So in a red dwarf system with two planets, both of them develop life, but the inner planet develops advanced life much quicker than the outer one and is equivalent to current human tech, maybe a little more advanced. They don’t like how the outer planet already has life (think of humans in the early 1900s) and want to sterilise it completely as they fear that they could be wiped out by them if they continue to develop. How would they try to do this quickly? I want the sterilisation to be realistic too, so no black hole gun or stuff like that.

Edit: this is different to this as i do require some form of interplanetary delivery and that the time frame for that question requires tech that we pretty much have today, whereas my question allows tech that is near future, say, 20 years ahead.

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    $\begingroup$ It's sure a black hole would certainly do more than sterilising the planet :p. Here are a few questions you should perhaps answer : What kind of life is there currently on the outer planet : Only bacteria or multicellular like trees and animals? What kind of tech does your inner planet have : Today, near future...? $\endgroup$
    – Tortliena
    Oct 10 at 11:13
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    $\begingroup$ Two other things to note : First, don't set your expectations too high as to how quickly a complete neutralisation of the planet will happen with today's technology. Nowadays, we need quite some time to design a rocket and send it, and one rocket is very unlikely be enough to take down a whole planet. The cost will be high, and so will the time needed. On the other end, excepted bacterias and viruses, life evolves extremely slowly, easily 10M years if not rmore. Having a new sentient species capable of sending armed rockets to another planet will require a lot of time. $\endgroup$
    – Tortliena
    Oct 10 at 11:21
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    $\begingroup$ If this has to be hard science, where are you looking? Plagues? Energy beams? Deprivation of oxygen (or whatever)? If it's not hard science but mere WorldBuilding, to what extent is handwavium allowed? $\endgroup$ Oct 10 at 19:41
  • $\begingroup$ humans couldn't sterilize a planet with current technology if the entire species put all their effort into it. Planets are big and we don't have the energy resources to do much. $\endgroup$
    – John
    Oct 10 at 20:32
  • $\begingroup$ Do they just want to eliminate the other planet as a threat, or do they plan to later colonize it? The solutions would be heavily influenced by this! Also, if they only fear that a technological species on the other planet would threaten them, it's orders of magnitudes easier to blast them back to the stone age and not having to worry for many thousands of years, than to completely sterilize the planet, including bacteria. $\endgroup$
    – vsz
    Oct 11 at 5:57

7 Answers 7


Just beam it.

Note, relativistic effects for the exhaust are disabled

I think one realistic, ish, approach is to use either a thruster or other kind of particle accelerating device to blast the planets surface. In the render i depict this as a ship hovering over the surface, or in an orbit, with the exhaust pointed down whilst the planet rotate underneath it. This does not have to look like this, you may also just collect a bunch of sunlight and concentrate it into a tight beam for the same effect. I just used this ship because i had the 3D model in Houdini.

Using a thruster, such as the Wakefield type relativistic thruster (A particle accelerator) pictured above, may be more to your liking because it produces truly an ungodly amount of radiation. If you simply focus light, you burn stuff. But if you use a thruster to accelerate propellant to relativistic speeds you create Gamma rays and particles similar to Cosmic Rays. Indeed with the setup shown here, the exhaust is best described as a Gamma Ray burst.

This has several upsides. For one, you will Definity delete the planets Ozon layer. With a light beam you have the issue that the atmosphere will absorb a lot of the energy, or reflect it. With particles, whilst the atmosphere still resists it cant really reflect the beam. Furthermore because the beam is so hot, billions of degrees, the instance it hits the Air an effect similar to the explosive shockwave around nuclear bombs may develop. In essence, the beam hitting the air may create something similar to a continuous nuclear detonation.

The exact nature of the event depends on the energy. If we assume the beams total energy to be 100 Mt, it would take around 300 hours to match the energy released by the KT-Extinction event.

Of course in our case, we would match the energy while also irradiating every cm² of the surface to the point the inside of Chernobyl looks like a radiation free zone. Another effect to consider is that since all of this energy cant really escape the planet efficiently, the Atmosphere will heat up to probably a few 100 or 1000 degrees, similar to what happened during KT.

