Birds flying or swimming in space

Question

I had a dream. Imagine the Moon as a bird nest the size of a dwarf planet. Flocks of adult birds travel through space to Earth in order to hunt their prey. (imagine gannet birds swimming in space)

They are born in a "tun" form, like tardigrades, with their bodies in a dormant state. When in this form, their bodies somehow protect themselves from UV rays and all sorts of dangers derived from exposure to an environment with no atmosphere. When they leave this form, they "swim" to Earth where they hunt their prey. I need to figure out:

1. How they can "swim" through space, reaching Earth.
2. How they don't die in space.

The reason why they go back to the titanic nest: without a proper egg and an active body, they can't protect themselves, hence they live in a place without predators.

I still haven't figured out how they built a giant nest in space.

Answer 1

You don't need any scientific justification for a good story. The Little Prince lived on an asteroid that would either be unable to hold an atmosphere, or would have such intense gravity gradients that people would be mortally wounded just by standing on it. But we suspend disbelief and enjoy it as one of the most beautiful stories ever. By the way, an anime was made of it in the late 70's and it featured birds flying through space, no explanation needed (the book briefly suggests this as a possibility but never goes into detail). This was even how the prince managed to take off of his little planet, as the birds would use ropes to pull him!

But if you do want some quasi-scientific explanation for how birds can survive and fly in space:

Luminiferous Aether

Luminiferous aether or ether ("luminiferous", meaning "light-bearing") was the postulated medium for the propagation of light. It was invoked to explain the ability of the apparently wave-based light to propagate through empty space (a vacuum), something that waves should not be able to do. The assumption of a spatial plenum (space completely filled with matter) of luminiferous aether, rather than a spatial vacuum, provided the theoretical medium that was required by wave theories of light.

From Wikipedia

This idea that space is completely filled with a fluid rather than being a hard vacuum began in the 1600's and ended in the late 1800's. In your world, though, it is true. This is how your moon birds can breath (supposing the aether has oxygen in it) and fly/swim, since they have a medium to push against. The aether may be cold and thin but it never reaches absolute zero nor 0 atm, and your birds have adapted to survive in it.

The aether in your case could be a supercritical fluid, which means it has the properties of both liquid and gaseous fluids at the same time.

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Absent a medium to provide lift through wings, your birds would need delta-v budget of a Saturn V rocket, the kind used in the Apollo missions. They wouldn't need to be as massive as the rocket since the payload would be a bird, but still each bird would be as massive as a large house - with most of the mass being rocket fuel and oxygen pressurized into a liquid (which then could be used for breathing as well). For comparison the Saturn V weights a hundred and ninety two metric tonnes with an empty tank, and two thousand, eight hundred and twenty-something hundred metric tonnes when fueled up.

Answer 2

Here is a picture of the wing of a Giant Space Bat as it approaches the Earth. Actually, no, it is the Planetary Society's LightSail 2 deployment.

A space bird could glide using the solar winds and light pressure. It would have trouble taking off from the moon, and lots of trouble taking off from the earth. Maybe they nest has little actual mass. This gives strange echos of the Iron Chicken that orbits the planet of the Clangers in Episode 3 of the link. If the Iron Chicken comes to the planet surface, it has trouble getting back up again.

A solar powered creature would use little energy, and could survive in space. If it was to breed, it would have to find more material, which it might get from asteroids. If it came to Earth, it would have trouble getting rid of the potential energy it had so it does not overheat or get damaged on re-entry.

A solar sail can fly 1000 Km above the earth according to this article. The highest balloon flights are only 50 Km, so it will have to have some other way of getting back up. Maybe it builds a rocket chrysalis in its juvenile phase, and hatches into the sky.

Answer 3

There's a few elements here

1. re-entry and escape velocity
2. radiation shielding
3. flight

Amusingly I think the answer to all 3 is... poop.

Assuming your 'world' and moon had lower gravity that would likely make the first two easier.

On both earth and the moon, the birds instinctively collect their poop in natural cavities which ferment, create gas, and launch the birds into orbit, incidentally creating the pods

Water is an efficient way to shield radiation - these pods of faeces travel through space, with a small orfice to make course correction by... matter ejection. This keeps the birds protected from the vacuum of space keeping moisture in and ablates and protects the bird during re-entry, cracking to allow the bird to glide down.

The nest is collected broken bits of old pods that initially was collected up by the birds, and eventually got a gravitational field of its own.