## What-If 0146: "Stop Jupiter"

What if there was a forum for discussing these?

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nowhereman
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### Re: What-If 0146: "Stop Jupiter"

Pfhorrest wrote:Ok so does this same principle apply to all other objects? If you were to blow up Titan (pump enough more energy than its gravitational binding energy into it), would Titan-dust scatter far and wide (getting sucked in by other nearby massive objects of course), or would Saturn just get another ring?

In the Jupiter case, it was open and shut because the angular momentum simply disappeared. This means that Jupiter can be described as an expanding sphere with nothing else affecting it (regardless of other planets that might impart some momentum, but do so by capturing the gasses and dust). When it comes to the general case I am not so sure. When Titan is blown up (or Jupiter if it was not done in so specific a manner) I could imagine it in one of two ways. If we continue with the expanding sphere analogy, this would be an expanding sphere on a rotating plane. I would expect no difference in this circumstance (since the expanding sphere would still be subject to the same forces in the rotating frame as in the stationary frame). That is an oversimplification though.

When you look at the exploding rotating body, each particle, by virtue of being in the larger body as a whole, has a velocity vector. When the planet explodes, this vector will change, but its final value will depend upon the speed of each particle before the planet blew up and its relative position on the planet (use vector addition). If we use exactly the gravitational binding energy to blow up the offending planet, then it stands to reason that at the surface of the planet (moon, asteroid, whatever) each particle would be moving at exactly escape velocity. Note that the vector that results from this will vary wildly based upon where they were when the planet blew up. So you can think of each particle having a completely new orbit from every other particle. In order for matter to collect in the fashion you would expect to reform the planet you blew up, they would need to be on similar orbital paths (or redirected into similar orbital paths). This isn't like the beginning of the solar system. We don't have a large collector of matter to suck in mass that is on a very different orbit. So until a large portion of this matter forms, the planet will not become a planet (or moon, or whatever).

Is there something that would reform? I doubt it, but my bet is go smaller. Like rock or astronomical dust bunny small. Ignoring everything else, the gravitational binding energy of such a small object is so low and the escape velocity is so small, that I imagine that the particulate would still be in a similar orbital path. Gravity is weaker of course so going smaller might not be useful, but at least it solves the proximity problem (and gravity's strength is proportional to the mass and the square of the inverse distance). If this does work, I don't know how small something needs to be to use this.
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Pelyphin
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### Re: What-If 0146: "Stop Jupiter"

The atmosphere of Jupiter is said to be 90% hydrogen, with most of the remainder being helium. How volatile is it?

Soupspoon
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### Re: What-If 0146: "Stop Jupiter"

Shadowman615 wrote:Wait, wait, so a spacecraft that travelled to pluto was powered by plutonium!? There's a bit of awesomeness in there somewhere...
Now we just need to warn Homeland Security to watch out for Americium-powered drones heading in from some foreign force or other...

05LGT
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### Re: What-If 0146: "Stop Jupiter"

[quote="ramblinjd"]Did anybody else notice the tennis ball says Pen 15 (penis)?

I'm assuming I know which AC/DC song was being hummed when that was drawn.

Mikemk
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### Re: What-If 0146: "Stop Jupiter"

leafar wrote:
Earth weighs almost exactly pi milliJupiters

Am I the only one who read that, went straight to Wolfram Alpha, and was quite amazed at that result?

Interesting, but not mathematically interesting
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Archgeek
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### Re: What-If 0146: "Stop Jupiter"

ramblinjd wrote:Did anybody else notice the tennis ball says Pen 15 (penis)?

Actually, that looks to say "Penn 15", Penn being a common brand of tennis ball (leastways, here in the states). The 15 of course, is for the ancient schoolyard wangerdoodle joke. See also T-shirts for the Pennsylvania state university class of 2015 -- "The Hardest Class in History".
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hamjudo
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### Re: What-If 0146: "Stop Jupiter"

SDK wrote:
hamjudo wrote:I still want to know the answer to the original what if question.

Answering that would have been long and boring. He probably just didn't want to dive into the complex math and change the entire content of the article.

New Horizons slowed Jupiter by 10-21 m/s, right? Jupiter is moving at 13.07 km/s. Therefore, you need 1.3x1025 (13 septillion) New Horizons to stop it. Right?

No, you need quite a few more than that. This is all based on how much energy New Horizons is able to take away while it gains that 4000 m/s. But as Jupiter slows (particularly once it gets below 4000 m/s itself), the probes will be extracting less and less... until eventually their own speed would match Jupiter's and nothing much happens (in an absolute sense, at least). To finish it off, you'd need to start in on angles of approach, the probe's initial speed and all that other crap that no one really wants to talk or read about.

Now take your several septillion spacecraft and be happy that he didn't give us more.

Which means it is on the order of 20 moles of New Horizons missions.

