The planet Mars has fascinated people for centuries. Its reddish color, visible to the naked eye, inspired myths, science fiction stories and, more recently, a long series of space missions. Today, Mars is the most explored planet after Earth, and scientists are still trying to answer one of the biggest questions in science: did life ever exist there?
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Basic facts about Mars
- Position: the fourth planet from the Sun.
- Size: about half the diameter of Earth.
- Gravity: about 38 percent of Earth’s gravity.
- Day: a Martian day, called a sol, lasts about 24 hours and 37 minutes.
- Year: one Martian year lasts about 687 Earth days.
- Moons: two small, irregular moons, Phobos and Deimos.
Why Mars is red
The red color comes from iron minerals in the soil and dust that have oxidized, a process similar to rust. Fine dust covers much of the surface and is often lifted into the atmosphere by winds, giving the Martian sky a pinkish or butterscotch tone during the day.
A thin, cold atmosphere
The atmosphere of Mars is very thin, with surface pressure less than 1 percent of Earth’s, and is composed mostly of carbon dioxide. Because of this, the planet cannot hold much heat. The average temperature is far below freezing, and temperatures vary widely between day and night.
Mars also experiences huge dust storms that can cover large regions or even the entire planet for weeks.
Remarkable landscapes
Mars has some of the most impressive geological features in the solar system:
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- Olympus Mons: the largest known volcano in the solar system, roughly two and a half times the height of Mount Everest above its base.
- Valles Marineris: a vast canyon system thousands of kilometers long, much larger than the Grand Canyon.
- Polar ice caps: made of water ice and frozen carbon dioxide, which grow and shrink with the seasons.
Water on Mars
Today, liquid water cannot remain stable on the surface for long because of the low pressure and cold temperatures. However, there is strong evidence that Mars was once wetter. Orbiters and rovers have found ancient riverbeds, deltas, lake sediments and minerals that form in the presence of water. Large amounts of water ice also exist at the poles and below the surface in some regions.
This history is why scientists believe ancient Mars may have had conditions suitable for microbial life.
The exploration of Mars
Humans have sent many spacecraft to Mars. Some key milestones:
- 1965: NASA’s Mariner 4 made the first successful flyby and sent the first close-up images.
- 1976: the Viking 1 and Viking 2 landers reached the surface and searched for signs of life.
- 1997: the small Sojourner rover became the first wheeled vehicle to explore Mars.
- 2004: the Spirit and Opportunity rovers landed. Opportunity worked for more than 14 years.
- 2012: the Curiosity rover landed in Gale Crater and found evidence of an ancient environment that could have supported microbial life.
- 2021: NASA’s Perseverance rover landed in Jezero Crater, a former lake, to collect rock samples. It carried Ingenuity, a small helicopter that made the first powered, controlled flight on another planet. In the same year, China’s Zhurong rover also landed on Mars.
The search for life
So far, no definitive evidence of life has been found on Mars. Scientists are looking for biosignatures, chemical or physical traces that could indicate past life, in ancient rocks. Samples collected by Perseverance could help answer this question if they are eventually brought back to Earth for detailed analysis, although the plans and timeline for such a mission are still uncertain.
Could humans live on Mars?
Sending people to Mars is a long-term goal of space agencies and private companies. The challenges are enormous: the long journey, radiation exposure, low gravity, the lack of breathable air and the need to produce water, food and fuel. Even so, research on these problems continues, and Mars remains the most likely destination for humans beyond the Moon.
How to see Mars in the sky
Mars is easy to spot as a bright, reddish point of light. It looks brightest during opposition, when Earth passes between Mars and the Sun and the two planets are relatively close. Astronomy apps can help you find it.
Mars missions that changed our understanding
- Mariner 4 (1965): the first successful flyby, sending back the first close-up images of Mars.
- Viking 1 and 2 (1976): the first successful American landers, which searched for signs of life.
- Mars Pathfinder and Sojourner (1997): the first rover on Mars.
- Spirit and Opportunity (2004): twin rovers that found evidence of past water; Opportunity operated for about 14 years.
- Curiosity (2012): a car-sized rover exploring Gale Crater and finding that it once could have supported microbial life.
- Perseverance and Ingenuity (2021): Perseverance collects samples for possible return to Earth, and Ingenuity became the first helicopter to fly on another planet.
Other countries have also sent missions, including China's Tianwen-1, which placed the Zhurong rover on Mars in 2021, and the United Arab Emirates' Hope orbiter.
Mars sample return
Scientists hope to bring samples collected by Perseverance back to Earth, where laboratories could study them in far more detail than instruments on a rover. The project is complex and expensive, and its plans and timeline have been under review.
Seasons and dust storms
Because Mars has an axial tilt similar to Earth's, it has seasons, but they last about twice as long because a Martian year is about 687 Earth days. Mars is also known for dust storms, some of which can cover the entire planet for weeks. A global dust storm in 2018 blocked sunlight and ended the solar-powered Opportunity rover's mission.
Martian moons
Mars has two small moons, Phobos and Deimos, irregular in shape and possibly captured asteroids or formed from debris after an impact. Phobos is slowly getting closer to Mars and, in tens of millions of years, may break apart or crash into the planet.
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Conclusion
The planet Mars is a cold, dusty desert today, but its rocks tell the story of a world that was once very different. Thanks to decades of missions, we know more about Mars than any other planet besides our own, yet its biggest mysteries are still waiting to be solved.