Mars

Mars is the fourth planet from the Sun, a cold desert world whose rusty red colour comes from iron oxide in its soil. It hosts Olympus Mons, the tallest volcano in the solar system, and Valles Marineris, a canyon system that would stretch across the United States.

A Martian day is close to our own at about 24 hours 40 minutes, but a year lasts 687 Earth days. Thin air and evidence of ancient rivers make Mars the leading target in the search for past life.

The figures above explain why Mars is the most Earth-like destination we have, and where the resemblance stops. Its 24.7-hour day is only about 40 minutes longer than ours, so a human working schedule almost transfers unchanged. But its radius of 3,389.5 km is barely over half Earth’s, its mass is 0.107 of ours, and surface gravity is 3.72 m/s² — a little over a third of what you feel here, so the same jump would carry you nearly three times as high and a 100 kg load would push back with the force of 38 kg at home.

Orbiting at 1.524 AU, Mars receives roughly 43% of the sunlight Earth does, which together with its thin atmosphere gives the mean temperature of −63 °C listed above. A Martian year runs to about 1.9 Earth years, so seasons last nearly twice as long as ours, and the two small moons Phobos and Deimos circle far too quickly and faintly to light the night the way our Moon does. To see where Mars sits in its orbit right now, open the 3D solar system simulator.