My world was once analogous to our own Earth, where life evolved in the light and heat of a nearby star. Unfortunately, a cataclysmic event knocked the planet out of orbit and sent it spiraling as a rogue planet into the dark, limitless void of space. Luckily, some of the inhabitants survived this cataclysm.

I need your expertise and scientific knowledge to help me answer a few questions about the feasibility of this.

What cataclysmic event could dislodge a planet from orbit around its star without instantly exterminating all intelligent life? What conditions could improve humanity's chances of survival in this scenario? (E.g. living in bunkers deep within mountains?)

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2 Answers 2


It seems there are three key questions here.

  1. Can the earth be pulled out of solar orbit? Yes. The Earth orbits the sun at 390 km/s. Solar escape velocity is 618 km/s. Anything that adds more than 228 km/s to Earth’s orbital speed will send it extra solar.

  2. Can it be pulled out of orbit in such a way that it does not kill all life? Yes. Objects ranging from several Jupiter masses to one solar mass could provide plenty of delta-v. A long slow acceleration from a larger mass would be less disruptive than a short quick acceleration from a smaller mass. Orbital dynamics, tidal forces and escape trajectories are going to be highly dependent on the details.

  3. Can life continue on Earth without orbiting the sun? Yes(*) with generations of time for planning. The good news is Earth would retain its magnetosphere, atmosphere, water, mineral resources, etc., including (presumably) the moon and tides. These are all important assets. Replacing all that lost solar energy would be key. A global economic shift toward energy production would be required. Fusion power would likely be a requirement for long term survival. Expect global flora and fauna extinctions during the years it takes Earth to leave the solar system. Plan on most people eventually working and living indoors for an energy, agriculture or environmental systems company and eating vegetarian.

Fun thought experiment... Love the question.

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    – JBH
    May 1, 2018 at 16:01
  • $\begingroup$ While I agree with #2 and #3, numbers in #1 seem to be off quite a bit. $\endgroup$
    – Alexander
    May 1, 2018 at 18:00
  1. It would need a large body to travel through the solar system, disrupting the orbits of the planets. A large rogue planet or brown dwarf star would be the most likely candidates. If it didn’t come very close to the Earth, which it wouldn’t need to, then it wouldn’t be particularly damaging to the Earth except for pulling it out of solar orbit.

  2. Underground bunkers with nuclear power and hydroponics could keep going more or less indefinitely. Some life would also remain around deep ocean geothermal vents, since the deep oceans would be insulated by the ice above them, and the Earth would remain geologically active.

  3. In theory it could eventually suffer the reverse catastrophe, but it would take hundreds of thousands of years at the fastest, and would be very very unlikely.

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    $\begingroup$ "You see, I hadn't been born when the dark star snatched us away from the Sun, and by now it's dragged us out beyond the orbit of the planet Pluto." - from A Pail of Air gutenberg.org/files/51461/51461-h/51461-h.htm $\endgroup$
    – Willk
    May 1, 2018 at 13:18

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