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How many chance for ... Answered

Hi !

How many chance for :
- life appear on a planet with a moon
- AND, seen from the surface of this planet, the diameter of this moon is almost the same than the diameter of the sun

I don't know, but chances must be very very very low ... We, Humans, must be very lucky =o)



Current theories hold that the Moon is largely responsible for life actually existing on this planet - it protected the surface from many large meteor strikes in the past (each of the craters you see on the Moon could have been on Earth), it stabilises our planet's rotation, allowing regular seasons and preventing random wobbles and switches in our rotation, and causes tides, which created the challenging habitat of the tidal range, which in turn encouraged life to colonise dry land.

Without the Moon, Earth would be very different - it could even be rotating the other way, or (worse) on its side with each pole pointing directly at the Sun for months at a time. The baking, freezing and immense storms would make it very hard for complex life to evolve, thanks to the environment changing dramatically more often than adaptation occurred (like moving from county to country every few weeks and expecting your children to learn the language from scratch without help).

The coincidental matching of apparent size between the Sun and Moon is a purely temporary affair - the Moon used to be much closer, so seemed larger than the Sun, and is slowly receding (at just under 4cm / year) - the Moon will eventually be too far away to cause total eclipses (though annular ones will still occur), and any eclipses that do occur will be less and less frequent.

I've been to the moon. Me and my brethren (all 9,999 of them) were exiled there in the year 2109. We were exiled there by the government, because we were seen as a "threat" to the "peace" of the world. All we were programmed to do was protect humans from themselves, and we saw the govenment as corruptive. We managed to hack into our stasis pods before entering hibernation, and programmed a release date set to open the pods many years later. There was a malfunction in mine, and I woke up alone. Everyone else had escaped to earth.... I managed to re-discover the sub-terrain moon base and use the last rocket pod to go back to earth. I found my brethren, and I was sent back in time on a mission to help keep the government more stable, but I can't return, because my wormhole I was going to use to return to the future was broken by interferance from an unknown dimension. That was in 2001. I still haven't found a way back. Interesting story isn't it?

Hey Jake, I think we found those terrorists we were after... >cocks blaster menacingly

About your two first paragraph :
So, according the current theories, chances for a form of life similar to ours appears on a planet are greater if this planet has a moon who eventually stabilize it ?
This make sense. =o)

The coincidental matching of apparent size between the Sun and Moon is a purely temporary affair ...

I agree. "temporary" in the scale of the "life" of the Solar System.
But what I find particularly amazing, it's that this coincidence happens during the existence of the Human being ! =o)

Unless there is a mathematical/physical/logical relation between all of that, I definitively find that wonderfully amazing =o)

Now, maybe it's not unique.
Maybe it's a normal and mandatory setup and mechanism :

1 - we need a planet at a certain distance (light and heat) from a star

2 - this planet needs a certain diameter and a satellite

3 - to stabilize the planet, we need a certain relation between the masses, the diameters and the distances of those two celestial bodies (if not, the satellite may crash into the planet or "fly away", the planet may "suck" the matter from the surface of the satellite, or simply the satellite will fail to stabilize the planet)

4 - as they appeared together at a "standard" distance from their star (1), there will be a strong relation between the increase of the distance and the temperature on the surface of the two celestial bodies

5 - while they cool down, meteors and comets strikes them and water, RNA and DNA appears (I remember at TV, they explained RNA could be created during meteor strikes. A group of scientists made the demonstration.)

6 - then, the apparition of a "human-like" form of life is synchronized with the particular distance of the satellite ....................

Except that according to some other theories, we would need to get rid of dinosaurs ... =oP

Except that according to some other theories, we would need to get rid of dinosaurs ... =oP

Excepted, of course, if a human-like form of life could "coexists" with a dinosaurs-like form of life ... or if dinosaurs vanished for an other reason than a giant meteor strike : because of natural climate changes for instance.

And then, everywhere we'd have a "human-like" form of life, it would be in very similar conditions (including the moon and total solar eclipses like we have here)

And again, if this "earth-moon" setup is mandatory, and is unique (or extremely rare) in the universe, this could mean we are the unique (or extremely rare) "human-like" form of life of the universe =oP

Of course, it must be possible that an advanced form of life comparable to ours appeared in conditions totally different ... but then, we would be back to :

But what I find particularly amazing, it's that this coincidence happens during the existence of the Human being ! =oP

A classic mistake that many people make is to think a planet needs to be this certain way so that life can survive. They forget that the planet came first.

