A rocky planet
Mars is the fourth planet from the Sun. Its mean diameter is about 6,780 km, a little over half Earth’s. Dust containing iron oxides gives its surface a reddish colour.
UNIVERSUM · MARS
Discover Mars
A red world, vast landscapes and traces of a history shaped by water.
≈ 6,780 kmMean diameter
24 h 39 minSolar day
687 Earth daysMartian year
2Moons
A wetter past
Valleys, deltas, sedimentary rocks and minerals record ancient environments where liquid water existed. Water ice occurs at the poles and underground. This evidence does not mean that life has been discovered.
A thin atmosphere
The atmosphere consists mainly of carbon dioxide. Mars is cold and dry, with low surface pressure. Rover landscapes may resemble terrestrial deserts, but the conditions are very different.
Explore Mars
Mars atlas →
Volcanoes, canyons and craters: get to know some of the red planet’s great landscapes.
Observe Mars →
Choose a time and location, then prepare to observe an orange point of light or a small telescopic disk.
Seasons and climate →
An almost Earth-length day, an almost twice-as-long year and seasons unlike our own.
Phobos and Deimos →
Two small, irregular moons accompany Mars. Their history remains an open question.
Missions to Mars →
From the first images to mobile laboratories: milestones in robotic exploration.
Sources and credits
Space-mission images; mosaics and processing are identified in the credits. NASA/JPL · Image use
Educational reference values and sources checked on 23 October 2026.