Mars: The Main Characteristics of the Red Planet

Why Is Mars So Fascinating?

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 it for billions of years.

The Enigma of Extraterrestrial Life

Mars, nicknamed the red planet, owes its iconic color to iron oxide, commonly known as 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 once harbored life that fuels passions.

A Unique Natural Laboratory

Its past similarities with Earth—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 contain the key to one of humanity's greatest questions: Are we alone in the universe?

A Close Neighbor to Earth

A Distance That Periodically Decreases

Did you know that Mars is the closest planet to Earth after Venus, but the one with the most accessible environment? At just 56 million kilometers during its most favorable oppositions (an event that occurs roughly every 26 months), it is an ideal candidate for robotic space exploration and, perhaps, future human colonization.

A Journey Within Reach of Our Technology

This relative proximity allows missions to be sent there in about six to eight months, a long but feasible journey with current technology. 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.

A Thin and Mysterious Atmosphere

A Pressure Equivalent to 35 km Altitude

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.

An Extreme Climate and Valuable Clues

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 valuable clues: the presence of methane, detected in some areas, whose origin could be geological or... biological. Studying this atmosphere, particularly its continuous escape into space due to the solar wind (studied by the MAVEN mission), is crucial to understanding how Mars transitioned from a potentially habitable world to the cold, arid desert we see today.

A Rhythm Similar to Earth's

A "Sol" of 24h39, an Asset for Future Settlers

On Mars, a day (called a "sol") lasts 24 hours and 39 minutes, just slightly longer than on Earth. This circadian rhythm, close to ours, is a considerable advantage for human adaptation. A Martian year, on the other hand, equals 687 Earth days, as its orbit is farther from the Sun.

Marked but Unequal Seasons

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 polar ice caps, which retreat and advance throughout the Martian year.

Two Mysterious Moons

Phobos and Deimos: Captured Asteroids?

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 asteroids from the main belt, captured by Mars' gravity billions of years ago. But their exact origin remains a fascinating subject of study.

Phobos, a Doomed Moon

Phobos, the larger and closer of the two, 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 drawing 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.

Amazing Landscapes

Olympus Mons: The Roof of the Solar System

Olympus Mons: the largest volcano (and the highest known mountain) in the Solar System, standing at 22 kilometers tall, 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 lack of plate tectonics on Mars: the hotspot remained fixed, accumulating lava over hundreds of millions of years.

Valles Marineris: A Canyon of Continental Proportions

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, likely formed by the uplift of the Tharsis volcanic region, pales in comparison to Earth's Grand Canyon. Its steep walls reveal kilometers of Martian geological history, and its secondary valleys may have been carved by water and ice.

Traces of Water: A Past Conducive to Life?

Rivers, Lakes, and Deltas: Evidence of a Wet Past

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 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.

The Hypothesis of a Northern Ocean

More than 3.5 billion years ago, Mars likely had a northern ocean covering much of its northern hemisphere. This water, which shaped the landscapes, makes the hypothesis of past (microbial) life entirely plausible. Today, water persists mainly as ice in the polar caps and underground, 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.

N.B.: Olympus Mons is a shield volcano, formed by fluid lava flows over millions of years, giving it its wide and gently sloping shape. Its summit overlooks a plateau 25 kilometers high, offering a unique spectacle in our Solar System. Its slopes, deceptively gentle, hide cliffs and lava tunnels. Learn more about Martian volcanoes.

The Exploration of Mars: A Human Adventure

From First Flybys to Landers

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 Martian soil.

The Current Robotic Fleet

Today, exploration is carried out by a fleet of sophisticated spacecraft: orbiters like Mars Express (ESA), which map the surface in high resolution, and especially rovers like the Chinese Zhurong or the American Perseverance. The latter, accompanied by the small Ingenuity helicopter (the first powered flight on another planet), had the mission to collect rock samples, but its mission ended after damage to its rotors during a landing.

Polar Ice Caps in Constant Motion

Water Ice and Dry Ice

At Mars' poles lie vast ice caps, composed of a mixture of water ice and dry ice (frozen CO₂). Unlike Earth's ice caps, they change significantly with the seasons: in winter, atmospheric CO₂ condenses and thickens the cap, before sublimating in spring. Today, they represent one of the largest known water reservoirs on the red planet.

Gravity Three Times Weaker

An Advantage and a Challenge for Future Explorers

On the surface of Mars, gravity is only 38% of Earth's. This allows for spectacular jumps but also raises serious physiological questions for future long-term human stays: bone loss, muscle atrophy, and cardiovascular adaptation are among the main challenges identified by space agencies.

A Planet Without a Magnetic Shield

An Atmosphere at the Mercy of the Solar Wind

Mars lost its global magnetic field about 4 billion years ago. Deprived of this protective shield, the planet is directly exposed to the solar wind, which gradually strips away atmospheric particles into space—a process now studied by the MAVEN probe and considered one of the major causes of Mars' transformation into a cold, arid desert.

Planet-Wide Dust Storms

When the Entire Planet Disappears Under an Ochre Veil

Mars regularly experiences dust storms, sometimes powerful enough to engulf the entire planet for several weeks. These events, unique in their scale in the Solar System, can drastically reduce solar brightness on the surface, as experienced by the Opportunity rover, which was taken out of service by a global storm in 2018.