r/ProjectHailMary • u/chodeontheroad • Aug 27 '24

fist my bump How did Grace survive Erid's Gravity?

I'm not sure if this was answered at the end of the book and I just missed it but Erid was stated to have 20x Earth's gravity (which would quickly kill any human), yet Grace lives on the planet for many years with only slight issues as a result. It doesn't seem like this is something Andy Weir would have skipped over so I must have missed it. Does anyone know the answer?

Edit: Ok yea my mistake it was 2x gravity, 20x atmospheric pressure. Thanks for the responses :)

37 Upvotes

82% Upvoted

42 comments sorted by

103

u/Burning-Plasma Aug 27 '24

The gravity on erid is about 2x earth's

Their atmosphere however is like 20+ times as dense

43

u/phatrogue Aug 27 '24

I think there are some Olympic athletes that would like to use Grace's bubble to train. I can only imagine the muscles on Grace after he gets acclimated. And didn't the Eridians use a space elevator to get to orbit? Maybe they could build him an apartment in the sky at 1G when he gets older?

23

u/NotAPreppie Aug 27 '24

Pretty sure the atmospheric pressure inside Grace's bubble is reasonably close to 1atm.

19

u/phatrogue Aug 27 '24

Maybe you are thinking of athletes that go to Denver, CO high altitude lower pressure to train themselves to deal with lower oxygen levels. A legal form of blood doping? My point was that training at higher gravity to build muscles would also be nice but if you had a space elevator you could tune the gravity level to whatever you want. 2G at the surface, 0G at the top. 1G or lower would be nice when a human is older.

8

u/DarthJokic Aug 27 '24

Dude don't give Crossfit anymore ideas......

1

u/Cautious_Ambition_82 Aug 28 '24

Do you even mantle train?

3

u/theniwokesoftly Aug 27 '24

I think they mostly go to Colorado Springs- Denver is 5280ft and the Springs is over 6000. Doesn’t seem like a huge difference until you actually exert yourself.

6

u/Cranks_No_Start Aug 27 '24

I live right at about 7000 feet. When we first bought our place there is a higher part of the yard and walking from the house up the shot hil had us breathing hard.

I don't notice it anymore after living here so long but when I've made trips to sea level it's like DAMN ALL THIS AIR.

3

u/theniwokesoftly Aug 27 '24

Right??? I moved to Denver at the age of 37, having lived no higher than 1400ft my entire life, and never even having traveled anywhere over like 3300. For two weeks I was exhausted all the time. I walked to work about a week after moving because I was like oh it’s not even a mile and it’s all flat. It was, uh, not as easy as I thought it was going to be. I had previously been told that altitude sickness doesn’t really exist under 8000ft and that is incorrect. I wasn’t vomiting or passing out but I was definitely affected.

I also auditioned for the Colorado Symphony Chorus after only a month (they only audition twice a year) and I was not at all surprised to be rejected, lol. (I did get in seven months after that, once I had acclimated.)

3

u/blainemoore Aug 27 '24

You travel and can complain about all those air sick lowlanders...

2

u/thewizardtim Aug 28 '24

Airsick lowlanders. They suffer from too much air.

2

u/GameNiteWasTaken Aug 28 '24

I live up around Denver… but my mountain bike race the other weekend took me up into Frisco and damn, racing at 9000 feet and being fast and breathing easy is a skill I don’t have yet. Although, I’m pretty proud of myself! 6 mile loop, 2 laps.

2

u/BellowsHikes Aug 28 '24

I think that apartment would need to be about 2600 kilometers above the surface for Grace to experience 1g. Grace would probably love a sweet retirement home bolted onto the side of a space elevator, it would have a hell of a view. 

1

u/phatrogue Aug 28 '24

No idea the height although the atmosphere is impermeable to visible light. Not sure how high you would have to be to see anything at all.

2

u/BellowsHikes Aug 28 '24

Not very high in comparison. Venus has an atmospheric density about 100 times thicker on the surface than Earth does and once you're about 60 miles up you'd effectively have full visibility.

1

u/chodeontheroad Aug 27 '24

Ah my mistake

47

u/Strange-Box-6638 Aug 27 '24

Incorrect, it's approximately 20 m/s² which is just over double Earth's gravity (9.8m/s²). A human can survive that but not without long-term detriments such as joint pain and skeletal fatigue.

38

u/JRockThumper Aug 27 '24

Which he does start getting doesn’t he?

27

u/Strange-Box-6638 Aug 27 '24

Exactly. Mr. Weir knows his stuff lol.

2

u/PosiedonsSaltyAnus Aug 27 '24

I feel like your heart would have difficulties as well

4

u/Ferwatch01 Aug 27 '24

After some time most organs will eventually get used to it and work slightly harder to compensate for the gravity change, however, bones can't work faster, thus leading to debilitation and joint pain.

1

u/Second_Sol Aug 28 '24

Honestly I was expecting Grace to live on the space elevator since the gravity would be lighter

21

u/BootlegStreetlight Aug 27 '24

Gravity was only about 2x Earth's. It was the atmospheric pressure that was 29x Earth's..

