A History of Mars Space Exploration

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From the Red Dot to the Red Planet

For as long as humans have gazed at the night sky, Mars has captured our imagination. It’s a pale orange point of light, a glowing cinder that moves with a strange, looping grace against the backdrop of fixed stars. To the ancients, its ruddy hue was reminiscent of blood, and so they named it for their gods of war. It was a mythological figure, a divine omen hanging above the world. Over centuries, with the advent of science and technology, that perception has been utterly transformed. Mars has shifted from a symbol in the heavens to a destination, a world in its own right, a place of intense scientific scrutiny and, perhaps, the key to understanding our own origins and future in the cosmos.

The story of Mars exploration is a grand narrative of human curiosity, ingenuity, and fallibility. It’s a journey that began with naked-eye observations from dusty Mesopotamian plains and has led to sophisticated robotic laboratories roving across the planet’s ochre deserts. Our understanding of the Red Planet has never been static; it has swung wildly between extremes, often reflecting the technological and cultural biases of the era. We have imagined it as a verdant world teeming with intelligent life, a frozen and cratered wasteland akin to our Moon, and, as we now know it, a complex and dynamic planet that was once warmer, wetter, and potentially habitable.

This journey of discovery is not just about a distant planet. It’s also a story about us. How we have perceived Mars has consistently mirrored our own state of being—our mythological fears, our industrial ambitions, our Cold War anxieties, and our modern scientific quest to find life beyond Earth. From a simple point of light, it became a world. From a world, it became a puzzle. And from a puzzle, it has become a frontier. This is the history of that transformation, a chronicle of how we turned a red dot in the sky into the Red Planet.

The World Before the Telescope

Long before the invention of lenses and rockets, Mars was a familiar yet enigmatic presence in the night sky. Ancient cultures across the globe were keen observers of the heavens, and Mars, one of the five “wandering stars” visible to the naked eye, stood out. Its distinct reddish color and its unusual movement made it an object of both reverence and meticulous study.

Egyptian astronomers, as early as the 2nd millennium BCE, recorded the planet’s appearances. They were intimately familiar with its most perplexing behavior: apparent retrograde motion. As Earth, on its faster, inner orbit, overtakes Mars, the Red Planet appears to slow down, stop, and move backward across the sky for a few weeks before resuming its normal eastward progression. This celestial dance was documented on ancient star maps, including the ceiling of the tomb of Seti I and the Senenmut star map, one of the oldest known astronomical charts.

In Mesopotamia, Babylonian astronomers took these observations to a new level of mathematical precision. They kept systematic records of planetary positions, and for Mars, they calculated that it completed 37 synodic periods—the time it takes for the planet to return to the same position in the sky relative to the Sun—every 79 years. They developed sophisticated arithmetic methods not just to track but to predict the planet’s future positions, a remarkable achievement of early science.

Chinese records of Mars date back to before 1045 BCE, with astronomers of the Zhou and Qin dynasties maintaining detailed accounts of its movements and conjunctions with other planets. This long tradition of observation was foundational. While early Greek astronomy, influenced by Mesopotamian culture, associated the planet with Ares, their god of war, the detailed study of its motion was not initially a primary focus.

The true significance of these ancient, naked-eye observations would culminate in the 16th century, in the work of the Danish nobleman and astronomer Tycho Brahe. From his observatory on the island of Hven, Brahe conducted a decades-long project to chart the positions of the stars and planets with unprecedented accuracy. His measurements, made without the aid of a telescope, were the most precise the world had ever seen. Mars, with its particularly non-uniform and eccentric orbit, became the ultimate test for the prevailing models of the cosmos.

The dominant model, inherited from the Greek astronomer Ptolemy, placed the Earth at the center of the universe. To explain the strange retrograde motion of planets like Mars, this geocentric system relied on a complex clockwork of circles upon circles, known as epicycles. For centuries, this model worked well enough. But Tycho’s data was so exact that it exposed the flaws in the Ptolemaic system. The predictions simply didn’t match the observed reality of Mars’s path.

After Tycho’s death, his young German assistant, Johannes Kepler, inherited this treasure trove of Martian data. Kepler was a brilliant mathematician and a firm believer in a divinely ordered, harmonious universe. He spent the better part of a decade wrestling with the “problem” of Mars, trying to force Tycho’s observations to fit the perfect circular orbits that were believed to be the only form of celestial motion. He failed. The data for Mars was stubbornly, irreconcilably off.

This failure was the critical turning point. Instead of dismissing the data, Kepler made the courageous leap to question the two-thousand-year-old assumption of circular orbits. He discovered that the path of Mars, and indeed all planets, was not a circle but an ellipse, with the Sun at one focus. This revelation, published in 1609 as his first two laws of planetary motion, shattered the old geocentric model and laid the mathematical foundation for Isaac Newton’s later theory of universal gravitation. Mars, the problem planet whose motion refused to conform, became the key that unlocked the true architecture of the solar system. Its erratic dance, so carefully charted by generations of sky-watchers, had finally led humanity to a new understanding of its place in the universe.

The First Glimpses

The invention of the telescope in the early 17th century marked a profound shift in humanity’s relationship with the cosmos. For the first time, the planets were not just wandering points of light but could be resolved into actual places. The exploration of Mars as a world, rather than an abstract orbit, began in 1610 when the Italian scientist Galileo Galilei turned his new instrument toward the Red Planet.

Galileo’s early telescope was too primitive to reveal any surface details. He could, however, see that Mars was a distinct disk, not a mere point of light like the stars. This simple observation was revolutionary, as it strongly suggested that Mars was a physical body, a world in its own right, much like the Earth. He also noted that Mars appeared to change in size, shrinking after its opposition, and that it exhibited slight phases, though he couldn’t resolve them clearly.

