Is Earth’s Neighbor Inhabited? Life on Mars Quiz

The atmosphere of Mars is approximately 95% carbon dioxide, which is toxic to humans but useful for certain types of microbes and plants. However, the air is 100 times thinner than Earth’s, meaning there is very little "blanket" to hold in heat. This thin atmosphere is the main reason why Mars is a frozen desert today instead of a habitable world.

Since we cannot bring Martian soil to Earth easily yet, rovers must act as mobile laboratories. They scoop up soil and heat it in tiny ovens to see what gases are released, or use lasers to zap rocks and analyze the light that bounces back. These chemical "sniff tests" help scientists determine if the soil contains the building blocks of life.

On Earth, the air pressure is high enough to keep water in a liquid state, but on Mars, the pressure is so low that liquid water would instantly boil away or freeze. This means that while we see evidence of past water, any water on the surface today exists only as ice or occasional, salty streaks that vanish almost instantly.

A delta is a fan-shaped geological feature created when a river enters a standing body of water, like a lake or ocean. As the water slows down, it drops all the sediment it was carrying, creating layers of rock. For scientists, these layers are like the pages of a history book, potentially holding fossils of anything that lived in the water.

Water is considered the universal solvent because it can dissolve more substances than any other liquid. On Mars, finding evidence of past liquid water is the primary goal for astrobiologists because all known life requires water to transport nutrients and perform chemical reactions within cells. Without liquid water, the complex biological processes that define life as we know it simply cannot occur.

Early observations of Mars were often hampered by poor telescope quality and optical illusions. Percival Lowell believed he saw straight lines that he interpreted as irrigation canals built by an advanced civilization. We now know these were just shadows and craters; however, his work sparked a massive public interest in space exploration and the possibility of extraterrestrial life.

The Viking lander experiments were the first to directly test Martian soil for signs of metabolism. While one experiment showed a release of gas that looked like a biological reaction, most scientists now believe it was caused by reactive chemicals in the soil called perchlorates. This ambiguity taught scientists that they need much more sophisticated tools to distinguish between complex chemistry and actual biology.

Scientists study organisms on Earth that survive in glaciers, acidic pools, or deep-sea vents to understand the limits of biology. These extremophiles prove that life is incredibly resilient and could potentially survive in the frozen, radiation-soaked environment of Mars. If life can thrive in Antarctica's dry valleys, it provides a powerful blueprint for how Martian microbes might survive.

Methane is an exciting discovery because, on Earth, the vast majority of this gas is produced by living microbes during digestion or decay. Because methane breaks down quickly in the Martian atmosphere due to sunlight, its presence suggests that something is actively releasing it right now. While it could be caused by volcanic activity, the biological possibility remains a major focus.

Unlike Earth, Mars lacks a global magnetic field to deflect high-energy particles from the Sun. This means the surface is constantly bombarded by solar radiation, which can rip apart DNA and destroy organic molecules. Any life existing on Mars today would likely need to be shielded by several feet of rock or soil to survive this relentless and invisible radiation.

A biosignature is any substance, such as an element, isotope, or molecule, that provides scientific evidence of past or present life. Examples include fossilized microscopic structures or specific patterns of organic chemicals that do not occur naturally through geological processes. Finding a confirmed biosignature on Mars would be the definitive "smoking gun" that life once existed on the Red Planet.

Jezero Crater was selected as the landing site for the Perseverance rover because it was once home to a massive lake and an active river delta. On Earth, river deltas are incredibly efficient at trapping and preserving organic matter in layers of silt and clay. This makes Jezero the most promising location to find fossilized microbial life buried in ancient mud.

Earth’s ozone layer acts as a shield against ultraviolet radiation, but Mars’ thin atmosphere provides almost no protection. UV rays are lethal to most bacteria and can sterilize the surface of a planet very quickly. This is why scientists believe that if life is present on Mars today, it is not on the surface but rather hidden in cracks or caves.

The presence of rounded pebbles and carved-out canyons provides undeniable proof that Mars once had a much thicker atmosphere and warmer temperatures. Billions of years ago, the planet had a climate stable enough for liquid water to rain from the sky and flow across the surface. This "warm and wet" period is when life was most likely to begin.

The Martian environment is hostile due to a combination of three major factors: extreme radiation, nearly zero air pressure, and average temperatures of minus 80 degrees Fahrenheit. Any organism would have to evolve specialized proteins to prevent freezing and thick cell walls to keep from exploding in the low pressure. These conditions make the search for life a search for "super-microbes."

Because the surface is so dangerous, the subsurface is the most logical place to look for life. Deep underground, the rock provides a natural shield against solar radiation and maintains a more stable temperature. Additionally, internal heat from the planet’s core could melt underground ice, creating pockets of liquid water where Martian life could potentially still be thriving today.

The distinct reddish color of Mars comes from iron oxide, which is the same compound that creates rust on Earth. This dust is spread across the entire planet by massive global dust storms. While it looks beautiful from a distance, the fine, abrasive dust is actually a major challenge for rovers and could be difficult for any surface-dwelling organisms to manage.

It is a common misconception that scientists are looking for large animals like rabbits or "little green men" on Mars. In reality, the search is focused entirely on microscopic organisms, which are far more likely to exist in such a harsh environment. Even on Earth, for most of our history, life was exclusively made up of tiny, single-celled microbes.

Organic molecules are the chemical building blocks of life, consisting of carbon, hydrogen, and oxygen. Curiosity has detected these molecules in ancient rocks, which proves that Mars once had the necessary ingredients for life to form. While organic molecules can be made by non-living processes, they are a vital requirement for any biological system to start.

NASA has sent several generations of rovers, including Viking, Curiosity, and Perseverance, each more advanced than the last. These missions work together; for example, Curiosity found the ingredients for life, while Perseverance is now specifically looking for signs of ancient life itself. This step-by-step approach is how scientists slowly solve the mystery of the Red Planet.