First contact with an alien life form often goes badly. In the case of Biothanata, it always goes badly. The first glimpse of this alien blob is in the form of a falling star, a meteorite. After burning off an ablative layer of rock and juicy outsides, it crash-lands. Once cooled, a red liquid leaks out of what is left of the meteor, quickly consuming any and all bio-matter around it. As it digests the grass, leaves, bugs, and other creatures, it grows, amoeba-like, sending out tendrils, splitting and reforming, but always consuming. It also digests rocks, or at least breaks them down into bite-size pieces to use, though at a much slower pace.

Eventually, if nothing stops it (and nothing has, yet) it consumes all available life on the planet, barring some hardy life forms that are difficult to access. Once it grows large enough, the now enormous blob of red goo begins bunching itself together, then hurling chunks of itself high into the sky. After enough attempts, the giant blob manages to throw one (or more) smaller blobs into space, escaping Earth's gravity. Each blob is packed with rocks and dirt to use as course adjustment. Eventually, over the course of thousands of years, the majority of the space-blob sends itself out to another planet; all that's left is a (relative) handful of indigestible dust and a tiny dried-up blob.

How big would the blob have to be to toss a 10-foot cube of itself out of Earth's orbit? Assume the thrown piece can start larger and accelerate itself by shooting pieces of itself off behind it, form itself into a basic wing or flying disk to catch the wind, and generally behave somewhat intelligently; also assume the "main" blob can lift and hold itself to a height of roughly half its base (higher is possible, but will cause it to fall afterwards). Edit: also assume the blob can be very, staggeringly large, nearing "planet sized" itself - as big as it needs to get before it can hurl blobs into space.

Once a blob breaks free of the world's gravity, it then breaks free of the Sun's gravity by tossing various space debris behind it. Assuming it has all the time in the universe, and manages to accelerate itself as much as possible, how long would it take before it found another planet?

Bonus question: Assuming a starting size of roughly one cubic foot, unchecked growth, and a digestion rate roughly equal to the most aggressive digestion of a creature on Earth, how long would it take for Biothanata to consume the majority of land-based organic life on an Earth-like planet?

  • $\begingroup$ How is it attempting to throw chunks into orbit? I'd think burning volatile organics and directing the output through some kind of nozzle could do it. Or take a page from "From the Earth to the Moon" and simply form into a large cannon. $\endgroup$ – Michael Richardson Mar 24 '16 at 19:06
  • $\begingroup$ How much of the 10 foot cube needs to get to it's destination? How fast will the larger blob shoot it? How fast does the small blob shoot parts of itself off? How quickly should it get to another planet? (no time frame makes it slightly easier, but not much. $\endgroup$ – Lacklub Mar 24 '16 at 19:08
  • $\begingroup$ @Lacklub - as much as possible, but at least a cubic foot or so; as fast as possible; also as fast as possible; some time within the heat death of the universe. $\endgroup$ – ArmanX Mar 24 '16 at 19:11
  • $\begingroup$ @ArmanX You might have to be ok with parts of the blob moving at large multiples of the speed of sound. It's hard (but not impossible) to shoot something into space ballistically, but that might be your best bet. The smaller blob can then accelerate with the mass it has by shooting out very small parts at very (very) high speeds. Your target velocity (once you're out of the atmosphere of the earth) is upwards of 40 km/s. $\endgroup$ – Lacklub Mar 24 '16 at 19:48
  • $\begingroup$ @Lacklub - that's what I had in mind. The main blob would accelerate the smaller blob to escape velocity, or as near as possible, from as high as it can get; the smaller blob would shoot out at very, very high speed - something like "snap the whip", where the end of the "whip" is released into the air. $\endgroup$ – ArmanX Mar 24 '16 at 20:37

Not going to happen

Let's start by assuming the blob is, like most life on Earth, mostly water. We'll also say that it is about the same density as water - 1000 kg/m^3.

Figuring out how hard it would be for the blob to escape the Earth's gravity well will be tricky because we have to take into account things like wind resistance due to the atmosphere. So first we'll ignore the Earth and look at how hard it would be to escape the Sun's gravity well and leave the solar system.

