“All these worlds are yours — except Europa. Attempt no landing there.” The famous quote, which some people can even quote from memory, comes from Arthur C. Clarke’s book 2010: Odyssey Two.
For those who aren’t familiar with the plot, the monolith aliens use stellar engineering to turn Jupiter into a second sun. Europa is off limits because it has life that can evolve intelligence.
Jupiter is a freakishly large planet. It’s larger than the smallest known main-sequence star in the Milky Way (ELBM J0555–57Ab).
So, why isn’t Jupiter a second sun?
The Simple Answer
It’s actually pretty simple. Although Jupiter’s diameter is larger than ELBM J055–57Ab (can somebody name that thing so I don’t have to keep typing that), it’s a lot less dense, and thus a lot lighter.
ELBM J055–57Ab has 85 times the mass of Jupiter, which appears to be about the minimum to allow the fusion of hydrogen into helium and thus turn your celestial body into a star.
So, Jupiter’s just not massive enough to ignite and thus stays a gas giant.
Does This Make Jupiter a Failed Star?
Jupiter is sometimes called a failed star, because it has a very similar composition to the sun, but its core never ignited. This isn’t accurate, though.
Stars and planets form in very different ways.
Stars are formed in interstellar clouds. A knot of matter gets denser, attracts more matter and then collapses in on itself. This causes the core to ignite. As the star forms, a large accretion disc remains around it.
Over time, gravity causes this disc to become lumpy and clumpy, and the lumps eventually form into planets.
True failed stars, brown dwarves, start at about 13 times the mass of Jupiter, and fuse deuterium, not hydrogen. They kind of glow dimly instead of properly shining. And sometimes a star will start to form and not even get there, but just sit there looking like a very lonely gas giant.
We know Jupiter isn’t a failed star because it has a rocky core somewhere in all of that gas.
Could Jupiter Become a Star?
So, back to our monolith aliens turning Jupiter into a star. They do so by adding a lot of mass.
The problem is that to make Jupiter a red dwarf (a brown dwarf wouldn’t be much use to the Europans), it would require that we increase Jupiter’s mass by, oh, about 80 times. That’s a lot of monoliths to throw into its core.
The only thing that could naturally increase its mass by that much would be if Jupiter somehow fused with a black hole. Unfortunately, that would…result in the black hole swallowing Jupiter. Also not very useful for the Europans.
Maybe those monoliths actually contained a set of very small black holes, carefully tuned. That still wouldn’t be stable, although we are talking about Sufficiently Advanced aliens here.
So, the “good” news is that Jupiter’s not going to spontaneously become a star.
What Would Happen to the Earth if Jupiter did Become a Star?
But let’s say it actually did ignite into a red dwarf: What would happen to us here on Earth.
First of all, it wouldn’t be that bright. It would be a red spotlight a little brighter than the full moon, somewhat visible during the day but easy to see at night. You would be able to look at it directly with the naked eye, but probably not with a telescope.
It wouldn’t heat the Earth much — I found this exchange which suggested a max of 6%, a bit less than normal seasonal changes. Of course, that could be bad combined with global warming…
But, it would cause all kinds of other problems because of that knotty little thing Clarke apparently forgot called “gravity.”
The Earth’s orbit would elongate in sync with Lucifer. This might speed up the normal ice age/melt cycle. This would take a long time to happen. It wouldn’t make Earth uninhabitable or anything, but we might have to get our winter coats ready. Or the extra heat would mean ice ages just don’t happen any more. We’ve already postponed the one that should be happening in the near future. And possibly replaced it with something else…
It would also shift the orbits of the other planets. This wouldn’t be a huge issue, except for throwing off all of our calculations. However, there’s the issue of Mercury and orbital resonance.
Jupiter could give Mercury a solid tug and pull it further out into the system, or into the sun. I watched a bad movie once where Mercury almost hit the Earth and caused all kinds of horrible science, but this is a way that could actually happen. Oh dear. (In fact, there’s a tiny, tiny chance of this happening with Jupiter the size it is…in a few billion years).
Oh, and it would also destabilize the asteroid belt, so we’d better get our planetary defenses in order, fast.
Thankfully, Jupiter isn’t going to become a star, although I suppose it would be kind of pretty.