If the super puffs truly are as candy-like as they seem (errors in measuring their mass would resolve the mystery in another way, the authors note), they won’t stay fluffy forever. The Kepler worlds orbit so close to their star that its energy must be blowing billions of tons of fluff out into space each second, the researchers calculated using a model. At that rate, one of the planets will naturally mature into a more common type of exoplanet, a “sub-Neptune,” in about five billion years. The other will remain usually light, but lose its super puff status. The Kepler-51 system, the researchers write, may represent a snapshot of mini Neptunes and oversized Earths in their “teenage” years (which for planets means their first billion or so years of life).