It would take several decades and more powerful telescopes for the first features on this new world to emerge. In 1636, the Italian astronomer Francesco Fontana produced a sketch of Mars, but the markings were indistinct and didn’t correspond to any known features. The first truly recognizable feature was drawn in 1659 by the Dutch astronomer Christiaan Huygens. His sketch clearly showed a large, dark, roughly triangular shape on the planet’s otherwise reddish surface. This feature is now known as Syrtis Major Planum, and it remains one of the most prominent dark regions on Mars.

Huygens’s observation was more than just a drawing. By tracking the movement of Syrtis Major across the face of the planet night after night, he was able to calculate the length of a Martian day. He determined its rotation period to be approximately 24 hours, a figure remarkably close to Earth’s. This discovery was a powerful piece of evidence suggesting that Mars was not just a world, but an Earth-like world.

A few years later, in 1666, the Italian-French astronomer Giovanni Domenico Cassini, working at the Paris Observatory, made further groundbreaking observations. He was the first to definitively identify the brilliant white polar caps. Like Huygens, he used the rotation of surface markings to refine the length of the Martian day, calculating it to be 24 hours and 40 minutes—a value less than three minutes off the modern measurement. In 1672, Huygens followed up by observing a fuzzy white cap at the north pole as well.

These early discoveries in the 17th century began to build a compelling, if perhaps misleading, narrative. Mars had a day length almost identical to our own. It had polar caps, which hinted at the presence of ice or snow. The next major leap in understanding came over a century later with the work of the great British astronomer Sir William Herschel. Beginning in the 1770s, Herschel conducted systematic studies of Mars. He confirmed that the polar caps grew and shrank in size in concert with the Martian year, providing the first strong evidence for seasons on another planet. He correctly inferred that the caps were likely made of ice and snow. In 1781, he measured the planet’s axial tilt and found it to be about 25 degrees, strikingly similar to Earth’s 23.5-degree tilt.

This accumulation of Earth-like characteristics—a similar day, seasons, axial tilt, and polar ice caps—cemented the idea of Mars as a sister world to our own. It was a seductive analogy, a reasonable inference based on the best available data of the time. This view of Mars as Earth’s twin became the dominant scientific and popular paradigm. It created a fertile ground for speculation about the planet’s environment and, inevitably, about the possibility of life.

The year 1877 proved to be a watershed moment for Mars observation. The planet made a particularly close approach to Earth, offering astronomers a spectacular view. It was during this opposition, in August, that the American astronomer Asaph Hall made a historic discovery. Using the powerful 26-inch “Great Equatorial” refractor at the U.S. Naval Observatory in Washington, D.C., Hall was conducting a deliberate search for Martian moons. The search was frustrating, and he was on the verge of giving up. His wife, Angelina Stickney, urged him to continue. The next night, he discovered a tiny moon, and six nights later, he found a second. At the suggestion of an English science instructor, Hall named them Phobos (Fear) and Deimos (Dread), after the mythological sons and attendants of the war god Mars. These tiny, potato-shaped moons were the first new objects discovered in orbit around a terrestrial planet since Galileo’s discovery of Jupiter’s moons. The discovery added yet another layer to the growing portrait of Mars as a complex planetary system, setting the stage for an even more dramatic, and ultimately illusory, chapter in its history.

The Great Canal Debate

The same favorable opposition of 1877 that led to the discovery of Phobos and Deimos also gave rise to one of the most fascinating and enduring myths in the history of astronomy: the canals of Mars. This saga began with the meticulous observations of the Italian astronomer Giovanni Schiaparelli, director of the Brera Observatory in Milan. Using a 22-centimeter telescope, he painstakingly charted the Martian surface, producing the most detailed map of the planet to date.

On his map, Schiaparelli noted a dense network of fine, linear features crisscrossing the lighter-colored regions of the planet. He gave them the Italian name canali, a word that translates to “channels” or “grooves,” terms that typically denote natural geological formations. He named these features after famous rivers on Earth, both real and mythological. Schiaparelli himself was cautious and never explicitly claimed that his canaliwere artificial.

However, when his work was translated into English, a fateful linguistic error occurred. Canali was rendered as “canals,” a word that carries a strong implication of artificial construction. This mistranslation, combined with the existing perception of Mars as an Earth-like world, ignited a firestorm of public and scientific speculation. The idea of a Martian civilization, capable of planet-wide engineering, suddenly seemed plausible.

This idea found its most fervent and influential champion in Percival Lowell, a wealthy Bostonian with a passion for astronomy. Captivated by Schiaparelli’s findings, Lowell dedicated his fortune and his life to proving the existence of intelligent life on Mars. In 1894, he established a state-of-the-art observatory on a hilltop near Flagstaff, Arizona—a site chosen for its clear, steady air—for the express purpose of studying the Red Planet. This site is still known today as Mars Hill.

From his observatory, Lowell and his assistants produced a series of increasingly elaborate maps that depicted a world covered in a complex, geometric network of hundreds of canals. Lowell went far beyond Schiaparelli’s cautious observations. He developed a grand, compelling narrative to explain what he saw. Mars, he argued, was a dying world, its ancient oceans long since evaporated. The canals were a colossal irrigation system, a last, desperate attempt by an advanced and ancient civilization to channel water from the melting polar ice caps to their parched equatorial cities.

Lowell’s theories, eloquently presented in a series of popular books like Mars (1895) and Mars as the Abode of Life (1908), created a full-blown “canal craze.” The idea of intelligent Martians captured the public imagination. It appeared in newspaper articles, advertisements, and popular songs. This cultural fixation provided fertile ground for the burgeoning genre of science fiction. In 1898, the British author H.G. Wells published The War of the Worlds, a chilling tale of technologically superior Martians invading Earth to escape their dying planet. The story’s power was amplified in 1938 when a young Orson Welles aired a radio dramatization presented as a series of realistic news bulletins. The broadcast famously caused a panic among some listeners on the East Coast who believed a real Martian invasion was underway.

