According to the California Planet Search, 358 “exoplanets” are known. “Exoplanet” is another term for a planet outside the solar system. The planet count seems to change by the minute these days. According to the Jet Propulsion Lab, the count is at 403. In technology races, the dust never settles. 

The first extrasolar planet was discovered in 1995 by Mayor and Queloz and immediately confirmed by Geoffrey W. Marcy, a professor from San Francisco State University. Since that time, scientists like Mayor, Queloz, and Marcy have been searching for more extrasolar planets. 

They seek a gem: A planet that has Earth-like characteristics such as an oxygen-rich atmosphere, a rocky surface, and water. Such a discovery would be as profound as Columbus’ exploration, but it has been elusive. 

As a statistical matter, such a planet probably exists. There are billions of galaxies and trillions of stars in the universe at least (estimates vary widely; by most estimates there are far more than that). That stars have a great deal of similarity has been established. As an empirical fact, Jupiter-like gaseous giants have been found. Further, researchers have found ice or water in more than a dozen places other than comets. The mathematical probability of finding another rock out there that is something like Earth is therefore good. 

Gravity theory predicts that larger bodies such as stars will attract smaller bodies such as planets. It was no surprise to most physicists that extrasolar planets were eventually discovered. Given that water is fairly common, it is quite likely that somewhere there is a planet that has land masses, oceans, and an atmosphere of oxygen.

Why hasn’t it been found yet? The technology to study planets in other star systems has only recently developed. Astronomers have only had the resources to find such planets for about fifteen years. They will continue the search.