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I'm looking to create a world with a predefined "once every X years" type of event, I realized that something like a comet would work for this purpose in terms of events but I need a planet with an atmosphere, oceans (even if frozen), landmasses, etc.

Halley's Comet comes around once every ~76 years; the Wikipedia article states the distances the comet will come within some of the planets. Included is this quote:

and then on 20 August 2061 will pass within 0.0543 AU (8,120,000 km) of Venus.

Based on information like this, would an Earth-like world on a similar orbital path to Halley's Comet warm up enough on the portion of its orbit near the sun to match Earth-like conditions (temperate/tropical) for a short time?

Would life be able hibernate for the long outer system orbit and then thaw out for the inner part? (I'm thinking something like mayflies but for ALL of the life plants/animals, etc.)

How long would the 'warm' inner part of the transition last?

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  • $\begingroup$ So are you asking about an earth like planet with a high <1 orbital eccentricity? Objects such as Sedna in our own solar system have such orbits and are larger than comets, though their periapsides are much greater than you desire. $\endgroup$ – Kys Aug 4 '16 at 19:55
  • $\begingroup$ Read the Helliconia trilogy by Brian Aldiss and A Deepness in the Sky by Vernor Vinge, which have similar setups to what you want. $\endgroup$ – Mike Scott Aug 4 '16 at 20:02
  • $\begingroup$ @Kys yep, I had imagined Halley as valid since it gets close enough to start shedding gas and dust. I thought that with an atmosphere it might trap/retain some of the heat a bit better $\endgroup$ – Culyx Aug 4 '16 at 20:09
  • $\begingroup$ Most of the time will be farther out, the farther from the sun, the slower it travels. The time in the warmer inner area will be far shorter than the time out in the frigid depths. $\endgroup$ – Seeds Aug 4 '16 at 20:14
  • $\begingroup$ Keep in mind anything going out as far as most comets will "drop" their atmosphere when too far away. It's not that Hally doesn't have "an atmosphere", it's that when that "atmosphere" isn't in solid form it doesn't have the gravity to hold on to it. $\endgroup$ – Uueerdo Aug 4 '16 at 22:14
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To stay long enough near enough the Sun, you need a very long orbit with moderate eccentricity and perihelion not too much inside Earth's orbit (or equivalent for a different solar system).

But at that point you'd have to stay far enough for long enough that the planet cools down a lot. So much than it won't thaw enough in the "summer" before winter sets in again.

You can play with an orbital calculator (see http://lasp.colorado.edu/education/outerplanets/orbit_simulator/ ) and see whether you can come up with something acceptable.

You might perhaps trick the system by keeping the planet "not too cold" during its winter phase. This can be done with internal heat from radioactive decay, for example. The problem here is that Earth's heat budget is only about 0.02% from radioactive heat; radionuclide contents of an Earth-like planet ought to be increased at least one thousandfold in order to maintain a temperature high enough to not require too much "thawing".

This would then result in a radioactive background much higher than Earth's; having no Moon and negligible plate tectonics might help in keeping all that radioactivity safely inside the crust. Also, there's no mechanism that would allow for the formation of such a planet, and when you factor in the original radionuclide content during that planet's Hadean era, I suspect you'd come up with the equivalent of an enormous fission bomb hanging in space.

Another possibility would be to complicate the orbit. You might have a P-type circumbinary planet around a long-period binary, which at that point can experience "summers" and "winters" of more or less arbitrary intensity.

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I don't think this would work.

The problem is that Halley's comet is about 11 km across, while Earth is 12,740 km, so a thousand times as big. If it were on a Halley-like orbit, there would not be enough time to thaw out all of the ice before it zooms off into deep space again.

If it passed really close to the sun, there might be enough melting, but a little variation or an ill-timed solar flare would scorch away any surface life, and the orbit would not be stable in the long run.

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