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October 24th, 2021, 16:09
Originally Posted by Atrachasis View Post
This thread has taken a gloomy turn!

But relax about the collision with the Andromeda galaxy, everybody! Stellar collisions are exceedingly unlikely even during a galaxy merger. Neither are we likely to be swallowed up by the central black hole.

Though the merger will most likely trigger an inflow of gas into the nucleus, feeding the hole, and activating a QSO right here in our own galaxy. But I guess that's survivable‚€¶?

I'd be more concerned about the billions of years of ennui that await us afterwards. The night sky in elliptical galaxies is exeedingly boring.
This is true, but it's much more likely that the gravitational pull of different stars as they swoop past the Solar system will knock some planets off their orbits and send them flying into dead space as rogue planets.

Either way, the sky will be a beautiful sight to watch for many years while the galaxies are close to each other and dancing back and forth, even if afterwards it will be no so much.

Edit: https://www.youtube.com/watch?v=4disyKG7XtU
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October 24th, 2021, 16:12
Originally Posted by Nereida View Post
Also the Sun would first turn into a red giant when it runs out of helium to fuse in its core, eventually swallowing Earth within its own body, far before it turns into a white dwarf.
Since we're at doomsday scenarios, main sequence stars like the sun aren't entirely stable either, but exhibit a gradual increase in luminosity, which would make Earth inhospitable well before the red giant phase (in a couple of hundred million years, maybe?). Mars, on the other hand, might experience a "second springtime" at that point, so you might consider purchasing some real estate now as a really long-term investment.

Originally Posted by Nereida
The problem with Mars is that its gravity is 43% of Earth's. That does not only mean that you will have physiological and cardiovascular problems that will lead to a premature death after prolonged exposure which is why astronauts aren't allowed to take missions for more than 6 month - that's how long it's considered to be "safe" for the human body to not be subject to Earth's 1g).
I would have presumed there to be a "middle ground" between 1g and microgravity (~0g] that would still be survivable in the long term. Are the physiological effects at 0.43g really that devastating? References would be appreciated.

But maybe you're just trying to drive prices on that Martian real estate down so you can snatch everything up cheap.
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October 24th, 2021, 16:14
Our Sun getting hotter reminds me of this proposal to adapt Earth's orbit by slowly moving the Moon with reactors. I don't have the link anymore, it was clever but sounded desperate anyway.

In the books section, there's Orphans of the Sky by Heinlein, by the way. It was the inspiration for Colony Ship. I haven't read it.

The current statement of the Mars Exploration Program, that I mentioned earlier, is not to directly live on the planet but to get more insight: "The goal of the Mars Exploration Program is to explore Mars and to provide a continuous flow of scientific information and discovery through a carefully selected series of robotic orbiters, landers and mobile laboratories interconnected by a high-bandwidth Mars/Earth communications network." They're investigating a series of questions, among which "the potential for Mars to have hosted life" and "the future exploration of Mars by humans".

If there is something about developing an atmosphere or living permanently there, I missed it.

EDIT: not very important, but gravity of Mars is closer to 37.5% of Earth's, not 43% (not sure where it's coming from).
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October 24th, 2021, 16:19
Originally Posted by Atrachasis View Post
I would have presumed there to be a "middle ground" between 1g and microgravity (~0g] that would still be survivable in the long term. Are the physiological effects at 0.43g really that devastating? References would be appreciated.

But maybe you're just trying to drive prices on that Martian real estate down so you can snatch everything up cheap.
It wouldn't be as devastating as zero-g, but it's an 8-month trip in zero-g in the most optimal orbital window to get to Mars to start with, so at that point, your cardiovascular system would be already gasping for a lifeline even before you set a foot on Mars. I don't have a ref, I believe Neil DeGrasse Tyson mentioned it in one of his science podcasts.

That's not even speaking about muscular mass loss, and bone weakening/osteoporosis that would never find an optimal setting for recovery in Mars, au contraire, it would only get worse every passing day.
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October 24th, 2021, 16:59
Originally Posted by Atrachasis View Post
References would be appreciated.
I'd appreciate to see the references as well.

Is the fact the gravity is 37.5% that of Earth really a limiting factor for a human to stay longer than 6 months? AFAIK it's something we are still studying.

