Habitability of different spectral classes of stars

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Habitability of different spectral classes of stars

Postby mitchellmckain on October 16th, 2018, 4:42 am 

The cool M class stars are the most numerous, about 80% of stars. These high numbers and long life times are a big advantage for the development of life. However there are a number of serious problems.
1. Planets in the habitability zone are likely to be tidally locked so only one side of the planet gets light.
2. Current models for stellar development suggest that due to a long period of high stellar activity and the higher absorption of red light by water means that planets in the habitability zone will have no water.

The hotter stars such as F class and hotter are more rare and short lived, making it difficult for life to develop. The high UV radiation is also a concern.

As a result, other than yellow dwarfs or G class stars like our own, it is the cooler K class stars which are considered to be good candidates for the development of life. They are more numerous and longer lived than G class stars and yet planets in the habitability zone won't be tidally locked like with M class stars. Also the lower UV radiation is considered to be another advantage. At least this is the usual dogma... I would suggest otherwise, that K class stars would make good stars for finding nice colonizable planets but not such great places for the development of life.

The reason is, I see good evidence that the UV radiation is needed as a source of mutation in the earliest eras of evolutionary development. As I have mentioned elsewhere, we know that E-coli have mechanisms to protect damage done by UV radiation from its own DNA repair mechanisms in order to introduce variation into the genome. This tells us that UV is an important source for variation and thus may be crucial before other means of introducing variation (like sexual reproduction) are developed. The only question is whether the longer life spans of the K class stars can make up for this reduced amount of UV radiation.
Last edited by Braininvat on October 25th, 2018, 2:59 pm, edited 2 times in total.
Reason: Fix typo
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Re: Habitability of different spectral classes of stars

Postby mitchellmckain on October 25th, 2018, 12:13 pm 

Fixing typos seems to be an endless task... argh! the "F class" in the last paragraph should also be "K class." F class stars are shorter lived than G class stars, K class stars are longer lived.
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Re: Habitability of different spectral classes of stars

Postby Scruffy Nerf Herder on November 4th, 2018, 6:17 am 

mitchellmckain » October 16th, 2018, 1:42 am wrote:The cool M class stars are the most numerous, about 80% of stars. These high numbers and long life times are a big advantage for the development of life. However there are a number of serious problems.
1. Planets in the habitability zone are likely to be tidally locked so only one side of the planet gets light.
2. Current models for stellar development suggest that due to a long period of high stellar activity and the higher absorption of red light by water means that planets in the habitability zone will have no water.

The hotter stars such as F class and hotter are more rare and short lived, making it difficult for life to develop. The high UV radiation is also a concern.

As a result, other than yellow dwarfs or G class stars like our own, it is the cooler K class stars which are considered to be good candidates for the development of life. They are more numerous and longer lived than G class stars and yet planets in the habitability zone won't be tidally locked like with M class stars. Also the lower UV radiation is considered to be another advantage. At least this is the usual dogma... I would suggest otherwise, that K class stars would make good stars for finding nice colonizable planets but not such great places for the development of life.

The reason is, I see good evidence that the UV radiation is needed as a source of mutation in the earliest eras of evolutionary development. As I have mentioned elsewhere, we know that E-coli have mechanisms to protect damage done by UV radiation from its own DNA repair mechanisms in order to introduce variation into the genome. This tells us that UV is an important source for variation and thus may be crucial before other means of introducing variation (like sexual reproduction) are developed. The only question is whether the longer life spans of the K class stars can make up for this reduced amount of UV radiation.


I'm curious to know something. That is, if you're willing to spend a little time explaining it: why is it that some planets are tidally locked?
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Re: Habitability of different spectral classes of stars

Postby Braininvat on November 4th, 2018, 12:04 pm 

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Re: Habitability of different spectral classes of stars

Postby mitchellmckain on November 5th, 2018, 11:57 am 

Scruffy Nerf Herder » November 4th, 2018, 5:17 am wrote:I'm curious to know something. That is, if you're willing to spend a little time explaining it: why is it that some planets are tidally locked?


In one word: friction. The tidal forces of one body causes the other body to be distorted in shape. If the body is rotating with respect to the body causing this distortion, then the distortion changes over time and there is a great deal of friction produced. For the effect of the moon on the earth this is mostly limited to water causing the tides, but even that involves some friction so the rotation of the earth is slowing down. The earth is expected to be tidally locked to the moon in tens of billions of years and thus not before the earth is engulfed by the sun when our star becomes a red giant.

So basically the larger the body causing the tidal forces and the closer it is the more the distortions of shape (tides) will cause friction in the body affected and thus the faster its rotation will slow down until one face is locked to the body it is orbiting.
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Re: Habitability of different spectral classes of stars

Postby Braininvat on November 5th, 2018, 12:41 pm 

Mitch, what did you think of that Simple Wiki explanation? Or Simple Wiki generally, for hard science topics.
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Re: Habitability of different spectral classes of stars

Postby mitchellmckain on November 6th, 2018, 4:46 am 

Braininvat » November 5th, 2018, 11:41 am wrote:Mitch, what did you think of that Simple Wiki explanation? Or Simple Wiki generally, for hard science topics.


It was fine as an explanation of what "tidally locking" meant, but I didn't see scruffy nerf Herder's question answered. So, I suppose that could be considered a weakness of the article. It should answer the question of what causes it. I didn't know about libration, so I learned something there. I was surprised that it did not say that all moons are tidally locked so I did a search and found some which are not -- some moons of Pluto have been discovered which are apparently prevented from tidal locking due to interactions with Charon. Another thing I looked for and did not find is the 3:2 orbital resonance of the rotation of mercury and the odd fact which results is that a mercury day is twice as long as its year.

In general, I think Wikipedia does a rather good job explaining things in science and mathematics. I have been frequently impressed by the articles and have been using it as reference quite a lot. My experience with simple wikipedia is much less extensive.
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