this post was submitted on 08 Sep 2024
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No Stupid Questions
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that's roughly a protoplanetary disk, what it's like before new planets form! jupiter's mass is 95% hydrogen-helium atmosphere with a core of ice and metals. because the solar system already has planets, though, we'd expect the ones currently here to "sweep" up the gas along their orbits in a fairly timely manner (jupiter's year is 12 earth-years). if the gas is spinning at about planetary speeds, most of the gas will gradually be pulled out of solar orbit and into planetary atmosphere, so basically all the planets will become gas giants (or possibly new dwarf stars! i haven't done the math). depending on how far out your protoplanetary disk goes you might need new planets form in the outer regions, past the regions where existing planets have formed. expect orbits to get really fucked up due to new gravity dynamics.
so for your questions:
A: yes, you should have enough air pressure to leave orbit in a plane, which is great to flee the planet because the new solar atmosphere will immediately plunge earth into an ice age for a few years as it first blocks most of fhe solar radiation, and then gradually heats up. the solar atmosphere wind dynamics will also fuck you up in a way that the dying Earth's scientific computing will struggle to help with, especially when all satellites burn up in air and fall to the surface
B: (1 AU / the speed of sound) = 5000 days. the distant, ominous howl of a vengeful sun will be the least of your concerns as the nations of earth turn violent in a desperate attempt to save some last trace of human civilization
C: a megacyclone, yes! a beautiful spiral as each planet sweeps up the protoplanetary gases to swell to gas-giant size or dwarf star status. perhaps some day the light of five suns may shine on Earth again, but all traces of what once was will be sunk under five thousand kilometers of a liquid nitrogen sea. in one possible delusion, the billion-year descendants of the last earthlings will live in orbit of a still-molten rock so far past the kuiper belt that the five stars of Sol look like a bright-hot constellation instead of the core of its orbit
D: at some point, yes! for a brief moment the pressure will be unchanged as the solar atmosphere orbits the sun instead of pressing on the earth. perhaps some would be wise enough to realize that the sudden dimming of the sun - eight minutes as it turns to a dull, occluded, sky-colored haze, as if it had just melted away - foretold an imminent disaster. those bright minds would struggle to be heard amid a hundred other apocalyptic visions, because who would believe the sudden, impossible appearance of so much mass? but maybe some would have the sway and the speed to take their calculations to an appropriately powerful spaceplane, or a convenient tanker aircraft, and set off before the earth's mass doubles in a year, then doubles again, like a snowball of oxygen rolling around in the deepening winter.
Huh. If it all snapped into existence, it'd catch the light traveling through space, at that moment. So Earth might briefly get brighter? The dark side obviously would, as Rayleigh scattering turns our penumbra blue... all the way out to fucking Neptune. On the bright side, at first, it would genuinely be more sky, but-- I don't-- I just cannot wrap my head around how to even model that. The entire solar system would flash as bright as the daytime sky, give or take a couple AU, for like a billisecond. And then that energy would bounce around until it's mostly absorbed, surely. The image of the sun might vanish instantly. Even on Earth I expect most photons do not arrive having dodged the entire atmosphere.
Thinking about modeling this ridiculous hypothetical is going to keep me up tonight.
I've been thinking about this alot, so if we change the scenario to the solar systems collides with a huge cloud of air just drifting in space, we would see the blue sky on the moving interface as the air spreads though the solar system.
It's quite magical in the minds eye.
Gradually gliding into a gaseous cloud that the sun lights up would be genuinely fascinating, but still probably kill everyone. Pros and cons.
... would it affect the northern hemisphere first? I have no idea which direction the solar system actually proceeds.
most everything in the milky way galaxy is orbiting the center of the galaxy clockwise relative to our north*, so we'd probably enter the gas cloud from the side by drifting into it faster than it is moving
*that's orbital north, the direction that's perpendicular to orbit and close-ish to the magnetic north pole (which is tilted relative to the orbit)