Planetary shields buckle under a fierce stellar wind from dying stars – life is almost impossible to survive

As the Sun evolves into a red giant, the Earth can be swallowed by the atmosphere of our stars, and the much more volatile solar wind can strip even the elastic protective magnetosphere of the giant outer planets. Credit: MSFC / NASA

Life identified on a planet orbiting a white dwarf almost certainly evolved after the star’s death, according to a new study led by the University of Warwick, in which the intense and ferocious stellar wind attacks the planet as it dies. The result is clear. The study was published in the monthly report of the Royal Astronomical Society and was presented today (July 21, 2021) by the lead author, Dr. Dimitri Veras, at the Online National Astronomical Society (NAM 2021).

This study provides new insights for astronomers looking for signs of life around these dead stars by examining the effects of wind on orbiting planets during the star’s transition to the white dwarf stage. To provide. This study concludes that it is almost impossible for life to survive cataclysmic stellar evolution unless the planet has a very strong magnetic field, or magnetosphere, that can protect it from the worst effects. ..

On Earth, solar wind particles can erode the protective layers of the atmosphere that protect humans from harmful UV rays. The Earth’s magnetosphere acts like a shield to divert those particles through their magnetic field. Not all planets have a magnetosphere, but the Earth is produced by its iron core. The iron core rotates like a dynamo to generate a magnetic field.

“We know that the solar wind of the past has eroded the atmosphere of Mars. The atmosphere of Mars, unlike Earth, does not have a large magnetosphere. Co-author of the study, Aline of Trinity College in Dublin. What we didn’t expect to find, Dr. Vidot, is that future solar winds could damage planets protected by the magnetic field as well.

All stars eventually run out of available hydrogen that promotes fusion. Under the sun, the core contracts and heats up, causing the star’s outside air to expand enormously into a “red giant.” The Sun then extends to tens of millions of kilometers in diameter, perhaps swallowing inferior planets, including Earth. At the same time, the loss of mass of the star means that it has a weaker attractive force, so the rest of the planets move farther.

At the stage of red giants, the solar wind is much stronger and fluctuates dramatically than it is today. Veras and Vidotto modeled winds from 11 different stars, with one to seven times the mass of the Sun.

Their model showed how the density and velocity of the stellar wind, combined with the expanding planetary orbit, collude to alternately shrink and expand the planet’s magnetosphere over time. In order for a planet to maintain its magnetosphere throughout all stages of stellar evolution, its magnetic field must be at least 100 times stronger than Jupiter’s current magnetic field.

The process of stellar evolution also results in a shift in the habitable zone of the star. This is the distance that allows the planet to reach the proper temperature to support liquid water. In our solar system, the habitable zone travels from about 150 million kilometers from the Sun (where the Earth is currently located) up to 6 billion kilometers, or beyond Neptune. Orbiting planets also reposition at huge divergence stages, but scientists have added challenges to existing life hoping that the habitable zone will move outwards faster than the planet and survive the process. I found it to bring.

Eventually, the red giant sheds its entire outside air, leaving behind the remains of a dark white dwarf. They do not emit a stellar wind, so once the stars reach this stage, the danger to the surviving planets is gone.

Dr. Belas said: “This study shows how difficult it is for a planet to maintain its protected magnetosphere throughout the huge divergence of stellar evolution.”

“One conclusion is that life on a planet in the habitable zone around a white dwarf will almost certainly be in the white dwarf stage if that life cannot withstand multiple extreme and sudden changes in its environment. It means that it develops in. “

Future missions such as the James Webb Space Telescope, which will be launched later this year, will include more for planets orbiting the white dwarf, such as whether the planets in the habitable zone show biomarkers that indicate the existence of life. Should be clear. Potential discovery.

So far, no terrestrial planets have been found that can support life around the white dwarf, but two known gas giants are close enough to the star’s habitable zone, and such planets could exist. It suggests that there is sex. These planets may have approached the white dwarf as a result of their interaction with other planets.

Dr. Belas adds: “These examples show that giant planets can get very close to the habitable zone. The habitable zone of a white dwarf emits much less light than a star like the Sun, so it is very close to the star. It’s close. However, the white dwarf is also a very stable star due to the lack of wind. Planets parked in the white dwarf’s habitable zone can stay there for billions of years, with conditions If appropriate, it can give time for life to develop. “

Conference: Royal Astronomical Society National Astronomical Society Conference Planetary shields buckle under a fierce stellar wind from dying stars – life is almost impossible to survive

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