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Will Galileo Make Jupiter a Star?

September 14, 2003


Galileo mission logo and link to JPL In October of 1989, NASA launched the Galileo spacecraft toward the planet Jupiter. Its mission was manyfold: to explore the moons of the giant planet, to investigate the environment of Jupiter's neighborhood, and to drop a probe into Jupiter's atmosphere to measure its physical characteristics.

After nearly eight years, Galileo's mission is over. It is out of fuel, and has been hammered by Jupiter's radioactive magnetic field for so long that its hardware is dying. NASA decided that the best thing to do is use the remaining fuel to drop the spacecraft into Jupiter, where it will burn up harmlessly. They feel this is better than letting it continue to orbit the planet, because it might eventually crash into one of the moons. One such moon, Europa, may just possibly have the right conditions for life to evolve, and they don't want Galileo to contaminate the moon, even given the extremely long odds of it happening. Galileo will plunge into Jupiter on September 21, 2003, around 20:00 hours Greenwich time.

But some people think that NASA had more plans for Galileo. They claim that NASA's nefarious scheme was to drop Galileo into Jupiter and use it to ignite Jupiter like a fusion bomb, either turning it into a star like the Sun, or simply blowing it to smithereens.

Can this be true? Could NASA accomplish such a dastardly plot?

As always, the short answer to this is to look at the title bar of your browser and read the name of this website. To save you time, I'll just say it here: no, Galileo will not do anything to Jupiter. Like a meteor, it'll burn up in the dense atmosphere, and become a part of the solar system's largest planet.

Yet the idea that Jupiter may explode is spreading across the web, sticking in this case (unlike the Moon Hoax or Planet X) mostly to the woowoo sites. So what are the main ideas behind it, and why are they wrong?

There are several ideas put forth, and they are wrong for lots of reasons. They sound legitimate, as many pseudoscientific ideas do, but that's different than actually being right. Let's take a look.

Here are the claims made by the alarmists:

  1. Galileo has plutonium onboard. This is what makes fission bombs! NASA plans on creating a fission bomb using Galileo.

  2. Fusion bombs are made by using fission bombs as triggers. The implosion caused by a fission bomb ignites hydrogen into fusion, generating a much bigger blast. Jupiter is made of mostly hydrogen! So it can be blown up like an H-bomb.

  3. Stars work by fusing hydrogen. Jupiter might turn into a star, or it might simply blow up like a bomb.

Got all that? OK, point-by-point, let's see why it's all wrong.


1) Galileo has plutonium onboard. This is what makes fission bombs! NASA plans on creating a fission bomb using Galileo.

Galileo does indeed have plutonium (Pu) onboard. The instruments onboard need power, and Jupiter is too far from the Sun to use solar power very well. The solar panels would need to be very large, too large and heavy to get to Jupiter.

Instead, Galileo uses a tried-and-true technology: radioisotope thermoelectric generators (RTGs). Basically, these are extremely simple devices: inside an RTG is a pellet of radioactive material. As the material decays, it generates heat. The heat is converted to electricity, which powers the spacecraft.

Galileo's RTGs use plutonium in the form of ceramic pellets of plutonium dioxide. There is about 50 pounds of Pu onboard, stored in 144 separate cylindrical pellets. There are two RTGs on Galileo, each with 72 pellets (a paper about RTGs with a diagram can be found at NASA's Space Science website). Note: I am not going to get into a discussion over whether RTGs are safe, and the dangers or lack thereof posed by launching radioactive materials into space. Please read Spaceviews' page on RTGs for more info, and their list of pro and anti RTG sites as well.


Drop da bomb on da pseudoscientists! But can the plutonium on Galileo explode like a bomb? No, it can't. That's because it's the wrong kind of plutonium. Like all elements, Pu has different isotopes. This means that in the nucleus of the atom, there are different numbers of neutrons. All plutonium atoms have 94 protons, but some of these atoms might have 144 neutrons, or 145. These isotopes are designated by the total number of protons plus neutrons. Plutonium 239, for example, has 94 protons and 145 neutrons.

These isotopes have different properties. The atomic nucleus of Pu239, for example, will split when hit by a neutron. This releases a lot of energy, as well as more neutrons. These hit other Pu239 atoms, which split, generating more neutrons, etc. This is called a chain reaction, and if there is enough Pu239 you get a runaway process, which is what powers an atomic (fission) bomb.

However, not all isotopes of Pu do this. Pu238, for example, won't. Although it can split, the products of this fission (called the daughters of the fission) just don't have the right characteristics to create a chain reaction, let alone a runaway process. In other words, the Pu238 aboard Galileo is simply not capable of exploding like a bomb.

