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Mars
Mars is the fourth planet from the Sun, a name that has echoed through human history for millennia, yet its true nature remained a mystery until the twentieth century. Ancient astronomers, from the Sumerians who named it Nergal, the god of war and plague, to the Babylonians who tracked its 79-year cycle, saw it as a wandering star of judgment. By 1534 BCE, Egyptian astronomers had already noted its retrograde motion, a backward loop in the sky that puzzled observers for centuries. The planet's distinctive orange-red hue, caused by iron(III) oxide dust, gave it a menacing appearance that fueled myths of war and destruction, a theme that persists in its modern symbol, a circle with a spear pointing to the upper right. Despite its visual dominance in the night sky, Mars is a desert world, a rocky sphere with an atmosphere so thin that its surface pressure is only 0.6% of Earth's, making it a place where liquid water cannot persist for long. The planet's surface gravity is roughly a third of Earth's, and its diameter, at 6,779 kilometers, is about half that of our own world, yet its surface area is equal to all the dry land on Earth. This vast, barren landscape is a testament to a violent past, scarred by impacts and shaped by forces that continue to mold its geology today.
A Violent Youth
Mars formed approximately 4.5 billion years ago, emerging from the random accretion of material in the protoplanetary disk that orbited the Sun. Its early history was marked by the Late Heavy Bombardment, a period of intense meteorite impacts that left 60% of the planet's surface scarred. One of the most significant events in this era was a collision with a Pluto-sized body, an impact so massive it created the Borealis basin, which covers 40% of the planet and is responsible for the Martian hemispheric dichotomy. This event flattened the northern hemisphere into low-lying plains while leaving the southern hemisphere as a rugged, cratered highland. The impact also likely stripped away Mars's magnetosphere, leaving the planet vulnerable to the solar wind and causing the loss of its atmosphere over billions of years. Evidence suggests that Mars may have once had a ring system 3.5 to 4 billion years ago, formed from a moon 20 times more massive than Phobos, which was later destroyed, leaving Phobos and Deimos as remnants. The planet's geological history is divided into three periods: the Noachian, Hesperian, and Amazonian, each marked by distinct volcanic and hydrological activity that shaped the landscape we see today.
Mountains and Canyons
The surface of Mars is dominated by colossal geological features that dwarf anything on Earth. Olympus Mons, the tallest volcano in the Solar System, rises over 21 kilometers above the surrounding plains, making it roughly three times the height of Mount Everest. This shield volcano, along with the Tharsis bulge, a vast volcanic upland, was formed during the Amazonian period, a time of extensive lava flows that continue to shape the planet's geology. In contrast, Valles Marineris, a canyon system stretching 4,000 kilometers, cuts across one-fifth of the planet's circumference, far exceeding the length of the Grand Canyon. This massive rift was formed by the swelling of the Tharsis region, which caused the crust to collapse and fracture. The planet's interior is equally complex, with a core that is at least partially molten and enriched with light elements like sulfur and oxygen. Seismic activity, known as marsquakes, has been detected by the InSight lander, with over 450 events recorded as of 2019, indicating that Mars is still geologically active. The planet's crust varies in thickness, ranging from 20 kilometers in Isidis Planitia to 70 kilometers in the southern Tharsis plateau, a stark contrast to Earth's average crustal thickness of 27.3 kilometers.
Mars is the fourth planet from the Sun and a desert world with a rocky sphere surface. Its diameter measures 6,779 kilometers and its surface area equals all dry land on Earth.
When did Mars form and what was the Late Heavy Bombardment?
Mars formed approximately 4.5 billion years ago from the random accretion of material in the protoplanetary disk. The Late Heavy Bombardment was a period of intense meteorite impacts that left 60% of the planet's surface scarred.
What are the largest geological features on Mars?
Mars features Olympus Mons, the tallest volcano in the Solar System rising over 21 kilometers above the surrounding plains. Valles Marineris is a canyon system stretching 4,000 kilometers that cuts across one-fifth of the planet's circumference.
Did Mars ever have liquid water and where is it now?
Evidence suggests liquid water flowed across Mars billions of years ago before becoming mostly locked in ice. The polar ice caps hold enough water to cover the entire planet to a depth of 35 meters and subsurface ice exists in regions like Utopia Planitia.
What is the composition of the atmosphere on Mars?
The atmosphere of Mars is a thin veil of carbon dioxide making up 96% of its composition. Surface pressure measures only 6 millibars and the sky often appears pink or butterscotch due to suspended iron oxide particles.
When did human exploration of Mars begin and what are current missions?
Human exploration of Mars began in earnest in the 20th century with the first successful flyby by Mariner 4 in 1965. Current missions include the Curiosity and Perseverance rovers which have uncovered evidence of past water activity and potential biosignatures.
