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Would the heat from the sun be transferred better to earth, since air is an isolator inferior to vacuum thus producing a hotter environment?

Or would the energy be absorbed and dissipated in the air, resulting in a colder environment?

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  • $\begingroup$ Do you mean air at 1 bar? $\endgroup$ – Martijn Weterings Aug 16 at 14:00
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    $\begingroup$ The earth would be MUCH hotter. Air drag would rapidly decrease earth's velocity around the sun, and the earth would spiral into the sun as a result. $\endgroup$ – David White Aug 16 at 15:39
  • $\begingroup$ @DavidWhite - If we played with a thought experiment and suddenly inserted 1 atm of any gas in place of the solar wind, the Earth's initial velocity (assume the gas is at rest with respect to sun) would vastly exceed the speed of sound (Mach number > 30 or something). The resulting shock would superheat the gas actually in contact with Earth's upper atmosphere and add extra heat. I suppose such a scenario would also cause a rapid deceleration of the planet... I wonder how rapid... $\endgroup$ – honeste_vivere Sep 11 at 19:59
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It is difficult to say what would be the effect of air because there's more than just the effect of heat transfer from sun to earth (heath transfer, which as you postulate might be larger/smaller when there would be a different matter in-between the two points).

Namely, the other effect is that the presence of matter/atmosphere changes the equilibrium between earth's surface temperature and the surroundings and make the surface temperature deviate from the planetary equilibrium temperature.


So, in the case of earth we are actually already in a space filled with air (our atmosphere) and, due to the greenhouse effect, this air makes earth warmer in comparison to the case when we would not have atmosphere (That is: on average. Since for planets without atmposphere the mean temperature will be lower, but the temperature variations will be higher, and thus maximum temperatures might be higher).

While earth is warmer due to the atmosphere, the situation might be different when the entire space in the solar system is filled with air (let's ignore that this would slow down earth's movement and make earth fall into the sun).


It is very difficult to say how that would turn out (not the least because the situation is very hypothetical). On the one hand it can be said that the air can reduce heat transfer (because it blocks light) and thus reduce temperature. Whereas you actually imagine the air can increase heat transfer (because of the insulating properties, which are less than vacuum), which does not relate to the transfer of energy by light, but to the transfer of energy by convection.

It may eventually depend on the actual density of the air. A very much complicating issue is that the atmosphere of the sun, the corona, is actually hotter than the layers closer towards the center of the sun. So, there must be some mechanism, other than energy transfer by light and convection, that gets energy from the inside to the outside, and that mechanism is not well understood.

If you imagine some kind of thick atmosphere throughout the entire solar system, then it might be expected that this isolates the heat/energy being transferred outward from the sun because it will reduce the radiative transfer of energy, and as a consequence it will reduce the temperature on earth.

But, it is difficult to predict since we have no information about such hypothetical (or maybe even non-physical non-real) systems. We know that stars have a convective zone on the outside and a radiative zone on the inside. Thus conduction, or rather advection, is as important as radiation and this extra layer of air might improve this conduction. But we have little idea how this would work when we extend the atmosphere by introducing gas into the solar/star system. I imagine that at first it would block the radiation, but at some density it will contribute to energy transfer by means of conduction (it is also a question whether you consider this air to be static or not).

There are stars which have an extended atmosphere (e.g. AGB stars) and the temperature of this atmosphere is typically low due to dust absorbing the radiation from the star, and it is characterized as a condensation zone (cold enough for molecules to form). But, these stars are also extended in size, the 'edge' reaching earth's orbit, and at earth's orbit it would be very hot (See for instance Planetary nebulae, thermal pulses and mass loss).