You might ask how plausible such a thruster is. The answer is "meh". Its really about efficiency. Particle accelerators are famous for being heaters that occasionally throw around a proton. But you can get away with more than conventional efficiency because we are building an engine, not a scientific device. And these things dont have to be large. A 10cm long Wakefield accelerator can already approach the speed of light. The reason installations like the LHC are so huge is because they need to get really close to the speed of light, but we are fine with idk 0.999999c. Which is well within the realm of modern tech. (Note, for Particle accelerators people use GeV as the measure of choice, from which you can deduce the velocity).

Naturally, this would be one hell a energy waste. But you also want to sterilize a planet sooooo


Alright because some people take issue with the stated realism, lets try to substantiate this a bit.

I am making, in essence, three cases.

  1. We can build particle accelerators that can achieve velocities of 0.999999c without being the LHC

  2. We can use the particle beam to destroy / Sterilize the planet below

  3. We can supply said accelerators with energy

On 1

That is not up for debate. Within Particle physics the measure of $GeV$, Giga-Electronvolt, is used to describe the power of a given accelerator. To get into some math, the particle velocity is given by

$$v_{p} = c \sqrt{1-\frac{1}{(\frac{J_G}{mc^2}+1)^2}}$$

Where $v_p$ is the velocity, $J_G$ is the energy and $m$ the mass of the particle. $GeV$ relates to Joule by the factor $J = 1.60217 \times 10^{-10}$. If we plug in the mass of a Proton, and assume an accelerator energy of $100 GeV$, the particle velocity works out to $v_p = 0.999957439158c$. Indeed to reach the desired speed of $0.99999c$, we need around $210 GeV$.

Plasma particle accelerators, otherwise Wakefield, are known to reach $2 GeV$ for 2cm track length. Though the record is $4.25 GeV$ for the same length. The Super Proton Synchrotron is currently operating a test article, AWAKE, at $400 GeV$ with a track length of 800 meters. Which incidentally is the length of the Accelerator in the render.

So this is not some sort of super speculative tech, this is what we have. The only question is how much you can scale this up. Because obviously a scientific accelerator is not spewing out the numbers of Protons you would want for a thruster.

On 2

The effects of a particle accelerator beam on the human body is known. One may look at Anatoli Bugorski to get an idea of what a Scientific accelerator can do. In my answer we are talking about a machine that spews out 10000s of times more particles per second. The Beam Anatoli was hit by had an energy of $76 GeV$ and did this;

enter image description here

One metric to look at is the Energy released by the beam per second. This is done using relativistic kinetic energy such that;

$E_{kin} = m_0c^2\left(\sqrt{\frac{1}{1-\frac{v^2}{c^2}}}-1\right)$

If we imagine a beam with a mass flow of say 0.0001 kg/s and a velocity of 0.99999c, the Energy works out to $2.01 \times 10^{15} J$, or roughly $480 \frac{kt}{s}$. Scale this up to 0.001 kg/s and we get 10 times more energy.

Of course, even ~500 kt is not really a big explosion. Its decent but not earth shattering. The magic is the whole $\frac{kt}{s}$ thing. Ideally you would let this run for many weeks or years, and probably not just have one ship doing it. Imagine say 12 ships blasting for 1 year. That will have released the equivalent of 181670 Teratons. 100s of times more than the Asteroid that killed the Dinos. That will, with 100% certainty, obliterate a planets surface and whip out any complex life.

On 3

Now this, is where yall got me. Doing this math is nice and fun until someone asks, where does all of this energy come from ?

At the end of the day, Particle accelerators have garbage efficiencies and if it was so dam easy to do, we would be doing it.

If we stay with the 12 ship example, at the very least we need about you know 24115951226000000 Watt. Otherwise known as twenty-four quadrillion. Also known as like 100 billion times more than the world consumes annually right now.

There are some saving graces. Whilst this is a lot of energy its not a significant portion of the suns total output. Which for all intend is the only possible energy source. If we go with an efficiency of the 1400 Watt/m² on Earth or whatever it is, you only need 17225679 km² of solar panels, also known as the land area of Russia, pretty much down to the km² interestingly enough.

Is this possible ? You know... probably not within the next 20 years. But it is not totally out there. By Sci Fi Standards anyways. So weather or not this is an obstacle depends on OP and their world. If for instance you place the solar panels half as close, you only need the square of the area for the same output. Or roughly the area of India plus a few 100000 km². Power beaming and similar technologies do exist, but are not available at this scale in any form.


Ill die on the hill that from a physics POV, this is entirely doable. From an economical perspective, it isnt in 20 years if OP starts with modern tech, or does not want to expand their timeline slightly.

