The researchers suggest that this type of world may a result of large “hot Jupiter” exoplanets migrating toward their host star. Exoplanet surveys have detected several such planets, and it’s believed that they likely formed at a greater distance from their respective stars and then slowly crept inward. When that happens, it’s possible that the change in gravitational forces would prompt large moons to break free from their existing orbits and become standalone worlds of their own. Computer simulations showed that this could indeed happen, and in those cases, the researchers believe we should call them ploonets. Remarkably, our own...