As we learned in the Mole of Moles What-If, any time you have a mole of anything of significant mass, they will become a planet under their own gravity, unless you keep them spread out. I strongly suspect that this means the project will take many Jupiter years, otherwise, we won't be able to treat the payloads independently.

In my question, I specified
Assume that some alien civilization wants to cause Jupiter to impact our sun. These distant aliens have developed a mass driver that can launch an insane number of payloads that will reach our solar system with a trajectory such that each one alters Jupiter's orbit just as much as the New Horizons mission did.

If a payload follows a parabolic trajectory relative to Jupiter, it will transfer the most momentum to Jupiter. In the limit, a parabola results in the payload going the exact opposite direction to the direction it came from, if Jupiter weren't also moving, and if it was just a two body problem. In any reference frame, but Jupiter's, the payloads will be traveling in a noticeably different direction. The aliens don't care, because their primary goal is to crash Jupiter into the sun. The aliens will have to take the sun and the other planets into consideration when planning the trajectories, or the payloads will miss their targets. They will also have to make sure that on the way out of the solar system, the payloads won't interact with other bodies in a way that will undo any of their work on Jupiter's orbit.

The aliens can use gravitational slingshot maneuvers around the sun and planets to get the payloads to approach Jupiter from places other than the alien launch point. With 20 moles of payloads, they will shift other planets around. They can either choose to alternate adding and subtracting orbital energy, or they can intentionally change the orbits of the other planets, to make them more useful as slingshots.

The most energy and mass efficient time to interact with Jupiter, will be the points in its orbit when it is traveling directly away from the alien launch point, and directly away from other planets which can be used for gravitational slingshots. Thus the aliens will be launching bursts of payloads only when the stars and planets are correctly aligned.

Soupspoon
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### Re: What-If 0146: "Stop Jupiter"

hamjudo wrote:The aliens can use gravitational slingshot maneuvers around the sun and planets to get the payloads to approach Jupiter from places other than the alien launch point. With 20 moles of payloads, they will shift other planets around. They can either choose to alternate adding and subtracting orbital energy, or they can intentionally change the orbits of the other planets, to make them more useful as slingshots.

...hmmm.

How about using probes on the smaller bodies to adjust those smaller bodies' orbits (quicker than they could with Jupiter) to use them to disrupt larger bodies?

Now, it may well be that the number of probes that could force (say) Pluto to now become a Jupiter-altering body would, if one were to skip the stage of involving Pluto, themselves give a Pluto-sized alteration straight to Jupiter (or an equivalent of trying to adjust enough of the asteroidal material shifted to change dwarf planets enough to shift the smaller rocky planets and moons enough to get the likes of Earth and Venus to shift the lesser gas-giants to eventually affect Jupiter), with the concept of conservation of orbital momentum in each encounter, but maybe some fancy low-cost orbital shift could create a chaotic resonance of the correct type to better milk-and-reasign the respective energies over an extended timescale.

(Just a thought. The maths necessary to is probably a bit involved.)

ps.02
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### Re: What-If 0146: "Stop Jupiter"

So, if the aliens want to crash Jupiter into the sun, I guess they're just interested in catching some cool gravitational waves?

hamjudo wrote:The most energy and mass efficient time to interact with Jupiter, will be the points in its orbit when it is traveling directly away from the alien launch point, and directly away from other planets which can be used for gravitational slingshots. Thus the aliens will be launching bursts of payloads only when the stars and planets are correctly aligned.

Oh, nice. Now I can just see the whole What-If concept moving into astrology.

Soupspoon wrote:Now, it may well be that the number of probes that could force (say) Pluto to now become a Jupiter-altering body would

Is there a new forum rule somewhere about the asymptotic probability over time of Pluto entering any discussion? Though I have to admit this instance is refreshing in that it's about treating Pluto as a ballistic load, not a tired attempt to rhetorically rescue it from a perceived travesty of classification.

Soupspoon
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### Re: What-If 0146: "Stop Jupiter"

ps.02 wrote:So, if the aliens want to crash Jupiter into the sun, I guess they're just interested in catching some cool gravitational waves?

Sheesh, that Zorlax the Mighty... always trying to find new ways to spam the universe!

Soupspoon wrote:Now, it may well be that the number of probes that could force (say) Pluto to now become a Jupiter-altering body would

Is there a new forum rule somewhere about the asymptotic probability over time of Pluto entering any discussion? Though I have to admit this instance is refreshing in that it's about treating Pluto as a ballistic load, not a tired attempt to rhetorically rescue it from a perceived travesty of classification.

Well, it's was a handy example. Pluto (or Eris) coming down from up-system seemed better than sending Ceres from down-system. (Although I'm sure somebody can tell me the delta-Vs necessary to shift Pluto into a Jupiter-like perihelion, rather than Ceres into a Jupiter-like aphelion. - Then you just need to time it right, for the right effect!)

