The Enduring Mysteries of the Red Planet

Mars has captivated human imagination for centuries, transforming from a wandering red light in the night sky to a tangible world of rust-colored deserts, ancient riverbeds, and towering volcanoes. While robotic explorers have mapped its surface and sniffed its thin atmosphere, the planet remains a place of deep contradictions and unsolved puzzles. We know that Mars was once wet and potentially habitable, yet today it appears freeze-dried and sterile. We understand the basic chemistry of its rocks, yet the specific processes that shaped its climate and geological evolution remain subjects of intense debate. As space agencies like NASA and the European Space Agency prepare for the next phase of exploration, including the return of samples to Earth, several fundamental questions stand between our current understanding and a complete picture of our planetary neighbor.

The Search for Biological Origins

The most persistent question regarding Mars is whether it has ever hosted life. This inquiry drives much of the funding and engineering effort behind modern planetary science. The initial optimism of the 19th century, which envisioned canals and civilizations, gave way to the stark reality of a cratered, barren world revealed by the Mariner missions. However, the pendulum has swung back toward a cautious hope that microbial life might have existed billions of years ago, or could perhaps persist in protected subsurface niches today.

The primary challenge in identifying past life lies in distinguishing biological evidence from non-biological chemistry. The Perseverance (rover) is currently collecting rock cores from Jezero (Mars), a location that was once a lake fed by a river delta. Scientists chose this site because the clays and carbonates found there are excellent at preserving organic molecules. In 2024 and 2025, analysis of a rock nicknamed “Cheyava Falls” revealed “leopard spot” patterns – millimeter-size blotches with dark rims containing iron and phosphate. On Earth, such textures can form when microbes thrive on chemical reactions in rock, but they can also form through abiotic chemistry.

The ambiguity of these findings highlights a significant gap in our knowledge. We do not yet know if the organic matter detected by rovers like Curiosity (rover) and Perseverance (rover) is the charred remains of ancient microbes or the product of abiotic chemistry that occurs throughout the solar system. Determining the difference requires analyzing the spatial distribution of carbon isotopes and looking for complex structural patterns that nature rarely produces without the machinery of life. This level of analysis is currently beyond the capabilities of robotic field labs, which is why the scientific community places high value on bringing samples back to Earth.

Another facet of this mystery involves the timeline of habitability. We know that early Mars had liquid water, but we do not know how long that water persisted. If the wet periods were transient, lasting only a few thousand years at a time, life may never have had the stability required to emerge and evolve. Conversely, if lakes and oceans remained for millions of years, the probability of biogenesis increases significantly. The geological record is fragmented, and reading it requires piecing together the history of a planet that has lost much of its surface to wind erosion and radiation damage.

The Methane Enigma

One of the most baffling atmospheric puzzles on Mars involves methane. On Earth, methane is primarily a byproduct of living organisms, though it can also be produced by geological activity like volcanism or the chemical alteration of rocks. Since the early 2000s, various instruments have detected plumes and spikes of methane in the Martian atmosphere, sparking excitement and confusion in equal measure.

The confusion arises from the inconsistency of the data. The Curiosity (rover) has detected repeated spikes of methane at the surface level in Gale (crater). These detections show a seasonal pattern, rising in the late summer and falling in the winter. This seasonality suggests a mechanism that releases the gas from the subsurface in response to temperature changes. However, the ExoMars Trace Gas Orbiter (TGO), which scans the atmosphere from orbit with incredible sensitivity, has failed to detect methane at higher altitudes.

This discrepancy defies standard atmospheric models. If methane is being released at the surface, it should mix into the global atmosphere and be detectable by orbiters. The fact that it is not implies that some unknown process is destroying the gas near the ground at a rate far faster than known chemistry can explain. Scientists have proposed various theories, from rapid oxidation by dust storms to electrical discharges, but none fully account for the observation.

