PLANET TYPE: Rocky
Our home planet is unique in the Solar System: liquid water covers 70 per cent of its surface. Its presence means Earth has access to a huge array of processes that can’t happen on other planets. Geologically, water acts as a lubricant between Earth’s tectonic plates, keeping them moving; as well as allowing the formation of minerals that otherwise might not exist such as hematite.
Most importantly, water is vital for life. As we search for life throughout the Solar System and beyond, the mantra is always ‘follow the water’.
We still don't know, however, why Earth has so much water: current theories of planet formation suggest early Earth should have been so hot that all its water boiled away. The leading explanations are that Earth managed to retain water in its core, that later bubbled to the surface, or that water was brought back to Earth after it had formed, possibly by asteroids impacting the surface. EXPLORED BY: Sputnik 1 (1957); Explorer 1 (1958); Landsat programme (1972–2013); European Remote-Sensing Satellite (1991–2011); TERRA (1999); Envisat (2002) NUMBER OF SPACECRAFT: 600+ (currently)
One theory for Earth’s high water volume is the unlocking of underground reserves by asteroid impacts early in the planet’s life cycle