Regarding biozones for supergiant stars

[Blue Ghost]

I came across a link for this video on another website, and it got me to thinking how there could be any habitable planets orbiting stars much larger than our own;

http://www.youtube.com/watch?v=BS88G5WBcfQ&feature=related

I look forward to your thoughts and impressions.

 

[BlackBat242]

Ummm... they are far enough out that, while still held in orbit by the gravity of those far more massive stars, the energy reaching their surface is approximately the same (per square mile, square kilometer, {insert favorite measure of area} as that which reaches Earth?

 

[RandyT0001]

I think that those really big stars are not going to have planets around them except for the occasional gas giant or maybe very remote icy planets. I think that the really big stars have collected all of the gases and other material that might have become planets for the smaller stars into themselves. Even if there was a little bit left over the rocky planets will not survive long enough to form a solid surface before the star burns through it's fuel and blows up in a supernova I'm thinking. I think any star over a F (the O's, B's and A's) will have these problems.

 

[aramis]

The only stars that won't have the possibility of habitable worlds are those that are around the smaller end... because they won't be getting enough energy per unit area.

Note that even some moons of gas giants, however, might generate enough energy radiation to support life...

 

[Rover]

If I remember my astronomy classes correctly the larger the main sequence star, the more intensly it burns therefor larger stars are relatively short lived. I don't think habitable planets would have the time to form.

R

 

[aramis]

One of the more interesting things about earth is that, in essence, it's less than half as old as the solar system. It got completely resurfaced due to a collision. 30 million years is a long time... and the lack of supernovae points to a severe rarity or a misjudge of duration.

Life on earth took 3.8 billion yearz to go from single cell to modern... and the impact event forming Luna is estimated at 4.5 billion years ago. 700 million years is within the lifespan of these stars, and it's easily possible that the time taken coule be ±50%...

It is true its unlikely to find life, but it's not impossible.

 

[RandyT0001]

The question wasn't about life bearing planets but 'habitable' planets. Habitable is generally defined as being suitable to sustain humans which requires a certain range of ultraviolet light, liquid water, air at a tolerable pressure with sufficient oxygen and no poisonous chemicals in deadly concentrations and a reasonable gravity. Earth for those 3.8 billion years was not 'habitable' to humans due to a lack of free oxygen, ozone and, most importantly, high ultraviolet light. It took our Sun that 3.5 billion years to finally cool down enough to diminish the UV light to a point that is low enough that the DNA required for more complex life forms is not broken down so quickly that the multicell lifeforms can evolve. Once the Sun reached that point in it's evolution the Earth may be considered 'habitable' even though it didn't have plants on the land surfaces yet. That's part of the reasoning why I don't think that those big stars (and most of them in the movie were blue, white, yellow and red supergiants off the main sequence) are going to have habitable planets around them.

 

[Keklas Rekobah]

So a barren, sterile world that fits the '867' model and orbits within its primary's habitable zone would be sufficiently 'Earth-Like' to support terrestrial life, regardless of the age and size of the star, and provided that the star itself is stable?

I'll buy that.

I also buy into the idea that if it weren't for the impact that created Earth's moon, there would be fewer heavy metals near Earth's surface, and that human civilization would be less metal-centric than it is now.

 

[RandyT0001]

So a barren, sterile world that fits the '867' model and orbits within its primary's habitable zone would be sufficiently 'Earth-Like' to support terrestrial life, regardless of the age and size of the star, and provided that the star itself is stable?

As weighted as Traveller's UWP is to be 'Earth-like' a planet might range in size from 6 to 9, hydrographics of between 5 and 9 (6,7,8) and a breathable atmosphere without the use of a filter or compressor.

I also buy into the idea that if it weren't for the impact that created Earth's moon, there would be fewer heavy metals near Earth's surface, and that human civilization would be less metal-centric than it is now.

There was a TV program on Discovery Channel titled "If We Had No Moon" (IIRC) that addressed the significance of the moon in the formation of Earth and the evolution of life on it. From what I remember of it Earth would be very different and probably would not have complex multi-celluar lifeforms on it without the Moon.

 

[aramis]

Habitability implies strongly the presence of life, even if only unicellular, because of the oxygen cycle. (Without photosynthesis, the free oxygen would have [remained/returned to being] bound to Nitrogen, Carbon, Iron, Silicon, and Florine and ceased being breathable.)

 

[RandyT0001]

According to http://en.wikipedia.org/wiki/Oxygen#Build-up_in_the_atmosphere Earth had about 2% oxygen 1.7 billion years ago. It then took another one billion years (or thereabouts) for enough plants to grow and raise the percentage levels comparable to our current 21%. So it took the Earth about 3.8 billion years of development before there was enough oxygen to sustain humans. That means that all of those stars that are so large that they burn through their life cycle in about four billion years or less (bigger than a F6v or so) have a very, very slim chance to have a habitable planet orbiting them. Even if we assume evolution at twice the rate of the Earth's historical record provides there is still a very low possibility of habitibility for humans for thes big and supergiant stars (IMO).

 

[Blue Ghost]

To me the whole prospect of living on a world around one of these colossal stars is something far beyond my scope of imagination. I can write about it, maybe even simulate the image in my imagination, but to really comprehend the full reality of it? Heck no.

Something tells me that for a world at the right distance for a biozone things probably wouldn't look all that different, other than the fact that the visible light might make things appear to be a different shade of whatever the color is supposed to be.

