<h2>Energy Intro</h2>
<p>I think any good discussion of planetary destruction should start by talking about energy!  Our SI base unit of energy is a Joule, which is defined as <span class="math-container">$\mathrm{J} = \mathrm{kg} \mathrm{m}^2 \mathrm{s}^{-2}$</span>, or the force of one newton acting over one meter. Of course energy can also be stored thermally: <span class="math-container">$1 \mathrm{J } \approx 0.239006 \mathrm{ cal}$</span>.  A calorie here is the energy needed to raise the temperature of 1 gram of water by 1 degree Kelvin.</p>
<h2>Minimum Planetary Destruction Energy</h2>
<p>Just how much energy is needed to permanently destroy a planet?  We can start with the idea of GBE (<a href="https://en.wikipedia.org/wiki/Gravitational_binding_energy" rel="nofollow noreferrer">Gravitational Binding Energy</a>), which is the minimum amount of energy required to cause a planet to cease being in a gravitationally bound state.  One way to calculate this is to compute the energy needed to push successive shells of a sphere out to infinity.  GBE is expressed by <span class="math-container">$$U=\frac{-3GM^2}{5R}$$</span>
where <span class="math-container">$G$</span> is the gravitational constant, <span class="math-container">$M$</span> is the mass of the planet, and <span class="math-container">$R$</span> is the planetary radius.  This energy can be pretty huge for planets.  Earth's GBE is about <span class="math-container">$2.49 \times 10^{32} \mathrm{J}$</span>, while Mercury's GBE is about <span class="math-container">$1.8 \times 10^{30} \mathrm{J}$</span>.</p>
<p>To practically destroy a planet, you need much more energy than the GBE.  That is because the GBE doesn't take into account any cohesive properties of the planet. It doesn't account for thermal energy losses. It assumes all ejecta moves at the same rate: escape velocity.</p>
<h2>Planetary Melting Energy</h2>
<p>How much energy is needed to melt a rocky planet?  We can start by looking at the <a href="https://en.wikipedia.org/wiki/Geothermal_gradient" rel="nofollow noreferrer">geothermal gradient</a> of Earth from wikipedia:</p>
<p><a href="https://i.sstatic.net/3Rrzp.jpg" rel="nofollow noreferrer"><img src="https://i.sstatic.net/3Rrzp.jpg" alt="enter image description here" /></a></p>
<p>Rock melts at between 900 and 1600 Kelvin, so there is more than enough heat already in the Earth for it all to be molten if the heat was uniformly distributed and the material was not under pressure!  We can estimate the energy just to melt the lithosphere, supposing average rock has a heat capacity of 2000 Joules per kilogram per °C.  If the lithosphere is about 1 percent of the total mass of the Earth or <span class="math-container">$6\times 10^{22} \mathrm{kg}$</span> and the current average temp is about 700K, then to raise the temp to 1600K, we would need <span class="math-container">$1.08 \times 10^{29} \mathrm{J}$</span>.</p>
<p>Suppose we had a cold-start rocky planet similar in shape and composition to Mercury, but at a uniform cold temp of 40K. Mercury has a mass of <span class="math-container">$3.285\times 10^{23} \mathrm{kg}$</span>.  So to bring its temp from 40K to 1600K, we would need <span class="math-container">$(1600-40)*2000*3.285\times 10^{23}= 1.025 \times 10^{30} \mathrm{J}$</span>.</p>
<h2>Answer</h2>
<p>For an Earth like planet, the melting energy (<span class="math-container">$1.08 \times 10^{29} \mathrm{J}$</span>) is <strong>much</strong> smaller than the GBE (<span class="math-container">$2.49 \times 10^{32} \mathrm{J}$</span>).  This means that even with a purely kinetic energy source, more than enough heat will be produced due to the friction and enthalpy that not much solid will be left after impact.  In addition, the material around the impact will be ionized (turned into plasma), and material further away will be vaporized.  As the Earth exploded, we could expect the ejecta to be in the form of droplets, gas, and plasma until they cooled as they expanded and passed through space.</p>
