Proxima Centauri

[Green Baron]

H,

sure, a suitably fit set of technology changes what is "habitable" for us.

"What technology do we need to survive elsewhere" is the base for "i want to go out".

But judging life on other worlds is more like "what does it take that it can emerge", which excludes technology and tries to get behind the natural processes. In both cases too i know too little to give definitive answers .....

[Diche Bach]

Well I really hope Mars "is habitable" because otherwise Elon and his groupies are truly insane!  

But back to Proxima Centauri, and in particular Augusts proclamation that "No planets do not work that way."

Can anyone elaborate what this means specifically? 

or to put it another way: If you have a clear idea of "how planets work" then perhaps you'd be so kind as to provide a description of the most hospitable planet you could imagine existing in orbit around a star like Proxima Centauri (and assuming it has for some reason, simply eluded detection up to this point, i.e., maybe this hypothetical planet is another one of comparable size to "b" and it has simply been missed so far).

For the purposes of my fiction project, I can always consider what G class stars are reasonably close and reposition the story there. Perhaps expanding to F and K class (assuming those are by virtue of being "close" to Sol's class more likely to host configurations of planets that resemble those in our syste) if that is necessary. But in truth, as long as SOMETHING around Proxima Centauri is "habitable" (in the sense that humans can with technology "live" there permanently and relatively self-sufficiently) I'm somewhat inclined to simply go with that for the simple reason: it is the closest and so might well be the first we reach and start to exploit.

Edited November 7, 2017 by Diche Bach

[Urses]

By this meanings we have to define a habitable planet by injection prinzip. You shot some sort of life seed in it and the planet can selfsuficient forgone in this way to generate a biosphere, i don't speak of terraforming but if as example a contaminated sonde land there the spores may evolve a form to sustain on the "infected" body. 

On otherr hand you have the ability to artificaly inhabitate a body but need a min. state of technology to install and provide the habitable status. But you need to become a status of selfsustainable operability or it is only a landed space ship and not a habitat.

This way Mars may become habitable for some bakterias with high radiation withstand ability and very low dense armospherical enviroment. But Moon or asteroids or planets around PC can be only "artifical habitable".

I know of presence of spores that can sustain vakuum exposation but they "sleep" untill they come in a habitable enviroment (that is why life infection is possible).

Edited November 7, 2017 by Urses

[Green Baron]

20 minutes ago, Diche Bach said:

But back to Proxima Centauri, and in particular Augusts proclamation that "No planets do not work that way."

Well, an osmium core is improbable. And osmium is too rare and too hard and has too high a melting point. Take iron or nickel, they are abundant, have low enough melting points for a partly liquid core that you would want for a magnetic field :-)

20 minutes ago, Diche Bach said:

... provide a description of the most hospitable planet you could imagine ...

Earth

20 minutes ago, Diche Bach said:

existing in orbit around a star like Proxima Centauri

It goes in the land of fiction and so you're free to go where ever you want :-) A world in the habitable zone is too close for comfort because of the flares and tidally locked, if it is far enough from the flares it is too cold.

20 minutes ago, Diche Bach said:

But in truth, as long as SOMETHING around Proxima Centauri is "habitable" (in the sense that humans can with technology "live" there permanently and relatively self-sufficiently) I'm somewhat inclined to simply go with that for the simple reason: it is the closest and so might well be the first we reach and start to exploit.

So, how about a technology that expands the "habitable" zone far enough like one that creates a planetary magnetic field. Take a look at the NASA pages, just today there came up one dreamer with a proposal for Mars ;-)

Irony: Life on Mars is so easy if you have magnetic field ;-)

[Diche Bach]

I figured someone would take issue with the idea that a planet might have a primary composition that was far higher in a super dense metal like Osmium . . . 

44 minutes ago, Green Baron said:

Well, an osmium core is improbable. And osmium is too rare and too hard and has too high a melting point. Take iron or nickel, they are abundant, have low enough melting points for a partly liquid core that you would want for a magnetic field :-)

Iron and nickel are abundant AT EARTH. They are also abundant in the other inner planets orbits and the asteroids . . . Osmium (along with many others that are sufficiently more dense that iron or nickel that their existence in high proportions might lend itself to fascinating, unexpected if not amazing planetary processes) is NOT abundant at Earth (nor as far as I know anywhere in our solar system).

However, it is my understanding that, many of the scarce metals of Earth are relatively much more abundant in the asteroids.

Osmium is I am confident more scarce on a galactic or universal scale than iron or nickel, but does that mean that local conditions could NOT arise where a planet might not form that had substantively more Osmium? A planet comprising a predominance of Osmium (or any of the scarce ones) which approached the predominance of iron and nickel for Earth (85% of the total mass, and comprable if not higher proportions of the total planetary volume) may well be unobtanium maximum. But what about a planet with even 5 or 10% of the more dense and scarce elements which Earth sports in miniscule proportions (~ 0.5% or less based on guesstimates is my understanding)?

