# How does a planet explode? **URL:** \ **Category:** Cafe Society\ **Created:** [June 19, 2011, 2:34am UTC](https://boards.straightdope.com/t/how-does-a-planet-explode/586000 "2011-06-19T02:34:18Z")\ **Posts on this page:** 20\ **Page:** 1
**Author:** ![BrainGlutton](https://avatars.discourse-cdn.com/v4/letter/b/82dd89/32.png) [@BrainGlutton](https://boards.straightdope.com/u/BrainGlutton)\ **Post date:** [June 19, 2011, 2:34am UTC](https://boards.straightdope.com/t/how-does-a-planet-explode/586000/1 "2011-06-19T02:34:18Z")
We know it happens occasionally, or there would be no Superman and Khan might have ended his days happily, but how? I mean, exploding is pretty much the opposite of what an Earthlike planet does, which is persist as a huge mass pulled into near-spherical shape by its own weight in its own gravity field. What does it take to overcome that?\* Is nuclear fission at the core on sufficient scale conceivable – say, from fissionable metals in the crust or mantle somehow and for some reason coming together in critical masses as they never have before in planetary history? If not that, then what? - Even that beam from the Death Star should only have overcome it momentarily. I mean, you would expect Alderaan to collapse back into a (lifeless) sphere of (nearly) its original mass almost immediately, wouldn’t you? ---
**Author:** ![Snarky\_Kong](https://avatars.discourse-cdn.com/v4/letter/s/a183cd/32.png) [@Snarky\_Kong](https://boards.straightdope.com/u/Snarky_Kong)\ **Post date:** [June 19, 2011, 2:39am UTC](https://boards.straightdope.com/t/how-does-a-planet-explode/586000/2 "2011-06-19T02:39:46Z")
> [@BrainGlutton](#): > > - Even that beam from the Death Star should only have overcome it momentarily. I mean, you would expect Alderaan to collapse back into a (lifeless) sphere of (nearly) its original mass almost immediately, wouldn’t you? No. Why would it? Do you expect Voyager to be coming back any time soon? ---
**Author:** ![Munch](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/munch/32/5281_2.png) [@Munch](https://boards.straightdope.com/u/Munch)\ **Post date:** [June 19, 2011, 3:01am UTC](https://boards.straightdope.com/t/how-does-a-planet-explode/586000/3 "2011-06-19T03:01:16Z")
> [@Snarky\_Kong](#): > > No. Why would it? Because that much mass in that localized a region WILL reform into a planet. BG - did you mean this to be in General Questions, by chance? ---
**Author:** ![friedo](https://avatars.discourse-cdn.com/v4/letter/f/8edcca/32.png) [@friedo](https://boards.straightdope.com/u/friedo)\ **Post date:** [June 19, 2011, 3:04am UTC](https://boards.straightdope.com/t/how-does-a-planet-explode/586000/4 "2011-06-19T03:04:12Z")
> [@Munch](#): > > Because that much mass in that localized a region WILL reform into a planet. Only assuming whatever blew it apart flings the chunks at something lower than the local escape velocity. ---
**Author:** ![Colibri](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/colibri/32/1841_2.png) [@Colibri](https://boards.straightdope.com/u/Colibri)\ **Post date:** [June 19, 2011, 3:12am UTC](https://boards.straightdope.com/t/how-does-a-planet-explode/586000/5 "2011-06-19T03:12:47Z")
> [@Snarky\_Kong](#): > > No. Why would it? Do you expect Voyager to be coming back any time soon? It would come back together because of a little force called gravity. Voyager long ago reached escape velocity and gravity is not strong enough to attract it back to Earth. It would take a titanically enormous force to fling the fragments of a planet far enough away so they would not be re-attracted to one another (much greater than the force required just to blow the planet into fragments). ---
