Facts About Mars: The Red Planet Explained

Mars is the fourth planet from the Sun and Earth's most-visited neighbour, with orbiters, landers and rovers sent there by several countries. It is a cold, dry world, but evidence suggests it was once warmer and wetter.

Key takeaways

• Mars looks red because its surface dust is rich in iron oxide, like rust.
• Its atmosphere is thin and mostly carbon dioxide.
• Olympus Mons is the tallest known volcano in the Solar System.
• Rovers have found signs that liquid water once flowed on the surface.
• No evidence of life has been found, but the search continues.

Basic facts

Mars is about half the diameter of Earth and has roughly one tenth of Earth's mass, so surface gravity is about 38 percent of ours. A Martian day, called a sol, lasts about 24 hours and 37 minutes, close to an Earth day. Its year lasts about 687 Earth days. It tilts on its axis by about 25 degrees, similar to Earth, so Mars has seasons, though they are longer.

Why it is red

Iron-rich minerals in the rocks and dust have reacted with oxygen over time, forming iron oxide. Dust is spread over much of the planet by winds, giving it a rusty colour. The sky is often a butterscotch or pinkish hue because suspended dust scatters light, while sunsets can appear blue, as shown in images from rovers.

A thin atmosphere

The Martian atmosphere is about 95 percent carbon dioxide, but it is extremely thin, with surface pressure under one percent of Earth's. That means liquid water is generally unstable on the surface today, since it would freeze or evaporate quickly. Temperatures vary from around minus 125 degrees Celsius near the poles in winter to above 20 degrees Celsius at midday near the equator in summer, averaging about minus 60.

Giant landforms

Olympus Mons, a shield volcano, rises about 22 kilometres above its surroundings, nearly three times the height of Mount Everest above sea level, and spreads wide enough to cover an area comparable to that of Arizona. Valles Marineris is a huge canyon system running about 4,000 kilometres, longer than the width of the United States and much deeper than the Grand Canyon. Both features show the scale of geological activity on Mars in the past.

Two small moons

Mars has two small moons, Phobos and Deimos, discovered in 1877. They are irregular and lumpy, and they may be captured asteroids, though their origin is debated. Phobos orbits very close to Mars and is slowly drifting inward.

Evidence for water

Orbiters have photographed ancient river valleys, delta-like fans and lake basins. Rovers such as Curiosity, which landed in 2012, and Perseverance, which landed in 2021, have found minerals that form in the presence of water and rocks laid down in ancient lakes. Ice exists at the poles and below the surface in some regions. These findings suggest Mars once had conditions that could have supported microbial life, though whether life ever existed is unknown.

Exploration

Robotic missions have studied Mars for decades. In 2021, the small helicopter Ingenuity made the first powered, controlled flights on another planet, completing dozens of flights before its mission ended in 2024. Perseverance is collecting rock samples that future missions may return to Earth. Space agencies and companies have discussed sending humans, but the challenges include radiation, long travel times and life support.

Dust storms

Mars has the biggest dust storms in the Solar System, which can sometimes cover the whole planet and last for weeks. The thin air means the wind pressure is weak, so the storms are less forceful than depicted in films.

Robots on the surface

Humans have explored Mars with robots for nearly half a century. The Viking landers of 1976 were the first to operate successfully on the surface and carried experiments searching for signs of life, with results that remain debated. In 1997, the Pathfinder mission delivered the small Sojourner rover. The twin rovers Spirit and Opportunity landed in 2004 and found evidence that liquid water once shaped the surface, with Opportunity working for nearly fifteen years. Curiosity, a car-sized rover, landed in Gale Crater in 2012, and Perseverance landed in Jezero Crater in 2021. China landed its Zhurong rover in 2021, and NASA's InSight lander recorded marsquakes between 2018 and 2022, giving the first look at the planet's interior.

Water and habitability

Jezero Crater was chosen because it holds a fan-shaped delta where a river once flowed into a lake, a place where signs of ancient life might be preserved. Scientists have also found ice under the surface at mid and high latitudes, and radar results have hinted at features under the south polar ice cap that some researchers interpret as water, though this is debated. Reports of methane in the atmosphere have been intriguing because methane can be produced by life or by geology, but measurements have been inconsistent. Current evidence suggests that Mars may have been habitable in its distant past, but whether life ever existed there is unknown.

Sample return

Perseverance is collecting rock and soil samples in sealed tubes, and some have been left on the surface so a future mission might collect them. Returning samples to Earth would let scientists use laboratory equipment far more powerful than anything that can be sent to Mars. The plans for retrieving them have been complex and costly and have been revised several times, so the timeline remains uncertain.

Challenges for human missions

Sending people to Mars is much harder than visiting the Moon. A journey takes six to nine months each way, and crews would be exposed to radiation from the Sun and cosmic rays beyond the protection of Earth's magnetic field. Landing heavy equipment through the thin atmosphere is difficult, and the dust can damage machinery. Crews would need years of supplies or ways to make fuel, water and oxygen from local resources. Psychological challenges include isolation and delays of up to twenty minutes in communications with Earth.

Mars in culture

Mars has fascinated people for more than a century. In the late nineteenth century, the astronomer Giovanni Schiaparelli described channels on the surface, and a mistranslation and the writing of Percival Lowell helped fuel the idea of canals built by intelligent beings, which was later disproved. H. G. Wells's novel The War of the Worlds appeared in 1898, and Mars has remained a favourite in fiction, from classic science fiction to recent films.

Frequently asked questions

Can humans breathe on Mars?

No. The air is thin and mostly carbon dioxide, so people would need a pressurised suit.

How long does it take to get there?

Typical robotic missions take around six to nine months, depending on timing.

Is there life on Mars?

None has been found so far, but scientists are looking for signs of past or present life.

How far away is Mars?

The distance varies as both planets orbit the Sun, from about 55 million kilometres at the closest approach to more than 400 million kilometres when they are on opposite sides of the Sun. Missions launch during windows when the trip is most efficient.

Does Mars have a magnetic field?

Mars does not have a global magnetic field like Earth, but it has patches of magnetised crust that suggest it had one in the past. Without a strong field, the thin atmosphere was gradually stripped away by the solar wind over billions of years.

Could we terraform Mars?

Terraforming, making Mars Earth-like, is speculative. Scientists estimate that it would be extremely difficult with current technology because there is not enough carbon dioxide easily available to thicken the atmosphere. It remains a topic for science fiction and theoretical study.

Sources and further reading

• Mars (Wikipedia)
• NASA Mars Exploration Program