The Solar System:
Weather, climate, and the atmosphere
The rotation axis tilt of Mars (25 deg) is similar to that of Earth (23 deg), so Mars has seasons.
Mars orbits at 1.5 AU – so it only gets about 45% of Earth’s solar energy.
Mars' thin atmosphere and sandy soil do not store much heat.
Surface temperature on Mars:
Average = −63 °C (−82 °F)
Winter low at poles = −143 °C (−225 °F)
coldest temperature on Earth = about -90 °C (−130 °F) [Antarctica]
Summer high at equator = 35 °C (95 °F)
warmest temperature on Earth = 54 °C (129 °F) [Death Valley, CA]
Atmospheric composition of Mars (from left to right: carbon dioxide, argon, molecular nitrogen, molecular oxygen, carbon monoxide). Even though Mars’ atmosphere is almost completely composed of a strong greenhouse gas, it is too thin to keep Mars warm. The atmosphere of Mars is about 100 times less dense than Earth’s atmosphere, giving a pressure of only 0.6% that of Earth's atmosphere at sea level. There is too little pressure and oxygen in Mars' atmosphere support human life.Credit: Melikamp (Wikimedia Commons), CC BY SA 3.0 [link]; based on public domain data from NASA/JPL-Caltech, SAM/GSFC [link]
Dust storms on Mars
In June 2018, NASA's Curiosity Rover used its Mast Camera to snap photos of the intensifying haziness on the surface of Mars, caused by a massive dust storm. The rover is parked inside Gale Crater looking out to the crater rim. The photos span a couple of weeks, starting with a shot of the area before the storm appeared.
Two 2001 images from the Mars Orbiter Camera on NASA's Mars Global Surveyor orbiter show a dramatic change in the planet's appearance when haze raised by dust-storm activity in the south became globally distributed.
At left, an image from late June 2001 shows clear conditions over much of the planet, with regional dust-storm activity occurring in the Hellas basin (bright oval feature) near the edge of the south polar cap.
At right, a July 2001 image from the same perspective shows the planet almost completely enveloped. Dust extends to altitudes of more than 60 kilometers (37 miles) during global-scale storms. The clearing phase can last for several months.Credit (image and some text): NASA/JPL-Caltech/MSSS [link]
Fanciful depictions of an unrealistically ferocious Martian dust storm from the movie The Martian (2015).Credit: The Martian (2015) [link]
The winds in a Martian dust storm blow as fast as the winds of a Category 1 hurricane (average wind speed 74-95 mph). On Earth, that’s enough to knock a person over. But on Mars it would feel like a light breeze.
Warning: mild spoilers for the 2015 movie “The Martian”
Read This! The Fact and Fiction of Martian Dust Storms
Warning: mild spoilers for the 2015 movie “The Martian”
Effect of wind on the sand under Curiosity while it was parked for a day. The pair of images in this animation shows effects of one Martian day of wind blowing sand underneath NASA's Curiosity Mars rover on a non-driving day for the rover. Each of the two images was obtained just after sundown a day apart in January 2017 by the rover's downward-looking Mars Descent Imager (MARDI). The area of ground shown in the images spans about 3 feet (about 1 meter) left-to-right.
Self-portrait of the Opportunity rover with dust-covered solar panels in January 2014.Credit: NASA/JPL-Caltech/Cornell University/Arizona State University [link]
Self-portrait of the Opportunity rover in March 2014, after wind had cleaned most of the dust off the solar panels.Credit: NASA/JPL-Caltech/Cornell University/Arizona State University [link]
A dust devil spins across the surface of Gusev Crater just before noon on Mars. NASA's Spirit rover took the series of images in this 21-frame animation with its navigation camera on the rover's martian day, or sol, 486 (15 May 2005). The event occurred during a period of 9 minutes and 35 seconds, with the dust devil's progressing in a northeasterly direction about 1.0 kilometer (0.62 mile) away from Spirit. The whirlwind was traveling at about 4.8 meters per second (16 feet per second) and covered a distance of about 1.6 kilometers (1 mile). Contrast has been enhanced for anything in the images that changes from frame to frame, that is, for the dust devil. The dust devil is about 34 meters (112 feet) in diameter.Credit (image and some text): NASA/JPL [link]
A towering dust devil casts a serpentine shadow over the Martian surface in this image acquired by the High Resolution Imaging Science Experiment (HiRISE) camera on NASA's Mars Reconnaissance Orbiter. The devil is 800 meters in height and 30 meters wide. The scene is a late-spring afternoon in the Amazonis Planitia region of northern Mars. The view covers an area about four-tenths of a mile (644 meters) across. North is toward the top.Credit (image and some text): NASA/JPL-Caltech/University of Arizona) [link]
Dust storm with water ice clouds (2009). This image shows a turbulent mass of thick, roiling, red Martian dust rising from a network of canyons and flowing diagonally toward the lower left corner of the frame. Above the storm front, wispy, white clouds of water ice are present.Credit (image and some text): NASA/JPL-Caltech [link]
Clouds and sand on the horizon of Mars. If you could stand on the surface of Mars, what might you see? Like the robotic Opportunity rover that obtained this panoramic image, you might well see vast plains of red sand, an orange tinted sky, and wispy light clouds.
