# Jupiter.. what is it? **URL:** \ **Category:** Factual Questions\ **Created:** [March 23, 2003, 10:36pm UTC](https://boards.straightdope.com/t/jupiter-what-is-it/163634 "2003-03-23T22:36:40Z")\ **Posts on this page:** 20\ **Page:** 1
**Author:** ![Bootieman](https://avatars.discourse-cdn.com/v4/letter/b/ecd19e/32.png) [@Bootieman](https://boards.straightdope.com/u/Bootieman)\ **Post date:** [March 23, 2003, 10:36pm UTC](https://boards.straightdope.com/t/jupiter-what-is-it/163634/1 "2003-03-23T22:36:40Z")
Any ideas what Jupiter really is? Is it a “failed” star? Any chance it would ever “Ignite”? What would happen to us if it did ignite? Just curious…🙂 ---
**Author:** ![Q.E.D](https://avatars.discourse-cdn.com/v4/letter/q/51bf81/32.png) [@Q.E.D](https://boards.straightdope.com/u/Q.E.D)\ **Post date:** [March 23, 2003, 10:41pm UTC](https://boards.straightdope.com/t/jupiter-what-is-it/163634/2 "2003-03-23T22:41:02Z")
Jupiter’s mass is too small to allow for ignition. It would need to be many times it’s current mass to do so. We’ve discovered planets orbiting several stars, so far, most with masses well over that of Jupiter, and they’ve not ignited, either. ---
**Author:** ![FaerieBeth](https://avatars.discourse-cdn.com/v4/letter/f/e95f7d/32.png) [@FaerieBeth](https://boards.straightdope.com/u/FaerieBeth)\ **Post date:** [March 23, 2003, 11:12pm UTC](https://boards.straightdope.com/t/jupiter-what-is-it/163634/3 "2003-03-23T23:12:13Z")
I’m not heavily into planetary study or astronomy, but if I remember correctly from those classes in college, Jupiter is a gas giant, but not a failed star. It’s interesting to ponder the ignition of Jupiter, though, and I believe it’s been theorized in a few SciFi books. I cannot seem to remember which, though, as my brain just locked up. ---
**Author:** ![Jude](https://avatars.discourse-cdn.com/v4/letter/j/bc8723/32.png) [@Jude](https://boards.straightdope.com/u/Jude)\ **Post date:** [March 23, 2003, 11:31pm UTC](https://boards.straightdope.com/t/jupiter-what-is-it/163634/4 "2003-03-23T23:31:37Z")
Isn’t it a brown dwarf? ---
**Author:** ![Q.E.D](https://avatars.discourse-cdn.com/v4/letter/q/51bf81/32.png) [@Q.E.D](https://boards.straightdope.com/u/Q.E.D)\ **Post date:** [March 23, 2003, 11:36pm UTC](https://boards.straightdope.com/t/jupiter-what-is-it/163634/5 "2003-03-23T23:36:32Z")
There’s sort of a grey area between what’s considered a planet and what’s called a brown dwarf. There’s really no hard-and-fast rule for determining which is which. Jupiter could be considered a very small brown dwarf, but most astronomers call it a planet. ---
**Author:** ![eburacum45](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/eburacum45/32/8690_2.png) [@eburacum45](https://boards.straightdope.com/u/eburacum45)\ **Post date:** [March 23, 2003, 11:45pm UTC](https://boards.straightdope.com/t/jupiter-what-is-it/163634/6 "2003-03-23T23:45:05Z")
No, it’s not a brown dwarf- there is a solid centre to Jupiter, although estimates of it’s compsition and size vary. No nuclear fusion is occurring inside our largest planet, althouh its gravity, internal radioactive decay and magnetic field together produce more energy than it recieves from the sun. Brown Dwarfs are objects between 13 to 80 times Jupiter’s mass, and produce energy by fusion although they do not get red hot. The smallest ones have methane in their atmospheres, while the larger ones are marked by significant amounts of Lithium. Sci-fi stories which involve artificially igniting Jovian planets, usually by increasing their density, include 2010 by A.C. Clarke and The Neutronium Alchemist by Peter F Hamilton. ---
**Author:** ![WillGolfForFood](https://avatars.discourse-cdn.com/v4/letter/w/82dd89/32.png) [@WillGolfForFood](https://boards.straightdope.com/u/WillGolfForFood)\ **Post date:** [March 23, 2003, 11:46pm UTC](https://boards.straightdope.com/t/jupiter-what-is-it/163634/7 "2003-03-23T23:46:04Z")
I don’t think it’s supposed to ignite until the black monoliths fall into it. ---
