# Can planets die of old age

I was wondering if planets die after a certain amount of time, perhaps because of decay?

If this is the case, how do they die and how long does it take?

Do they implode? Explode or perhaps just fall apart?

Incase of any of the causes mentioned above, would this make a sound, a sound is basically a wave travelling through the air, however there is no air in space.

And what if you put TNT inside the middle of the earth? Are you able to explode it then?

And what would happen to all the lava inside planet earth?

• They die, but don't expect a spectacular explosion of something else. I will answer, but I anticipate to you that in some cases the death of a planet is very long and very boring. And just to be precise, sound can't be heard in space. Jan 15, 2015 at 15:37
• Consider that there are many potential meanings for "die." It could mean they break apart, or it could mean they simply run out of energy sources, or it could mean that they cease to support life on their surface. It might be helpful to edit and specify which one you are referring to. Jan 15, 2015 at 16:02
• If you consider dieing via proton decay (if this in fact is possible) this would take a veeeeery loooong time. You might also consider universe death due to Big Crunch, Big Rip, Big Freeze, Heath Death or tunnelling to a True Vacuum, since this would also means the death of any planets. Jan 15, 2015 at 16:52
• I'm not suggesting cross-posting or migration, but this Earth science meta post deserves some input: meta.earthscience.stackexchange.com/questions/1395/… Jan 15, 2015 at 22:39
• I do think this question needs some clarification, though. Most planets aren't alive. There's no life. So nothing to die. I think you're asking if planets become physically destroyed. Which some of the answers below cover. But it'd be good to know what you actually mean by 'die'.
– DA.
Jan 16, 2015 at 22:44

A planet will "die" generally from one of the following "natural" fates:

# Death by Cooling

The planet core slowly cools. The planet then loses its magnetosphere, and solar winds begin stripping the planet of its atmosphere. This is likely what happened to Mars, and what is currently happening to Venus.

This is a very slow process, happening over millions of years. When the planet is completely cool, it will not likely be able to sustain life (due to lack of atmosphere), but will otherwise be the same: a cold hunk of rock in space.

# Death by Star

As a star ages, it gets bigger and brighter and hotter. For Earth, this means that we will be outside of the habitable zone of the Sun in 2-3 billion years. The brighter star will slowly cook the planet, killing everything on it.

As the star continues to grow, it may extend past the orbit of a planet, and draw that planet directly into the star. The Sun will likely expand beyond the orbit of Venus, but it may not quite reach Earth (making Earth the new Mercury).

If the star is massive enough (about 8-12x the Sun), it can go supernova. The supernova would completely disintegrate all objects in its solar system, and would be visible tens of thousands of light years away. However, before a star can go supernova, the slow death by absorption or overheating would already have happened.

# Death by Impact

A large object, such as a planetoid or asteroid, may impact a planet. Depending on the size, this may lead to an extinction event, wiping out all life on the planet, or it may literally rip the planet apart.

A leading theory for the formation of the Moon is that a Mars-sized planetoid smashed into Earth, creating the debris that become the Moon. However, even in this scenario, the Earth is still here. It would not destroy the planet so completely as to prevent it from reforming.

# Death by Gravitational Perturbation

An mass, such as a rogue planet, large Oort Cloud object on a weird orbit, or very nearby star, may provide enough gravitational force to perturb the orbit of the planet in question.

For example, a galactic collision may rearrange the star systems, putting two or more stars in close proximity, or sending large objects (like planets) into other star systems.

In the simple case, the planet is moved to a different orbit. This may move the planet close enough to a large planet to be torn apart via tidal forces. This won't happen super quickly, but it could completely destroy the planet, making another asteroid belt.

In the extreme case, the planet may either be sent deep into space, where everything on it dies due to lack of sunlight, or it is sent into the sun, where it burns up (see above).

## A couple notes:

unless the properties of a planet are significantly changed by manual intervention, a planet will never:

• Explode
• Implode
• Fall apart

Planets do not liberate energy from matter (otherwise, they would be stars), which is required for the first two. The matter in planets is bound by gravity, which is always present, and that's what prevents the third one.