The same goes for the atmosphere, my understanding is that it would be difficult to find enough matter to rebuild the atmosphere, but I don't see a limitation due to gravity. The real problem is the absence of magnetic field, which limits the protection of the atmosphere against ionization and which would also be a big problem for living organisms on the surface.

In any case, this wouldn't be my first choice destination for holidays.
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October 24th, 2021, 17:33
Originally Posted by Redglyph View Post
I'd appreciate to see the references as well.

Is the fact the gravity is 37.5% that of Earth really a limiting factor for a human to stay longer than 6 months? AFAIK it's something we are still studying.

The same goes for the atmosphere, my understanding is that it would be difficult to find enough matter to rebuild the atmosphere, but I don't see a limitation due to gravity.
As I said, I think it was either Neil DeGrasse Tyson or a video of Kurzgesagt where I heard it, but any simple Google search will produce results like this: https://scijinks.gov/pressure/#:~:te…%20Earth's.

Fortunately for us, Earth‚€™s gravity is strong enough to hold onto its atmosphere. Mars, for example, is less than half Earth‚€™s size and around one-tenth Earth‚€™s mass. Less mass means less gravitational pull. Mars‚€™ atmosphere is only about 1/100th as dense as Earth‚€™s.

[…]

Even then, since Mars has 38% of Earth's gravity, it can only retain an atmosphere of about 0.38 bar. In other words, even a terraformed Mars would be very cold by Earth standards and its air extremely thin and chilly.
That's just the top Google result, if you are keen I'm sure you can go as deep as you want down that rabbit hole. The fact that you don't see the limitation due to gravity doesn't mean it's not there.

And yes, the lack of a magnetic field is another big downside, though protection from ionising radiation is something we are technologically capable of doing, unlike manipulating gravity.
Last edited by Nereida; October 24th, 2021 at 19:02. Reason: It's Google, not Goggle.
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October 24th, 2021, 18:06
Regarding the "rare earth" hypothesis … How much likely is it that on a rare earth something like beer is invented ?


Originally Posted by Couchpotato View Post
Earth may be trapped inside a giant magnetic tunnel
Reminds me of a short story I had been writing when being in an a state of being totally … what's the word ? overwrought ? overexcited ? after visiting a theme park several years ago … I had totally psychedelic dreams, and one of them was then called by me "the Joiners", it was about ultra-wide beings, with "galaxies being the eyes" , and some other structures being the arms and legs … who had been growing into these proportions by growing from normal men and women …
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October 24th, 2021, 19:01
I was browsing through this "Live Science" site, and I foiund a few interesting articles :

All "titles" by me :

Adam and Eve just eat a fruit. No apple. https://www.livescience.com/what-was…t-in-eden.html

A capaign of misogyny put Marie Antoniett words into the mouth : https://www.livescience.com/let-the-eat-cake.html

Racism made the 24 Dollars appear : https://www.livescience.com/was-manh…4-dollars.html
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October 25th, 2021, 08:05
Originally Posted by Nereida View Post
As I said, I think it was either Neil DeGrasse Tyson or a video of Kurzgesagt where I heard it, but any simple Google search will produce results like this: https://scijinks.gov/pressure/#:~:te…%20Earth's.
Even then, since Mars has 38% of Earth's gravity, it can only retain an atmosphere of about 0.38 bar. In other words, even a terraformed Mars would be
Hm, but that quote you quoted can't be quite right, can it (although I acknowledge that you were making a point mostly about physiological effects of the trip, not the atmosphere)? Atmospheric pressure (or density) can't just be a function merely of surface gravity. Just from observation:

- There's Venus, which is about the size (and roughly the surface gravity) of Earth, but has 90 times the atmospheric pressure.
- There's Titan, which is even smaller than Mars with only 0.14g of surface gravity, but has an atmospheric pressure greater than Earth's.