<p>For a theoretical, small, cold, rocky planet near a Pluto like orbit, the melting energy (<span class="math-container">$1.025 \times 10^{30} \mathrm{J}$</span>) is the same order of magnitude to the GBE (<span class="math-container">$1.8 \times 10^{30} \mathrm{J})$</span>.  Hence, while heat will be sufficient for matter phase transitions near the impact, we could expect large chunks of solid ejecta away from the impact area.  This is a partial &quot;shattered marble&quot; scenario.</p>
<p>Out of any source of planetary destruction, I think a kinetic impactor has the smallest thermal component.  A nuclear bomb blast big enough to destroy a planet would likely liquify even our theoretical cold Mercury, since much of the energy of a nuclear bomb blast is thermal. Credit <a href="https://www.atomicarchive.com/science/effects/energy.html" rel="nofollow noreferrer">Atomic Archive</a>:</p>
<p><a href="https://i.sstatic.net/jXFEh.png" rel="nofollow noreferrer"><img src="https://i.sstatic.net/jXFEh.png" alt="enter image description here" /></a></p>
<p>Gamma ray bursts (<span class="math-container">$10^{50} \mathrm{J}$</span>) have enough energy to destroy a planet, but would transfer energy thermally since they are electro-magnetic. Direct, close exposure would vaporize (ionize?) a planet.  Sufficiently close supernovas (<span class="math-container">$10^{48} \mathrm{J}$</span>), hypernovas (<span class="math-container">$10^{46} \mathrm{J}$</span>), and AGN (Active Galactic Nucleus) bursts (<span class="math-container">$10^{55} \mathrm{J}$</span>) also have enough energy, but would also certainly vaporize (ionize?) a planet. (Energy estimates credit to <a href="https://en.wikipedia.org/wiki/Orders_of_magnitude_(energy)" rel="nofollow noreferrer">wikipedia</a>)</p>
<p>Finally, the Death Star's laser would also primarily transfer energy to the planet thermally, rather than kinetically. So, we would expect more of a melting and vaporizing effect than a kinetic explosion!</p>
<h2>Example:</h2>
<p>But a planet could never really be destroyed, right?</p>
<p>Maybe not! The &quot;de facto working model for lunar origin&quot; according to <a href="https://agupubs.onlinelibrary.wiley.com/doi/full/10.1002/2017JE005333" rel="nofollow noreferrer">Lock et. al 2018</a>, is that &quot;the proto-Earth suffered a collision with another protoplanet near the end of accretion that ejected material into a circumterrestrial disk, out of which the Moon formed.&quot;  Further, they suspect that the protoplanet might have been the size of Mars and have struck at &quot;near the mutual escape velocity.&quot;  This wouldn't impart more energy than Earth's GBE, so Earth would not have un-bound.  But it certainly would have rendered what was left of Earth fully molten, with a disk that was a &quot;multiphase mixture of liquid and vapor.&quot;</p>
<p>In the same paper, Lock et. al offer a variation on the standard giant impact hypothesis, that instead of a liquid/gas disk being formed, the collision fully vaporized both bodies and resulted in a <a href="https://en.wikipedia.org/wiki/Synestia" rel="nofollow noreferrer">synestia</a>, which is a rapidly rotating vaporized tauroid (donut shaped object).  As the synestia lost heat, the authors theorize that the gas condensed into liquid,  eventually allowing the Earth and Moon to form.  Here is a graphic from their paper:</p>
<p><a href="https://i.sstatic.net/xX5w5.png" rel="nofollow noreferrer"><img src="https://i.sstatic.net/xX5w5.png" alt="enter image description here" /></a></p>
<p>While the various lunar forming hypotheses don't permanently destroy the Earth, it seems very unlikely any life would survive.  The various hypotheses may vary on how much liquid matter would remain after such a high energy collision, but they agree that the ejecta certainly wouldn't be solid!</p>

