Why settle for one habitable planet, when you can have 60? An astrophysicist has designed the ultimate star system by cramming in as many Earth-like worlds as possible without breaking the laws of physics. Such a monster cosmic neighbourhood is unlikely to exist in reality, but it could inspire future exoplanet studies.

Sean Raymond of Bordeaux Observatory in France started his game of fantasy star system with a couple of ground rules. First, the arrangement of planets must be scientifically plausible. Second, they must be gravitationally stable over billions of years: there is no point in putting planets into orbit only to watch them spiral into the sun.

"The arguments were based on the recent scientific literature as well as some simple calculations I did," says Raymond. In some cases it was impossible to choose between two scenarios because of a lack of data, so he just picked the one he liked best.

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