From the Earth, the escape velocity for leaving the solar system is 42km/s. That's dang fast. For reference, the speed of sound in water is 1.48km/s. This is also a hard limit for how fast your blob could throw a chunk of itself - pressure energy can't realistically travel faster than that through water.

So imagine that somehow your blob can throw a chunk of itself at 1.48km/s, then that chunk can throw a chunk of itself at 1.48km/s, and so on until something gets to 42km/s. Simple math tells us the chunks-throwing-chunks needs to happen 29 times.

In order to propel 2/3 of itself forward at 1.48km/s, a chunk would have to propel the other 1/3 backwards at 2.96km/s. As I've already mentioned, that can't happen so the absolute best case scenario would be for the chunk to propel half of its mass forward at each stage.

Unfortunately for your blob, you've got to worry about exponential decay. Cutting itself in half 29 times doesn't leave it much to work with - you'll have $\frac{1}{2^{29}}$ as much left as you started with. So if you took the entire biomass of the Earth (around $4\times 10^{15}$kg), you could get $7.45\times 10^6$kg to escape velocity. That's enough for a 19 meter cube.

Now let's look at the energy densities involved. To keep things simple, consider a chunk as stationary and consider the kinetic energy of a chunk moving at 1.48km/s. This will give us an estimate of how much energy will be required to throw a chunk that fast. $K=\frac{1}{2}mv^2=1.095\times 10^{6}m$ joules, so for a mass to throw an equal mass with that much energy, it must be able to use 1.095 MJ/kg in a very short amount of time. However, that's almost within an order of magnitude of the total energy stored by carbohydrates. So basically the entire chunk has to consist of readily available energy storage and mechanism to propel itself forward.

Already this is very much stretching the bounds of plausibility, but this is the only way that it's going to work. If 2/3 of a chunk propelled 1/3 forward, only $\frac{1}{3^{29}}\approx 1.4\times 10^{-14}$ of the original would remain, so using the entire biomass of the Earth would get 58kg (about two cubic feet) of the cube out of the solar system.

Also, these cubes won't be roaring out of the solar system - by the time they left the solar system they'd be going around 800m/s. So they could potentially get to the next closest star after 50 trillion years. That's long after the destination star will have died.

Another way in which this gets worse for your blob is that 1.48km/s is actually sort of like the speed of light - it would actually require more and more energy to just get closer and closer to that limit. It's likely that getting to half of that, 740m/s, would take as much energy as what my simplification allowed to get to 1.48km/s. So it would require twice as many chunk-throwing-chunk steps, which squares the mass reduction - $\frac{1}{2^{57}}\approx 1.7\times 10^{-18}$ of the original mass could escape the solar system.

Oh, and remember how we completely ignored escaping the Earth's gravity well? Yeah, that problem wouldn't go away even if the blob consumed the entire Earth, rocks and all, because that doesn't somehow destroy the gravity well.

  • 1
    $\begingroup$ Good answer; I appreciate the math. It looks like my world-eater is going to need to acquire some jet fuel to make it back to space... $\endgroup$ – ArmanX Mar 25 '16 at 13:32
  • $\begingroup$ You don't need to expend all the energy to directly exist the solar system. Maybe ~12kms is enough. Some heliocentric orbits should exist where gravitational assists provide the rest of the acceleration. A solar sail (as proposed in other answers) may help in adjusting course. $\endgroup$ – Innovine Jul 11 '17 at 18:12
  • $\begingroup$ Having played High Frontier and merely looked at the board and understood how to calculate thrust and fuel consumption...leaving the solar system is Hard. And that's for freaking rockets. The easiest method involves no less than three refueling stops on the rocky bodies of the outer solar system. $\endgroup$ – Draco18s no longer trusts SE Jul 11 '17 at 20:11
  • $\begingroup$ The Voyager probes have left the solar system, with no refueling stops... Also, what kind of fuel is going to be found on rocky bodies? $\endgroup$ – Innovine Jul 11 '17 at 21:31
  • 2
    $\begingroup$ @Innovine according to this chart on Wikipedia, Voyager 2 had almost enough velocity to escape the solar system before it got any gravity assists. Also, the amount of planning required in order to intentionally get a single gravity assist (let alone multiple ones) is not something an amorphous blob could pull off. $\endgroup$ – Rob Watts Jul 11 '17 at 21:39

Meteorite impacts can splash parts of it into orbit.

