- Grandest canyon
- Tallest mountain
- Dust devils
- Polygonal patterns
- Global storms
- Near horizon
- Real estate
- Dry ice
- Slow leak
- Slow pitch
- Water of life
- Dune planet
- Sunset blues
- Noctilucent clouds
- Sons of war
- Phobos’s fate
- Mission impossible
- Martian meteorites
With the recent arrival of NASA’s Perseverance rover on Mars, all eyes have turned to the fourth planet from the sun. Our understanding of Mars’s past and present has been revolutionized over the past 50 years, and multiple missions this decade will yield new discoveries and perhaps pave the way for human exploration. Here is a look at the endlessly fascinating red planet.
Mars is both smaller and less dense than Earth, which means it has just over one-third of Earth’s gravity. The low gravity, which affects everything from the size of its volcanoes to the shapes of its dunes (like on this photo), will also have serious implications for future colonists—including whether or not we can successfully reproduce in a low-gravity environment.
Mars may be slightly smaller than Earth, but its tourist attractions put Earth’s to shame. A massive gash across the red planet’s face—the Valles Marineris—runs four times longer, five times deeper and 20 times wider than the Grand Canyon.
Mars is home to the solar system’s tallest peak, the Olympus Mons volcano—three times taller than Mount Everest and wide enough to cover most of the state of Arizona. The volcano’s size owes partly to the lighter gravity on Mars, which permits such a massive shape to rise (where Earth’s gravity would have caused it to sink into the crust). The other reason is that Mars has no plate tectonics, which allowed for very long-lasting eruptions.
Dust devils are ubiquitous on the red planet, and their impact on the Martian surface and atmosphere has been closely studied. The ephemeral whirlwinds lift away the brighter surface dust to reveal heavier, darker material beneath, leaving behind stunning patterns.
Mars is covered in pretty patterns. Polygons crop up in mysterious dune fields that could contain clues to Mars’s climate past, and in the freeze-thaw fracturing of lowland terrains, similar to patterns seen in Earth’s polar regions during the summer thaw. Giant polygons—measuring up to 20 kilometres (12 miles) across—could also be evidence of past oceans on Mars’s surface.
Dust storms on Mars are unparalleled in the solar system. They can rage across the entire planet and last for months at a time, though with just 1% of Earth’s atmospheric pressure, their winds are just half that of hurricanes on Earth. One such global dust storm deprived NASA’s 15-year-old rover Opportunity of the sunlight needed to recharge its batteries, ending its legendary mission in 2018.
Mars is a much smaller planet than ours—just about half the size of Earth—and this means the horizon at eye level on Mars is about 27% closer. Even standing at the outer edge of Olympus Mons, the tallest mountain in the solar system, you wouldn’t be able to see beyond its summit.
Mars and Earth have roughly the same landmass. Even though Mars is only about half the size of Earth, it’s all land—on Earth, the oceans cover 71% of the surface, leaving about the same area of dry land as on Mars.
Mars’s thin atmosphere is made mostly of carbon dioxide, which precipitates out as frost and ice in colder regions. This dry ice is an artful force in shaping the Martian terrain. As temperatures warm, frozen carbon dioxide sublimates—going straight from ice to gas—in an explosive fashion, speckling the landscape. Slabs of frozen CO2 are also believed to be responsible for carving out gullies that would be the work of flowing liquid here on Earth.
Mars may once have had an atmosphere as thick as Earth’s, enough to support flowing water. Without a magnetic field to shield it from the solar wind, and sufficient gravity to hold it down, however, Mars’s once-bountiful atmosphere was stripped by the sun’s radiation and slowly leaked into space.
Sound travels slower on Mars. The thinner atmosphere can still transmit vibrations, but much more quietly and only at about two-thirds the speed of sound on Earth. Only low-frequency noises can travel very far, as CO2 in the air tends to absorb higher-pitched sounds; a bird would need to perch on your shoulder to have its chirps heard in those conditions. NASA’s instruments have recorded audio of Mars’s internal rumblings as well as the Perseverance rover’s early moments on the red planet’s surface. (On this photo: NASA’s Mars Perseverance rover.)
Water of life
Evidence of liquid surface water on Mars has been steadily accumulating. The orbiting Mars Express radar found signs of an ancient, planet-wide groundwater system and recently discovered one of these subterranean lakes still contains water. The findings have exciting implications for the potential of life on ancient Mars and whether life may still exist in underground reservoirs.
Mars is home to some of the most spectacular dune fields in the solar system (as well as the tallest). Despite the thin atmosphere, Martian dunes have slowly piled up into richly varied, mesmerizing forms (like on this photo.) Many of these dune fields are visited by subtle changes over time, while some have remained virtually unchanged for a billion years, giving a priceless insight into Mars’s distant past.
On Mars, the sun sets blue. It’s an inversion of Earth’s sky colours—the ruddy daytime Martian skies turn blue only at sunrise and sunset. This is because of the fine dust suspended in the atmosphere: the particles are just the right size to let more blue wavelengths through, whereas the gas molecules in Earth’s atmosphere tend to scatter blue light, giving us red-yellow sunsets.
Clouds shine at night on Mars. Noctilucent clouds, as they are known—literally “night-shining”—are located so high in the atmosphere they can still catch the sun’s light at night. The same phenomenon can occasionally be seen on Earth.
Sons of war
Just as Mars is named for the Roman god of war, its two moons were named after the sons of the Greek god of war, Ares. The twins were the personification of fright and flight: Phobos represented panic, flight and rout, while Deimos represented terror and dread. The Japan Aerospace Exploration Agency (JAXA) is planning a round-trip mission to the Martian moons to bring back samples that may shed light on their origins and available resources as potential waystations.
Phobos, the larger of Mars’s two moons, orbits the planet more closely than any other known moon, and it is gradually spiralling in closer. Scientists estimate that within 50 million years, the satellite will either crash into Mars, or break up in fragments to form a ring around Mars.
The first lander to successfully touch down on the surface of the red planet was NASA’s Viking 1 in 1976. Since then, an additional 10 landers, seven rovers and one helicopter have made it to the planet’s surface (not all of them in one piece, admittedly). China’s Tianwen-1 rover and lander, and the joint Euro-Russian ExoMars Rosalind Franklin rover and Kazachok surface platform, are set to arrive in 2021 and 2023, respectively, bringing the robot population—both operational and defunct—on the surface of Mars to a whopping 23.
Many of the nearly 50 missions to Mars have ended in failure—before the year 2000, the odds of getting a probe to Mars in a functional state was about one in three. The Martian landscape still bears the remnants of a few of these doomed missions. One of the most infamous was the Mars Climate Orbiter, which burned up in the Martian atmosphere in 1999 when a failure to convert navigational commands to metric went undetected. (On this photo: a Boeing Delta II expendable launch vehicle lifts off with NASA’s Mars Polar Lander on December 11, 1998.)
Mars sent emissaries to Earth long before we sent our probes to Mars. As the red planet has been pummelled by asteroids through the aeons, debris from larger impacts has made its way to Earth in the form of meteorites. At least 252 pieces of Mars have been discovered on Earth. Many are in the hands of private dealers, valued at nearly US$1,000 per gram.