Extrasolar systems shed light on our own

Abstract

A planet smaller than Mercury circles a star 210 light-years away. Around another star, two planets live so close together that each periodically rises in the other’s sky. Other alien skies are home to two suns that rise and set, casting double shadows over their double-sunned worlds. Planets so dense they might have diamond rinds, worlds whose year is shorter than an Earthday, others that orbit their star backward—the cosmos holds many exotic and diverse objects.