Oh, I don’t know. If Jupiter were composed of one part propane gas and 14 parts Earth air, I think one lit match could set it off. 
Of course a natural meteor strike would have done that long before we showed up.
Has everyone forgotten about Comet Shoemaker-Levy so soon? It isn’t every day that we watch dinosaur killers slam into a planet.
No, I didn’t forget Shoemaker-Levy 9. In fact, I mentioned in in a similar GQ thread which was already linked to in this thread. But, I’d bet money that Jupiter has suffered hits MUCH larger before humans ever evolved.
Absolutely. Jupiter’s sweeping up debris and taking impacts in the early days of the solar system is one of the reasons that life has managed to thrive here.
Forget about? Hell, it’s mentioned in the OP! How the hell can anyone watch a two-kilometer rock slam into Jupiter and go on to think that an itty-bitty NASA probe is somehow going to do more damage?
Right.
Far be it from me to inject some numbers into the discussion, but I’m feeling a bit randy tonight… No doubt I screwed this up somewhere, but no doubt someone will tell me. 
And since my computer crashed taking my notes with it, I have that as an excuse…
Start with the solar abundance of plutonium 4.5 billion years ago: The numbers I found give a Pu244/U238 ratio of 0.005, a U238/10^6 Si of 0.015 and H1/10^6 Si of 3E10. Put 'em together and you get something like 2.5E-15 for Pu244/H1 4.5 billion years ago. However, you get to multiply that ratio by 244 since we want the mass ratio of 244Pu to 1H-> 6E-13 or so.
Jupiter’s mass is about 2E30 grams. Assume it’s all hydrogen (yes, I know). That gives an initial amount of about 1E18 grams of Pu244, which is a lot more than I was expecting. The half-life of that isotope of Pu244 is 80 Myr, so we’ve had 56.25 half-lives since the beginning and our Pu has decayed to a fraction about 1e-17 of its initial amount: 10 grams total. If we go back a billion years, though, there’s still a relatively whopping 68 kg of initial plutonium 244 spread around Jupiter.
The late Galileo spacecraft was carrying about 7.5 kg of plutonium. It was a different isotope than the one discussed above, with a shorter half-life (80 years instead of 80 Myr). Within 1000 years, there will be less than 1 gram of that isotope left on the whole planet (barring additional spacecraft plunges), while there will still be 10 grams of Pu244 left from the formation of the planet. For the vast majority of Jupiter’s history, the amount of plutonium already present on the planet was much larger than the amount that we just added, and in a very very short time geologically speaking, it will be again. The only real danger to any putative jovian life is would be if it got conked on the head by debris…
ps: hi, Podkayne!
Grey, I’m claiming your quote
as my new sig line.
I find all these numbers pretty funny, actually. That’s because they don’t matter! Here’s why:
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The plutonium on board is Pu 238, and cannot fission like a bomb.
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Even if it could, there is not a critical mass on board Galileo.
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Even if there were a critical mass, it’s in the wrong configuration to produce a fission explosion.
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Even if it were in the right configuration, it would get blown apart by the pressure from entry into the atmosphere, and melt away the components to boot.
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Even if it held together, you need to have a fusion source, and plain old hydrogen won’t do it.
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Even if you had the right kind of hydrogen, it would have to be placed just so to fuse. See (4) above.
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Even if you got a fusion detonation, you wouldn’t get a runaway reaction because fusion isn’t self sustaining. You need containment to do that, and there isn’t any in this case.
I could assign some made-up probabilities to all these, but it isn’t necessary. That’s because the probability at any step of the way is zero. Zero. As in, like, zero.
What evidence do I have, you might ask? Go outside, say, an hour before sunup. See that “star” in the southeast? That’s Jupiter. Note that it is roughly the same brightness it was yesterday, and the day before, and even the day before Galileo went in.
My cite is therefore the sky itself, and the evidentiary process of looking up. I wrote the above list in present tense, but it should have been in the past tense. Galileo went in, and nothing happened.
I never do this, but this is The Pit, so what the heck:
I was right, and the cranks were wrong. NYAH NYAH NYAH!
Wow. I feel better. I should have done that years ago.
But how do you all know that Professor Seyetik didn’t stow away on that probe, despondent over the telekinetic projections of his wife that were getting it on with the commander, in order to light the planet into a star himself?
[sub]if you don’t get it, trust me you’re not missing much, it’s 6:40 AM and I haven’t slept.[/sub]
Enjoy!
As opposed to Europa, which has no substantial atmosphere, Jupiter has an extremely thick one.
Pieces of the Galileo spacecraft would have survived an impact on the surface of Europa, with the potential to spread contamination.
It was instead totally and completely vaporized when it screamed into Jupiter’s dense atmosphere at about 55 miles per second.
No more bugs – no more chance of contamination.
Hope that answers your question.
Knew that. (Well, I didn’t actually have the rate memorized.) Not sure what your point is here.
True Blue Jack
Points aren’t really aryk29 speciality.
It is clear that we should have crashed Galileo into Europa, along with some serious nuclear weapons. The whales need air holes to breathe! Won’t someone think of the whales!
Kinda nitpicky, but I don’t think that you understand state changes quite well enough. Though “pressure equals heat” is a good shorthand way to think of some phenomena, it doesn’t work here.
Consider the pressure cooker. It cooks faster than boiling because it is able to heat liquid water beyond it’s boiling point. It does this by putting the water under pressure. For water to boil the vapor pressure within the liquid (produced by the heat) has to exceed the ambient air pressure. This is also why we have to cook things longer at higher altitudes. The pressure is lower and the water boils at a lower temp.
My point here is that there probably is some liquid water in Jupiter. I’d bet that at some point in the atmosphere you’d have a temp/pressure combo that would allow liquid water. No oceans, of course. Think of it as humidity on earth. Humidity isn’t steam - it’s liquid water dissolved in a gas.
To adress a different point. Aryk, yes, I suppose it is conceivable that Jupiter has some form of life that is completely alien to our earth-bound conceptions of life. However, it would be just that - alien. So alien that the possibility of forward contamination would be zero because the hitchiking bacteria from Earth could not survive in that highly alien environment. Unlike europa, which could possibly sustain earth-type life.
Monkey: Thanks for the correction!