Obviously, total atmospheric mass will play a role. Sure, there will be atmospheric mass loss due to interaction with solar wind and radiation, but I would guess that Mars should be able to hold on to a denser atmosphere for quite a while. Of course there are the minutiae of where to get all that gas from.
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October 25th, 2021, 10:36
Originally Posted by Atrachasis View Post
Hm, but that quote you quoted can't be quite right, can it (although I acknowledge that you were making a point mostly about physiological effects of the trip, not the atmosphere)? Atmospheric pressure (or density) can't just be a function merely of surface gravity. Just from observation:

- There's Venus, which is about the size (and roughly the surface gravity) of Earth, but has 90 times the atmospheric pressure..
I already explained this briefly in another post. Another trait of Venus' atmosphere is that at its surface the pressure is equivalent to being 900 meters under an ocean in Earth. Even standing on it without equipment would get you crushed - but that is not before you get incinerated by the C450+ temperature that could cook a pizza in about 6 seconds - let alone a human body. This is because of its composition, with a very dominant presence of CO2 (over 96% of its atmosphere is this chemical compound alone).

Titan may actually be a more valid candidate than Mars in that it receives most of its heat from Saturn tidal gravity waves, and so it's a whole different beast. We don't know enough about it yet to tell.

The bottom line is yes, indeed, you can make Mars atmosphere denser by using GHGs (I mean, in theory, not that we can embark on such an enterprise at this moment, but let's imagine we actually can) - However, for the atmosphere to get there, and due to the distance from the Sun (and the amount of heat that Mars receives because of it), the atmosphere would become toxic for humans in the process. You can't have it both ways, either you have an atmosphere with Earth's composition that is too thin and cold for humans to be able to breathe it safely, or you have a thicker, heavier atmosphere with a high content of CO2 or other similar chemical compounds to reach a pressure similar to Earth, but then it would be toxic for humans. If Mars was a bigger planet, its own gravity may be able to make up for it, requiring fewer GHGs to get the atmosphere to a desirable pressure before it becomes too toxic, but that is not the case.

In a nutshell, this is why planets need to be in the Goldilocks zone to be even candidates at all. In theory, if we had the technology necessary, we could terraform any planet within the Goldilocks zone to have a breathable atmosphere by altering its composition in a sustainable way related to the heat that it receives from its local star.

Neither Venus nor Mars are in the Goldilocks zone, and they will never be planets that humans, as we know them, can stand on their surface unassisted by technology to survive for even more than a few seconds.


Edit: Wanted to add that of course, we're always speaking about humans. As species, we have evolved over hundreds of thousands of years from other species, and everything in our physiology, our bone structure, our muscular tissue, our senses, every tiny cell in our body has evolved and grown "cozy" around surviving in Earth's environment. Any tiny alteration to that would put us at a heavy evolutionary disadvantage. That does not mean that Mars or Venus could not be "Terraformed" to sustain other kinds of life comfortably that may evolve acclimated to those different rules - just not human life as we know it.
Last edited by Nereida; October 25th, 2021 at 11:10.
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October 25th, 2021, 12:17
Originally Posted by Atrachasis View Post
Hm, but that quote you quoted can't be quite right, can it (although I acknowledge that you were making a point mostly about physiological effects of the trip, not the atmosphere)? Atmospheric pressure (or density) can't just be a function merely of surface gravity. Just from observation:

- There's Venus, which is about the size (and roughly the surface gravity) of Earth, but has 90 times the atmospheric pressure.
- There's Titan, which is even smaller than Mars with only 0.14g of surface gravity, but has an atmospheric pressure greater than Earth's.

Obviously, total atmospheric mass will play a role. Sure, there will be atmospheric mass loss due to interaction with solar wind and radiation, but I would guess that Mars should be able to hold on to a denser atmosphere for quite a while. Of course there are the minutiae of where to get all that gas from.
Indeed. As a scientific by formation, I'm not trusting Google results without understanding them. It's too easy to reach the wrong conclusion - like several people explaining that the pressure of the atmosphere is proportional to the height because it's the weight column of air above. The idea is right, but the conclusion is completely wrong.

Stating that p0 is the same on Earth and Mars with a rule of three seems naive, but I won't pretend to be all-knowing in the subject since I'm not an expert. All I saw is that the quantity of atmosphere could be estimated from the escape velocity of molecules, so why shouldn't that depend on other parameters like the temperature profile, the planet radius and the composition in the different layers of the atmosphere? Some of which vary with time. I'm more familiar with those parameters on Earth, and it's far from trivial.

It's a moot point anyway. As said before, even if we could bring enough molecules there, the atmosphere won't be stable without the protection of a strong magnetic field because of the ionization and solar winds, and it will erode like it previously did (I doubt we have the technology to solve that part). Besides, humans would have to live indoors with a protection against radiations anyway. So if there is to be a colony, it won't be in open air. And that's without mentioning the possible physiological issues mentioned before.

