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We explore several exoplanets whose features make us think they shouldn't even have been able to form in the first place!

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Reid: Pretty much as long as humans have looked up at the night sky, we’ve been studying astronomy. In all this time, we’ve learned so much about the universe beyond our Solar System, and have found lots of exoplanets orbiting other stars. But there’s a lot that scientists still don’t know. In fact, three relatively recent exoplanet discoveries are completely baffling researchers because, according to what we know about astronomy, they shouldn’t exist!

The first of these planets is called Kepler-78b, which was discovered using data from NASA’s Kepler space telescope, and orbits a star about 400 light years away from Earth. Based on changes in its star’s light, astronomers calculated that Kepler-78b’s radius is about 1.2 times the radius of Earth and it’s around 1.7 times as massive as the Earth.

This means it also has a similar density to the Earth, so the researchers think its composition is similar, too, with lots of rock and iron. But that’s where the similarities stop. Kepler-78b is about 100 times closer to its star than the Earth is to the Sun, and its surface temperatures might even get up to 3,100 Kelvin. Basically, it’s kind of like Earth... if Earth was a blazing inferno.

This planet’s super close orbit to its host star means that a year only lasts 8. 5 hours, and scientists don’t understand how Kepler-78b even exists, because it doesn’t fit any of the current theories of planetary formation. It’s just too close to its star. See, when Kepler-78b was first forming from the gas and dust-filled protoplanetary disk, its host star was even larger. So if the planet was orbiting where it is now, it would’ve been inside its star, which is... impossible.

Another option is that it formed farther away and migrated closer, but scientists think that’s pretty unlikely, since it probably would’ve kept going and plummeted into the star. As of now, it’s a mystery. The main thing we do know about Kepler-78b is that it’ll probably only be around for another three billion years or so. It’ll move closer and closer to its host star, until the gravity eventually tears it apart.

Our next mysterious planet is called Kepler-10c, which was also detected using data from the Kepler space telescope, and is about 560 light years away from us. It’s radius isn’t all that special. It’s only about 2.3 times the radius of the Earth. And initially, because of its size, scientists predicted that Kepler-10c would have a thick, gaseous atmosphere, making it like a mini-Neptune.

Instead, they found a planet with a mass that might be between 14-17 times the Earth’s, which suggests that it’s a really dense rocky planet without much of an atmosphere. A mass that large is basically unheard of in a planet that size, which is why astronomers dubbed it a mega-Earth. Which, y’know, sounds pretty cool.

Based on our current understanding of planets, one this massive without an atmosphere shouldn’t even exist. Theoretically, it would’ve grabbed a bunch of nearby lighter elements with its huge gravitational force as the star system was forming, and turned into a gas giant like Jupiter. But it probably never even had an atmosphere, because if it did at some point, it would’ve held onto it. So, right now, scientists are just left with another giant rock in space that they can’t really explain.

Last but not least, we have a gas giant named HD 106906 b, which is 11 times as massive as Jupiter, and discovered using data from the Hubble Space Telescope and the Magellan telescope in Chile. This planet orbits a really young star 300 light years away from Earth. The system is only 13 million years old. But that’s not what makes it weird.

See, HD 106906 b orbits its star at a distance of 650 astronomical units. That’s more than 20 times the average distance between the Sun and Neptune. A planet that far away from its host star shouldn’t have had enough gaseous and rocky materials to grow that huge, especially in such a relatively short period of time.

Somehow, it exists. Some researchers think it might have formed inside the dust-filled debris disk surrounding its host star, and got kicked out later, but they’re still not sure. A recent study seems to support this idea, suggesting that the planet might have even captured some of that dusty material, and might be surrounded by a ring or shroud. But that’s just one hypothesis and, until astronomers get more data, the planet is still an enigma.

These three planets are just a drop in the bucket that is our universe, and we still have so much to learn. It’s really the strangest discoveries that make astronomy so cool. Every time we start to think we understand how certain things work, like planetary formation, amazing surprises get thrown our way.

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