Privileged Planet: comparing suns (Introduction)

by David Turell , Friday, April 22, 2022, 18:39 (947 days ago) @ David Turell

Our is best so far, examining other planetary systems:

https://www.sciencenews.org/article/orange-dwarf-stars-radiation-goldilocks-habitable-p...

"If you’re an aspiring life-form, you might want to steer clear of planets around orange dwarf stars.

"Some astronomers have called these orange suns “Goldilocks stars” (SN: 11/18/09). They are dimmer and age more slowly than yellow sunlike stars, thus offering an orbiting planet a more stable climate. But they are brighter and age faster than red dwarfs, which often spew large flares. However, new observations show that orange dwarfs emit lots of ultraviolet light long after birth, potentially endangering planetary atmospheres, researchers report in a paper submitted March 29 at arXiv.org.

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"As yellow sunlike stars age, they spin more slowly, causing them to be less active and emit less UV radiation. But for orange dwarfs, this steady spin-down stalls when the stars are roughly a billion years old, astronomer Jason Lee Curtis at Columbia University and colleagues reported in 2019.

“'[Orange] stars are just much more active for a longer time than we thought they were,” Richey-Yowell says. That means these possibly not-so-Goldilocks stars probably maintain high levels of UV light for more than a billion years.

"And that puts any potential life-forms inhabiting orbiting planets on notice. Far-ultraviolet light — whose photons, or particles of light, have much more energy than the UV photons that give you vitamin D — tears molecules in a planet’s atmosphere apart. That leaves behind individual atoms and electrically charged atoms and groups of atoms known as ions. Then the star’s wind — its outflow of particles — can carry the ions away, stripping the planet of its air.

"But not all hope is lost for aspiring life-forms that have an orange dwarf sun. Prolonged exposure to far-ultraviolet light can stress planets but doesn’t necessarily doom them to be barren, says Ed Guinan, an astronomer at Villanova University in Pennsylvania who was not involved in the new work. “As long as the planet has a strong magnetic field, you’re more or less OK,” he says.

"Though far-ultraviolet light splits water and other molecules in a planet’s atmosphere, the star’s wind can’t remove the resulting ions if a magnetic field as strong as Earth’s protects them. “That’s why the Earth survived” as a life-bearing world, Guinan says. In contrast, Venus might never have had a magnetic field, and Mars lost its magnetic field early on and most of its air soon after.

“'If the planet doesn’t have a magnetic field or has a weak one,” Guinan says, “the game is over.'”

Comment: more proof of our uniqueness. Our magnetic field is just right for u-v protection. In view of dhw's weird take on the universe's size question of 'why so big' if only a proper life-supporting Earth was needed, my answer is don't second guess God with your tiny human brain. God knows exactly what is needed to create what He wants/needs to create.