Newly discovered exoplanet is literally boiling away

A newly discovered exoplanet orbiting a distant star is literally boiling away as heat from its sun melts rock and turns it into dust that trails the planet in its orbit, according to Massachusetts Institute of Technology researchers. They reported in the Astrophysical Journal that this is apparently the first time that such a disintegrating planet has been observed.

A team headed by physicist Saul Rappaport of MIT discovered the planet using the Kepler Observatory, a space-based telescope that monitors more than 160,000 stars in the Milky Way looking for exoplanets. If a star has a planet and the planet passes between the star and the Earth, there will be a slight, regular dimming of the star’s luminosity. Astronomers generally consider this a strong indication of the presence of a planet.

Rappaport and his colleagues observed an unusual pattern of dimming in a star named KIC 12557548, about 1,500 light-years from Earth. The light from the star dimmed every 15 hours, but the amount of dimming varied each time. The team initially suspected that the dimming might be attributable to two planets, but calculations showed that two planets could not coexist in orbits that would produce the observed effect.

An orbital period of 15 hours is the shortest ever observed, and that indicates that the planet is orbiting very close to its sun. That suggests that it would be heated to very high temperatures by the orange-hot parent star -- about 3,600 degrees Fahrenheit, or hot enough to melt rock. The team hypothesized that the planet melts and evaporates at such high temperatures, forming a wind that carries gas and dust into space. The dust cloud trails the planet much like the tail of a comet, varying in size slightly from orbit to orbit. This is, the team says, the only explanation that fits the data. To allow the dust to escape into space, the planet must have a relatively low gravitational field, which would make it about the size of Mercury.

“We think this dust is made up of submicron-sized particles,” Rappoport said. “It would be like looking through Los Angeles smog.” The team estimates that complete destruction of the planet will take about 100 million years.

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