While Lowell’s ideas were immensely popular, they were always controversial within the astronomical community. Many astronomers with powerful telescopes simply could not see the sharp, linear canals that Lowell drew. They saw only diffuse, irregular patches and smudges. Critics suggested that the canals were an optical illusion, a psychological phenomenon where the human brain, struggling to make sense of faint, blurry details at the very limit of visibility, connects unrelated dots and splotches into straight lines.

The debate raged for decades, but the death knell for the Martian canals came in 1909. During another favorable opposition, the Greek-French astronomer Eugène Antoniadi used the new 33-inch Great Refractor at the Meudon Observatory outside Paris, then the largest telescope in Europe. In moments of exceptional atmospheric clarity, Antoniadi was able to see the Martian surface with unprecedented resolution. The supposed canals dissolved before his eyes into myriads of discrete, irregular features—chains of small craters, dark patches, and other natural geological formations. It was clear that the canals were, as the critics had long suspected, an illusion.

The saga of the Martian canals was more than just a scientific mistake. It was a perfect storm of perception and technology. It began with a simple mistranslation, which planted the seed of an idea in a culture already primed to see Mars as a sister world. It was fueled by the limitations of the era’s telescopes, which were just good enough to hint at surface detail but not good enough to resolve it clearly, leaving a canvas of ambiguity for the pattern-seeking human brain to fill in. And it was driven by the powerful narrative crafted by Percival Lowell, whose confirmation bias led him to interpret every faint smudge as evidence for his grand theory. The story of the canals serves as a powerful lesson in the history of science, demonstrating how our perception of the universe is shaped not only by what we see, but by the tools we use and the ideas we bring to the eyepiece. The illusion was only shattered when a more powerful instrument provided a clearer view, a recurring theme in the exploration of Mars.

The First Robotic Emissaries

The dawn of the Space Age in the late 1950s opened a new chapter in the exploration of Mars. For the first time, humanity had the ability to break free from the bottom of Earth’s atmospheric ocean and send robotic emissaries to visit other worlds. The journey to Mars, however, would prove to be extraordinarily difficult. The early years of interplanetary exploration were marked by a staggering number of failures, so much so that engineers and journalists spoke of a “Great Galactic Ghoul” or a “Mars Curse” that seemed to devour spacecraft destined for the Red Planet.

The Soviet Union was the first to attempt the journey, launching a series of probes as part of its Mars program beginning in 1960. The challenges were immense, from building rockets powerful enough for the interplanetary voyage to designing spacecraft that could operate autonomously for months in the harsh environment of deep space. The Soviet program suffered a string of heartbreaking setbacks. Multiple missions failed during launch when their rockets malfunctioned. Others, like Mars 1 in 1962, successfully began the trip only to fall silent millions of kilometers from Earth.

Despite the failures, the Soviets achieved a series of historic firsts. In November 1971, the Mars 2 lander became the first human-made object to reach the surface of Mars, though it crashed due to a descent system malfunction. Just days later, on December 2, 1971, its twin, Mars 3, successfully executed the first soft landing on the Red Planet. It began transmitting a television image from the surface, but after just 14.5 seconds, all communication ceased, likely a victim of the massive, planet-encircling dust storm that was raging at the time.

The United States, through NASA’s Jet Propulsion Laboratory, pursued its own program of Mars exploration with a series of spacecraft called Mariner. After an initial failure with Mariner 3, whose protective shroud failed to separate after launch, NASA achieved the first great success of the robotic era. On July 14, 1965, Mariner 4 flew past Mars, executing the first successful flyby of another planet.

Over the course of its brief encounter, Mariner 4 transmitted 22 grainy, black-and-white images back to Earth. The pictures were a profound shock to the scientific community and the public. They revealed not a world of canals and dying civilizations, but a stark, barren landscape dominated by impact craters, looking disturbingly like the Moon. The data also showed that the Martian atmosphere was far thinner than even the most pessimistic estimates, with a surface pressure less than 1% of Earth’s. In an instant, the romantic, Lowellian vision of Mars was replaced by the image of a cold, dead, and geologically inactive world. This was the low point in the perception of Mars, a view reinforced by two more successful flybys in 1969 by Mariner 6 and Mariner 7, which returned more images of cratered terrain.

The pendulum of perception swung back dramatically with the next mission, Mariner 9. Originally planned as a dual-orbiter mission, its twin, Mariner 8, was lost in a launch failure. Mariner 9 carried on alone, and on November 13, 1971, it became the first spacecraft in history to enter orbit around another planet. This was a fundamental shift in strategy, from the fleeting snapshot of a flyby to the long, lingering gaze of an orbiter.

When Mariner 9 arrived, it was greeted by the same global dust storm that had silenced the Mars 3 lander. The entire planet was a featureless, hazy ball. Mission controllers at JPL patiently waited. For weeks, the spacecraft circled the shrouded planet. Slowly, as the dust began to settle, the highest points on the surface began to emerge from the haze. These were not the rims of giant craters, but the colossal peaks of four enormous shield volcanoes in a region that would come to be known as Tharsis. One of them, Olympus Mons, was the largest volcano ever seen in the solar system.

As the atmosphere continued to clear, Mariner 9 revealed a world of stunning geological diversity that the flyby missions had completely missed. It discovered Valles Marineris, a vast canyon system that dwarfs Earth’s Grand Canyon, stretching for 4,000 kilometers across the planet’s equator. Most astonishingly, it found unmistakable evidence that water had once flowed in abundance across the Martian surface. The images showed sinuous, branching channels that were clearly ancient, dried-up riverbeds. Mariner 9 had discovered a different Mars entirely—not the living world of Lowell, nor the dead world of Mariner 4, but a planet with a dynamic and dramatic past, a world that had once been warmer, wetter, and much more Earth-like than it is today. The orbiter went on to map 85% of the planet’s surface and provided the first close-up images of the tiny, irregular moons Phobos and Deimos, revealing them to be cratered, asteroid-like bodies.

The success of Mariner 9 laid the scientific groundwork for the next, even more ambitious, step in the exploration of Mars: to land on the surface and search directly for signs of life.

