Main sequence stars by definition burn hydrogen. The catch with the brightest of the Os and Bs is just that they don’t stay on the main sequence very long.
No. Jupiter is a lot smaller than the Sun, & further away from us than the Sun is.
What some people don’t understand is that it’s most likely not a matter of simply “igniting” Jupiter. It’s probably a direct function of mass-induced pressure. Earth is massive enough to have uranium fusion at its core; Jove is massive enough it might have some fusion at its core, but not enough energy output for its upper atmosphere to glow in the visible-light range. Sol is massive enough to become hot enough to have white-hot plasma in its upper atmosphere!
Or something.
Are you talking about the irrational hysteria surrounding the Galileo probe being deorbited in to Jupiter back in 2003, or have the nutters come up with a new outlandish doomsday theory?
Uranium fusion? I don’t think that’s right. Any radioactive heating inside the Earth is a result of the decay of unstable elements that have been there since its formation. I’m pretty sure Jupiter isn’t massive enough for any kind of fusion either.
(There were some naturally occurring fission reactors on Earth a couple billion years ago, but that’s not really relevant to the current topic.)
I think you mean elements inside Earth such as uranium produce heat through radioactive decay. There’s no fusion occuring naturally on Earth. I don’t think uranium fusion is occuring naturally anywhere.
Is uranium fusion not theoretically happening in supernovae? I thought that’s where transuranic elements come from.
No, that Star was named Jones. 
(running and ducking)
Yes, that slipped my mind. But as far as the main sequence goes…
Yes, but the OP talked about “igniting” Jupiter. Jupiter can’t ignite in the sense of burning something with oxygen, because Jupiter only has a trace of oxygen. Stars are sometimes said to “ignite” when they start nuclear fusion of some sort. Jupiter can’t ignite that way because it doesn’t have enough mass to sustain fusion at its core. The minimum mass for igniting deuterium fusion is about 13 times the mass of Jupiter, and the minimum mass for igniting hydrogen fusion is higher than that.
Another thread that may be of interest: Real science Q? about an Arthur C. Clarke plot point - In My Humble Opinion - Straight Dope Message Board
Since we’re engaging in fun speculation, what would the effects be from a 5% increase in light / heat from the sun? I can’t help but feel that this would be pretty devastating to us, given our fairly narrow temperature comfort zone, but I’m not really sure.
This gets into climate modeling, which is complex and well outside my area of expertise.
This would be even more complicated than calculating what would happen if the Sun got 5% brighter or something happened to Earth’s climate that was the equivalent of 5% more sunlight, too, because the day/night cycles would be different in this case.
Wikipedia says that the light of the Sun at Saturn is slightly brighter than the light of a sunrise or sunset on Earth. The second (or third, if you like) sun that we magically replaced Jupiter with is going to be brighter than that, because it will be closer (4-6 AU as opposed to 9.5 AU for Saturn’s distance from the Sun).
We’ll pretend that this second sun orbits the Sun in the same orbit that Jupiter does, and that its gravity doesn’t affect our Sun. Its gravity would, of course, affect the Sun, and might even eject some planets from the solar system, but we’ll pretend it wouldn’t (because the three-body problem is too hard to calculate). We’ll also ignore any effects that moving a star the size of the Sun into the solar system would have on the planets.
We wouldn’t have fully dark nights except when the second sun and the Sun were close together in the sky as seen from Earth. At other times, which is going to be most of the year, we’d have something like the White Nights that St. Petersburg, Russia has near the summer solstice, but all over the world. It wouldn’t necessarily be partially light all night all the time, but it would be partially light for part of the night through most of the year.
Today in Pittsburgh, for example, Jupiter is rising at 2:53 AM and setting at 1:20 PM. If Jupiter were a second sun, we’d have had a very long morning twilight today.
I’ll predict that people’s and animals’ circadian rhythms would get really screwed up. Maybe the aliens that did this had invested in a company that makes blackout curtains?
You still won’t actually get uranium fusing. Any trace transuranics that you got this way would come from things lighter than uranium, but heavier than half of uranium, fusing. Practically, though, to the extent that transuranics occur naturally at all, they mostly come from beta decay of uranium.
Yeah, I hear it’s full of stars.
Depends on what you mean by “in” a supernova. During a supernova explosion, uranium (and all elements heavier than Iron) are produced. I think it’s fusing from the blast forces but it’s not a sustained chain reaction of fusion.
Leading up to going supernova, they are not being produced.
Transuranics happen later, iirc, as the uranium decays or is bombarded by curious graduate students.
the OSCARS?
Argh. I meant uranium (or plutonium) fission, which is a minority viewpoint but more in line with current thinking than heavy-metal fusion. Typo. Which led to some interesting discussion. But typo.
Can you go into more detail? I am trying to figure out what you’re referring to, but I don’t have the context or something. Are you saying that a minority of scientists think earth’s mass pressing on uranium caused it to fission? Or that (a minority of scientists believe) earth’s core itself is uranium?
I think it’s a minority of one. One Dr Herndon contends that Earth’s magnetic field is generated by fission.
http://www.sfgate.com/cgi-bin/article.cgi?f=/c/a/2004/11/29/MNGPIA17BL45.DTL
But I find the theory slightly more plausible than, “the Earth is a giant dynamo.”
Was that supposed to say “slightly less plausible”? Because so far as I know, the dynamo model for the Earth’s magnetic field is pretty much undisputed.