus 80 degrees Fahrenheit (minus 60 degrees Celsius), although it can vary from minus 195 F (minus 125 C) near the poles during the winter to as much as a comfortable 70 F (20 C) at midday near the equator.
Like Earth, Mars has four seasons but due to the Red Planet's eccentric orbit, the length of each season varies more than on Earth, according to NASA science (opens in new tab).(opens in new tab)
|Season (Northern Hemisphere)||Length of Martian season (sols)||Length of Earth season (days)|
Mars' ice caps — made of water ice and carbon dioxide, shrink and grow in response to the seasons. These seasonal changes to the ice caps affect Mars' atmosphere, which responds as one large interconnected system, according to a statement from ESA. "The lower and middle levels of Mars' atmosphere appear to be coupled to the upper levels: there's a clear link between them throughout the martian year," says Beatriz Sánchez-Cano, a planetary scientist at the University of Leicester, UK.
"Each winter, up to a third of the mass in Mars' atmosphere condenses to form an icy layer at each of the planet's poles. Every spring, some of the mass within these caps sublimates to rejoin the atmosphere, and the caps visibly shrink as a result," ESA stated.
Giant dust devils routinely kick up the oxidized iron dust that covers Mars' surface. Dust is also a permanent part of the atmosphere, with higher amounts of it in the northern fall and winter, and lower amounts in the northern spring and summer. The dust storms of Mars are the largest in the solar system, capable of blanketing the entire planet and lasting for months. These usually take place in the spring or summer.(opens in new tab)
These dust storms can play havoc with Mars exploration missions and can even ground flights (yes Earth isn't the only planet where flights can be delayed due to poor weather!). NASA's Ingenuity Mars helicopter was due to make its 19th flight on the Red Planet on Jan. 5, 2022, when a dust storm near Jazero Crater had other plans.
"Most notable was a sharp drop in air density — about a 7% deviation below what was observed pre-dust storm," Jonathan Bapst and Michael Mischna, of Ingenuity's weather/environment team, said in a statement. "This observed decrease would have put density below the lower threshold of safe flight and would have imparted undue risk to the spacecraft. We also observed the effect of dust in the amount of sunlight absorbed by Ingenuity's solar array, which fell well below normal 'clear sky' levels, a drop of about 18%." Over a month passed until Ingenuity was clear to fly again, finally acing its 19th flight on Feb. 8, 2022.
One theory as to why dust storms can grow so big on Mars starts with airborne dust particles absorbing sunlight, warming the Martian atmosphere in their vicinity. Warm pockets of air flow toward colder regions, generating winds. Strong winds lift more dust off the ground, which in turn heats the atmosphere, raising more wind and kicking up more dust. A 2015 study further suggested that the momentum of Mars — which is affected by other planets — generates planet-circling dust storms when that momentum is at its greatest during the early part of the dust storm season.
At times, it even snows on Mars. The Martian snowflakes, made of carbon dioxide rather than water, are thought to be very small particles that create a fog effect rather than appearing as falling snow. The north and south polar regions of Mars are capped by ice, much of it made from carbon dioxide, not water.
How did Mars lose its atmosphere?
At some point in Mars' history, the Red Planet lost much of its atmosphere, transforming it from a warm wet world to the cold arid plains we see today, said ESA in a statement (opens in new tab)
Mars' atmosphere continues to "leak" out into space but how?
The leading theory is that Mars' light gravity, coupled with its lack of global magnetic field, left the atmosphere vulnerable to pressure from the solar wind, the constant stream of particles coming from the sun. Over millions of years, the sun's pressure stripped the lighter molecules from the atmosphere, thinning it out. This process is being investigated by NASA's MAVEN (Mars Atmosphere and Volatile Evolution) mission. Other researchers hypothesize that perhaps a giant impact by a small body would have stripped the atmosphere away.
If you would like to see where NASA's Maven mission is right now check out their mission page (opens in new tab) with a real-time simulated view of the spacecraft. Interested in terraforming? Check out our article on whether we can terraform Mars to make it more hospitable. Explore the science of becoming "Interplanetary" with this engaging article from Interesting Engineering (opens in new tab).
- Ramstad, Robin, et al. "Global mars‐solar wind coupling and ion escape. (opens in new tab)" Journal of Geophysical Research: Space Physics 122.8 (2017): 8051-8062.
- Sánchez‐Cano, Beatriz, et al. "Spatial, seasonal, and solar cycle variations of the Martian Total Electron Content (TEC): Is the TEC a good tracer for atmospheric cycles? (opens in new tab)." Journal of Geophysical Research: Planets 123.7 (2018): 1746-1759.
- Smith, David E., Maria T. Zuber, and Gregory A. Neumann. "Seasonal variations of snow depth on Mars. (opens in new tab)" Science 294.5549 (2001): 2141-2146.
- Banfield, Don, et al. "The atmosphere of Mars as observed by InSight. (opens in new tab)" Nature Geoscience 13.3 (2020): 190-198.