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Conditions for life on planets

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#21 Yoto32


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Posted 19 January 2017 - 12:43 PM

To further expand on my hypothesis that we might be the first, consider this:


Although we may not be sure what alternate life may be like, whether it's carbon or silicon based, it is guaranteed to need heavier atoms than hydrogen and helium to exist. Well, how do these heavier atoms -referred to as metallic atoms in astronomy- come to exist? For iron and everything lighter, that is the fusion that fuels a star up until its death. For everything heavier than iron, it's the fusion that occurs when that star dies and undergoes supernovae. When the star dies, it explodes and scatters its neighborhood with these newly minted elements. In essence, it takes time to even seed the universe with the materials necessary for life.


So when did metallic production start? Population I stars -of which our Sun is one- didn't actually exist until ~10 billion years ago. It took 3 billion years just to create enough metallic elements to support life, and before this the formation of rocky planets was impossible - there just wasn't enough matter to do it! 


And if you look at that timeline, you'll notice that the Milky Way Galaxy also started forming at around 10 billion years ago. Think about that: our galaxy is one of the first galaxies to exist with metal rich stars!


However, 13 billion years is a long time, right? What is the life-expectancy of the universe? Well, star formation is ultimately crucial towards the development of life, and it's expected to continue for an upper bound of 100 trillion years. Even if the lower-bound of 1 trillion years is true, the fact remains that the Universe is still basically a teenager- it has a long life ahead of it.


With a sample size of one, we have no idea how long it takes for intelligent life to evolve, or life to exist at all. However, it's very clear that if life isn't just a fluke on earth, then the vast majority of life has yet to exist, if nothing else because their star has yet to exist. We could very well be the first- it certainly seems more likely than us being the last.


To answer W13's speculation on why the universe is so quiet, it's important to note that even for Earth, our radio waves can only go out to 100 light-years before being essentially undetectable, which is a pitifully small area. There are roughly 1,400 star systems in a 50 light-year radius, so if I've done my math right [1,400/(50^3)*(100^3)] and the density of star systems remains constant, then there should be about 11,000 star systems that are within "shouting distance" of us- the chance of other intelligent life being within that 11,000 is rather small.


 Although looking for life on Mars is an important step, it will take looking at our neighborhood stars and their planets to get a clearer picture of just how rare life in the universe: If even single-celled life is possible on the star next to us, then the universe must be teeming with life, and intelligent life could be even more common than we thought. I'm of the opinion that simple life is relatively common, but intelligent life is exceedingly rare.


Edit: neat little story I found.

Edited by Yoto32, 19 January 2017 - 02:27 PM.

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#22 W13



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Posted 22 January 2017 - 09:25 AM

Creepy story :lol:

I also agree with you, I think. Very simple life isn't out of the question. I wouldn't be surprised if we found chains of amino acids or a bunch of vesicles. But that's as far as I'll agree with you. I think the jump from amino acids and vesicles to a multicellular self-replicating DNA-powered unit with built-in evolution capability (gene mutation, etc) is way bigger than the jump from that to a dog, for example (See: https://en.wikipedia...lution_of_cells ). So either we'll find barren planets with at-most soupy "life" of bubbles and some chemistry like proteins or amino acids -- or we'll find macro-sized life like animals and plants. That's because evolution happens much more rapidly once a complex metazoan (multicellular life) has evolved. (See: https://en.wikipedia...brian_explosion ). To go from a chunk of algae to a dog, for example, happens in the blink of an eye compared to go from a barren planet to a metazoan. Hmm.. does this mean that intelligent life is almost certainly present on planets with complex life? Yes. But will we find it? Nope. We'll only find single-celled life. The time it takes to evolve complex multicellularity also shows the evolutionary difficulty. On most planets, the difficultly may be so great that anything beyond single-celled life may never get a chance to evolve.

We need to launch more missions to Jovian and Saturnian moons. I'm not sure we'll find anything beyond fossils on Mars, but there's a real potential on finding something currently living in the sub-ice oceans on moons like Enceladus, Titan, Europa.

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