Mars, often called the Red Planet, has captured human imagination for millennia, standing out as a bright, rust-colored beacon in the night sky. This celestial neighbor, the fourth planet from the Sun, is the most explored world in our solar system aside from Earth, having been visited by dozens of orbiters, landers, and rovers. The ongoing fascination with Mars stems from its surprising geology and dynamic environment, which hints at a warmer, wetter past and presents a possibility for future human exploration. Details about this world are far more complex and unexpected than its simple red facade suggests.
Colossal Geography Mountains Canyons and Ice
The Martian surface hosts geological features of a magnitude unseen anywhere else in the solar system, a result of its unique, mostly static tectonic history. The shield volcano Olympus Mons stands as the largest volcano known, towering approximately 22 kilometers (13.6 miles) above the surrounding plains, nearly three times the height of Mount Everest above sea level. Its base spans about 600 kilometers, roughly the size of the state of Arizona. Its immense size is due to the lack of moving tectonic plates, which allowed the magma plume to build up in one spot over billions of years.
Equally immense is Valles Marineris, an enormous canyon system that stretches over 4,000 kilometers (2,500 miles) long, a distance covering the entire continental United States. This rift is up to 7 kilometers deep in places, dwarfing Earth’s Grand Canyon in both length and depth. The canyon likely formed as the crust fractured and collapsed due to stretching caused by massive volcanic activity in the nearby Tharsis region.
Vast quantities of water exist on Mars, but nearly all of it is locked away as ice, not liquid. The planet’s polar ice caps are primarily made of water ice, though the southern cap is permanently topped with a layer of frozen carbon dioxide (dry ice). Scientists have also detected extensive sheets of water ice buried beneath the surface, particularly at mid-latitudes, representing a substantial reservoir. This subsurface ice suggests water played a significant role in shaping the planet’s history, even though current atmospheric conditions prevent it from flowing freely on the surface.
The Unique Martian Calendar and Sky
The rotation of Mars is similar to Earth’s, but its orbit introduces significant differences to its calendar and seasons. A Martian day, known as a Sol, is just over 24 hours and 37 minutes long, making the daily cycle familiar. However, the Martian year is much longer, lasting 687 Earth days, which is nearly double the time it takes Earth to orbit the Sun.
This extended year means that Martian seasons are proportionally much longer than those on Earth, and the planet’s highly elliptical orbit leads to more extreme seasonal changes. Mars possesses two small, irregularly shaped natural satellites, Phobos and Deimos, which are thought to be captured asteroids. Phobos, the inner moon, orbits Mars three times a day and moves so quickly that from the surface, it appears to rise in the west and set in the east.
Phobos is also slowly spiraling inward and is predicted to be torn apart by Mars’s gravity in tens of millions of years, potentially forming a temporary planetary ring. The appearance of the Martian sky offers a dramatic contrast to Earth, especially at dusk. While the daytime sky on Mars appears a butterscotch color due to fine, reddish iron-oxide dust suspended in the air, the sunsets are distinctly blue. This blue hue occurs because the dust particles scatter red light away from the Sun’s disk, allowing the blue light to be concentrated and visible near the horizon.
Atmospheric Extremes and Global Dust Storms
The Martian atmosphere is extremely thin, possessing less than one percent of the density of Earth’s atmosphere at sea level. It is composed overwhelmingly of carbon dioxide, accounting for about 95% of the total gas. This low pressure and composition mean liquid water cannot remain stable on the surface for long, as it would rapidly boil away or freeze.
The planet experiences vast temperature swings due to the thin atmosphere’s inability to retain heat. Temperatures range from a high of about 20 degrees Celsius (70 degrees Fahrenheit) at the equator during the day to frigid lows of -153 degrees Celsius (-225 degrees Fahrenheit) at the poles. The temperature difference between ground level and an explorer’s head can be significant, highlighting the atmosphere’s poor thermal regulation.
The suspended iron-oxide dust that gives the planet its reddish appearance fuels the most dramatic weather phenomenon: global dust storms. These storms occur roughly every three Martian years and can completely envelop the entire planet, blocking out the Sun for months. These massive events challenge robotic explorers, as they drastically reduce the sunlight available for solar-powered equipment. Even in calm conditions, atmospheric moisture condenses into clouds and frost; the snow that sometimes falls is composed of frozen carbon dioxide particles, rather than water ice.