Mars is a cold, dusty, desert planet with a thin atmosphere, known for its red color and a history of water, making it a key target in the search for life beyond Earth.

Key idea: Mars has a varied surface with huge inactive volcanoes, massive canyons, and two small moons, and experiences seasons similar to Earth, but much longer.

The surface of Mars is divided into two main parts. The northern half is mostly flat, low plains. The southern half has many craters and is much higher up. Geologically, Mars is still somewhat active. Scientists have detected "marsquakes," which are like earthquakes on Mars. The planet also has many huge, but now inactive, volcanoes. One of these, Olympus Mons, is the tallest mountain in our entire solar system. Mars also boasts one of the largest canyons, called Valles Marineris, which is much bigger than Earth's Grand Canyon.

Mars has two small, irregularly shaped moons named Phobos and Deimos. Like Earth, Mars has seasons because its axis is tilted. However, a year on Mars is much longer than an Earth year, lasting almost two Earth years. A day on Mars, called a "sol," is only slightly longer than an Earth day.

Key idea: Mars has a long and active geological history, with evidence of past water and volcanic activity, making it a key focus in the search for life.

Mars formed about 4.5 billion years ago, at the same time as the other planets. Early in its history, during a period called the Noachian, Mars was hit by many meteors. It also had valleys, erosion, and possibly even oceans of water. During this time, it lost its global magnetic field. The next period, the Hesperian, saw a lot of volcanic activity and floods that carved out huge channels.

The current period, called the Amazonian, continues to shape Mars today. Because of this long and active geological history, scientists are very interested in whether life ever existed on Mars, or if it could still exist there now. This is a major area of ongoing research.

Scientists believe Mars formed from a swirling disk of gas and dust around the young Sun. Its position in the solar system gave it unique chemical features. For example, elements that boil easily, like chlorine and sulfur, are more common on Mars than on Earth. This might be because the early Sun's strong solar wind pushed these elements outwards.

“Because of Mars's geological history, the possibility of past or present life on Mars remains an area of active scientific investigation.”

Key idea: Mars's early history was shaped by massive impacts, possibly including a giant collision that created its distinct northern plains, and it may have once had a ring system.

After the planets formed, the inner solar system might have gone through a time called the Late Heavy Bombardment, when many objects crashed into planets. About 60 percent of Mars's surface shows scars from these impacts. Some scientists, however, question if this event happened exactly as thought.

There is evidence of a massive impact basin in Mars's northern half, much larger than any other known basin. It is thought that a Pluto sized object hit Mars about four billion years ago, creating this huge basin and causing the difference between Mars's northern and southern hemispheres.

Recent studies of Mars's small moon Deimos suggest that Mars might have had a ring system between 3.5 and 4 billion years ago. This ring system could have formed from a much larger moon that broke apart, and Phobos, Mars's other moon, might be a leftover piece of that ring.

“It is possible that, four billion years ago, the Northern Hemisphere of Mars was struck by an object one tenth to two thirds the size of Earth's Moon.”

Key idea: Mars's geological timeline includes periods of heavy impacts, widespread volcanic activity, and ongoing, though limited, geological processes.

Mars's history is divided into three main geological periods:

The Noachian period (4.5 to 3.5 billion years ago): This was when Mars's oldest surfaces were created. It is marked by many large impact craters. A huge volcanic area called the Tharsis bulge formed, and there was a lot of liquid water, possibly even floods.

The Hesperian period (3.5 to 2.9 billion years ago): This period is known for widespread lava flows that created vast plains.

The Amazonian period (2.9 billion years ago to today): This is the current period. It has fewer new impact craters but shows a variety of features. Olympus Mons, the giant volcano, formed during this time, along with other lava flows.

Even today, Mars still has some geological activity. For example, lava flows in an area called Athabasca Valles are only about 200 million years old. Water flows in certain canyons happened less than 20 million years ago, suggesting recent volcanic activity. The Mars Reconnaissance Orbiter has even taken pictures of avalanches happening on Mars.

