Shulou(Shulou.com)11/24 Report--

This article comes from the official account of Wechat: SF Chinese (ID:kexuejiaodian), author: SF

Recently, astronomers were fortunate to witness a special event in the universe: a star is using its powerful radiation to gradually peel off the atmosphere of one of its planets. The process is very unstable, just as the star sometimes loses its temper, vents its anger on the planet, and sometimes calms down.

(by Chen Qiang / tr. by Robert Taylor)

About 32 light-years away from our solar system, there is a red dwarf star called AU Mic. Although red dwarfs are smaller and darker than our sun, studies have shown that even the quietest red dwarfs are wilder than the sun. To make matters worse, AU Mic is a young star, about 2.3 million years old and full of energy. It can be said that AU Mic is a young red dwarf star who loses his temper.

Around AU Mic, there is a planet about four times the diameter of Earth. The planet, called AU Mic b, is very close to its star, only about 90,000 kilometers. Recently, astronomers have discovered with the help of the transit phenomenon that a mass of atmospheric material has been stripped out of AU Mic b under the action of intense radiation from the star.

Intense radiation causes the atmosphere to escape when an exoplanet passes between its star and us, it obscures the light of some stars, causing the brightness of the stars we observe to decrease slightly. This phenomenon is called "Ling Xing". Through the detection of this slight light change, astronomers can deduce the existence of exoplanets and some basic parameters, such as size, orbit, period and so on.

In 2020, astronomers discovered AU Mic b for the first time using the transiting phenomenon. However, the telescopes used by astronomers at that time were NASA's Spitzer Space Telescope and the exoplanet Survey Satellite. Now, with the help of the Hubble Space Telescope, astronomers have made a new discovery about the AU Mic system.

This time, astronomers see not only ordinary transits, but also some matter that darkens the brightness of stars more than normal, according to the data. Moreover, the matter seems to be in front of the orbit of the planet, far away from the planet. As a result, AU Mic b transits occur much earlier than expected, and the star's brightness changes in an unusual way.

When astronomers first got the data, they thought there must be some mistake. But no matter how many different methods they use to reanalyze, the result is the same. What on earth is going on? Astronomers believe that what they see is a mass of planetary atmospheric matter freed from the gravitational shackles and away from the core of the planet. In other words, part of the planet's atmosphere is "blown away". Astronomers speculate that ultra-high-energy flares produced by red dwarfs caused the planet's atmosphere to escape. It produces flares that are more than 1000 times as intense as our sun.

Even weirder, the process is unstable: stars sometimes lose their temper, vent their anger on the planets, peel off some of the atmosphere, and sometimes calm down. Astronomers believe that the stellar wind generated by AU Mic may cause turbulence when it interacts with the planet's atmosphere, leading to this hiccup-like atmospheric escape.

Interestingly, astronomers have also predicted what the planet might look like in billions of years: if the planet's atmosphere is completely stripped off, the rest will be a naked rocky core, which may eventually look like Mercury, but if it can retain its lower atmosphere, we may get a planet similar to Neptune.

The most common planets reveal the mystery of the evolution of celestial bodies. The phenomenon that the atmosphere of the surrounding planets escapes due to the intense activity of stars is nothing new. But this observation is new because it is the first time astronomers have witnessed this atmospheric escape on an ordinary planet.

In the past, astronomers have observed atmospheric escape only on some planets called hot Jupiter. These planets are a bit like Jupiter, but very hot because they are very close to the stars. But the problem is that they are one of the rarest exoplanets in our Milky way. Astronomers say using hot Jupiter's information to understand the evolution of other planetary systems is like "extrapolating the experience of the middle class from the experience of an economically wealthy person". It is not accurate to do so.

What is special about AU Mic b is that it is not special at all. The star it surrounds is still a red dwarf, which is the most common type of star in the Milky way. This discovery gives us an idea of what a planet's atmospheric escape looks like in one of the most common planetary systems.

Atmospheric escape is one of the key factors affecting the evolution of exoplanets. It can change the temperature, pressure, chemical composition and possibility of life of the planet. Therefore, this discovery not only allows us to understand the mechanism of atmospheric escape, but also helps to reveal the history and future of these distant worlds. In addition, the discovery will give astronomers a deeper understanding of the characteristics of red dwarfs and how they differ from our sun or other stars.

Next, astronomers hope to use the Hubble Space Telescope and the more advanced James Webb Space Telescope to study exoplanets that can burp out atmospheric matter.

References:

Https://iopscience.iop.org/article/10.3847/1538-3881/ace536

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