Hot nights, scorching days: Extreme super Earth baffles astronomers

Scientists looking to probe the atmosphere of a super Earth have discovered a nearby planet with strange properties – including a day side that’s about 1,300 degrees kelvin more than the night side.

The planet 55 Cancri e, described in the journal Nature, could shed light on the behavior of increasingly Earth-sized planets in extreme situations.

As telescopes like NASA’s Kepler spacecraft have pinpointed all manner of alien worlds, from super Jupiters to planets smaller than Earth, scientists’ attention has turned to those planets’ atmospheres. After all, it’s the composition of the atmosphere (if a planet has one at all) that will help determine if a planet is suitable for life as we know it.

Finding planets, however, is delicate work; examining the thin sliver of atmosphere around those planets is exceedingly difficult. For the most part, researchers have only really been able to do it for enormous gas giant planets.

But for this paper, the researchers tried to characterize the atmosphere of 55 Cancri e, which sits about 40 light-years away from Earth. 55 Cancri e is thought to be almost twice the Earth’s size and hold eight times its mass, and it circles its star in a mere 18 hours – which gives scientists a lot of opportunities to observe it.

“There’s really no other planet like it,” said study co-author Stephen Kane, an astrophysicist at San Francisco State University.  

Using NASA’s infrared-seeking Spitzer Space Telescope, an international team of astronomers observed the planet for a total of 75 hours over the course of a month in 2013. This planet, which sits just 1.2 million miles from the star's surface, has been tidally locked because of the star’s gravity, which means that the same face of the planet remains turned toward the star (just as the same side of the moon faces Earth).

The researchers mapped out a single region within a single central pixel in the detector, and then used that information to remove sensitivity variations in their observations.

“This is a really hard measurement to make,” said study co-author Jessica Krick, an astronomer with the Spitzer Space Telescope at Caltech. “In fact, they did it a few times to make sure that what they were seeing was real.”

That side turned out to be a broiling 2,700 degrees kelvin – not that far off from the stellar surface temperature. On the other side, it was a mere 1,380 degrees kelvin – which, relatively speaking is dramatically cooler.

This perplexed the researchers – after all, atmospheres tend to take the heat from the day side and spread it around to the dark side.

On Earth, “that’s good for us, because otherwise we’d all freeze to death when it’s nighttime,” Kane said.

This could mean a number of things. Perhaps there isn’t really an atmosphere at all on this planet – it’s simply been boiled away by its proximity to the star’s surface.

The researchers also found a particular source of heat on the day side, which they think could potentially be significant volcanic activity that might be contributing to the temperature difference between both sides.

“I think it’s interesting that we don’t really understand how this could happen,” Krick said.

The mystery may be solved with the completion and launch of NASA’s James Webb Space Telescope, the scientists said.

In the meantime, she added, theorists will probably need to come up with better models to explain this planet’s strange behavior.

“There’s a lot of theory work that needs to be done in the future as well to understand what it could mean that we’re seeing this big temperature variation,” she said.  

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