# Could flying insects re-enter the Earth's atmosphere from space without burning up?

Huge numbers of genetically modified flying insects (purpose not disclosed here but it relates to affecting the whole of humanity) are to be dropped into the Earth's atmosphere from space so that they spread far and wide.

The insects are not in any kind of container whilst falling. Once dropped, they have to make their way to Earth individually without any protection or assistance.

Question

Could any flying Earth insects survive re-entry from space without burning up?

Notes

By 'space' I mean anywhere that a satellite could sustain Earth orbit for at least a week.

You may assume a method of release that you calculate would give the insects the best chance of survival. However they must re-enter the atmosphere individually.

The 'drop' can be made at zero velocity relative to the atmosphere.

Midges can fly and so can large beetles (see below).

Please assume that the insects can survive a hard vacuum for 15 minutes (They can survive a partial vacuum see below).

Video of Hercules beetle - https://youtu.be/OyuAt-_Nj_o?t=2

It is known that ordinary houseflies can survive a vacuum and recover.

Video of housefly being subjected to a vacuum chamber and finally being released

https://youtu.be/tA9jcIwvge0?t=57

• Comments are not for extended discussion; this conversation has been moved to chat.
– L.Dutch
Mar 4, 2019 at 16:10

If by ‘from space’ you mean dropped from above the Karman line: then any. Humans have skydived ‘from space’.

If, however, you mean any other definition of ‘from space’ then... Erm.. None really.

The issue here is one of velocity. If by ‘from space’ you mean ‘in-orbit’ or ‘after being captured by earth’ then your bugs will be hitting the atmosphere at speeds on the order of 10km/s.

The heat on re-entry is caused by compressive heating, not friction. Essentially all the air can’t get out of the way because the object re-entering is moving too fast, so it gets squished up and (because physics) heats up too.

If they don’t cause compressive heating and (briefly) turn into glowing bug-cinders then they’re still going to squish up all that air, and also squish up all of themselves.

If they don’t get burnt to a very well-done cricket-croquette or splattered on the windshield of Mother Earth then they still have to deal with the air around them rushing past at hypersonic speeds. Legs, wings, shell casings; anything that is a tiny crevice will get them sent into a high speed tumble and also torn apart.

There is no size of bug that can survive re-entry as it’s commonly understood. The speeds involved are just a bit more than biology was designed to handle.

• I'm not sure that bugs with exoskeletons would be inherently burnt up. The thing is, they're very small and will thus decelerate very quickly in the atmosphere. So long as they come in in the right orientation will they burn through the carapace before shedding their speed? (Now, whether they survive the deceleration is another matter...) Mar 2, 2019 at 5:26
• @LorenPechtel: Even if you approach it from a purely g-force perspective it’s brutal. Let’s say the atmosphere is 20 km thick. That means the insect will have (at best) 2 seconds to go from 10km/s to their terminal velocity (which is low enough that I’ll call it 0 km/s). However you slice it that leaves your insect pulling upwards of 500g while being hit by some very energetic winds. Mar 2, 2019 at 7:53
• Nope. That there survival corridor is too thin. Since (to the bugs) the atmosphere is thick there’s no angle of descent that won’t either require bug-on-a-windshield kind of decelerations or keep skimming the bug back into orbit until it enters steeply enough to fry or squish... I think. It’s very early and I have not yet coffee’d. Mar 2, 2019 at 8:03
• @DaveSherohman : You mean those two different scenarios I explicitly note at the start of the answer?? Mar 2, 2019 at 11:17
• @chaslyfromUK: You haven't invalidated anything in my answer as I covered the multiple cases, but the answer to your question is now very definitely: 'You can drop any insect (aside from maybe some really big ones) and they'll be just fine.' Mar 2, 2019 at 11:20

Almost all of them. The terminal velocity of most insects isn't fast enough to generate the friction required to burn. The only issue would be a sustained lack of Oxygen, likely for several minutes depending on the height dropped, in the upper atmosphere. but seeing as you've hand-waved that problem it looks like your bugs are going to be just fine.

Edit: Just FYI this statement only applies if the insects are dropped from a stationary position (or at least relatively slow moving position) If they are traveling at 1000s of km/s they will likely be burnt to a crisp the moment they are released from whatever drop pod they are in.