Edited November 7, 2017 by Diche Bach

[KerikBalm]

On 11/3/2017 at 5:07 PM, Diche Bach said:

For my purposes at this point, I'm curious about a couple questions:

(1) How far would the "radiation kill zone" described in the "No Earth-like atmosphere" article extend out from the star? My physics is too elementary for me to know if the bad rads the article focuses on (apparently " high-energy extreme ultraviolet radiation" is the main culprit?) would have diminishing effects at any of the distances involved 

(2) How large or potent of a magnetosphere would be required to "protect" Proxima b from the atmosphere-stripping effects described?

(3) Are there geologically and cosmologically feasible processes which could shield a celestial body from the harmful rads described? For example, (and going entirely hypothetical here, not referring specifically to any features known about the Proxima system) could a moon orbiting a large parent (say Neptune) with a large enough magnetosphere be protected?

Lastly,

(4) I was edified some years ago when one of the more knowledgeable KSP forum members clarified that Jupiter is highly radioactive.

Ok....

Start here: https://en.wikipedia.org/wiki/Proxima_Centauri#Characteristics 

Also note "rads" is a unit of absorbed radiation dose, not radiation output. You are using the wrong units to describe radiation

1) Radiation comes in many forms, UV and Xrays are electromagnetic- high energy light. Then there are charged particles

The star Proxima centauri's total light output is just 0.17 % of our sun. That means at 1 AU from the sun, it receives just 0.0017x as much light. Thus the planet has to be roughly 25x closer to its star as Earth is to our star. Now the star is a red dwarf, so 85% of its output is in the infrared, not visible light. Its visible light output is just 0.0056% as much as our sun's. So any plants on an otherwise earthlike planet orbiting at the distance that proxmia b is from Proxima centauri would have to make due with only about 3% of the light they have available on Earth.

But we get to another problem. Proxima B is a variable flare star. This means that it produces more x-rays for its size than it normally would. In fact, its X-ray output is about equal to that  of our much larger sun.

Quote

The star's magnetic field is created by convection throughout the stellar body, and the resulting flare activity generates a total X-ray emission similar to that produced by the Sun.^[20]

So at proxima b's distance from its sun, we can expect the X-rays to be roughly 500x stronger than what we see on Earth. Also as its a flare star, its going to be putting out proportionately much greater amounts of charged particles, so a planet like proxima b orbiting at ~0.05 AU is going to encounter intense solar wind.

All this does decrease with distance in accordance with the r^2 law, but so does visible and IR light, leaving any world frozen if its far enough that the radiation environment isn't so bad.

2) No idea for the charged particle radiation. The EM radiation is unaffected by a magnetic field. A magnetic field could still be useful for preventing atmosphere loss though. When EM radiation hits hydrogen containing molecules (like water) it can split off the hydrogen (photolysis) - which will easily escape from the planet and cause a loss of water and other hydrogen containing compounds (as occurred on Venus) - a magnetic field can trap this hydrogen, and prevent its escape - but the UV light will still give you a bad sunburn

3) Again, incorrect use of rads. A moon wouldn't do much. The planet needs to generate its own magnetic field to retain its atmosphere (or at least the lighter elements of its atmosphere, heavy gasses like CO2 are easier to retain, but a pure CO2 atmosphere isn't very interesting if the planet lacks nitrogen and water on the surface).

4) Jupiter is not the radioactive (well, its core surely is)... again, incorrect terminology. What is going on at jupiter is that it has a *massive* magnetic field that traps the solar wind (charged particle radiation) into radiation belts just as Earth's magentic field does... but Jupiter is *a lot* more massive with *a lot bigger* magnetic field. Most of its moons orbit inside that belt of trapped charged particles, rendering their surfaces quite deadly to us.

On 11/5/2017 at 8:32 PM, Diche Bach said:

I'm leaning toward a very small dense planet with a core disproportionately made of osmium or some other very high density metal, very volcanic, permanent ice age with only relict oceans, very seismically active, no native vertebrates, though some simple animals forms and quite a few plant/fungi forms. Insufficient atmosphere but breathable for brief periods (perhaps about like being above Base Camp III on Everest? . . . not sure if 21% O2 composition but lower pressure, or lower O2 or a combination of both is better . . .). That all fits nicely with the project objectives and doesn't seem like it stretches plausibly horrifically . . . end of the day, it is sci-fi, so some "stretching" is inherent.

Still haven't decided on the orbit. That "habitable" zone is quite close and the logic that tidal locking is inherent at that range from the star seems fairly "law like." But then 40K for that "cold dust" belt, is clearly not warm enough for anything that couldn't evolve in a ice cube

This elemental composition is unlikely. I'm assuming you intend for this body to be farther out from the star so that the radiation is less severe. In that case you can kiss the idea of photosynthesis goodbye (even at proxima b, its a shaky proposition with just 3% of the light we have on Earth) - thus you can kiss the 21% oxygen atmosphere goodbye. Earth had life all over the place before we had a high oxygen concentration in our atmosphere, so that's worth noting. Anyway, farther out from the sun, its going to be frozen, and your most interesting world would be something like Europa.

