Mars, nicknamed the red planet, owes its iconic color to iron oxide, commonly called rust, which covers its surface and dust dunes. This world, both close and mysterious, has captured the attention of scientists and dreamers since humanity first looked up at the sky. But beyond its characteristic hue, it is its potential to have harbored life that fuels passions.
Past similarities with Earth—presence of liquid water, volcanic activity, seasonal cycles—make it a unique natural laboratory for understanding the evolution of planets and the emergence of life. Every new image, every piece of data sent back by rovers like Perseverance or Curiosity is scrutinized, as it could hold the key to one of humanity's greatest questions: are we alone in the universe?
Did you know that Mars is the closest planet to Earth after Venus, but the one with the most accessible environment? At only 56 million kilometers during its most favorable oppositions (an event that occurs about every 26 months), it is an ideal candidate for robotic space exploration and, why not, future human colonization.
This relative proximity allows missions to be sent there in about six to eight months, a long but feasible journey with current technologies. It is this distance, combined with a day length similar to ours and the presence of resources like water ice, that makes Mars the most realistic option for human expansion beyond Earth.
Mars' atmosphere is 100 times less dense than Earth's, with a surface pressure equivalent to that found at about 35 km altitude in our atmosphere. This thin gaseous layer, composed of 95% carbon dioxide (with traces of nitrogen and argon), makes life as we know it impossible without protection.
It is unable to retain heat (negligible greenhouse effect), which explains the extreme temperature variations, and offers no protection against ultraviolet and cosmic radiation. Yet, it holds precious clues: the presence of methane, detected in places, whose origin could be geological or... biological. The study of this atmosphere, especially its continuous escape into space under the effect of the solar wind (studied by the MAVEN mission), is crucial to understanding how Mars went from a potentially habitable world to the cold, arid desert we see today.
On Mars, a day (called a "sol") lasts 24 hours and 39 minutes, just a little longer than here. This circadian rhythm close to ours is a considerable advantage for human adaptation. A Martian year, on the other hand, is equivalent to 687 Earth days, because its orbit is further from the Sun.
Thanks to the tilt of its axis (about 25 degrees, very close to Earth's 23.4 degrees), Mars also experiences marked seasons, just like our planet! However, due to Mars' more elliptical orbit, these seasons are of unequal length: the northern winter is shorter and milder than the southern winter. These seasonal climatic variations cause spectacular phenomena such as the formation of ice clouds, giant dust storms, and the sublimation of the polar caps, which recede and advance over the Martian year.
Phobos ("Fear") and Deimos ("Terror"), Mars' two small moons, are quite modest compared to our Moon. Irregular in shape, they resemble dark, cratered asteroids. The dominant theory is that they are ancient main belt asteroids, captured by Martian gravity billions of years ago. But their exact origin remains a fascinating subject of study.
Phobos, the largest and closest, orbits Mars in just 7.6 hours, faster than the planet's own rotation! Seen from the surface, it rises in the west and sets in the east. Above all, Phobos is doomed: tidal forces are inexorably bringing it closer to Mars. In a few tens of millions of years, it will either crash into the surface or (more likely) break apart to form a ring of debris around the red planet.
Olympus Mons: the largest volcano (and the highest known mountain) in the solar system, rising to 22 kilometers in altitude, nearly three times the height of Everest. Its summit caldera, 80 km wide, testifies to the immense magma chambers that fed it. Its gigantic size is explained by the absence of plate tectonics on Mars: the hotspot remained fixed, accumulating lava for hundreds of millions of years.
Valles Marineris: a colossal canyon 4,000 kilometers long (the width of the United States), up to 200 km wide and 7 kilometers deep. This fault system, probably formed by the uplift of the Tharsis volcanic region, pales in comparison to the terrestrial Grand Canyon. Its steep walls reveal kilometers of Martian geological history, and its secondary valleys may have been carved by water and ice.
Space missions, from orbiters like Mars Reconnaissance Orbiter to rovers like Curiosity and Perseverance, have revealed undeniable and abundant evidence: Mars once hosted liquid water for extended periods. Today, we observe dried-up riverbeds, sedimentary deltas (such as the one in Jezero Crater explored by Perseverance), and hydrated minerals (clays, sulfates) that can only form in the presence of water.
More than 3.5 billion years ago, Mars probably had a northern ocean covering much of its northern hemisphere. This water, which shaped the landscapes, makes the hypothesis of past (microbial) life quite plausible. Today, water mainly persists as ice in the polar caps and subsurface, and potentially as very salty liquid brines at certain depths. The current quest of the rovers is precisely to find signatures of ancient life in these once favorable environments.
Did you know? Olympus Mons is a shield volcano, formed by fluid lava flows over millions of years, giving it this broad, gently sloping shape. Its summit overlooks a plateau 25 kilometers high, offering a unique spectacle in our solar system. Its deceptively smooth flanks hide cliffs and lava tunnels. Learn more about Martian volcanoes.
The history of Mars exploration is marked by successes and failures. Since the first successful flybys by Mariner 4 in 1965, humanity has sent dozens of missions to the red planet. The 1970s marked a turning point with the Viking landers, the first to directly search for signs of life in the Martian soil.
Today, exploration is carried out by a fleet of sophisticated spacecraft: orbiters like Mars Express (ESA) that map the surface in high resolution, and especially rovers like the Chinese Zhurong or the American Perseverance. The latter, accompanied by the small helicopter Ingenuity (the first powered flight on another planet), has the mission to collect rock samples.
The ultimate, ambitious goal is to bring them back to Earth through the Mars Sample Return mission, a joint NASA-ESA program that would allow these materials to be analyzed with instruments too heavy and complex to be sent to Mars. This is undoubtedly the next big step in our understanding of the planet and its past biological potential.
N.B.: The official definition of a planet (since 2006) requires that it orbits the Sun, has a spherical shape due to its own gravity, and has "cleared" its orbit. Mars, of course, meets these criteria brilliantly, dominating its spatial region without sharing for billions of years.
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