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(Big Think)   NASA's Kepler mission taught us that practically all stars possess exoplanets. Now we're learning something deeper: many of them don't. Here's why   (bigthink.com) divider line
    More: Cool, Planet, Star, Gas giant, Solar System, Hydrogen, Extrasolar planet, parent stars, Jupiter  
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932 clicks; posted to STEM » on 10 Aug 2022 at 6:52 PM (16 weeks ago)   |   Favorite    |   share:  Share on Twitter share via Email Share on Facebook



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TWX
2022-08-10 6:59:48 PM  
It makes sense, if your universe only has hydrogen and helium, then it doesn't have the sort of stuff necessary to condense into planets.

It's after enough stars have fused heavier elements that it becomes possible for planets to form.

I wonder if a sand-grain within an oyster to form a pearl is an apt analogy.  Without the grain for the pearl to be constructed around, nothing forms.
 
2022-08-10 7:00:52 PM  
We are the First Ones.
 
2022-08-10 7:06:57 PM  
Because they are violent machines of destruction, every bit as capable as a black hole of farking shiat up.
 
2022-08-10 7:14:40 PM  

TWX: It makes sense, if your universe only has hydrogen and helium, then it doesn't have the sort of stuff necessary to condense into planets.

It's after enough stars have fused heavier elements that it becomes possible for planets to form.

I wonder if a sand-grain within an oyster to form a pearl is an apt analogy.  Without the grain for the pearl to be constructed around, nothing forms.


Gravity is whack. If the earth were hollow, the entire inside would be zero earth gravity, give or take a Himalaya.

Bits of hydrogen gravity goes to reach each other and they gravitate. And they all do that together instead of needing a grain. They are the grains.
 
2022-08-10 7:15:39 PM  

TWX: It makes sense, if your universe only has hydrogen and helium, then it doesn't have the sort of stuff necessary to condense into planets.

It's after enough stars have fused heavier elements that it becomes possible for planets to form.

I wonder if a sand-grain within an oyster to form a pearl is an apt analogy.  Without the grain for the pearl to be constructed around, nothing forms.


That's an Old Wives' tale. In truth, Twain mentioned 3 things worth not knowing, sausages, how laws are made, and when 2 clams love each other very, very much...
 
2022-08-10 7:17:03 PM  

Be polite walk on the right: TWX: It makes sense, if your universe only has hydrogen and helium, then it doesn't have the sort of stuff necessary to condense into planets.

It's after enough stars have fused heavier elements that it becomes possible for planets to form.

I wonder if a sand-grain within an oyster to form a pearl is an apt analogy.  Without the grain for the pearl to be constructed around, nothing forms.

That's an Old Wives' tale. In truth, Twain mentioned 3 things worth not knowing, sausages, how laws are made, and when 2 clams love each other very, very much...


Joyce, on the other hand..
 
2022-08-10 7:26:59 PM  
That or the planets around those stars are too small for us to detect with current instruments and techniques. There's a reason most of the exoplanets we HAVE found are both bigger and closer than any planets in our own solar system.

If there was an identical twin of our system just 50 light years from us right now, we wouldn't be able to detect ANY of the terrestrial planets using the equipment we have today. We'd be able to detect Jupiter, but only BARELY, and only if the ecliptic  was aligned edge-on to us.
 
2022-08-10 7:41:43 PM  

akallen404: That or the planets around those stars are too small for us to detect with current instruments and techniques. There's a reason most of the exoplanets we HAVE found are both bigger and closer than any planets in our own solar system.

If there was an identical twin of our system just 50 light years from us right now, we wouldn't be able to detect ANY of the terrestrial planets using the equipment we have today. We'd be able to detect Jupiter, but only BARELY, and only if the ecliptic  was aligned edge-on to us.


That's the case for not seeing smaller planets around younger stars.

Without enough heavy elements, it's impossible to form the grains that drive core accretion. And without core accretion, there's no way to form gravitationally bound planets before the star switches on and evaporates the disk (which shuts down planet growth). Once the star initiates fusion, the UV radiation flow photoevaporates all the gas in the disk that has a direct line of sight to the star. This also occurs if there is a nearby massive star in the cluster.

There's another interesting factor that heavy elements are relevant to that TFA doesn't get into. Without dusty - specifically carbonaceous - grains mopping up electrons, the midplane of the disk will remain ionized. As long as it's ionized and conductive, the magnetorotational instability will continue to efficiently drive mass into the star and keep things too turbulent for grains to accrete onto each other.
 
2022-08-10 8:10:30 PM  

KarmicDisaster: We are the First Ones.


I call shotgun on being Booji, the Vorlon god of buckets.
 
2022-08-10 8:25:15 PM  

erik-k: That's the case for not seeing smaller planets around younger stars.


Or not seeing ice giants around older ones. or not seeing brown dwarves around the oldest ones. Or not seeing ANYTHING AT ALL in systems where the central star never accretes enough mass to achieve fusion.

You COULD make the case that the oldest stars in the universe are unlikely to have terrestrial planets, but that's still just a hypothetical considering the things Ethan is claiming can't exist are WELL below our detection threshhold either way.
 
