Why is Mars red?
Mars is red because its dust and rocks contain lots of iron oxide, which is basically rust.
Mars is often called the Red Planet, and you can see why when you look at it in the night sky: it shines with an orange-red glow.
The colour comes from iron oxide, a chemical made when iron combines with oxygen. On Earth, we call it rust, the orange-brown coating that forms on old bikes and nails left out in the rain. Mars's surface is covered with fine dust and rocks rich in iron oxide, so the whole planet looks reddish.
Scientists are still studying exactly how Mars became so rusty. Billions of years ago, Mars had liquid water on its surface, and water helps iron turn into rust. Sunlight breaking apart water and other chemicals in the air may also have released oxygen that reacted with iron.
Here is a connection with meteorites: many meteorites contain iron too. When a meteorite sits on Earth's damp ground, its iron rusts, turning its black crust brown. Meteorites lying on Mars rust as well, which is how rovers have spotted iron meteorites there.
Interestingly, Mars is not red everywhere. Underneath the dusty surface, rocks are often grey. When rovers drill into rocks, the powder they make is grey, not red. Martian meteorites found on Earth are usually dark grey or greenish inside.