My planet is Earth like in size (I can change it, if needed), however its day-night cycle is somewhere around 1,000 Earth days long. How hot would day get, and how cold would night get? Is it possible to have plants and animals on this planet? Oh, it also has around the same amount of ocean as Earth, yet again, can be changed if needed.

  • $\begingroup$ Over some amount of time, the temperatures are going to change drastically, right? $\endgroup$ – user80605 Nov 15 '20 at 2:31
  • $\begingroup$ Hmmm, actually nevermind what I said. It's more obvious in my mind what would happen with long periods of night since it would be worse than winter. For some reason my brain isn't interpreting extended daylight the same way. $\endgroup$ – DKNguyen Nov 15 '20 at 2:49
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    $\begingroup$ You forgot to tell us which star it orbits and how far from it. Without those info there is no way to answer. $\endgroup$ – L.Dutch - Reinstate Monica Nov 15 '20 at 5:54
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    $\begingroup$ Does this answer your question? Climate of a No-Axial-Spin Earth? $\endgroup$ – AlexP Nov 15 '20 at 7:08
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    $\begingroup$ This is not a duplicate of "No axial spin Earth", although it should be linked to it as they do share some calculations and a good answer to one can reference a good answer to the other. Consider this a "Do not close as duplicate" vote. $\endgroup$ – Ash Nov 15 '20 at 8:06

-120 to +102 degrees C

You've used "Earth-like" so I'm assuming everything else is Earth-like too, with the only difference being the slight counter-rotation allowing a day to be 3 times longer than a year.

So I can answer this by building on this detailed breakdown of an Earth-like planets weather where the rotation was 0, but the planet still went around the sun, giving a year-long day - ie it was calculated for a world with 6 months of sun followed by 6 months of night. Yours will be about 3 times more intense, you have 500 day nights and 500 day days. The "midday" storms will move about 1/3rd the speed across the surface but will keep the basketball sized hail. You'll get the strong winds at dusk blowing everything away. You'll get carbon dioxide falling at night. And you'll get the devastating floods and Earthquakes at Dawn. Plus everything else detailed in that link.

The same maximum temperature (102 degrees C) will be hit in both cases, however your planet will get a little colder than the one in that maths. Exactly how much colder is hard to estimate but a few extra degrees colder (to about -120) seems reasonable.

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    $\begingroup$ Yikes... would you happen to know about dawn/dusk? $\endgroup$ – user80605 Nov 15 '20 at 3:25
  • $\begingroup$ @user80605 hellish with winds strong enough to blow you off your feet, entire continents flooded, and earthquakes that will knock down anything interesting and turn the world into a uniform sphere. See worldbuilding.stackexchange.com/a/185473/78800 $\endgroup$ – Ash Nov 15 '20 at 3:27
  • $\begingroup$ I'm not denying what you just said, but would you give me the science of why all of that would happen? $\endgroup$ – user80605 Nov 15 '20 at 3:33
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    $\begingroup$ Okay, thanks; I'll read it ^^ $\endgroup$ – user80605 Nov 15 '20 at 4:03
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    $\begingroup$ Am I the only one who interpreted "Earth like" to mean "the scenario is Like Earth"? $\endgroup$ – Ash Nov 15 '20 at 7:55

On average, a little bit colder than Earth.

But that's on average. The dayside will be really hot, the nightside will be really cold. The average a bit cooler because the increase in radiant heat loss on the hot side will be greater than the reduction of radiant heat loss on the cool side.

Actually, don't think of it as a "day" and "night" side.
Rather think of it as "500 day long sunless winter", followed by "500 day long summer with no nights"

Fortunately, the atmosphere will do a lot to help distribute the temperatures. Expect wind. A LOT of wind. Very disorganized wind, likely channeled by surface topographic features, because there is almost no planetary rotation to induce coriolis-powered rotation. So despite the plenty of wind, don't go looking for rotating storm systems. No traditional hurricanes for you, sorry.

So I expect the locals talking weather would be like:

In the morning the wind blows off the glacier down this here canyon as the CryoSnow (dry ice snow) evaporates. It's still a bit chill then, of course, but you can shuck the EVA suit, you should need only the heavy parka. Gotta remember to wear your mask. A couple weeks later the winds will turn, blow back down. This time its a hot, dry wind coming from HighSun. That's when we expect the spring floods. No, not from the winds, you silly! From the glacier. Then there's growing season. We got's to pop out four crops of corn before it gets too dry. By HighSun everyone is in the shelter, of course. Its quiet, and dry, and ... did I mention not to leave your tools outside? At least not until the clouds come back. That should be a week or five after HighSun. Not that they ever bring rain, mind you, its just warm, and steady wind. This is when we rebuild shelters, and enjoy the outdoors as much as we can.

For remember: The winter is coming! A week or two before sunset the winds build up, cover the sky with clouds and bring the Darkness. You will never see a sunset, the dark skies will just gradually become the Dark, then the DARK.

Around day 50 the Dark becomes the Cold, and it starts snowing. No more, no less than 73 meters of HydroSnow. Remember to charge your shelter's air supply before this!

Around day 250-300 of the Dark it starts snowing again, this time its the fluffy CryoSnow. Not so much of that though, 5m of dry ice is a heavy fall.

And then you just wait for the summer to rise again

Personal P.S. I strongly suspect the dominant Religion will be: Cursing the blighters that thought colonizing this excrescence of a planet was a good idea!!

  • $\begingroup$ Yup, not much to talk about. Meteorologist would not be a viable career option. I second that notion of main religion. Probably a few cults dedicated to cursing the ancestors stupid enough to fall for the colonist recruitment speeches as well. $\endgroup$ – Gwyn Nov 15 '20 at 16:54

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