The Viking Mission: A Search for Life

Building on the revolutionary discoveries of Mariner 9, NASA embarked on its most ambitious and expensive robotic planetary mission to date: the Viking program. Launched in 1975, the mission consisted of two identical spacecraft, Viking 1 and Viking 2. Each spacecraft was a two-part system: an orbiter designed to survey the planet from above and a lander designed to touch down on the surface, conduct scientific experiments, and, for the first and only time, search directly for evidence of life on another world.

The Viking orbiters were powerful mapping platforms. Arriving at Mars in 1976, they produced the first comprehensive, high-resolution global maps of the planet. Their images confirmed the stark hemispheric dichotomy—the ancient, heavily cratered southern highlands and the younger, smoother northern lowlands—that Mariner 9 had first revealed. They provided stunning views of the Tharsis volcanoes and the Valles Marineris canyon system and imaged vast outflow channels that suggested catastrophic floods in Mars’s distant past. The orbiters also carried instruments to study the atmosphere, mapping the seasonal transport of water vapor between the polar caps and providing a wealth of data on atmospheric temperature and composition.

The landers were the technological centerpiece of the mission. After the orbiters had carefully surveyed and certified safe landing sites, the landers separated, entered the thin Martian atmosphere protected by an aeroshell, deployed parachutes, and finally used retrorockets to achieve a soft touchdown. Viking 1 landed on the plains of Chryse Planitia on July 20, 1976, followed by Viking 2 in Utopia Planitia on September 3.

From the surface, the landers returned the first detailed color panoramic images of the Martian landscape. They showed a desolate, rock-strewn desert of reddish, iron-rich soil under a pale pink sky—a color caused by fine red dust suspended in the thin atmosphere. The landers also acted as the first Martian weather stations, monitoring temperature, pressure, and wind for years, far exceeding their planned 90-day missions.

The most anticipated part of the mission was the landers’ sophisticated, miniaturized biology laboratory. Each lander used a robotic arm to scoop up samples of Martian soil and deliver them to a package of three distinct experiments designed to detect signs of microbial life.

The Gas-Exchange (GEX) experiment worked by adding a nutrient-rich broth—a “chicken soup” for microbes—to a soil sample and then monitoring the air above it for any changes in gas composition, such as the release of oxygen, carbon dioxide, or hydrogen, which could indicate metabolism. When the experiment was run, a significant amount of oxygen was released.

The Labeled Release (LR) experiment was designed to be even more sensitive. It added a small amount of a nutrient solution in which the carbon atoms were replaced with radioactive Carbon-14. The idea was that if microorganisms consumed the nutrients, they would release waste gases containing the radioactive carbon, which could be easily detected. The LR experiment produced a dramatic and immediate positive result. A steady stream of radioactive gas was detected, and when a control sample of soil was first heated to 160°C to sterilize it, the effect disappeared—a result perfectly consistent with the presence of life.

The Pyrolytic Release (PR) experiment took a different approach. It exposed a soil sample to an artificial atmosphere containing radioactive carbon dioxide and carbon monoxide, under a simulated sunlamp. After several days, the soil was baked at high temperature to see if any of the radioactive carbon had been incorporated into the soil, a process analogous to photosynthesis. This experiment also returned a weakly positive result.

At first, the results seemed momentous. Two, and possibly three, of the life-detection experiments had returned positive signals. However, another instrument on the landers, the Gas Chromatograph-Mass Spectrometer (GCMS), cast a long shadow of doubt. The GCMS was designed to detect the building blocks of life—organic molecules—in the soil. It worked by heating a soil sample to high temperatures to vaporize any organic compounds, which would then be identified by the spectrometer. The GCMS found no trace of Martian organic molecules at either landing site, down to a sensitivity of parts per billion. The only organic compounds it detected were two simple chlorinated hydrocarbons, which were dismissed at the time as contaminants from cleaning fluids used to prepare the spacecraft on Earth.

This created the “Viking Paradox”: the biology experiments seemed to indicate the presence of active metabolism, but the GCMS found no bodies, no organic building blocks from which life could be made. For most scientists, the lack of organics was the decisive factor. The consensus became that the positive biology results were not due to life, but to some exotic, unknown, non-biological chemical reactivity in the Martian soil.

The mystery of Viking’s results persisted for more than three decades. The crucial missing piece of the puzzle was finally discovered in 2008 by NASA’s Phoenix lander, which found that the Martian soil contains significant amounts of perchlorate salts. Perchlorates are highly oxidizing compounds, especially when heated. Subsequent laboratory experiments on Earth showed that when a small amount of perchlorate is added to soil containing organic matter and then heated—mimicking the GCMS experiment—the perchlorates destroy the organics and produce the very same chlorinated hydrocarbons that Viking had detected. The Viking GCMS hadn’t just failed to find organics; its method of analysis had actively destroyed them.

Furthermore, scientists now understand that the interaction of perchlorates with cosmic radiation can produce other highly reactive compounds, like hypochlorite. These compounds, when exposed to the water and nutrients in the Viking biology experiments, can produce chemical reactions that perfectly mimic the results of the GEX and LR experiments, releasing oxygen and breaking down the nutrients without any need for biology.

The Viking mission stands as a profound lesson in the challenges of searching for life on other worlds. It was designed with Earth-based assumptions about biology and chemistry. It sought Earth-like life using methods that, on Mars, may have destroyed the very evidence it was looking for, while simultaneously discovering a uniquely alien soil chemistry that masqueraded as life. Viking didn’t prove that Mars was lifeless. It proved that Mars was far more complex and chemically strange than anyone had imagined, and that before we can find life, we must first understand the exotic, non-living world it might inhabit.

A Return to the Red Planet

After the monumental Viking missions, Mars exploration entered a long period of quiet. The ambiguous results from the biology experiments and the high cost of the program led to a hiatus in new missions from the United States that lasted nearly two decades. The Soviet Union attempted to break the silence in 1988 with its ambitious Phobos program, sending two spacecraft to study Mars and its larger moon. Unfortunately, the Mars Curse seemed to linger. Phobos 1 was lost en route due to an erroneous software command, and Phobos 2 successfully entered Mars orbit and returned images of Phobos before its onboard computer failed, ending the mission prematurely.

