Terraforming scenarios revolve around increasing Mars’ temperature and atmospheric density, providing a breathing air, liquid water, and temperatures that contribute to human and plant life, and there are three main ideas for how to do this. In the first, giant space mirrors would pave the planet, reflecting the sunlight back on Mars and warming it. They would weigh in the order of £ 200,000, too large to create and launch from the earth. The second is to build greenhouse gas plants on Mars, using them to heat the Martian climate in the same way as today’s fossil fuels cause global warming. The third is perhaps the most extraordinary: capture large, nitrogen-rich asteroids, attach engines to them and fly them to Mars until they collide with their surface. It is estimated that four such effects would be sufficient to create soil-like conditions on Mars.