In any scenario... The only "habitable" places I can imagine are underground.

Also yes, with this planet orbiting at 0.05 AU, its going to tidally lock. Once the atmosphere thickness gets below a certain level, there will be an atmospheric collapse as the atmosphere freezes out on the dark side of the planet. One is left with a barren rock, that doesn't have tidal heating, and the only place with access to visible light (~3% of what we have on Earth), is also going to be a vacuum that gets blasted by X-rays. If the planet's core has radioactive elements, it can stay warm, and there may be an underground biosphere, but that's the best one could hope for.

20 hours ago, _Augustus_ said:

No.

That's not how planets work, and 1.6 AU is well beyond the habitable zone of Proxima.

Who brought up 1.6 AU... and yes, it is.  At 1.6 AU, one would receive only 40% of the light at 1 AU. Proxima B only emits 0.17% of the total light of our sun. At 1.6 AU, thus the total light influx is 0.066% as much as we get here on Earth. Total visible light (usable for photosynthesis) would be just 0.00224%. IR light is too low energy to break chemical bonds and such... UV is too high energy and starts breaking stuff. Visible light is really the sweet spot for chemistry based on C/H/O/N.

[Diche Bach]

Ah thanks Kerik!

So what you are saying is: not all "Earth-sized exoplanets in the habitable zone" are as titillating as the scientists who discover them else the media who report their findings might like us to imagine!

I had long suspected as much.

It sounds like prospects of the Proxima Centauri system hosting any native life are pretty bleak. About as bleak as the "Kuiper belt and farther out + closer in than Mercury" in our own system.

So Proxima system: highly unlikely to have any planets that host native life (even of simple nature), and with (at best) planets that are only about as hospitable as Mercury or Mars, i.e., not very, and certainly highly dependent on intensive tech for humans to habitate . . . Thus . . . unless the system has an abundance of resources of such fabulous value that it is deemed worthy of a manned program to exploit those resources . . .and given its sister stars are only slightly farther away . . . seems more likely that the first interstellar human presence will be in one of the alpha's orbits.

I'm glad I asked!

I think I'm now leaning toward one of the Alphas, which I'm surprised to realize are a G and a K class star . . . I had either forgotten that or it never clicked.

Edited November 7, 2017 by Diche Bach

[Diche Bach]

My cunning attempt to pick your brains for the sake of my own fiction is now probably blatantly obvious, though I don't think I was TOO cryptic about it at the outset.

I suppose I can continue to solicit feedback on topics that are divergent to "Proxima Centuari" without feeling I'm taking my own thread too far off topic eh?

So . . . Alpha A and Alpha B! How about those beauties!? Damn, and "Proxima Rising" had such a ring to it too . . .

Let me ask you (any of you! who might have any valuable insight): what natural resources might either of the two alpha systems have in sufficient abundance that the first probes discoveries (hinting at the abundances) would unleash a cavalcade of additional probes as well as the enormous impetus necessary to actually get a fiscally-oriented exploitation expedition going?

I'm not inclined to include a "garden planet just waiting for eager colonists to arrive and turn it into New Earth" sort of scenario. Rather more of a "Antarctica/Spitzbergen like planet with an atmosphere (at "sea level") akin to being at 3000m on Earth . . . limited fauna, and a narrow semi-temperate equatorial zone where summer daytime temperatures may get up to 20 Celsius. In other words, a harsh but survivable place (as long as you keep your oxygen bottle handy and/or have spent enough time acclimating while also staying in low altitude zones).

What abundance of natural resources could you imagine driving efforts to establish presence in such a place?

[Urses]

This means only that life based on carbonate cicle is more Impossible as otherway. But what about silicium based? The same molecules are possible by substituting carbon with silicium and will suppport the same processes as carbon like, but need much higher energy levels to do so? We think to strong carboncentered in a multiversum defined (at the moment) enviroment. We only define life as we know it and every other lifeform may it be slower or faster as our own, we don't recognaise as such? Like what we name "ghosts" are beeings on higher energy levels maybe? And they are wondering why is there a planet populated with billions of statues whom slowly changes their positions through many of decades?....

Edited November 7, 2017 by Urses

[Diche Bach]

3 minutes ago, Urses said:

This means only that life based on carbonate cicle is more Impossible as otherway. But what about silicium based? The same molecules are possible by substituting carbon with silicium and will suppport the same processes as carbon like, but need much higher energy levels to do so? We think to strong carboncentered in a multiversum defined (at the moment) enviroment. We only define life as we know it and every other lifeform may it be slower or faster as our own, we don't recognaise as such? Like what we name "ghosts" are beeings on higher energy levels maybe? And they are wondering why is there a planet populated with billions of statues whom slowly changes their positions through many of decades?....