• "It would not destroy the planet so completely as to prevent it from reforming." - well, that's just because it didn't hit hard enough. Jan 15, 2015 at 22:15
• @Random832 You're talking about something hitting the Earth unbelievably hard. The gravitational binding potential of earth is on the order of 10^32 J. Taking relativistic kinetic energy into account, you'd have to take an object as massive as Mercury, and smash it into Earth at approximately 30km/s to impart enough energy to prevent Earth from reforming. And that's not considering the additional gravitational binding energy the new object contributes. Jan 15, 2015 at 22:44
• "The planet will never ... implode" tell that to Gene Roddenberry: en.wikipedia.org/wiki/The_Naked_Time Jan 18, 2015 at 5:01

Note, I am not an expert in this, but I am giving my best guess. If you think that something here is wrong, post a comment.

There are indeed many ways to kill a planet:

• Descontruct it - Just send rockets and robots there to grab it piece by piece until nothing else left. This would not sound very interesting, just the sound of robots and ships working. Nothing special happens to the lava in the interior of the planet, which would probably be cooled down by whoever is descontructing it. How long it would take depend on your workers.

• Shatter it with a big impact - If you get a large projectile (large a moon or another planet) and throw it with a large relative velocity to a direct impact against the planet, both will be completely obliterated and the pieces (including the lava) will be thrown out in high velocity escaping trajectories to many directions. The velocity must be sufficiently high, otherwise the two might just merge or the pieces might join together again due to the gravity. Also, the heat might vaporize some of things, converting them into plasma. The sound of that would be a explosion so huge that just the sound waves alone might be enough to blow up your body. This would take just a few minutes I guess.

• Swallow it - If the planet orbits sufficiently close to a star that enters the Giant Red phase, the star will swallow it. Inside the star, the planet would be teared apart in pieces and mixed with the rest of the star, becoming much hotter. Don't know how this would sound. This would take some years counting from the point that the star atmosphere makes contact to the planet, supposing that it survives being teared apart by tidal forces, of course (see next item).

• Crunch it - If a planet comes too close of a larger planet or a star, passing its Roche limit, the tidal forces would destroy it. I guess that this would probably sound like a lot of continuous thunders, but way louder. The lava will be teared apart and depending of the environment (distance to the star and temperature) it might either cool down or get hotter. This might take from a few days to some thousand of years, depending on the orbital trajectory, both bodies gravity and your planet rigidity. Depending on the orbital trajectory the pieces might end being swallowed by the larger body, being sent away in large elliptic or parabollic or hyperbolic orbits or just keep orbiting the star as an asteroid ring.

• Crash and merge it with something bigger - If a planet crashes into a larger planet, into a star or into a black hole, it will be destroyed. The effects would be similar to the last two methods above. This would probably take something between a few minutes to a few days, depending on the orbital properties. If the object is a star, a brown dwarf or a gas giant, this is essentially the same as being swallowed. If it is a white dwarf, a neutron star or black hole, all the matter will be converted to what the larger body is.

• Crash and merge it with a rocky planet - If your planet is small and rocky and you crash it in a larger also rocky planet, the planets core will merge, the mantles will also merge, a rock-vapour atmosphere will form. It is something similar to the shatter impact, except by the fact that the planets merge instead of being exploded apart.

• Slowly boil it - If a planet orbits very close to a star and it is made mostly of gas content, the stellar wind will blow out the atmosphere of the planet given enough time, making it progressively lighter with progressively less and less gravity. The process is silent because it is very slow and would take millions or billions of years to finish. Not much to say to the lava here, because this is unlike to be able to boil away the lava, which would just cool down until reaching thermal equilibrium.

• Rapidly boil it - If you put the planet in a star-grazing hyperbolic orbit around a blue giant star, when reaching the perihelion or somewhere near, it might be blown away and vaporized just like comet Ison was, including the lava. Don't know how this would sound though. This might take just a few days.

