1
$\begingroup$

In my setting, one of the fallouts due to interstellar war between civilisations is that a planet's gravity can be removed. This capability is part of the setting's hyperspace mechanics so the exact details aren't that relevant here. However, in terms of scale, civilisations can affect up to Earth-sized planets. Super-earths, gas giants, and stars will at best end up with localised issues on their surface.

What I'm concerned is with are the consequences to the planet. Obviously any atmosphere, oceans, and loose surface material would quickly get ejected, though the exact shape of the result gas cloud eludes me. Any mountains and other large structures would likely start tearing apart along weak points wouldn't otherwise matter.

But what I really want to know is what happens to the core. Without any gravity, would the core and mantle actually expand and break the crust, leading to a period of increased vulcanism before the planet started cooling? Or would this not actually matter and would an Earth-like planet simply start cooling due to the reduced pressure on the core?

The following assumptions are also relevant

  1. The effect is local. That is, only the mass on the planet at the time of the fallout lacks gravity.
  2. The effect is effectively one way. So a planet isn't going to automatically leave its current orbit. And if a planet has a large moon, like Earth, then the moon will start collecting matter. A gas giant moon system would probably also be interesting, but I am more concerned with Earth-like planets.
  3. The effect isn't strictly zero gravity. It simply isn't reaching as far due to more of it being directed into hyperspace. So it is tapering off faster than the square progression. I assume that the fifth power is sufficient to make gravity have a negligible impact.
  4. Inertia is unchanged. This one is mostly to keep both search & rescue and unscrupulous mining operations somewhat honest. No dragging a planet around with a small tug.
  5. Atomic and molecular physics are otherwise unaffected. This just the necessary handwaving to ensure that lifeforms and electronics on a planet still operate normally, they're just operating under microgravity conditions.
  6. The effect is temporary. Removing a planet from orbit and mucking up the rest of a solar system's orbital mechanics isn't part of the intended effects. Obviously, this particular point has no bearing on any answers.
$\endgroup$
  • $\begingroup$ Where have you found that gravity decreases with the square root of the distance? Last time I was in school I was told it was decreasing with the square of the distance. $\endgroup$ – L.Dutch - Reinstate Monica May 10 at 10:39
  • $\begingroup$ Gravitational fields are generated by not just mass but any form of energy. The only way they could cease to produce a gravitational field is to cease to have any energy at all, which would effectively the same as ceasing to exist in any way. $\endgroup$ – StephenG May 10 at 10:47
  • $\begingroup$ I've added a tag that will stall the "it's impossible" comments. Feel free to revert if you want. $\endgroup$ – Tantalus' touch. May 10 at 11:08
  • $\begingroup$ Still a mess of conflicting goals. I think the OP would be better to post the intended plot effect of the weapon so maybe alternatives can be suggested. I do not see the point of such a "weapon" - you don't neutralize your opponent or destroy them and removing the planet's gravitational field is presumably something an opponent at a similar technological level can counter or undo or prevent (or overcome easily). $\endgroup$ – StephenG May 10 at 11:36
5
$\begingroup$

The planet will instantaneously explode.

The earth has a gravitational binding potential of about 2.25×10^32 joules, or the weekly energy output of the sun. This energy also currently being counterbalanced by potential energy of the compression of rock in the earth which prevents the earth collapsing to a point. Without gravity, it will all be released at once since the rock of the earth is no longer being compressed.

Given the energy scales involved, interesting high energy physics will happen before the earth disappears in a cloud of hot gas. For all intents and purposes that will be instantaneous.

| improve this answer | |
$\endgroup$
  • $\begingroup$ +1 except the high energy physics. The energy of the particles will be in the order of magnitude of the gravitational acceleration down to the center. Not a big deal, except the fact that we don't have the Earth anymore. $\endgroup$ – fraxinus May 10 at 13:52
  • 1
    $\begingroup$ Worth noting that the energy can only really be liberated at the speed of sound in the rock, so it’ll take on the order of hours for the planet to totally disintegrate from the surface down. Also of note is that all the fragments would also tend to fragment down to the point where they’re materially held together against the expansive forces, so there would be a lot of high velocity sand, followed by rocks, followed by very hot semi molten lumps of iron and heavier metals. All told: Fun! $\endgroup$ – Joe Bloggs May 10 at 16:24
  • $\begingroup$ It would take a while for the lack of gravity to tear the Earth apart. Obviously the atmosphere and anything loosely bound will fly off. However the solid part of the planet could survive as lack of gravity only means force that could hold planet together. If there is no force trying to tear the planet apart the planet will not be torn(Unless of course only Earth's gravity is turned off and the moon of Earth will rip Earth apart because of tidal forces.) $\endgroup$ – Roghan Arun Jun 1 at 1:42
  • $\begingroup$ @RoghanArun That is not correct. The rock is currently under compression, which is currently counteracted by gravity. Remove gravity, and the rock will expand $\endgroup$ – Whitecold Jun 1 at 5:38
  • $\begingroup$ There is still tensile forces. $\endgroup$ – Roghan Arun Jun 1 at 12:16

Your Answer

By clicking “Post Your Answer”, you agree to our terms of service, privacy policy and cookie policy

Not the answer you're looking for? Browse other questions tagged or ask your own question.