NASA’s grand return to Mars was planned with the Mars Observer, a large, sophisticated orbiter launched in 1992. It was designed to be a planetary observatory, carrying a suite of instruments to study the geology, climate, and magnetic field of Mars in unprecedented detail. Tragically, on August 21, 1993, just three days before it was scheduled to enter orbit, all contact with the spacecraft was lost. An investigation later concluded that the most probable cause was a rupture in a fuel line, which likely caused the spacecraft to spin uncontrollably.

The loss of the billion-dollar Mars Observer was a devastating blow. It forced NASA to fundamentally rethink its approach to planetary exploration. The old model of building large, expensive, “do-it-all” spacecraft was deemed too risky. A single failure meant the loss of an entire decade’s worth of scientific investment. In response, NASA adopted a new mantra: “Faster, Better, Cheaper.” The strategy was to fly a series of smaller, more focused, and lower-cost missions more frequently. If one mission failed, others would still be in the pipeline. This new philosophy quickly bore fruit, leading to a triumphant return to the Red Planet in the late 1990s with two highly successful missions.

The first was Mars Global Surveyor (MGS), launched in 1996. It was designed as a recovery mission, carrying many of the instruments that had been lost on Mars Observer. Arriving at Mars in September 1997, MGS became one of the most productive missions in history, operating for over nine years. Its instruments completely revolutionized our view of Mars. The Mars Orbiter Laser Altimeter (MOLA) fired billions of laser pulses at the surface, creating the first precise, 3D topographic map of the entire planet. This map revealed the dramatic scale of Mars’s features, from the heights of Olympus Mons to the depths of the Hellas impact basin, and definitively quantified the great elevation difference between the northern and southern hemispheres. The Thermal Emission Spectrometer (TES) mapped the mineral composition of the surface from orbit. Its most celebrated discovery was a large, concentrated deposit of gray, crystalline hematite near the equator—a mineral that on Earth often forms in the presence of standing water. This discovery would later make the region, Meridiani Planum, a prime landing site for a future rover. The Mars Orbiter Camera (MOC) returned a stunning gallery of over 240,000 high-resolution images. It revealed a dynamic and active planet, capturing images of shifting sand dunes, tracking the paths of giant dust devils, and, most tantalizingly, discovering hundreds of small gullies carved into crater and canyon walls. These gullies looked remarkably fresh, suggesting that liquid water might have flowed on or near the surface of Mars in the geologically recent past, and perhaps even today.

The second mission of this new era was Mars Pathfinder, also launched in 1996. Primarily a technology demonstration mission, Pathfinder was designed to test a radical new way of landing on Mars. On July 4, 1997, the spacecraft plunged into the Martian atmosphere, slowed by a parachute and then solid-fuel rockets. In the final seconds, a cocoon of giant airbags inflated around the lander. It hit the surface at about 40 miles per hour, bouncing high into the air before rolling to a stop in an ancient floodplain called Ares Vallis. The landing was a spectacular success.

Once settled, the lander, renamed the Carl Sagan Memorial Station, opened its three petal-like solar panels and revealed its precious cargo: Sojourner, the first robotic rover ever to operate on another planet. The small, six-wheeled rover, no bigger than a microwave oven, rolled down a ramp onto the Martian soil. For the next three months, Sojourner explored the area around the lander, analyzing the chemical composition of nearby rocks and soil with its Alpha Proton X-ray Spectrometer (APXS). Its analysis showed that the rocks were of diverse types, suggesting they had been transported and deposited by a great flood in the distant past, confirming the reason the site was chosen.

The Pathfinder mission was an overwhelming public success. For the first time, the public could follow a planetary mission in near-real-time via the nascent World Wide Web. NASA’s website was flooded with hundreds of millions of hits as people around the world watched the plucky little rover navigate the rocky Martian terrain.

The failures of the early 1990s, while painful, had forced a strategic rebirth. The “Faster, Better, Cheaper” approach, embodied by the complementary successes of Mars Global Surveyor and Mars Pathfinder, created the modern template for Mars exploration. MGS provided the global, orbital reconnaissance needed to understand the planet as a whole and to identify the most promising places to explore. Pathfinder proved that we could get to those places affordably and, once there, begin to rove. The ashes of the old, monolithic approach had given rise to a more resilient and ultimately more successful strategy that would pave the way for a continuous robotic presence at Mars in the 21st century.

The 21st Century Flotilla

The dawn of the 21st century marked the beginning of an unprecedented golden age of Mars exploration. Building on the successes of the 1990s, NASA and other international space agencies dispatched a veritable flotilla of spacecraft to the Red Planet. Since the arrival of Mars Odyssey in 2001, there has not been a single day without at least one active robotic probe orbiting or roving on Mars. This continuous presence has transformed our understanding, turning Mars from a distant object of study into a familiar, though still mysterious, neighboring world. This era is characterized by highly specialized missions, each designed to answer specific questions, working in concert to build a complex, multi-layered picture of the planet’s past and present.

The Orbital Fleet: Eyes in the Sky

The foundation of modern Mars exploration is a network of sophisticated orbiters that serve as powerful scientific platforms and vital communication relays for surface missions.

NASA’s 2001 Mars Odyssey, launched in April 2001, is the longest-serving spacecraft in Mars orbit. Its primary mission was to map the chemical composition of the surface. Using its Gamma Ray Spectrometer (GRS), Odyssey created the first global map of hydrogen distribution. The data revealed vast quantities of hydrogen concentrated in the top meter of soil in the high-latitude polar regions, a clear indication of immense deposits of subsurface water ice. This discovery was a landmark, confirming that while liquid water is unstable on the surface today, a huge reservoir of frozen water remains locked just beneath the ground. Odyssey has also served as the workhorse communications relay, transmitting the majority of data from NASA’s surface missions back to Earth.

