Astronomers mapped the nearest exoplanet super-earth for the first time, finding that one of its hemispheres is almost completely molten rock, while the other half is almost completely solid.
The study used the NASA Spitzer space telescope to obtain a precise map of temperatures of 55 Cancer e, which is 40 light-years away from Earth in the Cancer constellation. This is the first time such a map has been made for such a small rocky world with a mass of 8 times the mass of the Earth.
Cancer 55's orbit is so close to its parent star, making one revolution around its axis in 18 hours, that it has become tidal blocked — one hemisphere of the world constantly looks at the star, while the opposite side is trapped in eternal night. This has a significant effect on the surface of the exoplanets; the side facing the star has a temperature that soars up to 2500 degrees Celsius (4500 Fahrenheit), while the dark side is less heated to 1, 100 degrees Celsius (2000 Fahrenheit). Although the far side is not quite cold, there is a temperature difference, and what is most striking, Spitzer was able to record a steep temperature gradient over the surface of the planet.
“We have not yet found any other planet that is so small and its orbit is so close to its parent star, and is relatively close to us, so 55 Cancer e offers many possibilities,” said Bris Olivier Demury from the Cavendish Laboratory of the University Cambridge "We still do not know exactly what this planet is made of - it is still a mystery. These results add another brick in the wall, but the exact nature of this planet is still not completely understood." Demuri is the lead author of a study published in the journal Nature.
On Earth, extreme temperature gradients from the day side to the night side are prevented by our 24 hour rotation and effective atmospheric circulation — warm air is quickly distributed throughout the globe. 55 Cancer e do not have this capability; it does not rotate, so that one hemisphere constantly boils and it seems to have practically no global atmosphere for transporting heat from the side facing the star to the night one. "We believe that there may still be an atmosphere on the night side, but the temperature on the day side is so high that the atmosphere can evaporate completely, which means that the heat is not efficiently transferred or not transmitted at all from the day to the night side," Demuri.
However, there is a secret. The researchers realized that the day side 55 of Cancer e is much hotter than one would expect only from stellar heating - there seems to be “extra heat”, which, for the time being, will remain a mystery until more advanced space telescopes will be launched. Perhaps the NASA space telescope, James Webb, will direct his eyes in the hope of finding out more about this very alien world.