Could rocky, Earth-like exo-planets exist? If so, how common are they? This question had plagued astronomers for years, until recently. Early discoveries of exo-planets were mostly of the so-called "hot Jupiter" planets. These types of planets were monstrous planets, some larger than Jupiter, and orbiting very close to their star. This at first looked discouraging to astronomers hoping to find an Earth-like exo-planet. It turns out, however, that the reason astronomers are finding so many hot Jupiters is that the current method of detecting planets is only sensitive enough to detect very massive planets by measuring the wobble imparted on its parent star. However, new data from the Spitzer space telescope point towards rocky, terrestrial exo-planets being more common than we had thought.
Astronomers started their hunt by choosing six sets of stars similar in mass to our own, but differing in age. Then, by utilizing Spitzer's infrared capabilities, astronomers can estimate the temperature of the star's surrounding dust cloud. Dust near the center of each stellar system would be warmer than the more distant dust. Astronomers can look at the distribution and temperature of this dust, and get useful data about the star's evolutionary progress. Michael Meyer, of the University of Arizona, Tucson, has found that after 300 million years of evolution, most of the dust which corresponds to planet formation is gone.
This, of course, does not imply that these stars have rocky exo-planets. It does, however, imply that stars between the ages of three million and 300 million years are undergoing similar planet-forming stages as our own solar system. Using this data, astronomers have estimated that up to 62% or stars may either have or are creating rocky, terrestrial exo-planets. This may be an optimistic estimate, but it points to a universe where planets like our own are not a freak accident.