**Author:** ![AlsoNamedBort](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/alsonamedbort/32/3213_2.png) [@AlsoNamedBort](https://boards.straightdope.com/u/AlsoNamedBort)\ **Post date:** [June 19, 2011, 3:13am UTC](https://boards.straightdope.com/t/how-does-a-planet-explode/586000/6 "2011-06-19T03:13:12Z")
The Bad Astronomer has discussed this a [couple](http://www.badastronomy.com/bad/movies/mib2_review.html) [times.](http://blogs.discovermagazine.com/badastronomy/2008/09/08/ten-things-you-dont-know-about-the-earth/) > [@](#): > > What would it take to vaporize the planet? Let’s define vaporization as blowing it up so hard that it disperses and cannot recollect due to gravity. How much energy would that take? > > Think of it this way: take a rock. Throw it up so hard it escapes from the Earth. That takes quite a bit of energy! Now do it again. And again. Lather, rinse, repeat… a quadrillion times, until the Earth is gone. That’s a lot of energy! But we have one advantage: every rock we get rid of decreases the gravity of the Earth a little bit (because the mass of the Earth is smaller by the mass of the rock). As gravity decreases, it gets easier to remove rocks. > > You can use math to calculate this; how much energy it takes to remove a rock and simultaneously account for the lowering of gravity. \*\*If you make some basic assumptions, it takes roughly 2 x 1032 Joules, or 200 million trillion trillion Joules. That’s a lot. For comparison, that’s the total amount of energy the Sun emits in a week. It’s also about a trillion times the destructive energy yield of detonating every nuclear weapon on Earth. > \*\* > If you want to vaporize the Earth by nuking it, you’d better have quite an arsenal, and time on your hands. If you blew up every nuclear weapon on the planet once every second, it would take 160,000 years to turn the Earth into a cloud of expanding gas. > > And this is only if you account for gravity! There are chemical bonds holding the Earth’s matter together as well, so it takes even more energy. > > This is why Star Wars is not science fiction, it’s fantasy. The Death Star wouldn’t be able to have a weapon that powerful. The energy storage alone is a bit much, even for the power of the Dark Side. > > Even giant collisions can’t vaporize the planet. An object roughly the size of Mars impacted the Earth more than 4.5 billion years ago, and the ejected debris formed the Moon (the rest of the collider merged with the Earth). But the Earth wasn’t vaporized. Even smacking a whole planet into another one doesn’t destroy them! ---
**Author:** ![Little\_Nemo](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/little_nemo/32/3120_2.png) [@Little\_Nemo](https://boards.straightdope.com/u/Little_Nemo)\ **Post date:** [June 19, 2011, 3:21am UTC](https://boards.straightdope.com/t/how-does-a-planet-explode/586000/7 "2011-06-19T03:21:26Z")
Because melting Alderaan wouldn’t have looked cool. ---
**Author:** ![Bryan\_Ekers](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/bryan_ekers/32/183_2.png) [@Bryan\_Ekers](https://boards.straightdope.com/u/Bryan_Ekers)\ **Post date:** [June 19, 2011, 4:00am UTC](https://boards.straightdope.com/t/how-does-a-planet-explode/586000/8 "2011-06-19T04:00:25Z")
Superman comics actually discussed this in a “return to Krypton” story. The planet is described as suffering massive disruption and upheaval but from a distance, looked whole. Only a deeper scan showed that the mass was still roughly planet-shaped but consisted mostly of mountain-sized asteroids bumping against each other, tightly orbiting a molten core. As best I can recall, the author (John Byrne) had Superman observing: “It’s been fifty years since Krypton exploded. It might take fifty **million** years for a solid planet to condense out of that mess. Another billion for the first chance at life…” Ref: _Superman_ (Volume 2) #18, June 1988 ---
**Author:** ![Snarky\_Kong](https://avatars.discourse-cdn.com/v4/letter/s/a183cd/32.png) [@Snarky\_Kong](https://boards.straightdope.com/u/Snarky_Kong)\ **Post date:** [June 19, 2011, 4:38am UTC](https://boards.straightdope.com/t/how-does-a-planet-explode/586000/9 "2011-06-19T04:38:15Z")
> [@Colibri](#): > > It would come back together because of a little force called gravity. Voyager long ago reached escape velocity and gravity is not strong enough to attract it back to Earth. It would take a titanically enormous force to fling the fragments of a planet far enough away so they would not be re-attracted to one another (much greater than the force required just to blow the planet into fragments). I’m aware of gravity, thanks. Ever see Star Wars? That shit goes flying. ---