Key idea: Mars has a layered internal structure similar to Earth, with a thick crust, a rigid mantle, and a partly molten core, and is still seismically active.

Like Earth, Mars has layers: a dense metal core in the center, surrounded by rocky layers. The outermost layer is the crust, which is much thicker than Earth's crust in some places. It ranges from about 42 to 56 kilometers thick on average, but can be as thin as 6 kilometers or as thick as 117 kilometers. The main elements in Mars's crust are silicon, oxygen, iron, magnesium, aluminum, calcium, and potassium.

Scientists have confirmed that Mars is seismically active, meaning it has marsquakes. In 2019, the InSight lander detected over 450 marsquakes. Beneath the crust is the mantle, a rocky layer that causes many of the surface features like volcanoes. The upper part of the mantle is very rigid, making Mars's outer rocky layer, called the lithosphere, much thicker than Earth's. Deeper down, the mantle becomes more flexible.

Mars's core is made of iron and nickel and is at least partly melted. It is about half the size of Mars's radius and contains lighter elements like sulfur, oxygen, carbon, and hydrogen. The temperature of the core is estimated to be around 2000 to 2400 Kelvin, which is cooler than Earth's core. Scientists are still researching whether Mars has a solid inner core, with recent studies offering conflicting evidence.

Key idea: Mars's surface is a dusty, rocky desert colored by iron rust, with soil containing both plant nutrients and toxic chemicals.

The surface of Mars is made of minerals containing silicon and oxygen, metals, and other elements found in rocks. It is mainly composed of a type of rock called tholeiitic basalt, similar to volcanic rocks on Earth. However, some areas have more silica, making them similar to other Earth rocks like andesite.

The red orange color of Mars comes from iron oxide, which is essentially rust. Other colors like gold, brown, tan, and green can also be seen depending on the minerals present. Fine iron oxide dust covers much of the surface.

The Phoenix lander found that Martian soil is slightly alkaline and contains nutrients like magnesium, sodium, potassium, and chlorine, which are important for plant growth on Earth. However, it also found a toxic chemical called perchlorate in concentrations that would be harmful to humans.

Dark streaks are common on Mars, especially on steep slopes. These streaks start dark and become lighter over time. They are thought to be caused by avalanches of bright dust revealing darker soil underneath, or by dust devils. Some theories also involve water or even tiny organisms, but these are less accepted.

Key idea: Mars once had a global magnetic field and possibly plate tectonics, but it lost this protection, leading to its thin atmosphere today.

Mars does not have a strong, global magnetic field like Earth does today. However, observations show that parts of its crust were magnetized in the past. This suggests that Mars once had a magnetic field that protected it, similar to how Earth's magnetic field works. This ancient magnetism, called paleomagnetism, is found in bands across the Martian crust, much like the magnetic patterns found on Earth's ocean floors.

One idea is that these magnetic bands mean Mars had plate tectonics about four billion years ago, before its internal engine that creates the magnetic field stopped working. If this is true, Mars would have been much more like Earth in its early days. The loss of this magnetic field meant that the solar wind, a stream of charged particles from the Sun, could directly hit Mars's atmosphere, slowly stripping it away over billions of years. This is why Mars's atmosphere is so thin today.

Key idea: Mars's surface features are named using a system that reflects its history of observation, with a unique elevation reference called the areoid.

Early astronomers, like Johann Heinrich von Mädler and Wilhelm Beer, were the first to map Mars in detail in the 1800s. They confirmed that Mars's surface features were permanent and accurately measured how fast it spins. In 1840, Mädler created the first map of Mars.

Features on Mars are named from many different sources. For example, large craters are named after famous scientists and writers who studied Mars. Smaller craters are named after towns with populations under 100,000. Large valleys are named after the word "Mars" or "star" in different languages.

The red plains on Mars, covered in iron rich dust, were once thought to be continents and given names like Arabia Terra. Darker areas were thought to be seas, hence names like Mare Erythraeum. The largest dark feature visible from Earth is Syrtis Major Planum. The permanent ice caps at the north and south poles are called Planum Boreum and Planum Australe, respectively.

