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The Question

(Submitted March 10, 1998)

My first grade son is doing a project on Jupiter. We have been able to find the answers to most of his questions using the internet or reference books, however, I can't explain to him why Jupiter and the other gas giant planets are not stars. Is there a difference in the way they were formed? Will they eventually become stars? Is it possible to explain this to a first grader?

The Answer

You have asked an excellent question!

A "gas giant" would only be considered a "star" if it generated its own energy through nuclear reactions in its core and Jupiter is just not massive enough to do this. Jupiter would have to be about 50 times more massive than it is to undergo nuclear reactions, and thus be a star and not just a planet.

Steve Bloom
for Ask an Astrophysicist

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