"Blowing Up Planets - Q of Gravity" Topic

Can someone with more Science education answer this?

So in Star Wars and elsewhere, a big baddie literally blows up a planet. Assuming it really goes boom and its mass is scattered through the solar system, would the now new gravity situation destabilize other planet orbits?

If I blow up Mars or Venus, does that affect Earth?

Depends on the distance.
Mars and Venus would change Earths orbit very little.
Would be only a matter of time before parts would hit Earth.

Not to worry… we have Space Force :)

The only sci-fi I know of where the destruction of a planet affected the orbit of any of the others was Star Trek 2, I guess Ceti Alpha 6 was pretty close to Ceti Alpha 5 at the time.

And in the anime Gall Force 3 a planet killer weapon is fired a planet or moon is blown up and it affects a planet they were trying to do a restart on the system making it habitable again.

Now blow up Jupiter and it would likely affect the whole solar system, that is a rather huge gravity well out there.

Depends on the distance… which means, probably not.

But keep in mind that "blowing up" a planet doesn't remove the mass. It just gives that mass a briefly energetic acceleration away from its own center of mass (that would be quite the explosion!)
But notice that this would be instantaneous acceleration, not sustained. The mass itself is still the same and still has the same attraction to its constituent bits. As a result, they would all begin to decelerate towards each other from the instant of the explosion. So then it becomes an issue of how much kinetic energy was given to the various parts by the explosion vs. how much (at what rate) the gravitational attraction will overcome that brief application of energy.

It might entirely be possible that the acceleration is minimized— only what was needed to universally "crack the crust," which would be quite sufficient to kill every living thing on the planet, after which it all "falls" back together again.

But as can be seen on film, the Empire is not a big believer in conservation of energy, or efficiency in destruction (minimum effort for maximum casualties). It would appear that they went for full disruptive separation of the agglomerated planetary matter, applying enough energy to fracture the planetary core into relative small particles— small enough that even the Millennium Falcon's deflector screens and hull can essentially handle the various bits. That's some serious overkill.
On the other hand, at the time of the Falcon's arrival from hyperspace, the particulate elements of Alderaan are not moving at any great speed, if the screens and hull plates can treat the impacts so casually. The assumption here must be that the mass is already falling back in on itself, and that it is the Falcon's relative speed which is causing the impacts.
Also, the fact that it's stated that "it's not there," means that the hyperspace window for arrival is relatively close to the planet's actual location, and that the "asteroid belt" is thus the planet's own matter, which is already slowing, or in a moment of relatively little momentum, or possibly even already reversing its acceleration back towards all the mass's combine center of gravity.
If that is the case, then any disruption to the orbit of other planets would be minimal, if even registering. As far as these distant bodies are concerned, the entire gravitational effect of Alderaan is still fully present in essentially the same place and orbit it always was.

So give the Empire credit for carefully planned, selective destruction with no environmental impact on distant planets or their system.

If the explosion imparts sufficient velocity to achieve escape for a significant portion of the planet, the gravity well of the planet will be altered. If other planet's orbits are very close to that of the bloom of the explosion, they will assist in ejecting some of the mass.

Like I said, that would be quite the explosion! 8-O

We were just talking about realism in science fiction wargaming. Blowing up a planet requires so much energy that a civilization capable of doing it may be beyond an interesting human-scale drama.

There are definitely simpler ways of killing off offending planetary populations. But none make quite so effective a demonstration, as Grand Moff Tarkin would say.

And Happy Star Wars Day!