Since Mars has no oceans, it does not have a "sea level" like Earth. So, scientists defined a zero elevation point based on atmospheric pressure. This reference level is called the areoid, similar to Earth's geoid. The United States Geological Survey divides Mars's surface into 30 map sections, each named after a classical feature.

Key idea: Mars features immense geological structures like the giant Olympus Mons volcano and the Valles Marineris canyon, alongside countless impact craters and potential caves, all shaped by its violent past.

The Tharsis region on Mars is a huge upland area that contains several enormous volcanoes. The most famous is Olympus Mons, a shield volcano that is over 600 kilometers wide. It is so large that it is difficult to measure its exact height, but from its base to its peak, it is over 21 kilometers tall. This makes it either the tallest or second tallest mountain in the entire solar system, roughly three times the height of Mount Everest.

Mars's surface shows a striking difference between its northern and southern halves. The northern plains are flat, likely smoothed by ancient lava flows. The southern highlands are heavily cratered from old impacts. Scientists believe a massive object, perhaps one tenth to two thirds the size of Earth's Moon, struck Mars's northern hemisphere four billion years ago. This impact would have created a crater 10,600 by 8,500 kilometers in size, making it the largest impact crater in the solar system.

Mars has about 43,000 impact craters that are 5 kilometers or larger. The largest visible crater is Hellas, which is 2,300 kilometers wide and 7 kilometers deep. Because Mars is closer to the asteroid belt, it has a higher chance of being hit by space rocks. Some Martian craters show signs that the ground was wet after the impact, suggesting the presence of water.

The giant canyon system, Valles Marineris, is 4,000 kilometers long and up to 7 kilometers deep. Its length is about one fifth of Mars's circumference. It is thought to have formed when the Tharsis area swelled, causing the crust to crack and collapse. Some scientists even propose that Valles Marineris is a plate boundary, suggesting Mars might have had a two plate tectonic system in the past.

Images from NASA's Mars Odyssey orbiter have shown seven possible cave entrances on the side of a volcano called Arsia Mons. These caves, known as the "seven sisters," are very deep and could offer protection from the harsh radiation and micrometeoroids on Mars's surface. This makes them interesting places to consider for future human exploration.

Key idea: Mars's thin, carbon dioxide rich atmosphere is constantly being stripped away by the solar wind due to the planet's lost magnetic field, leading to unique atmospheric phenomena like global auroras and slower sound travel.

Mars lost its protective magnetic field about four billion years ago. This meant that the solar wind, a stream of charged particles from the Sun, could directly interact with Mars's upper atmosphere. Over time, this solar wind has stripped away atoms from the atmosphere, making it very thin. Spacecraft like Mars Global Surveyor and Mars Express have detected these atmospheric particles escaping into space.

The atmosphere of Mars is much thinner than Earth's. The air pressure on the surface is only about 0.6 percent of Earth's sea level pressure. It is mostly made up of about 96 percent carbon dioxide, with small amounts of argon and nitrogen, and traces of oxygen and water. The atmosphere is also very dusty, with tiny particles that give the Martian sky a tawny or pinkish color when seen from the surface.

Scientists have detected methane on Mars, but they are not sure where it comes from. It could be produced by non biological processes, like certain reactions between water and minerals, or it could be a sign of life. The amount of methane seems to change with the seasons. Because the atmosphere is so thin, sound travels differently on Mars. Researchers using recordings from the Perseverance rover found that sound travels at about 240 to 250 meters per second, which is slower than on Earth.

Auroras, similar to Earth's Northern and Southern Lights, have also been detected on Mars. Since Mars does not have a global magnetic field, its auroras are different. They are not limited to the polar regions and can happen across the entire planet. In 2017, a massive solar storm caused radiation levels on Mars's surface to temporarily double and created an aurora 25 times brighter than any seen before.