**Author:** ![The\_Bad\_Astronomer](https://avatars.discourse-cdn.com/v4/letter/t/f05b48/32.png) [@The\_Bad\_Astronomer](https://boards.straightdope.com/u/The_Bad_Astronomer)\ **Post date:** [March 23, 2003, 11:46pm UTC](https://boards.straightdope.com/t/jupiter-what-is-it/163634/8 "2003-03-23T23:46:59Z")
I was just thinking of adding this topic [to my website](http://www.badastronomy.com). Jupiter is not a star, not by a long shot. A star is something which can fuse one element into another in its core (or did so stably at one time). The _minimum_ mass needed for this is about 0.077 times the mass of the Sun. Jupiter is about 0.00095 times the mass of the Sun, a factor of 80 too small to be a star. I hear people say it’s a failed star, but that’s giving Jupiter way too much credit. A brown dwarf is a different story. BDs are lower than the 0.077 mass limit, but there is no well-defined lower mass limit. There probably shouldn’t be; BD and/or planet are just names we hang on objects, and some things defy categorization. FWIW, the lowest mass BD I know of is S Ori 70, which has from 2 - 8 times Jupiter’s mass. For more about brown dwarfs, [try my website](http://www.google.com/custom?q=brown+dwarfs&cof=LW%3A500%3BL%3A%2Fpix%2Fbalogo500x100_2.jpg%3BLH%3A100%3BAH%3Aleft%3BAWFID%3A335a96841179147e%3B&domains=www.badastronomy.com&sitesearch=www.badastronomy.com). ---
**Author:** ![Bootieman](https://avatars.discourse-cdn.com/v4/letter/b/ecd19e/32.png) [@Bootieman](https://boards.straightdope.com/u/Bootieman)\ **Post date:** [March 24, 2003, 12:05am UTC](https://boards.straightdope.com/t/jupiter-what-is-it/163634/9 "2003-03-24T00:05:26Z")
Funny that you mention 2010 eburacum45, that is what got these crazy questions in my head in the first place. Now, supposing Jupiter IS a brown dwarf then, wouldn’t that make Saturn it’s “companion”? Being similar in composition, relative in size and mass?? What are the chances of two brown dwarves in the same solar system? ---
**Author:** ![eburacum45](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/eburacum45/32/8690_2.png) [@eburacum45](https://boards.straightdope.com/u/eburacum45)\ **Post date:** [March 24, 2003, 1:00am UTC](https://boards.straightdope.com/t/jupiter-what-is-it/163634/10 "2003-03-24T01:00:42Z")
Jupiter and Saturn are both the Sun’s companions, not companions to each other. Neither are really brown dwarfs anyway. I have read that two large brown dwarfs could not form in one solar system, one would eject the other. On the other hand , a small red dwarf star like Gliese 876 has got two large jupiter-like planets in harmonic orbits around it, so perhaps a larger star could have larger planets still. [(My fictional version of Gl 876)](http://www.orionsarm.com/worlds/Aardwolf.html) ---
**Author:** ![Polycarp](https://avatars.discourse-cdn.com/v4/letter/p/82dd89/32.png) [@Polycarp](https://boards.straightdope.com/u/Polycarp)\ **Post date:** [March 24, 2003, 2:34am UTC](https://boards.straightdope.com/t/jupiter-what-is-it/163634/11 "2003-03-24T02:34:33Z")
Brown dwarfs as a rule heat up by gravitational contraction, not by fusion. Jupiter is half the mass of the smallest known brown dwarf, but is also 100K warmer than it would be as a “black body” heated totally by solar insolation. So by really stretching a point, you could consider Jupiter the coldest “failed star” known, with a surface temperature (observable surface = cloud tops) of something like -220° F. ---
**Author:** ![raisinbread](https://avatars.discourse-cdn.com/v4/letter/r/8491ac/32.png) [@raisinbread](https://boards.straightdope.com/u/raisinbread)\ **Post date:** [March 24, 2003, 3:03am UTC](https://boards.straightdope.com/t/jupiter-what-is-it/163634/12 "2003-03-24T03:03:11Z")
> [@](#): > > \*Originally posted by Bootieman \* > **Now, supposing Jupiter IS a brown dwarf then, wouldn’t that make Saturn it’s “companion”?** I believe Jupiter prefers the term “special friend”. ---
**Author:** ![Polycarp](https://avatars.discourse-cdn.com/v4/letter/p/82dd89/32.png) [@Polycarp](https://boards.straightdope.com/u/Polycarp)\ **Post date:** [March 24, 2003, 3:57am UTC](https://boards.straightdope.com/t/jupiter-what-is-it/163634/13 "2003-03-24T03:57:23Z")
> [@](#): > > \*Originally posted by raisinbread \* > \*\*I believe Jupiter prefers the term “special friend”. \*\* No, if Jupiter is a life partner with any other celestial body, it would be [Gany](http://seds.lpl.arizona.edu/nineplanets/nineplanets/ganymede.html)[mede](http://www.pantheon.org/articles/g/ganymede.html). ---
