Mars and its moons at a glance

Mars is the fourth of the Sun’s nine planets – the next in order from the Sun after Earth itself. It is the planet that most resembles Earth and although now dry, Mars was once probably awash with water. Mars has two tiny moons, Phobos and Deimos, which may be captured asteroids.

 This photograph of Mars and its two moons, Phobos (right) and Deimos, was taken by the Hubble Space Telescope in Mid-July, 2018, shortly before the planet came closest to the Earth. Image credit: NASA/ESA/STScI

Key facts about Mars

Mean distance from Sun: 228,000,000 km/141,700,000 miles (1.524 AU)
Diameter: 6,792 km (4,220 miles)
Length of year: 687 days
Rotation period: 24 hr 37 min
Mean orbital velocity: 24.14 km/sec (15 miles/sec)

 This colour image of Phobos was taken by the Mars Reconnaissance Orbiter spacecraft in March 2008. The large crater to the right is called Stickney. Image Credit: NASA/JPL-Caltech/University of Arizona

Key facts about Phobos

Mean radius: 11 km (6.8 miles)
Distance from Mars: 9,380 km (5,830 miles)
Period of Rotation: 0.3188 days

 Two views of smaller satellite Deimos, taken by the Mars Reconnaissance Orbiter spacecraft. Image Credit: NASA/JPL-Caltech/University of Arizona

Key facts about Deimos

Mean radius: 6.2 km (3.9 miles)
Distance from Mars: 23,460 km (14,580 miles)
Period of rotation: 1.2625 days

Fun facts about Mars

Blood relation
Mars represented the god of war for the Vikings, the Greeks and the Romans. In Assyria, it was known as the “Shedder of Blood”.

Rusty world
The surface area of Mars is around the same as the land area of Earth. Its red colour is due to oxidised iron minerals in the surface rocks – in other words rust!

Close call
Mars was at its closest for centuries in 2003 and will not come as close again until 28 August 2287. But in 1924 it was only 12,500 miles (20,000 km) farther away.

Email scare
Since 2003, a silly email has been doing the rounds warning that Mars will appear as big as the Moon in the sky. Ignore it!

Early find
English author Jonathan Swift eerily described the existence of two moons around Mars in his 1726 masterpiece Gulliver’s Travels – more than 150 years before Phobos and Deimos were discovered in 1877.

War classic
The idea of intelligent life on Mars inspired H G Wells to write his classic novel The War Of The Worlds.

Quick on the draw
As data slowly dribbled back from Mariner 4 as a stream of numbers, impatient NASA scientists used it to scribble out rough images of the pictures on a grid.

High jinx
The string of failed missions to Mars in the 1980s and 1990s led wags to suggest that there was a jinx at work.

Face facts
As well as the famous face, some have seen ancient monuments on Mars including pyramids on spaceprobe photos – but closer study reveals them to be tricks of the light like patterns in the clouds.

Peak form
Olympus Mons is the largest volcano in the Solar System, standing 26km across and 600km across. By contrast Hawaii’s Mauna Loa is ‘only’ 8km high.

Smash hit
Several meteorites found on Earth have been identified as coming from Mars. Asteroid impacts millions of years ago blasted a lot of Mars rock into space. It floated around the Solar System before colliding with Earth 13,000 years ago.

Big freezer
Antarctica acts as a giant deep freeze, preserving meteorites that fall from space. Many have been found lying in the snow thousands of years after they fell.

More about Mars

Introduction to Mars

Where you can find Mars and what you can see

Humankind’s fascination with Mars throughout history

Missions to Mars

The search for life on Mars