World Habitability in a binary system

[altasilvapuer]

World Habitability in binary systems

So, I was rolling up a few CT-Book 6 systems today, and I ended up with a potentially opportunistic situation and a strange thought experiment.

Consider the following diagram:

Primary: M0II
Companion: G5V
[Sizes not to scale, except that orbit levels are regularly numbered and evenly spaced, irrespective of actual distances]

The green orbits represent the habitable zones of each star. The red orbits are inner orbits. Orbits 1-3 of the primary are not shown, as they lie within the star.

Although the diagram appears to show the planet intersecting the surface of the primary, if my math checks out it will never come any closer than just outside orbit Primary-4, which is the next orbit inward.


Now for the craziness:
The planet shown falls within the theoretical habitable zone of the companion, but because the entirety of the companion subsystem falls within the 'inner' zone of the primary, one would assume this renders the companion 'habitable' zone null and void.

However, what if you had some way of blocking some or all of the heat and radiation from the primary? This is the white disc shown offset from the planet. It would have to be immensely large, but theoretically not much larger than the diameter of the world, correct? And also not necessarily all that thick, provided it blocks the majority of the heat and light from the primary, right?

What do you guys think? Would you let this situation permit treating the planet as if it were in a habitable zone? Also: any ideas on the requirements of the barrier, itself?

I'm not actually using anything like this in the system that generated the inspiration, but the thought intrigued me, so I decided to post it here for others to elaborate and use as they wished.

-asp

 

[samuelvss]

Not my area of expertise, but that has never stopped me from offering my uninformed opinion.

It would be possible to put something like this up, but the scale of endeavor is something akin to terraforming, IMHO. The thickness would not have to be that great, but this would be something that would have to be maneuvered against solar wind. I would think something like a series of redundant solar sails, weighted on the periphery and spun, with some method of correcting the spin/attitude, that was strong enough to hold together, but allowed meteors to puncture without endangering the whole. Even at microns thick, they would be incredibly massive: someone smart can do the math...

The scale of such a thing would need to be justified: why not just go somewhere else?

 

[HG_B]

The difficulty of creating something this massive might rival the ability to accelerate the planet in question to a better orbit.

 

[far-trader]

Would it necessarily be that massive though?

What about seeding the planetary orbit with reflectors? Even ones with station-keeping thrusters to maintain a screening effect.

Without knowing more about the actual orbits and stellar and planetary specifics I'm more inclined to worry about tidal effects at a gut check level. Super quakes and tsunamis on a daily basis are not my idea of "habitable"

Or, another thought, with a slow enough planetary orbital period in the proper plane you might have a world that is habitable when on the outer track of it's orbit (with the second star shielding it from the first*) and cooks when it comes around to the inner side. So residents (and native life forms) cycle through dormancy in "summer" and active during the "winter".

* I think I might even maybe recall a sci-fi story with a similar if not exact premise

 

[McPerth]

Not my area of expertise, but that has never stopped me from offering my uninformed opinion.

This also applies to me

It would be possible to put something like this up, but the scale of endeavor is something akin to terraforming, IMHO.

More than comparing it with terraforming, it seems to me closer to make a ringworld.

How would you keep this 'umbrella' in place (relative to planet)? Any tie you do would interfere with rotation of the planet.

Also see that avery year, in the season where the planet is farthr than the primary, the 'ubrella' would create a planetary wide eclipse (from partial begining to partial ending, a season long one), and that would alter strongly the climate, I think.

 

[gammamutant]

This doesn't seem like something a human would do for several reasons noted in other posts. However, if a sentient species lived on the world when the larger star began to expand (or gave early warnings of its expansion.) They may have had no method of traveling between the stars and built the device as a panic method. Using solar energy to power a magnetic field to collect solar wind would provide fuel to power thrusters used to hold it in place. How would they have the technology to build it but not the ability to travel the stars and why not build an ark ship? Well, they are alien and think differently of course.
Of course there is the possibility of one of Grandfather's brood building the shield to collect solar energy to power a device on the shaded planet's surface.

 

[gammamutant]

Also see that every year, in the season where the planet is farther than the primary, the 'umbrella' would create a planetary wide eclipse (from partial beginning to partial ending, a season long one), and that would alter strongly the climate, I think.

unless it was variable opacity.

