As Earth’s closest planetary neighbor at an average of 140 million miles away, Mars has stirred human imagination for centuries, from speculations it hosts alien species to whether it could ever become humanity’s refuge from a dying Earth.  

The fourth terrestrial (or rocky) planet from the sun is half the size of Earth, with just a fraction of its atmosphere and two irregular-shaped moons, Phobos and Deimos (Mars 101).

Mars is continuously studied by a fleet of orbiters, landers, and rovers—which once included a minihelicopter—that provide continuous lessons into the planet’s climate, geology, and potential for human habitation (see timeline of exploration). 


Mars formed roughly 4.5 billion years ago when a cloudy nebula of dust and gas collapsed into a swirling disk of material and gave rise to our solar system with the sun at its center.

Over millions of years, smaller clumps of matter beyond the sun smashed together and solidified into the distinct planets we know today: the four inner rocky planets and the outer gas and ice giants. 

Before attaining its current dry desert landscape—which hasn’t changed much for nearly 3 billion years—Mars’ initially dense atmosphere rained down a steaming, world-spanning ocean. 

Over time, its atmosphere thinned, most of its water evaporated, and volcanic activity increased. This era produced the solar system’s tallest volcano, 16-mile-high Olympus Mons, three times the size of Mount Everest. 

Geography and Climate

Mars’ most salient feature, its red color, is the result of a rusted iron-rich surface. When iron is exposed to oxygen, it oxidizes—the fancy term for rusts. 

In what is known as the Martian dichotomy, the red planet’s northern regions are much lower in elevation and feature fewer craters, while the south is much higher and more rugged, suggesting the north's surface formed more recently. 

Mars’ atmosphere is extremely thin—allowing the sun’s strong ultraviolet rays to hit the surface unimpeded—and consists almost entirely of carbon dioxide. It exerts just 1% of the surface pressure of Earth’s atmosphere. The average temperature is roughly -80 degrees Fahrenheit.

Mars rotates on a tilted axis similar to Earth as it revolves around the sun in an oval-shaped orbit, giving rise to hot and cold seasons. During the Southern Hemisphere’s summer, global dust storms can cover the planet for weeks at a time.

The Next Frontier

Both NASA and Elon Musk-owned SpaceX are developing programs to send humans to Mars. Aside from the distance astronauts would travel—roughly 33 million miles when Mars is closest—new fuel-efficient propulsive technologies are needed, as well as safe landing techniques. 

Martian living conditions, while technically habitable, are still extreme. Astronauts would need to harvest subterranean ice deposits for water, compress the atmosphere to grow plants, deploy weather-independent power systems, and construct or maintain a habitat—all while staying sane so far from home. NASA aims to land humans on Mars in the 2030s.

Some theorists speculate humans could "terraform" Mars or make its climate livable for humans using sophisticated technology.

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Relevant articles, podcasts, videos, and more from around the internet — curated and summarized by our team

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Mars has long captured astronomers’ (and the public’s) imagination—the fourth planet from the sun may have once harbored life, may be the first stop in humanity’s expansion from Earth, and has been reached by a number of rovers and probes. With interest in human colonization of the red planet rapidly growing, learn the basics with this fascinating visualization and fact sheet from NASA.

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Launched in 2020, NASA's Perseverance rover landed in Mars' Jezero crater, equipped with a deployable helicopter with the mission of searching for evidence of ancient life. Designed as the successor to the Curiosity rover—and nicknamed “Percy”—the vehicle has covered more than 10 miles, collected dozens of samples, and taken hundreds of images. Explore its path and see a 3D model of the rover here.

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As telescope technology progressed in the 19th-century, astronomers became able to make detailed observations of the surface of objects in our solar system. The dips, valleys, lines crisscrossing Mars in particular captured onlookers imagination, leading some to speculate the seemingly organized features could only have been made by an intelligent civilization, with some school textbooks even speculating what Earth looked like to the Martian population

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NASA's Mars robotic rover Opportunity was launched in 2003 to study the planet's surface, craters, and more. Staying alive for a whopping 57 times longer than the planned mission, “Oppy” traveled across Mars, gathering unprecedented insights into the Red Planet and earning a place in the hearts of the scientists and engineers overseeing the mission. Watch the trailer of the award-winning documentary here.

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Spacecraft have been taking pictures of Mars from space since 1965, when the pioneering probe Mariner 4 became the first to beam back an image to Earth of a planet other than our own. The technology since then has significantly evolved, and the views of the fourth planet from the sun have inspired the public’s imagination. See a collection of Mars taken by various spacecraft over the past few decades.

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While the idea of humans living on Mars has long been the realm of futurists and science fiction, the concept is rapidly becoming a realistic effort. But what happens once we reach the surface? The planet is cold, dry, and the virtually nonexistent atmosphere means solar radiation is constantly raining on the surface. There is one possibility—terraforming, or gradually transforming the atmosphere until it resembles Earth.

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Search and uncover even more interesting information in our vast database of curated Mars resources