How a young planet hydrogen atmosphere is evaporation due to continuous, torrential bursts of energy.

Astronomers have just made an exciting new discovery – a young planet whirling around a petulant red dwarf star is changing in unpredictable ways orbit-by-orbit. Located 32 light-years from Earth, the parent star AU Microscopii (AU Mic) is only 100 million years old – a tiny fraction of the age of our own Sun. The innermost planet, AU Mic b, has an orbital period of 8.46 days and is just 6 million miles from the star (about 1/10th the planet Mercury’s distance from our Sun). This close proximity to its parent star causes it to experience a consistent, torrential blast of energy, which evaporates its hydrogen atmosphere – causing it to puff off the planet.

NASA’s Hubble Space Telescope was used to observe this distant planetary system and the results were shocking. During one orbit observed with Hubble, the planet looked like it wasn’t losing any material at all, while an orbit observed with Hubble a year and a half later showed clear signs of atmospheric loss. This extreme variability between orbits was unexpected. As Keighley Rockcliffe of Dartmouth College in Hanover, New Hampshire, said, “We’ve never seen atmospheric escape go from completely not detectable to very detectable over such a short period when a planet passes in front of its star. We were really expecting something very predictable, repeatable. But it turned out to be weird.”

The observation of the atmosphere puffing out in front of the planet was equally puzzling – like a headlight on a fast-bound train. Rockcliffe went on to say that “This frankly strange observation is kind of a stress-test case for the modeling and the physics about planetary evolution. This observation is so cool because we’re getting to probe this interplay between the star and the planet that is really at the most extreme.” This is an incredibly exciting development for astronomers as they attempt to further understand planetary evolution and interplay between stars and planets.

The discovery of AU Mic b provides us with valuable insight into how stars and planets interact with one another, and how planets can change over time. This extreme variability between orbits is a remarkable find and reveals just how much we still have to learn about our universe.

The discovery of AU Mic b – a planet orbiting a red dwarf star – has sparked excitement in the scientific community. This exoplanet was found using the transit method, meaning telescopes can observe a slight dip in the star’s brightness when the planet crosses in front of it. Red dwarfs like AU Microscopii are the most abundant stars in our Milky Way galaxy and they may potentially host a large number of planets, yet researchers question whether these planets can be hospitable to life.

The major challenge is that young red dwarfs have powerful stellar flares that emit intense withering radiation that could make inhabiting these planets difficult. As the magnetic fields of the star’s atmosphere become more tangled, the fields break and reconnect, releasing huge amounts of energy that are 100 to 1,000 times more energetic than our Sun’s outbursts. These stellar winds, flares and X-rays could strip a planet’s atmosphere and render it uninhabitable for life.

To understand how these conditions might affect life on a planet orbiting a red dwarf star, scientists seek to study the composition of such planets. Do they eventually lose most of their atmosphere and become super-Earths, or do they remain habitable? What will be the final composition of such planets? These are questions that researchers hope to answer soon. In order to answer these questions, scientists need to continue to observe AU Mic b and other similar exoplanets. As learn more about these planets and their atmospheres, may be able to better understand the possibility of habitability on exoplanets orbiting red dwarf stars.

The Hubble telescope, though unable to directly observe planets due to the star’s glare, is capable of measuring changes in the star’s apparent brightness caused by the presence of the planet. This is due to hydrogen molecules escaping the planet’s atmosphere heating to a point where they bleed off and dim the starlight. When the planet transits the star, this effect can be easily detected.

AU Mic b’s odd variability.