 

[Mithras]

Mmm, unless the world is the ONLY habitable world in your universe, explorers can move on to the next G type and there are plenty around ...

 

[samuelvss]

Why not just go somewhere else?

As often, I end up answering my own questions...

We tend to think of these star systems as static, which statistically speaking they Almost All are; the universe is full of millions of exceptions among trillions of stars. If this subject world were the homeworld ("for the ashes of our fathers and the temples of our gods...") of a race that advanced far before the system BECAME a binary one, then saving it might have some more variables in the cost-benefit equation.

As to this being comparable to a ring-world project, it might be in that direction FROM terraforming, but many orders of magnitude more complex/massive.

I think the idea of many overlapping structures is feasible, as is the slow orbit/seasonal burrowing.

As to the massiveness, hmmm...some waling around numbers: Assuming 1 gram per square meter (REALLY light stuff!), would be 1 ton per square km. 3.14 x (5,000 km)^2 = about 75 million tons, just for an absolute minimum film. Of course, if my assumptions are low by a couple of orders of magnitude on the mass, then we are talking about 750 Billion tons: a lot, but only if we're trying to do it all at once. Now, If these were put up in disks of 5 km radius, though, each would instead mass more like 75 tons, or 750,000 tons for the "worst case" assumptions; I envisage a system of spinning them to an extremely high rotational velocity in a tube-like dispenser that deloyed the already spinning film, so that the rotational inertia would tend to keep the attitude.

The answer to a lot of the engineering questions may be a constant deplyment of such smaller, disposable structures. As to the solar wind, the bunch might be deployed "upstream," with an outward vector such that they kept a stream of these arcing in front of where they were needed. They could, of course, be of the requisite opacity, with replacements / additions to make up for variations in solar wind from solar flares and damage to the structures before the end of their useful life.

A massive, expensive, continuing engineering project, but for a TL16, population B world, say, with a strong cultural/religious attactment to their Rich Industrial homeworld, possibly it would be child's play for the lower end assumptions and certainly feasible for the upper end assumptions. (Assume 1.5 trillion tons of material to be placed in a 360 day year, 1,000,000 ton ships, 30 year useful life on the ships, about 7,200 ships, MCr .25/ton for the ships, 100 Cr/ton for the material, it would be 210 Trillion credits annually, 10's kCr for every inhabitant; of course, with the lower set of assumptions, it would be 10's of Cr per inhabitant. Make the material cost 10%, the ships last twice as long, theen it becomes feasible even for a pop 8 or 9 world).

 

[altasilvapuer]

As to the numerous comments about the engineering massiveness of the project: I rather assumed as much, and catalogued it in my head in the space reserved for Dyson spheres and ringworlds. Mostly, I conceived this situation mostly as a thought experiment and for some creative mental aerobics.

It intrigues me to see the ways that people in the science fiction community will sometimes stubbornly come up with ways to rationalize or make feasible situations which baffle and defy logic and science.

I also like it for stuff like this:

Or, another thought, with a slow enough planetary orbital period in the proper plane you might have a world that is habitable when on the outer track of it's orbit (with the second star shielding it from the first*) and cooks when it comes around to the inner side. So residents (and native life forms) cycle through dormancy in "summer" and active during the "winter".

* I think I might even maybe recall a sci-fi story with a similar if not exact premise

Brilliant idea, FT. And even if someone comes along and maths it to death, I'm still okay with that, because I feel like this opens up lines of thought in other types of biologies in the same vein, irrespective of the aforementioned barrier.

Maybe a planet in a highly elliptical orbit around a single-star system, where life has adapted to living only in periods of a few tens or scores or years, and remaining dormant for centuries?

Or even stranger, a species with a hemimetabolitic or holometabolitic life cycle, potentially on near-stellar time spans. Maybe a drastic change in a star's output (such as the transition from the Main Sequence elsewhere) is what provides the conditions necessary for transition into the adult stage and thus mating? Is such a creature bafflingly improbable based on our current understanding of evolution? Sure. But does that mean we can't (and shouldn't) explore the concept in hopes of finding more reasonable ones? I don't think so, personally.