• Terminal velocity is determined by gravitational acceleration versus atmospheric friction. - in space there is no friction, acceleration would continue over time at 10 m/s/s without friction of an atmosphere. Terminal velocity would tend to the speed of light till it hit the atmosphere. What do you mean a "stationary position" - stationary relative to what? Mar 2, 2019 at 0:12
• @Agrajag There is no point within the area where Earth's gravitational pull is dominant that an object can accelerate from stationary with respect to any point on Earth to anywhere near relativistic speeds before hitting heavy atmosphere. While the 10 m/s/s is a good estimate for long enough for it to be a problem for some distances, it is subject to the inverse square radius rule. Mar 2, 2019 at 3:09
• @EdGrimm Sure but insects die at a lot lower than relativistic speeds, e.g. say... 1km/s Mar 2, 2019 at 4:30
• biology.stackexchange.com/questions/59528/… Mar 2, 2019 at 8:49
• Thanks for your answer. To satisfy the vtc anal-retentives on the site and hopefully prevent closure, I've added some extra info. I don't think I have invalidated anything in your answer. Mar 2, 2019 at 9:47

As expressed in previous answers and comments, this is primarily an issue of atmospheric entry velocity, rather than insect biology. At least some naturally-occurring insects are able to withstand hard vacuum, so it's extremely plausible that insects genetically engineered for that specific purpose would also be able to do so.

The entry velocity problem is (relatively) easily resolved by dropping the insects from a craft which is traveling at a low velocity relative to the upper atmosphere at the time of the drop. To do so, it cannot be in anything resembling a stable orbit[1], so it will need to be under active thrust to avoid crashing into the planet, unless your setting includes anti-gravitic technology.

This would be a high-fuel-expenditure operation, but that probably isn't a major issue for a civilization which conducts interplanetary operations frequently enough to have made the effort of creating genetically-engineered planetary assault insects, nor for any civilization capable of interstellar travel. It would also most likely reveal the presence of the dropping craft to observers on the surface, as they would be able to see the exhaust flare.

[1] If it were in anything resembling a stable orbit, then it would, by definition, need to be moving at orbital velocities, and the bugs would instantly burn up on contact with the atmosphere.

They'll need to grow in pods

Since you're doing genetic engineering anyway, have each insect grow in its own little cone-shaped pod. Even if dropping from a point that is stationary relative to the atmosphere, I think your insects will reach hypersonic velocities before aerodynamic drag is high enough to slow them down (see some math below, and the transitional drag paper below for more math and some pretty graphs). They will still experience heating, and may tumble hard without some aerodynamic help. They're also going to have to deal with subzero temps after they do slow down, which an insulating pod will help with. You could optionally make the pod vacuum-tight as well, with a little vent or trapdoor that seals from the inside with some sort of secretion. The little pod can be ablative -- it turns out that the material emitted from ablation helps slow down at these sizes (also in the paper).

Hypersonic Housefly

As I mention above, deployment speed may not matter much. The potential energy even at a "stationary" point above Earth's gravity well is impressive; all that potential energy will get converted to kinetic on the way down.

Play with calctool, referencing upper atmosphere models and various drag coefficients to get a better feel for this. For example, calctool will tell you that the terminal velocity of a 10 mg housefly at 100 km altitude is 6213.60 m/s (assuming a drag coefficient of .5 and a cross-sectional area of around 20 mm^2).

But, as @JanHudec points out below, our fly won't reach terminal velocity at 100 km (but will hit terminal at slightly lower altitudes). The speed it will reach at 100 km depends on how high it's dropped from. If we somehow arrange for a stationary release at 600km altitude, then gravity will still have the fly screaming straight down at close to 3000 m/s as it enters the upper atmosphere at around 100 km.

The NASA Glenn Mach number calculator tops out at 76 km, but it tells us that 3000 m/s at that altitude is just above Mach 11. At hypersonic speeds, the fly will experience compressive heating from its own shock wave. The GRC stagnation temperature calculator also tops out at 76 km, but should help with heating estimates.

For the several seconds it takes to slow down, this fly's temperature is going to be somewhere above the boiling point of steel. The transitional drag paper tells us that something the size of a housefly will slow down sooner if ablating though, which again puts it back into a pod.

By the time our fly is down around 80 km, after dumping all that energy into heat, it's slowed to the terminal velocity for that altitude of around 1000 m/s, or about Mach 4. It looks like the fly finally goes subsonic and starts cooling off around 50 km.

At 20 km altitude, our fly will finally be drifting down at a lazy 14.4 m/s, but now has the opposite problem, because at that altitude the ambient temperature is around -67 C. After a few seconds of blistering heat, it's now going to spend maybe half an hour drifting down at subzero temps.

