From 1000 to 2700°C!

In the new study co-signed by Michaël Gillon, the main results are not about the internal structure or composition of the planet, but on "weather" that reigns on its surface. As in 2012, still using NASA’s Spitzer Space Telescope, the researchers measured the planet's thermal emissions. But this time, the measurements have been repeated over about two years, revealing a drastic evolution of this thermal emission, with temperatures of the hot ‘day’ side (4) of the planet swinging between 1000 and 2700 degrees Celsius.

“Up to now, super Earths were just fixed abstract objects. We could conclude to their existence by measuring their subtle influence on their host stars, we could estimate more or less precise physical dimensions for some of them, and that's it.” said Dr Michaël Gillon of the University of Liège, second author of the study. “With this result, we show that they are all but immutable objects. They are dynamic, constantly evolving worlds, just like the planets and moons hosted by our own solar system.”

Volcanic hell

Although the interpretations of the new data are still preliminary, the researchers believe the variability in temperature could be due to huge plumes of gas and dust which occasionally blanket the surface, which may be partially molten. The plumes could be caused by exceptionally high rates of volcanic activity, higher than what has been observed on Io, one of Jupiter’s moons and the most geologically active body in the solar system.

Indeed, the planet is very close to its star, and its orbit is maintained in a slightly elliptical geometry by the presence of a more distant giant planet. This configuration must subject the planet to gigantic tidal forces that can produce intense volcanic activity on its surface.
“We saw a 300 percent change in the signal coming from this planet, which is the first time we’ve seen such a huge level of variability in an exoplanet,” said Dr Brice-Olivier Demory of the Cambridge's Cavendish Laboratory, lead author of the new study. “While we can’t be entirely sure, we think a likely explanation for this variability is large-scale surface activity, possibly volcanism, on the surface is spewing out massive volumes of gas and dust, which sometimes blanket the thermal emission from the planet so it is not seen from Earth.”

(4) A planet so close to its star, as is 55 Cancri e, is trapped in a resonance state. That is to say, it turns on itself at the same speed as its orbital period and will always show the same face to the star, in exactly the same manner as for the Moon to the Earth. It therefore has a continuously irradiated hemisphere and a hemisphere in perpetual night.