**Author:** ![BrainGlutton](https://avatars.discourse-cdn.com/v4/letter/b/82dd89/32.png) [@BrainGlutton](https://boards.straightdope.com/u/BrainGlutton)\ **Post date:** [June 19, 2011, 4:44am UTC](https://boards.straightdope.com/t/how-does-a-planet-explode/586000/10 "2011-06-19T04:44:50Z")
> [@Munch](#): > > BG - did you mean this to be in General Questions, by chance? No, but it was a close decision. ---
**Author:** ![Boyo\_Jim](https://avatars.discourse-cdn.com/v4/letter/b/87869e/32.png) [@Boyo\_Jim](https://boards.straightdope.com/u/Boyo_Jim)\ **Post date:** [June 19, 2011, 4:45am UTC](https://boards.straightdope.com/t/how-does-a-planet-explode/586000/11 "2011-06-19T04:45:43Z")
I assume that every exploding planet has a huge anitmatter reservoir at its core, and when when the fields collapse and allow matter to mix in… KABLOOIE!! Why would there be such a reservoir? Well, to blow shit up, of course! ---
**Author:** ![Dallas\_Jones](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/dallas_jones/32/3277_2.png) [@Dallas\_Jones](https://boards.straightdope.com/u/Dallas_Jones)\ **Post date:** [June 19, 2011, 4:49am UTC](https://boards.straightdope.com/t/how-does-a-planet-explode/586000/12 "2011-06-19T04:49:01Z")
\*\*How does a planet explode? \*\* Planets are held together by surface tension, much like a droplet of water. That whole gravity thing is just a theory. Once the surface tension is broken everything goes ‘splat’ or '‘blewie’ and comes apart. Hey, I checked, and this is not in General Questions. ---
**Author:** ![Der\_Trihs](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/der_trihs/32/233_2.png) [@Der\_Trihs](https://boards.straightdope.com/u/Der_Trihs)\ **Post date:** [June 19, 2011, 4:49am UTC](https://boards.straightdope.com/t/how-does-a-planet-explode/586000/13 "2011-06-19T04:49:32Z")
> [@BrainGlutton](#): > > We know it happens occasionally, or there would be no Superman and Khan might have ended his days happily, but how? Here’s my totally unsupported fan theory for mysterious explosions like what happened with Ceti Alpha VI in Trek. Recall the mirror universe? They are very different than the “regular” universe, but despite that there are many similarities like the mirror-characters that shouldn’t be possible thanks to the butterfly effect. The universes are connected somehow; some force keeps certain aspects of each universe identical or close to it no matter how others diverge. Well; if you blow up a planet in such a mirror universe, what happens to the mirrored planet? If a “regular” planet explodes, perhaps it’s because in a linked mirror universe, some space fleet made _their_ version of that planet explode; and whatever force it is that keeps the universes mirrored tore apart the “regular” planet. ---
**Author:** ![Colibri](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/colibri/32/1841_2.png) [@Colibri](https://boards.straightdope.com/u/Colibri)\ **Post date:** [June 19, 2011, 4:53am UTC](https://boards.straightdope.com/t/how-does-a-planet-explode/586000/14 "2011-06-19T04:53:45Z")
> [@Snarky\_Kong](#): > > I’m aware of gravity, thanks. > > Ever see Star Wars? That shit goes flying. Your understanding of gravity is based on what happens in Star Wars? ---
**Author:** ![Snarky\_Kong](https://avatars.discourse-cdn.com/v4/letter/s/a183cd/32.png) [@Snarky\_Kong](https://boards.straightdope.com/u/Snarky_Kong)\ **Post date:** [June 19, 2011, 4:58am UTC](https://boards.straightdope.com/t/how-does-a-planet-explode/586000/15 "2011-06-19T04:58:15Z")
> [@Colibri](#): > > Your understanding of gravity is based on what happens in Star Wars? Go watch a video, take a guess at the speed the planet flies apart, compare it to a reasonable escape velocity, then get back to me. ---
