if jupiter gained enough mass to trigger fusion and ignite into a star...
if jupiter gained enough mass to trigger fusion and ignite into a star...
a'la 2010, would any moons that survive then be considered 'planets' ?
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Im pretty sure none of Jupiters moons would survive. But I suppose if they did perhaps they would change classification from moon to planet, but I think planet classification now also depends on size, so depending on size they still may not qualify. I don't know if any of Jupiter's moons are larger thaan Pluto, Ceres, etc.
The IAU's list of requirements to be a planet is:
- Orbit a star
- Be big enough that it becomes round
- Clear the neighbourhood (meaning you're way bigger than anything else in your orbit)
The last one is the one that disqualifies Pluto. For comparison, Pluto is roughly 8% of the mass of the other stuff in its orbit (not including Neptune, given that their orbits cross), whereas Neptune is thousands of times more than the rest of its orbit. The closest non-planet to meeting this criterion is Ceres, which is roughly one third of the rest of its orbit (in the asteroid belt).
Based on this list, I think Jupiter's four biggest moons (Io, Europa, Ganymede, and Callisto) would make the cut.
Why wouldn't they survive? I think even if Jupiter gained enough mass to start fusion, it would not become significantly larger. It would just become more dense.
The moons would almost certainly fall into Jupiter or be thrown from its orbit if itsuddenly gained enough mass to become a star.
I assumed in this scenario that orbits would be left unchanged aside from orbital velocity - if we can magic Jupiter much bigger, we can magic the orbits too :P
I mean if we're talking magic now, then all bets are off haha
Not sure how else you would increase Jupiter's mass that much :P
We feed it everything else in the system except for the sun and hope it is appeased for another cycle :)
The sun and Jupiter are pretty close in terms of density, and Jupiter would need to get at least an order of magnitude heavier to start fusion. I think it's just a coincidence that the outward pressure of the sun's fusion makes these numbers roughly line up.
Thirteen Jupiters seems to be a commonly-given lower limit for fusion, so let's go with that. To increase mass by thirteen times while maintaining density (and assuming the whole thing is a perfect sphere, which it obviously isn't), Jupiter needs to increase its radius by a factor of about 2.35. This increases its equatorial radius to about 168,000 km, which does swallow up the three innermost moons, but leaves the four big ones alone
For the four remaining do you know if they'd be clear of the Roche Limit?
Oh, good call, I didn't think of that! Assuming I did my sums right, the Roche limit probably destroys the fourth innermost moon, but it still leaves the big four (which are the fifth through to ninth in ascending order of size of orbit). They're quite substantially farther out than the prior four
There are also like eighty smaller moons even farther out, but they don't meet the roundness criterion to be a planet because they are too small
They’re in an orbit that works with jupiters current mass. If Jupiter gained enough mass to trigger fusion then I would think that many of them would with fall in or be slung out of orbit.
I’d be interested to see if anybody has done the math though to see how that would all play out.
Aside from the orbit change mentioned, the huge increase in stellar radiation would certainly blow much of the lighter elements including water away. The core and some residuals that might remain on the far sides would be all that's left.