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My entry for the fortnightly topic challenge:

You are a space explorer. You are visiting this weird habitable planet in the Alpha Centauri System as part if the first manned expedition to another world. You see weird things floating in the upper atmosphere/space but think nothing of it, despite how much they look like living things. On a trip to the surface you see a similar shaped animal. At first you think it is a coincidence, but while exploring, you see one on a ledge on a tall cliff. It runs, jumps and takes off, using ocean thermals to rise, then flapping its wings as it got higher. Eventually it was out of sight. You had your space station base scan for it and found it was rapidly approaching the upper atmosphere.

We have talked about how a plant could do inter-planetary travel via seeds. Is there any way for my creature to reach the upper stratosphere, near the mesosphere? Is there any evolutionary advantage that could be gained that would spark this creature into existence? How would the creature re-enter the planet without burning up?

CRITERIA THE CREATURE MUST MEET

  • must have wings
  • must at least reach the very top of the troposphere, preferably the stratosphere, though.

Regions of the atmosphere

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  • $\begingroup$ Re-entry by gliding is doable if the creature is light enough; conceivably, a paper plane could do it. Reaching the orbital velocity of 7km/s or thereabouts? I don't think it can be done unless your creature has a jet engine, and even then it's a stretch. $\endgroup$
    – Mike L.
    Commented Mar 10, 2015 at 15:28
  • $\begingroup$ @MikeL. Could flying to the top of the troposphere or stratosphere be feasible? $\endgroup$
    – Jax
    Commented Mar 10, 2015 at 15:31
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    $\begingroup$ @DustinJackson Your troposphere requirement entirely changes your question. Already there are birds that can fly into the stratosphere. Altitude requirements are very, very different than escape velocity requirements. $\endgroup$
    – Nick2253
    Commented Mar 10, 2015 at 15:39
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    $\begingroup$ @DustinJackson Can you clarify what you are looking for? Do you want a winged creature that can reach escape velocity? Or are you just looking for a creature that can reach a certain altitude? Your question implies that you are looking for a creature that can orbit and deorbit a planet. But your criteria implies you are simply looking for a creature that can fly really high. $\endgroup$
    – Nick2253
    Commented Mar 10, 2015 at 16:14
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    $\begingroup$ @DustinJackson Then you are only looking for something that reaches a certain altitude. Getting into space and getting into orbit (escaping the planet) are very different things. If I set you in space, you'd be in space, but you'd come crashing down in a hurry. In order to orbit, you'd have to have tremendous speed. $\endgroup$
    – Nick2253
    Commented Mar 10, 2015 at 16:21

3 Answers 3

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In a word: absolutely.

Already, there are species of birds, like Rüppell's griffon vulture, that fly into the the stratosphere. It would be quite easy for a winged creature to evolve that floats or glides at an even higher altitude. I imagine that there are a few paths that could result in such a creature.

First, I could envision sexual selection as a driver the pushes the species into the upper atmosphere: the male that flies the highest gets the females kind of thing.

However, there's a limit to what wings do for you. Once you get above a certain altitude, the air density gets too low, and a winged creature would be unable to control themselves, or provide lift. Larger and larger wingspans could accommodate this deficiency, and that would lead more to lazy gliding/floating in the upper atmosphere, rather than high-speed flying.

Second, there could be a predator/prey relationship, which caused two species to evolve in an arms race, where high-altitude was the evolved escape path. In this scenario, a bird-like species would have to be an apex predator, which means that other bird-like creatures are at risk. Perhaps, a species has evolved a way to fly above the apex predator, which, due to the predators' weight, would be unable to fly as high.

This relationship already exists with the Common Crane and their eagle predators. If the eagle were a more effective predator, or they had fewer prey options, going even higher would continue to be a viable survival strategy for the crane.

To cover our bases, let's talk about air density and survivability at upper altitudes.

As we go up in altitude, the air pressure rapidly decreases. This makes breathing, flapping, and gliding harder. The first one could be handled by holding your breath, or specially adapted lungs (the combination is what we see in high-altitude birds today). The second two can be corrected by lower body mass and larger wingspans. That combination can be challenging, because you need more muscle to pump larger wings, but we already see birds that are balancing those two elements to fly to astonishing altitudes.

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    $\begingroup$ This isn't accurate. Escape velocity is the velocity you need to leave an object with no further acceleration. For example, your 2.4km/s number is the velocity you would need to launch from the moon's surface and coast the rest of the way. An object that's constantly rising is effectively constantly accelerating, and can escape at any positive speed - theoretically you can reach space going 1 m/s. $\endgroup$
    – Dan Smolinske
    Commented Mar 10, 2015 at 15:48
  • $\begingroup$ @DanSmolinske Absolutely correct Dan; no disagreements here. You're missing two issue: 1) the question asked how a creature would reach escape velocity, and 2) how would something with wings maintain any kind of positive velocity once it reaches space? In other words, a winged creature will have to reach that velocity in the atmosphere, where it can propel itself, in order to reach and stay in orbit. $\endgroup$
    – Nick2253
    Commented Mar 10, 2015 at 15:52
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    $\begingroup$ That's technically correct, but I think what they're actually asking for is whether or not it's possible for the creature to escape earth's gravity, and escape velocity isn't necessarily a good judge of that. At the very least, it will be a smaller value if you can fly up near the top of the useful atmosphere. $\endgroup$
    – Dan Smolinske
    Commented Mar 10, 2015 at 15:54
  • $\begingroup$ @DanSmolinske Most of the energy needed to go to orbit is actually used in order to go sideways and not to go up. This is a funny way to present this: what-if.xkcd.com/58 $\endgroup$
    – Maxime Lucas
    Commented Mar 10, 2015 at 16:00
  • $\begingroup$ The OP changed his question so much that this doesn't actually answer the question anymore. Would you update your answer to reflect this? $\endgroup$
    – Mermaker
    Commented Mar 10, 2015 at 18:29
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So by flapping it isn't going to be able to reach the altitudes you are wanting at all.

Basically your creature is probably somewhat naturally lighter than air with a very large wingspan. Your creature has the ability to rapidly fold up its wing span, fill up and compress large volumes of gas, which it then expels at high velocity. The creature would also have to be highly heat resistant, especially where it has created the rocket/ram jet. It would probably have to be photosynthetic and also a carnivore; how such a creature would evolve and what advantage it would have by being mildly explosive with a heat resistant shell but also basically a flame jet (regardless of there necessarily actually being a flame) is not something that I am willing to speculate on.

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If the creature does not have to go into orbit then it can build up speed before pitching up and trading speed for altitude. It will only be able to stay their for a moment before gravity will take over and it will come back to earth.

The main issue with reentry is speed. If you are only suborbital you won't have as much speed. I think a good model to look at would be the Virgin Galactic ships Spaceship 1 and Spaceship 2.

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