**Author:** ![Boyo\_Jim](https://avatars.discourse-cdn.com/v4/letter/b/87869e/32.png) [@Boyo\_Jim](https://boards.straightdope.com/u/Boyo_Jim)\ **Post date:** [June 19, 2011, 5:05am UTC](https://boards.straightdope.com/t/how-does-a-planet-explode/586000/16 "2011-06-19T05:05:51Z")
It’s all about Dark Matter and Dark Energy. ---
**Author:** ![Alka\_Seltzer](https://avatars.discourse-cdn.com/v4/letter/a/c89c15/32.png) [@Alka\_Seltzer](https://boards.straightdope.com/u/Alka_Seltzer)\ **Post date:** [June 19, 2011, 12:57pm UTC](https://boards.straightdope.com/t/how-does-a-planet-explode/586000/17 "2011-06-19T12:57:13Z")
If you want to fanwank it, you could say Krypton was very rich in radioactive isotopes, resulting in an abundance of [natural nuclear reactors](http://en.wikipedia.org/wiki/Natural_nuclear_fission_reactor), such as we had at [Oklo](http://en.wikipedia.org/wiki/Oklo) 2 billion years ago. Some sort of geological event could have injected lots of water, which would have acted as a neutron moderator. This would increase the reaction rate, leading to an explosion. I don’t think a natural nuclear explosion is completely impossible, just very unlikely. Early in the history of the solar system, there was a much greater abundance of radioactive isotopes, which have since decayed. ---
**Author:** ![DrFidelius](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/drfidelius/32/3447_2.png) [@DrFidelius](https://boards.straightdope.com/u/DrFidelius)\ **Post date:** [June 19, 2011, 1:03pm UTC](https://boards.straightdope.com/t/how-does-a-planet-explode/586000/18 "2011-06-19T13:03:23Z")
> [@Snarky\_Kong](#): > > No. Why would it? Do you expect Voyager to be coming back any time soon? Delta Quadrant is a very long distance away, and the commander has a habit of stopping at every tourist trap along her route, so no. ---
**Author:** ![shijinn](https://avatars.discourse-cdn.com/v4/letter/s/cc9497/32.png) [@shijinn](https://boards.straightdope.com/u/shijinn)\ **Post date:** [June 19, 2011, 1:26pm UTC](https://boards.straightdope.com/t/how-does-a-planet-explode/586000/19 "2011-06-19T13:26:20Z")
the same way cars explode. ---
**Author:** ![Andy\_L](https://avatars.discourse-cdn.com/v4/letter/a/c67d28/32.png) [@Andy\_L](https://boards.straightdope.com/u/Andy_L)\ **Post date:** [June 19, 2011, 1:48pm UTC](https://boards.straightdope.com/t/how-does-a-planet-explode/586000/20 "2011-06-19T13:48:31Z")
> [@Colibri](#): > > It would come back together because of a little force called gravity. Voyager long ago reached escape velocity and gravity is not strong enough to attract it back to Earth. It would take a titanically enormous force to fling the fragments of a planet far enough away so they would not be re-attracted to one another (much greater than the force required just to blow the planet into fragments). I did the calculation a while back on how much energy it would take to give escape velocity to every part of a planet (so it wouldn’t reassemble after the explosion). Here’s what I wrote: For objects large enough to be rounded by gravity (into which category objects considerably smaller than the Moon fit), the dominant force holding them together is gravity. It’s surprisingly easy to calculate how much energy is required to overcome that force: start at the outside of the object and calculate how much energy it takes to accelerate a infinitesimal shell of material to escape velocity, and iterate for shells closer and closer to the center of the object until there’s nothing left (the onion-peeling approach to planetary-level destruction). If you assume that the object has uniform density, the answer is 3/5_G_M\*M/R where M is the mass of the object, R is its radius and G is the universal gravitational constant (G=6.67300 ? 10^-11 m^3 kg^-1 s^-2). This is a lower bound for three reasons - first, it ignores other forces holding the object together, second, big objects will tend to be denser in the middle, which increases the energy required to pull them apart, and third, inefficiencies (like parts of the planet colliding with each other) will naturally exist - but a lower bound can be useful… [Next page](https://boards.straightdope.com/t/how-does-a-planet-explode/586000.md?page=2)