Looks like we'll have to look further for a good candidate and find a way to get there.
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October 25th, 2021, 12:26
I mean, you can believe what you want. Fortunately, science is not a religion, and belief does not get computed into it. The thing I love about the Universe is that, as Neil DeGrasse Tyson quotes in one of his books, "The Universe is under no obligation of making sense to you".

It is what it is, regardless of whether our primitive senses, that evolved around foraging for food and surviving predators in the plains of Africa hundreds of thousands of years ago, can get a grasp on it or not.

PS: And by the way, if it wasn't obvious, I recommend Neil DeGrasse Tyson's books for those who want to learn a bit about how things really work. Pretty great entry-level reads that don't require a lot of previous knowledge on otherwise daunting fields like astrophysics.

"Astrophysics for People in a Hurry" is particularly good and well structured.
Last edited by Nereida; October 25th, 2021 at 13:02.
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October 25th, 2021, 13:11
Originally Posted by Nereida View Post
I mean, you can believe what you want. Fortunately, science is not a religion, and belief does not get computed into it".
I wish I could share that sentiment. Perhaps it is true in your field, but you wouldn't believe the amount of belief that people managed to shove into prior probabilities in mine.
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October 25th, 2021, 14:03
Well, at their origins, science and religion had many things in common. People tried to explain why things were the way they were. Some of the most notorious scientists of old were either religious people or philosophers that tried to think outside of the box and beyond what had been established. "God did it" was just not enough for them.

These days science is based on empirical evidence, any claims need to be disputed, tested and revised by a whole scientific community that probably does not want your idea to succeed, because it will debunk theirs, or they are simply jealous that they didn't come up with it. So when something becomes an established truth, it's not because scientists chose to believe it, it's because there is sufficient evidence that it is considered to be true.

I don't know what's your field, but if people are shoving belief into it, I would just disregard them. They don't even need to take your word for anything you say. And nobody needs to take my word for anything I say in this thread either.

Go out there, read, research, experiment, observe. Come to your own conclusions, see if they match the conclusions that others reached. That is what science is about, and what makes science true for everyone, regardless of whether they believe in it or not.
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October 25th, 2021, 15:47
Originally Posted by Nereida View Post
Well, at their origins, science and religion had many things in common. […] I don't know what's your field, but if people are shoving belief into it, I would just disregard them.
Not always that easy. There are power structures in science as everywhere else, and as a lowly grad student, you don't always have that liberty. I still vividly remember how I was once informed by my advisor that some of the faculty were doubting my "scientific reliability". My crime? I quite openly hung out with some persons of ill repute, meaning astronomers who had proposed alternative cosmological theories.

But I fondly remember how the old department head came to me later and said something to the effect that of course it was preferable to be correct about exciting new ideas - but that you wouldn't get anywhere in science just by always being correct about boring ideas.

Originally Posted by Nereida View Post
Go out there, read, research, experiment, observe. Come to your own conclusions, see if they match the conclusions that others reached. That is what science is about, and what makes science true for everyone, regardless of whether they believe in it or not.
Words to live by! And with vast numbers of journals and huge data archives, from clinical trial results to deep-sky catalogues, being increasingly accessible, opportunities to see for yourself "what holds the world together at its core" have never been better.
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October 26th, 2021, 20:09
Can we agree upon saying that Mars is more hospitable for us humans than Venus ?
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October 26th, 2021, 20:15
Originally Posted by Alrik Fassbauer View Post
Can we agree upon saying that Mars is more hospitable for us humans than Venus ?
Yes, if you believe that a slow death is better than a fast death…
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October 26th, 2021, 20:27
By the way, since we should always do things properly, we shouldn't start terraforming Mars before we have successfully finished venusforming Earth, which is on a good way right now.
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October 26th, 2021, 21:03
Originally Posted by bkrueger View Post
By the way, since we should always do things properly, we shouldn't start terraforming Mars before we have successfully finished venusforming Earth, which is on a good way right now.
Comment of the day!
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October 26th, 2021, 21:50
Keep the human infestation limited to one planet, por favor! Before we, as a race, even consider venturing forth, we need to do right by the planet we're currently destroying. And by doing right I mean actually start fixing things, and not making them worse here or elsewhere!
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