Could Jupiter become a star?

It may be the biggest planet in our Solar System but it would still need more mass to turn into a second Sun.

29th November 2017
Could Jupiter become a star? © Alamy

Asked by: Louise Dryden, Cardiff

Jupiter is often called a ‘failed star’ because, although it is mostly hydrogen like most normal stars, it is not massive enough to commence thermonuclear reactions in its core and thus become a ‘real star’. But the term ‘failed star’ is a bit of a misnomer. Theoretically, any object at all could be made into a star, simply by adding enough matter to it. With enough mass, the internal pressure and temperature of the object will reach the threshold needed to start thermonuclear reactions. That threshold is the least for the simplest element, hydrogen. In order to turn Jupiter into a star like the Sun, for example, you would have to add about 1,000 times the mass of Jupiter. But, to make a cooler ‘red dwarf’ you would only need to add about 80 Jupiter masses. Although the exact numbers are still a bit uncertain, it is possible that a ‘brown dwarf’ could still form (in which deuterium, rather than hydrogen, fuses in the star’s core) with only about 13 Jupiter masses. So, Jupiter cannot and will not spontaneously become a star, but if a minimum of 13 extra Jupiter-mass objects happen to collide with it, there is a chance it will.

Read more:

SFQASubscribe to BBC Focus magazine for fascinating new Q&As every month and follow @sciencefocusQA on Twitter for your daily dose of fun facts.