Fascinating stuff! But a little too "exotic" for the themes I want to explore.

[KerikBalm]

Well, to be clear, *if* the planet has a strong magnetic field, then it should be able to retain an atmosphere for some amount of time... but I know almost nothing about the strength of the magnetic field needed for its distance and its star. Certainly we see a lot of "hot jupiters" that can retain atmospheres. There's also the question of how long it can retain an atmosphere. Supposedly Venus may have had oceans for nearly 1 billion years... today its pretty much hell.... but 3.8 billion years ago when life was well established on Earth (probably), could there have been life on Venus, that would only last another 100 million years?

Also, tidal locking isn't instant... it takes time to occur... so how old is this planet? Even if it is tidally locked, if it has a significant atmosphere, there may be a band near the terminator where liquid water could exist. If the atmosphere becomes too thin, the dark side won't be warmed sufficiently by atmospheric convection, and the atmosphere will start to freeze out... so there would be a certain point at which further atmosphere loss becomes completely catastrophic once the planet is tidally locked - which should happen very fast at 0.05 AU from a star 12% as massive as our sun. Gravity also follows the R^2 law, so I'm going to assume that since our sun is 8.2x as massive as Proxima Centauri, a planet can get root(8.2) x closer before tidal locking in the same time frame... thats 2.862x closer. Mercury orbits with an SMA of 0.387 AU... so proportionately around Proxima, that would be  0.135 AU. Proxima b is thus proportionately 2.7x closer, where tidal forces should be 7.3x stronger. Now... Mercury isn't completely tidally locked... but that's because its got a highlt eccentric orbit... without its eccentricity, it would be tidally locked. Proxima b's eccentricity isn't precisely known, it may be high enough for a 3:2 spin orbit resonance like Mercury has. In that case the nights would be really long, but probably not long enough for the entire atmosphere to freeze out... although portions of it would probably do so... a spin:orbit resonance could allow for atmospheric pressure to go lower before catastrophic consequences occur. 

Of course, a highly eccentric orbit can cause problems of its own for more complex life.

Anyway, assuming its not in a spin:orbit resonance (ie, it has a nearly circular orbit), it will be tidally locked, and thus there will be a tipping point at which atmosphere loss causes atmospheric collapse. Until that tipping point, it may be habitable for microbes, life on Earth probably went on for quite a while before photosynthesis evolved. Also, plants in direct sunlight here on Earth have way more energy than they need. You can find moss growing by the energy of a dim electric light in a cave that would otherwise be completely dark. 3% visible light may be enough... but photosynthetic output will be quite low, so the number of trophic levels would be low, and biodiversity would pale in comparison to what is found on Earth.

 

14 minutes ago, Urses said:

The same molecules are possible by substituting carbon with silicium and will suppport the same processes as carbon like, but need much higher energy levels to do so? 

No, they arent. Silanes are boring.

https://en.wikipedia.org/wiki/Hypothetical_types_of_biochemistry#Silicon_biochemistry

Quote

However, silicon has several drawbacks as an alternative to carbon. Silicon, unlike carbon, lacks the ability to form chemical bonds with diverse types of atoms as is necessary for the chemical versatility required for metabolism. Elements creating organic functional groups with carbon include hydrogen, oxygen, nitrogen, phosphorus, sulfur, and metals such as iron, magnesium, and zinc. Silicon, on the other hand, interacts with very few other types of atoms.^[10] Moreover, where it does interact with other atoms, silicon creates molecules that have been described as "monotonous compared with the combinatorial universe of organic macromolecules".^[10] This is because silicon atoms are much bigger, having a larger mass and atomic radius, and so have difficulty forming double bonds (the double bonded carbon is part of the carbonyl group, a fundamental motif of bio-organic chemistry).

Silanes, which are chemical compounds of hydrogen and silicon that are analogous to the alkane hydrocarbons, are highly reactive with water, and long-chain silanes spontaneously decompose. Molecules incorporating polymers of alternating silicon and oxygen atoms instead of direct bonds between silicon, known collectively as silicones, are much more stable. It has been suggested that silicone-based chemicals would be more stable than equivalent hydrocarbons in a sulfuric-acid-rich environment, as is found in some extraterrestrial locations.^[11]

Of the varieties of molecules identified in the interstellar medium as of 1998, 84 are based on carbon while only 8 are based on silicon.^[12] Moreover, of those 8 compounds, four also include carbon within them. The cosmic abundance of carbon to silicon is roughly 10 to 1. This may suggest a greater variety of complex carbon compounds throughout the cosmos, providing less of a foundation on which to build silicon-based biologies, at least under the conditions prevalent on the surface of planets.

 

[Green Baron]

And i thought all this was clear meanwhile :-)

It may sound trivial but carbon is indeed the best suited stuff if you want life with a somewhat lively metabolism that is able to run around and develop a somewhat exciting diversity, "evolves" if i may say so. Visit the Wikipedia article on silicon based life then i don't have to type it again :-)

As a result: Silicon is far more abundant in the earths crust than carbon, yet there is no silicon based life. I would think that most of the solar systems don't last long enough that a slow evolving silicon based form would have any chance.