Key idea: Mars experiences extreme seasons due to its axial tilt and oval shaped orbit, leading to wide temperature swings and massive global dust storms.

Mars has seasons, just like Earth, because its axis is tilted. However, Mars's orbit around the Sun is more oval shaped than Earth's. This means that when Mars is closest to the Sun, it is summer in its southern hemisphere and winter in its northern hemisphere. When it is farthest from the Sun, it is winter in the south and summer in the north. As a result, the seasons in the southern hemisphere are more extreme, with hotter summers and colder winters, while the northern seasons are milder.

Temperatures on Mars can range from about minus 110 degrees Celsius to a high of 35 degrees Celsius in the equatorial summer. This huge temperature difference is due to the thin atmosphere, which cannot trap much heat, and the low atmospheric pressure. Mars is also about 1.5 times farther from the Sun than Earth, so it receives much less sunlight.

Mars is famous for having the largest dust storms in the solar system. These storms can reach speeds over 160 kilometers per hour and can sometimes cover the entire planet. They tend to happen when Mars is closest to the Sun and have been shown to increase the planet's overall temperature. The seasons also cause dry ice, which is frozen carbon dioxide, to cover the polar ice caps.

Key idea: Mars holds a large amount of water, mainly as frozen ice beneath its surface and at its poles, but its thin atmosphere prevents liquid water from existing stably on the surface today.

While Mars does have a significant amount of water, most of it is frozen water ice, covered by dust, especially at its polar ice caps. If the water ice in the south polar ice cap alone were to melt, it would be enough to cover most of the planet's surface with 11 meters of water.

Liquid water cannot exist on the surface of Mars for long periods today. This is because of the extremely low atmospheric pressure, which is less than one percent of Earth's. At such low pressures, water boils and freezes at much lower temperatures, meaning it would quickly evaporate or freeze. Only at the very lowest elevations, where pressure and temperature are slightly higher, might liquid water exist for very short times.

Even though there is little water in the atmosphere, there is enough to form clouds of water ice, as well as different types of snow and frost. Sometimes, this is mixed with snow made of frozen carbon dioxide, also known as dry ice.

Key idea: Mars's surface is covered with geological evidence, such as vast channels, valley networks, and gullies, strongly indicating that liquid water was once abundant and shaped the planet.

Many features on Mars's surface strongly suggest that liquid water once flowed there. For example, huge channels, called outflow channels, cut across the surface in about 25 places. Scientists think these were carved by massive floods of water released from underground aquifers. One of the largest, Ma'adim Vallis, is 700 kilometers long, much larger than the Grand Canyon, and up to 2 kilometers deep.

In older parts of Mars, you can see networks of smaller valleys that look like river systems. These suggest that early Mars had rainfall and surface runoff. Underground water flow might have also played a role in shaping some of these features.

Along crater and canyon walls, there are thousands of features that resemble gullies on Earth. These gullies are often found in the southern highlands and face the equator. Many scientists believe they were formed by liquid water from melting ice, although others suggest they could be from dry dust flows or frozen carbon dioxide. These gullies appear to be very young, possibly still forming today.

Other geological features, like deltas and fan shaped deposits in craters, also point to a warmer, wetter past on Mars. These conditions would have required many crater lakes across the planet. Minerals like hematite and goethite, which often form in the presence of water, have also been found, providing more evidence of past water.

Key idea: Numerous missions and discoveries have provided strong evidence of abundant past water on Mars, including subsurface ice and minerals formed in water, though the extent of past surface oceans and current liquid water remains an active area of research.

In 1963, scientists first clearly showed that water vapor existed on Mars using telescopes on Earth. In 2004, the Opportunity rover found the mineral jarosite, which only forms in acidic water, proving that water was once present. The Spirit rover found concentrated silica deposits in 2007, also indicating past wet conditions. In 2011, gypsum, another mineral that forms with water, was found by the Opportunity rover.

Scientists estimate that the amount of water in Mars's upper mantle, stored as hydroxyl ions in minerals, is equal to or greater than Earth's. This would be enough to cover the entire planet with 200 to 1,000 meters of water if released.

