Is Jupiter a proto star?

I guess the thread title says it all. I just read about the planet in Encyclopædia Britannica and while it contains much information, this part isn’t mentioned. In many ways, Jupiter and its moons is like a small solar system. One moon is even bigger than Mercury. So is Jupiter a planet that could have been a star?

Jupiter would have to be about 80 times the size it is to ignite fusion. Does that count? I’d say no, unless you’re going to claim any gas giant could have been a star.

As Andrew said it would of needed to accrete a considerably greater amount of mass to ignite. In some ways you could look on Jupiter as a proto-satr that failed to reach the requisite mass.

Here is a (somewhat) related thread from not to long ago.

I agree…doesn’t count. Not even close really.

The roughly lower limit on a Brown Dwarf (which might be said to be a failed star) is 13x the mass of Jupiter. At that point the Brown Dwarf ‘glows’ an eensy bit. As you said, for full scale fusion and a star to be a ‘star’ the mass is around 84x the mass of Jupiter. For comparison our star is about 1,000x the mass of Jupiter.

Well, that’s why I called it proto-star. According to EB, it emmits twice the amount of energy, it receives from the sun. To phrase my question in another way: Had Jupiter acquired 13x or 84x the mass it did, could our solar system have been a double star? Or in yet another way - Is Jupiter’s composition the same as that of a star, only smaller?

IANAA, but I would assume that Jupiter formed from the same material as the Sun. Had it not been for the bigger blob in this part of the nebula hogging all the juice, Jupiter very well could have become a star. So, sure, if it was a lot bigger, Jupiter would be a star, and the solar system would be a lot different.

A “protostar” is a young star, an object that will evolve into a star on its own. Jupiter isn’t one. But the only difference is mass; the composition is basically the same and not very important for a star. As long as you have some hydrogen and a lot of mass to compress the hydrogen, you’ve got a star.

However, if Jupiter had such a large mass, it would influence the orbits of other planets. I haven’t done any calculations but it may be that if Jupiter had been a star, Earth wouldn’t be here now.

I have no idea how earth would have fared had Jupiter become a star but I have heard it mentioned that Jupiter (as it is) was a big help in allowing life to evolve on earth. Essentially Jupiter acted like a big sweeper clearing our solar system of comets and asteroids. By sucking in a goodly portion of these items it meant that earth was much less likely to get bombarded by asteroids and such which allowed the time necessary to let life get a foothold without being smashed. (Of course the earth still gets hit on occasion but the frequency is, supposedly, far less due to Jupiter).