if jupiter gained enough mass to trigger fusion and ignite into a star...

mesamunefire , 4 days ago

Go on universe simulator and find out.

fossphi , 4 days ago

You mean the outside/real life?

Bishma , 4 days ago

If memory serves, 2010 ignited Jupiter by crashing Saturn into it. But you’d actually need about 250 Saturns (or 85 Jupiters) worth of hydrogen to get the job done. A lot of the moons would be within that new super gas giant’s roche limit even before fusion began.

JohnDClay , 4 days ago

It’d need to be 13 to 80 times more massive to be a brown dwarf.

en.m.wikipedia.org/wiki/Brown_dwarf

If it gained mass rapidly, most all the moons would likely destabilize since they’d have way too little velocity for the orbit they’d now be in. But if they sped up to accommodate, it’d depend on the density change of Jupiter. The fusion would push out material a bit, but the density would probably just increase because of the increased mass.

But if the density stayed the same, the radius would be 2.4 to 4.3 times larger than currently. With Jupiter having a radius of 70,000 km, that’d put it at 170,000 to 300,000 km radius. That’d put Metis and Adrastea inside 170, and Amalthea and Thebe inside 300. They’d already be heavily inside the jovian atmosphere, so they’d be toast. Io, Europa, and maybe others might also fall due to higher atmospheric drag at those levels.

en.m.wikipedia.org/wiki/Moons_of_Jupiter

I think the rest of the moons would be planets then, and the solar system would be a binary system.

RightHandOfIkaros , 4 days ago

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.

SorteKanin , 4 days ago

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.

Apollo42 , 4 days ago

The moons would almost certainly fall into Jupiter or be thrown from its orbit if itsuddenly gained enough mass to become a star.

SorteKanin , 4 days ago

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

Apollo42 , 3 days ago

I mean if we’re talking magic now, then all bets are off haha

SorteKanin , 3 days ago

Not sure how else you would increase Jupiter’s mass that much :P

Apollo42 , 3 days ago

We feed it everything else in the system except for the sun and hope it is appeased for another cycle :)

SzethFriendOfNimi , 4 days ago

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.

Skua , 4 days ago (edited 4 days ago)

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

Davel23 , 4 days ago

For the four remaining do you know if they'd be clear of the Roche Limit?

Skua , 4 days ago

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

Rhaedas , 4 days ago

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.

Skua , 4 days ago

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.

loaExMachina , 4 days ago (edited 4 days ago)

Four of them, the galilean moons would be. The others would be dwarf planets [EDIT not all moons, many would be asteroids].

fuzzy_feeling , 4 days ago

sad pluto noises

loaExMachina , 4 days ago

One must imagine Pluto happy.

MelodiousFunk , 4 days ago (edited 4 days ago)

At least as happy as Ceres. People non-nerds still remember Pluto.

gedaliyah , 4 days ago

I don’t think they would be dwarf planets, but something else.

The International Astronomical Union (IAU) defined in August 2006 that, in the Solar System, a planet is a celestial body that:

1 is in orbit around the Sun, 2 has sufficient mass to assume hydrostatic equilibrium (a nearly round shape), and 3 has “cleared the neighbourhood” around its orbit.

A dwarf planet must meet 1 & 2. Are Jupiter’s smaller moons round?

Jupiter has rings, so any planet would have to have cleared the rings around their orbit. I think that applies to the Galilean moons. Juno orbits outside the solar plane, so I’m not sure if that is a rule for a planet or not.

KillingAndKindess , 4 days ago

From Wikipedia

Of Jupiter’s moons, eight are regular satellites with prograd and nearly circular orbits that are not greatly inclined with respect to Jupiter’s equatorial plane. The Galilean satellites are nearly spherical in shape due to their planetary mass, and are just massive enough that they would be considered major planets if they were in direct orbit around the Sun.

loaExMachina , 4 days ago

The largest ring of Jupiter is just about 129 000 km of radius. The nearest Galilean moon to jupiter has a semi-major axis of 421 800 km, so the rings aren’t in any of their orbital neighborhoods.

Beside, the largest of them, Ganymede, is more massive than Mercury.

But you’re right that not all the moons would be either planets or dwarf planets, many would be asteroids.