Mars: Planetary Science and Exploration

Mars’s position and basic planetary characteristics

Mars is the fourth planet from the Sun, orbiting at an average distance of about 1.524 astronomical units (228 million kilometers). Its orbit is moderately eccentric, ranging from approximately 206.7 million kilometers at perihelion to 249.3 million kilometers at aphelion. Mars completes one orbit in about 687 Earth days, or 1.88 Earth years, and has two small natural satellites, Phobos and Deimos. Mars is a rocky, desert-like planet known as the "Red Planet" because iron-rich minerals on its surface produce its orange-red color. It has a mean diameter of about 6,779 kilometers, roughly half that of Earth, and a surface gravity about 38% as strong as Earth's. Its thin atmosphere is composed primarily of carbon dioxide, with surface pressure less than 1% of Earth's. Mars rotates once every approximately 24 hours and 39 minutes, and its axial tilt of about 25 degrees produces Earth-like seasons. Surface temperatures vary widely, and the planet retains water mainly as underground ice, atmospheric vapor, permafrost, and polar ice caps.

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Mars’s orbit, rotation, and seasons

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