Life on Mars

Astrobiologists study Mars to understand if life can exist beyond Earth.

Mars is a primary subject of interest because of its proximity to our planet. It shares many similarities with the early Earth. Scientists want to know if Mars once hosted life or if it still does. To date, no conclusive evidence of life has been found. However, the planet holds a massive record of prebiotic conditions. Prebiotic conditions are the chemical environments that lead up to the start of life. Because Mars lacks plate tectonics, it has remained almost unchanged for billions of years. At least two-thirds of the surface is more than 3.5 billion years old. This makes Mars a unique laboratory for studying how life begins.

Understanding the history of Martian habitability requires looking at its changing environment. During the ancient Noachian period, Mars had a much different climate. The surface environment once held liquid water. This water flowed through river networks and settled in lakes. A magnetic field once protected the atmosphere from the solar wind. This shield allowed the atmosphere to remain dense enough for liquid water to exist. When the magnetic field was lost, the solar wind stripped the atmosphere away. This loss caused temperatures to drop significantly. Much of the liquid water either sublimed into gas or became trapped in permafrost. Permafrost is a layer of ice found beneath the soil.

Scientists use specific factors to predict if a location is habitable. They look for water availability and suitable temperatures. They also search for nutrients and an energy source for metabolism. Protection from ionizing radiation is another critical requirement. Currently, the Martian surface is bathed in intense radiation. The soil also contains perchlorates, which are chemicals toxic to many microorganisms. Because of these harsh surface conditions, scientists believe life might be best preserved in the subsurface. This means looking beneath the top layer of soil. If life ever existed, it likely lived as tiny microbes in fluids or sediments.

Human interest in Mars has evolved through centuries of observation. In the mid-17th century, observers first noticed the polar ice caps. In the late 18th century, William Herschel proved these caps grow and shrink with the seasons. By the mid-19th century, astronomers noted that Mars has a day length similar to Earth. They also found the axial tilt is similar, which creates seasons. In 1854, William Whewell theorized that Mars had seas and land. In the late 19th century, speculation grew due to observations of Martian canals. Percival Lowell published books claiming these canals were built by a civilization. However, these canals were actually optical illusions. By 1909, better telescopes and observations by Eugène Antoniadi proved they did not exist.

Modern exploration relies on sophisticated robotic rovers to find chemical clues. The Curiosity rover has provided vital data about the Gale Crater. It confirmed that this area once contained a freshwater lake. Curiosity also identified key ingredients for life, such as sulfur, nitrogen, and phosphorus. It even discovered organic compounds inside sedimentary rocks. Organic compounds are the essential building blocks for life.

In 2018, NASA announced the detection of seasonal variations in methane. Methane is a gas that can be produced by microorganisms or geological processes. This discovery keeps the search for biological activity active.

Recent missions continue to push the boundaries of our knowledge. The Perseverance rover is currently exploring the Jezero Crater. On September 10, 2025, NASA reported that Perseverance found a possible biosignature. A biosignature is a substance or feature that provides evidence of past life. This finding in the rock hints at ancient microbial activity. Perseverance is also collecting many drill samples. These samples may be transported to Earth laboratories in the late 2020s or 2030s. Other missions, like the ExoMars Trace Gas Orbiter, help map atmospheric gases.

These efforts aim to find fossils or organic molecules.

Mars also offers insights into how geological events affect life. A large impact from an asteroid can create a hydrothermal system. This is a system of hot, mineral-rich water. On Earth, such systems can last for millions of years. On Mars, a large crater could sustain such a system for 2 million years. This is long enough for microscopic life to potentially emerge. Scientists also study impactite, which is rock formed by an impact. These rocks may preserve ancient biosignatures if they were present during the impact.

By studying these complex systems, we move closer to answering if we are alone in the solar system.