  • $\begingroup$ Irradiating the surface can’t sterilise a planet. There are bacteria a kilometre underground. There are complex life forms under kilometres of sea water. The rock and water will block all radiation. $\endgroup$
    – Mike Scott
    Oct 10 at 15:31
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    $\begingroup$ But where are you getting the energy from, with technology “maybe a little more advanced” than our current technology? Boiling oceans needs a lot of energy, many orders of magnitude more than we could put to that purpose. $\endgroup$
    – Mike Scott
    Oct 10 at 15:50
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    $\begingroup$ You are drastically over-estimating the capability of our current technology. $\endgroup$
    – Mike Scott
    Oct 10 at 16:02
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    $\begingroup$ If we assume the beam consumes 100 Mt of energy per hour, it consumes the entire annual world energy budget in about 4 days. "Just harness the power of the Sun" basically requires that we are already a Kardashev Type-II civilization, which we certainly are not. $\endgroup$ Oct 10 at 16:45
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    $\begingroup$ "Its just a lot of energy" is pretty much handwaving the entire field of physics away. How do I delete a planet? Pump it with enough energy to turn it into a black hole. It's just a lot of energy. $\endgroup$
    – Passer By
    Oct 11 at 8:03

It isn't realistic for two planets to be anywhere close to each other in technological and biological development towards a technological species.

The level of coincidence would be insane. It would be like discovering that every mass extinction triggered by asteroid impacts in the last billion years all hit the exact same spot on the planet out of pure chance.

At our current level of technology and industry, the closest we could get would be a radioactive bomb that wipes out most large animals. This still wouldn't sterilize the planet.

Sterilizing the planet is pretty much a K1 level civilization (Kardashev 1) feat. Basically, you have to heat the surface of a planet to the point where everything is hotter than life can survive - boil it.

Before K1, you can redirect comets or asteroids at the target planet and get decent leverage. But the level of bombardment required to sterilize the planet is simply crazy.

Any civilization capable of sterilizing a planet has to exist substantially off a planet's surface. Either you need a space based industrial chain to build the comet and asteroid redirecting armada of ships (probably reaching the oort cloud, and with plans reaching 100s to 1000s of years to complete it), or you are close to K1 and the very industrial technology you have is enough to boil your home world.

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    $\begingroup$ Could you let us know what K1 is? $\endgroup$
    – jcaron
    Oct 11 at 12:09
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    $\begingroup$ It's short for Kardashev 1 on the Kardashev Scale. It basically means "a civilisation sufficiently technically advanced to capture and control almost all of the energy recieved by their home planet"; imagine mirror satellites beaming down energy, easy transfer of materials into and out of orbit, etc. $\endgroup$
    – V. Jackson
    Oct 11 at 13:14
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    $\begingroup$ @jcaron As VJackson says, it is Kardashev 1, or 10^16 Watts, or as much energy as an Earth like planet gets from its Sun, or equivalently the amount of energy an Earth like planet can radiate. A K1 civilization on a planet will boil the planet from raw energy use; but at the same time, boiling a planet sterile is a K1 level of energy use. Hence my conclusion; any civilization capable of sterilizing a planet is not bound to a planet. Asking about a planet-bound civilization sterilizing a planet is like casually asking why Rome didn't neutron bomb Carthage. $\endgroup$
    – Yakk
    Oct 11 at 14:24

You can’t sterilise a planet with any technology that we can conceive of creating — it would require some kind of technology that is sufficiently advanced to be magic. Planets are very large and life is very widespread and persistent. You might manage to kill all large surface animals, but that’s a very very long way from complete sterilisation and is not what you’ve asked for.

  • $\begingroup$ How could we reliably kill large animals and plants therefore? I mean, the main concern of the inner planet inhabitants is to make surer there's no bad guys on the outer planet (#xenophobia :p). If you can get rid from those, that would be a good -even if incomplete- start. $\endgroup$
    – Tortliena
    Oct 10 at 16:07
  • $\begingroup$ @Tortliena That’s a different question and should be asked as such, not buried here in the comments. And you can’t edit the existing question, because that would invalidate existing answers, which isn’t allowed — it has to be a new question. $\endgroup$
    – Mike Scott
    Oct 10 at 17:02
  • $\begingroup$ That's actually part of the original question. When you say you can't do it (frame-challenge), it's much, much better to also provide an alternative close to the intents behind the question. Saying that with this far future tech you could do it is a way, or imagining a way to just neutralize meaningful threats (the goal behind sterilizing the planet) on the planet is another. $\endgroup$
    – Tortliena
    Oct 10 at 18:46

Find asteroids almost on a collision course with the target, and nudge them into a collision course. Expensive but thinkable with present-day tech, impossible to stop with 1900-era tech.

