It means we are entering an exciting time, according to Dr Mark Marley, a researcher who studies the atmospheres of other planets at Nasa Ames. “In the next few years people will start to be able to identify the true Earth twins,” he says.
But compared to stars, planets are very hard to decipher in general, points out Burrows. Simply put, many more things can happen to them. Earth, for example, has a moon because it was hit by another object in its early life; Venus, although similar in size to Earth, has been left with a greenhouse effect caused by a toxic and thick atmosphere; and Saturn has its famous rings, which could have once been a moon. “Each one seems to have its own unique story [of how it formed],” says Marley, “details matter a lot.”
Of course, theories will be adapted as more observations come in. While “super Earths” are currently the most common category of exoplanets, Beicham believes that the smaller rocky planets will soon overtake them in number, purely on the basis that it seems reasonable that smaller things may be more common in the Universe. Similarly, we will know more about whether our own solar system is atypical or commonplace. Just a quarter of 1% of the sky has been surveyed by planet hunters so far, which means there will almost certainly be many more outlandish discoveries to come.
Burrows is philosophical about the point of all this effort. “If you want to understand your origins, you have to understand them in the context of everything else,” he offers. By that metric, the human species seems a very long way from an objective appreciation of its place in the Universe. “You can’t really say you understand Earth until you understand others like Earth.”