# Travelling through space around Worlds inside Nebulas

I am building a habitable, Earth like planet, but instead of it being in a solar system, it is inside a Nebula.

The actual composition of the Nebula is uncertain at this point, but I am considering something like the Orion Nebula.

Imagine if there was a vast cloud of gases, similar in composition to the gases that make up our atmosphere, that covered the Earth and the Moon and everything in between.

Would this make traveling to the Moon easier?

Could modified Balloons and Dirigibles be used for short range space flight? If gases lighter than the gases of the nebula were used inside Balloons, in what direction would they "rise"?

Would the nebula open up new forms of space transport? Could the clouds and dust be used as propulsion, or at the very least, something to push against in space?

• Though your concept of a nebula is not quite right, the world you describe sounds similar to the one Larry Niven built in The Integral Trees. The setting is a gas torus, a ring of air, around a neutron star. You should check it out, it might be possible to build one inside your nebula. Commented Dec 2, 2014 at 17:29
• Also, it's important to note the nebula would probably appear very faint and it would definitely be colorless from the inside. As the accepted answer pointed out, the gases are incredibly diffuse; while they mat technically be pink and blue, the gas is so thin that the colors won't show up without special photography. Commented Dec 2, 2014 at 22:20

Unfortunately the gas inside the nebula is far too spread out to be useful for things like balloons to work. The density of nebula is discussed here:

https://physics.stackexchange.com/questions/26326/how-dense-are-nebulae

They are very sparse. Typical densities are in the range of 100 to 10,000 particles per cm3.

This is much more dense than the general interstellar medium (1 particle per cm3), but much, much less dense than anything you are used to - air is around 10^19 particles per cm3.

(So our atmosphere has 10 000 000 000 000 000 000 particles per cubic centimeter)

This means that the nebula is a lot lower density than atmosphere and things like balloons would not work at all. However it is still much denser than in normal space so you would get a small amount of resistance to movement and in theory some sort of ramscoop arrangement might be able to gather in the material at the front of the craft and then fire it out the back for propulsion.

You should also be aware that stars (especially the solar wind coming out from them) tends to blow the gas of the nebula away from solar systems too. Around the inner solar system in particular there would be very little nebula left.

• thank you very much for all your help in this. Unfortunately the reality of planets in nebula's isn't half as cool as the idea's I have in my head. Damn you reality! Commented Dec 2, 2014 at 15:23
• If you want to use hot air balloons to travel between planets you should look at a pair of tidally locked planets at the roche limit with shared atmosphere in the roche lobes as described (and pictured) here: worldbuilding.stackexchange.com/questions/1274/… Commented Dec 2, 2014 at 15:53

Traveling to the 'Moon' would be harder, at least the way we did it. The nebula would drag on the space ship and you'd need to bring more fuel to counter that loss of speed.

Also the moon would experience drag and either scoop up it's orbit and leave a nebula-free ring or be dragged enough to loose speed and spiral into an ever lower orbit. (Which, at least, making traveling to the moon very easy if yo wait long enough ;)