It's a recipe that won't win any culinary awards, but when turned into a computer model, it could explain the strange sighting last year of a rapidly disappearing exoplanet around the small sunlike star KIC 12557548. The model hints that this world is now about the size of Earth's moon and may even be down to its naked iron core, which would make it the smallest known exoplanet. If true, the tiny remnant could help us better understand what's inside our home world.

Dubbed KIC 12557548b, the planet was discovered using NASA's Kepler space telescope. Kepler spots exoplanets by looking for the regular dimming of stars caused by orbiting planets that transit them – pass in front of their star – as seen from Earth. The more light is blocked, the larger the planet.

KIC 12557548b is small and so close to its star that its year lasts just 16 hours. But the dimming caused by the planet varies wildly, suggesting it is surrounded by a gigantic, ever-changing cloud of material.

"It basically looks like a comet that's very erratic, with a long trailing tail of dust," says Eugene Chiang of the University of California, Berkeley, who was part of a team that found the planet last year. The team thinks the rocky surface is being evaporated away by the intense heat of its star.