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Earth is destroyed in explosive fashion by an unknown force. How does this affect the rest of the Solar System? Does sudden absence of that mass affect the orbits of the other planets at all? Let's say that the moon is relatively unscathed in that it missed some of the major chunks expelled out in the initial boom. With the earth gone, does its previous orbital momentum launch it towards the Sun or towards the asteroid belt to be pummeled into oblivion by stray rocks? Where would the chunks of planet be flung to? How would all of this affect a halfway terraformed Mars?

  • There is a sizeable population on Mars, which as mentioned is halfway terraformed with five major cities and a rail system connecting them.
  • The moon has a pretty big population as well, though it's mostly novelty tourist stuff, space cruise terminal, and mining barge construction bays.
  • There are science outposts on some of the moons of the outer planets, and one on Pluto, plus mining stations within the asteroid belt. I tried to simulate this in Universe Sandbox, but before I could even press the boom button, the moons of Jupiter and Saturn decided to fly off into oblivion for some reason.
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    $\begingroup$ One thing I've learned from this site is that people really destroying the Earth, which makes me wonder if this is just going to turn into a Super Villains SE some day. $\endgroup$ – Crabgor Dec 15 '14 at 17:37
  • $\begingroup$ @Cragor Yep! Destroy humanity, Destroy Earth, Destroy the sun. How evil are you?! ;) $\endgroup$ – bowlturner Dec 15 '14 at 17:39
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    $\begingroup$ My usual tagline is 'your future robot overlord' and my personal blog is titled 'voted most likely to cause a galactic civil war'. That's about an 8 on the Malevolent Villain Scale. $\endgroup$ – Arad Dec 15 '14 at 17:46
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    $\begingroup$ When you say that the Earth is exploded, do you mean it is broken up into chunks with the same mass the whole Earth used to have, or that the entire mass of the Earth just vanishes? The distinction makes a huge difference in what happens to the rest of the solar system. (Frankly, the first scenario is rather boring - with the same mass in roughly the same spot, other planets wouldn't be affected in any way whatsoever.) $\endgroup$ – Kevin Dec 15 '14 at 20:20
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    $\begingroup$ @Kevin: The first scenario is only boring if the chunks have little kinetic energy. If the earth is broken up into chunks that are expelled at 90% of the speed of light (one hell of an explosion, I know) then I can see that being much more exciting since the mass will disperse rapidly and have a chance (relatively small admittedly) of hitting other planets. Though I guess there is a much higher chance of it hitting something in the asteroid belt and then cascading... My point though is that those aren't the only two options. $\endgroup$ – Chris Dec 16 '14 at 11:02
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Mostly likely, immediately after a planet shearing explosion the pieces of the Earth would not fly off into space. I doubt you could add enough energy to all the mass of the Earth to escape the mutual gravitation and somehow also protect the moon from that release.

If the Moon is still there, then most of the mass of the Earth is also likely still there, think Praxis rather than Alderaan.

In that case, the Moon's Earthly orbit might be highly disturbed. With the pull of Earth severely weakened, the Moon would continue in its orbit around the Earth while spiraling outward at some significant, but not necessarily exciting, velocity. The spiral would only be from the point of view of the Earth. Even the ellipitcal orbit doesn't look like much from the point of view of the Sun.

This spiral (or wobble from the Sun's perspective) would increase its deviation until the pull of the Sun was too strong for the Earth shards to pull it back. enter image description here

The gray line is the Moon's orbit around Earth from the point of view of the Sun. Blue is the Earth, naturally.

At that point, the Moon would be defined as an asteroid by the artificial brain holding the uploaded mind of Neil DeGrasse Tyson. However, some small, but vocal, group of people would hate scientists for this terrible act. They would demand, as if science were a democracy, that the Moon is still a moon.

The orbit of Mars would not be significantly disturbed. It would be altered, but not in any significant or noticeable way.

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  • $\begingroup$ This is closer to what I was thinking, with most of the mass still technically there but some chunks still getting launched out in the initial boom. Broken planet with trail of debris works a hell of a lot better for in the long run than Alderaan style disintegration, at least story-wise. $\endgroup$ – Arad Dec 15 '14 at 18:39
  • $\begingroup$ How did you create the diagram? $\endgroup$ – machinaut Dec 15 '14 at 19:58
  • $\begingroup$ The diagram is from Wikipedia. It's linked to in the answer already, but here it is again. $\endgroup$ – Samuel Dec 15 '14 at 20:01
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Where would Moon go is obvious and answered by others - interesting is how will human colonies deal with the consequences?

Where would Earth debris fly, depends of the energy and direction of the death blow.

  • With enough energy, debris would fly all over the inner solar system - and Moon, after surviving first impact, will continue near Earth orbit (which will be also path of most of the Earth debris). Such debris are danger for Mars and Moon (and other asteroid mines), but not Pluto.
  • With less energy, debris will fly close to original Earth orbit and with just little energy, Moon might be able to orbit remnants of the Earth, and debris would be less of a danger for Mars.

Big chunk of the debris might re-accrete into new Earth - it will not be habitable for millions of years, but at least other human colonies would be safe from debris. If not, we have new (inner) asteroid belt - some chunks could cool down in few hundred/thousands years to be useful for mining for resources like metals. Good source of iron, already orbiting - and we will need it.

