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I have this idea of homicidal alien beings that upon death (after their body ceases living and begins to decompose) release enough poisonous gas into earth's atmosphere to wipe out all life on the planet. In the novel-in-progress, the younger of the aliens uses this to provide justification for her murdering the townspeople, saying that if she and her father (the other alien being) die, they will wipe out life on earth, three times over.

Is it possible to fit enough gas to wipe out a planet into into two human-sized beings?

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  • $\begingroup$ @RELavendar Welcome to the Site! $\endgroup$ – sdrawkcabdear Mar 31 '16 at 1:06
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This would mean that the gas has a total mass of the initial body (at max), because gas is not simply generated but results of a conversion process. If certain bacteria cause this it may be possible to generate more gas than body mass but than the additional mass and energy has to come from something else than the aliens (like said, bacteria, air, water or something like this).

Aside from that, if you calculate the mass of the aliens to lets say 200kg and if we assume the gas is only generated in this mass. For full earths atmosphere (lets say the gas could spread up into the Thermosphere (250km) this would mean you would have to cover a volume of VolumeEarthTotal(4/3*pi*radius((~6378.1km+250km)=6628km)^3=1.086.781.292.542km3)- VolumeEarthMass(4/3*pi*radius(~6378.1 km)^3=~1.083.206.916.845 km3)= 136.445.578.160 km3

(I hope i did not mess up the original numbers in here but my calculation/result should be quite right for an estimate)

So you would have to cover this huge volume with 200kg worth of mass. If we additionally assume the gas is similar to methane (which is usually generated on most composition processes) one kg of the gas is 1,47017 m3 -> 1,47017*10^-9 km3 -> 200kg of gas are 2.94034E-7 km3

And the Volume of the Atmosphere divided by the Volume of the Gas would result in a density of 2.1549544*10^-20 which is 0.0000000000000000021549

Meaning the chance to stumble into a gas particle is very very low (I won't calculate this too as it is late and as I am not sure how exactly). You could now calculate how much gas they need to generate in mass to make it at least possible for many humans to breath the gas, or you scale the atmosphere (spreading height of the gas) down until the numbers get better.

Tinker with the numbers, or take s bit of exaggeration out of her saying so it only relates to a smaller area of earth. Or get more aliens to earth...

I hope the calculations and assumptions helped and were at least nearly correct. Sources were: http://nssdc.gsfc.nasa.gov/planetary/factsheet/earthfact.html

https://www3.epa.gov/cmop/resources/converter.html

12 Years of German Education System

Ignoring this post I am curious about your story (trial reading application) ;)

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  • $\begingroup$ Thank you! That clarifies it up a lot. I kind of had the notion that it would not be probable for only two beings, one having a relatively small mass, to emit enough gas to wipe out the earth. But, if one takes into account that both the alien sending the information, and the human receiving the information are 14 year old girls I thought I may be able to play it off as an exaggeration on both ends. Having actual science rather than hypothetical science to back it up helps a lot though. $\endgroup$ – RE Lavender Mar 31 '16 at 2:29
  • $\begingroup$ Actually this sounds very possible. This would only be a 10C homoeopathic dilution. - en.wikipedia.org/wiki/Homeopathy $\endgroup$ – KalleMP Jul 20 '18 at 20:51
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No, there is just not enough mass to produce enough chemical to kill everyone in more than a few dozen square kilometers at most.

A more credible scenario is that the dying alien will release a self-reproducing pathogen which will replicate over the earth killing everything.

In fact, the danger of transmitting microbes from planet to planet is so grave it is unlikely that any humans will ever land on a life bearing world or allow a living alien to reach earth.

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The volume of the earths atmosphere is 17 and a quarter trillion cubic kilometres. Lets say the bombs contained 2 cubic meters of gas combined. The ratio once mixed with the atmosphere would be roughly 1 part per 8.625x10^18.

The most toxic known gas is sarin gas. the lethal concentration of sarin in air is approximately 35 mg per cubic meter per minute for a two-minute exposure time by a healthy adult breathing normally. or very roughly 1 part per 28,000,000.

Given, you're talking about longer term exposure, but I'm going to estimate that the planet would still be habitable.

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  • $\begingroup$ The most toxic chemical by mass is actually Aflatoxin, produce by fungus growing on peanuts. The most toxic nerve gas is VX about 1,000 times more lethal per mass dose than Sarin. Sarin is old school from 1942, only about a 100 times more toxic than mustard gas. The most lethal substance by dose mass is ingested, breathed or injected plutonium. On your skin, its harmless, get in side and the beta emission will shred every organic molecule. $\endgroup$ – TechZen Mar 31 '16 at 2:04
  • $\begingroup$ oh... That's what I get for googling the most lethal gas. $\endgroup$ – Lorry Laurence mcLarry Mar 31 '16 at 3:50
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Gas density,absorption, and catalytic properties (and similar) would matter. Suppose the aliens body decomposed slowly by bacteria action and magical whatsits, in contact with some heavy gas or other material in the environment. The extraneous material provides a higher density and the alien body compound is a small part of its relative mass but exceedingly lethal. What you end up with is a gas that may never reach more than a few hundred meters above ground level and won't pervade the whole atmosphere. While this won't reach mountaintops, it will allow much greater ground coverage to start. Then perhaps wind can carry it, and maybe its lethal not by being absorbed, but by some catalytic effect impacting crucial functionality for life, so maybe it isn't lost when a lifeform dies but is eventually re-released. Slower and less dramatic than insta-death but I think this is a way it could be done...?

I wouldn't worry about such a trivial threat much, myself... Just spray with liquid helium a bit and place inside sealed cryogenic chamber, then store in a few meters of concrete until cheaply exportable into space (solar-bound orbit preferred). The only thing this says to me is any killing method mustn't let gas out; that's easy.

By the way, I'm intrigued by this "wipe out all life on earth three times over" deal. How do they plan to wipe out the 2nd and 3rd time over?

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