• Instantly boil it - If the star which the planet orbits explodes in a supernova or is gamma-ray bursted, the planet will probably be vaporized in some seconds. Don't know how this would sound.

• Destroy it using particle physics - You might create or find a large quantity of antimatter or strange matter and drop into the planet to blow it up, which would sound like a big explosion. Or build a mini black hole to swallow it up. Or build huge pressures in the planet core to there to create something like a mini pair instability supernova (if you can build a mini black hole, this might be doable also, but don't ask me how). All of those would only take a few seconds. Thanks to @jamesqf for the suggestion.

Now to what I think that you are really interested:

• I used the Google calculator to figure out the number 10^10^76, and Google just said infinity (relative to us, it pretty much is). Jan 15, 2015 at 18:22
• @ShadowZ. The number is indeed finite, but very f***ing large. There are something between 10^78 and 10^82 atoms in the universe. Lets assume that it is 10^78. This means that just to write the number of years in its decimal form, I would need to give a digit to 1% of all atoms of all the universe. Now think about waiting all that time... Jan 15, 2015 at 18:34
• You forgot finding/creating a large chunk of antimatter, and dropping it on the planet. Or having it inhabited by tool-using life forms who figure out how to create a mini black hole... Jan 15, 2015 at 19:33

What generally kills planets (at least those orbiting a sun) is the supernova of the star. Some might fall into the sun from orbital decay or a rogue body coming through the system sending the planet into the star. But there isn't a 'half' life of a planet so unless something else causes it to be destroyed it will just exist.

• Are you sure? Isn't it possible it explodes? Jan 15, 2015 at 15:38
• why would it explode? planets are generally a very low energy source, and they usually continue to stabilize (lose energy) as they age. Where would the energy come from to make it explode? Jan 15, 2015 at 15:41
• what would cause explosion? Planet has very little internal source of energy. @bowlturner you beat me by 25 sec! Jan 15, 2015 at 15:42
• @PeterMasiar some days the fingers just work well! ;) Jan 15, 2015 at 15:45

Another way for a planet to die is to cool. When its core is cold, the planet's tectonics and volcanic activity ceases and planet "dies".

Mars is in this stage. It's core is cold; the molten part of its mantle is very deep. Its only hotspot is under Olympus Mons, the tallest mountain (volcano) in the solar system, 22 km tall, with a footprint about the size of France.

• I read this as, "Another way for planets to die is cool" and thought, "that's not cool, it actually seems pretty boring." Jan 15, 2015 at 16:32
• Mars in particular (and presumably many as-yet-undiscovered exoplanets) probably had a magnetic field comparable to Earth's, that was lost when the core was no longer moving enough to maintain it. This increased the rate at which the solar wind could strip its atmosphere, affecting surface temperature. To a fictional planet with life on it, losing the atmosphere implies a more literal sense of "dying". Jan 15, 2015 at 16:50
• @SteveJessop But if that happens, can't you just send Hilary Swank and Aaron Eckhart to set off some nukes and restart it? Jan 16, 2015 at 17:09

Gravity holds planets together and is a passive thing. They can't "fall apart" as their own weight holds them together. The only way to break up a planet is to supply massive amounts of energy. For example a collision with a rogue planet or moon, passing close to a gas giant, etc. Something with enough energy to rip apart a planet is going to be something very massive.

Planets can die, but it either takes a lot of energy and effort, or is very boring.

1. Boring
Planets can just stop working. As stated by some other answers here, if a planet has no life on it and its processes such as the rock cycle and atmospheric phenomena such as weather have stopped, it can be fairly safely considered dead.

2. Interesting
As you can see in this question, you need $2.4 \times 10^{32}$ joules to counter the Earth's gravitational binding energy - if you want to explode it you need a lot more. This kind of energy does not come lightly (it's roughly equivalent to a small asteroid travelling at very close to the speed of light). You'd need to put in a lot of time and effort to 'kill' a planet this way - it would be far easier just to kill all the life on it.
However, the nearby star can deliver this kind of energy more trivially - if it reaches the end of its life and goes supernova, pretty much the entire local solar system will be destroyed.

