The study concludes that it is nearly impossible for life to survive cataclysmic stellar evolution unless the planet has an intensely strong magnetic field — or magnetosphere — that can shield it from the worst effects.“We know that the solar wind in the past eroded the Martian atmosphere, which, unlike Earth, does not have a large-scale magnetosphere.
What we were not expecting to find is that the solar wind in the future could be as damaging even to those planets that are protected by a magnetic field”, says Dr Aline Vidotto of Trinity College Dublin, the co-author of the study.Their model demonstrated how the density and speed of the stellar wind, combined with an expanding planetary orbit, conspires to alternatively shrink and expand the magnetosphere of a planet over time.The process of stellar evolution also results in a shift in a star’s habitable zone, which is the distance that would allow a planet to be the right temperature to support liquid water.
In our solar system, the habitable zone would move from about 150 million km from the Sun — where Earth is currently positioned — up to 6 billion km, or beyond Neptune.
Although an orbiting planet would also change position during the giant branch phases, the scientists found that the habitable zone moves outward more quickly than the planet, posing additional challenges to any existing life hoping to survive the process.“One conclusion is that life on a planet in the habitable zone around a white dwarf would almost certainly develop during the white dwarf phase unless that life was able to withstand multiple extreme and sudden changes in its environment.”.Future missions like the James Webb Space Telescope due to be launched later this year should reveal more about planets that orbit white dwarf stars, including whether planets within their habitable zones show biomarkers that indicate the presence of life, so the study provides valuable context to any potential discoveries.So far no terrestrial planet that could support life around a white dwarf has been found, but two known gas giants are close enough to their star’s habitable zone to suggest that such a planet could exist.
These planets likely moved in closer to the white dwarf as a result of interactions with other planets further out?
Veras adds: “These examples show that giant planets can approach very close to the habitable zone.
The habitable zone for a white dwarf is very close to the star because they emit much less light than a Sun-like star!
A planet that’s parked in the white dwarf habitable zone could remain there for billions of years, allowing time for life to develop provided that the conditions are suitable.”!
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