I imagine the star wouldn't look that much larger to a filtered lens, and things would be pretty much be the same as here on Earth. Again, this is assuming the proper distance to allow habitation. As to whether life of any sort would arise on such a world... I think it's tough to say. All the theories I've heard suggest that complex molecules were sparked, literally and figuratively, from lightning interacting with pools of salt water containing the right elements and simple molecules; the kind that react with other elements; carbon.

So, based on that, I'm with Carl Sagan in that life of any kind is a crap shoot. If the right materials and events are there, then it may happen.

I think habitable worlds probably do exist around such stars, but as to whether or not those worlds contain life I really think is anyone's guess. There're probably barren worlds with the potential for atmosphere, or perhaps even ones that have a hydrosphere, possibly even suitable for colonization. Of course how you would live there is another matter.

More thoughts?

 

[RandyT0001]

I came across a link for this video on another website, and it got me to thinking how there could be any habitable planets orbiting stars much larger than our own

I think habitable worlds probably do exist around such stars, but as to whether or not those worlds contain life I really think is anyone's guess. There're probably barren worlds with the potential for atmosphere, or perhaps even ones that have a hydrosphere, possibly even suitable for colonization. Of course how you would live there is another matter.

Well, if you're now talking about barren worlds with a potential for an atmosphere (I'm assuming you mean one that humans can breath and not one like Venus has), ones with perhaps a hydrosphere, and ones that may or may not contain life then you're really not asking about the likelihood of 'habitable' planets orbiting stars larger than ours but are really asking about the possibilities about 'rocky' planets orbiting stars larger than ours in that star's habitable zone. The probabilities of finding 'rocky' planets orbiting large stars is considerable greater than finding 'habitable' planets orbiting large stars. In general a 'habitable' planet is more narrowly defined than a 'rocky' one. (As a comparison it's like the difference between 'fruit' and 'apple'.)

 

[Blue Ghost]

I suppose that's true.

How about this; how many lush worlds are orbiting such stars?

That verse how many worlds that could be terra formed or made habitable do you think could be orbiting these stars?

 

[Starviking]

Earth for those 3.8 billion years was not 'habitable' to humans due to a lack of free oxygen, ozone and, most importantly, high ultraviolet light. It took our Sun that 3.5 billion years to finally cool down enough to diminish the UV light to a point that is low enough that the DNA required for more complex life forms is not broken down so quickly that the multicell lifeforms can evolve.

Well then one important question is - how long do the larger stars have a low enough UV output to permit multicell evolution?

 

[aramis]

Well then one important question is - how long do the larger stars have a low enough UV output to permit multicell evolution?

Doesn't much matter the UV output, if there is deep enough water.

Once you get sufficient O2, you'll get O3 at altitude, and block UV.

 

[Icosahedron]

'Habitable' planets fall into two distinct categories, IMO.

a) The planet has the resources necessary for a permanent, self-sufficient colony to be established. You may not be able to walk outside and breathe the air, but you are not utterly dependent on the monthly supply ship for your air, water, food, and raw materials.
In this sense, almost any planet that has a solid surface and does not have corrosive/insidious conditions, could be habitable - particularly at higher TLs. There might be nothing to prevent arcologies from being established on (or in) almost any world around almost any star, provided that Hydrogen, Oxygen, and certain minerals and metals are present.

b) The planet has a breathable atmosphere and surface conditions in which a TL0 human culture could thrive. This will almost certainly require indigenous and human-compatible life-forms to create a human-friendly environment. These are likely to be much rarer, and probably will not be found around very big or very small stars. They may even be exceedingly rare around sun-like stars.
This type of world could, perhaps, be terraformed from the other type, but even so, would need to have orbital conditions that would not destroy the terraforming over time. Therefore terraformed worlds (whether by humans or Ancients) again, probably would not often be found around very small or very large stars.

However, because we like our sci-fi, and we want to enjoy a good game, we have to suspend a certain amount of disbelief. Depends how 'hard' you like your sci-fi.

 

[RandyT0001]

Well then one important question is - how long do the larger stars have a low enough UV output to permit multicell evolution?

IIRC (and I'm not sure if it was a TV program on Discovery Channel, Science Channel, UCTV or the Research Channel that I'm remembering this from) the UV light is high at the beginning and the end of a star's life cycle. For our Sun that 'low UV' period was calculated by one of the program's interviewed scientists to last between one billion and one and a half billion years. So if the expect lifetime of our Sun is about 10 billion years then it's 'low UV' window is 10%-15% of the total lifetime. My assumption would be that larger stars would have a equivalent period of 'low UV' provided they were not classified as some type of 'variable' star. So for a F0v star (only about 1.6 Sun mass and radius - not really 'large') with a lifetime of about 1.6 billion years the 'low UV' window would last 160-240 million years. Since the really big stars have decreasing lifetimes as their size increases (a B7v's lifetime is about 200 million years, an O6v lifetime is about 5 million years) they will probably have very small 'low UV' windows (if they even have them).

 

[Peter Schutze]

>It then took another one billion years (or thereabouts) for enough plants to grow and raise the percentage levels comparable to our current 21%

according to the latest thinking it was more a problem of needing time for the algae etc to feed oxides into the plate tectonics cycle. a couple of % oxygen was the limit the cyano (anerobic) life could tolerate so once that limit was reached there was a die-off

once the algae and lichen could start breaking down oxides being released from the volcanic outgassing, vulcanism stopped being a counterbalance and started feeding a virtuous cycle and normal aerobic life could start to develop