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

crazyminner@lemmy.ml ⁨1⁩ ⁨month⁩ ago

• kichae@wanderingadventure.party ⁨1⁩ ⁨month⁩ ago

  The paper doesn’t calculate the radius of the star’s Roche limit, instead opting to calculate the orbital period of the Roche limit. I’ve never done a Roche limit calculation for stars, but I have for planets/moons, and I’m not seeing anything that suggests it’s different than for planets. So, I think I did this correctly (excepting typos):

  The star’s Roche limit is about 1.5 million km from its centre (~1 million km above its surface), and the planet’s orbit is about 2 million km from the star’s centre. Assuming a circular orbit, which should be the case at these distances, the orbit has a circumference of about 12.7 million km, and the planet is whipping around at a speed of about 2.3 million km/h, or 0.2% the speed of light.

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  • Typotyper@sh.itjust.works ⁨1⁩ ⁨month⁩ ago

    The article mentions the star being a dwarf. Are dwarf stars older and in a degrading state. Would the star have had less gravitational force when younger.

    How would a plant form that close if the gravitational pull from the star was this strong.

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    • kichae@wanderingadventure.party ⁨1⁩ ⁨month⁩ 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 ⁨1⁩ ⁨month⁩ 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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  • HurlingDurling@lemmy.world ⁨1⁩ ⁨month⁩ ago

    So much math here that my head is already overheating. I need to find the time to learn all this math. Kudos to you internet stranger on your examplary calculations.

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    • kichae@wanderingadventure.party ⁨1⁩ ⁨month⁩ ago

      The numbers are big, so it can be intimidating, but the math isn’t too bad. It’s a little bit of multiplication and division. The most daunting bit is a cube-root, which you can find on most scientific calculators these days.

      It’s hunting down the numbers you need to use that’s the trick, and making sure they’re all in the right units.

      The equation for the Roche limit is the most complex math, but that’s just something you look up:

      Roche Limit = 2.44 x {the radius of the star} x cube-root(( {the mass of the planet} / {the radius of the planet}^3 ) / ( {the mass of the star} / {the radius of the star}^3 ))

      All of the things in the braces are also just values you look up.

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