  • Maneuver a probe with a nuclear weapon next to the asteroid.
    Pro: High energy in a relatively light package. Getting the same thrust with chemical fuel is harder.
    Con: Hard to control without a good survey of the asteroid. How much will ablate? Could it splinter?

  • Land a probe with an engine on the asteroid.
    Pro: Fine adjustments are possible.
    Con: Chemical fuels are rather heavy. Ion drives use much power and specialized reaction mass. Mass driver engine? Again power hogs.

Enough of that should kill all large fauna on the surface.


The simplest way would be to cause some kind of mass-extinction event by altering the planet's temperature.

The easiest way to do this is with foil mirrors, a fraction of a millimetre thick to save material and weight. You could use them in one of two ways, either:

  1. Reflect a lot of sunlight towards the planet to increase its temperature, ideally enough to boil the oceans.
  2. Reflect a large amount of sunlight away from the planet to decrease its temperature and cause a permanent ice age, ideally freezing the oceans solid.

The issue which you may or may not want to tackle in your story is how to make and launch enough foil mirrors. Maybe the planet committing this mass-genocide is rich in aluminium or another light-weight reflective material and has a way of cheaply producing rocket fuel. Maybe it's more likely they are capable of launching several probes that can mine asteroids or small rocky inner planets to produce duplicates of themselves enough to produce the mirrors quickly. Is cost a factor, or does the population consider this enough of an existential threat that a large portion of the planet's economy is focused on this goal?

The speed at which the extinction could occur also depends on the size and geology of the target planet (e.g. are there polar ice caps which may release a lot of methane when they melt, increasing a greenhouse warming effect?), how quickly mirrors can be produced and the strength of the solar radiation reaching the surface, etc.

  • $\begingroup$ This probably wouldn't sterilize the planet, and certainly not quickly. This plan would likely take hundreds of years to change temperatures enough to kill all life on the surface, but subterranean bacterial life could likely persist for millenia $\endgroup$ Oct 11 at 10:57
  • $\begingroup$ Wouldn't it be quicker and simpler to strap some engines to these astroids and altering their orbit to crash onto the rival world? Even if it's more mass to move, the whole process of mining them, refining the materials, turning them into foil mirrors, and placing them is non-trivial. $\endgroup$ Oct 11 at 10:59

Guns Germs and Steel it

I am going to assume that you mean that the outer planet has some sort of intelligent life because you say "wiped out by them"

There is a trend that species from larger landmasses (continents, islands, etc.) generally have an advantage and colonize and beat out species from smaller landmasses since they have been under more selective pressure coming from larger places with more competitors, predators, diseases, etc. Think of rabbits and cane toads in Australia and smallpox in the americas. I think Jared Diamond and Tim Flannery talked about this. To me, it sounds like the inner planet may be larger, have more life on it, etc. Perhaps sending probes to the outer planet filled with species, plants, bacteria, and diseases that can run rampant there and see how it goes is a good start, the inner planets bacteria and life may be highly fatal to the outer ones. Then you can see how life interacts between the world (if the inner planets species has a chance to survive) and if so start colonizing and killing everything off manually (sorry to get grim).

With current human tech, our nukes couldn't sterilize a planet. So you'd be better off seeding it and colonizing it in my opinion.


Completely sterilizing a planet is borderline impossible. There are microbes living in rocks miles below the surface.

The most low-tech way to attempt this would be to find an asteroid on an almost colliding orbit, and divert it slightly. With a large impact one might hope to wipe out all large terrestrial life, as Chixulub did for the dinosaurs (apart from the small avian ones).

To knock a species back into the stone age is much easier. A targeted nuclear bombardment with multi-megatonne bombs ought to do it. "Salt" the bombs (to create large amounts of long lived radioactive fallout) if you want to be really evil. The victims are at a technology level where they cannot retaliate, and the other lot get tens of centuries to decide what to do next.


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