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We think we discovered a Hot Jupiter being consumed by its star! Hank Green explains this and the birth of carbon planets in this episode of SciShow News.

Hosted by: Hank Green
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Hank: Last week, astronomers were talking about some pretty extreme planets.

So let’s start with one that sounds like it comes straight out of Greek mythology: Like a god eating his children, there’s a star that seems to be eating a huge gas planet that orbits it. The star is called PTFO 8-8695, and it’s about eleven hundred light-years away from Earth. Its planet, PTFO 8-8695 b, was first suggested by data from a survey done back in 2012, but astronomers needed more evidence before they could be confident that a planet was actually there.

They were specifically skeptical because the star is only about two or three million years old – around a thousandth the age of our Sun. Planets around such young stars are pretty rare, and when they are found, they’re usually far away from the star. But this planet is an example of a “hot Jupiter:” a gas giant orbiting very close to its home star, that can be anywhere from the size and mass of Saturn to more than ten times as massive as Jupiter.

This planet, for example, is probably around two times Jupiter’s mass, and seems to complete an orbit once every eleven hours. So its year is half as long as our day. That’s really short, and it puts the planet incredibly close to its star – close enough that PTFO 8-8695 might actually be able to steal gas from the atmosphere of the planet, according to one group of astronomers whose study was accepted by The Astrophysical Journal last week.

They came to this surprising conclusion after using telescopes in Texas and Arizona to study the light emitted by the planet and the star. When hydrogen gas is really energized, one of the wavelengths of light it can emit is in the red side of the visible spectrum – also called H-alpha emissions. And the astronomers found that the H-alpha emissions from the planet’s outer atmosphere were almost as bright as the emissions from the star itself!

Now, hot Jupiters can typically get as hot as a couple thousand Kelvin, but the hydrogen atoms in their atmospheres shouldn’t have as much energy as the atoms in a huge nearby star. So, the astronomers think that the gas in the planet’s atmosphere could be interacting with the star’s stellar wind – the stream of charged particles constantly flowing off of its surface. And because of this, the gas could be escaping the planet’s gravity – and get trapped by PTFO 8-8695’s gravity and pulled to the star’s surface. It’s possible that the entire atmosphere could get stripped off like this, leaving a sad remnant of a world. Or maybe an equilibrium will be reached someday – only time will tell.

The astronomers admit that there are other explanations for some of their data: like, extreme sunspots or a ring of dust around the star. But they do think that planet-eating is the most likely cause.

And, now, let’s turn from killing planets to forming them. Our Sun is thought to be a third-generation star – meaning that it formed from the ashes of the stars, that formed from the ashes of the first stars, that coalesced after the Big Bang created the universe. By the time the Sun was born, there were lots of heavier elements in the cosmos – elements like aluminum and silicon and iron, which make up a lot of the Earth’s crust.

But in a lot of second-generation stars, there weren’t as many of these heavier elements, since they’re made in the cores of dying stars, and only one generation of stars had come and gone. Some of these stars without many heavy elements are called carbon-enhanced metal-poor, or CEMP, stars. As their names suggest, CEMP stars also have a pretty high percentage of carbon.

And last week, a pair of researchers at Harvard showed for the first time that planets can and probably did form around these CEMP stars – and these could’ve been some of the first planets to form in the universe. Because of all the carbon around, these planets would’ve been like gigantic lumps of graphite or diamond, depending on the conditions when they formed. There are still some CEMP stars around the Milky Way that we can study, so we can look for these carbon-rich, elusive remnants of the very early universe.

And here’s the thing: interspersed with all the carbon in CEMP stars are elements like oxygen and hydrogen. And those elements are also some of the most important elements for all life on Earth. So that raises the exciting possibility that these planets might not have just been the first planets in the universe, but they could’ve been the first places in the entire universe where life formed. Now all we have to do is find some to study.

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