This is a real thing. We have identified Martian meteorites which landed on earth, identified by isotope analysis. They were spalled off the surface of Mars by meteorite impacts and launched into orbit. We currently have identified 132 Mars rocks on Earth.


This is a real and logical way for your blob to take the spacetrain. In fact, it is nearly unavoidable for any blob covered planet. The only factor in the way of this process is a thick atmosphere, which is simply overcome by a bigger hit. Once enough matter is flying about it will surely infect the entire solar system over time.

I do not know if an impact could push it interstellar. If the blob is intelligent enough, stage two could involve forming a thin film, and propelling itself as a solar sail.

  • 2
    $\begingroup$ Stage two doesn't even need intelligence, just an instinctive reaction to low gravity. $\endgroup$ – Joe Bloggs Dec 20 '16 at 11:41
  • 2
    $\begingroup$ Martian meteorites left Mars through an atmosphere around 1% as thick as Earths. The reverse process isn't very likely. $\endgroup$ – Innovine Jul 11 '17 at 18:07

Uhm... unless this blob is made of rocket fuel, it will not happen.

The reason for that is found in the so called Rocket Equation. One factor here is the "effective exhaust velocity". Without getting too technical — noting that this is actual "rocket science" — that velocity needs to be really high. And you cannot achieve that by "tossing stuff backwards". You need to set something ablaze so that you essentially have an ongoing explosion that you can direct backwards.

If you like you can try this question over at the Space Exploration SE and they can give you all the technical details but in short: it won't happen.

  • $\begingroup$ If tossing pieces from sea level doesn't work, I expect if the blob gets large enough (read: a significant percentage of the planet), it should be able to "reach" to the edge of space and toss pieces from there; how big is "big enough", as a percentage of the planet's size? $\endgroup$ – ArmanX Mar 24 '16 at 19:17
  • 2
    $\begingroup$ Still will not work, for the same reason as we do not have mountains that reach into space: the ground will crumble and give way. Remember that the Earth's crust is relatively thin and malleable when we are talking dimensions like that. It cannot support any kind of structure that reaches into space unless that structure is very light and extremely strong. $\endgroup$ – MichaelK Mar 24 '16 at 19:21
  • 1
    $\begingroup$ So essentially, the blob would have to actually be a significant portion of the planet, needing to not only absorb the crust, but somehow cool and consume the inner planet as well... hmm. Ok. Looks like my Eater of Planets may need a (jet) boost! $\endgroup$ – ArmanX Mar 24 '16 at 19:24

Instead of a blob, it could be a whispy structure that spreads out, and once parts of it are out of the atmosphere it acts as a solar sail.

I think Fred Hoyle's creature was something like that. Maybe David Gerrold used that too. I don't recall exactly.


Does the creature have to splash down completely in the first place?

Or could the majority of it take position in orbit and extend a pseudopod of some kind down to the planet (and up in the opposite direction). During the consumption of the planet's resources, this acts as giant root for the orbiting mother blob. When the planet is nearly exhausted, the blob climbs back up the pseudopod, space elevator style, and then drifts off to its next interstellar victim.

  • 1
    $\begingroup$ I think it was A.C. Clarke who wrote about a giant spinning creature, which had two long arms. It'd sit in orbit, rotating, with one arm brushing the surface of the planet, and the other stretched far out into space as a counterweight. Creatures would hop onto the arm, get a free lift into space, and let go at the furthest end, slingshotting into much higher orbits $\endgroup$ – Innovine Jul 11 '17 at 18:18

Others have pointed why it's impossible that the creature propelled itself as a rocked, but it could climb to orbit. If the creature could build a tree-like or reef-like structure tens or hundreds of thousands kilometres high, Earth rotation could give it enough velocity to stay in orbit. Once in orbit, the solar sail proposed by JDługosz could lead it to another planet or even another star.