The European Space Agency (ESA) joined the effort with Mars Express, which entered orbit on Christmas Day, 2003. It carried a powerful suite of instruments, including the Mars Advanced Radar for Subsurface and Ionospheric Sounding (MARSIS). This was the first radar to probe beneath the Martian surface from orbit. MARSIS mapped the thickness of the polar ice caps and, in 2018, returned data suggesting the presence of a large body of liquid water—a subglacial lake—buried 1.5 kilometers beneath the southern polar ice cap. This tantalizing finding is still being debated, but it points to the possibility that liquid water might exist on Mars today. Mars Express was also the first to make a confirmed detection of methane in the Martian atmosphere, a gas that on Earth is primarily produced by biological or geological activity and which should be quickly destroyed by sunlight, hinting at an active source.

NASA’s Mars Reconnaissance Orbiter (MRO), arriving in 2006, is a powerhouse of high-resolution observation. Its High Resolution Imaging Science Experiment (HiRISE) camera can see features on the surface as small as a dinner table, allowing it to spot landers, rovers, and even their tracks from orbit. Its images have revealed a stunningly dynamic surface, with active avalanches, shifting sand dunes, and the mysterious seasonal appearance of dark streaks called recurring slope lineae, which were once thought to be caused by seeping brines. MRO’s Compact Reconnaissance Imaging Spectrometer for Mars (CRISM) has created detailed mineral maps, identifying specific types of water-altered minerals like clays and sulfates. These maps have been instrumental in guiding the exploration of surface rovers, allowing scientists to send them to the most promising locations to study past habitable environments.

The international fleet has continued to grow. NASA’s MAVEN (Mars Atmosphere and Volatile EvolutioN) orbiter, which arrived in 2014, is specifically designed to study the planet’s tenuous upper atmosphere. Its mission is to understand the processes by which Mars lost its ancient, thicker atmosphere to space, stripped away over billions of years by the solar wind after the planet’s protective global magnetic field died. In the same year, India’s first interplanetary probe, the Mars Orbiter Mission (Mangalyaan), successfully entered orbit, making India the fourth space agency to reach the Red Planet. In 2016, the ESA/Roscosmos ExoMars Trace Gas Orbiter arrived with instruments designed to make the most sensitive measurements yet of methane and other trace gases in the atmosphere. The 2020s saw the arrival of two more orbiters: the United Arab Emirates’ Hope mission, the Arab world’s first interplanetary probe, designed to provide the first complete picture of the Martian climate throughout a full day and year; and China’s Tianwen-1 orbiter, which served as the relay for its companion rover and is conducting its own global survey of the planet.

The Surface Explorers: Boots on the Ground

While the orbiters provide the global context, the most detailed discoveries have come from the robotic geologists on the surface.

In January 2004, NASA landed the twin Mars Exploration Rovers (MER), Spirit and Opportunity, at two different locations on Mars. Designed to last for 90 days, these golf-cart-sized rovers became two of the greatest marathon explorers in history. Opportunity landed inside a small crater named Eagle in Meridiani Planum, a site chosen because of the hematite signature seen by Mars Odyssey. It hit the scientific jackpot immediately. The rocks in the crater wall were sedimentary, clearly laid down in water, and were filled with tiny, iron-rich spherules nicknamed “blueberries,” which are concretions that form in water. Opportunity had landed on the shoreline of what was once a salty, acidic sea. It went on to explore for nearly 15 years, driving over 45 kilometers and cementing the story of a watery past. Spirit landed in Gusev Crater, which appeared from orbit to be an ancient lakebed. The crater floor, however, was covered in volcanic rock. Undeterred, Spirit drove for miles into a range of hills, the Columbia Hills, where it found ancient rocks that had been extensively altered by water. Its most stunning discovery came when a broken wheel churned up the soil, revealing a patch of nearly pure silica—a mineral that on Earth forms in hot springs or volcanic fumaroles, environments teeming with microbial life. Spirit had found evidence of a past habitable environment.

NASA’s Phoenix lander touched down in the far northern arctic plains in 2008. Its robotic arm dug trenches in the soil and, for the first time, directly touched and analyzed water ice, which lay just centimeters below the surface. Phoenix also made the pivotal discovery of perchlorate salts in the soil, finally resolving the 30-year-old puzzle of the Viking biology experiments.

In 2012, NASA landed its most ambitious rover yet, the car-sized Curiosity rover, in Gale Crater. Curiosity is a mobile chemistry lab. Its primary mission was not just to find evidence of past water, but to determine if Mars ever had a truly habitable environment—one with liquid water that was not too acidic or salty, and that contained the key chemical ingredients for life. Within its first year, Curiosity drilled into a mudstone rock named “John Klein” and found exactly that. The analysis revealed that it had landed in the bed of an ancient, long-lived freshwater lake that contained all the essential elements for life—carbon, hydrogen, oxygen, nitrogen, phosphorus, and sulfur. Curiosity had discovered the first definitively habitable environment on another planet. It has since gone on to make the first definitive detection of complex organic molecules preserved in these ancient rocks and continues to monitor mysterious, seasonal plumes of methane in the atmosphere.

The 2020s have brought even more robotic explorers. NASA’s InSight lander, which arrived in 2018, was a geophysical station. Its primary instrument, a highly sensitive seismometer, detected hundreds of “marsquakes.” By analyzing the seismic waves traveling through the planet, scientists have been able to measure the thickness of the Martian crust, probe the structure of its mantle, and determine the size of its large, liquid metal core for the first time.

In 2021, two more missions successfully reached the surface. China’s Zhurong rover, part of the Tianwen-1 mission, landed in the vast northern plains of Utopia Planitia, using ground-penetrating radar to study the structure of the subsurface. Just days earlier, NASA’s Perseverance rover landed in Jezero Crater, the site of an ancient river delta and lake. Perseverance represents the next logical step in the scientific strategy. Its mission is not just to find a past habitable environment, but to actively search for signs of past microbial life, or biosignatures, within it. To this end, it is collecting and storing a set of pristine rock core samples. Perseverance also carried a technology demonstration: the Ingenuity helicopter. This small, autonomous drone successfully performed the first powered, controlled flight on another planet, proving that flight in the thin Martian atmosphere is possible and opening a new dimension for future exploration.

