Three eras of planetary exploration

Abstract

The number of known exoplanets rose from zero to one in the mid-1990s, and has been doubling approximately every two years ever since. Although this can justifiably be called the beginning of an era, an earlier era began in the 1960s when humankind began exploring the Solar System with spacecraft. Even earlier than that, the era of modern scientific study of the Solar System began with Copernicus, Galileo, Brahe, Kepler and Newton. These eras overlap in time, and many individuals have worked across all three. This Review explores what the past can tell us about the future and what the exploration of the Solar System can teach us about exoplanets, and vice versa. We consider two primary examples: the history of water on Venus and Mars; and the study of Jupiter, including its water, with the Juno spacecraft.