But maybe it's the Godwin's Law of astronomy.

keithl
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### Re: What-If 0146: "Stop Jupiter"

What if we tried more planets?

This will take gigayears and ludicrously precise measurements to arrange.

Stopping Jupiter requires a lot of mass, and there is not nearly enough mass in the solar system and Oort cloud to do it. However, there are a lot of dwarf planets out there, moseying between the stars.

Out of all those dwarf planets, there are likely to be some that can be ever-so-slightly deflected into galactic orbits that intersect ours. Perhaps by deflecting other, smaller planets past them. With an absurdly precise map of all the matter in the Virgo supercluster, we might be able to compute interstellar dwarf planet orbits with enough precision so that flybys of asteroid-sized objects can do the necessary midcourse corrections of the remaining trajectory errors.

For esthetic reasons, we would like to drop Jupiter quickly, so it plunges straight through the inner solar system and splashes into the sun without disturbing earth's orbit too much. So, we have the additional constraint of passing this Jupiter-scale mass of converging objects through the solar system in a fraction of an earth year, without hitting the earth itself.

A few strays might smash Mars and Venus, but after paying to arrange this show, plus an ungodly amount of compounding interest charges accumulating between the setup launches and ticket sales billions of years later, we won't have enough money left over for planetary missions or even astronomy.

Splashing Jupiter into the Sun is likely to trigger some gigantic solar storms, so the good seats will be deep underground. Those tickets, plus the concessions prices for food and drink just prior to the annihilation of the earth-surface biosphere, are likely to be expensive. Start saving now.

Martijngamer
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### Re: What-If 0146: "Stop Jupiter"

SDK wrote:
hamjudo wrote:I still want to know the answer to the original what if question.

Answering that would have been long and boring. He probably just didn't want to dive into the complex math and change the entire content of the article.

New Horizons slowed Jupiter by 10-21 m/s, right? Jupiter is moving at 13.07 km/s. Therefore, you need 1.3x1025 (13 septillion) New Horizons to stop it. Right?

No, you need quite a few more than that. This is all based on how much energy New Horizons is able to take away while it gains that 4000 m/s. But as Jupiter slows (particularly once it gets below 4000 m/s itself), the probes will be extracting less and less... until eventually their own speed would match Jupiter's and nothing much happens (in an absolute sense, at least). To finish it off, you'd need to start in on angles of approach, the probe's initial speed and all that other crap that no one really wants to talk or read about.

Now take your several septillion spacecraft and be happy that he didn't give us more.

Would it work to have one spacecraft (possibly in the form of a tennisball) with the mass of 1.3x1025 New Horizons do a flyby?

dawolf
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### Re: What-If 0146: "Stop Jupiter"

Archgeek wrote:Actually, that looks to say "Penn 15", Penn being a common brand of tennis ball (leastways, here in the states). The 15 of course, is for the ancient schoolyard wangerdoodle joke. See also T-shirts for the Pennsylvania state university class of 2015 -- "The Hardest Class in History".

It's not the first time Randall has used that joke

https://xkcd.com/842/

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### Re: What-If 0146: "Stop Jupiter"

Jeff_UK wrote:
Echo244 wrote:
Jeff_UK wrote:
The situation is similar to the one in the tennis ball analogy from earlier

Am I being thick, what tennis ball analogy is this referring to?

Stopping a truck/lorry with a tennis ball.

ramblinjd wrote:

That's later, not earlier, I think I answered it myself though, I think he's referring to https://what-if.xkcd.com/38/ (Voyager)
Yes, he is, and it's "from earlier" because he links to that in the first note.

TheMasonX wrote:
Soupspoon wrote:Although I wonder if, in the second picture's titletext, Randall meant to write "IPV6"?

I'm almost certain of it. Just to be sure, I even checked the numbers, and samsclass.info/ipv6/exhaustion.htm (spam blocked 'cause I'm new) puts the estimate around then too.

leafar wrote:
Earth weighs almost exactly pi milliJupiters

Am I the only one who read that, went straight to Wolfram Alpha, and was quite amazed at that result?

No, I did that before continuing as well.
It's almost like you people don't still remember that Jupiter is about 318 times the mass of Earth from when you read it in some science book or other when you were young.
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### Re: What-If 0146: "Stop Jupiter"

gmalivuk wrote:
TheMasonX wrote:
leafar wrote:
Earth weighs almost exactly pi milliJupiters

Am I the only one who read that, went straight to Wolfram Alpha, and was quite amazed at that result?

No, I did that before continuing as well.
It's almost like you people don't still remember that Jupiter is about 318 times the mass of Earth from when you read it in some science book or other when you were young.
Curriculums vary. I never had that in school, although my science education was relatively extensive.
Mikeski wrote:A "What If" update is never late. Nor is it early. It is posted precisely when it should be.

patzer's signature wrote:
flicky1991 wrote:I'm being quoted too much!

