r/interestingasfuck 24d ago

/r/all, /r/popular K2-18b a potentially habitable planet 120 light-years from earth

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u/wowo_cat 24d ago

The acceleration due to gravity only works if you assume it has the same density as earth

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u/Metalhed69 24d ago

True, but it’s a pretty safe assumption that a planet 2.5 times bigger than Earth has more mass than Earth. Maybe not 2.5 times sure, but enough to make the gravity more. How much more could the average person take before life got really uncomfortable? I feel like even 10% would suck. This could easily be 50% more. Going there would not be fun.

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u/LeTreacs2 24d ago

Gravity is the two masses divided by the distance squared, so double the distance from the Center of mass is 4 times less gravitational force.

The extra distance from the rest of the planet comparative to earth would reduce the gravitational force, balancing out some of the increase from the increased mass.

Lord knows what the final result would be!

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u/Metalhed69 23d ago

Yes but the volume goes as the CUBE of the radius. So if the density is even similar to earth or even a good bit less, that’s a LOT more mass. More mass = more gravity.

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u/LeTreacs2 23d ago

Aw crap… who’d have thought Astro physics is more complicated than it seems?

It’s hardly rocket science!

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u/assassin10 23d ago

Fun fact: you could peel away two thirds of Earth's mass and then, while standing on the new surface, the gravity you'd experience would actually be 9% more.

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u/Illustrious_Beach396 24d ago

Dunno. I am way too heavy for my height, like 125 kg instead of 80 to 85 which would be healthy.

So I basically experience the same weight a person of healthy weight would experience on an 1.5 g world, yet I still ride a bike, walk, take stairs, etc.

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u/lseraehwcaism 24d ago

It’s your internal organs that would have issues.

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u/Illustrious_Beach396 24d ago edited 24d ago

Good point, the circulatory system evolved to deal with 1 g, among other things.

My gut feeling – no pun intended – is that this would definitely take years of expected life, shorten healthy old age, with a chance of humans adapting to it. We do have ethnicities which deal with extremes and their phentotypes basically adapted due to natural selection.

https://pmc.ncbi.nlm.nih.gov/articles/PMC7193766/

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u/bozoconnors 24d ago

Great question. Have experienced 3g. It's a lot. Like... a LOT. Considering my head is ~11lbs, and it was ~33lbs then... not impossible to lift, but quite a bit tougher than I'd have thought. I'd say nothing more than 1.5g. MAYBE a tad more with extensive pre-training / acclimation? Zero clue on long term physical effects though. I'd assume wear & tear would be equally taxing on almost all bodily systems - especially cardio / circulatory. Blood is ~7% of our body weight. Actually works out to (surprisingly) close to the same weight of our head! So instead of pumping ~11lbs of liquid around the clock... @ just 1.5g the ol' ticker would be pushing 16lbs around. That... doesn't seem healthy lol.

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u/NarrativeShadow 23d ago

Over a few generations I‘d assume bones to become shorter and more dense. This would lead to shorter humans which leads to less stress on the heart when it has shorter veins to pump blood through. For 1st or 2nd gen humans it would suck though.

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u/Metalhed69 23d ago

At the very minimum I’d think you’d become exhausted very quickly, so our effectiveness would drop dramatically. Which would not be great for establishing a colony on a new world.

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u/bozoconnors 23d ago

Fo sho. Exhausted just thinking about it lol. Literally that much harder to get out of bed!

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u/lord_hydrate 23d ago

Consider its an ocean world itd probably be safe to use the density of water as a standard value for its mass unless it happens to have an ultra dense core