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This exoplanet whizzes around its star once a week and is bombarded by flares

NASA’s TESS, Spitzer Missions Discover World Orbiting Unique Young Star

Around 32 light-years away from Earth, practically in our backyard, lies a dramatic young star named AU Microscopii or AU Mic for short. This star is just 20 to 30 million years old. This might sound ancient, but by star standards, it’s a baby — for reference, our sun is 150 times older.

Orbiting this baby star is a planet of dramatic events, AU Mic b, recently discovered using data from NASA’s Transiting Exoplanet Survey Satellite (TESS) and the now-retired Spitzer Space Telescope.

A year on this Neptune-sized planet lasts just over one Earth week as it orbits extremely close to its star. And it is constantly bombarded with flares from the star, caused by the star’s strong magnetic fields. The star is often covered with starspots — similar to sunspots — which erupt with flares that bathe the planet in radiation.

rendering of the young planet AU Mic b
This rendering of the young planet AU Mic b is part of NASA’s fun-but-informative Galaxy of Horrors poster series. The planet’s star, AU Microscopii, emits powerful, fiery flares that would likely terrorize any lifeforms that tried to make a home here. NASA's Exoplanet Exploration Program

Because the star AU Mic is so young, both it and its planet are still surrounded by the disk of dust and gas from which they formed. That makes this system the ideal place for researchers to observe to understand more about how planetary systems develop over time.

“We think AU Mic b formed far from the star and migrated inward to its current orbit, something that can happen as planets interact gravitationally with a gas disk or with other planets,” coauthor Thomas Barclay, associate project scientist for TESS at NASA’s Goddard Space Flight Center, explained in a statement.

artist's concept shows the dusty disk surrounding the star AU MIcroscopii
This artist’s concept shows the dusty disk surrounding the star AU MIcroscopii. Astronomers have studied this system extensively but only recently identified the presence of a planet there. The find provides a laboratory for studying planet evolution and formation. NASA's Goddard Space Flight Center/Chris Smith (USRA)

Barclay and his team have also compared the system to planets in another nearby system, the Beta Pictoris Moving Group. “By contrast, Beta Pictoris b’s orbit doesn’t appear to have migrated much at all. The differences between these similarly aged systems can tell us a lot about how planets form and migrate,” he said.

There may even be more planets hiding in the orbit of AU Mic, so the scientists will return to this system to study it more and see if they can find them.

“There is an additional candidate transit event seen in the TESS data, and TESS will hopefully revisit AU Mic later this year in its extended mission,” lead researcher Peter Plavchan said. “We are continuing to monitor the star with precise radial velocity measurements, so stay tuned.”

The research is published in the journal Nature.

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