Predicting frequency of Earthlike planets and systems

  • #1
DaveC426913
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TL;DR Summary
With all the exoplanets we've confirmed, can we extrapolate to predict Earth-twins?
Each new report of a confirmed exoplanet adds to the database of knowledge. For obvious reasons, our confirmations seem to stack up in the areas we are currently best able to detect. eg.:

Large bodies: Jupiter-sized down to Sub-Neptune-sized, with a smattering of super-Earths.

Nape-of-star bodies that orbit extremely close.

I presume our dataset finds lots of these because of our detection methods. The implication is that our detection methods are still too rough to find a good cross-section of Earth-twins. It does not mean they not there to be found.

But are we reaching a point where we can start to apply some numbers to our blind spots?

Can we predict with any confidence how many Earth-sized bodies we are likely to find in the Goldilocks Zone and yet still be distant enough (meaning a sunlike star) to dodge the exigencies of tidal-locking?
 
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  • #2
Don't forget about large moons orbiting jumbo planets and being kept warm by tidal forces.
if you are interestd in possible sites for life.
 
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  • #3
DaveC426913 said:
TL;DR Summary: With all the exoplanets we've confirmed, can we extrapolate to predict Earth-twins?

Each new report of a confirmed exoplanet adds to the database of knowledge. For obvious reasons, our confirmations seem to stack up in the areas we are currently best able to detect. eg.:

Large bodies: Jupiter-sized down to Sub-Neptune-sized, with a smattering of super-Earths.

Nape-of-star bodies that orbit extremely close.

I presume our dataset finds lots of these because of our detection methods. The implication is that our detection methods are still too rough to find a good cross-section of Earth-twins. It does not mean they not there to be found.

But are we reaching a point where we can start to apply some numbers to our blind spots?

Can we predict with any confidence how many Earth-sized bodies we are likely to find in the Goldilocks Zone and yet still be distant enough (meaning a sunlike star) to dodge the exigencies of tidal-locking?

Do not forget our tilt so not just distance from the star, size and composition. Important for cycles and seasons.
 
  • #5
I wonder why everyone assumes that a tidally locked planet would be uninhabitable. With the right conditions, it could be perfectly fine. I can imagine beings that evolved on a tidally locked planet thinking, "these non-locked planets are obviously uninhabitable because it gets dark!"
 
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  • #6
phyzguy said:
I wonder why everyone assumes that a tidally locked planet would be uninhabitable. With the right conditions, it could be perfectly fine. I can imagine beings that evolved on a tidally locked planet thinking, "these non-locked planets are obviously uninhabitable because it gets dark!"
I think there are some common assumptions that often arise in origin of life discussions.
  1. Tectonics (a change of sorts) is needed to supply new raw materials for life to arise or sustain itself long term.
  2. Changes may be required to force (or permit) existing life forms to evolve new more sophisticated forms and thereby reach more complex structures and functions.
Personally, I am not convinced either is necessary, but there are arguments that have some logic to them.
 
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  • #7
phyzguy said:
I wonder why everyone assumes that a tidally locked planet would be uninhabitable.
I'm not assuming that, no. I just happen to be interested in chasing down Earth-twins.


Before getting into the weeds of tectonics and axial tilts; it would be nice to know how big the set is likely to be for the gross characteristics of planetary gravity and irradiation.

I suppose I'm thinking about it less from an exo-biology POV than from an eventual human colonization POV.
 
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  • #8
pinball1970 said:
Do not forget our tilt so not just distance from the star, size and composition. Important for cycles and seasons.

And how important our moon may have been in all of this. Theia impact, if it happened, could have been responsible for tilt and strength of magnetic field among other things, which in turn could have been partially responsible for life.
 
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  • #9
JLowe said:
And how important our moon may have been in all of this. Theia impact, if it happened, could have been responsible for tilt and strength of magnetic field among other things, which in turn could have been partially responsible for life.
There are several early evolution of life considerations that posit life on earth, once it formed, benefited from the environmental changes (possibly triggering further evolution) and the introduction of new chemicals that resulted from various periodic changes. Not so much its origin.

A possibly more consequential result of such an impact on the actual origin of life on has been proposed to involve global redox changes that resulted from such an impact and could drive reactions. Its kind of obscure but has been around for several years:

Screenshot 2024-05-25 at 6.53.02 AM.png

Non-Graphical Abstract:
The Moon-forming impact vaporized part of Earth's mantle, and turned the rest into a magma ocean, from which carbon dioxide degassed into the atmosphere, where it stayed until water rained out to form the oceans. The rain dissolved CO2 and made it available to react with transition metal catalysts in the Earth's crust so as to ultimately generate the organic compounds that form the backbone of microbial metabolism. The Moon-forming impact was key in building a planet with the capacity to generate life in that it converted carbon on Earth into a homogeneous and accessible substrate for organic synthesis. Today all ecosystems, without exception, depend upon primary producers, organisms that fix CO2. According to theories of autotrophic origin, it has always been that way, because autotrophic theories posit that the first forms of life generated all the molecules needed to build a cell from CO2, forging a direct line of continuity between Earth's initial CO2-rich atmosphere and the first microorganisms. By modern accounts these were chemolithoautotrophic archaea and bacteria that initially colonized the crust and still inhabit that environment today.
Quoted from here.

Most currently viable theories of life's origin on earth (and many other potentially life bearing rocky planets) involve a chemistry based on hydrogen released from inside the planet interacting with more oxidized chemicals (like carbon dioxide) at the surface. Geochemical forces continue to bring hydrogen to the surface where it can feed these reactions.
Although plates tectonics (long term supply of chemicals to the surface) is thought to have taken a while to get started (at least hundreds of millions of years) volcanic activity is considered to have been present very early.
This is the basis of NASA's best known approach for directing the search for life off earth.
The "transition metal catalysts" refers to geochemically available nano-sized metal or sulfur metals. These can catalyze reactions that create simple organics (like those in the Krebs (or tricarboxylic acid (TCA)) cycle). They are found naturally, and are found even today in the enzymes involved in those reactions in modern life forms.
 
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  • #10
phyzguy said:
I wonder why everyone assumes that a tidally locked planet would be uninhabitable. With the right conditions, it could be perfectly fine. I can imagine beings that evolved on a tidally locked planet thinking, "these non-locked planets are obviously uninhabitable because it gets dark!"
Dave did use the term twin.
 
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  • #11
JLowe said:
And how important our moon may have been in all of this. Theia impact, if it happened, could have been responsible for tilt and strength of magnetic field among other things, which in turn could have been partially responsible for life.
Again, I was really more interested in the gross characteristics of exo-planet astro - getting a set of Earth-twin planets. The consideration of whether life might spontaneously occur on them is actually a digression.

It might help to consider the question to be: are we starting to get an idea of how many potentional human colony planets there might be?

I'm getting the impression the answer is: no. Or at least, no one has sifted through the data this way to make the extrapolation.
 
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