2022-08-10 9:10:33 PM  
I am going to go way out on a limb and say that we should not be sure that we are seeing "most" of the stars anyway. All of the dwarfs and holes, etc. that must be undetected could easily have more planets and circling bodies than the stars which are readily visible.

Despite our wonderful detection abilities, we are likely to be erring when we make these broad generalizations based on what we can detect. We are still babies looking at the universe.

Maybe the post above is saying something like this in the last sentence. Oh well. I said it anyway.
 
2022-08-10 9:36:31 PM  
Another variable further constrained in the Drake Equation.  The elements required for complex life weren't available in sufficient quantities until almost the time the Earth formed.  Sure, there's still a billion years or two of margin involved, but it's no longer possible to say, "Hey, maybe there were people around a mere billion years after the Big Bang".

You're probably looking at 4-6 bya, which means we could very much be among the first 'generation' of living creatures to crawl out of the muck on a wet rock.  And on planets similar to Earth, that would imply a strong possibility that any who came before us are still around, their stars and planets not yet to the end of their habitability span.
 
2022-08-10 9:48:20 PM  
We're the only life in the Universe.

/the Kronos out front shoulda told ya
//me or your own farthing eyes
///5th D 4TW!
 
2022-08-10 9:49:42 PM  

2fardownthread: I am going to go way out on a limb and say that we should not be sure that we are seeing "most" of the stars anyway. All of the dwarfs and holes, etc. that must be undetected could easily have more planets and circling bodies than the stars which are readily visible.

Despite our wonderful detection abilities, we are likely to be erring when we make these broad generalizations based on what we can detect. We are still babies looking at the universe.

Maybe the post above is saying something like this in the last sentence. Oh well. I said it anyway.


It's actually horrendously more complicated than that, but there are university libraries full of very consistent math all agreeing with observations on the content of the universe.

Astronomers actually have a very good grasp on how much 'stuff' is out there in the form of gas clouds and stars (planets are basically a rounding error, and so more difficult to pin down).   From what is visible and understanding the formation rate curve between different masses, they can even figure out how much 'stuff' is out there that we can't directly observe.   Planetary formation and planetary disk models are getting to the point where they can even get reasonable estimates of how many planets are wandering around without parent stars because they were kicked out of the systems of their birth.

I'm not saying they should stop looking for things because they're all found, but I am saying that focusing on looking for significant numbers of planets in some sort of 'dark orbit' is probably a good way to waste your career.
 
2022-08-10 10:40:18 PM  
If you live in a rural area and didn't have access outside information, you can't extrapolate how many people live on Earth because you can't see the large cities. All your calculations would be wildly wrong because they would be based on rural population density.

We humans only see part of what's out there, aka the known universe. There could be something ten feet past the farthest point we can detect and that thing, whatever it is, would change everything we know about the universe. But too bad, we'll never know because we'll never detect it.
 
2022-08-10 10:42:35 PM  

TWX: It makes sense, if your universe only has hydrogen and helium, then it doesn't have the sort of stuff necessary to condense into planets.

It's after enough stars have fused heavier elements that it becomes possible for planets to form.

I wonder if a sand-grain within an oyster to form a pearl is an apt analogy.  Without the grain for the pearl to be constructed around, nothing forms.


It would be better to compare it to rain seeding.  Rain works because dust in the atmosphere allows water to condense.
 
2022-08-10 11:09:12 PM  

akallen404: That or the planets around those stars are too small for us to detect with current instruments and techniques. There's a reason most of the exoplanets we HAVE found are both bigger and closer than any planets in our own solar system.

If there was an identical twin of our system just 50 light years from us right now, we wouldn't be able to detect ANY of the terrestrial planets using the equipment we have today. We'd be able to detect Jupiter, but only BARELY, and only if the ecliptic  was aligned edge-on to us.


I was going to say, "what if they revolved the other way and never transited?"

/   glad I'm not crazy
//  or at least I have company if I am
/// THREE exoplanets
 
2022-08-11 3:48:52 AM  

KarmicDisaster: We are the First Ones.


So what you're saying is...I'm an Ancient. And that means I have a shot with Kira Clavell. There's a chance, and I'm fine with that.
 
2022-08-11 4:08:31 AM  
Polaris

external-content.duckduckgo.comView Full Size


/Polaris A
///Polaris AB
//Polaris B
 
2022-08-11 5:54:36 AM  

BenSaw2: akallen404: That or the planets around those stars are too small for us to detect with current instruments and techniques. There's a reason most of the exoplanets we HAVE found are both bigger and closer than any planets in our own solar system.

If there was an identical twin of our system just 50 light years from us right now, we wouldn't be able to detect ANY of the terrestrial planets using the equipment we have today. We'd be able to detect Jupiter, but only BARELY, and only if the ecliptic  was aligned edge-on to us.

I was going to say, "what if they revolved the other way and never transited?"


If the planet were large enough, you might be able to detect the wobble of the star and at least know there is another body orbiting it.
 
2022-08-11 9:00:59 AM  

Be polite walk on the right: Polaris

[external-content.duckduckgo.com image 850x1062]

/Polaris A
///Polaris AB
//Polaris B


That should go Polaris A, Polaris A flat, Polaris G.  Or change A flat to B flat.
 
2022-08-11 3:13:45 PM  
neatorama.comView Full Size


i.makeagif.comView Full Size
 
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