Space eagles

This thread on ZBB, started by Eddy the Great, got me thinking about how a creature could evolve to survive both on planets and in space.

On planets, the creature will need all the adaptions associated with living on land, for example: skeletal and protective structures; locomotive features; energy capture, storage and digestion systems; metabolic control and excretion systems; an internal mass transit system; some form of reproductive strategy.

There will need to be a reason for creatures to venture into space. There's no food out there, no potable water. So the only reasonable possibility (to me) seems to be that the creature is either escaping something on the planet, or is aiming to get somewhere better. Which seems to suggest that we're dealing with a twin planet system (2 planets orbiting each other around a common point, which in turn orbits the star), or perhaps a system where 3 (or 6) similar sized planets are locked in similar orbits around a star each roughly at the lagrange points of the other planets. To be exotic, we could go with a combination option.

So, let's start with something that I'll call a space eagle. Big, birdlike, but definitely not a bird. They evolved in a starsystem that had 4 similar sized planets (say between Mars and Earth size) in a lockstep orbit around their star, 2 of the planets circling each other and the other two at the lagrange points to the binary (no, it's not a stable setup, but then we only need it to last for say 20 million years or so to allow the evolution to develop and refine our space cadets).

Now we need a way to get our space eagle into space. From Earth's surface you need to be going slightly faster than 11km/s to escape the planet's gravity well. On Mars the space eagle could soar into space if it were going faster than around 5km/s. The only way I can think of an organism achieving such speeds is through some sort of organic spacegun. Let's imagine a plant-like organism that's developed a gun-like mechanism for launching its seeds into space. Then our proto space-eagles come along and co-adaptive evolution 5 million years down the road leads to a plant - I'll call it gunweed - that will launch an eagle into space alongside its own seeds.

Whatever planet we're launching from, our eagle is going to need some protection against air friction. Let's say our gunweed provides this through the seed's outer layers. So, plant grows seed, waits for eagle to burrow into seed, then completes the growing process and launches seed into space.

Now, if the space eagle stays inside the seed it should be relatively safe in space (if it is in deep hibernation) until just before the seed hits the next planet. We'll assume that the evolutionary deal between gunweed and space eagle is that the gunweed gets seed and eagle into space, but it's the space eagle's job to get the essential part of the seed safely to the surface of the next planet. So the space eagle needs to "hatch" as the seed nears the next planet.

At this point, the space eagle needs some sort of locomotive system - farts could do it. Gas could be generated from food stored in the seed (which the space eagle could eat before breaking the seedcase). Once outside the seedcase, the space eagle needs to be impermeable (except when it's farting) - to maintain body pressure and prevent waterloss, so maybe a structure of interlocking feathers with a tough outer coating of oils and waxes.

Radiation is going to be a bugger. I assume the space eagle is going to develop some sort of sensory apparatus to warn it that a solar flare is on its way, then it can use the bulk of the planet that it's orbiting to hide between during the radiation storm. The alternative would be to have plates of subcutaneous lead, or filigrees of lead across the feathers, but that would be too much weight to launch. A really efficient way to clean up free radicals in the body would be fairly essential, together with especially effective ways of dealing with the resultant tumours. Another option is to just let the older space eagles die of cancer.

What next? Wings, with parachute-like properties, to get through the new planet's atmosphere. We'll assume that the space eagle has enough fart to get it into some sort of low geostationary orbit, after which it's just a case of losing speed and altitude slowly enough to allow for re-entry without excessive incineration.

Then all that's left to do is navigate passport control, declaring the ready-to-germinate remnants of the seed if necessary, and its Welcome to Your New World! Breed! Grow Gunweed! Be Happy! Until it's time for the next space voyage ...