this post was submitted on 02 Feb 2025
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...in what proximity would you have to be to the sun and how fast would you have to be spinning (like a rotisserie chicken) so that your light side didn't burn and your dark side didn't freeze; rotating just enough to keep a relatively stable temperature?

Absolutely absurd, I know but this question somehow popped into my head and won't leave. πŸ˜†πŸ”πŸ”₯🧊

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[–] [email protected] 5 points 1 hour ago

Even once you achieve the perfect rotation, the unfiltered UV would likely eventually give you cancer.

[–] tomi000 11 points 4 hours ago

You should post this in c/askScience

[–] [email protected] 18 points 6 hours ago (1 children)

Seems like a good question for Randall Monroe, if he hasn't already done something similar.

[–] [email protected] 4 points 2 hours ago* (last edited 2 hours ago)

The "how high to drop a steak for it to perfectly cook" and "does a submarine work as a spaceship" comes to mind, but afaik nothing similar to this one

[–] [email protected] 42 points 8 hours ago (2 children)

Outside of all the assumptions to make this work, the real issue is that the "dark side" doesn't cool you like you're thinking. Getting rid of heat in space is actually a hard problem to solve as a vacuum is a great insulator. Heat has to be radiated away, and that takes time and lots of surface area.

[–] [email protected] 1 points 13 minutes ago

This is exactly what I am curious about. I'm fully aware of the mountain of assumptions needed to make this work lol. I guess its the "its ~-200Β°C out here but I'm not frozen" thing that makes my head spin a bit.

[–] tomi000 11 points 7 hours ago* (last edited 6 hours ago) (3 children)

Interesting and does make sense. Where does this image of stuff freezing instantly as it "enters" space vacuum come from?

[–] supercriticalcheese 7 points 4 hours ago

Moisture as any other fluid when exposed to vacuum of space expands and boils this transforms to vapour and that process absorbs energy which could cause the freezing.

[–] FourPacketsOfPeanuts 5 points 3 hours ago

Probably because many pop science articles will mention that the background radiation of the universe is at about 2-3 degrees above absolute zero. Plus things like the night side of mars being freezing, pluto being a frozen rock, comets being made of ice etc...

[–] [email protected] 5 points 7 hours ago (3 children)

Depends on the entry I suppose. A liquid being sprayed out you'd imagine would do exactly that (assuming it's not being heated by sunlight), but that's probably because spraying means it's a lot of tiny droplets, all with very little heat energy individually and lots of surface area to lose it. A big block of something like hot metal wouldn't suddenly freeze, but cool as fast as its surfaces could radiate the internal heat.

This is going strictly as a thought experiment, the math or physics is probably different to some degree.

[–] [email protected] 7 points 4 hours ago (1 children)

Boiling/freezing depends on pressure as well as temperature, I think water would actually turn into steam if sprayed into space. There's a story of a spacesuit technician being accidentally exposed to a vacuum and he says his last memory is feeling the saliva bubble on his tongue.

https://www.spacesafetymagazine.com/aerospace-engineering/space-suit-design/early-spacesuit-vacuum-test-wrong/

[–] [email protected] 3 points 4 hours ago

It will do both. The initial boiling will draw heat away from the other molecules, eventually freezing them. So I suppose it wold depend on how fine the spray pattern is as well as the beginning temperature as to how much goes to gas vs. solid.

[–] [email protected] 5 points 6 hours ago

I think an additional effect is that, the drop in pressure causes any liquids exposed to it to vaporise, which is an exothermic process, and it's a race to see whether it boils off entirely or the inner part freezes to solid from the drop in temperature through conduction. So the immediate surface of your body would either dry out or flash freeze but the inner part take a while to solidify.

Why there is any ice in space and it doesn't just sublimate away over time I'm not sure.

[–] tomi000 1 points 4 hours ago (1 children)

What I had in mind was stuff like people getting shot into space in sci-fi, stuff like that. Theyre usually shown to freeze in the matter of seconds. So I guess thats unrealistic, though its a little sad because that means its a much more painful death by suffocation

[–] [email protected] 3 points 4 hours ago

Yes, that's correct. Scenes like from Total Recall or Mission to Mars are totally wrong. It will be more like the opposite of drowning but about as bad. I'm trying to remember if The Expanse got it right in the several examples, they usually do pretty good hard science. It may have been a combination, since anyone seeing someone NOT freeze will say it looks fake.

[–] mkwt 15 points 8 hours ago (2 children)

As an earthling, you have evolved over the course of billions of years to deal with sunlight at a distance of one astronomical unit. That's the distance of the earth's orbit. That's probably the most comfortable distance.

The Apollo moon missions used a so-called "barbecue" mode that rotated the capsules at three revolutions per hour. They did this during the 3-4 day coast phases to and from the moon. As far as I know this was able to mostly hold the interior temperatures in the "survivable" range.

[–] NeoNachtwaechter 2 points 2 hours ago

earthling, you have evolved over the course of billions of years to deal with sunlight at a distance of one astronomical unit.

...plus a planet's magnetic field, plus a few kilometers of atmosphere!

[–] [email protected] 10 points 8 hours ago (1 children)

That's a good starting point, but caveats:

  • My bet is that most of our thermal circulation is via the movement of our blood. That's probably not directly analogous to spacecraft.

  • If one isn't just talking thermal, we do burn at 1AU. Go lie in the sun without cover long enough -- especially if you're pale-skinned -- long enough, and you'll get burned. Without the atmosphere, we'd be hit by more UV light, too.

[–] [email protected] 6 points 6 hours ago (1 children)

Without the atmosphere, UV is going to be among the least dangerous wavelengths for you to have to worry about.

[–] [email protected] 6 points 6 hours ago (1 children)

looks puzzled

I don't think that it mostly stops more-energetic stuff.

Hmm.

Are you thinking of the magnetosphere rather than the atmosphere? I didn't mention that, but I guess that'd also be a factor.

[–] cynar 2 points 2 hours ago

The atmosphere stops a lot of the high energy stuff. It gets absorbed, and turned into a shower of lower energy particles.

I remember reading once about an astronaut seeing blue flashes in their eyes. When they realised, they got behind the water tank sharpish. It was high energy particles passing through their eyeballs.

[–] AbouBenAdhem 11 points 8 hours ago* (last edited 6 hours ago) (1 children)

Probably significantly further away than the earth’s orbit, given that (1) you can die of heatstroke from exposure to the sun at earth’s surface, and that’s with miles of air still absorbing much of the radiation; and (2) in the vacuum of space, there would be no air or other substances to conduct away your body heat, so you’d have to rely solely on radiative heat to cool off.

[–] [email protected] 6 points 8 hours ago (2 children)

So even though its minus hundreds of degrees, your skin wouldn't freeze instantly on your dark side in this situation?

[–] AbouBenAdhem 22 points 8 hours ago (1 children)

It’s not minus hundreds of degrees, it’s body temperature. Vacuum has no temperature, and it’s an insulator, not a conductor.

[–] [email protected] 1 points 10 minutes ago

That makes perfect sense to me on paper. It still makes my head spin thinking about though lol

[–] [email protected] 8 points 7 hours ago

Yep, in space, getting rid of excess heat is a much harder problem than you'd think, because radiation is a lot less efficient compared to convection (distribution of heat through movement of fluid like air or water).

[–] Rhynoplaz 9 points 9 hours ago

I have no idea where to even start with this one, but I love the question!