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  • $\begingroup$ An AGB star may have an atmosphere extending as far as 1 earth orbital radius, but the density of this atmosphere must be very much smaller than that of air under room conditions. Otherwise it would have to have a mass far exceeding the 3000 solar masses I estimated on my answer and a black hole would inevitably form. $\endgroup$ – my2cts Aug 19 at 8:07
  • $\begingroup$ @my2cts yes, but is air defined to be 1 bar? There are lots of ambiguities in this question. Which is on the one hand sad because it makes it less easy to resolve the question (maybe it should be put in hold?) but on the other hand it is great for useless conversations. This is nice futter for astronomy students to discuss while sitting at the bar. $\endgroup$ – Martijn Weterings Aug 19 at 8:13
  • $\begingroup$ I assumed default temperature and pressure conditions. $\endgroup$ – my2cts Aug 19 at 17:00
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Note that the temperature of each body in the solar system is actually due to its distance from the Sun. Solar system is not an isolated body in the universe. If "only" the solar system was filled with air it would have to be isolated from the rest of the universe and the hotter regions of the system would probably migrate heart to the cooler regions as temperature (or potential or anything like these two) always goes from higher to lower. The energy wouldn't be absorbed as there is another part of the system that is the hottest which would heat up the air surrounding it and it would flow from hottest region to colder regions. Also, the temperature of the planets would no longer depend on it's distance from the Sun. And that might even change the physical conditions of the gas giants a lot. This is just a small part of the complete answer the most probable situation is difficult to tell due to different densities having different effects. Also if the air is filled up to an appreciable distance, there might be lumps of air molecules surrounding the solar system bodies. Again this is just a thought process and what would exactly happen cannot be said as there are too many factors to consider.

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One solar mass of air occupies a sphere of order 10 million km radius, at room temperature and pressure. So if the space be tween earth and sun was filled with air that would represent 3000 solar masses. A black hole of 10000 km radius would form. The Earth would probably end up ground to bits in its accretion disk and whatever remains of it and thus would be very hot!

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  • $\begingroup$ Would it necessarily form if it's spread so wide? Also there are stars with masses > 3000 solar mass and their existence doesn't immediately invoke a black hole. Or am I not understanding something correctly? $\endgroup$ – Jiraiya Aug 18 at 18:48
  • $\begingroup$ There are no such stars known. The heaviest known star is 236 sat masses, see nl.m.wikipedia.org/wiki/R136a1. $\endgroup$ – my2cts Aug 18 at 20:17
  • $\begingroup$ Any object heavier than 3-4 solar masses collapses into a black hole. See en.m.wikipedia.org/wiki/…. $\endgroup$ – my2cts Aug 18 at 20:24
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Traveling through so much air would significantly attenuate the heat radiation that reaches earth. Visible light attenuates to a tenth for every 10 nautical miles, so there would be pretty much nothing left after 14.000.000 attenuations of x10. The numbers are slightly different for infrared, and this all depends heavily on the density of this planetary air, but it's pretty clear that the remaining irradiance would be negligible.

On the other hand, since earth is moving at a speed of 30 km/sec around the sun, friction with this air would heat up the leading face of the earth to scorching temperatures, and the back side of the earth would suffer from intense storms cause by the wake. This friction would quickly halt the earth from orbiting around the sun and whatever would be left of earth would fall into the sun.

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  • $\begingroup$ But, if the light gets blocked then what happens to it's energy? $\endgroup$ – Martijn Weterings Aug 16 at 13:59
  • $\begingroup$ It is absorbed in the air and heats it up. $\endgroup$ – daniel r Aug 16 at 14:05
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    $\begingroup$ And what would happen to the hot air? Would it not, at some point, radiate as much energy as it receives? (e.g. in the current situation, the big amount of gas around the core of the sun is not resulting in all the light/energy to be blocked) $\endgroup$ – Martijn Weterings Aug 16 at 14:06
  • $\begingroup$ Realistically, the air molecules would break down and ionize near the sun. Also, they would fall into the sun and increase its mass incredibly as @my2cts wrote. The fun part is to pick and choose which laws of physics you apply and which not, to explore absurd scenarios, which often enough end up being relevant for an entirely different system. $\endgroup$ – daniel r Aug 16 at 14:11
  • $\begingroup$ Now I see your point, but the next layer of radiating air would itself only radiate a few hundred km away, and so forth. I don't think that in equilibrium this would deliver much energy at 140000000 km. $\endgroup$ – daniel r Aug 16 at 14:14

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