Ninja'd :-)

Edited November 7, 2017 by Green Baron

[Diche Bach]

Good stuff KerikBalm! Keep it coming, as long as you feel like!

So 3% visible light . . . does that mean that "at high noon" when the sunshine is at its brightest, Proxima Centauri B would be akin to a rather gloomy dusk period here on Earth?

[Green Baron]

Let me ask back: why do you insist on Proxima C. and don't take a somewhat more promising setup, so you don't have to do so many tricks ?

Asks a naive Green Baron ....

Edited November 7, 2017 by Green Baron

[KerikBalm]

I'm guessing he's asking because its the closest star, and if he's going to have hard-sci fi interstellar travel, its the most convenient destination without massive time scales and relativity problems

[Diche Bach]

Well I already said a post or two back that I'm now leaning toward Alpha A and/or Alpha B (which are a G and K class).

[Green Baron]

Then you have a problem with stable orbits between the two stars.

Candidates in the vicinity are mostly flare stars, close binaries or both.

Check https://en.wikipedia.org/wiki/List_of_nearest_stars_and_brown_dwarfs

- Tau Ceti (impending impacts could make for a story :-))

- Groombridge 1618 (?)

- others ?

 

If what @KerimBalm said is true than also look for the relative velocities. If they are 100km/s or more it'll be difficult with chemical propulsion ...

 

Edit: put the ecliptic plane almost rectangular towards us to have an excuse for undiscovered planets :-)

 

Edited November 7, 2017 by Green Baron

[KerikBalm]

Well, as far as I know, they don't have any planets around them.

https://en.wikipedia.org/wiki/Alpha_Centauri

Quote

 During the pair's 79.91-year orbit about a common centre,^[15] the distance between them varies from nearly that between Pluto and the Sun (35.6 AU) to that between Saturn and the Sun (11.2 AU).

Something about 1000x the mass of jupiter coming to where saturn is would be VERY disruptive to a planetary system. They may share a common Oort cloud, but if that's all your interested in, you might as well go to proxima after all, or just stick around our own Oort cloud. Either way you'll be so far away from a star that you can forget solar power and heating, you'll need nuclear fission/fusion. Luckily the oort clouds should have plenty of lighter elements (since they remain frozen at that distance) used in fusion and as propellant. Heavier elements are probably harder to come by.

 

1 hour ago, Diche Bach said:

Good stuff KerikBalm! Keep it coming, as long as you feel like!

So 3% visible light . . . does that mean that "at high noon" when the sunshine is at its brightest, Proxima Centauri B would be akin to a rather gloomy dusk period here on Earth?

Yes, but you'd be surprised how bright it may seem once your eyes adjust. If you consider the brightness of indoor lighting at night compared to how bright direct sunlight is, I think you'll come to a similar figure.

If I may make an analogy. Imagine you are in a dark room with only 2 sources of light, and your hands are cold. You have two things to warm them up, which are also the 2 light sources: #1) is an old incandescent lightbulb that has been on a while - its hot so you don't want to touch it, just put your hand next to it. It makes a lot of light.

#2) is a red hot piece of iron - its glowing red and emits some light - you *really* don't want to touch it. Both are just hot pieces of metal (old incandescent lightbulbs had a metal filament that gets heated). The ratio of light to heat is very different. When one defines the habitable zone around a star by the zone that the temperature may be right for liquid water, one has a range of "habitable zones" with *very* different lighting conditions.

A bigger star would appear even brighter to a planet in the habitable zone than the sun appears on Earth, because more of its output is shifted from infra-red to visible light.

Now... back to Proxima b. It does have some things going for it. Its eccentricity is known to be less than 0.35, that still means an eccentricity of 0.2 is possible, which is what mercury has. So a 3:2 spin resonance is still plausible. That means 1 "solar day" will last exactly 2 revolutions around the star. As its so close to the star, 1 revolution is 11.2 Earth days. So it could have a day of 22.4 Earth days. With only 11.2 "days" of darkness during the night, thats probably enough to avoid atmosphere collapse or reaching an equilibirum where most of the atmosphere is frozen on the night side (with a small amount of atmosphere caused by frozen portions coming into sunlight at the same rate that the thin atmosphere freezes on the still dark and newly dark side).

So, if you go with this planet after all, you've got your day length (otherwise, eternal day, eternal night, and a circular orbit).

Proxima b is also much bigger than Earth. Its mass is probably between 1.6 to 3 Earth masses. If its 3, its going to be more like a mini-Neptune, not a rocky Earth. The center would be too hot (radiogenic heat from the core + strong greenhouse effect), and any life would have to be fanciful like life in the clouds of Jupiter. At 3 earth mass, we can imagine it retaining helium, and maybe even hydrogen.