I'd also be curious to hear ideas of that vein, too. As I said, the purpose of the situation was mostly to incite creative mental aerobics as to what might be necessary for such a system and/or what might result from similar systems.

 

[fusor]

You're forgetting the evolution of the giant star. As it evolved from a main sequence star to a giant, it would have heated up the planet and other planets in the companion's system. That would have made the planet uninhabitable long before anyone colonized it.

Also, the system is presumably very old or very young. If the giant evolved from a sunlike star then it must be over 10 billion years old to reach that stage. If it evolved from a more massive star then it can become a giant much more quickly. If the companion is the same age then that means it and its planet are very old or very young too.

 

[far-trader]

You're forgetting the evolution of the giant star. As it evolved from a main sequence star to a giant, it would have heated up the planet and other planets in the companion's system. That would have made the planet uninhabitable long before anyone colonized it.

I don't think anyone is actually forgetting or ignoring that. It's just more grist for the imagination. For example...

Ages ago the main star began to grow. The native life of the world in the habitable zone of the smaller second star at first thrived on the shorter "winters", evolving and growing. Eventually though the "summers" became too hot to endure without sheltering, ever deeper, ever deeper. Tales hold that some had even evolved to the stage where they could leave their homeworld and move out further in the system, possibly even to other worlds around other stars to escape the heat.

More ages passed and a new life came from the stars to the system. They may even have been the distant descendants of those who originally left here for the stars but if they were they had no memory of this world. Maybe they choose poorly as a place to start anew. Maybe they were misled. Or perhaps they were simply lost. In any case they arrived in early "autumn" and found the planet around the second star habitable. There was even abundant native flora and fauna. With little other choice they settled in and began building their new homes. As the seasons passed into their first "summer" the observations led to one inescapable conclusion. The surface would soon be uninhabitable for the entire season. With few resources and choices they did the only thing they could. The same thing native life had been doing for ages. They burrowed below the surface to wait out the heat.

As it happened searchers looking for the colonists arrived at the height of that first "summer" and found only a charred world too hot for survival. There were no signs of the lost group as what had not been used and saved deep under the surface had already been burned by the main star. No one in the search party believed the planet capable of supporting any life, let alone that the colonists could be in this system and the search moved on...

...but that is all just an old legend

 

[fusor]

There is no "waiting out the heat" though. Since it looks from the diagram as if the companion is deep within the giant's Inner Zone, the increased luminosity of the giant star will roast the planet completely. Trying to escape that by "burrowing below the surface" is futile since the atmosphere will either be blown away or will turn into something similar to Venus. The world becomes uninhabitable and any local life (with the possible exception of deep crust microbes) will inevitably become extinct.

The same thing will happen to Earth in about a billion years as the sun slowly brightens with age and the habitable zone moves outwards, and that is even before the sun becomes a red giant. Life on Earth won't survive that, so what makes you think life could survive the much larger change to a red giant?

 

[far-trader]

There is no "waiting out the heat" though. Since it looks from the diagram as if the companion is deep within the giant's Inner Zone...

The diagram is not to scale though, so any interpretation based solely on it is erroneous for lacking specifics. Note my earlier caveat to the same. And the effects of the second star that may help, including since you mentioned it, it's own solar wind and magnetics may deflect a degree of the main star's own solar wind.

The world becomes uninhabitable and any local life (with the possible exception of deep crust microbes) will inevitably become extinct.

Now who's forgetting the time scale Yes eventually, inevitably, that will happen. There could well be literally millions of years where the main sun is still growing where the above will maintain life. That's what I'm proposing. A snapshot in the life of the system. Not the conditions at the end of the life you seem to be using.

 

[altasilvapuer]

There is no "waiting out the heat" though. Since it looks from the diagram as if the companion is deep within the giant's Inner Zone, the increased luminosity of the giant star will roast the planet completely. Trying to escape that by "burrowing below the surface" is futile since the atmosphere will either be blown away or will turn into something similar to Venus. The world becomes uninhabitable and any local life (with the possible exception of deep crust microbes) will inevitably become extinct.

The same thing will happen to Earth in about a billion years as the sun slowly brightens with age and the habitable zone moves outwards, and that is even before the sun becomes a red giant. Life on Earth won't survive that, so what makes you think life could survive the much larger change to a red giant?