In 2013, the Curiosity rover found evidence of hydrated minerals, like calcium sulfate, in rock samples. Its DAN instrument also showed subsurface water, up to 4 percent water content, down to 60 centimeters deep.

In 2015, NASA announced strong evidence of salty liquid water flows, called recurring slope lineae, on Martian slopes. These dark streaks appear in Martian summer when temperatures are above minus 23 degrees Celsius and freeze when it gets colder. While this supported the idea of liquid water just below the surface, later research suggested these might be dry granular flows with only a small role for water. So, a definite conclusion about liquid water on the surface is still being sought.

Many scientists suspect that much of Mars's northern plains were once covered by an ocean hundreds of meters deep, possibly as large as Earth's Arctic Ocean. This idea is supported by the ratio of different types of hydrogen in Mars's atmosphere today, suggesting Mars lost a lot of water. However, some scientists caution that climate models have not yet shown Mars was warm enough for such large bodies of liquid water. The Korolev Crater, near the northern polar cap, is filled with a massive amount of water ice, equivalent to about 2,200 cubic kilometers. In 2016, NASA also found a huge amount of underground ice in the Utopia Planitia region, comparable to the volume of water in Lake Superior.

Key idea: Mars's orbital motion dictates its longer year, seasons, and how often it comes closest to Earth, leading to unique celestial events like retrograde motion.

Mars orbits the Sun at an average distance of about 230 million kilometers. It takes Mars 687 Earth days to complete one orbit, which means a Martian year is about 1.88 Earth years. A day on Mars, called a "sol," is only slightly longer than an Earth day, lasting about 24 hours and 39 minutes.

Mars's axis is tilted by about 25.19 degrees, very similar to Earth's tilt of 23.5 degrees. This tilt is why Mars experiences seasons, just like Earth. However, because a Martian year is nearly twice as long, its seasons are also nearly twice as long. Currently, Mars's north pole points towards the star Deneb.

Mars's orbit is more oval shaped than Earth's. This means its distance from the Sun changes more throughout its year. In the past, Mars had a much more circular orbit. Its cycle of how oval shaped its orbit becomes lasts for 96,000 Earth years.

Mars comes closest to Earth every 780 days, which is about every 2.1 years. This event is called an opposition. During opposition, Mars appears brightest and largest in our sky. The distance between Mars and Earth during these close approaches can vary significantly, from about 54 million to 103 million kilometers, because both planets have elliptical orbits. When Mars is farthest from Earth, it can be as far as 401 million kilometers away.

When Mars approaches opposition, it sometimes appears to move backward in the sky relative to the background stars. This is called retrograde motion and lasts for about 72 days. During this time, Mars reaches its brightest point.

Key idea: Mars has two small, irregularly shaped moons, Phobos and Deimos, whose origins are debated, with theories suggesting they are captured asteroids or fragments from a past impact.

Mars has two small natural moons, Phobos and Deimos. Phobos is about 22 kilometers wide, and Deimos is about 12 kilometers wide. Their origin is not fully understood, but a popular idea is that they are asteroids that were captured by Mars's gravity.

Both moons were discovered in 1877 and named after characters from Greek mythology: Phobos (panic and fear) and Deimos (terror and dread), who were companions to Ares, the Greek god of war. Mars is the Roman equivalent of Ares.

From the surface of Mars, Phobos and Deimos move differently than Earth's Moon. Phobos rises in the west, sets in the east, and rises again in just 11 hours. Deimos rises in the east but moves very slowly across the sky. Phobos's orbit is getting lower over time due to Mars's gravity. In about 50 million years, it might crash into Mars or break apart to form a ring around the planet.

Another idea for their origin is that they formed from debris ejected after a large impact on Mars, similar to how Earth's Moon is thought to have formed. Recent studies suggest Phobos has a very porous inside and contains minerals similar to Mars, supporting this impact theory. It is also possible that Phobos and Deimos are fragments of an older, larger moon that was destroyed.

