Mars, the fourth planet from the Sun, has long captured the human imagination. Its reddish glow has inspired countless stories and scientific inquiries. As the most explored planet beyond Earth, a wealth of data has been gathered, revealing a dynamic and varied celestial body.
The Red Planet’s Immense Landscape
The Martian surface features geological formations of staggering scale, far exceeding anything observed on Earth. Towering over the plains is Olympus Mons, the largest volcano. This volcano is approximately 22 kilometers (13.6 miles) high, making it nearly three times taller than Mount Everest above sea level. Its base stretches across an area roughly the size of the state of Arizona.
Stretching a distance comparable to the width of the United States is Valles Marineris, an immense canyon system. This network extends over 4,000 kilometers (2,500 miles) long, reaching depths of up to 7 kilometers (4 miles) in some places. By comparison, Earth’s Grand Canyon is only about 446 kilometers (277 miles) long. The vast size of the canyon is thought to be the result of a massive crack in the Martian crust, possibly caused by tectonic stresses from the nearby Tharsis region.
Despite its smaller size, Mars has a surface area nearly equivalent to the total dry land area of Earth. Although Mars is only about half the diameter of Earth, the lack of extensive oceans means its available solid surface territory is comparable to all the continents on our planet combined.
At the planet’s poles are ice caps that expand and contract with the changing Martian seasons. These polar caps are composed of two distinct materials: seasonal layers of frozen carbon dioxide (dry ice), and substantial permanent deposits of water ice beneath. The seasonal caps of dry ice can cause up to a third of the thin Martian atmosphere to freeze out and then sublimate back into the air annually.
Time, Weather, and the Martian Sky
A Martian day, referred to as a “sol,” is only slightly longer than an Earth day, at 24 hours and 39 minutes. This near-match in rotation period simplifies the scheduling and operation of robotic landers and rovers.
The length of a Martian year is significantly different from our own due to its slower orbit around the Sun. It takes Mars approximately 687 Earth days to complete one revolution, which equates to about 668.6 sols. This longer orbit means that seasons on Mars last nearly twice as long as they do on Earth.
Perhaps one of the most unexpected atmospheric phenomena is the appearance of blue sunsets on Mars. While the daytime sky appears a butterscotch color due to fine dust particles scattering red light, the effect reverses at sunset. As the Sun dips below the horizon, the dust particles scatter blue light more efficiently into the area immediately around the solar disk. This causes the area around the setting Sun to glow with a distinctive blue hue before fading into the reddish-grey sky.
Unique Physics and Companion Moons
The gravitational pull on Mars is considerably weaker than on Earth. Surface gravity on Mars is approximately 38% of Earth’s gravity. This means a person standing on Mars would feel less than half their Earth weight, allowing them to jump significantly higher. The lower gravity also contributes to the immense size of features like Olympus Mons, as it places less stress on the planet’s crust.
The planet’s characteristic reddish appearance is caused by iron minerals that have oxidized, or rusted, over billions of years. The surface is covered in dust rich in these iron minerals. This iron oxide dust is suspended in the atmosphere and coats the surface, giving the entire planet its recognizable ruddy color.
Mars is orbited by two small satellites named Phobos and Deimos. These moons are tiny compared to Earth’s Moon. Phobos, the larger and innermost of the two, orbits remarkably close to Mars, completing an orbit in just 7 hours and 39 minutes. Its orbit is so low that it is gradually spiraling inward, and in about 50 million years, it is expected to either crash into Mars or break apart to form a planetary ring.