Astronomers saw how a star rips off the atmosphere from its planet

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Summarize this content to 100 words As the artist envisioned AU Mic b. Astronomers have seen how a young star tears off the atmosphere from one of its planets in huge volumes.This exoplanet is called AU Microscopii b (or AU Mic b) and orbits a very young red dwarf star located just 32 light-years from Earth. The age of the system is only 23 million years, almost a child’s age, and its wild behavior gives an idea of ​​the turbulent period of the early life of recently formed planets. The results of the study were published in The Astronomical Journal.What is particularly interesting about this Neptune-sized world is that the atmospheric emission does not occur all the time. On the contrary, it seems to turn on and off again quickly, becoming visible and then invisible – and this is during one revolution around the star. And when the process becomes visible, the atmosphere flows from the surface of the planet towards the star, instead of following it with its tail, as usual.”When I first saw it, I thought, ‘That can’t be happening,'” says Dartmouth College astronomer Keighley Rockcliffe, who led the study. – This frankly strange observation became a kind of stress test for the modeling and physics of planetary evolution. This observation is so interesting because we get the opportunity to investigate one of the most extreme interactions between a star and a planet.”An early drawing by the artist who depicted AU Mic b AU Mic b was discovered in 2020, and already then scientists realized that it must be interesting. It is slightly larger than Neptune: its mass is 20.12 Earth masses and 4.19 Earth radii; the mass of Neptune is 17.15 Earth masses and 3.88 Earth radii. However, unlike Neptune, AU Mic b is very close to its star: it orbits once in just 8.5 days.Such proximity allows the exoplanet to observe the warlike behavior of the star in the first row, and it is known to be turbulent. Young stars are much more active than old stars, and even old red dwarfs are quite active.AU Mic is on a rampage, throwing out more than 6 flashes a day. This is the constant pressure of wild stellar wind, flares and hard X-rays.Rockcliffe and her team wanted to take a closer look at this exoplanet because it could help explain an interesting gap in exoplanet detection – it contains worlds 1.5 to 2 times the radius of Earth that are in close proximity to their stars.AU Mic b is on the larger side of this gap, but if it is actively losing its atmosphere and therefore shrinking in size, this may shed light on the mechanisms causing the gap. Young worlds exposed to violent stars can lose their atmosphere and contract. Larger worlds may have enough gravity to maintain a dense atmosphere, while smaller worlds turn to bare rock.Image of an evaporating exoplanet. “We want to find out what types of planets can survive under these conditions,” explains Rockcliffe. – What will they look like when the star calms down? … We don’t know what these stable systems look like because there is nothing like it in our solar system.”What exactly is happening with AU Mic b is still unclear, but whatever it is, the process is actively underway. It seems that all the mechanisms of the destruction of the atmosphere occur at the same time, therefore, this is an excellent natural laboratory for the study of such exoplanets.

Astronomers saw how a star rips off the atmosphere from its planet

As the artist envisioned AU Mic b.

Astronomers have seen how a young star tears off the atmosphere from one of its planets in huge volumes.

This exoplanet is called AU Microscopii b (or AU Mic b) and orbits a very young red dwarf star located just 32 light-years from Earth. The age of the system is only 23 million years, almost a child’s age, and its wild behavior gives an idea of ​​the turbulent period of the early life of recently formed planets. The results of the study were published in The Astronomical Journal.

What is particularly interesting about this Neptune-sized world is that the atmospheric emission does not occur all the time. On the contrary, it seems to turn on and off again quickly, becoming visible and then invisible – and this is during one revolution around the star. And when the process becomes visible, the atmosphere flows from the surface of the planet towards the star, instead of following it with its tail, as usual.

“When I first saw it, I thought, ‘That can’t be happening,'” says Dartmouth College astronomer Keighley Rockcliffe, who led the study. – This frankly strange observation became a kind of stress test for the modeling and physics of planetary evolution. This observation is so interesting because we get the opportunity to investigate one of the most extreme interactions between a star and a planet.”

An early drawing by the artist who depicted AU Mic b

AU Mic b was discovered in 2020, and already then scientists realized that it must be interesting. It is slightly larger than Neptune: its mass is 20.12 Earth masses and 4.19 Earth radii; the mass of Neptune is 17.15 Earth masses and 3.88 Earth radii. However, unlike Neptune, AU Mic b is very close to its star: it orbits once in just 8.5 days.

Such proximity allows the exoplanet to observe the warlike behavior of the star in the first row, and it is known to be turbulent. Young stars are much more active than old stars, and even old red dwarfs are quite active.

AU Mic is on a rampage, throwing out more than 6 flashes a day. This is the constant pressure of wild stellar wind, flares and hard X-rays.

Rockcliffe and her team wanted to take a closer look at this exoplanet because it could help explain an interesting gap in exoplanet detection – it contains worlds 1.5 to 2 times the radius of Earth that are in close proximity to their stars.

AU Mic b is on the larger side of this gap, but if it is actively losing its atmosphere and therefore shrinking in size, this may shed light on the mechanisms causing the gap. Young worlds exposed to violent stars can lose their atmosphere and contract. Larger worlds may have enough gravity to maintain a dense atmosphere, while smaller worlds turn to bare rock.

Image of an evaporating exoplanet.

“We want to find out what types of planets can survive under these conditions,” explains Rockcliffe. – What will they look like when the star calms down? … We don’t know what these stable systems look like because there is nothing like it in our solar system.”

What exactly is happening with AU Mic b is still unclear, but whatever it is, the process is actively underway. It seems that all the mechanisms of the destruction of the atmosphere occur at the same time, therefore, this is an excellent natural laboratory for the study of such exoplanets.

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