THE COMPLETE GUIDE MARS
Mars is the fourth planet from the Sun. Befitting the Red Planet’s bloody colour, the Romans named it after their god of war. The bright rust colour Mars is known for is due to iron-rich minerals in its regolith – the loose dust and rock covering its surface. The soil of Earth is a kind of regolith, too, albeit one loaded with organic content. The iron minerals on Mars oxidise, or rust, causing its soil to look red.
The planet’s thin atmosphere means liquid water likely cannot exist on the Martian surface for any appreciable length of time. Features called recurring slope lineae may have spurts of briny water flowing onto the surface, but this evidence is disputed; some scientists argue the hydrogen spotted from orbit in this region may instead indicate briny salts. This means that although this desert planet is just half the diameter of Earth, it has the same amount of dry land.
The Red Planet is home to both the highest mountain and the deepest, longest valley in the Solar System. Olympus Mons is roughly 25 kilometres (16 miles) high, about three times as tall as Mount Everest, while the Valles Marineris system of valleys – named after the Mariner 9 probe that discovered it in 1971 – reaches as deep as ten kilometres (six miles) and runs east to west for roughly 4,000 kilometres (2,500 miles), about one-fifth the distance around Mars and close to the width of Australia.
Scientists think that Valles Marineris formed mostly by rifting of the crust as it got stretched. Individual canyons within the system are up to 100 kilometres (60 miles) wide. The canyons merge in the central part of Valles Marineris in a region 600 kilometres (370 miles) wide. Large channels emerging from the ends of some canyons and layered sediments within suggest that the canyons might once have been filled with liquid water.
