What happens when a hot young world orbits a dangerously unstable young red dwarf? The answer for AU Microsopii b is: flares from the star tearing away the atmosphere. That catastrophic loss occurs in bits and spurts, with the atmosphere “hiccuping” out at one point and then losing almost none the next.
That level of activity is quite startling. Interactions between stars and their planets are usually more consistent. However, not this one. “We’ve never seen atmospheric escape go from completely undetectable to very detectable in such a short period when a planet passes in front of its star,” Dartmouth College’s Keighley Rockcliffe in Hanover, New Hampshire, said. “We were hoping for something very predictable and repeatable.” But it turned out to be strange. When I initially saw it, I thought to myself, ‘That can’t be right.'”
Rockcliffe and her colleagues are developing hypotheses for this strangely varied atmospheric loss. Such behavior is crucial to comprehend when astronomers discover more planets, particularly red dwarfs, close to their sun. “We want to know what kinds of planets can survive in these conditions.” What will they look like once the star has settled? And will they ever be habitable, or will they just be charred planets?” asked Rockcliffe. “Do they eventually lose most of their atmospheres, with the surviving cores transforming into super-Earths?” We don’t know what those ultimate compositions look like because nothing like that exists in our solar system.”
How Red Dwarf Stars Affect Planet Atmospheres
A planet the size of Neptune called AU Microscopii b (AU Mic b) has a hydrogen atmosphere. By NASA’s Spitzer Space Telescope and the Transiting Exoplanet Survey Satellite) in 2020, it was first identified as orbiting its parent star. As the planet transited (passed in front of) the star, they were able to see it.
The distance between the star and its planet is 32 light-years. The star itself, AU Microscopii (AU Mic), is rather young, having only existed for 32 million years. This young star, a red dwarf, has astounding flaring activity and variability. This has an impact on its planets, especially AU Mic b, which is only 9.6 million kilometers from the star.
The majority of the stars in the Milky Way galaxy are red dwarfs like AU Mic. They appear to be the hosts of the majority of the planets in our galaxy. There is a catch, though. These stars unleash violent stellar flares that irradiate any surrounding planets. The activity in the powerful magnetic fields in the star atmospheres is what causes the flares. The fields occasionally disconnect and then re-connect. Massive amounts of energy are released as a result, sending X-rays, flares, and torrential stellar winds into space. Any planets in the path are baked. The atmosphere of the Earth is being impacted by a highly unrestrained and, to be honest, terrifying stellar wind environment, according to Rockcliffe. Around these young stars, young planets occasionally entirely lose their atmospheres.
What Happens to AU Microscopii’s Neptune-Sized Planet
Rockcliff’s team used data collected by the Space Telescope Imaging Spectrograph (HST/STIS) on board the Hubble Space Telescope to comprehend the highly erratic atmosphere loss at AU Mic b. It is sensitive to ultraviolet light, which is emitted as the parent star’s intense heat and flare activity photoionizes the departing atmosphere. As the star heats its immediate surroundings with flares and other activity, the STIS device collected enough data to allow the science team to at least hypothesize about what is happening in this system.
A quick, dramatic variability in the star’s outbursts may be indicated by changes in the atmosphere outflow from AU Mic b. That variability is attributed by astronomers to turbulent magnetic field lines. The hydrogen leaving from the planet may have been photoionized by a strong star flare to the point where it turned transparent to light. It was hence undetected.
The escape of hydrogen from the planet before it as it orbits its parent star is the most perplexing. The atmospheric hydrogen may be being shaped into a “leading tail” that precedes the star by the high-energy radiation from the star. Astronomers will need to conduct more subsequent observations of AU Mic b as it transits its star in the future to confirm that. Furthermore, additional measurements will aid in the explanation of air loss in such planets. This will not just link atmospheric loss to stellar variability.
Rockcliff’s team used data collected by the Space Telescope Imaging Spectrograph (HST/STIS) on board the Hubble Space Telescope to comprehend the highly erratic atmosphere loss at AU Mic b. It is sensitive to ultraviolet light, which is emitted as the parent star’s intense heat and flare activity photoionizes the departing atmosphere. As the star heats its immediate surroundings with flares and other activity, the STIS device collected enough data to allow the science team to at least hypothesize about what is happening in this system.
A quick, dramatic variability in the star’s outbursts may be indicated by changes in the atmosphere outflow from AU Mic b. That variability is attributed by astronomers to turbulent magnetic field lines. The hydrogen leaving from the planet may have been photoionized by a strong star flare to the point where it turned transparent to light. It was hence undetected.
The escape of hydrogen from the planet before it as it orbits its parent star is the most perplexing. The atmospheric hydrogen may be being shaped into a “leading tail” that precedes the star by the high-energy radiation from the star. Astronomers will need to conduct more subsequent observations of AU Mic b as it transits its star in the future to confirm that. Furthermore, additional measurements will aid in the explanation of air loss in such planets. This will not just link atmospheric loss to stellar variability.