**Author:** ![Q.E.D](https://avatars.discourse-cdn.com/v4/letter/q/51bf81/32.png) [@Q.E.D](https://boards.straightdope.com/u/Q.E.D)\ **Post date:** [March 24, 2003, 3:58am UTC](https://boards.straightdope.com/t/jupiter-what-is-it/163634/14 "2003-03-24T03:58:52Z")
> [@](#): > > \*Originally posted by Polycarp \* > \*\*No, if Jupiter is a life partner with any other celestial body, it would be [Gany](http://seds.lpl.arizona.edu/nineplanets/nineplanets/ganymede.html)[mede](http://www.pantheon.org/articles/g/ganymede.html). \*\* Next on FOX: _When Coding Attacks_. ---
**Author:** ![eburacum45](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/eburacum45/32/8690_2.png) [@eburacum45](https://boards.straightdope.com/u/eburacum45)\ **Post date:** [March 24, 2003, 10:49am UTC](https://boards.straightdope.com/t/jupiter-what-is-it/163634/15 "2003-03-24T10:49:57Z")
Saturn was Jupiter’s Father anyway, but I think you will find that all Jupiter’s moons are named after his paramours, male and female… apart from the ones with just numbers, perhaps. ---
**Author:** ![AHunter3](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/ahunter3/32/368_2.png) [@AHunter3](https://boards.straightdope.com/u/AHunter3)\ **Post date:** [March 24, 2003, 8:37pm UTC](https://boards.straightdope.com/t/jupiter-what-is-it/163634/16 "2003-03-24T20:37:13Z")
Except Amalthea. I don’t think he had an affair with her, she just changed his imperial diapers when he was little. ---
**Author:** ![Chronos](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/chronos/32/134_2.png) [@Chronos](https://boards.straightdope.com/u/Chronos)\ **Post date:** [March 24, 2003, 8:39pm UTC](https://boards.straightdope.com/t/jupiter-what-is-it/163634/17 "2003-03-24T20:39:09Z")
The closest thing I’ve seen to a consensus on the lower bound for a brown dwarf is deuterium fusion. It’s not until you get to about 80 times the mass of Jupiter that you can “burn” regular hydrogen (at which point you have a full-fledged star), but deuterium is easier to fuse, and an object 13 times the mass of Jupiter can “burn” deuterium. So most astronomers now call anything heavier than 13 Jupiters a brown dwarf, and anything lighter a planet (or just a MACHO, if it’s not associated with a star). But it is probably on the same continuum as stars. The process for forming a gas giant is probably very similar to that for forming a companion dwarf star. It’s just that Jupiter (or Saturn, Uranus, or Neptune) has a heck of a lot less mass than a star. ---
**Author:** ![eburacum45](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/eburacum45/32/8690_2.png) [@eburacum45](https://boards.straightdope.com/u/eburacum45)\ **Post date:** [March 24, 2003, 9:14pm UTC](https://boards.straightdope.com/t/jupiter-what-is-it/163634/18 "2003-03-24T21:14:40Z")
> [@](#): > > \*Originally posted by AHunter3 \* > \*\*Except Amalthea. I don’t think he had an affair with her, she just changed his imperial diapers when he was little. \*\* Heh, heh. Yes, I remembered his foster mother after I posted… small story about [Amalthea](http://www.orionsarm.com/worlds/Amalthea.html) ---
**Author:** ![eburacum45](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/eburacum45/32/8690_2.png) [@eburacum45](https://boards.straightdope.com/u/eburacum45)\ **Post date:** [March 24, 2003, 9:18pm UTC](https://boards.straightdope.com/t/jupiter-what-is-it/163634/19 "2003-03-24T21:18:32Z")
> [@](#): > > \*Originally posted by Chronos \* > \*\* The process for forming a gas giant is probably very similar to that for forming a companion dwarf star. It’s just that Jupiter (or Saturn, Uranus, or Neptune) has a heck of a lot less mass than a star. \*\* But Jovian type planets all have rocky cores. At what stage do you think a companion star condenses as pure(ish) hydrogen, or are they all metal rich bodies? ---
**Author:** ![KneadToKnow](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/kneadtoknow/32/3999_2.png) [@KneadToKnow](https://boards.straightdope.com/u/KneadToKnow)\ **Post date:** [March 24, 2003, 10:51pm UTC](https://boards.straightdope.com/t/jupiter-what-is-it/163634/20 "2003-03-24T22:51:33Z")
> [@](#): > > \*Originally posted by The Bad Astronomer \* > I hear people say it’s a failed star, but that’s giving Jupiter way too much credit. Story of my friggin’ life, man. [Next page](https://boards.straightdope.com/t/jupiter-what-is-it/163634.md?page=2)