CC BY-SA 4.0
2022-03-16T19:03:24.080Z
2022-03-17T15:02:15.533Z
2022-03-17T15:02:15.533Z
Connor Garcia
<p>Well...  a few issues here.</p>
<p>Firstly, the mantle of the Earth isn't molten.  It is solid.  It is hot enough for there to be slowly moving currents of solid rock.  On the other hand, the outer core <em>is</em> liquid, and very liquid. It is about as viscous as water.</p>
<p>Now, superlasers aren't real, but planetary collisions are real, and did occur in the early evolution of the solar system. However neither the &quot;shattering&quot; nor the &quot;cracking&quot; metaphor would describe the consequence of such collisions. Instead the impact would have sufficient energy to completely melt, (and probably vaporise) the planet.  In any case, the forces resulting from such an impact would be so great that solid rock would behave like a liquid or gas.</p>

CC BY-SA 4.0
2022-03-15T23:31:00.767Z
2022-03-17T06:30:08.450Z
2022-03-17T06:30:08.450Z
James K
<p>Its worth noting that not all plants have a liquid core and not all planets are rocky. You can't expect a gas giant like Jupiter to shatter like glass.</p>
<p>To shatter a <em>rocky</em> planet like earth into a gazillion number of pieces needs very high amount of energy which is unlikely to happen. Talking about super-lasers, There are only naturally occurring events than can be as energetic to even vaporize earth can be from events like Gamma ray bursts from Supernovae happening near Earth. And destroying the whole earth by a collision is very <a href="https://en.wikipedia.org/wiki/Impact_event" rel="nofollow noreferrer">unlikely</a></p>
<p>And like you say, when a rocky planet with molten core inside, <em><strong>bursts</strong></em> or cracks up due to a collision ,say Earth, the molten core will not be <a href="https://physics.stackexchange.com/questions/169192/why-doesnt-liquid-metal-vaporize-in-a-vacuum">liquid anymore</a> due to the absence of the pressure to keep them in liquid state (most of the core will vaporize), rocky mantle and crust will then form a ring around the sun which one day may become planet by the same way our moon is said to have formed.</p>

CC BY-SA 4.0
2022-03-16T13:42:19.500Z
2022-03-16T13:52:10.970Z
2022-03-16T13:52:10.970Z
Kavin Ishwaran
<p>I remember seeing Star Wars, where Darth Vader shoots a superb laser (Death Star) to obliterate a populated planet, Alderaan (how inhumane).</p>
<p>The problem is, the planet cracked into a gazillion rocky pieces, like you would get if you dropped a marble ball from the top of the empire state building.</p>
<p>But, rocky planets (and perhaps other sufficiently large rocky bodies) have molten mantle. So I think, it should have cracked open like an egg, the crust shattering into a zillion pieces like an eggshell, with the viscous mantle liquid being sprayed across in space.</p>
<p>[Note that I am not referring to the firing of 'Jedha' (Rogue One) where a much reasonable planetary destruction was shown. I am referring to the original Star Wars, later dubbed The New Hope]</p>
<p>From Wikipedia's <a href="https://en.wikipedia.org/wiki/Terrestrial_planet" rel="nofollow noreferrer">Terrestrial planet</a>:</p>
<blockquote>
<p>A <strong>terrestrial planet</strong>, <strong>telluric planet</strong>, or <strong>rocky planet</strong>, is a planet that is composed primarily of silicate rocks or metals. Within the Solar System, the terrestrial planets accepted by the IAU are the inner planets closest to the Sun, i.e. Mercury, Venus, Earth and Mars. Among astronomers who use the geophysical definition of a planet, two or three planetary-mass satellites – Earth's Moon, Io, and sometimes Europa – may also be considered terrestrial planets; and so may be the rocky protoplanet-asteroids Pallas and Vesta. The terms &quot;terrestrial planet&quot; and &quot;telluric planet&quot; are derived from Latin words for Earth (Terra and Tellus), as these planets are, in terms of structure, Earth-like.</p>
</blockquote>