Since you seem to want a planet to explode, here's an option: The smallest known star is approximately the same size as Jupiter, and there seem to be extrasolar gas giants up to 80x the size of Jupiter.

So, possibly a large gas giant could absorb enough matter to start undergoing fusion and become a star (a red dwarf). This doesn't match the standard method of star formation though, and it seems more likely that the planet would become a brown dwarf.

The good news is that brown dwarfs can undergo deuterium fusion if they're massive enough, so they're technically exploding. The bad news is that they don't give off enough energy to rip apart in the kind of explosion you're wanting.

One other problem with this is that planets aren't completely stable, so a planet is probably more likely to lose mass over time than gain more (especially if the planet is in orbit around a star, since the star's solar wind will push new mass away).

Regarding your question about sound: even if a release of energy were involved in some way (a collision, etc) a dying planet wouldn't make a sound for the same reason dying stars don't--there is nothing to conduct the vibrations.

Planets sometimes commit suicide. Ours is midway through the process already.

The first step is to spawn some life.

Then you wait while that life becomes sentient.

A little more waiting while that life starts to play with technology: nukes, nanites and artificial intelligence.

Then a singularity occurs. The AI launches the nukes to get rid of the life. Meanwhile, it explores enhancing the nanites.

The waiting is almost over. The planet begins to dissolve, becoming a massive swarm of nanites with an artificial intelligence at the center.

The nanite swarm swims away in search of neighboring planets.

The planet is dead. Long live the planet.

• I, for one, welcome our new sentient nanite overlords.
– DA.
Jan 16, 2015 at 22:46

There are many ways in which a planet can die. Most of them however require an external factor, as a supernova or a meteor impact. However planet can also die of old age. Imagine a planet without atmosphere and without life. Still that planet is "alive" due the rock cycle The rock cycle is a basic concept in geology that describes the dynamic transitions through geologic time among the three main rock types: sedimentary, metamorphic, and igneous. Even Moon has a rock cycle. However, if the cycle stops, the planet is dead.

Proton decay in at minimum 6^66 Years

Another way would be a A massive change in acceleration of the expansion of the universe to an extent that not even nuclear forces will hold atoms toguether will effectively disolve a planet or anything else outside or inside of it.

Further to this I would like to explain that the expansion of the universe is determined by the energy density of the universe. This has changed in the past as per which was the dominant force in the universe. In its infancy photon energy dominated the energy density (this is in the first 300K years - the radiation era); as the universe expands, the wavelength of photons decreases, carrying less energy and so diluting itself. After that the universe was dominated by matter (gravity) until aproximatedly 3 to 4 billion years ago as this expansion continued the average density per cubic meter decreased also as with light (now it's around the energy density of four protons per cubic meter). Since then the universe has been dominated by negative energy and the expansion of the unverse has accelerated. Because the energy density of the university is close to the critical $10^{-26} \text{ kg/m}^3$ (or in energy terms $9 \times 10^{-10} \text{ Joules/m}^3$, we know that space is close to flat right now. Right now only 4% of the energy density is provided by matter while dark matter (basically neutrinos and ultraheavy particles WIMPS) provide 23%. The rest is provided by dark energy,y which is an energy field not made by matter or particles and provides $6.6 \times 10^{-10} \text{ Joules/m}^3$. Now in regard, to the shape of the universe, the current accelerated expansion is equal to the initial slowdown (the universe only dominated by matter or phottons) so we live in a flat universe.

Absent of dark energy, a flat universe expands forever but at a continually decelerating rate, with expansion asymptotically approaching zero. With dark energy, the expansion rate of the Universe initially slows down, due to the effect of radiation and gravity, but eventually increases. The ultimate fate of the Universe is the same as an open universe or an ever increaseasing acceleration. This rate of change in the acceleration of the universe is expanding at a rate of $74.3 \pm 2.1$ kilometers per second per megaparsec.

