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SYFY WIRE Exoplanets

Teenage exoplanets are finally telling us about their growing pain angst

By Elizabeth Rayne
Liz Teenage Exoplanets

The terrible teens are a rite of passage that usually involves tears, awkwardness, rebellion, and usually all of the above, but it isn’t limited to humans — planets also go through it.

Teen angst goes beyond high-schoolers who could have come straight out of a John Hughes flick. Planets also have a phase of unpredictable outbursts before they finally grow up. The intermediate stage of planetary evolution has never been well understood, but now NASA’s planet hunter TESS has found “teenage” rocky planets in a two-star system. These planets are orbiting hot young stars and throwing tantrums in the cosmic version of adolescence.

Astrophysicist George Zhou of the University of South Queensland in Australia, who recently coauthored a study published in The Astronomical Journal, believes teen planets could also tell us more about how our Sun evolved. 

“Go back 4 billion years, and our own Sun would have been rotating just as quickly, and was just as energetic,” Zhou told SYFY WIRE. “These 'teenage' planets can give us a window into the evolution of planets and their atmospheres early in their evolution.”

Misbehaving starts with the stars these planets orbit. Stars of that age are always more active than those that have been around a while. These stars, known as TOI 2076 and TOI 1807, are only 200 million years old (less than 5 percent of the Sun’s age) and are often erupting in solar flares. The planets, TOI 2076 b and TOI 1807 b, feel these flares almost like peer pressure from the popular kids. TOI 1807 b orbits its star 22,000 times more than Earth orbits the Sun, and TOI 2076 b gets hit with 400 times more UV light than we do.

To give you an idea, the Sun rotates once every 24.5 days, while the stars TESS found live much faster. They both rotate once every 7-8 days. It’s almost like extreme hormonal behavior, except objects in space don't tearfully apologize.

The faster the rotation, the more active the star, because rotation is connected to that star’s magnetic field, which gives it the almost boundless energy you would expect out of a human teen. Speaking of which, Zhou believes TOI 1807 b probably formed somewhere else and ran away from home.

“We do not know where TOI 1807 b originated from, and how it got to its current orbit, and that's fascinating,” he said. “We do know that around older stars, we do occasionally find rocky worlds in these extremely close orbits, so there might be some way to form these planets and move them inwards within the time frame of 200 million years.”

What TESS beamed back also told Zhou and his team about the size of TOI 1807 b, which could mean it has at least some semblance of an atmosphere, something that most rocky planets in short orbits around older stars are missing. It is possible that observing TOI 1807 b is like seeing a throwback of what those planets used to be like when they first formed and moved out, millions of years before they fell into their current orbits. Orbiting way too close to a star is going to eventually strip a planet’s atmosphere. Stellar radiation will do that.

TOI 2076 B has its own issues. There are multiple Neptune-sized planets orbiting with it, so it’s kind of like the lone underclassman in a hallway crammed with seniors. More will come to light when the James Web Space Telescope finally launches later this year and probes the atmospheres of these planets to see whether they are made of the same stuff. Finding that out could reveal where they were born before sneaking out, and how their star changed their atmospheres.

“Searching for newly formed planets around other young stars is the closest we can get to a time machine,” said Zhou. “We hope TESS will help us answer questions such has how large and gaseous these planets were when they first formed, and how quickly they lost their atmospheres and settle into their present-day orbits.”

These young planets still have some growing up to do. Wait until they have to look for a prom date.