I'm writing a science fiction story based on:

  1. turning Jupiter into a star.
  2. colliding Callisto and/or Io into Ganymede to increase mass and changing the orbit to provide warmth, atmosphere, and rotation.
  3. using Neo-Ganymede for human habitation and a stepping stone to the stars.

This will require gargantuan energy and a lot of mass - of the right kind.

I realize that the amounts of energy to accomplish this project are unrealistic, but I want an estimation in order to write the story with as few "fiction" theories as possible. thanks

  • 8
    $\begingroup$ Jupiter has about 1.5 to 7% (competing models) of the mass needed for it to become a faint brown dwarf star. So you need to add about 15 to 50 times more mass than it currently has. There is not enough matter in the rest of the solar system for this. To make it into a bright normal star you would need to increase its mass some 100 times. And all that mass must of course be accelerated to match Jupiter's orbital speed. $\endgroup$
    – AlexP
    Feb 18, 2018 at 18:08
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    $\begingroup$ Kudos for at least trying to stick to science, though I think this might be a duplicate of some existing question on the site. You may want to check out Can Jupiter be ignited? on our sister site Physics. Also searching this site for questions using the words "Jupiter" and "star" may be useful. There's also at least this and this answer on our sister site Astronomy. $\endgroup$
    – user
    Feb 18, 2018 at 18:20
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    $\begingroup$ Colliding two planets (or large moons) would result in, at best, a enormously hot object that would take millions, possibly billions, of years to cool sufficiently for habitation. It's also not credible that a civilization would have the technical capability to do these things but still need a moon or planet or as base to travel to the stars. $\endgroup$ Feb 18, 2018 at 18:35
  • 3
    $\begingroup$ I'm voting to close this question as off-topic because the question has been answered on other SE sites. $\endgroup$
    – JBH
    Feb 18, 2018 at 23:42
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    $\begingroup$ @JBH Questions can be asked and answered on multiple sites as long as they are on topic for each site. $\endgroup$
    – sphennings
    Feb 19, 2018 at 2:23

2 Answers 2


On a merely human timescale, you can turn Jupiter into a "star" by dumping in deuterium to turn it into a brown dwarf. The amount involved is quite reasonable: only about 13 times Jupiter's existing mass. Astronomers won't call it a star because it isn't big enough to fuse hydrogen, but until the deuterium runs out, it'll look and act exactly like one.

If you want to keep the astronomers happy rather than merely provide a source of light and heat, you'll need far more material. To get a red dwarf, you'll need to dump in hydrogen to the tune of 80 times Jupiter's current mass.


The smallest star ever observed (AB Doradaus C) has about 100 times more mass than Jupiter with 20% larger size and about .03% the brightness of the sun. So to make it short, unless smaller stars than the smallest ever observed exist, you'd need to smash about 100 Jupiter's together to make a very tiny star.

  • $\begingroup$ And, there isn't nearly that much mass in the entire solar system outside the Sun. You'd need an extrasolar source of mass. $\endgroup$
    – ohwilleke
    Feb 19, 2018 at 19:20
  • $\begingroup$ Also, if you just smashed the added material together, you would have an essentially identical dwarf star, and still have Jupiter. It's not like there's a threshold where one additional Jupiter mass will turn a non-star into a star. $\endgroup$ Oct 10, 2022 at 15:44

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