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I'm working on a story involving life on Europa being upturned dramatically by contact from a probe sent from Earth. Found this community while researching, and have found a lot of great ideas. I know the chances of life, let alone intelligent life, are pretty slim on Europa, but I'm ignoring that for the sake of the story. The driving force of the story is that a probe that's come from Earth crashes/malfunctions after melting through the ice.The probe sinks to the bottom of a trench and sets off some sort of ecological disaster/collapse, that then has cascading effects on the civilizations living there. In retaliation, a fairly advanced society that has adapted to living in the ice (most of society is less advanced and lives on the sea floor), makes plans to retaliate against the Earth by breaking off a chunk of the outer ice crust and hurling it at Earth.

I know that's kind of crazy, but I'm trying to gauge HOW crazy, and if it can be explained reasonably (not that they are necessarily acting reasonably/rationally). I'm thinking they would be able to freeze, or otherwise build a barrier around the area that's going to be broken off, to sort of protect most of the rest of the moon from being destroyed or sucked out into space. They then break along an area of the ice all the way through, and let the force/pressure of the ocean pushing up 'throw' the ice where they want it to go. It is supposed to be somewhat of a desperate move where the ones working on the project think they have nothing to lose, and aren't concerned with the fact that it would definitely cause a lot of damage to the moon, so long as they survive.

My question is whether this is even remotely feasible, or if I have gone completely off the rails?

Thanks for your help!

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    $\begingroup$ You have multiple questions in here, which probably won't go over so well. You might revise this by first researching the size of asteriod/comet impacts on Earth vs their estimated devastation, choose the scale you want, and then start with a question solely about how your Europa-aliens might be able throw out something that big. $\endgroup$ Jul 29 at 22:07
  • $\begingroup$ Take a time to breathe and ask one question at a time :). It's because multiple questions diffuse the answers between multiple topics, reducing their overall value. You can always create more topics to dig deeper into the subject later if you wish! $\endgroup$
    – Tortliena
    Jul 29 at 22:48
  • $\begingroup$ I have tried researching the size, etc, but I've had trouble finding an answer as most sources specifically talk about rocks rather than ice, and if they are talking about ice, it's comets, which I think would be moving a LOT faster than this potential item would be. I will try breaking this up into multiple separate questions though! $\endgroup$
    – Brooke
    Jul 29 at 23:02
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    $\begingroup$ This sounds like a case where a bioweapon in a small chunk of ice would be a much better option. $\endgroup$ Jul 30 at 13:19

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Lifting enough mass from Europa and breaking orbit (both Europa's and Jupiter's orbit) is insanely energy-intensive, and a great waste. The better option in my opinion is to find a suitable rock/iceball near Jupiter to accelerate to intercept Earth. If the Europa aliens can launch a miles-wide chunk of their own moon's crust, they should be capable of launching a much, much smaller spacecraft loaded with fuel to change the orbit of an already-existing, equally-sized chunk of ice.

With the same amount of energy needed to raise a wholesale slice of crust into interplanetary space, they could instead launch thousands of smaller spacecraft+fuel missions and redirect thousands of comets at Earth.
It would definitely be less of an engineering challenge, too.

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  • $\begingroup$ Well, part of the issue is that they don't actually have any sort of space-travel/rockets. My thought was that they would essentially have figured out how to engineer their own plumes, but on a grander scale. Like, what space travel they could manage would rely on 'riding' a plume up out of the thin atmosphere rather than relying on any sort of engine, etc. $\endgroup$
    – Brooke
    Jul 29 at 22:58
  • $\begingroup$ @Brooke Hmm, that's an interesting dilemma. Europa aliens would be at a massive disadvantage. It's hard to smelt ore underwater. In a story I wrote with aliens from a Europa-like world, I just handwaved away that detail, made a point of how mysterious it was that they were able to advance technologically. $\endgroup$
    – BMF
    Jul 29 at 23:56
  • $\begingroup$ @Brooke Anyway, I don't think there's enough energy in the small moon to do something like that. It would be an enormous feat of engineering, too. A mountain-sized chunk of ice weighing ~1 billion metric tons into interplanetary orbit. All at once? If you gave humanity a century to divert all resources (the more of it we'd have, considering we're not trapped in an ocean) to do the same, I don't think we could. It's just an insane amount of energy. We're probably talking millions of nukes worth of energy here... $\endgroup$
    – BMF
    Jul 29 at 23:58
  • $\begingroup$ @Brooke just a rough calculation to show my point. Earth-Europa transfer is about 15 km/s delta-v. To accelerate a small mountain of ice ~1 billion tons on that trajectory requires ~1.4M "Fat Man" nukes, assuming all the energy of the blast(s) is somehow translated straight into kinetic energy. $\endgroup$
    – BMF
    Jul 30 at 0:16
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    $\begingroup$ @Brooke are you confusing Europa with Enceladus? nasa.gov/feature/goddard/2021/… The mechanism for the creation of plumes is well-known: flexing due to tidal forces. Europa might have such plumes, but "Scientists warn that Europan plumes, even if they’re there, could be hard to detect even from up close. They may be sporadic, and they may be small and thin, given that Europa’s gravity, which is much stronger than Enceladus’, likely would keep these water plumes close to the surface." $\endgroup$
    – RonJohn
    Jul 30 at 20:52
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No