Now, J.C. Goliathan, one of the main proponents of this "Jupiter ignition" idea, says that Pu238 can turn into Pu239, and that there is now Pu239 on Galileo. However, he does this without the benefit of such things as facts, truth, any idea what he is talking about, etc. He says:

Of course, Pu-239 is very fissile and capable of a sustained reaction. In fact, it is the key component of most nuclear bombs. Since Galileo was launched in 1989, we know that its Pu-238 will have been sitting in the RTG reactors for at least 15 years by September 2003, maybe longer if the fuel cells were created beforehand. In an analysis of whether the fuel cylinders contain fissionable as well as fissile elements, we have to conclude that it is very possible.

Why should we conclude that? Because Goliathan says so? He is quite wrong. He quotes this website, which says that Pu238 can become Pu239 through neutron capture. However, I have not found one single credible source that corroborates this statement. In fact, that website appears to be a personal site, not something from, say, experts in the field of radioactivity. Of course, what I am writing is on a personal site, but I have links to good sources (see the bottom of this page for those links).

Even if Pu238 could catch a neutron and become Pu239, where would the neutrons come from? He seems to think that since Jupiter's environment is radioactive, there are neutrons there. However, again, this is wrong.


Jupiter's Magnetic Field, click to read more Jupiter's intense magnetic field has trapped particles from the solar wind (and perhaps Io's volcanoes). These particles are accelerated to very high speeds/energies by the magnetic field. This is the "radiation" talked about.

However, this radiation has to be charged particles. Only charged particles are accelerated by magnetic fields. In other words, neutrons, which are neutral, need not apply. So the basis of the claim that somehow Pu 238 will go to Pu 239 is already wrong because there doesn't seem to be any mechanism for it to happen, but it's also wrong because there aren't any neutrons out there to do it. So there is no way that the RTGs onboard Galileo have Pu239 on them, and no way to explode.

Oh, one more thing before moving on. In the quote above, Goliathan calls the RTGs "reactors". They are not reactors. They are simply containers holding a radioactive material, which is slowly decaying and producing heat. Calling the RTGs reactors is like calling your fireplace a reactor. It's a word meant to push buttons. It's also sleight of hand: he says that Pu 239 can be created in reactors, so he uses that word to describe RTGs. That's more than misleading. It's at best a very careless use of language.

Conclusion: The plutonium on Galileo cannot fission to become a bomb.


2) Fusion bombs are made by using fission bombs as triggers. The implosion caused by a fission bomb ignites hydrogen into fusion, generating a much bigger blast.

A hydrogen bomb explodes because atomic nuclei of hydrogen are squeezed together. If squeezed hard enough, the atomic nuclei fuse (stick together), and that releases energy. You have to apply a lot of pressure and heat to get the hydrogen to do this, and one way to do that is to use the blast wave from a fission bomb.

Basically, a fission bomb is used to trigger a process which creates the hydrogen fuel for the fusion reaction (more on this in a moment). The shock wave and heat from the fission explosion must work in a very specific way to do this. When it works, the fusion releases far more energy than a fission explosion, which is why H-bombs have so much more explosive yield than A-bombs.

And hey, isn't Jupiter mostly hydrogen? Yikes, a fission explosion can make Jupiter explode like a bomb!

No, it can't, and for two reasons. Well, three if you include the fact that the Pu238 on Galileo can't explode. But even if it could, (let's say NASA has been lying, and put Pu239 on board), it wouldn't make Jupiter detonate, because the RTGs aren't configured to be used as a fission trigger, and because Jupiter doesn't have the right stuff in it to fuse.

While Jupiter is mostly hydrogen, it's the wrong kind. Remember isotopes; atoms with different number of neutrons? Hydrogen has them too. A hydrogen nucleus at its simplest is just a lone proton. Deuterium (D2) is hydrogen with a neutron and a proton, and tritium (T3) is a proton with two neutrons. Fusion bombs need the neutron-added isotopes. Regular old hydrogen won't do it. Simply taking a sample of hydrogen gas and compressing it won't make it fuse; you need a fuel enriched with D2 and T3. Finding these materials isn't all that easy, and a randomly selected pocket of Jupiter's gas is unlikely in the extreme to have them in sufficient quantities to explode.

What's worse, the way we make bombs these days, you need lithium to make them work, and that's not terribly common in Jupiter either. Here's how a fusion bomb works. You need a fission explosion to start with, which is used to do two things: it generates X-rays, which heat and compress the fusion fuel, and it actually helps create the fuel. As I have discovered while researching this article, the process is somewhat complicated. In a very brief nutshell, the fission explosion is used to irradiate lithium. Neutrons from the fission explosion combine with the lithium to create tritium. The heat and pressure from the X-rays compress the tritium, and bang!

Again, this sequence of events is highly unlikely to occur on Jupiter. You need lots of lithium, which is not terribly abundant. You need it to make tritium, which is highly unstable (it doesn't last long once created) and again unlikely in the extreme to be found in Jupiter's atmosphere. It's really just plain old silly to think this could happen with Galileo, even if it had the right kind of fission material. Which it doesn't.