CC BY-SA 4.0
2022-03-13T13:05:51.323Z
Welcome to Astronomy SE !. Its worth noting that not all planets have a molten core and not all planets are *rocky*
Kavin Ishwaran
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2022-03-13T13:07:26.910Z
I guess this post is on-topic in Science fiction and fantasy SE
Kavin Ishwaran
CC BY-SA 4.0
2022-03-13T13:46:43.927Z
I'm not sure if this can be reasonably said to be on topic as astronomy. - and it's not really world*building* either! However any event that is energetic enough to break up a planet wouldnt' leave many chunks. You wouldn't "see" much since you'd be vaporised by the heat of the explosion.
James K
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2022-03-13T15:12:40.963Z
@kavin this question was closed there
Sage of Seven Paths
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2022-03-13T15:23:38.823Z
I believe this question could be on-topic here: It is a phenomenon observed in the heavy-bombardment phase of planetformation when two planetary embryos of approximately equal size collide, e.g. also like the impact creating Earth's moon.
planetmaker
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2022-03-13T15:28:54.427Z
@SageofSevenPaths Ok then. probably it can be on-topic here if we see the question in a different way.
Kavin Ishwaran
CC BY-SA 4.0
2022-03-13T21:57:42.133Z
I think this question might be improved by specifying how it was broken apart.  If we want o keep it realistic, is this the result of a collision with another object?  If so that's something that can probably be answered, at least qualitatively.
GrapefruitIsAwesome
CC BY-SA 4.0
2022-03-13T21:57:45.020Z
This question is **centrally on-topic** in solar system formation. At one point we think there were many more planets than there are now, and so certainly models of solar system evolution will have had to address this somehow. *Great question!*
uhoh
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2022-03-13T22:03:16.517Z
**No** not a "great" question.  A poorly phrased question that is marginal at best. (sorry)  There might be a "great" question about planetary formation, but this isn't it.  It is about superlasers, which (as far as I know) played at most a minimal part in planetary formation.  I wish you'd stop describing questions as "great" and start making construction suggestions on improving them.  In this case I'd suggest removing the "superlaser" aspect (or moving it to an introductory "background context" paragraph) and changing the question to ask about planetary collisions.
James K
CC BY-SA 4.0
2022-03-14T12:17:59.123Z
I agree with James. The destruction of Aldaraan in *Star Wars* isn't consistent with known physics, and we don't normally answer unrealistic hypothetical questions on this site.
PM 2Ring
CC BY-SA 4.0
2022-03-14T12:22:51.977Z
BTW, the [Earth's mantle](https://en.wikipedia.org/wiki/Earth%27s_mantle) isn't exactly molten. "It is predominantly solid but, on geologic time scales, it behaves as a viscous fluid [...] Although the higher temperatures far exceed the melting points of the mantle rocks at the surface (about 1200 °C for representative peridotite), the mantle is almost exclusively solid. The enormous lithostatic pressure exerted on the mantle prevents melting, because the temperature at which melting begins (the solidus) increases with pressure".
PM 2Ring
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2022-03-14T13:44:25.587Z
Will somebody tell which SE site this question actually suits?
Sage of Seven Paths
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2022-03-14T23:01:54.893Z
If you change it from a Death Star to an [Astrophysical Jet](https://en.wikipedia.org/wiki/Astrophysical_jet) it'd be on-topic here, or on Physics. A related option is a [megamaser](https://en.wikipedia.org/wiki/Megamaser).
PM 2Ring
CC BY-SA 4.0
2022-03-15T00:54:38.433Z
SE Physics would probably be the most appropriate site for this question. The question currently lacks focus - it requires much detail to be answered. What form of massive energy transfer system would impact a planet, causing it to be destroyed: a single large planet, multiple planets or planetesimals, or a [death ray](https://www.universetoday.com/82592/death-ray/)? Each of these scenarios have multiple possibilities. One hypothesis concerning the Earth & the Moon is a Mars sized planet [collided with Earth](https://en.wikipedia.org/wiki/Giant-impact_hypothesis). Earth survived!
Fred
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2022-03-15T22:13:53.547Z
@uhoh What's up with the bounty? This question is about a planet being blasted by an energy beam. It's *not* asking about what happens when rocky bodies collide.
PM 2Ring
CC BY-SA 4.0
2022-03-15T22:25:20.900Z
@PM2Ring the question is not about "what happened in a movie I saw". The reference explains what got the OP thinking about the question in the first place. We often encourage users to include explanation of their current thinking about a question or what they have read or learned, and this user is simply being honest and open about what got them to the point of posting a question here. I'm simply saying that there may indeed be theoretical work on how rocky planets break apart, what it's like (e.g. fragmenting vs oozing) and citing those could be the basis of an answer.
uhoh
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2022-03-15T22:29:37.120Z
@PM2Ring so in this particular case I think it's okay to provide this user and future readers whatever science does have to offer on this topic, and the larger +200 rather than my usual +100 bounty is for the extra work it might be locating whatever theoretical work is out there. Perhaps one can see this as a tiny micro-version and in the spirit of [Kip Thorne's contributions to Interstellar](https://en.wikipedia.org/wiki/Interstellar_(film)) in that science fiction and science can work together to help educate the public.
uhoh
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2022-03-15T22:37:10.730Z
@PM2Ring If someone sees something in a film and it leads them to join a science-based SE site and ask a question, let's welcome both them and their question and provide science-based answers.
uhoh
CC BY-SA 4.0
2022-03-15T22:49:29.467Z
@uhoh I haven't voted to close the question, and I made suggestions about how to modify it slightly so that it's on-topic. An earlier comment made a suggestion about protoplanetary collisions, but the OP didn't respond to that. If the OP wants to change the question so that it's about collisions, that's quite ok, since there are no answers posted yet. But attempting to change the topic via a bounty notice clearly conflicts with the author's intent.
PM 2Ring
CC BY-SA 4.0
2022-03-15T22:55:27.057Z
I did not "attemp(t) to change the topic via a bounty notice". I did encourage answers that address *the scientific aspects of the OPs question* to the extent possible, and reproduce with quotes my thinking of how this could be accomplished.
uhoh
CC BY-SA 4.0
2022-03-17T10:58:13.360Z
While death star is well, not real, our future generations will possibly be able to create mega structures such as dyson spheres, and "black hole bombs", which definitely have potential to gather enough energy output for planetary destruction. This question is not a star wars question, but it is a astrophysics one, on what are the possibilities for a planet blasted by a overpowered astrophysical jet/relativistic missile/etc would do to a planet.
Sage of Seven Paths
CC BY-SA 4.0
2022-03-17T11:01:06.503Z
Further i have been thinking about a third possibility- sufficiently powered energy sources can also 'blow' a planet away, just like a solar sail satellite like IKAROS, making it leave its orbit and so on
Sage of Seven Paths
<planet><planetary-science><collision>
How do rocky planet break up? Would they fragment into "a gazillion" rocky pieces pieces, or crack open like an egg?
Sage of Seven Paths
# How do rocky planet break up? Would they fragment into "a gazillion" rocky pieces pieces, or crack open like an egg?