Determining the source of this methane is a priority. If the source is biological, it would imply that microbial life exists deep underground today, metabolizing hydrogen and carbon dioxide. If the source is geological, it would indicate that Mars is not as geologically dead as previously thought, with active serpentinization – a reaction between water and olivine-rich rocks – occurring in the crust. Both possibilities reshape our understanding of the planet, but until we understand the destruction mechanism that hides the methane from orbiters, the origin of the gas will remain obscure.

The History and Persistence of Water

The surface of Mars is carved by features that are unmistakably the work of liquid water. Huge outflow channels, branching river networks, and ancient lakebeds provide a clear record of a wet past. Yet, the specific climate conditions that allowed this water to exist remain a subject of intense modeling and debate. The “Faint Young Sun” paradox complicates the picture: billions of years ago, the Sun was about 30% dimmer than it is today. For Mars to have been warm enough to sustain liquid water, it would have needed a massive greenhouse atmosphere.

Current models struggle to produce a climate that is warm and wet for long durations. Some researchers suggest that Mars was effectively a cold, icy world where water flowed only during brief episodes of melting caused by volcanic eruptions or asteroid impacts. Others argue for a sustained, thick atmosphere of carbon dioxide and hydrogen that kept the planet temperate. Resolving this debate is necessary for understanding the window of opportunity for life to arise.

Beyond the ancient history, the question of modern water is equally contentious. For years, the consensus was that liquid water could not exist near the surface due to low pressure and freezing temperatures. However, in May 2025, a new analysis of seismic data from the InSight lander suggested the presence of a vast reservoir of liquid water deep within the Martian crust, located between 11 and 20 kilometers beneath the surface. This “mid-crustal” aquifer, detected by the way seismic waves slowed down as they passed through the rock, contains enough water to cover the entire planet to a depth of over one kilometer.

This discovery shifts the focus from surface ice to deep subterranean environments. While this water is too deep to access with current drilling technology, its presence suggests that Mars retained much of its primordial water rather than losing it all to space. It also provides a potential long-term habitat for microbial life, shielded from the harsh radiation of the surface.

Atmospheric Collapse and Climate Change

Mars today has a thin atmosphere composed mostly of carbon dioxide, with a surface pressure less than 1% of Earth’s. We know this was not always the case. To support the water that carved the ancient valleys, the atmosphere must have been significantly thicker. The question of where this atmosphere went is a major focus of the MAVEN mission and the recently launched ESCAPADE mission, which lifted off in November 2025 aboard a Blue Origin rocket.

Data indicates that much of the Martian atmosphere was stripped away by the solar wind after the planet’s global magnetic field shut down. Without a protective magnetic shield, the upper atmosphere was exposed to the high-energy particles from the Sun, which slowly eroded the lighter gases. Isotopic ratios of argon and other gases confirm that a large fraction of the atmosphere was lost to space.

However, loss to space may not be the whole story. Some of the carbon dioxide may have been sequestered into the crust, forming carbonate rocks. While rovers have found carbonates, they have not yet found the massive limestone deposits that would be expected if a thick CO2 atmosphere had been captured by the ground. This “missing carbon” problem forces scientists to reconsider their estimates of the original atmospheric mass or to look for other reservoirs.

Understanding the rate and timing of this atmospheric collapse helps us reconstruct the planetary history. Did the atmosphere vanish gradually over billions of years, or was there a catastrophic collapse that ended the wet era abruptly? The answer affects our understanding of how planetary habitability evolves and dies.

The Internal Heart of Mars

Until recently, our knowledge of the Martian interior was based on gravity data and inferences from meteorites. The InSight lander changed this by placing a seismometer on the surface to listen for “marsquakes.” These quakes have provided the first direct look at the planet’s internal structure, revealing a crust that is likely layered and a liquid core that is larger and less dense than previously predicted.

The size of the core suggests it contains a significant amount of lighter elements, such as sulfur, oxygen, and carbon, mixed with iron and nickel. This composition has implications for the planet’s thermal history. A core rich in lighter elements would remain liquid at lower temperatures. The question remains: why did the Martian dynamo – the internal generator of its magnetic field – fail?

