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0 pointswaps11y ago0 comments

It's actually unknown whether there's an atmosphere there. Temperature in space is very cold, sure, but if there are no gas collisions nothing carries the heat away (like, say, on Antarctica). So the lander would only really be cold where it touches the comet, and the comet actually gets quite hot at times. Wikipedia mentions that Haley's comet was 70 degrees celcius (above zero) last time it passed by Earth.

Despite geostationary satellites operating in an environment that's nominally -265 or so degrees celcius, the problem they usually experience is overheating, not freezing. Blackbody radiation will eventually carry the heat away, but we're talking decades to get to -100 or so.

For instance, a human body at rest generates about 150 watts of power, which would kill you in geostationary orbit without a cooling system. It would kill you because it wouldn't take long for your body temperature to rise to 52 degrees, at which point your cell metabolism abruptly stops (your mitochondria will stop generating energy). It would take longer than it takes you to choke though. Though nobody's ever tried for obvious reasons, you should be able to exit a space station and get back in with just a helmet that protects your mouth and nose and ears from decompression. You wouldn't freeze, you wouldn't explode. You'd overheat in 10-15 minutes or so. If you survive that, you'd die 2 weeks later from radiation poisoning. On the moon you need heating, because it actually has an atmosphere that would carry heat away.

It is fun reminiscing about just how special our place in the universe is. Human bodies wouldn't be able to survive on planets 30% closer to the Sun, or about 15% farther away. We wouldn't be alive without a mostly oxygen atmosphere, because without the ozone layer, solar radiation would kill us. Without the earth magnetic field, solar radiation would kill us. Without the sun protecting us from interstellar radiation, we'd die. If our solar system was further to the outside of the milky way, we wouldn't survive the radiation, solar protection or not. If it was closer to the middle, we wouldn't survive. It's unknown whether it's a black hole at the center or something else, but it sure outputs a lot of radiation. Oh, and we're in the < 0.1% of the milky way that hasn't experienced a supernova explosion for about 3 billion years (a supernova explosion at 20 lightyears or less would kill all life on earth. 50 lightyears is considered the minimum safe distance for large mammals to survive). The milky way has collided with at least 3 other (tiny) galaxies, none of the collissions were (are) anywhere near us, as the tidal stresses would alter planetary orbits, and so on and so forth.

All of this is ignoring the physical necessities for life to exist. If the fine structure constant, for instance, was 0.1% bigger or smaller, there would be no chemistry, and no humans. If the speed of light was ~5% bigger or smaller, there would be no atoms, as there would not be any stable electron orbitals, and so on.

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SCHiM11y ago· 2 in thread

> "It is fun reminiscing about just how special our place in the universe is..."

I think you have it slightly backwards there. Life on earth, and us specifically, don't look the way we do because of chance. The reason we only operate in this specific environment is because we were shaped by our environments. Who knows in what environments life can exist. If you think of life as some sort of self-organizing system it's not unthinkable that 'life' could be possible in places that seem extremely inhospitable to us. Inside a star for example.

acqq11y ago

In order to have "life" in the sense that can be interesting to us (that means, not the "life" in the sense of something that is organized inside of a some star which is unreachable by us) the properties of chemical elements can be studied and apparently the properties of carbon are such that it is the most probable element for organic chemistry. There are possible alternatives, like silicon, but every alternative is less probable and less efficient that carbon:

http://en.wikipedia.org/wiki/Hypothetical_types_of_biochemis...

"Sagan used the term "carbon chauvinism" for such an assumption. Carl Sagan regarded silicon and germanium as conceivable alternatives to carbon; but, on the other hand, he noted that carbon does seem more chemically versatile and is more abundant in the cosmos."

wapsOP11y ago

This is the anthropic principle, and applies to some of the coincidences. But there are open questions ...

If life can adapt, why isn't Mars green ? Why isn't Venus ? At the very least, why aren't the landers picking up cells constantly ? We're seeding those planets with fresh living cells on a daily basis according to a number of papers published 2 years ago.

Second it is very unclear how it applies to other required coincidences, like the fine structure constant, or the speed of light. If they weren't in a very narrow range, and at a specific fraction of each other, there wouldn't be any real amount of complexity in the universe. No way in hell there'd be life. You should consider just how narrow the range is and the fact that there's over 20 constants that each have their narrow range. If you wanted to "try" them all, have you considered just how huge a project it would be to search a 20-dimensional space for the right values ?

But yes, at the moment the Copernican principle stands in the "consensus" sense, I personally don't believe in it. I don't know where people get it from, in my data space does not look uniform at all. So, please, do realize what it is : it is an article of faith, nothing more. There is no data, nor theory, to justify it.

I will say, of course, it is a useful principle. Any pattern you see should be assumed to be nothing special, as that will make you search for new science, which is good. That's just good practice, a way to avoid over fitting. But in popular science it is a dogma, and that's not at all what it's intended to be.

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