(Asked by: username_0 on 2022-03-13)

I remember seeing Star Wars, where Darth Vader shoots a superb laser (Death Star) to obliterate a populated planet, Alderaan (how inhumane).

The problem is, the planet cracked into a gazillion rocky pieces, like you would get if you dropped a marble ball from the top of the empire state building.

But, rocky planets (and perhaps other sufficiently large rocky bodies) have molten mantle. So I think, it should have cracked open like an egg, the crust shattering into a zillion pieces like an eggshell, with the viscous mantle liquid being sprayed across in space.

[Note that I am not referring to the firing of 'Jedha' (Rogue One) where a much reasonable planetary destruction was shown. I am referring to the original Star Wars, later dubbed The New Hope]

From Wikipedia's [Terrestrial planet](https://en.wikipedia.org/wiki/Terrestrial_planet):

> A **terrestrial planet**, **telluric planet**, or **rocky planet**, is a planet that is composed primarily of silicate rocks or metals. Within the Solar System, the terrestrial planets accepted by the IAU are the inner planets closest to the Sun, i.e. Mercury, Venus, Earth and Mars. Among astronomers who use the geophysical definition of a planet, two or three planetary-mass satellites – Earth's Moon, Io, and sometimes Europa – may also be considered terrestrial planets; and so may be the rocky protoplanet-asteroids Pallas and Vesta. The terms "terrestrial planet" and "telluric planet" are derived from Latin words for Earth (Terra and Tellus), as these planets are, in terms of structure, Earth-like.