The scientific strategy of the 21st century has followed a clear and deliberate path. The initial phase, “Follow the Water,” was triumphantly achieved by missions like Odyssey and the MER rovers. This led to the next phase, embodied by Curiosity, which was to characterize these watery environments and confirm their habitability. Now, with Perseverance, the strategy has evolved to its ultimate goal: “Follow the Life,” by searching for direct evidence of ancient organisms in the most promising locations and collecting the samples that might finally provide the answer.

The Future: Return and Footprints

The coming decades of Mars exploration are poised to be the most ambitious yet, driven by two monumental and interconnected goals that represent the culmination of centuries of inquiry: returning the first pristine samples from Mars to Earth, and landing the first human explorers on its surface. These two objectives represent the twin peaks of future exploration, one fulfilling the ultimate scientific quest for knowledge, the other realizing humanity’s oldest dream of interplanetary travel.

The scientific quest to determine if life ever existed on Mars has reached a point where it can no longer be answered by robots alone, no matter how sophisticated. The definitive evidence, if it exists, is likely to be subtle and complex, requiring the full power of Earth’s most advanced laboratories. This is the motivation behind the Mars Sample Return (MSR) campaign, a multi-mission, multi-agency endeavor being planned primarily by NASA and the European Space Agency (ESA).

The first step of this campaign is already underway. NASA’s Perseverance rover is currently drilling core samples from the most scientifically compelling rocks in Jezero Crater, sealing them in ultra-clean titanium tubes, and caching them on the surface. These are the first pieces of another planet to be collected with the express purpose of being brought back to Earth.

The subsequent steps are technologically daunting. The plan involves launching a Sample Retrieval Landerto Mars. This lander would carry a small “fetch” rover or, as recently proposed, a pair of small helicopters inspired by Ingenuity, to retrieve the sample tubes left by Perseverance. The lander would also carry the Mars Ascent Vehicle (MAV), a small, two-stage solid-fuel rocket. A robotic arm would transfer the collected samples into a container at the top of the MAV. The MAV would then launch from the surface of Mars—a historic first—and place the sample container into orbit.

The final piece of the puzzle is the Earth Return Orbiter, to be built by ESA. This spacecraft would rendezvous with and capture the basketball-sized sample container in Mars orbit, seal it within a high-integrity containment vessel to prevent any possible contamination, and then fire its engines for the long journey back to Earth. Upon arrival, it would release an Earth Entry Vehicle to bring the precious cargo safely through our atmosphere for a landing in a secure facility.

The MSR campaign is one of the most complex robotic endeavors ever conceived. It faces significant challenges, including a projected cost of many billions of dollars and a tight schedule. In parallel, China is also developing its own ambitious sample return mission, Tianwen-3, with a potential launch in the late 2020s and a sample return in the early 2030s. The race to bring back the first pieces of Mars is on.

Uncertainty

The NASA-ESA Mars Sample Return (MSR) mission, aimed at retrieving and returning to Earth the rock and soil samples collected by the Perseverance rover, is currently in a precarious but not fully canceled state. The mission has been plagued by escalating costs—previously estimated at up to $11 billion—and delays that could push sample return to 2040 or later. In response to these issues, NASA paused aspects of the program in late 2023 and solicited industry proposals for more affordable architectures in 2024. As of early 2025, NASA was considering reworked landing options for the Mars Ascent Vehicle and other components to reduce risks and expenses.

The Trump administration’s proposed FY2026 budget, released in spring 2025, sought to terminate the U.S. portion of MSR entirely, citing unsustainable finances, as part of a broader 24.3% cut to NASA’s overall budget. However, on July 24, 2025, the House Appropriations Committee’s Commerce-Justice-Science subcommittee rejected this cancellation and allocated $300 million to advance MSR, describing it as a lifeline to preserve U.S. leadership in planetary science—particularly in light of China’s competing efforts—and to support technologies for future human exploration of Mars. The funding includes directives for NASA to explore commercial partnerships to cut costs and speed up the timeline, with a report due to Congress within 30 days of enactment on potential collaborations. The Senate’s appropriations report did not specifically address MSR, and the overall NASA science budget faces cuts, but the House’s action keeps the mission viable for now.

Despite this support, uncertainties persist. Congressional concerns have been raised about whether NASA will spend the appropriated funds as intended, with reports of the Office of Management and Budget (OMB) releasing money incrementally and the possibility of impoundment (withholding funds), which could stall progress. Industry proposals are actively being considered to salvage the mission, including a notable $3 billion firm-fixed-price plan from Lockheed Martin unveiled in July 2025. This approach would use a simplified lander based on NASA’s InSight mission (which landed on Mars in 2018), a smaller Mars Ascent Vehicle, and an optimized Earth entry system, leveraging Lockheed’s experience from prior sample return missions like OSIRIS-REx. The goal is to reduce complexity, risks, and costs while aiming for a return in the 2030s. Other companies, such as Rocket Lab, have submitted competing ideas.

Perseverance continues to collect and depot samples on Mars, with the rover completing a sample depot in July 2025. The ESA component, including the Earth Return Orbiter, is progressing, with key hardware like the orbit insertion module shipped in July 2025. Final budget reconciliation between the House, Senate, and administration will determine if MSR proceeds, but as of August 8, 2025, it remains funded and under active redesign to address fiscal challenges.

Separately, China’s Tianwen-3 Mars sample return mission is advancing steadily, with a planned launch around 2028 and sample return by 2031. Chinese officials have expressed openness to international cooperation, particularly on planetary protection (to prevent Earth contamination) and sample analysis, though collaboration on the mission itself appears limited. This puts pressure on the U.S. program, as China could achieve the first Mars sample return if NASA’s delays continue.