On Earth, the magnetic field is generated by the churning of the molten outer core. Mars once had a strong magnetic field, as evidenced by the magnetized crustal rocks in the southern hemisphere. Something caused this internal motion to cease roughly 4 billion years ago. Theories range from a giant impact that disrupted the heat flow to the natural cooling of a smaller planet. Understanding this shutdown is key to understanding why Mars diverged so sharply from Earth.

Furthermore, recent seismic data implies that the mantle of Mars is not completely quiet. InSight has detected quakes originating from the Cerberus Fossae region, a fractured area that shows signs of geologically recent volcanism. This raises the possibility that magma may still be moving deep underground. If Mars is still volcanically active, even at a low level, it could provide heat sources for subsurface aquifers, maintaining potential habitats for life far longer than surface conditions would suggest.

The Puzzle of Phobos and Deimos

Mars is orbited by two small, irregular moons: Phobos (moon) and Deimos (moon). Their origins are a longstanding debate in planetary science. Visually, they resemble C-type asteroids – dark, carbon-rich bodies common in the outer asteroid belt. This led to the “capture theory,” which suggests that Mars’s gravity snagged passing asteroids.

However, the capture theory has dynamic problems. It is very difficult for a planet to capture an asteroid into a circular, equatorial orbit, which matches the paths of both moons. Captured objects typically end up in elliptical, inclined orbits. This discrepancy supports the “giant impact theory,” which posits that a massive object struck Mars, blasting debris into orbit that coalesced into the moons. This is similar to how Earth’s moon formed, but on a smaller scale.

The composition of the moons is the deciding factor. If they are captured asteroids, they should be made of primitive material from the solar nebula. If they are impact remnants, they should be a mix of the impactor and Martian crustal rock. JAXA plans to address this with the Martian Moons eXploration (MMX) mission, which is designed to land on Phobos (moon) and return a sample to Earth. Resolving this mystery provides insight into the impact history of the early solar system and the formation of satellite systems.

Challenges for Future Human Presence

While scientific curiosity drives robotic exploration, the possibility of human exploration raises a different set of questions regarding safety and survival. The Martian environment poses severe risks that we do not yet have fully tested solutions for.

Radiation is a primary concern. Mars lacks a global magnetic field and has a thin atmosphere, meaning the surface is bombarded by galactic cosmic rays and solar particle events. These high-energy particles can damage human DNA and electronic equipment. Quantifying the long-term health risks of this exposure is an active area of research. We do not know if shielding materials or underground habitats will be sufficient to keep astronaut cancer risks within acceptable limits for a long-duration mission.

The toxicity of the Martian soil is another major hurdle. The Phoenix (spacecraft) lander discovered high concentrations of perchlorates in the soil. Perchlorates are salts that can disrupt thyroid function in humans. Because Martian dust is fine and electrostatically charged, it will cling to spacesuits and equipment, making it difficult to keep out of habitats. We need to understand the global distribution of these chemicals and develop effective decontamination protocols.

Finally, the physiological effects of partial gravity are unknown. We have extensive data on human health in the microgravity of the International Space Station and in the 1G environment of Earth. Mars, with 38% of Earth’s gravity, sits in an unexplored middle ground. We do not know if this level of gravity is sufficient to prevent the bone density loss, muscle atrophy, and vision problems seen in zero gravity. If 0.38G is not enough to maintain human health, future colonies might require rotating habitats or genetic interventions, radically changing the architecture of colonization.

Summary

The study of Mars is a study of our own origins and potential future. Each robotic mission peels back a layer of the planet’s history, revealing a world that is more dynamic and complex than previously imagined. From the microscopic search for ancient biosignatures to the global questions of atmospheric loss and core dynamics, the Red Planet continues to challenge our models of planetary evolution.

The answers to these questions are linked. The loss of the magnetic field led to the stripping of the atmosphere, which caused the surface water to vanish, which in turn drove any potential life underground. Understanding one piece of the puzzle often requires solving the others. As we stand on the precipice of a new era of sample return and potential human exploration, we accept that our current knowledge is merely a prologue. The true nature of Mars is written in the rocks we have yet to break open and the deep aquifers we have yet to drill.