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Apparent equality between Jovian esc. velocities and Sol's esc. vel.
Okay, I've never heard anything about this before=E2=80=A6Somebody =
please explain this: In scanning the wikipedia entry on "Escape Velocity", at https://en.wikipedia.org/wiki/Escape_velocity , I noticed in its list of escape velocities that for the Jovian planets alone (but not for smaller planets) the tabulated escape velocities for each Jovian was almost exactly identical to the escape velocity for the sun itself AT that planet's orbit. IE: (1) Jupiter's esc. vel. = 60.2 km/s Sol's esc. vel. = at J's orbit = 60.4 km/s (2) Saturn's esc. vel. = 36.09 km Sol's esc. vel. a= t S's orbit = 36.3 km/s (3) Uranus's esc. vel. = 21.38 km/s Sol's esc. vel. = at U's orbit = 23.7 km/s (4) Neptune's esc. vel. = 23.56 km/s Sol's esc. vel. = at N's orbit = 23.7 km/s i.e.: Sol/planet ratios very close to unity. On the other hand, the analogous values for the smaller terrestrial planets are in a ~Sol/planet ratio very roughly equal to ~1.5 to ~2 or so Am I the victim of a vast astronomical hoax, or just some blitheringly obvious well known phenomenon, or can I get a door prize at the Nobel's shindig next year? :-) [[Mod. note -- You're very likely just seeing approximate coincidences. If I've done my algebra correctly the escape velocity at a distance r from a mass M is given by sqrt(2GM/r) where G is the Newtonian gravitational constant, so you're essentially asking where there's any special relationship between the ratios M_sun / planet_orbit_radius_about_sun and M_planet / planet_radius There no reason to expect any such relationship, since these ratios are set by quite different physical phenomena, and the first ratio may change over time if the planet migrates in the solar disk during the early formation of the solar system. -- jt]] |
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Apparent equality between Jovian esc. velocities and Sol's esc. vel.
On Saturday, November 25, 2017 at 9:01:01 PM UTC-8, stargene wrote:
Okay, I've never heard anything about this before=E2=80=A6Somebody = please explain this: In scanning the wikipedia entry on "Escape Velocity", at https://en.wikipedia.org/wiki/Escape_velocity , I noticed in its list of escape velocities.... [[Mod. note -- You're very likely just seeing approximate coincidences. If I've done my algebra correctly the escape velocity at a distance r from a mass M is given by sqrt(2GM/r) where G is the Newtonian gravitational constant, so you're essentially asking where there's any special relationship between the ratios M_sun / planet_orbit_radius_about_sun and M_planet / planet_radius There no reason to expect any such relationship, since these ratios are set by quite different physical phenomena, and the first ratio may change over time if the planet migrates in the solar disk during the early formation of the solar system. -- jt]] Thanks, JT. You're not only right, but when I bothered to actually check wiki's data on the Jupiter and Sol values, their "60.2 km/s" for Jupiter's esc. vel. is correct but the esc. vel. for Sol at Jupiter's orbit is 18.46 km/s, NOT their "60.4 km/s". Catch me trusting wikipedia as an authority again. Embarrassing. We can cancel that door prize. stargene |
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Apparent equality between Jovian esc. velocities and Sol's esc.
Dne 26/11/2017 v 06:00 stargene napsal(a):
[...] In scanning the wikipedia entry on "Escape Velocity", at https://en.wikipedia.org/wiki/Escape_velocity , I noticed in its list of escape velocities that for the Jovian planets alone (but not for smaller planets) the tabulated escape velocities for each Jovian was almost exactly identical to the escape velocity for the sun itself AT that planet's orbit. IE: (1) Jupiter's esc. vel. = 60.2 km/s Sol's esc. vel. = at J's orbit = 60.4 km/s [...] You confuse Sun escape speed at Jupiter orbit with Sun-Jupiter system escape speed 60,4 km/s V = sqrt ( ((v_S . k )^2 + (v_J)^2 ) where k = 1-1/sqrt(2) = cca 0.2929 for circular orbits v_S is Sun escape speed at Jupiter orbit v_J is Jupiter escape speed v_Sys is Sun-Jupiter system escape speed to escape both Jupiter and Sun gravity. Read the section Multiple bodies. https://en.wikipedia.org/wiki/Escape...ultiple_bodies -- Poutnik ( The Pilgrim, Der Wanderer ) A wise man guards words he says, as they say about him more, than he says about the subject. |
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Apparent equality between Jovian esc. velocities and Sol's esc.
Dne 27/11/2017 v 07:41 stargene napsal(a):
Thanks, JT. You're not only right, but when I bothered to actually check wiki's data on the Jupiter and Sol values, their "60.2 km/s" for Jupiter's esc. vel. is correct but the esc. vel. for Sol at Jupiter's orbit is 18.46 km/s, NOT their "60.4 km/s". Catch me trusting wikipedia as an authority again. Embarrassing. We can cancel that door prize. stargene It is not their, but of the OP info he provided. There are 2 columns in Wikipedia and he confused them. 60.4 is Sun-Jupiter system escape speed ( velocity is vector). Sun escape speed at Jupiter orbit is displayed there correctly. -- Poutnik ( The Pilgrim, Der Wanderer ) A wise man guards words he says, as they say about him more, than he says about the subject. |
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