Destroying the Earth by means of a supernova is a geocide method which comes in two broad varieties. In one of them, we move the Earth to the vicinity of a star which is about to go supernova and wait. Transit time is a factor, and then we have to consider just how long we wish to wait. Imminently collapsing stars are not easily come by in space. All in all, such a proposal is thoroughly tedious and mundane. Somehow, it smacks of effort and laziness. It lacks panache.
The other option we have is to leave the planet where it is and induce the Sun to go supernova manually, and this is the task I want to consider today.
What causes a supernova, anyway?
The Sun, like all stars, is a vast mass of hydrogen gas which collapsed under its own gravity. As more hydrogen gathered around the central point, the heat at the core of the ball of gas rose to the point where nuclear fusion began to occur spontaneously. Each time hydrogen nuclei (protons) fuse into heavier nuclei, a little energy is released, raising the temperature nearby and enabling further fusion to occur. Thus, the fusion process is self-sustaining for as long as there is enough hydrogen fuel.
Stars are generally in hydrostatic equilibrium. This means that the radiation pressure of energy trying to escape from the core (where it was produced by fusion) is equal to the gravitational force pulling the star together. When, after millions or billions of years, the hydrogen fuel begins to run out, fusion slows down and the radiation pressure decreases. Gravity takes over and pulls the star into a smaller ball. This increases the pressure and temperature at the core, to the point where helium can now fuse into carbon. The star finds a new hydrostatic equilibrium at a smaller, more svelte diameter, with helium fusion at its core, and the remaining hydrogen continuing to fuse in a shell around the core, heated from within by helium fusion.
As time passes, even the helium begins to run out. Two more facts come into play now. Firstly: the heavier the element, the more energy it takes to cause it to fuse. The energy in the core of a star is a function of temperature which is a function of pressure which is a function of its mass. Thus, the more massive the star, the more elements it could theoretically fuse. (Balls of gas which do not have enough mass to even fuse hydrogen do not start shining at all and don't become stars.) The majority of stars aren't massive enough to get far past helium. So far so good.
But in the case of truly gigantic stars, above eight solar masses, the second fact arises: the heavier the element, the less energy you get back from fusing it. We end up with descending layers of fusing elements, like an onion: hydrogen fusing into helium in the outer layer, helium fusing into carbon in the next layer, then carbon fusing into neon, neon fusing into oxygen, oxygen fusing into silicon and finally silicon fusing into nickel. Once you get to nickel (which in this case undergoes radioactive decay into iron), fusion doesn't generate any energy at all. Beyond the iron point, it actually requires a net energy input to fuse anything. Thus, the very bottom layer in the onion does not fuse or generate any energy. It does not support itself with radiation pressure. It just sits there and accumulates.
The iron core is a different thing entirely. This is not just a lump of metal. It is under such intense pressure that it becomes something called electron-degenerate matter which is an extremely dense phase of matter in which the iron nuclei are kept separate from one another only by the Pauli Exclusion Principle.
Electron-degenerate matter is completely awesome. Because the individual iron nuclei are packed so closely together, so are their surrounding electrons. Because the electrons' positions are so constrained, the uncertainty in their position is very low. Thanks to the Heisenberg Uncertainty Principle, this means that the uncertainty in the electrons' momentum is very high which means the electrons move at very high, relativistic speeds. This creates an outward pressure. If, as here, the pressure due to fast-moving electrons exceeds the pressure due to thermal motion in the matter, the matter is called degenerate. Oh, and, paradoxically, adding more iron to this core causes its pressure to increase and its volume to contract further.
Even now, it is still possible for a star to run out of fuel. You would simply get a white dwarf, with some layers of fusing material above a tiny electron-degenerate iron core. But if the star started out with nine or more solar masses, a point is reached where even the Pauli Exclusion Principle isn't strong enough to prevent the core from collapsing. The system breaks down, the core collapses still further forming a neutron star. A neutron star is just a few tens of kilometres in diameter but has about the same density as an atomic nucleus. The rest of the star - suddenly having no supporting bottom layer - implodes in on the core at relativistic speeds, the majority of its remaining fusable material fuses all at once, and more energy is released in a few days than the Sun will release in its entire ten-billion-year lifetime. The rest is history. Literally.
Basically the crux of this method of geocide is this: create a large, momentary "power vacuum", or rather, a literal vacuum, in the core of the Sun. Do this by removing something that was already there. The Sun will instantly collapse into the space, and the sudden increase in pressure and temperature will liberate orders of magnitude more energy than the Sun typically puts out, incinerating the Earth and most of the Solar System besides.
The reason why we can't do it is this.
At 1.45 solar masses, a lump of iron is massive enough that it will actually implode in the manner described enough. We need a hair less than 1.45 solar masses of iron. We then need to fire that iron bullet into the core of the Sun, and then have the Sun manufacture enough additional iron to put it over the Chandrasekhar limit and cause it to implode.
Even combining all the physical objects (planets and miscellaneous) in the solar system, we only have 0.14 solar masses of material, almost none of which is iron. We would have to ship the iron in from another star system entirely.
The Sun is not massive enough to manufacture iron, period. It doesn't have eight solar masses. It has 1.00 solar masses. Any amount of iron in the Sun's core is either 1) never going to collapse or 2) already collapsed. There is no middle ground and unfortunately the additional weight of the Sun's upper layers cannot be used as the tipping point; the electron degeneracy pressure inside the electron-degenerate iron is a purely quantum-mechanical effect which is not increased by whatever is sitting on top.
We could ship in the equivalent of eight other Suns' worth of hydrogen, raise the Sun's mass to 9 solar masses and then wait for nature to take its course. But that's stupid. Could it be possible to open a bubble inside the Sun using titanic electromagnetic fields? Perhaps these electromagnets could be solar-powered? But what shape would they form? What current would be required? Could we remove the Sun's core using teleportation? We're verging on fantasy.
What we wanted was a magic bullet. We wanted to take Venus or Mercury or something equally small and conveniently-placed and poison the Sun with it-- a low-effort solution. Unfortunately it seems like this would not give the desired effect.
There is no feasibility rating today. But we haven't failed; we've successfully eliminated a possibility.