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The Small Planets

Asteroids have become notorious as celestial menaces but are best appreciated in a positive light, as surreal worlds bearing testimony to the origin of the planets

By Erik Asphaug

The Origins of Water on Earth

Evidence is mounting that other planets hosted oceans at one time, but ONLY EARTH has maintained its watery endowment

By James F. Kasting

The Oort Cloud

On the outskirts of the solar system swarms a vast cloud of comets, influenced almost as much by other stars as by our sun. The dynamics of this cloud may help explain such matters as mass extinctions on Earth

By Paul R. Weissman

The Hidden Ocean of Europa

Doodles and freckles, creamy plains and crypto-icebergs--the amazing surface of Jupiter's brightest icy moon hints at a global sea underneath

By James W. Head, Robert T. Pappalardo and Ronald Greeley

Mercury: The Forgotten Planet

Although one of Earth's nearest neighbors, this strange world remains, for the most part, unknown

By Robert M. Nelson

Global Climate Change on Venus

Venus's climate, like Earth's, has varied overtime--the result of newly appreciated connections between geologic activity and atmospheric change

By David H. Grinspoon and Mark A. Bullock

Bejeweled Worlds

What an impoverished universe it would be if Saturn and the other giant planets lacked rings. Planetary scientists are finally working out how gravity has sculpted these elegant ornaments

By Douglas P. Hamilton, Joseph A. Burns and Mark R. Showalter


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