**Tags:** planet, planetary-science, collision
> **Comments:**
> **username_1**: Welcome to Astronomy SE !. Its worth noting that not all planets have a molten core and not all planets are *rocky*  
> **username_1**: I guess this post is on-topic in Science fiction and fantasy SE  
> **username_2**: I'm not sure if this can be reasonably said to be on topic as astronomy. - and it's not really world*building* either! However any event that is energetic enough to break up a planet wouldnt' leave many chunks. You wouldn't "see" much since you'd be vaporised by the heat of the explosion.  
> **username_0**: @kavin this question was closed there  
> **username_3**: I believe this question could be on-topic here: It is a phenomenon observed in the heavy-bombardment phase of planetformation when two planetary embryos of approximately equal size collide, e.g. also like the impact creating Earth's moon.  
> **username_1**: @SageofSevenPaths Ok then. probably it can be on-topic here if we see the question in a different way.  
> **username_4**: I think this question might be improved by specifying how it was broken apart.  If we want o keep it realistic, is this the result of a collision with another object?  If so that's something that can probably be answered, at least qualitatively.  
> **username_5**: This question is **centrally on-topic** in solar system formation. At one point we think there were many more planets than there are now, and so certainly models of solar system evolution will have had to address this somehow. *Great question!*  
> **username_2**: **No** not a "great" question.  A poorly phrased question that is marginal at best. (sorry)  There might be a "great" question about planetary formation, but this isn't it.  It is about superlasers, which (as far as I know) played at most a minimal part in planetary formation.  I wish you'd stop describing questions as "great" and start making construction suggestions on improving them.  In this case I'd suggest removing the "superlaser" aspect (or moving it to an introductory "background context" paragraph) and changing the question to ask about planetary collisions.  
> **username_6**: I agree with James. The destruction of Aldaraan in *Star Wars* isn't consistent with known physics, and we don't normally answer unrealistic hypothetical questions on this site.  
> **username_6**: BTW, the [Earth's mantle](https://en.wikipedia.org/wiki/Earth%27s_mantle) isn't exactly molten. "It is predominantly solid but, on geologic time scales, it behaves as a viscous fluid [...] Although the higher temperatures far exceed the melting points of the mantle rocks at the surface (about 1200 °C for representative peridotite), the mantle is almost exclusively solid. The enormous lithostatic pressure exerted on the mantle prevents melting, because the temperature at which melting begins (the solidus) increases with pressure".  
> **username_0**: Will somebody tell which SE site this question actually suits?  
> **username_6**: If you change it from a Death Star to an [Astrophysical Jet](https://en.wikipedia.org/wiki/Astrophysical_jet) it'd be on-topic here, or on Physics. A related option is a [megamaser](https://en.wikipedia.org/wiki/Megamaser).  
> **username_7**: SE Physics would probably be the most appropriate site for this question. The question currently lacks focus - it requires much detail to be answered. What form of massive energy transfer system would impact a planet, causing it to be destroyed: a single large planet, multiple planets or planetesimals, or a [death ray](https://www.universetoday.com/82592/death-ray/)? Each of these scenarios have multiple possibilities. One hypothesis concerning the Earth & the Moon is a Mars sized planet [collided with Earth](https://en.wikipedia.org/wiki/Giant-impact_hypothesis). Earth survived!  
> **username_6**: @uhoh What's up with the bounty? This question is about a planet being blasted by an energy beam. It's *not* asking about what happens when rocky bodies collide.  
> **username_5**: @PM2Ring the question is not about "what happened in a movie I saw". The reference explains what got the OP thinking about the question in the first place. We often encourage users to include explanation of their current thinking about a question or what they have read or learned, and this user is simply being honest and open about what got them to the point of posting a question here. I'm simply saying that there may indeed be theoretical work on how rocky planets break apart, what it's like (e.g. fragmenting vs oozing) and citing those could be the basis of an answer.  
> **username_5**: @PM2Ring so in this particular case I think it's okay to provide this user and future readers whatever science does have to offer on this topic, and the larger +200 rather than my usual +100 bounty is for the extra work it might be locating whatever theoretical work is out there. Perhaps one can see this as a tiny micro-version and in the spirit of [Kip Thorne's contributions to Interstellar](https://en.wikipedia.org/wiki/Interstellar_(film)) in that science fiction and science can work together to help educate the public.  
> **username_5**: @PM2Ring If someone sees something in a film and it leads them to join a science-based SE site and ask a question, let's welcome both them and their question and provide science-based answers.  
> **username_6**: @uhoh I haven't voted to close the question, and I made suggestions about how to modify it slightly so that it's on-topic. An earlier comment made a suggestion about protoplanetary collisions, but the OP didn't respond to that. If the OP wants to change the question so that it's about collisions, that's quite ok, since there are no answers posted yet. But attempting to change the topic via a bounty notice clearly conflicts with the author's intent.  
> **username_5**: I did not "attemp(t) to change the topic via a bounty notice". I did encourage answers that address *the scientific aspects of the OPs question* to the extent possible, and reproduce with quotes my thinking of how this could be accomplished.  
> **username_0**: While death star is well, not real, our future generations will possibly be able to create mega structures such as dyson spheres, and "black hole bombs", which definitely have potential to gather enough energy output for planetary destruction. This question is not a star wars question, but it is a astrophysics one, on what are the possibilities for a planet blasted by a overpowered astrophysical jet/relativistic missile/etc would do to a planet.  
> **username_0**: Further i have been thinking about a third possibility- sufficiently powered energy sources can also 'blow' a planet away, just like a solar sail satellite like IKAROS, making it leave its orbit and so on  