Absence of Earth will not have any major impact on the other planets - Sun's gravity sets the rules.

What would have impact would be flying debris. Bombardment of human colonies on Mars and especially Moon by Earth remnants would be great danger for centuries. Moon would have likely most of the colonies on the Earth side - and they would be heavily impacted by original explosion.

What about other human colonies?

Survival of the other the human colonies would depend on how independent their ecologies are. It will be rather hard, I presume, to grow all the food, but food production would be obviously highest priority. Quality of life would decrease substantially on Mars - but it's better to struggle than to be dead. If Moon is just tourist trap, most or all population would quickly starve.

Pluto is so far that it has to be independent (nuclear-powered hydroponics anyone?) - so Pluto most likely will survive, even if Mars could not survive bombardment by Earth debris and damage to its ecology. Any rogue debris from Earth will take long time to get to Pluto, and it's trajectory could be simply changed to less dangerous. So maybe it will be Pluto which will repopulate Solar system.

If Earth debris form another asteroid belt, survivors from Pluto and Mars would have excellent mining base to build interstellar spaceships.

Terraforming Mars is IMHO fools errands, Mars would lose new atmosphere for exactly same reasons it lost old one, especially with the extremely limited resources on Mars. Of course it depends of danger of bombardment by Earth debris, and how close is terraforming from being finished. Maybe if some chunks of frozen Earth water can be safely dropped on Mars, destruction of the Earth could even speed up terraforming Mars - not sure what plans has OP, it depends on the storyline.

Possibly, scarce resources on Mars would be better spend to build underground cities on Mars (protection from bombardment of Earth debris), and developing interstellar travel.

It will be most important to settle some asteroids and get them moving toward other solar systems: whatever destroyed Earth, may return and destroy rest of the human colonies. You definitely want to get out of there. This Solar system is doomed, dude.

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    $\begingroup$ With regards to the moon, it orbits earth with an average velocity around 1km/s, but orbits the sun at around 30km/s, so it would keep going around the sun, regardless of which direction it was going when the earth vanished. The direction it was going would determine how elliptic that orbit would be, but it would be reasonably close to the current orbit of the earth. $\endgroup$ – ckersch Dec 15 '14 at 18:20
  • $\begingroup$ Mars is the most independent of the colonies at the point in time that this story takes place, but still relies a lot on supplies from Earth. Terraformation of Mars itself isn't unfeasible, just very difficult, resource consuming, requires constant maintenance and monitoring, and is expensive as hell. Let's just say some groups of people saw enough benefits from maintaining it that offset whatever costs they put into it. Why it happened doesn't matter, what matters is that the process is partially completed only to suddenly lose most of its backers and outside resources. $\endgroup$ – Arad Dec 15 '14 at 18:50
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    $\begingroup$ You know your story of course: I just think that it should be obvious for humanity to not waste huge resources to terraform mars and instead develop interstellar travel in a hurry to get out of the doomed solar system. Your world and your preferences, I just say what makes sense to me. I did not want to limit myself just on trajectory of Moon like other answers $\endgroup$ – Peter M. Dec 15 '14 at 19:06
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According to physics a systems center of mass does not change, unless external force is applied. So if earth blows up on its own accord, then the earth remains would just stay in much same orbit slightly dispersed, gravitationally nothing much would change until debris start to hit other bodies than earth moon system. Mostly it would just collapse back.

If earth was hit by something then earth debris and the hitting body don't change their internal center either, but now it would be different orbit. Again presumably not much gravitational problems, as the collider presumably existed previously but now you have a new orbit to consider. This is a major problem possibly for inner planets.

If earth gets disintigrated by some mystical thing that annihilates matter, then the energy needs to go somewhere, and that is like a supernova going off.

Most likely you'd just end up with a new planet, or asteroid (or shall we say eartheroid) belt.

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I think the biggest problem that could happen is where does the pieces of Earth go? What destroys the planet could affect other things, especially in how much kinetic energy it applies. If it blows up like putting a stick of dynamite in a bowling ball, you are going to have a lot of material expanding away from the center point. The moon is unlikely to be unscathed, it might not be destroyed but it will take a lot of damage in the form of meteors. Over time depending on how much of the earth is left in orbit, it might become the center for a small planet. Just because the earth is destroyed doesn't mean the mass affecting the moon is just 'gone'.

If there is a lot of kinetic energy it might push pieces of earth all the way into the orbits of the nearby planets would could be some very big meteors. Maybe in as little as a matter of 5-10 years, once again depending on the energy used.

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I ran this in Universe Sandbox and the moons did not fly off. The best thing was that nothing happens except to the moon which goes into a more elliptical orbit. Sadly this orbit takes its average temperature down to about -4 degrees Celsius every lunar year (assuming it had an Earth-like atmosphere). Mars is completely not affected and neither are any of the other planets. If Earth "blows up" then the pieces sometimes fly close to the moon, but not enough to affect it.

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  • $\begingroup$ Something must be up with my settings on there then, 'cause mine keeps messing up. $\endgroup$ – Arad Dec 19 '14 at 23:45

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