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Old 26th August 2019, 08:31 AM   #41
lomiller
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While interesting, I worry that the number of observed earth sized planets in goldilocks zone may be to slow to make real conclusions. It’s true the method for discovering planets favors hot Jupiter’s and super Earths the prevalence of them could also be pointing to models of planetary formation that suggest truly earth like planets are less common.

If we assume a hot Jupiter formed farter from the star then migrated inwards, it would be impossible for a earth like planet to form as the giant planet would have cleaned up everything in its path and not leave enough for an earth like planet to form. However, without a giant planet there is too much material in the inner solar system and a super-Earth forms instead.

If this is the case then earth like planets can only form if you have a giant planet migrate inwards, then back out collecting just enough material to leave the right amount for earth sized planets. This condition could be difficult to meet.

There may be other ways to get an earth sized planet in the habitable zone, but the question becomes how long they would remain habitable. Remember we need to find planets that would remain habitable for billions of years. It could be that life is somewhat common, but only in very simple forms because planet/moons that remain habitable for billions of years are exceedingly rare.
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Old 26th August 2019, 08:35 AM   #42
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Originally Posted by Skeptic Ginger View Post
Sure, "common" is relative. I agree, not only should we be looking for planets in the Goldilocks Zone relative to their star, but also relative to the location within the galaxy and probably a planet with water and tides, though I'm not positive that the tides are crucial.
I know itís been suggested that a large moon is required but IIRC it isnít tides that are a requirement, rather, the moon plays a role in the Earth retaining its magnetic field for so long.
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Old 26th August 2019, 11:08 PM   #43
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Originally Posted by lomiller View Post
I know it’s been suggested that a large moon is required but IIRC it isn’t tides that are a requirement, rather, the moon plays a role in the Earth retaining its magnetic field for so long.
I do not think that is right. I have been told that without a large moon the Earth's axis will wobble. This means that the arctic circle could be close to the equator at sometimes and at others be near the poles. Imagine a world where a large % of the planet had 6 months of daylight and 6 months of nighttime. Would give life a very hard time.

Edit. Link to what I am talking about https://www.space.com/12464-earth-mo...-universe.html
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Old 27th August 2019, 04:43 AM   #44
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Originally Posted by rjh01 View Post
I do not think that is right. I have been told that without a large moon the Earth's axis will wobble. This means that the arctic circle could be close to the equator at sometimes and at others be near the poles. Imagine a world where a large % of the planet had 6 months of daylight and 6 months of nighttime. Would give life a very hard time.

Edit. Link to what I am talking about https://www.space.com/12464-earth-mo...-universe.html
If you are only looking for life taking the path it did to humans on Earth then it might be an issue. But given the conditions on Earth that life exists, I don't see wide swings being any kind of absolute prohibition on life developing.
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Old 28th August 2019, 03:25 PM   #45
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Originally Posted by Skeptic Ginger View Post
If you are only looking for life taking the path it did to humans on Earth then it might be an issue. But given the conditions on Earth that life exists, I don't see wide swings being any kind of absolute prohibition on life developing.
So no large moon = only simple life forms can exist.
With a large moon = complex life forms might exist.

I would accept that.
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Old 29th August 2019, 03:00 AM   #46
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Originally Posted by Skeptic Ginger View Post
If you are only looking for life taking the path it did to humans on Earth then it might be an issue. But given the conditions on Earth that life exists, I don't see wide swings being any kind of absolute prohibition on life developing.

On what basis do you make that assessment?

I can't see that there's any way to calculate it at all.
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Old 29th August 2019, 04:26 AM   #47
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Originally Posted by 3point14 View Post
On what basis do you make that assessment?

I can't see that there's any way to calculate it at all.
If I'm understanding her point correctly it's that life on earth is adapted to all sorts of different environments. Many of which would be deadly to humans, but not for some kind of extremophile. Basically the existence of extremophiles and ubiquity of life on the surface of this planet argue for a wider range of environments under which life could conceivably exist.
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