For instance, if there is a dense atmosphere and a strong greenhouse effect, as there is on Venus, temperatures at the surface could be very hot and not suitable for life as we know it. If the planet is too small to hold an atmosphere, it will not have water on the surface no matter how comfortable the temperatures are. Water would evaporate, and the gas molecules would just wander away. Planets far from their sun, like Saturn in our solar system, receive little heat from the sun and are thought to be made mainly of frozen gases. However, local conditions might generate some heat.
Gravity can exert forces that cause friction in rocks and ice.
The friction can generate heat even on dark planets. Can Cause Stresses that Generate Heat for more information. Elizabeth Anne Viau. All rights reserved. This material may be used by individuals for instructional purposes but not sold.