4 ms·

wow 50 light years is indeed "nearby" in relative terms nearly 6x the size of earth though, good luck trying to launch a probe off that surface NASA has a nea

• pixl97 3mo ago
  6x time size (diameter?) or 6 times the mass. Evidently the Earth used to be much larger in size but not mass because of large amounts of trapped hydrogen/helium. It's since leaked from the crust and been blown off into space.
  • ck2 3mo ago
    the catalog says 6.38x mass in one place and 5.6x mass in another they must be able to calculate mass from orbital physics? so you'd need a rocket 6x the size of SaturnV or whatever they are using for Artemis to escape it and most of that rocket is to lift the weight of the fuel for said rocket so it might be physically impossible to build such a creature at current level of tech (might be yet another angle to "why no ETs" unless they are WAY more advanced)
    • deleted 3mo ago
      [deleted]
    • inigyou 3mo ago
      √(G × mass÷radius) [escape velocity] = v_e × ln(m_0 ÷ m_f) [Tsiolkovsky] Impossible to tell how much extra mass you need but it's exponential. Adding a unit of v_e [effective exhaust velocity] to escape velocity means you need 2.717 times as much fuel in an ideal rocket. Earth escape velocity is 11000m/s ignoring atmosphere (which is not ignorable). If the new planet is 6x mass and 2x radius then √3 times escape velocity (about 1.73) would be about 8000m/s extra velocity which is about 3 times a random v_e which means you need about a 25 times bigger rocket. Ignoring the denser atmosphere which makes it even worse.
      • shagie 3mo ago
        From the archives ... How much bigger could Earth be before rockets wouldn't work? https://space.stackexchange.com/q/14383 https://space.stackexchange.com/q/14383 Feb 3, 2024 https://news.ycombinator.com/item?id=39243303 https://news.ycombinator.com/item?id=39243303 And related... https://worldbuilding.stackexchange.com/questions/178131/what-is-the-maximum-size-of-a-planet-that-a-chemical-rocket-can-leave-it https://worldbuilding.stackexchange.com/questions/178131/wha... https://physics.stackexchange.com/questions/117347/when-a-planet-has-a-high-gravity-is-it-impossible-to-build-and-launch-a-success https://physics.stackexchange.com/questions/117347/when-a-pl...
        • Cthulhu_ 3mo ago
          Man I love this. > Up above 10g, something really interesting happens that is kind of a theoretical limit. The mass of the rocket reaches a measurable fraction of the mass of the entire planet it's launching from.
          • ck2 3mo ago
            one thing about physics, particularly astro-physics, is it's NEVER boring been diving into PBS-Space-Time and DrBecky past few years as distraction from the endless nightmare of the world we are living in this has been a great educational thread on HN too, I knew rockets would have to be bigger but didn't realize exponential and the 10g upper-limit also puts the "Mars sample return" mission into perspective, very difficult
            • shagie 3mo ago
              Playing with the trajectory browser at NASA is kind of neat. https://trajbrowser.arc.nasa.gov/traj_browser.php?NEAs=on&NECs=on&chk_maxMag=on&maxMag=25&chk_maxOCC=on&maxOCC=4&chk_target_list=on&target_list=Mars&mission_class=roundtrip&mission_type=rendezvous&LD1=2020&LD2=2040&maxDT=4&DTunit=yrs&maxDV=6.0&min=DV&wdw_width=-1&submit=Search#a_load_results https://trajbrowser.arc.nasa.gov/traj_browser.php?NEAs=on&NE... The "view" at the bottom has an animation of the various routes. They're all EM-ME though... If you pick some other interesting targets you can get EVJS or something like that (launch from Earth, Gravity assist at Venus, Gravity assist at Jupiter, rendezvous with Saturn)... and then the trajectory animations are much more interesting.
  • Tagbert 3mo ago
    Do you have any reference for that? I have a hard time seeing how that would be true once the components were coalesced but maybe before that.