Unlike other Martian vistas, few rocks are visible in this exaggerated color image mosaic. The distant red horizon is so flat and featureless that it appears similar to the horizon toward a calm ocean on Earth. Clouds on Mars can be composed of either carbon dioxide ice or water ice, and can move quickly, like clouds move on Earth. The red dust in the Martian air can change the sky color above Mars from a blueish tint, like on Earth, to a more reddish hue, with the exact color depending on the density and size of the floating dust particles.Credit: Mars Exploration Rover Mission, Cornell, JPL, NASA; image processing: M. Howard, T. Öner, D, Bouic & M. Di Lorenzo for unmannedspaceflight.com; Astronomy Picture of the Day on 2006 Oct 17 (adapted text) [link]
How did Mars lose (most of) its atmosphere?
Low planet mass = Less gravity to hold atmosphere
Core cooled quickly + possible giant impact = No magnetic field to protect atmosphere from solar wind
Earth density atmosphere was stripped away more than 4 billion years ago
After that, Mars' surface water evaporated, and the atmospheric water vapor was subsequently lost due to photodissociation (i.e., UV light from the Sun breaks down water molecules in the upper atmosphere into hydrogen and oxygen atoms, which are then stripped away by the solar wind)
Thin atmosphere = Cold surface temperatures, remaining “free” water frozen
Loss of atmosphere and surface water, plus locking remaining water in ice and rocks leads to...
Reverse Greenhouse Effect or “Runaway Refrigerator”
In this artist’s concept, the solar wind interacts with Mars’ upper atmosphere, but is deflected past Earth by a global magnetic field.Credit (image and some text): NASA/GSF [link]
Mars' atmosphere loss is still ongoing. This figure shows three views of the escaping atmosphere, obtained by MAVEN's Imaging Ultraviolet Spectrograph, are shown here. By observing all of the products of water and carbon dioxide breakdown, MAVEN's remote sensing team can characterize the processes that drive atmospheric loss on Mars. These processes may have transformed the planet from an early Earthlike climate to the cold and dry climate of today. MAVEN is NASA's Mars Atmosphere and Volatile Evolution (MAVEN) spacecraft.Credit: NASA/University of Colorado [link]
Seasons and the polar ice caps on Mars
North pole winter
South pole summer
North pole summer
South pole winter
These images show the polar ice caps of Mars during different seasons. Just like on Earth, when it is summer at the north pole, it is winter at the south pole, and vice-versa.Credit: NASA/JPL/MSSS [link]
The polar ice caps of Mars contain a mix of water and CO2 (carbon dioxide) ices.
The water (mostly) stays frozen all the time.
The CO2 freezes out of the thin atmosphere of Mars - about 1/3 of the atmosphere is frozen in winter/summer vs. spring/fall
This detailed image of the south polar ice cap of Mars was obtained by ESA’s Mars Express, which has been exploring and imaging the martian surface and atmosphere since 2003. We may be used to seeing numerous images of red and brown-hued soil and ruddy landscapes peppered with craters, but the Red Planet isn’t always so red.
The bright white region of this image shows the icy cap that covers Mars’ south pole, composed of frozen water and carbon dioxide. While it looks smooth in this image, it is actually a layered mix of peaks, troughs and flat plains. The southern cap reaches 3 km thick in places, and is around 350 km in diameter. This icy region is permanent; in the martian winter another, thinner ice cap forms over the top of it, stretching further out across the planet and disappearing again when the weather warms up.Credit (image and some text): ESA/DLR/FU Berlin/Bill Dunford [link]