Bringing the alien life debate back to reality

[Doc Dutch]

That corroborates precisely what I wrote.

Rather than tossing around the admitedly impressive 100 billion number, the actual amount of possibly habitable stars is only a tiny fraction of one percent of those.

And that doesn't even include estimates for how many of those actually have rocky planets with magnetic fields or a large lunar companion, and within the Goldilocks zone which are critical to all life on earth .

All of which reduces the possibility of extraterrestrial life making life of Earth very rare.

[Doc Dutch]

Absent any compelling evidence, I am on Team rare life myself.

I've never been that impressed with the math of a hundred billion stars in the Milky Way and a hundred million galaxies.

It's not the sheer number that matter.

We live in a very large and complex galaxy. If we can't find evidence of life in this galaxy, I see no reason to expect it to be in other galaxies.

Many galaxies and many stars are depleted in heavy elements, which are required for life.

None of the blue giants or Red supergiant stars would be expected to have planets with life, those stars don't live very long.

The white dwarfs are the dead embers of sun-like stars, I wouldn't expect life there.

As for the red dwarfs and G type stars, how many of them are depleted in heavy elements, and how many are in potentially gravitationally unstable binary and trinary systems? Solo stars like our sun tend to be the exception rather than the rule. And of those, how many have rocky planets with a magnetic field in the Goldilocks habitable zone of it's star's orbit?

So the number of potentially habitable star systems in our galaxy probably gets whittled way down from 100 billion. And the percentage of those that have intelligent life probably whittled it way down from there.

In statistics, the higher the number, the more likely a rare event will occur. It doesn't matter if the odds of life are low, the more opportunities, the more likely life will develop.

Our Sun will eventually become a white dwarf. It's too small to nova. After a few billion years, it'll become a red giant and smoke the Earth, but warming the gas giants where life could develop (or move to) their moons. Eventually the Sun will shrink to a white dwarf.

https://www.nasa.gov/image-feature/g...e-a-black-hole

Will the Sun become a black hole? No, it's too small for that!

The Sun would need to be about 20 times more massive to end its life as a black hole. Stars that are born this size or larger can explode into a supernova at the end of their lifetimes before collapsing back into a black hole, an object with a gravitational pull so strong that nothing, not even light, can escape. Some smaller stars are big enough to go supernova, but too small to become black holes — they'll collapse into super-dense structures called neutron stars after exploding as a supernova. But the Sun's not big enough for this fate, either: It has only about one-tenth of the mass needed to eventually become a neutron star.

So what will happen to the Sun? In some 6 billion years it will end up as a white dwarf — a small, dense remnant of a star that glows from leftover heat. The process will start about 5 billion years from now when the Sun begins to run out of fuel.

Like most stars, during the main phase of its lifetime, the Sun creates energy by fusing hydrogen atoms in its core. In about 5 billion years, the Sun will start to run out of hydrogen in its core to fuse, and it will begin to collapse. This will let the Sun start to fuse heavier elements in the core, along with fusing hydrogen in a shell wrapped around the core. When this happens, the Sun's temperature will increase, and the outer layers of the Sun's atmosphere will expand so far out into space that they'll engulf Earth. (This would make Earth uninhabitable for life as we know it — though other factors in planetary evolution might make it uninhabitable before that point.) This is the red giant phase, and it will last about a billion years, before the Sun collapses into a white dwarf.

[Cypress]

In statistics, the higher the number, the more likely a rare event will occur. It doesn't matter if the odds of life are low, the more opportunities, the more likely life will develop.

Our Sun will eventually become a white dwarf. It's too small to nova. After a few billion years, it'll become a red giant and smoke the Earth, but warming the gas giants where life could develop (or move to) their moons. Eventually the Sun will shrink to a white dwarf.

https://www.nasa.gov/image-feature/g...e-a-black-hole

Before our sun becomes a white dwarf it will vaporize our oceans and incinerate our atmosphere. So we aren't going to be looking to white dwarfs as candidates for habitable systems.

NASA's estimate of 300 million systems with rocky planets that potentially could host life is only based on being located in the Goldilocks zone, and even the authors admitted this was a weakness of their paper since there are other criteria that make a planet habitable.

This is my thought experiment on other potentially neccessary criteria for a planet to possibly host life:

Probability liquid water exists - 50% (p50). Our system has two near-Earth sized rocky planets in the Goldilocks zone, only one of which has liquid water. So p50 seems like a reasonable guess.

Probability of a strong magnetic field - 33% (p33). Of three rocky planets in the Goldilocks zone of our system, only one has a strong magnetic field. So p33 seems like a reasonable guess.

Probability of permanent stable orbital mechanics - 50% (p50). In the absence of tangible information, an even chance seems like a reasonable guess.

Probability of large gas giant in outer system to clear out any frequent incoming asteroids of a lethal size - 50% (p50). In the absence of tangible information, an even chance seems like a reasonable guess

Probability abiogenesis will actually take place, even if all conditions are met: if we assume the emergence of cellular life for prebiotic materials is difficult to achieve and something of a fluke, assume probability of 1%. If we assume life readily emerges in the presence of liquid water, assume probability 50%.

Water = p50.
Magnetic field = p33
Stable orbital mechanics = p50
Gas giant clearing asteroids = p50.
Abiogenesis, low confidence = p1
Abiogenesis, high confidence = p50

High end estimate: 6.25 million planets in Milky Way host life.

Low end estimate: 125,000 planets in Milky Way host life.

Either way, that is less than 0.00001 percent of star systems in Milky Way that would host life.

And that is without further culling for the probability intelligent life would emerge on a planet that happens to have a biosphere.

[Doc Dutch]

Before our sun becomes a white dwarf it will vaporize our oceans and incinerate our atmosphere. So we aren't going to be looking to white dwarfs as candidates for habitable systems.

NASA's estimate of 300 million systems with rocky planets that potentially could host life is only based on being located in the Goldilocks zone, and even the authors admitted this was a weakness of their paper since there are other criteria that make a planet habitable.

This is my thought experiment on other potentially neccessary criteria for a planet to possibly host life:

Probability liquid water exists - 50% (p50). Our system has two near-Earth sized rocky planets in the Goldilocks zone, only one of which has liquid water. So p50 seems like a reasonable guess.

Probability of a strong magnetic field - 33% (p33). Of three rocky planets in the Goldilocks zone of our system, only one has a strong magnetic field. So p33 seems like a reasonable guess.

Probability of permanent stable orbital mechanics - 50% (p50). In the absence of tangible information, an even chance seems like a reasonable guess.

Probability of large gas giant in outer system to clear out any frequent incoming asteroids of a lethal size - 50% (p50). In the absence of tangible information, an even chance seems like a reasonable guess

Probability abiogenesis will actually take place, even if all conditions are met: if we assume the emergence of cellular life for prebiotic materials is difficult to achieve and something of a fluke, assume probability of 1%. If we assume life readily emerges in the presence of liquid water, assume probability 50%.



High end estimate: 6.25 million planets in Milky Way host life.

Low end estimate: 125,000 planets in Milky Way host life.

Either way, that is less than 0.00001 percent of star systems in Milky Way that would host life.

And that is without further culling for the probability intelligent life would emerge on a planet that happens to have a biosphere.

By that time that happens to our Sun, life would have either moved off planet or destroyed itself. I think white dwarfs are an excellent place to look for ancient life.

Looking for planets in the Goldilock Zone are a great way to find planets for colonization.