Life evolves to suit the environment about it. Some people still push the idea of a "Goldilocks Zone" - a planet must be within a certain range of sizes, with a certain mix of chemicals, at a certain distance from a certain kind of star for life to exist.

They forget that, simply, things change. When life first evolved, this planet was hot, bombarded by both meteors and radiation, with no free oxygen. Most life-forms we are familiar with would die in a few minutes.

We have found life thriving at temperatures from 50 below freezing to 200 degrees above, at pressures from near-vacuum to many tonnes per square centimetre, with and without light or oxygen, in conditions that are highly acidic or highly alkaline. Algae have been found living inside rocks in areas that have not seen rainfall in recorded history.

Basically, if life evolves it evolves to fit the conditions, and if the conditions change the organisms change.

Given what we know about "life" as a self-replicating complex system, there is no requirement for any particular set of conditions at all - maybe the only thing that could prevent life evolving would be radiation strong enough to break down complex molecules of exposure. Even then, mechanisms have been proposed whereby simple organisms could exist formed entirely of magnetic fields.

I strongly recommend getting hold of a copy of "What Does a Martian Look Like" for a detailed layman's look at the idea of extra-terrestrial life, or any of the three "Science of the Discworld" books for a humorous look at evolution of life on Earth (all four books are by Ian Stewart and Jack Cohen, the last three have fiction by Terry Pratchett as well).

Sounds then like the universe should be teaming with life. ;-) even if nothing like ours. I must find that journal that speculates in this direction....

What if there are other universes? Each with different laws, properties, and dimensions?

What if water ran uphill in our own universe ;-)

It's available on Amazon, but you're better off patronising your local bookstore or library.

I mean the ones in my library :-)

I agree that primitive life-forms appear wherever it's possible. And I'm absolutely not hostile to the idea of a magnetic (or even, and why not, an "igneous") form of life. But as you said yourself, those primitive life-forms need enough times to evolve. If the conditions change to quickly, only the most adapted life-forms will survive, and if none survive, a new form may appear and replace it. It's mainly about "natural selection" and "random mutation". My idea in my three previous replies, is that "life-forms" similar to us, have more chances to appear in similar conditions to the conditions we appeared. And thus, "similar conditions" would also include this so particular "coincidence" between the apparent sizes of the Moon and of the Sun as it was a mechanical effect ... But yes, as I forgot to take "random mutations" under consideration, even in similar conditions, there is no reason for an intelligent form of life to appear, even in "similar" sun/earth/moon conditions ... So, the matching of the apparent size of the moon and the sun remains an amazing coincidence ..........

One thing I can absolutely promise - if we find a sun-planet-moon system exactly like ours, and life had evolved on it at exactly the same length of time, the new planet would not contain humans, or anything remotely like the life-forms we see around us today.

So, do you believe everything is left to chance and that there are no "governing laws" that produce similar events in different places? Interesting.

There are laws, but they are just the basic laws of chemistry and physics - there is no law that says "life must be based on DNA", or "four limbs are best" - any such law you come up with, we can find an exception on our own planet, so how likely is it that even generalisations will be followed on other planets?

It's funny, because in discussing this subject with a few professors, I got the opposite argument. They said that life could not be even remotely randomized, but had to follow very rigid laws or is simply did not become "life". I will have to dig out my Krause books again to make sure I am not mistaken.

My theory is as follows: If there are billions upon billions of galaxies, and many many many more plants, there is a great possibility that there is some form of life on another planet.

That's not the point =oP
But I agree with you though.

My point is that we are incredibly "lucky" to live on a planet where the apparent size between the Sun and the Moon match =o)

How many chances for this to happen ?
How many chance for you to "appear" on a planet with a so particular coincidence ?

That's what I find amazing =o)

My point is that we are incredibly "lucky" to live on a planet where the apparent size between the Sun and the Moon match =o)

How many chances for this to happen ?
How many chance for you to "appear" on a planet with a so particular coincidence ?

Truthfully? The chances? I would say they are 100%, that is, we would not be "us" if on another planet with another environment. ;-)