Key idea: Human observation of Mars dates back to ancient civilizations, evolving from mythical interpretations to detailed telescopic mapping, which, despite early misconceptions about "canals," revealed fundamental truths about planetary motion.

Humans have been observing Mars for thousands of years. Ancient civilizations like the Sumerians, Egyptians, and Babylonians tracked its movement in the sky. The Sumerians called Mars "Nergal," the god of war and plague. The ancient Greeks called it "Pyroeis" or "Ares," and the Romans named it "Mars" after their god of war, which is where the planet gets its modern name.

In the 4th century BCE, the Greek philosopher Aristotle noted that Mars disappeared behind the Moon, showing that Mars was farther away. Ptolemy, another Greek astronomer, developed models to explain Mars's orbital motion, which were used for centuries. Chinese astronomers also knew about Mars by the 4th century BCE and called it the "fire star."

In 1609, Johannes Kepler used observations of Mars to figure out that planets orbit the Sun in ellipses, not perfect circles. A year later, Galileo Galilei used a telescope to observe Mars. In 1672, Giovanni Domenico Cassini made the first attempts to measure the distance to Mars using a method called parallax.

By the late 1800s, telescopes were good enough to see details on Mars's surface. In 1877, Italian astronomer Giovanni Schiaparelli drew maps of Mars that showed features he called "canali," meaning "channels" or "grooves." This word was mistakenly translated as "canals" in English, leading many people to believe there were artificial waterways built by intelligent Martians. Percival Lowell, an American astronomer, strongly promoted this idea, even building an observatory to study Mars. However, as telescopes improved, it became clear that these "canals" were mostly optical illusions.

The idea that Mars had vast seas and vegetation, and even intelligent life, was widely believed for a long time. But with better observations, these ideas faded. By 1909, astronomers using more powerful telescopes saw irregular patterns but no straight "canals."

Key idea: Spacecraft exploration of Mars began in the 1960s, dramatically changing our understanding of the planet and leading to continuous robotic presence since 1997, with many active missions still gathering data.

The first spacecraft to visit Mars was the Soviet Union's Mars 1 in 1963, but it lost contact. NASA's Mariner 4 made the first successful flyby in 1965, sending back the first close up images of another planet. These early missions completely changed our understanding of Mars, showing it was a cratered, lifeless world, not a lush planet with canals.

In 1971, Mariner 9 became the first spacecraft to orbit Mars, providing much more detailed images. That same year, the Soviet Union's Mars 3 made the first successful landing on Mars, though it only transmitted for a short time.

After a period with few successful missions, continuous robotic exploration of Mars began in 1997 with the Mars Pathfinder rover and the Mars Global Surveyor. Since then, many advanced spacecraft, including orbiters, landers, and rovers from various countries, have been sent to Mars. These missions have created detailed maps, studied its geology and climate, and searched for signs of past water and potential life.

As of 2023, there are ten active spacecraft at Mars: eight orbiting the planet and two rovers, Curiosity and Perseverance, on its surface. These missions continue to send back incredible data, helping us understand Mars's past and present. You can explore Mars yourself using online tools like Google Mars, NASA's Mars Trek, and Experience Curiosity.

Key idea: Future plans for Mars include numerous robotic sample return missions and ambitious long term goals for human exploration and colonization, with the search for life being a top scientific priority.

Many future missions to Mars are planned. NASA's EscaPADE spacecraft is set to launch in 2025. The Rosalind Franklin rover, designed to look for signs of past life, is now aiming for a launch in 2028. There are also plans for joint NASA European Space Agency missions to bring samples of Mars back to Earth, possibly launching in 2026. China also plans a sample return mission, Tianwen 3, for 2028 or 2030.

