# Why does Jupiter Shine? **URL:** \ **Category:** Factual Questions\ **Created:** [January 7, 2003, 10:34pm UTC](https://boards.straightdope.com/t/why-does-jupiter-shine/147192 "2003-01-07T22:34:51Z")\ **Posts on this page:** 6\ **Page:** 1
**Author:** ![ready29003](https://avatars.discourse-cdn.com/v4/letter/r/71e660/32.png) [@ready29003](https://boards.straightdope.com/u/ready29003)\ **Post date:** [January 7, 2003, 10:34pm UTC](https://boards.straightdope.com/t/why-does-jupiter-shine/147192/1 "2003-01-07T22:34:51Z")
Is Jupiter bright because it reflects sunlight? Or does shine due to gravitational compression or something? I have heard both. Which effect is more relevant to its brightness? 90% reflected sunlight? 90% gravitational compression?? Thanks! ---
**Author:** ![rowrrbazzle](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/rowrrbazzle/32/414_2.png) [@rowrrbazzle](https://boards.straightdope.com/u/rowrrbazzle)\ **Post date:** [January 7, 2003, 10:48pm UTC](https://boards.straightdope.com/t/why-does-jupiter-shine/147192/2 "2003-01-07T22:48:03Z")
What we see is all reflected sunlight. For it to shine by gravitational compression, I believe it would have to be collapsing, and it ain’t because it ain’t massive enough. Jupiter does emit radio waves. I would think also a bit of infra-red, but no more than any other object at its temperature. ---
**Author:** ![Desmostylus](https://avatars.discourse-cdn.com/v4/letter/d/c57346/32.png) [@Desmostylus](https://boards.straightdope.com/u/Desmostylus)\ **Post date:** [January 7, 2003, 10:55pm UTC](https://boards.straightdope.com/t/why-does-jupiter-shine/147192/3 "2003-01-07T22:55:59Z")
[From here:](http://csep10.phys.utk.edu/astr161/lect/jupiter/interior.html) > [@](#): > > Jupiter radiates 1.6 times a much energy as falls on it from the Sun. Thus, Jupiter has an internal heat source. It is thought that much of this heat is residual heat left over from the original collapse of the primordial nebula to form the Solar System, but some may come from slow contraction (liquids are highly incompressible, so Jupiter cannot be contracting very much.) This internal heat source is presumably responsible for driving the complex weather pattern in its atmosphere, unlike the Earth where the primary heat source driving the weather is the Sun. If by “brightness” you mean “brightness visible to the human eye”, it’s 100% reflected sunlight. The rest of the energy it emits is infrared. ---
**Author:** ![Desmostylus](https://avatars.discourse-cdn.com/v4/letter/d/c57346/32.png) [@Desmostylus](https://boards.straightdope.com/u/Desmostylus)\ **Post date:** [January 7, 2003, 10:59pm UTC](https://boards.straightdope.com/t/why-does-jupiter-shine/147192/4 "2003-01-07T22:59:24Z")
Er, my last sentence would be better as “The energy emitted from its internal heat source is infrared.” ---
**Author:** ![Kamandi](https://avatars.discourse-cdn.com/v4/letter/k/5daacb/32.png) [@Kamandi](https://boards.straightdope.com/u/Kamandi)\ **Post date:** [January 7, 2003, 11:15pm UTC](https://boards.straightdope.com/t/why-does-jupiter-shine/147192/5 "2003-01-07T23:15:20Z")
Would nuclear fission - as in the decay of naturally occurring fissionable atoms, not LGMs with nuclear powered aircraft - be a significant contributor to Jupiter’s emitted energy? I vaguely recall that the decay of fissionable atoms is a significant contributor to Earth’s heat balance. ---
**Author:** ![Desmostylus](https://avatars.discourse-cdn.com/v4/letter/d/c57346/32.png) [@Desmostylus](https://boards.straightdope.com/u/Desmostylus)\ **Post date:** [January 7, 2003, 11:55pm UTC](https://boards.straightdope.com/t/why-does-jupiter-shine/147192/6 "2003-01-07T23:55:01Z")
Rather controversial subject **Kamandi**. Some say yes, others say no way. Try googling “Herndon” “Jupiter” “fission”