This doesn't stop Goliathan from speculating wildly, though. He says:

However, conventional belief says that Deuterium and Tritium (isotopes of Hydrogen) are necessary to accomplish fusion. Both may be present or created during a reaction within the dense liquid hydrogen of Jupiter.

Again, he doesn't state how this might happen. I am not an expert on such things, and won't speculate, but it seems unlikely that Jupiter can create these elements, given that it takes nuclear reactions to do it (specifically, a proton has to absorb an electron and an anti-neutrino to become a neutron). Jupiter isn't big enough to do it.

The other reason this won't work is that the fission trigger explosion has to be set up in such a way that the sequence of events described above works in a very specific manner. On Galileo, it simply won't work that way. The RTGs extend along a long boom, a rod that extends out from the main body of the spacecraft, and not in a way that works as a fission trigger. The geometry is all wrong.

The doomcriers at YOWUSA makes a big deal of how Pu is used in a bomb, and even show the geometry of a fission-induced fusion bomb (here, for example). But that's not how the RTGs are constructed! Posting that image is grossly misleading. The RTGs are not in anything like the geometry of a fission bomb. This is more obfuscation on the part of the doomsayers. Also, the YOWUSA folks, when quoting Goliathan, appear to think that somehow the pressure from the passage of Galileo through Jupiter's atmosphere will compress the plutonium enough to start a chain reaction, which will then trigger fusion. But the fission has to happen with precise timing, and in a certain geometry. How do they propose that will happen, exactly, with Galileo tumbling down into Jupiter, parts of it flying off due to the heat and pressure of supersonic atmospheric entry? They somehow conveniently left that part off of their description.

Even if you supplied a fission bomb, you won't get hydrogen (tritium) to fuse. And Galileo doesn't have what it takes to make a fission explosion.


3) Stars work by fusing hydrogen. Jupiter might turn into a star, or it might simply blow up like a bomb.

OK, so we don't have fission, and we don't have fusion. So let's suppose, contrary to all evidence, that NASA is really lying to us, and has put fission bombs and fusion fuel aboard Galileo. When they go off, will Jupiter explode, or turn into a star?

Nope, and nope. Fusion is not a runaway process. Once you start it up, it generates a lot of heat, which tends to expand the material violently (this is what we technically call a bomb). This means the fuel gets scattered, and it won't fuse. Making really big hydrogen bombs run into this problem, making it hard to make really big bombs, which in my book is perhaps a good thing.

So the process tends to damp itself off. Jupiter won't explode. It won't turn into a star, either. Stars work by maintaining fusion in their cores. Now, I just said fusion isn't self-sustaining, so how do stars keep it going? They do it by containing the hydrogen in a small volume. This is accomplished by piling a lot of mass on top of the hydrogen: the mass of the star.

The star has enough gravity that all that mass squeezes and heats the core enough for fusion to not only take place, but to continue at a relatively stable pace. But it turns out there is a lower limit to that mass; if you don't have enough, then you don't get the high temperatures and pressures necessary to ignite fusion. That mass is about 0.077 times the mass of the Sun, or 80 times Jupiter's mass. In other words, Jupiter is 1/80th the mass it needs to turn into a star. Some people call Jupiter a failed star, but in reality it ain't even close.

Conclusion: Jupiter won't explode, or turn into a star, because it lacks the containment to keep fusion going.


There's more, of course. Goliathan, in his article, makes lots of statements as if they are facts, but are actually wrong. For example, it might be relevant to ask why NASA doesn't simply boost Galileo out of the Jupiter system and into space, rather than smack it into Jupiter. Goliathan takes that farther:

Some argue that the craft is caught in Jupiter's pull now, but with all of the gravity assist tricks available, and still some propellant left, the craft should be able to break free even if they had to use an assist of one of the larger moons.

Here he shows a profound ignorance of the situation. Jupiter's gravity is immense. Escape velocity is quite high, nearly 6 times (*) that of Earth's! If Galileo had enough fuel to escape from Jupiter, then we wouldn't have needed to use gravity assists from Venus and twice with Earth. As an example, the propellant used to get to Jupiter needed to change Galileo's velocity by about 15 kilometers/second (the difference between the Earth's orbital speed and Jupiter's). The rocket could not provide that on its own, so we needed help from the gravity of Venus and Earth. But, to escape Jupiter from, say, the distance of Europa, Galileo needs to add 6 km/s to its velocity, a healthy chunk of what it needed to get to Jupiter in the first place. Closer in to Jupiter the situation is even worse, making it virtually impossible to leave the Jupiter system once Galileo got there.

If I have time I will add to this article over the next few days, but I think I've made it pretty clear that this idea that Galileo will somehow cause a nuclear explosion on Jupiter is wrong. Remember, if you hear something on the web about how some astronomical event may cause doomsday here on Earth, read it with a very skeptical eye. And check Bad Astronomy before you start putting your affairs in order!


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