Beyond robotic missions, there is significant interest in sending humans to Mars. While no crewed mission is currently planned, NASA was asked to study the feasibility of a human mission in the early 2030s, though they concluded it would be unfeasible. Private companies like SpaceX are actively developing technology, such as the Starship rocket, with the long term goal of colonizing Mars. Elon Musk, the head of SpaceX, envisions a Mars colony within the next twenty years, supported by resupply from Earth and local resources on Mars.

Scientists are also working to define the top priorities for human exploration on Mars. The main goal is to search for current or extinct life on the planet. The optimal time to launch a mission to Mars, when Earth and Mars are aligned, happens every 26 months.

It is worth noting that over seven tons of debris, including crashed spacecraft and discarded components, have accumulated around Mars from these missions.

Key idea: While early beliefs about a habitable Mars were disproven, the planet's past water and ongoing discoveries, including potential biosignatures, keep the question of whether life exists or existed on Mars an active area of scientific inquiry.

In the late 1800s, many astronomers believed Mars had qualities that could support life, including oxygen and water. However, observations by W. W. Campbell in 1894, and later in 1909, showed that Mars had very little water vapor or oxygen. It took until 1925 for these findings to be widely accepted, finally breaking the myth of an Earth like, habitable Mars. Even so, some people continued to publish ideas about Martian biology into the 1960s.

Today, scientists understand that for a planet to support life as we know it, it usually needs liquid water on its surface. While Mars is sometimes within the "habitable zone" of the Sun, its thin atmosphere prevents liquid water from staying on the surface for long. The evidence of past liquid water on Mars, however, shows that it once had the potential for life. Recent findings suggest that any past water on Mars might have been too salty and acidic to support Earth like life.

The conditions on Mars are very challenging for life. It has poor heat transfer, little protection from the Sun's harmful solar wind because it lacks a strong magnetic field, and not enough atmospheric pressure to keep water liquid. Mars also appears to be mostly geologically inactive, meaning it does not recycle chemicals and minerals between its surface and interior as much as Earth does.

Despite these challenges, the question of whether life ever existed on Mars remains open. The Viking probes in the 1970s conducted experiments that showed some positive results for microorganisms in the soil, though these were later debated. Some scientists, like NASA's Gilbert Levin, still argue that Viking may have found life. More recent discoveries, such as chlorate and perchlorate ions in Martian meteorites, suggest that any organic molecules would need to be buried underground to survive the radiation. The detection of small amounts of methane and formaldehyde could also be signs of life, though they could also come from geological processes. Impact glass, which can preserve signs of life on Earth, has also been found on Mars.

In June 2024, the Perseverance rover found a rock called Cheyava Falls, which NASA has called a "potential biosignature," meaning it might contain signs of life. This rock has been sampled for possible return to Earth for further study, but scientists cannot yet say for sure if its origin is biological or not.

Key idea: Mars has profoundly influenced human culture, from ancient mythology linking it to war to inspiring countless science fiction stories about intelligent life, reflecting our hopes and fears about other worlds.

Mars has had a significant impact on human culture throughout history. It is named after the Roman god of war, Mars, and its symbol, a circle with a spear, is also used to represent the male gender. This association with war dates back to ancient Babylonian astronomy, where the planet was linked to the god Nergal, god of war and destruction.

In the late 19th century, the idea of intelligent Martians became very popular, fueled by the mistaken interpretation of "canali" as artificial canals. This led to a period known as "Mars Fever," where many believed Mars was a dying world with advanced civilizations building irrigation systems. This inspired many science fiction stories, such as H. G. Wells's "The War of the Worlds," where Martians invade Earth, and Ray Bradbury's "The Martian Chronicles."

Even after spacecraft showed Mars to be a lifeless, canal less world, pseudoscientific ideas about intelligent life on Mars continued, based on perceived features like "pyramids" or the "Face on Mars." As planetary astronomer Carl Sagan wrote, "Mars has become a kind of mythic arena onto which we have projected our Earthly hopes and fears."

Modern science fiction has adapted to the new understanding of Mars, with authors like Kim Stanley Robinson creating stories based on the planet's actual geology and challenges, showing how our evolving knowledge continues to inspire new narratives.