Since the hard part of the process is building such structure, once built it could be producing solar-sailed offsprings in large amounts to colonise the whole galaxy.

Off course, the mechanical properties of the materials need to build the structure are far beyond anything known, but you know that evolution and natural selection are powerful forces even when faced with such hard problems.

  • $\begingroup$ Seems very unlikely. It would need to climb at least 35,786 kilometers up, which is 3 times the earths diameter. And it'd need to prevent itself turning in to a spiral due to all the suborbital mass causing drag as it rotates. $\endgroup$ – Innovine Jul 11 '17 at 17:56
  • $\begingroup$ If it had some elastic properties, it might be able to bend itself over to one side, like a catapult, and then straighten out, using earths rotation and its own movement to accelerate the projectile to orbital speeds without needing to reach geosynchronous orbit altitude. Still, Im not sure what kind of energy you can get out of a 20,000km long bendy whippy blob arm, nor how blob structure holds itself up in the first place $\endgroup$ – Innovine Jul 11 '17 at 17:57
  • $\begingroup$ Answer to first comment: Yes, it's unlikely. However, I since all answers to the question are going to be unlike, our goal can just be to find interesting answers which make sense in spite of being unlikely. $\endgroup$ – Pere Jul 11 '17 at 18:01
  • $\begingroup$ @Innovine: To second comment: The catapult idea may be the basis for a new answer, although I find it very problematic. $\endgroup$ – Pere Jul 11 '17 at 18:03
  • $\begingroup$ It would be much easier for the blob to remain in orbit, and extend long tentacles down to the surface, eat up the food, and then retract the tentacles. $\endgroup$ – Innovine Jul 11 '17 at 18:16

It is not possible to throw something into orbit, and it doesn't matter how fast or how much energy you use.

You don't need any knowledge of orbital velocities or rocket equations to know this cannot work. The simple fact is this: you cannot achieve orbit by using only a single impulse, like a cannonball from a cannon, or a bullet from a gun, or a giant blob throwing bits of itself. The projectile will always go up, around a bit, and back to hit the surface. In practice, it'll immediately burn up when attempting to leaving the atmosphere, and if anything survives that, it'll burn up when re-entering again.

The following diagram may help:

enter image description here

The points where the red orbital line and the surface of the planet intersect are the launch and impact points. No matter what angle or speeds you launch at, this red ellipse always passes through the launch point.*

So after launching, all rockets, bullets and blobs only travel in a large arc. The rocket engine can be (and usually is) turned off slightly after launch, just after getting out of the atmosphere, and the ship, bullet or blob would coast all the way to the highest point. It is here, at the apoapsis, that a second burn needs to be made, accelerating the projectile. This accelerating raises the periapsis (the shortest distance from the planets center to the ellipse), eventually raising the periapsis above the surface. When the periapsis has been raised higher than the atmosphere, the rocket will go around and around with no further input.

The first impulse (or burn) also needs to keep the speed low, to get through the thickest bottom layer of the atmosphere without losing all the energy to friction, or without overheating, or exploding due to aerodynamic stress. The more energy you try to add here, the worse these problems get.

  • There is only one possible class of orbits achievable by a single impulse. In a pure vacuum (no atmosphere), if you launch exactly horizontally at high enough speed, the launched projectile returns horizontally to the launch point, tangental to the surface. The faster you launch, horizontally, the higher the appapsis will be, at the opposite side of the planet. But at the launch site, the altitude will always be zero. Any mountains near the launch area would be a problem (as is the vacuum to your lifeforms).

The only time anything unpowered leaving the surface with a single impulse can get to an orbit above an atmosphere, is if it is hit by something else when near its apoapsis, providing the second impulse and accelerating it in the prograde direction (so it gets rear ended, speeding it up in the direction it is travelling). It is theorized that a load of melted rocks were blasted out from earth in a gigantic collision, and they bumped each other, forming orbits, which coalesced into the moon, eventually, and anything that didn't get bumped just right rained back down.

