I have a planet in a solar system that is for all intents and purposes identical to ours that I want to play like a bongo drum with asteroids or other extra terrestrial rocks to destroy most of the inhabitants, but I need the planet to be inhabitable within a short time frame afterwards (about a year). What plausible event could happen in the next 20-30 years that could cause such an apocalypse. Additionally it should be observable for at least 2 months prior to the big percussion show.

EDIT If the asteroid impacts can't leave a suitably habitable planet after 1 year, what would the minimum time be in this scenario?

  • $\begingroup$ I'm glad that my post is helpful to you, however I would hold off on picking an answer just yet. It discourages other people from replying, and you never know what sort of ideas you might get from other users. I would suggest waiting 24 hours until you select an answer (unless one clearly stands out above all others) $\endgroup$ – AndreiROM May 4 '16 at 19:56
  • $\begingroup$ Yeah, I have an unhelpful habit of getting a touch over enthusiastic about accepting answers. Thanks for the poke in the correct direction. $\endgroup$ – Universalerror May 4 '16 at 19:59
  • $\begingroup$ I don't understand what your asking. $\endgroup$ – Bryan McClure May 4 '16 at 20:29
  • $\begingroup$ I want to know what the most plausible scenario would be that causes an apocalypse via meteor shower. It should be something that could happen in the next 20-30 years, provided everything happens correctly. $\endgroup$ – Universalerror May 4 '16 at 20:31
  • $\begingroup$ What is the definition of "habitable" and "inhabitable"? For the dinosaurs the meteorit that caused their extinction made Earth "inhabitable", nowadays we could count in modern technology (food storage, hydroponics, greenhouses, artificial light, nuclear & wind & hidro & fosil energy) so that a small but significant human population would survive the same event. $\endgroup$ – SJuan76 May 4 '16 at 21:31

Throwing rocks at a planet won't really accomplish what you're after as they will either kill the people they land on, or cause dirt to block the Sun out for much longer than a year (the only way to cause mass extinction).

Your best bet is some kind of solar flare which kills the vast majority of living things on the surface.

We may be able to observe the build-up leading up to the flare, and get some people into bunkers, submarines etc. however the vast majority of land animals would be doomed.

Then the solar flare would have to keep frying the Earth for a couple of days so that it has a chance to saturate it over the entire surface (both sides, as it were).

Once it was over the vast majority of the planet's surface would be a little toasty, but otherwise OK. The survivors (or invaders) could probably inhabit the vast majority of the now devastated planet.

Some plants and animals will have survived, and would slowly start repopulating the Earth, but we will have lost a huge number of species, and it will be centuries until the ecosystem recovers.

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An asteroid impact that could kill all inhabitants will not let the planet inhabitable within one year : climate will be change for a while due to the dust and ashes, for example.

An option could be to use one of the most energetic event in the universe : a Gamma Ray Burst. GRB are extremely energetic rays caused (supposedly) by the collapse of stars to black holes : their energy during a few seconds is equivalent to the sun's energy during its whole lifetime. GBR are very narrow, as they are likely emitted along the rotational axis of a collapsing object. Only out-of-our-galaxy GBR were observed until now, but the Ordovician–Silurian extinction is sometimes attributed to a Milky-Way GBR.

In your case, a very nearby star could show signs of collapse, and end up emitting a GBR. The atmosphere may somewhat protect, but you may decide that it is powerful enough to sterilize your planet (at least on the exposed side).

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  • $\begingroup$ Jets from GRBs will likely be emitted along the polar axes of the progenitor, and they'll miss the planet. That said, the event that caused the GRB would likely make the planet pretty inhospitable. $\endgroup$ – HDE 226868 May 4 '16 at 23:45
  • $\begingroup$ The atmosphere isn't any protection against a GRB. It's what kills you if the radiation doesn't kill you more directly.. The gamma rays ionize the atmosphere. Nitrogen oxides destroy the ozone layer and then create a decade of acid rain. Being on the other side of the planet helps only for a day or two until winds bring the air from the other side. $\endgroup$ – nigel222 May 5 '16 at 21:59
  • $\begingroup$ @HDE226868 : right, the GBR cannot be emitted by the planet the system orbits around, that'w why I mentionned a nearby star. If your star collapse, I foresee some issue to have your planet inhabitable in the near future :) $\endgroup$ – Uriel May 6 '16 at 8:32
  • $\begingroup$ @nigel222 Agreed : the atmosphere is heavily affected by a GBR. The scenario may be adapted somehow to fit the "back within one year". In practice, a GBR will have effects for a while. $\endgroup$ – Uriel May 6 '16 at 8:35

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