---

## 3 answers

### Answer by username_8 on 2022-03-16. Score: 9

## Energy Intro

I think any good discussion of planetary destruction should start by talking about energy! Our SI base unit of energy is a Joule, which is defined as $\mathrm{J} = \mathrm{kg} \mathrm{m}^2 \mathrm{s}^{-2}$, or the force of one newton acting over one meter. Of course energy can also be stored thermally: $1 \mathrm{J } \approx 0.239006 \mathrm{ cal}$. A calorie here is the energy needed to raise the temperature of 1 gram of water by 1 degree Kelvin.

## Minimum Planetary Destruction Energy

Just how much energy is needed to permanently destroy a planet? We can start with the idea of GBE ([Gravitational Binding Energy](https://en.wikipedia.org/wiki/Gravitational_binding_energy)), which is the minimum amount of energy required to cause a planet to cease being in a gravitationally bound state. One way to calculate this is to compute the energy needed to push successive shells of a sphere out to infinity. GBE is expressed by $$U=\frac{-3GM^2}{5R}$$
where $G$ is the gravitational constant, $M$ is the mass of the planet, and $R$ is the planetary radius. This energy can be pretty huge for planets. Earth's GBE is about $2.49 \times 10^{32} \mathrm{J}$, while Mercury's GBE is about $1.8 \times 10^{30} \mathrm{J}$.

To practically destroy a planet, you need much more energy than the GBE. That is because the GBE doesn't take into account any cohesive properties of the planet. It doesn't account for thermal energy losses. It assumes all ejecta moves at the same rate: escape velocity.

## Planetary Melting Energy

How much energy is needed to melt a rocky planet? We can start by looking at the [geothermal gradient](https://en.wikipedia.org/wiki/Geothermal_gradient) of Earth from wikipedia:

[![enter image description here](https://i.sstatic.net/3Rrzp.jpg)](https://i.sstatic.net/3Rrzp.jpg)

Rock melts at between 900 and 1600 Kelvin, so there is more than enough heat already in the Earth for it all to be molten if the heat was uniformly distributed and the material was not under pressure! We can estimate the energy just to melt the lithosphere, supposing average rock has a heat capacity of 2000 Joules per kilogram per °C. If the lithosphere is about 1 percent of the total mass of the Earth or $6\times 10^{22} \mathrm{kg}$ and the current average temp is about 700K, then to raise the temp to 1600K, we would need $1.08 \times 10^{29} \mathrm{J}$.

Suppose we had a cold-start rocky planet similar in shape and composition to Mercury, but at a uniform cold temp of 40K. Mercury has a mass of $3.285\times 10^{23} \mathrm{kg}$. So to bring its temp from 40K to 1600K, we would need $(1600-40)\*2000\*3.285\times 10^{23}= 1.025 \times 10^{30} \mathrm{J}$.

## Answer

For an Earth like planet, the melting energy ($1.08 \times 10^{29} \mathrm{J}$) is **much** smaller than the GBE ($2.49 \times 10^{32} \mathrm{J}$). This means that even with a purely kinetic energy source, more than enough heat will be produced due to the friction and enthalpy that not much solid will be left after impact. In addition, the material around the impact will be ionized (turned into plasma), and material further away will be vaporized. As the Earth exploded, we could expect the ejecta to be in the form of droplets, gas, and plasma until they cooled as they expanded and passed through space.

For a theoretical, small, cold, rocky planet near a Pluto like orbit, the melting energy ($1.025 \times 10^{30} \mathrm{J}$) is the same order of magnitude to the GBE ($1.8 \times 10^{30} \mathrm{J})$. Hence, while heat will be sufficient for matter phase transitions near the impact, we could expect large chunks of solid ejecta away from the impact area. This is a partial "shattered marble" scenario.

