Life in the Universe


Have any exoplanets been discovered yet that are like Earth?

Alas, not yet. Astronomers have been able to detect a few exoplanets that are only slightly more massive than Earth, but their orbits imply that they would be far too hot to have an environment like Earth. Even with the best current technology, astronomers cannot yet see Earth-like planets in exoplanetary systems directly. We do know, how ever, that just about all the exoplanetary systems that have been detected so far have at least one large gas giant planet, about the mass of Saturn or greater, orbiting very close to its host star. It is possible that some of these systems have smaller, terrestrial planets, but we can neither see nor detect them right now. Generally speaking, since the laws of physics are the same around our Sun as they are around any other star, it is safe to guess that Earth-like planets might even be common in exoplanetary systems. Until we can observe them directly, though, we will not know for certain.

At left, an image of the Milky Way with a section marked off as “Kepler Field of View” that shows the region of space where the Kepler spacecraft has been searching for planets. At right, a closer look at that region and where planets of various sizes have been discovered. (Carter Roberts/EastbayAstronomical society/NASA)


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