Even forgetting the questions of time-scale that FT raised, what if the companion was in orbit 9, the last inner zone orbit prior to the habitable zone? (Also: I just noticed that I mistakenly colored the 13th orbit green when it should be the 10th; the three innermost orbits are consumed by the star and thus not shown, so I forgot to account for them in numbering outwards for the primary's HZ).

I'll grant you that that close (even accounting for distance discrepancies resulting from the not-to-scale presentation) to the primary, everything's cooked and possibly pushing the capability of even having an atmosphere, let alone a habitable one. But let's move outwards, to the possibility that the planet on the outermost ranges of it's orbit falls just shy of the HZ (or perhaps barely within it, after accounting for the companion's shielding effect from the primary's radiation), but lies in the IZ for the larger percentage of its orbit? Would it not be reasonable to suggest that life could have evolved there in extended periods of dormancy? Or that life might not have evolved prior to the primary's entrance into the Bright Giant category, and adapted to life after the conversion (which as I understand it would take place over a somewhat extended period of time, as well, correct?)

I can diagram that situation, as well, if you're interested.

-asp

 

[samuelvss]

I would also be interested in the prospect that this system occurred from a relatively slow collision of two, after the techological maturity of the proposed mainworld's population. I imagine that the immediate tidal forces might be immense and "world scouring" (sp?), but the possibilities for arcs and temporary (even multi-generational) vacation flow from the technology base and scales contemplated.

 

[altasilvapuer]

Okay, guys; I was rolling another system today, and I've come across another curiosity:

Consider this system:
F3V star, large gas giant in orbit 4; 5 is HZ.
In theory, would it be possible for a satellite of that GG to be tidally locked to the planet on the outside of the planet's orbit?

Second, anyone think that orbit could be potentially far enough to reach the inner edge of the HZ? If my calcs are correct, the closest the GG could get is about 2.2 AU (.6 away).

Just thought I'd try throwing a little more kindling on the fire for the sake of odd planetary systems to scatter throughout people's TUs for the sake of curious oddities and whatnot.

 

[FreeTrav]

Okay, guys; I was rolling another system today, and I've come across another curiosity:

Consider this system:
F3V star, large gas giant in orbit 4; 5 is HZ.
In theory, would it be possible for a satellite of that GG to be tidally locked to the planet on the outside of the planet's orbit?

Second, anyone think that orbit could be potentially far enough to reach the inner edge of the HZ? If my calcs are correct, the closest the GG could get is about 2.2 AU (.6 away).

Just thought I'd try throwing a little more kindling on the fire for the sake of odd planetary systems to scatter throughout people's TUs for the sake of curious oddities and whatnot.

Your first question is wrongly phrased; you're actually asking "Would it be possible for a satellite of the GG to have an orbital period around the GG that is the same as the GG's orbital period around the primary?". I won't go so far as to say that it's outright impossible - I don't have the math for that - but I wouldn't find it believable.

Your second question can be answered "Yes", if you allow it to have a fairly high eccentricity - i.e., orbits are not circular, they're ellipses. An ellipse with low eccentricity is one that's closer to being circular; the higher the eccentricity, the more visibly elongated the ellipse is. Comets tend to have very high eccentricity; non-captured planets tend to have very low eccentricity. I'm not sure how you'd explain a planet with unusually high eccentricity, unless you postulate that it's a captured planet. If a captured planet is in an inner-zone orbit, even if it is in the HZ at apastron, most of its orbital cycle will be spent below the habitable zone, and the planet is unlikely to be habitable.

 

[aramis]

Your first question is wrongly phrased; you're actually asking "Would it be possible for a satellite of the GG to have an orbital period around the GG that is the same as the GG's orbital period around the primary?". I won't go so far as to say that it's outright impossible - I don't have the math for that - but I wouldn't find it believable.

It's actually quite plausible... Trojan/Lagrange points.


But I dont know that your interpretatin is actually what he meant.

 

[fusor]

It's actually quite plausible... Trojan/Lagrange points.

An object in a planet's lagrange points is not a satellite of the planet (it isn't orbiting the planet); it would be a co-orbital instead.