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### Re: What-If 0146: "Stop Jupiter"

Unless stated otherwise, I do not care whether a statement, by itself, constitutes a persuasive political argument. I care whether it's true.
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Neil_Boekend
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### Re: What-If 0146: "Stop Jupiter"

In that case I don't understand your post.
Mikeski wrote:A "What If" update is never late. Nor is it early. It is posted precisely when it should be.

patzer's signature wrote:
flicky1991 wrote:I'm being quoted too much!

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### Re: What-If 0146: "Stop Jupiter"

Science books exist outside of schools. I read lots of them when I was younger. At least one of them had the 318 figure in it. For some reason that has stuck with me ever since.
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### Re: What-If 0146: "Stop Jupiter"

To add to Earth being pi milliJupiters in mass, a bit of quick (and dirty, so may be wrong!) checking reveals:
The force of gravity at the Sun's surface appears to be pi decaUranuses-worth of gravity;
Saturnian escape velocity is almost exactly pi times that of Earth's;
Neptune orbits at pi times the distance of Saturn;
Eris appears to have an escape velocity that is e deciMarses;
Haumea is likely to have a local gravity of e centiJupiters;
Mars has e deciEarths of surface area;
The Sun is e decaUranuses in radius;
Mercury has a surface area of Phi deciVenuses;
The density of Ceres is Phi times that of Jupiter;
Jupiter rotates once every Phi centi Sun'days';
Saturn rotates Phi times faster than Uranus does; and, interestingly, so does Jupiter to Neptune;
Haumea takes a tenth of Phi Mars'days';
Earth's year is Phi Venusian years (as I'm sure was noted by natural philosophers, of times past);
Root(2) Jovian days is a Mercurial centiday;
Root(2) deciSaturnianEscapeVelocities would only marginally fail to get you off Mars (should you ever be stranded there, for some obscure reason);
Your weight on Venus would be Root(2) decaPlutos, as an equivalent force;
It would probably take Root(2) myriad* Haumea's to equal the mass of Saturn;
Neptune weighs Root(3) decaEarths; Mercury, however, is Root(3) myriadths*[/i] of Jupiter;
Jupiter orbits at Root(3) deciNeptunes from the Sun; (Much harder to justify saying that Eris is at about Root(3)'s Pluto's mean orbit.)

...I'll stop there, I've just rapidly scanned five 'useful' values against 10 properties (or as many as knowable) of 14 solar bodies. Of course I've managed to find 20-odd interesting' relationships (for you to check further!). ...and that's ignoring many other non-unity integer factors of a constant against various SI(/ish)-prefixed relationships.

* In its strictest sense as a the precise multiple (or, for "myriadths", equivalent fraction).

x7eggert
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### Re: What-If 0146: "Stop Jupiter"

hamjudo wrote:I still want to know the answer to the original what if question.

Assume that some alien civilisation wants to cause Jupiter to impact our sun. These distant aliens have developed a mass driver that can launch an insane number of payloads that will reach our solar system with a trajectory such that each one alters Jupiter's orbit just as much as the New Horizons mission did.
(…)

In that case, why not just inject iron into the sun? How much iron does it take to kill a star?

HAL 10000
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### Re: What-If 0146: "Stop Jupiter"

hamjudo wrote:I still want to know the answer to the original what if question.

Assume that some alien civilisation wants to cause Jupiter to impact our sun. These distant aliens have developed a mass driver that can launch an insane number of payloads that will reach our solar system with a trajectory such that each one alters Jupiter's orbit just as much as the New Horizons mission did.

We don't need a justification for a What If, just a scenario. The payloads are entering our solar system from far away. They will have a much higher velocity than an Earth launched payload. Does this mean the scenario is much more plausible, because it uses much less mass?

The answer will vary a lot based on details that haven't been specified. I assume it would take much less energy, and therefore fewer payloads to make Jupiter's orbit so highly elliptical that it impacts the sun with more kinetic energy than if it was "just" a Jupiter mass object dropped into the Sun from the same distance as Jupiter's current position in orbit. Also, it will take less energy if they wait until the Sun becomes a red giant. I am not sure if spreading the operation over a billion years will save any energy. It would make the payload launch rate more plausible. In any case, any answer is good for me, just describe the conditions you use and give answer in terms of quantity of New Horizon equivalents.

Note that the aliens were not influenced by human society at all. Given the distances and velocities involved, the payloads flight time vastly exceeds the length of human civilization.

Believe it or not, something extemremty similar to this happened in Arthur Clarke's book Sunstorm. A gas giant was shot into our Sun to cause a giant sunstorm. I won't discuss further because spoilers, if you want to read it.