Mars holds a complex relationship with water, a substance that was once abundant on its surface but is now mostly locked in ice. Evidence from orbiters and rovers suggests that liquid water flowed across the planet billions of years ago, carving outoutflow channels and valley networks that are still visible today. The mineral jarosite, detected by the Opportunity rover in 2004, forms only in the presence of acidic water, providing strong evidence that Mars once had a wetter climate. More recently, the Curiosity rover found hydrated calcium sulfate in rock samples, indicating that water was present in the planet's subsurface. Despite these findings, liquid water cannot persist on the surface due to the low atmospheric pressure, which is less than 1% of Earth's. The planet's polar ice caps, composed of water ice and carbon dioxide dry ice, hold enough water to cover the entire planet to a depth of 35 meters. Subsurface ice has been detected in regions like Utopia Planitia, with a volume equivalent to Lake Superior, and in the Valles Marineris canyon system. The presence of recurring slope lineae, dark streaks that appear to flow downhill during Martian summers, has sparked debate about whether they are caused by liquid water or dry granular flows. The mystery of Mars's water history continues to drive scientific inquiry, with researchers seeking to understand how the planet transitioned from a potentially habitable world to the cold, dry desert it is today.
The Sky of Dust
The atmosphere of Mars is a thin veil of carbon dioxide, making up 96% of its composition, with trace amounts of argon, nitrogen, and oxygen. This tenuous atmosphere, with a surface pressure of only 6 millibars, is unable to retain heat or protect the surface from cosmic radiation, resulting in extreme temperature fluctuations that range from -125 degrees Celsius to 20 degrees Celsius. The planet's sky, often appearing pink or butterscotch due to suspended iron oxide particles, is frequently obscured by global dust storms that can cover the entire planet and last for months. These storms, which occur when Mars is closest to the Sun, can increase global temperatures and disrupt the operations of rovers and orbiters. Despite the thin atmosphere, sound can travel on Mars, though it is attenuated more than on Earth, with the speed of sound varying between 240 and 250 meters per second depending on frequency. Auroras have been detected on Mars, but unlike Earth's polar auroras, they can encompass the entire planet due to the lack of a global magnetic field. In September 2017, a massive solar storm caused radiation levels on the surface to double, accompanied by an aurora 25 times brighter than any previously observed. The atmosphere's composition and behavior continue to be studied by orbiters like MAVEN, which has detected ionized particles escaping into space, shedding light on the planet's atmospheric loss over billions of years.
The Twin Moons
The exploration of Mars began in earnest in the 20th century, with the first successful flyby conducted by Mariner 4 in 1965, which captured the first images of another planet from deep space. This mission, along with subsequent orbiters and landers, shattered the myth of a habitable Mars, revealing a cold, barren world with no evidence of life. The Viking probes of the mid-1970s carried experiments designed to detect microorganisms, yielding results that remain debated to this day. Since 1997, Mars has been continuously visited by robotic missions, with more than ten probes operating simultaneously at times, more than at any other planet beyond Earth. Current missions include the Curiosity and Perseverance rovers, which have uncovered evidence of past water activity and potential biosignatures, such as the Cheyava Falls rock discovered in 2024. Future missions, including the Rosalind Franklin rover and China's Tianwen-3 sample return mission, aim to further explore the planet's history and search for signs of ancient life. The history of Mars exploration is a testament to human curiosity and technological advancement, with each mission building on the knowledge gained from its predecessors to unravel the secrets of the Red Planet.
Mars has long captured the human imagination, inspiring myths, stories, and dreams of colonization. From H. G. Wells's The War of the Worlds to Ray Bradbury's The Martian Chronicles,
The Age of Exploration
the planet has been a canvas for humanity's hopes and fears. In the 19th century, the discovery of Martian canals, later proven to be optical illusions, fueled speculation about intelligent life and led to the phenomenon known as Mars Fever. Today, the dream of human exploration continues, with plans for crewed missions to Mars in the early 2030s. Private companies like SpaceX, led by Elon Musk, envision a self-sustaining colony on the planet, enabled by the mass production of the Starship launch vehicle. National space agencies, including NASA and CNSA, are developing technologies for in situ resource utilization, which would allow future astronauts to extract water and other resources from the Martian surface. The challenges of human exploration are immense, from the planet's harsh radiation environment to the logistical difficulties of long-duration spaceflight. Despite these obstacles, the dream of Mars remains a powerful symbol of human ambition, driving scientific inquiry and technological innovation. As we look to the future, Mars stands as both a destination and a mirror, reflecting our own hopes and fears about the universe and our place within it.