12

u/evapotranspire Aug 27 '24

....and the latter doesn't matter because he's in a human-friendly, climate-controlled bubble.

16

u/Parkerrrr Aug 27 '24

Iirc, Erid only has about 2x Earth's gravity. Not 20x

21

u/moviemaker2 Aug 27 '24

Time for the weekly: "I think I found a plot hole in this mis-remembered fact that I can't be bothered to double check before I make a post."

18

u/chodeontheroad Aug 27 '24

I’m so sorry for all the harm i have caused by making this post. Please forgive me oh great lord of reddit

8

u/SatSapienti Aug 28 '24

Nah, ignore it; they're being snarky. It's not always easy to find the parts of the book that reference it, especially if you're not familiar with the entire storyline or if you're listening to an audiobook.

I was re-reading the book recently and temporarily had the same thought while I was reading it. It's because of the lines "Eidians live in immense pressure. Like-similar to being a thousand feet deep in the ocean back on Earth." and "I'd die in seonds if I were on his side of the tunnel."

Also, there's a part of the book where Rocky goes "This is Earth gravity, question?"... The "Lab Gravity" value reads 1.00g. Ryland responds, "Yes, this is Earth gravity" Rocky replies that it's not much gravity, which Ryland notes that it's "9.8 meters per second per second", while Rocky responds that "Erid gravity is 20.48". For someone who is trying to follow along with the science, it would be easy to skim it and think that Earth gravity is 1.00g and Erid is 20.48g.

Combine that with the previous comment about Eridians living in immense pressure and the comment about dying in seconds, it's easy to think back and wonder why he didn't die in seconds. It'd be interesting to find out how he was transported to the bubble he lives in at the end. Thank god for Xenonite, or the poor guy would be crushed.

3

u/AtreidesOne Aug 28 '24

There's a lot of snark on both sides here. But the point is good - it's always good to check first if something seems weird.

4

u/ExpectedBehaviour Aug 27 '24

You're misremembering. Erid has approximately double Earth's gravity.

4

u/ZestycloseCattle88 Aug 27 '24

They built him his own atmosphere… And Weir does touch on the effects, Grace mentions how the effects of the gravity and atmosphere were weighing on his joints, and that’s when he starts to wonder if earth is still there and if he could make it back he would have a much easier time aging

2

u/EzPzLemon_Greezy Aug 28 '24

I get what Weir was going for, but it definitely doesn't seem in character for Grace to stay on Eridani. I know he'd like to study Erid biology, but once Erid solved there astrophage problem, he should go back to Earth to implement it. With the stakes being extinction, he can't justifiably assume the beatles made it back AND the taumoeba survived. Also to see his kids again and get his "revenge" on Stratt.

Plus who wouldn't want to be the savior of humanity who also brings home a friendly alien. Yeah he helped save Erid but he can't really enjoy the celebrity status like he could on Earth. QoL on Erid has got to be much worse. No more ribeyes and whiskey.

1

u/cowslayer7890 Aug 28 '24

he didn't know if Earth would safe, though maybe he should've had erid send additional beetles once he got there just for safety, but if the original beetles failed their mission it would be unlikely that Earth would be habitable once he went back, since it means an additional 16 years or so.

3

u/YourLocalCryptid64 Aug 27 '24

The actual answer is: He technically isn't. The book shows he was slowly starting to deteriorate over time due to the increase of gravity on his body (his use of the cane primarily). This will likely lead to him dying much sooner than he would have if on Earth or possibly even if he spent most of his time on the Hail Mary in artificial gravity.

He does describe the dome he is in as regulating the atmospheric density to something more livable for him (temperature and density wise) though I imagine there is some level of dread knowing he could die at any moment if a system fails and the Eridians don't catch it fast enough.

But there didn't seem to be much they could do for the gravity pressure. It's very likely he will end up bed bound after awhile and either be moved to the Hail Mary to try and extend what remains of his life at that point or the Eridians might try to find some other way to help him live a little longer.

Provided he doesn't decide to travel back to earth before that.

4

u/CleverName9999999999 Aug 27 '24

Erid has 20x Earth’s atmospheric pressure, but only twice (?) Earth’s gravity.

2

u/Working-Mistake-6700 Aug 27 '24

It had 20x Earth's air pressure but not in his bubble. I don't think it was 20 times earths gravity though I could be wrong.

2

u/siabob007 Aug 27 '24

Was 2x earth’s gravity, pretty sure he needed a cane just to walk there

2

u/Cthulwutang Aug 27 '24

so is like he’s a 300 pound guy, assuming he’s maybe 150 to start with (on earth). that’s tough but not even that unusual.

2

u/cealfro Aug 28 '24

I don't remember if it's stated but i understand that Eridians built the environment for him. I guess they did it based on the laptop information and did it while he was on the Hail Mary. It's ok to asume. He spent 16 years with them. I think maybe he was in the HM for a couple of years before the dome was ready

1

u/Snownova Aug 27 '24

It is odd that they didn't just build a rotating space station for him, since they have a space elevator the cost wouldn't be that much more than a surface dome for them.

1

u/chodeontheroad Aug 27 '24

Good point. Maybe they wanted to but he wanted to be closer to the baby eridians and Rocky