Mars Exploration: What We Know About the Red Planet

Mars is the fourth planet from the Sun, a cold rocky world with a very thin atmosphere, two small moons, polar ice, giant volcanoes, deep canyons, and strong evidence that liquid water shaped parts of its surface early in its history.[a][b]

This page follows the evidence from basic planetary data to water history, rover discoveries, orbiters, sample collection, and the places where the science still has real uncertainty. You will also see why some common one-line claims about Mars leave out the most useful part of the story.

Mars in Numbers

Mars is about half Earth’s size, but its land area is close to the area of Earth’s dry land. Its day is 24.6 hours, its year is 687 Earth days, and the planet has two small moons, Phobos and Deimos. Surface temperatures can range from about 20°C down to about −153°C depending on place and season.[a]

The term Red Planet is accurate from a distance, but close-up views show many tones, including brown, tan, and gold. Mars looks red mainly because iron-bearing dust and rock have oxidized, which is the same broad chemical idea behind rust on Earth.[c]

Water Then and Now

The broad answer is simple: Mars was wetter before, and Mars is drier now. The more useful answer is that Mars still holds water today, but mostly as ice or water locked into minerals, not as stable lakes or rivers on the surface. NASA notes that a large share of ancient Martian water may still be trapped in the crust, with one study estimating roughly 30% to 99% stored in minerals rather than lost entirely to space.[d]

That distinction matters because it changes the old picture of Mars from “a planet that lost all its water” to “a planet that redistributed much of its water into new places and forms.” It is one reason Mars remains so scientifically useful: the planet preserves traces of climate change in rock, ice, salts, and atmosphere at the same time.

Atmospheric escape is still part of the story. NASA’s MAVEN mission has helped scientists measure how Mars loses gas from its upper atmosphere to space, which helps explain how a planet that once supported surface water became colder and less hospitable over long spans of time.[e]

How Scientists Read Mars

Mars science works best when each mission does a different job. Orbiters show regional patterns. Landers and rovers test local rocks directly. Instruments compare mineral chemistry, textures, layers, atmosphere, and season-to-season change. That mix is what turns a red disk in the sky into a readable planetary record.

Places That Changed the Story

The strongest Mars articles usually mention water, life, and rovers, but they often underplay place. On Mars, location is everything. A crater floor, an ancient delta, and a layered mountain do not tell the same climate story.

Missions Still Shaping the Picture

Current Mars knowledge is built by overlap, not by a single flagship result. The missions below fill different roles, and together they create a far more reliable picture than any one instrument could on its own.

• Perseverance is collecting and caching samples in Jezero Crater, including rock, regolith, and atmosphere samples for future Earth-based study.[k]
• Curiosity remains active and continues to read the sedimentary record in Gale Crater.[l]
• Ingenuity completed 72 flights and ended its mission in January 2024 after proving powered flight on another planet.[m]
• Mars Express, ESA’s long-running orbiter, remains in operation and continues to study the atmosphere, surface, subsurface, and the moons Phobos and Deimos.[n]
• MOXIE, the oxygen demonstration carried by Perseverance, showed that oxygen can be produced from Mars’s carbon-dioxide-rich atmosphere. NASA reported a total of 122 grams of oxygen produced during the experiment.[o]
• Mars Sample Return is still under development. NASA announced in January 2025 that it would study two landing approaches before choosing a single path forward, with formal design confirmation expected later in 2026.[p]

Where People Often Get Mars Wrong

Key Terms Used on This Page

Examples That Show Why Mars Is So Useful

• Layered sediments in Gale Crater help scientists read environmental change through time.
• Delta deposits in Jezero Crater offer a setting where fine sediments may have trapped organic or environmental clues.
• Atmospheric measurements show that even a thin atmosphere can still behave in seasonally complex ways.
• Oxygen production by MOXIE shows that Mars science is not only about the past; it also tests future exploration tools.

Where Evidence Still Stops

Mars science is strong, but it is not finished. We still do not know exactly how long the most favorable surface environments lasted, how much water remains deep below the surface, or what fully explains the methane and oxygen behavior measured at Gale Crater. NASA has described those atmospheric patterns as unresolved, and that is a good reminder that uncertainty is part of the real answer, not a flaw in it.[q]

Mars is easiest to understand when its story is split into three parts: a wetter early planet, a long transition shaped by atmosphere loss and geology, and a modern cold desert that still preserves an unusually readable record of change. That is what makes Mars more than a popular target. It is one of the best places in the Solar System for asking how habitable worlds begin, change, and sometimes narrow their own options.

Sources

1. [a] NASA – Mars: Facts Basic planetary values, seasons, temperature range, surface features, and moon data. ↩
2. [b] NASA – The Five Most Abundant Gases in the Martian Atmosphere Surface atmosphere composition data used for the carbon dioxide figure. ↩
3. [c] NASA – Mars: Facts Used for the explanation of why Mars appears red from a distance. ↩
4. [d] NASA – New Study Challenges Long-Held Theory of Fate of Mars’ Water Used in the section on crustal water storage and the long-term water budget. ↩
5. [e] NASA – MAVEN Atmospheric escape and upper-atmosphere science. ↩
6. [f] NASA – Mars Reconnaissance Orbiter Orbital mapping, water-history objectives, and ongoing mission role. ↩
7. [g] NASA – Mars Odyssey Long-running orbital observations of clouds, fog, frost, and surface chemistry. ↩
8. [h] NASA – Mars 2020 Perseverance Jezero Crater lake-and-delta setting and mission objectives. ↩
9. [i] U.S. Geological Survey – Geologic Map of the Mars 2020 Perseverance Rover Landing Site Regional geologic context for Jezero Crater and its delta deposits. ↩
10. [j] NASA – Mars Science Laboratory: Curiosity Rover Gale Crater habitability findings and current rover context. ↩
11. [k] NASA – Mars Rock Samples Sample collection and caching work by Perseverance. ↩
12. [l] NASA – Curiosity Rover Updates Recent Curiosity activity and continuing surface operations. ↩
13. [m] NASA – Ingenuity Mars Helicopter Mission completion date and total flight count. ↩
14. [n] ESA – Mars Express Status, mission scope, and continuing operation of Europe’s long-running Mars orbiter. ↩
15. [o] NASA – NASA’s Oxygen-Generating Experiment MOXIE Completes Mars Mission Oxygen production totals and the technology result. ↩
16. [p] NASA – NASA to Explore Two Landing Options for Returning Samples from Mars Current development status of Mars Sample Return. ↩
17. [q] NASA – With Mars Methane Mystery Unsolved, Curiosity Serves Scientists a New One: Oxygen Used for the unresolved methane and oxygen discussion in the uncertainty section. ↩