Planetology: Comparing Other Worlds to Our Own

Life requires just the right amount of energy trom the sun and just the right amount and kind of atmosphere.

If water sources dry up or if extraterrestrial bodies crash into a planet, life can be destroyed.

These are the lessons humans can learn by comparing the surfaces, interiors, and atmospheres of other worlds to those of Earth.

Life is precious and rare. Will we heed this warning or will we risk losing it all?
Fred Schaat writes the popular monthly "Stars and Planets" column in Sky and Telescope magazine and an almanac column on astronomy and weather for Mother Earth News. He has also written articles for Omni and Astronomy.