The Next Giant Leap: Humans on Mars

While robots lay the scientific groundwork, the ultimate goal for many is to see human footprints in the red dust. Sending astronauts to Mars is an immense undertaking, a challenge that dwarfs the Apollo program in complexity, duration, and risk.

NASA’s current strategy uses the Moon as a stepping stone. The Artemis program, which aims to establish a sustainable human presence on and around the Moon, is explicitly designed as a proving ground for a future Mars mission. Astronauts will test long-duration life support systems, practice surface operations in a partial-gravity environment, and potentially learn to utilize resources like lunar water ice. The technologies developed for Artemis, including the powerful Space Launch System (SLS) rocket and the Orion deep-space crew capsule, are foundational elements of NASA’s Mars architecture. The agency’s current timeline envisions a human mission to Mars in the late 2030s or early 2040s.

Private industry is also a major player in the push toward Mars. The most prominent is SpaceX, led by Elon Musk, whose stated goal is to make humanity a multi-planetary species. The company is developing Starship, a massive, fully and rapidly reusable transportation system designed to carry dozens of people and hundreds of tons of cargo to Mars. SpaceX’s vision relies on orbital refueling to enable these massive payloads and aims for a much more aggressive timeline, with the first crewed missions potentially occurring in the early 2030s.

The challenges for any human mission are staggering. The journey itself would take six to nine months each way, with launch windows to and from Mars opening only once every 26 months, locking crews into missions that could last up to three years. Throughout this time, astronauts would be exposed to the constant threat of deep-space radiation, including solar flares, far beyond the protection of Earth’s magnetic field. They would need perfectly reliable life support systems to provide air, water, and food, and would have to contend with the physiological effects of long-term weightlessness and the psychological stress of extreme isolation. The communication delay, up to 24 minutes one-way, would make real-time conversation with Earth impossible, forcing a level of autonomy and on-the-spot problem-solving never before required in human spaceflight. Finally, landing a heavy spacecraft with crew and supplies on Mars and, critically, launching it back off the surface to return to Earth, are monumental engineering feats that have yet to be accomplished.

The future of Mars exploration is advancing along these two parallel tracks. The robotic quest for scientific truth, culminating in sample return, will provide the ground truth needed to understand Mars’s history and its potential for life. The human quest for exploration, culminating in crewed missions, will push the boundaries of technology and human endurance. These two paths are deeply connected. The decades of robotic exploration have given us the knowledge—of the environment, the resources, and the hazards—that makes a human mission even conceivable. In turn, the technologies developed for human exploration will enable a new generation of even more capable scientific missions. The next chapter in our long history with Mars is about to be written, and it promises to be the most exciting one yet.

Summary

The story of Mars is a reflection of humanity’s own journey of discovery. For millennia, it was a mythological figure, a ruddy wanderer in the night sky that embodied human concepts of conflict and chaos. The invention of the telescope transformed it into a physical place, a world with a geography that seemed, for a time, to mirror our own. This perception of an Earth-like twin, with seasons and polar ice caps, fueled a grand and romantic vision of a dying planet crisscrossed by the canals of an ancient, intelligent civilization—a story born of a linguistic mistake and the limits of our own perception.

The Space Age brought a harsh dose of reality. The first robotic flybys in the 1960s revealed a cratered, seemingly lifeless wasteland, shattering the popular myths and replacing them with a stark image of a geologically dead world. But this, too, was an incomplete picture. The patient, persistent gaze of the first orbiters revealed a planet of stunning complexity and epic scale, a world of giant volcanoes, vast canyons, and the unmistakable, ghostly traces of ancient rivers and catastrophic floods. Mars was not dead; it had a dynamic and watery past.

This revelation set the stage for the modern era of exploration, a continuous robotic presence on and around the Red Planet for more than two decades. A flotilla of international orbiters has mapped the planet in exquisite detail, while a series of increasingly sophisticated landers and rovers have acted as robotic field geologists on the surface. They have followed the water, finding definitive evidence of ancient lakes, hot springs, and salty seas. They have assessed the habitability of these past environments, finding places that once contained all the necessary ingredients for life as we know it. They have uncovered the planet’s strange soil chemistry, solving the decades-old puzzle of the Viking life-detection experiments. And they have begun the search for the ultimate prize: direct evidence of past life, preserved in the ancient rocks of a river delta.

Today, we stand on the cusp of the next great chapters in this story. The ambitious Mars Sample Return campaign seeks to bring pieces of the Red Planet back to Earth, allowing us to analyze them with a precision and depth impossible for any robotic mission. In parallel, nations and private companies are developing the technologies to send the first human explorers to Mars, a monumental undertaking that would mark a new stage in the evolution of our species.

From a god of war to a potential second home, our understanding of Mars has always been a measure of our own scientific and technological reach. It has consistently challenged our assumptions, overturned our expectations, and forced us to look more closely, not only at the universe, but at ourselves. The journey is far from over. The return of Martian samples and the arrival of human explorers will undoubtedly answer some of our oldest questions, but they will just as surely unveil new mysteries we cannot yet imagine, continuing the timeless story of our fascination with the Red Planet.

What Questions Does This Article Answer?

• How has humanity’s perception of Mars evolved from ancient times to the modern era?
• What did ancient civilizations understand about Mars’ movement and properties?
• How did the invention of the telescope change our view of Mars?
• What were the major discoveries about Mars made through the telescope observations in the 17th century?
• Who were the key astronomers involved in early Mars observations, and what did they discover?
• How did the idea of Martian “canals” originate and why was it significant?
• What were the challenges and achievements of early Mars missions in the space age?
• How did Mariner 9’s mission contribute to changing our understanding of Mars?
• What were the main findings of NASA’s Viking mission and why were they controversial?
• How do modern missions contribute to our understanding of Mars, and what have they discovered?

Last update on 2026-01-10 / Affiliate links / Images from Amazon Product Advertising API