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Inspired by this question Would going underground into a planet offer protection from a supernova?, I am proposing the following scenario:

A distant supernova is created by hostile aliens, as an attempt to wipe out humans.

The supernova happens to be at a distance where it would severely affect things on surface, however, it is far enough that assured destruction is not possible.

As far as I understand from other questions on the topic, it means the supernova should be somewhere between ~40 and 100 light years away.

Is it possible for the event to happen in such a manner or at such distance, that for humanity to dig itself some reasonable depth underground (let's say 1-2km) would make a difference between life and extinction(or significant risk thereof)?

And if yes, what would the supernova effect, against which 1-2km of rock helps, be on the surface?

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    $\begingroup$ A couple of comments/questions - this seems like a very long-game plan by the aliens. It would mean that after triggering the supernova, they would have to wait a century for humanity to be wiped out. They clearly have FTL travel themselves, or else this is a suicide ploy. So why not go to Earth and just use the tech on our sun, or just apply vast amounts of energy directly to Earth? $\endgroup$ – jdunlop Jul 9 '20 at 0:51
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    $\begingroup$ Follow-on question - humanity also must have some limited FTL capabilities, else we'd have no idea that the supernova was coming. If that's the case, it seems more practical to leave than to dig into the Earth, for the most part. $\endgroup$ – jdunlop Jul 9 '20 at 0:52
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    $\begingroup$ Also, 40-100 ly is not a guaranteed kill - nor even a likely kill. 100ly is at the range where some bad things might happen to Earth. If the aliens want to wipe out humanity, they'd set something off that was a bit closer. There may be some good white dwarf candidates in the vicinity that would work. $\endgroup$ – jdunlop Jul 9 '20 at 1:01
  • $\begingroup$ @jdunlop I realize the issues you pointed out, but for the purpose of question we might leave aliens out of it, except maybe as a source of information about what is going to happen. $\endgroup$ – Gnudiff Jul 9 '20 at 5:25
  • $\begingroup$ In the question, you have aliens as the inciting influence. "A distant supernova is created by hostile aliens". It's hard to leave aliens out when they're the ones causing the supernova. $\endgroup$ – jdunlop Jul 9 '20 at 9:04
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The supernova would have to be around 33 light years from us for it to be surviveable by digging.

There is a whole Wikipedia article about this: Near-Earth Supernova.

It seems that the scenario you propose happens very often:

On average, a supernova explosion occurs within 10 parsecs (33 light-years) of the Earth every 240 million years.

So statistically it could have happened twice ever since life began. Further ahead in the article there is a section about past events:

Gamma ray bursts from "dangerously close" supernova explosions occur two or more times per billion years, and this has been proposed as the cause of the end Ordovician extinction, which resulted in the death of nearly 60% of the oceanic life on Earth.

Ouch.

What really called my attention, though, was this statement at the intro:

Historically, each near-Earth supernova explosion has been associated with a global warming of around 3–4 °C (5–7 °F).

We are having an increase in temperature like that on a century basis and it is destroying ecossystems. But in a flash? Immediate global death. The asteroid that killed dinosaurs didn't hit the whole surface of the Earth, but it did kill all dinosaurs in a matter of hours by cooking them alive when the global temperature rose a few degrees in under a day.

Back to novae, I'll spare you the math and just quote this:

It is estimated that a Type II supernova closer than eight parsecs (26 light-years) would destroy more than half of the Earth's ozone layer.

This would wreck havoc on us. Everybody going out as usual by day would get really bad sunburns. We would develop skin cancer within months to years. Many animals would also go extinct. Frogs are particularly susceptible to damage from UV. This could break every tropical ecosystem.

Also:

Gamma rays are responsible for most of the adverse effects a supernova can have on a living terrestrial planet. In Earth's case, gamma rays induce radiolysis of diatomic N2 and O2 in the upper atmosphere, converting molecular nitrogen and oxygen into nitrogen oxides, depleting the ozone layer enough to expose the surface to harmful solar and cosmic radiation (mainly ultra-violet). Phytoplankton and reef communities would be particularly affected, which could severely deplete the base of the marine food chain.

This would destroy farming worldwide as well. With global food production gone, living in an underground vault with a supply of food and viable seeds for reseeding the planet is the way to go.

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