There is a science-fiction novel (2010: Odyssey Two) in which someone compresses the mass of Jupiter so that it achieves fusion and becomes a small star. Never mind that this is impossible and that there may not even be enough mass for it to happen. I’m wondering what we would observe from Earth if it did happen. This would be another star rotating our sun, so it would be relatively close only part of the year. How bright would it be? Just as bright as one of the brighter stars in our night sky? I assume it would be brighter when we’re both on the same side of the sun.
Didn’t the thingys add mass to Jupiter until it achieved stellar ignition? (And I guess they tamped down any power excursions that the glowing Jupiter would have exhibited before settling at a steady-state of radiative output.)
I guess what I’m asking is: how much mass does this new Jupiter star have? That’ll help us (or someone like @Anne_Hedonia) calculate how bright the new star would be, and how much extra insolation we’d receive. Talk about global warming…
There’s no real GQ answer to this since it depends on how much mass was added.
There’s a wide range of possibilities, though it is likely to be much brighter than any object in the sky from earth, save the sun itself.
Let’s assume just enough was added to make it a viable star, although I don’t know if that helps in making the calculations.
As said, it would be the brightest star in the night sky, although unlike the rest, its brightness would vary based on its and our orbits round the sun.
Per the novel, mass wasn’t added. A portion of Jupiter was made much denser, making fusion possible in the remaining gas. Maybe new Jupiter is a neutron star surrounded by hydrogen - that might work.
It really depends on how Jupiter gets to be a star. If we assume it’s a minimum-mass main sequence star, that’d make it an M9V red dwarf at 7.5% of a solar mass with 0.015% solar luminosity. Note that this isn’t just a little bit more massive than Jupiter - it’s about 80 times more massive than Jupiter. Jupiter ranges between 629 million km and 928 million km from Earth. If we plug those numbers into a luminosity calculator we get an apparent magnitude ranging from -13.2 to -14.1. That’s pretty bright (lower numbers are brighter). It’s a bit brighter than the full moon at -12.7, but would probably seem significantly brighter given that its luminosity would be concentrated in a much smaller angular size. Jupiter as it is now runs about -3, while Venus at -4 is the brightest object in the sky besides the Sun (-26.4) and moon. Apparent magnitude figures taken from Wikipedia.
If Jupiter becomes a star in some non-standard way then who knows. It could be dimmer if there were some way to get sustained fusion without scaling it up to M9V class mass.
Let’s start with the Sun having an absolute magnitude of +4.8
Jupiter is 0.0009X the mass of the Sun meaning it would have 0.00000000002187X the luminosity from the above chart which works out to mean that Jupiter would be 26.65 magnitude dimmer than the Sun so StarJupiter would have an absolute magnitude +31.45
At its closest to Earth, Jupiter is 365,000,000 miles from Earth and at its furthest it is 601,000,000 from Earth. Using this calculator that means StarJupiter would range in apparent magnitude from +2.85 to +3.93. If this math is right, it means StarJupiter would be dimmer than PlanetJupiter.
IANAAP (I am not an astrophysicist) so perhaps one will come along and explain this apparent paradox (or my error).
It already is brighter than most stars.
So how much brighter would it be as a star?
Not much, I would imagine. It’s already reflecting light from the sun. Hold a match-flame sized marble and a lit match a few feet from a campfire. Is the match really that much brighter than the marble?
How much heat would it add, if any?
Hmmmmm. If only someone did the calculations to figure out its magnitude two posts before yours.
Hint: it gets dimmer as a star.
Wow. There was an article in an issue of Analog in the early 1990s titled “Stellating Jupiter” about the physics behind this. Googling for that phrase returns exactly one hit, and it isn’t relevant. That’s impressive.
Well, IANAAP either, but you can’t use the mass/luminosity relationship for objects that are smaller than the smallest red dwarf, so the estimate for StarJupiter’s intrinsic luminosity is going to be wrong.
And don’t forget that StarJupiter will also reflect light, so you have to add the luminosity to the reflected light. The object will almost certainly be brighter than PlanetJupiter. Exactly how much brighter really does depend on the method used to achieve fusion.
Looking at this graph, the mass/luminosity relationship seems to change slope towards the lower end anyway, so luminous substellar objects would probably be brighter than a simple arithmetic relationship might suggest.
Since Dewey Finn asked (in his fourth post) for details of the luminosity of Jupiter as a low-mass viable star, then Gorsnak’s answer is the best one, since it describes the brilliance of the smallest possible red dwarf in Jupiter’s position.
But we could also imagine that Jupiter is turned into a brown dwarf instead, perhaps by adding only deuterium. If we added 12 Jupiter-masses of deuterium to PlanetJupiter then fusion would occur for several million years, producing a self-luminous brown dwarf that would be much hotter (and therefore larger) than Jupiter. Even after fusion stopped the object would shine for many more years due to gravitational contraction.
But then we would have a starlett 13 times the mass of Jupiter, which is already by far the heaviest object in the solar system bar the sun. I think that would greatly disturb the orbits of the other planets, including Earth’s, and of the asteroids, which brings memories of the dinosaur’s demise. I do not think this would work out well in the medium to long term. I for one oppose this idea.
We could try my way, then.
If we can use hydrogen as a fuel for fusion rockets, we can cover the planet in so-called ‘fusion candles’. These are rockets that burn in two directions at once, downwards to support their weight, and upwards to illuminate the sky. Here’s an image I’ve made showing them in action.
Make enough of these, and the planet will become significantly hotter and brighter, and also expand somewhat to increase the surface area. Calculating the luminosity of Jupiter in this state is something I would leave to the imagination.
That is, of course, an extrapolation well beyond the range that chart covers. And any extrapolation runs the risk that you’re into a range where something qualitative changes. Which we in fact know to be the case here.
That said, though, if we’re going to be getting into “magical alien supertech makes Jupiter into a star without adding mass”, then I suppose that sort of extrapolation is about as good a guess as any.
Actually his OP is
someone compresses the mass of Jupiter so that it achieves fusion and becomes a small star. Never mind that this is impossible and that there may not even be enough mass for it to happen.
Hence my answer using Jupiter’s mass not smallest possible star mass.
This is sounding like “If something outside of what known physics says is possible happened on Jupiter, what do physics say would be the result?” Could be hard to answer.