Lets go with the 1.6 earth mass estimate... more mass = higher escape velocity = less atmosphere loss. It also means a larger core that should have more radiogenic heat and a lower surface area to mass ratio, so it stays hotter for longer. All this is good for generating a stronger magnetic field... but not 2000x stronger, and the solar wind (according to wikipedia) would be 2,000x stronger. The X ray flux is ~500x stronger. It should still be able to hold on to heavy elements and gasses.... but too much of those can make it too hot. Venus in its current state would still be way too hot even if we changed its SMA to 1 AU.

There are so many variables when it comes to habitable zones, even when you define it as just "the right temperature for liquid water on the surface". Supposedly, Earth 4 billion years ago was outside of the habitable zone... yet the evidence indicates both it and mars had water on their surface... what gives? atmospheric composition could be one thing, but the evidence doesn't indicate an atmosphere that could solve this paradox... so it remains:

Give this whole page a read:

https://en.wikipedia.org/wiki/Faint_young_Sun_paradox

If you really want an extra-solar destination with conditions capable of supporting life on the surface... just wing it.... a 3:2 spin:orbit resonance, 22.4 eath-day long days, 1.6 Earth masses,about 1.3 G. Despite its larger mass (and thus longer period of out-gassing, and greater total out-gassing), its slowly been losing lighter elements, and its a 25% CO2 atmosphere (although I think it would actually be much higher). Significant water loss has occurred, leaving not a lot of liquid water on the surface. It freezes at night, it all evaporates during the day, so its just got liquid water near the terminators. The loss of water is disrupting its plate tectonics, which (combined with the slow spin) is weakening its magnetic field. The planet is in entering a death spiral... on the geologic time scale (here, we're winging it to say that it lasted this long, since it seems to be on the order of 4.5 to 5 billion years old). Its still got millions of years more or less in its current condition. Its too hot at noon to go out, too cold at midnight to go out, but dusk and dawn are fine. Agriculture is done mostly in hydroponics underground to protect against the temperature swings. Living space is also underground, but at least the colonists can go outside for a couple days every ~11 days. They can mine for thorium/Uranium for power, or just have massive solar farms to supply power (given that most solar panels have absolutely terrible efficiency with IR light ... I'm not sure how well we could make solar panels which use very high frequency UV light). When going outside, they need to keep their skin covered, and wear a respirator because the high CO2 concentration can rapidly cause hypercapnia, but at least pressure suits aren't needed. The atmosphere itself protects against Xrays and charged particles (even if that strips away the atmosphere over time).

The conditions for abiogenesis seem to have never been met, and the planet has no native life to complicate the lives of the colonists and cause biohazard concerns.

OR: it does have life, and that is the motivation to go there to study it, and maybe preserve it before the entire planet succumbs to its looming fate.

*edit* and a few other hard-sci fi concerns: Its sun will appear much larger (angular diameter) than ours. A larger disk, but much dimmer. This doesn't make it safer to look at, and colonists have to be careful not to look at it. Just as an IR-laser can blind someone, this sun can too. Its total output is roughly the same as our suns, but it is visually dimmer and wont trigger the blink/squint reflex. Colonists could easily inadvertently blind themselves looking at this "dim" disk

Edited November 7, 2017 by KerikBalm

[Diche Bach]

Wow this thread taking a definitely pessimistic turn!  Talk about Goldilocks problems . . . Sheeze.

I was wondering if the orbital patterns in the two Alphas would run havoc with stable orbits.

Surely, someone has already done the maths on that and possibly even come up with Celestia-esque graphical presentations to show what was tenable?

Quote

OR: it does have life, and that is the motivation to go there to study it, and maybe preserve it before the entire planet succumbs to its looming fate.

For my purposes, resource harvesting is what I'd like to highlight as the main motivation for the interstellar penal colonies. Are there resources which might occur in a nearby system which are so precious that they could spark a "Centauri Rush?"

[Diche Bach]

19 minutes ago, KerikBalm said:

There are so many variables when it comes to habitable zones, even when you define it as just "the right temperature for liquid water on the surface". Supposedly, Earth 4 billion years ago was outside of the habitable zone... yet the evidence indicates both it and mars had water on their surface... what gives? atmospheric composition could be one thing, but the evidence doesn't indicate an atmosphere that could solve this paradox... so it remains:

