Which planet is known as the Red Planet?

Mars, and the colour is rust in the ordinary sense - iron oxide dust covering the surface and suspended in the atmosphere, which also makes the Martian sky butterscotch by day. Sunsets there are blue, for exactly the inverse of the reason ours are red: the fine dust scatters red light widely and lets blue through near the sun.

It has the largest volcano and the largest canyon in the Solar System. Valles Marineris runs some 4,000 kilometres, about the width of the United States, and is up to seven kilometres deep - the Grand Canyon would be a side channel. Both exist because Mars has no plate tectonics: nothing moves the crust off the hot spots, so volcanoes pile up in place and the crust simply splits under the strain.

It also lost its air. Mars has no global magnetic field, and without that shield the solar wind has been stripping the atmosphere away for billions of years - the MAVEN mission measured it happening. What is left is about one per cent of our surface pressure, too thin for liquid water to be stable, which is why the riverbeds and lake deltas the rovers keep photographing are dry.