Mars

 Mars Facts

• 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 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. 

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.