Give this whole page a read:

https://en.wikipedia.org/wiki/Faint_young_Sun_paradox

If you really want an extra-solar destination with conditions capable of supporting life on the surface... just wing it.... a 3:2 spin:orbit resonance, 22.4 eath-day long days, 1.6 Earth masses,about 1.3 G. Despite its larger mass (and thus longer period of out-gassing, and greater total out-gassing), its slowly been losing lighter elements, and its a 25% CO2 atmosphere (although I think it would actually be much higher). Significant water loss has occurred, leaving not a lot of liquid water on the surface. It freezes at night, it all evaporates during the day, so its just got liquid water near the terminators. The loss of water is disrupting its plate tectonics, which (combined with the slow spin) is weakening its magnetic field. The planet is in entering a death spiral... on the geologic time scale (here, we're winging it to say that it lasted this long, since it seems to be on the order of 4.5 to 5 billion years old). Its still got millions of years more or less in its current condition. Its too hot at noon to go out, too cold at midnight to go out, but dusk and dawn are fine. Agriculture is done mostly in hydroponics underground to protect against the temperature swings. Living space is also underground, but at least the colonists can go outside for a couple days every ~11 days. They can mine for thorium/Uranium for power, or just have massive solar farms to supply power (given that most solar panels have absolutely terrible efficiency with IR light ... I'm not sure how well we could make solar panels which use very high frequency UV light). When going outside, they need to keep their skin covered, and wear a respirator because the high CO2 concentration can rapidly cause hypercapnia, but at least pressure suits aren't needed. The atmosphere itself protects against Xrays and charged particles (even if that strips away the atmosphere over time).

The conditions for abiogenesis seem to have never been met, and the planet has no native life to complicate the lives of the colonists and cause biohazard concerns.

OR: it does have life, and that is the motivation to go there to study it, and maybe preserve it before the entire planet succumbs to its looming fate.

There we go! You see that bit about the Faint Young Earth is precisely what I had in mind and I'm confident I've read that stuff in the past but did not recall it precisely.

What that is basically saying (as you also said): the "habitable zone" for a planet is only in part determined by it distance from its star and that stars energetic output. Geological and atmospheric factors can also come into play! Thus my concept of a small, extraordinarily dense and volcanic (with a ridiculouly strong magnetic field) planet that would otherwise be considered far outside the habitable zone if not for greenhouse effects, radiogenic effects and/or tidal heating.

If a planet had an asteroid belt immediately at the edge of is clearing zone wouldn't that exert tidal effects, which: if large enough would generate tidal heating? I seem to recall the Greeks and Trojans exerted some tidal force on Jupiter though the relative sizes are probably nowhere near enough to cause heating.

[KerikBalm]

22 minutes ago, Diche Bach said:

What that is basically saying (as you also said): the "habitable zone" for a planet is only in part determined by it distance from its star and that stars energetic output. Geological and atmospheric factors can also come into play! Thus my concept of a small, extraordinarily dense and volcanic (with a ridiculouly strong magnetic field) planet that would otherwise be considered far outside the habitable zone if not for greenhouse effects, radiogenic effects and/or tidal heating.

If a planet had an asteroid belt immediately at the edge of is clearing zone wouldn't that exert tidal effects, which: if large enough would generate tidal heating? I seem to recall the Greeks and Trojans exerted some tidal force on Jupiter though the relative sizes are probably nowhere near enough to cause heating.

Well, this is just operating in the gaps of our knowledge. It seems more like fictional science rather than science fiction. There are a number of things that could explain the paradox, but we have so little surviving evidence from that time, we can't be sure. Yes, geological and atmospherics come into play... but not so much that we can say the habitable zone can go from 0.05 AU (proxima b) to 1.6 AU (this debris ring of an "unknown source" in one of the linked articles). The difference in solar flux between those two is over 1000x!  I could excuse a factor of 2x (like Earth vs Mars), or even 3x due to differences in atmosphere, albedo, internal heat production* etc. But 1000x? ummm, I'm going to say no.

As for an "extraordinarily dense and volcanic (with a ridiculouly strong magnetic field) planet " how would that form? What makes it so dense? We can see the spectrograph of the dust clouds and stars... there's no reason the composition should be so different. A planet like that would almost have to be an artificial construct.

As to tidal heating I think not. One is that debris rings are extremely low density, and the mass isn't concentrated in a point. The force from them is more or less constant, unlike the moons of jupiter which pass each other and the tugging is not constant. Earths moon has almost no tidal heating from the Earth now because the tidal locking is complete. There aren't tidal variations anymore (only variation are due to eccentricity, and the fact that Earth still rotates and isn't perfectly homogenous). Tidal heating from a belt would be miniscule.

* U235 has a half life of roughly 0.7 billion years, that mean 4.5 billion years ago... there was a lot more of it... 6 half lives have passed. Radiogenic heating a long time ago was much greater. Most radioactive elements are either short lived, and won't supply heat that long, or long lived (like Uranium 238... with a half life of ~4.5 billion years, and Thorium 232 witha half life of 14 billion years) but their decay doesn't supply much energy. Radiogenic heating is just like a RTG on a spacecraft, its not a reactor, its just from radioactive decay which exponentially declines. To have a relatively constant power output, you need a long halflife, which also means a low power output.... but 2 billion years ago and possibly earlier, Earth experienced some heating (caused by radioactive elements) of a very different sort. U235 was so abundant, Uranium ore could have been used in a nuclear reactor without enrichment. In fact, Natural nuclear reactors were operating!!!

https://en.wikipedia.org/wiki/Natural_nuclear_fission_reactor

Who knows what was going on 4 billion years ago... 

