|MadSci Network: Astronomy|
Nope, not true. But there is a grain of truth there, since Jupiter is sometimes called a "failed star". Jupiter has essentially the same composition as the sun (90% hydrogen and 10% helium), and in principle has plenty of fuel for nuclear fusion (hydrogen converted into helium). However, the fusion processes require very high temperatures, which require immense pressures, which require a very strong gravitational field. Jupiter simply doesn't have the gravity which is required to permit fusion. It would have to be about 100 times as massive (the Sun is 1000 times as massive as Jupiter). Now, if by some feat of magical technology, someone "squeezed" Jupiter, this could increase the central pressure and temperature to the point where fusion would ignite. However, the moment that external pressure was relaxed, the internal pressure would expand Jupiter outward, relieving the pressure, and "stopping the fire". (We have the same problem in our laboratory fusion reactors -- once we get the fire going, it's impossible to contain, so far; we're trying to use fancy magnetic fields to provide the containment.) So no, Jupiter could not be coaxed into becoming a star without continual outside intervention on a preposterous scale. Good question! -Aaron p.s. Jupiter and the other giant planets are actually emitting more energy than they receive from the Sun (by a factor of about two). This is because they are in the final stages of their gravitational collapse from a less dense ball of gas to a denser ball of gas (with metallic hydrogen at the center). As I said, this kind of contraction will increase temperature and give off heat, but in the case of Jupiter, it will never get hot enough for nuclear reactions, and the planet simply settles down and cools off over billions of years. The Earth was similarly hot in its youth, but would have lost its internal heat long ago, were it not for another source of heat. This is the radioactive decay of unstable elements, which keep the Earth's interior hot and partly molten, driving continental drift. These elements were produced in supernova explosions billions of years ago (but that's another story).
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