In their hunt for exoplanets, scientists have discovered a whole host of exotic and surreal worlds, wild beyond the most eccentric of imaginations. Now, a new Nature study has described one of the most remarkable exoplanets yet: a two-faced super-Earth, where one side hides in perpetual night, while the other is bombarded by its powerful star, leaving it constantly molten.

55 Cancri e, a world 41 light-years from our own, was discovered way back in 2004. It was notable for being the first super-Earth – a planet with a mass exceeding our own world’s but not reaching that of Neptune’s – that was orbiting around a main sequence star. There’s an ongoing debate as to the composition of the planet, which some have proposed to be mostly carbon in the form of diamond.

55 Cancri e is so close to its parent star that one entire orbit takes just 18 hours, which means it has 487 years for every Earth-year. Researchers have thought that this planet’s surface could therefore be unbelievably hot, around 2,000°C (3,600°F). In addition, a previous paper revealed that its atmosphere is rich in a highly poisonous form of cyanide, so combined with the heat, this planet would be a rather unpleasant place to live.

^{The surface facing the star would be almost entirely molten, with lava pooling on the surface. ESA/Hubble, M/ Kornesser}

This new study, led by astrophysicist Brice-Olivier Demory at the University of Cambridge, adds another fascinating chapter to this celestial tale. Using data from NASA’s Spitzer Space Telescope, one that can detect infrared emissions, his team produced a thermal map of the far-flung orb, the first of its kind for a super-Earth, and revealed that it’s a world of two halves.

Due to the gravitational influence of its host star, the planet is tidally locked, meaning that only one hemisphere faces the star at all times – much like how we only ever see one side of our own Moon from Earth. Their thermal mapping showed that the daytime side would be a terrifying 2,500°C (4,530°F), meaning it would be entirely molten; remarkably, the side in constant darkness would be just 1,100°C (2,010°F).

 

 

^{An artist’s impression of the two-faced magma ocean world, 55 Cancri e. University of Cambridge}

This “cold” side, covered in landscapes of solidified lava, probably retains a semblance of an atmosphere, whereas the magma ocean side would likely have very little, if any. Curiously, the planet is even hotter than it should be: The mapping shows that the stellar irradiation it is receiving is not enough to cause it to be as hot as it actually is. This means that there’s an unknown source of heat coming from within the planet, and the researchers currently have no idea as to what that could be.

“We still don’t know exactly what this planet is made of – it’s still a riddle,” Demory said in a statement. “These results are like adding another brick to the wall, but the exact nature of this planet is still not completely understood.”

Either way, this bizarre world isn’t the first of its kind – CoRoT-7b, 480 light-years away from Earth, is another two-faced magma world tidally locked to its star. Some think that this ghostly planet is the rocky core of a gas giant whose atmosphere was destroyed as it tumbled towards its host star. It’s not clear whether this is the case with 55 Cancri e, but one thing is for certain – both worlds are volcanic hells in the depths of space.

 

 

^{Charting the discovery of the first ever exoplanet detected orbiting a main sequence star. University of Cambridge}