According to inflation theory the rate of expansion the preinflationary period does not follow the traditional big bang time line. Space may not have expanded at all from its inception until an unknown time where inflation started until its end at 10^-32 seconds. (Gravity would have already been separated from the unified force first and then the two forces eltromagnetism and weak interaction). Allan Gut the father of inflation mentions that as the early universe cooled, it was trapped in a false vacuum with a high energy density. (A false vacum could have seen a drastic change in the energy density content of space due to a decay out of through the process of bubble nucleation via quantum tunneling.) However there was a problem Bubbles of true vacuum spontaneously form in the sea of false vacuum and rapidly begin expanding at the speed of light. but the model did not reheat properly: when the bubbles nucleated, they did not generate any radiation. Radiation could only be generated in collisions between bubble walls. But if inflation lasted long enough to solve the initial conditions problems, collisions between bubbles became exceedingly rare. In any one causal patch it is likely that only one bubble will nucleate. In a solution Andrei Dmitriyevich Linde, instead of tunneling out of a false vacuum state, he through that not only inflation could occur in the false vacuum, but also during a slow transition away from the false vacuum by a scalar field rolling down a potential energy hill. When the field rolls very slowly compared to the expansion of the Universe, inflation occurs. However, when the hill becomes steeper, inflation ends and reheating can occur.

The way a planet will be torn appart is if expansion would occurr instanly due to the same cause that caused the inflation period.

It seems that at very high energy levels, the Higgs boson (provides some of the mass to particles) is megastable at energies above 100bn giga-electron-volts and could cause space and time suddenly collapse. This could mean that the universe could undergo catastrophic vacuum decay as explained above . This is unlikely for a while as the dimesion of this particle accelerator would be larger than the size of earth. http://www.dailymail.co.uk/news/article-2746727/Maybe-shouldn-t-looking-quite-hard-God-particle-destroy-universe-warns-Stephen-Hawking.html#ixzz3PGTjkHqF. However if very advanced civilizations exist it is possible that they develop such machine, however they may be cautious or not yet exist such a machine in the universe.

Another way would be if an ever growing accelerated expansion as explained in big rip theory. (negative energy is called phantom energy takes over). Some sources http://star-www.st-and.ac.uk/~hz4/cos/cosLec3to8.pdf

• No; the expansion of the universe only occurs on extremely large (i.e. intergalactic) scales. Jan 15, 2015 at 22:34
• if the acceleration of expansion overcomes gravity at any scale and then nuclear forces (imagine infinite acceleration of space). Expansion is noticed in very large scales but occurss also at the micro level but is overwelmed by nuclear forces and gravity Jan 16, 2015 at 2:49
• The expansion of space is noticed on large scales due to that its acceleration changes through time and is a weak force in comparison to gravity. Now is accelerating Jan 16, 2015 at 3:03
• I would love to see some sources for this. There are also a few things wrong: For example, neutrinos are not dark matter and are actually extremely low-mass Jan 17, 2015 at 16:26
• Made Edit for the neutrinos - You are right neutrinos are not massive just that there are a lot of them. The massive expansion is called a different form of negative energy called phantom energy (Also initially for those accepting inflation the inflation era had a different type of dark energy which caused inflation - so maybe negative energy changes its nature across time or due to some other reason wich is not matter or energy related) Some sources star-www.st-and.ac.uk/~hz4/cos/cosLec3to8.pdf Jan 17, 2015 at 17:02

Death by Cooling and Erosion - This is not usually considered, but consider what happens when the Earth's core gets cool enough to stop tectonic processes. No more orogeny. Uplift and plate collisions cease, and erosion becomes dominant. Whenever rock is washed into the sea, it stays there. Eventually the entire surface becomes deeper or shallower ocean. That's fine for aquatic life, but not for any other forms.