TL;DR: You can't get something into orbit by throwing it. Orbital mechanics says no. This is unfortunate, because if you can get to a stable orbit, you have all the time in the universe to deploy a solar sail and eventually float away somewhere else.

You CAN however, break free entirely, with nothing more than brute force. You just need to somehow survive getting through the atmosphere at speeds higher than escape velocity. This will mean burning up, like a shooting star in reverse, but given sufficient ablative protection, it may be possible. Escape velocity, at ground level, is Mach 33 (12km per second), but that speed will decrease rapidly due to friction and drag forces, so the actual launch would need to be much, much faster indeed.

It would require much greater sums of energy than rocket launches, since its very inefficient. But as long as the projectile gets through the atmosphere above 12km/s it will fly off into an orbit around the sun. And that's in theory enough to make it to any point in the solar system and beyond, given aeons of time and the right gravity assists.

  • $\begingroup$ You second-to-last paragraph is actually a really good point. The whole purpose of leaving the planet is to, eventually, travel to another solar system, so saying "orbit" is not actually what I wanted. Given a sling or trebuchet, it could probably fling chunks high enough to achieve escape velocity... $\endgroup$ – ArmanX Jul 12 '17 at 19:34
  • $\begingroup$ Actually, getting to orbit is probably the best plan. You can then use solar light pressure to very gradually (and energy efficiently) move further afield. Direct to escape velocity probably requires something like gigatons of an explosive force $\endgroup$ – Innovine Jul 13 '17 at 17:27
  • $\begingroup$ @ArmanX The centrifugal forces on slings and trebuchet arms would likely cause them to fail long before they get their tips to tens of kilometers per second speeds. Linear acceleration would be best... and high above the atmosphere if at all possible.... maybe if your blob could raise itself up 50-100km, then perhaps some kind of blowdart or cannon mechanism..? spit instead of throw? $\endgroup$ – Innovine Jul 13 '17 at 17:32
  • $\begingroup$ Something else I thought of; while a single blob arm would crush the surface of the planet before it was long enough to reach into space, if the blob has eaten the entirety of the planet, it could squash itself into a disk, with multiple throwing arms to toss smaller blobs away. And, it may be able to digest the atmosphere, too; some chemical process that binds the various atoms to solids or liquids, or just stores the air in pockets. No atmosphere means a lot less drag. $\endgroup$ – ArmanX Jul 14 '17 at 18:14
  • $\begingroup$ @armanx if you can digest the atmosphere then things get more interesting alright :) note that you will want to throw the bits from west to east, to take advantage of the planets rotation. $\endgroup$ – Innovine Jul 14 '17 at 19:44

Consuming all life on the target planet is counterproductive - the organism will run out of food, and then it's really up the creek.

Might be better to have a more subtle organism that lives in some form of symbiosis with whatever it encounters on the planet. Then, it can wait (this being a very patient organism) for the inhabitants to develop space travel, and just hitch a ride. Why do the hard work, when you can get the native organisms to do it for you?

A truly imaginative organism might even guide the evolution of native creatures in a specific direction, with the goal of just getting back into space.

  • $\begingroup$ The creature's entire point is to consume all life; it eats everything from organic life to plain ol' rocks and sea water. Its life cycle is spending hundreds, thousands, even millions of years travelling from one solar system to another, splashing down, eating everything, and leaving again. It's fairly mindless, and probably left over from some alien evil genius... $\endgroup$ – ArmanX Jul 12 '17 at 19:08
  • $\begingroup$ It would be interesting to estimate if the calorie content of the entire planets biomass is enough to overcome the friction of getting from the surface through the atmosphere and emerginging above escape velocity. $\endgroup$ – Innovine Jul 13 '17 at 17:36

Your Answer

By clicking “Post Your Answer”, you agree to our terms of service, privacy policy and cookie policy

Not the answer you're looking for? Browse other questions tagged or ask your own question.