Iron in the rocks and dust on Mars's surface is oxidising in the thin atmosphere, giving the planet its warm, rust-coloured hue.
Explore facts about the red planet.
- Equator circumference: 21,297km
- Radius: 3,390km
- Average distance from Sun: 228 million km
- Surface temperature: -153°C to 20°C
- Average orbital speed: 86,700km/h (24km/s)
- Day length: 24.6 hours
- Year length: 687 Earth days
- Moons: 2
- Planet type: terrestrial
How big is Mars?
Mars is around two times smaller than Earth. It has an equatorial circumference of about 21,000 kilometres, and a radius (the distance from the middle of its core to the surface) of around 3,400 kilometres.
It's thought that Mars's core is predominantly made up of iron, but also nickel and sulphur. The core is about half the size of the planet and may be entirely liquid, or have a solid iron centre and a liquid exterior.
Mars boasts the largest volcano in the solar system. Olympus Mons is a shield volcano around 25 kilometres in height and 624 kilometres in diameter - the largest volcano on Earth, Mauna Loa in Hawaii, is just over four kilometres in height and 120 kilometres wide.
The deepest canyon on the planet is Valles Marineris at 7 kilometres - Earth's Grand Canyon is only 1.8 kilometres deep. Valles Marineris was mostly formed by tectonic processes.
How hot is Mars?
Mars's thin atmosphere makes for extreme temperature differences on the planet. When the Sun's energy enters the atmosphere, it is not equally dispersed and easily escapes back out into space.
The temperature ranges from around -153°C at the poles to possible highs of 20°C elsewhere on the planet's surface.
How far from the Sun is Mars?
Mars is the fourth planet from the Sun, orbiting at an average of 228 million kilometres away from the star. The planet moves at a speed of around 24 kilometres per second, making it slightly slower than Earth.
It has an elliptical orbit, meaning it is egg- or oval-shaped. This means that throughout its year, Mars's distance from the Sun ranges between around 206 million and 249 million kilometres.
How long is a day on Mars?
A day on Mars lasts 24.6 hours, comparable to a day on Earth. But its years are far longer than ours, at 687 Earth days per trip around the Sun.
The planet is tilted at 25° on its axis - slightly more than Earth. A planet's tilt is one of the reasons that seasons occur - in this case, Mars's seasons are twice as long as Earth's due to its longer orbit around the Sun.
What is Mars's atmosphere made of?
Mars's atmosphere is made up of around 96% carbon dioxide. It also contains small quantities of argon, nitrogen, oxygen and water vapour.
The atmosphere is very thin, but it is thought that in the past it was much thicker. The loss has been attributed to the solar winds, although there are other processes that can thin an atmosphere (such as the impacts of astronomical bodies).
Is there water on Mars?
Mars almost certainly had surface water in the past, interpreted from the evidence of canyons, dry lakebeds and river networks.
Although these features could only have been formed by liquid water, there is none left on the surface now due to the cold, thin atmosphere. But the planet has polar ice caps. If these melted, the planet would be covered by 20- to 30-metre-deep water.
How many moons does Mars have?
Mars has two moons: an inner moon called Phobos and a much smaller outer moon, Deimos. They are unevenly shaped, rocky satellites and may be asteroids caught in the planet's gravity.
Phobos is slowly moving towards Mars and is likely to crash into the surface in about 50 million years. Deimos appears smoother than Phobos as loose dirt, known as regolith, fills its craters.
Why is Mars red?
Like Earth, Mercury and Venus, the planet Mars is a rocky, terrestrial planet.
Its famous colour is caused by the iron in rocks and dust of the crust's surface oxidising - similar to the process of iron on Earth rusting.
Dust is heavily present in Mars's atmosphere, making the planet appear red to us on Earth. But the surface is actually a variety of colours when seen up close.
Mars has a large, dark patch on its surface, known as the Syrtis Major Planum. It reaches around 1,500 kilometres north from the equator and is around 1,000 kilometres in width. The dark colour is due to its primarily basalt rock composition.
Who discovered Mars?
Mars is one of the five classical planets visible to the naked eye. It was known at least 4,000 years ago - its course was charted by astronomers in Ancient Egypt. We don't know who first discovered the planet, however.
As of 2016 there have been over 40 missions attempting to reach Mars and its moons and just over half have been either a success or partially successful.
The first mission to reach the red planet was NASA's Mariner 4, launched in 1964. This was an identical craft to its predecessor, Mariner 3, whose mission had been unsuccessful because of a technical fault. Mariner 4 completed the first flyby.
Perhaps the best known missions are the wheeled vehicles that have driven over the Martian surface. The latest is NASA's Curiosity, which landed in Gale Crater in 2012.
NASA's InSight Mars Lander is set to launch in May 2018, with the aim of landing on the planet in November 2018. One of the main purposes of the mission is to gather data that will aid scientists in understanding how the planet formed about 4.5 billion years ago.
NASA's current goal is to send humans to Mars during the early 2030s. Data supplied by previous and future missions, such as sample returns, are set to guide this initiative.