Hubble observes 'angry' stars and planets whose atmospheres are evaporating

【Editor's Note】The vastness of the universe is always a mystery to human beings, and there is no way to know its essence. What modern astronomy recognizes is only the moment of change that can be observed in celestial bodies captured by modern high technology in human space. Scientists seize the observation data at this moment and put forward theories and hypotheses. Like a blind man feeling an elephant, it is difficult to see the whole and its essence . If we only explore the mysteries of the universe in the space of human beings, it will be a waste of time after all. I hope that readers can think about the true meaning of the universe, human body and life from the discoveries of modern astronomy.

An artist's impression of a planet transiting in front of a red dwarf star. In indigo, the planet's atmosphere appears to be "blowing away." (Image credit: NASA, ESA, Joseph Olmsted (STScI))

NASA's Hubble Space Telescope has given them an important new look at this interstellar nightmare, scientists announced July 27, 2023. In a way, these new Hubble results could have a dual impact on the field of astronomy: They could tell us that exoplanets are undergoing some sort of atmospheric evaporation, while also giving us a better understanding of the stars that may be continually stripping them of their atmospheres .

AU Mic b is only four times the diameter of Earth, and unfortunately, it's only about 6 million miles (9.6 million kilometers) away from its star -- a star classified as a red dwarf, the most extreme class of stellar objects in the universe . For example, studies have shown that even the quietest examples, like this red dwarf, are wilder than our fiery sun. But that's not all. To make matters even more intense, AU Mic is one of the youngest stars, adding to its dynamism.

"It's 23 million years old, very, very young, basically An infant star." "Stellar astronomers are excited because AU Mic is an example of a red dwarf star (the most common type of star in the Milky Way) when it was young, turbulent."

Because Hubble is in Earth's orbit, it can capture starlight to identify when a distant planet passes between its host star and Earth (a phenomenon known as a planetary transit).

When a planet transits, it temporarily dims the star, alerting anyone who is watching that something must be causing the dimming. In fact, this derivation mechanism is actually how scientists began locating AU Mic b in 2020. NASA's Spitzer and TESS (TESS) Space Telescope first observed it.

When Rockcliffe and other researchers looked at AU Mic b with Hubble, they saw more than just the regular dimming of transiting stars. Some of the light waves associated with this dimming told them that the material causing the dip was much deeper than the planet itself. Also, this material appears to have preceded the planetary transit by a long time. After zooming out the field of view, it looks like the AU Mic b transitions much earlier than expected and has some erratic quirky patterns.

The only explanation is that the planetary material they were looking at was so far from the core that it escaped the planet. Or as Rockcliffe puts it, it must have been "blown away!"

"I remember when I first used the Hubble data to create the light curve of this planet, and found that the transit occurred much earlier than the predicted transit of the planet," she said. "I immediately thought, 'Well, I must have made a mistake.' However, no matter how many times I reanalyzed it with different methods, the result was the same."

Presumably, the disappearance of the planet's atmosphere is due to the red dwarf's ultra-high-energy flare (think, a thousand times the flare of our sun) bombarding the planet with radiation.

Although this process of atmospheric escape due to an aggressive host star is nothing new, Rockliffe explained that what makes this observation so novel is that it is the first time scientists have witnessed it on an ordinary, ancient planet. This shedding phenomenon.

"Atmospheric escape is probably one of the most influential evolutionary processes for most exoplanets," explained Rockliffe.

Essentially, this work could help scientists decode what worlds beyond our solar system look like, where they live, and perhaps create guides to help us write knowledge about them.

One of the questions scientists are still trying to answer is how exoplanets lose their atmospheres, Rockliffe added. "For exoplanet astronomers, among other things, what mechanism primarily drives this atmospheric escape? Is it the heating of intense energetic radiation from the star, or is it the newly formed hot planetary core heating the planet from the inside out?" she said. atmosphere?"

For example, one of the strangest things about the recent observation of atmospheric escape on AU Mic b is that it seems unstable. It's almost as if the stars are sometimes in a bad mood and carry that mood over to the planets, but other times, it's just chilling.

A paper on the work was published July 27 in The Astronomical Journal.