Some planets cannot hold atmospheres. It is believed that most of Mars’ atmosphere, which was retained by Earth and Venus, was wiped out by the solar wind billions of years ago. However, some planets orbit so close to their stars that loss of atmosphere is unavoidable. At least one of them turned out to be unpredictable.
exoplanet Oh mic b That planet. It orbits the young, hot, and capricious red dwarf Au Microscopii (Au Mic), which is only 23 million years old, compared to our 4 billion-year-old Sun. does not become NASA’s Hubble Space Telescope captured this scorching world that has lost part of its atmosphere.
A team of scientists from NASA Goddard Space Flight Center, Dartmouth College, the University of California, Santa Cruz, and others analyzed the Hubble observations and were confused by the unusual behavior of the planet. Some data had evidence of atmospheric loss, but suddenly it’s gone altogether. It was unpredictable.
What could cause this planet to occasionally evaporate its atmosphere and then seem to escape its fate for some time? Further analysis revealed that Au Mic B is unlikely to escape the star’s wrath. The researchers realized that sometimes the ruthless destruction of the atmosphere is just invisible, and could explain why.
take heat
Hot young stars frequently experience a phenomenon known as magnetic reconnection, in which magnetic field lines break and reconnect, releasing a blob of scorching hot plasma into space. Although the Sun has tantrums, flares and coronal mass ejections caused by magnetic reconnection are more powerful in young, hot stars like Au Mic. Au Mic b is particularly susceptible to plasma eruptions because it orbits at her 9.7 million kilometers (about 6 million miles) distance, which is uncomfortably close to its star. Mercury, the closest planet to the Sun in our solar system, orbits 10 times further away and still has little of an atmosphere.
The Au Mic b makes the Mercury feel like a treat. Roughly the size of Neptune, it lives fast, orbiting the star in just eight days, under constant stellar winds and ultraviolet radiation. Planets born within the first 100 million years of their stellar life are likely to lose the most material from their atmospheres (depending on time of formation and distance), and this planet is no exception. The flare heats the hydrogen atmosphere to the point where the gas is no longer held by the planet’s gravity and is released into space.
now you’re looking at me…
Hubble observed Au Mic b during two passes. Then it passed in front of the star, causing the star’s light to fade. These observations were made at wavelengths that allow us to observe the flow of hydrogen from the Earth. Oddly enough, the loss of hydrogen was only occasionally apparent.
“Although we could not clearly confirm absorption by the planet, [transit] 1, [transit] 2 indicates that the planet’s neutral hydrogen escapes in front of AU Mic b and is being accelerated away from the host star,” they said. study It was recently published in the Journal of Astronomy.
The outflow of atmospheric gas is probably formed by the stellar wind from Au Mic, and not all the escaped gas can follow Au Mic b. These winds are so powerful that they actually push some of that gas in front of the Earth. This wind may have shaped the tail in such a way that it could not be observed from Hubble’s point of view.
Another possible reason for the non-observability of all Au Mic b efflux is photoionization. Oh Mick had just exploded a huge stellar flare hours before its first pass. The flare was so energetic that it heated and ionized gas particles, making them invisible at the wavelengths observed by Hubble. The aftermath of the flare is believed to have lasted throughout the first pass. It could have probably still been going on while Hubble was watching.
There are still many unknowns about planets like Au Mic b. Will hot Neptune, Jupiter, and Saturn, with their atmospheres devoured, turn into super-Earths when their cores are exposed? For now, Hubble will keep an eye on this strange planet.
Astronomical Journal, 2023. DOIs: 10.3847/1538-3881/ace536