First, from the description I read "thrown" as "launched on a trajectory with no subsequent in-flight guidance". If there is (somehow) the ability to make course-corrections in-flight then the first part may be less relevant.

Space is big. Really big... you can look up the rest of the quote from The Hitchhikers Guide to the Galaxy on your own. Jupiter - and to all practical purposes its moon Europa and the 79 other satellites - orbits at an average of slightly over 5 AU from the sun, while Earth orbits at an average of 1 AU. Let's be generous and say that when the aliens want to make their attack, they can launch their chunk of ice such that it only has to travel 4 AU to get to Earth, or about 600 million kilometres.

Earth has a radius of a bit over 6000 km (yes, I'm rounding massively with all the numbers in order to get nice round numbers). In other words, the accuracy of the "throw" must be to within about 1 part in 100,000. It's like asking someone to shoot at a target 100 metres away and have a needle on the tip strike within 1 mm of the point of aim using a gun with no barrel, just a chamber that can barely contain the bullet. Some may fault the analogy due to the lack of air in space. However, the Europa cold crust "bullet" has more than enough problems to make up for that one little advantage - its initial trajectory will be affected by the roughness of the "barrel" it is launched from and the gravity of Jupiter and all 80 of its satellites. As it continues on, outgassing from any faults resulting from its violent launch and sublimation of the surface facing the sun will affect its trajectory further. Given the very long duration of its journey (see below) it will be far more affected by the various influences than a bullet would in its short flight.

However, none of that will matter if the projectile cannot be thrown. Europa has an escape velocity of a bit over 2 km/second. Let's say that the vengeful Europans want to throw it twice that quickly so that the residual velocity after escaping Europa's gravity will allow it to reach Earth in a bit over 9 Earth years to get their revenge. (I am going to assume that they can plot the trajectory to let the projectile escape Jupiter's gravity too so it doesn't just become another Jovian satellite.) As other answers have stated, ocean pressure is not going to do it.

So, there is a cylinder of crust 50 km in diameter (as seen from above) and (assume) 50 km deep that has been isolated from the surrounding crust. It needs to get accelerated to 4 km/second before the base of the 50 km cylinder clears the top. Plugging in the numbers, the acceleration needs to be 160m/s^2, or about 16 G. Let's just ignore where the mind-boggling amounts of energy come from to accelerate roughly 10^14 cubic metres of crust. The simple fact is that it will not hold together for the 25 seconds of acceleration needed to throw it towards Earth. The centre may be OK initially, but the sides will start shearing away once they are no longer contained. Unpredictably shearing away, which makes a nonsense of even attempting to accurately aim this projectile anywhere as it will be unbalanced as it launches.

To summarise - no. It is impossible to aim with sufficient accuracy given unpredictable deflections in flight; energy required for launch is completely prohibitive; and the projectile would disintegrate unpredictably as it was launched.

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For your specific question, the answer is "no." And while you have the "science-based" tag on the question, that's the end of the matter.

The pressure under Europa's ice layer is not adequate to propel a block of the ice into space. Not at all. If it were, Europa would already have burst: the structural strength of an ice layer, even one many miles thick, is not adequate to contain that kind of pressure.

In any case, enough force to propel a block of ice clear of Europa's surface is a lot less than enough force to put it into orbit around Jupiter. Enough force for that is way less than is needed to get out of orbit around Jupiter and into an elliptical orbit round the Sun, which is needed to hit Earth.

And even if you had enough force to do that, hitting Earth is essentially impossible. You've created something very much like a comet, which will start to evaporate when it gets closer to the Sun. Since its shape is unavoidably irregular, that evaporation will create some thrust, which will change its orbit. There's no practical way to predict that in advance and correct for it. The Earth is a tiny target compared to the range, and moving quite fast. You will miss.

If you want this event in a story, you're going to have to give up any claim to it being science-based. On the Mohs Scale Of Science Fiction Hardness you're falling off the bottom, into the Worlds in Collision ghetto of things that are too crazy for Hollywood to believe in.

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