Out of any source of planetary destruction, I think a kinetic impactor has the smallest thermal component. A nuclear bomb blast big enough to destroy a planet would likely liquify even our theoretical cold Mercury, since much of the energy of a nuclear bomb blast is thermal. Credit [Atomic Archive](https://www.atomicarchive.com/science/effects/energy.html):

[![enter image description here](https://i.sstatic.net/jXFEh.png)](https://i.sstatic.net/jXFEh.png)

Gamma ray bursts ($10^{50} \mathrm{J}$) have enough energy to destroy a planet, but would transfer energy thermally since they are electro-magnetic. Direct, close exposure would vaporize (ionize?) a planet. Sufficiently close supernovas ($10^{48} \mathrm{J}$), hypernovas ($10^{46} \mathrm{J}$), and AGN (Active Galactic Nucleus) bursts ($10^{55} \mathrm{J}$) also have enough energy, but would also certainly vaporize (ionize?) a planet. (Energy estimates credit to [wikipedia](https://en.wikipedia.org/wiki/Orders_of_magnitude_(energy)))

Finally, the Death Star's laser would also primarily transfer energy to the planet thermally, rather than kinetically. So, we would expect more of a melting and vaporizing effect than a kinetic explosion!

## Example:

But a planet could never really be destroyed, right?

Maybe not! The "de facto working model for lunar origin" according to [Lock et. al 2018](https://agupubs.onlinelibrary.wiley.com/doi/full/10.1002/2017JE005333), is that "the proto-Earth suffered a collision with another protoplanet near the end of accretion that ejected material into a circumterrestrial disk, out of which the Moon formed." Further, they suspect that the protoplanet might have been the size of Mars and have struck at "near the mutual escape velocity." This wouldn't impart more energy than Earth's GBE, so Earth would not have un-bound. But it certainly would have rendered what was left of Earth fully molten, with a disk that was a "multiphase mixture of liquid and vapor."

In the same paper, Lock et. al offer a variation on the standard giant impact hypothesis, that instead of a liquid/gas disk being formed, the collision fully vaporized both bodies and resulted in a [synestia](https://en.wikipedia.org/wiki/Synestia), which is a rapidly rotating vaporized tauroid (donut shaped object). As the synestia lost heat, the authors theorize that the gas condensed into liquid, eventually allowing the Earth and Moon to form. Here is a graphic from their paper:

[![enter image description here](https://i.sstatic.net/xX5w5.png)](https://i.sstatic.net/xX5w5.png)

While the various lunar forming hypotheses don't permanently destroy the Earth, it seems very unlikely any life would survive. The various hypotheses may vary on how much liquid matter would remain after such a high energy collision, but they agree that the ejecta certainly wouldn't be solid!


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### Answer by username_2 on 2022-03-15. Score: 2

Well... a few issues here.

Firstly, the mantle of the Earth isn't molten. It is solid. It is hot enough for there to be slowly moving currents of solid rock. On the other hand, the outer core *is* liquid, and very liquid. It is about as viscous as water.

Now, superlasers aren't real, but planetary collisions are real, and did occur in the early evolution of the solar system. However neither the "shattering" nor the "cracking" metaphor would describe the consequence of such collisions. Instead the impact would have sufficient energy to completely melt, (and probably vaporise) the planet. In any case, the forces resulting from such an impact would be so great that solid rock would behave like a liquid or gas.


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### Answer by username_1 on 2022-03-16. Score: 1

Its worth noting that not all plants have a liquid core and not all planets are rocky. You can't expect a gas giant like Jupiter to shatter like glass.

To shatter a *rocky* planet like earth into a gazillion number of pieces needs very high amount of energy which is unlikely to happen. Talking about super-lasers, There are only naturally occurring events than can be as energetic to even vaporize earth can be from events like Gamma ray bursts from Supernovae happening near Earth. And destroying the whole earth by a collision is very [unlikely](https://en.wikipedia.org/wiki/Impact_event)

And like you say, when a rocky planet with molten core inside, ***bursts*** or cracks up due to a collision ,say Earth, the molten core will not be [liquid anymore](https://physics.stackexchange.com/questions/169192/why-doesnt-liquid-metal-vaporize-in-a-vacuum) due to the absence of the pressure to keep them in liquid state (most of the core will vaporize), rocky mantle and crust will then form a ring around the sun which one day may become planet by the same way our moon is said to have formed.


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