Extraterrestrial liquid water
The Gliese 581 planetary system contains multiple planets that may be candidates for surface water, including Gliese 581c, Gliese 581d, might be warm enough for oceans if a greenhouse effect was operating, and Gliese 581e.
Geology of solar terrestrial planets
The physical features of land are remarkably varied. The largest mountain ranges—the Himalayas in Asia and the Andes in South America—extend for thousands of kilometres. The longest rivers are the river Nile in Africa () and the Amazon river in South America (). Deserts cover about 20% of the total land area. The largest is the Sahara, which covers nearly one-third of Africa.