Comment on This Earth-sized Exoplanet is On a Death Spiral

• kichae@wanderingadventure.party ⁨12⁩ ⁨hours⁩ ago

  Dwarf stars are technically any star that is in its core phase of life. They are dwarves in comparison to giant stars. The sun is a G-type dwarf star, for instance.

  The star is a K-type dwarf, which means it is cooler and smaller than the sun (stars are labelled froom hottest/most massive coolest least hot/least massive: O, B, A, F, G, K, and M for historical reasons).

  Planet formation is a complicated and still somewhat young field of study. Planets being close to their stars was a real shock 20 years ago when we stared finding them. The best models we have for this is planetary migration, where the planets form farther aewy from the star, but friction/drag forces from the nebula from which they formed causes them to slow down and fall into smaller orbits.

  This planet continues to see its orbit degrade for even more complex reasons, related to both drag – it is interacting with the star’s atmosphere, which is causing it to slow – and tidal effects. When you’re close enough to a massive, rotating body that the differences in gravitational pull strength due to things like variations in density become significant, the rotating body will force you into an orbit that matches its rotation length. If you’re already orbiting faster than it is spinning, that means it will slow you down. But slowing down will cause your orbit to shrink, which shortens the time it takes you to complete an orbit, which will make the central body slow you down more, which will shrink your orbit, which…

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  • Typotyper@sh.itjust.works ⁨11⁩ ⁨hours⁩ ago

    So you’re saying as our own system ages the planets will get pulled in and eaten up.

    Would Jupiter being a gas giant get slowed down equally to the outer planets or would it eat some planets on its own.

    Maybe eat is too much imagery. Would it accelerate those planets decline.

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    • kichae@wanderingadventure.party ⁨11⁩ ⁨hours⁩ ago

      typotyper@sh.itjust.works said in How fast is that in kilometers per hour?: So you’re saying as our own system ages the planets will get pulled in and eaten up.

      Not in the same way, no. None of our planets are touching the Sun’s atmosphere in the same way this planet is, and none of them are orbiting at rates that are faster than the Sun’s rotation. If anything, tidal interactions would want to speed up the planet’s orbits, and push them into higher orbits.

      But eventually the Sun will become a red giant star, which will change some of these relationships. We will see competing effects then: The Sun will begin shedding its outer layers, which will create a higher drag environment for the planets (that were not swallowed during the Sun’s expansion) which would tend towards inward migration, but this will also lower the Sun’s mass, which will lend itself toward an outward migration.

      typotyper@sh.itjust.works said in How fast is that in kilometers per hour?: Would Jupiter being a gas giant get slowed down equally to the outer planets or would it eat some planets on its own.

      All of the outer planets are gas giants.

      Jupiter is not currently migrating inward, nor are any of the other planets. If inward migration happens after the Sun becomes a red giant, those other outer planets will not get anywhere close to it. As a red giant, the Sun will approximately fill Earth’s orbit. Jupiter’s orbit is 5x larger than this; Saturn’s is 10x larger, and by the time the Sun actually grows this large, all of the planets’ orbits will be even larger than they are today, thanks to gradual mass loss.

      None of the outer planets are expected to fall into the Sun at any point in time.

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      • Typotyper@sh.itjust.works ⁨9⁩ ⁨hours⁩ ago

        Thanks for the answers (and time). It’s cool to learn these things.

        I could ask another 100 questions and still not understand half of it.

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