LEO orbit is typically around 7000 m/s anyway, so in summary you may not be gaining as much as you'd think by dropping from an atmo-stationary point. Because insulation matters more than deployment speed, with a pod you could go back to dropping from a normal low orbit so you can get better swarm distribution, which dropping from a stationary point won't let you do.

Further Research

For more background on speeds and conditions at higher altitudes, look for papers like The Transitional Aerodynamic Drag of Meteorites -- that paper, for instance, covers micrometeorites (particle sizes of a few microns), as well as mesometeorites (particle sizes of a few millimeters). Insects are going to perform somewhere in that size range.

For lower altitudes and speeds, take a look at jumps like Felix Baumgartner's, and subspace balloon flights like those of JP Aerospace -- they've learned a lot about the environment around 100,000 feet, but you'll need to get down to that altitude first.

• Ah, good point about the release altitude, and I'll have to revise a lot of my numbers and text above (can't do it right now, about to head out). Mar 2, 2019 at 23:37
• @JanHudec I still get velocity in vacuum of around 3000 m/s at 100 km when starting from 600 km. I'm basing that on a 500km fall, using the gravitational constant of 8.8 m/s^2 at 350km. I wonder why we're getting different results? Mar 3, 2019 at 0:56
• 'meteorites' does assume heliocentric orbit, right? so a meteorite already has significant velocity/inertia.(From wikipedia:atmospheric entry) The Apollo command module used a spherical section forebody heat shield with a converging conical afterbody. It flew a lifting entry with a hypersonic trim angle of attack of −27° (0° is blunt-end first) to yield an average L/D (lift-to-drag ratio) of 0.368.for a purely ballistic (slowed only by drag) trajectory to 4–5g) as well as greatly reducing the peak reentry heat Mar 3, 2019 at 9:09
• @stevegt, hm, I had an error in the calculation. You are right. Way too much to avoid heating. Mar 3, 2019 at 11:16
• Wrt pods, well of course inscts do this naturally. The form pupae when they change from a grub to an adult. This is a great idea. The pupae could be dropped and be triggered to emerge by the heat of re-entry. Mar 3, 2019 at 19:59

Ok. I’m a scientist of Psychology and curious hobbyist of others so please forgive my ignorance at this subject level. But, I’m just going to break this down in laymen terms for the general readership that may stop by and please feel free to comment for better or worse 😁 be gentle..

If a winged insect weighing of less that a 10 milligrams as does a common average housefly; Flys up to only the height of where the air is 45 degrees, they will severally slow down due to imparement and die when they fly around a temperature below 32 which is at the height of some low fog. https://www.weather.gov/jetstream/layers This site will show you the actual information and if you dig farther you can see in your area of the world, how high Flys’ Fly. So No it can’t and it could even if it could’nt even due to biological size and mass.

The moment it was released into exosphere, after about 10 seconds or so it would vaporize, human skin and the tissue underneath begins to swell as the water in your derma (skin) layers begin to vaporise due to the absence of atmospheric pressure. Thats a human with pretty tough skin. the human body is capable of slowing down radiation. Passing through its body. It does make its way through it but by then we are dead. A common fly is made up of primarily liquid so as a human, it too would vaporize, but much faster due to its 10 milligram weight.

• Welcome to worldbuilding.SE. It's great that you contribute, however I can't really see what your point is. Please clarify how this would answer the question, and either elaborate or give concrete references for the details. Mar 2, 2019 at 7:56
• The moment it was released into exosphere I think it would evaporate to freeze dried pieces basically. It’s basic science. Mar 2, 2019 at 7:58
• So you argue that the low-temperature, low-pressure environment would kill them regardless of any burning-up concerns. Possibly, I know very little about insects – however, the question specifically asked “without burning up”, and provided references that vacuum is survivable for insects. I would presume the cold is survivable too. But if you know of evidence that it's not, do edit that into your answer. Mar 2, 2019 at 8:04
• The moment it was released into exosphere, after about 10 seconds or so, human skin and the tissue underneath begins to swell as the water in your derma (skin) layers begin to vaporise due to the absence of atmospheric pressure. Thats a human with pretty tough skin. the human body is capable of slowing down radiation. Passing through its body. It does make its way through it but by then we are dead. A common fly is made up of primarily liquid so as a human, it too would vaporize, but much faster due to its 10 milligram weight. Mar 2, 2019 at 8:10
• @KellySwanson, if you are clarifying your answer it is better to edit it, rather then writing comments.
– L.Dutch
Mar 2, 2019 at 8:29