# 'Air' in Space & Planetary Rotation

I recently heard that before anyone had begun to build practical aircraft of any kind, it was thought by some that once flight was achieved you would be able to simply fly to another planet. The discovery that space was a vacuum put paid to this idea, as did realisation of just how large the solar system actually is.

The idea of being able to use conventional aircraft in space is interesting because it justifies a lot of the common tropes about how spaceships work in softer science fiction. The adherence to a aircraft-like flight model being the main one, along with spacecraft needing continuous thrust, and coming to a stop when thrust is no longer applied.

To this end I postulate a kind of air or 'ether' which while it has the properties of air is not affected by gravity, allowing it to be evenly distributed throughout space. This has several issue however.

The first is planetary motion. If space is filled with a medium that creates drag the surface of any orbiting body would be scoured clean, unable to support any kind of biosphere. But what if we assume that planets do not obit the sun, but are instead stationary relative to it, and only rotate.

I'm not sure that this would be enough, however. If such a universe existed, would planetary surfaces be habitable? Would you get a layer of air relatively stationary to the planet's surface? Would there be gigantic 'whirlpools' formed at each pole?

• When did scientists discover that there is no air in interplanetary space? As I remember barometers to measure air pressure were invented in the 1600s then scienctis began taking them up mountains and discovering that air got thinner higher up. After manned balloons were invented in 1783 scientists began measuring thinner and thinner air at greater heights. So I guess by 1800 scientists knew there was no air in outer space. – M. A. Golding Oct 25 '19 at 17:26

# You're going to have to break a lot of laws

You've indicated that gravity holds no sway over the aether, but I'm assuming it's supposed to continue operating normally otherwise... in which case, stationary planets aren't an option. Orbits are objects in space falling towards each other and missing. If they are stationary, they won't be for long - they'll fall towards each other, but without the convenient "missing" part that makes up an orbit. So you'd have to dismiss orbital mechanics as well, which means that, for the most part, gravity isn't working.

If gravity isn't working, the sun won't work either, because it depends on gravity to keep its fusion reaction contained. It won't matter, though, because if the aether behaves like air, you're going to have attenuation. This would mean that if the planets are at normal planet distances, they're not going to be habitable because they won't be receiving any light, even if the sun were working.

But even assuming that the aether has perfect optical properties and is not subject to Rayleigh scattering or absorption, you then have the issue of 4 x 10^26 watts of energy (total solar output) with a convective medium between it and the planet. Even if heat isn't conducted, there's the problem of sound.

However, at a distance of 92,957,130 miles from the Sun, things start to change and the monstrous sound of our star doesn’t seem that loud at all. Sound intensity decreases with distance, which means that the Sun would deliver a much smaller 125 decibels to the surface of our planet. In comparison, 120 decibels is a train horn about one metre away whereas 130 decibels is physical pain.

So you'd have a blazing hot wind blowing away from the invisible sun, scouring the surface of the planet while blasting it with sound so loud that rock concerts would be a welcome relief.

To sum up, reality-check is an unsuitable tag for this question, as anything resembling a normal planetary relationship will not work without nice, empty vacuum between your planets and their stars - unless you break a lot of laws and replace them with what would effectively be magic.

As a side note, it wouldn't just have to be the planets that would be stationary - our solar system is rocketing through space at 230 km/s relative to our galaxy, which is, in turn, moving at 600 km/s. You would have to have a static universe... which presents its own problems, and more law-breaking would have to ensue.