36 minutes ago, Diche Bach said:

For my purposes, resource harvesting is what I'd like to highlight as the main motivation for the interstellar penal colonies. Are there resources which might occur in a nearby system which are so precious that they could spark a "Centauri Rush?"

I'm going to say this premise is a non-starter for me. We have all the resources we could want right here. Heavy elements aren't that rare. "Rare-Earth metals" aren't rare in the Earth, just in the crust... due to our planets mass and internal heat, we've got a differentiated interior, and the heavier elements have sunk down to the core where we can't get to them. This isn't the case in the asteroid belt, which is why asteroid mining for heavy metals could make sense (especially 16 psyche). For lighter elements... well those are volatiles, and rare in the inner solar system... Earth is a bit unique in holding on to most lighter elements... but helium escapes, relatively speaking, we don't have a lot of hydrogen (although large amounts were still retained thanks to hydrogen's ability to form chemical bonds unlike helium)... but bodies like the moon, Mercury, etc will only have volatiles on perpetually dark craters. Some asteroids may have some in subsurface deposits... but for the lighter elements, we'd want to go to icy moons of the gas giants, Icy kuiper belt objects, or even the gas giants themselves (perhaps Uranus is the best candidate due to its lower mass and orbital/escape velocity, and its not as far away as nepture... maybe Saturn could work if we assume a high enough tech level).

... my point is, we have MASSIVE resource reserves right here in our own system that we don't have to travel at significant fractions of the speed of light to obtain. I can't see it ever being viable to send resources here from another star system. If resources become so scarce, or competition so great, that such a thing is even considered, someone would have long ago decided to escape the condition of scarce resources and move on to "greener pastures"... they'd go to another star to use that star's resources for themselves, without sending any back to Sol.

They'd go as colonists or as researchers. If they are mining, they are mining for resources to be used locally. If there's a penal colony, its doing work to support rich colonists who want the resources that those prisoners are mining.

In the case of colonization, we don't even need a habitable planet. We can image a system of colonies like in "the Expanse"... mine the outer solar system for volatiles, and the smaller bodies of the inner solar system for metals (as you go farther out, the heavier metals are not so enriched because more mass is in the form of volatiles that would be lost if they were closer to the sun, so the heavy elements make up less of the total mass of stuff that they mine). A life and economy "unbound" to a planet, but spanning the moons and minor planets and asteroids of a system.

If there is a habitable planet... great, that makes certain things easier, but I don't see why its a requirement.

[Diche Bach]

So no elements that are scarce in the Sol System which could ostensibly be abundant in another system. You seem pretty confident on that and I'm certainly in no position to dispute it. I suppose it is possible there is something yet to be discovered? or that there is something you are overlooking?

Dilithium crystals maybe? 

Distant Worlds Universe, fun game except for the HORRIFIC graphics, has a crap load of these totally cheese ball luxury and strategic resources: Dantha Fur, Arcosium spice, Wisocisum fluid, etc. . . . Of course there is always that route, but as I've said: would like to keep it as much toward the "tinny" end of the hard-to-soft sci fi spectrum as I can. Diamond hard is right out, and even tungsten is probably no go (hell even the Great Arthur C himself invoked strange black monoliths and ancient Precursors and such like! His stuff [some of it] was tinny!) . . .

End of the day, a computer game has to be more FUN than it is REALISTIC, but I'm still in the early stages (very early) so thinking about overall design in terms of how it can be more hard than soft is a good use of my time. Really appreciate your feedback KB. I'd like to name a 'good guy or gal' character after your screen name if that would be okay.

ADDIT: that natural fission reactor in Gabon is farging cool

I've put a few hours in to imagining back history for the game. Extensive exploitation of solar system resources is something I had envisioned as the "pre-existing condition;" but the story I want to tell would be fairly far out on the historical far edge of all that.

Edited November 7, 2017 by Diche Bach

[Green Baron]

Man, you have time, @KerikBalm :-)

 

Guys, it is completely unrealistic to get anything more than surface dust even from a near asteroid. Maybe one day in the future, but not foreseeable. And even then it'll cost billions (estimating inflation) for a homeopathic dose and is a complete folly energy wise.

Developing technologies for recycling stuff is much more effective in every respect. Of course, nasa will make you believe that we urgently need it, that's what they are paid for ;-)

[Diche Bach]

2 minutes ago, Green Baron said:

Man, you have time, @KerikBalm :-)

 

Guys, it is completely unrealistic to get anything more than surface dust even from a near asteroid. Maybe one day in the future, but not foreseeable. And even then it'll cost billions (estimating inflation) for a homeopathic dose and is a complete folly energy wise.

Developing technologies for recycling stuff is much more effective in every respect. Of course, nasa will make you believe that we urgently need it, that's what they are paid for ;-)

That stance is dramatically divergent from what the norm about Sci Fi junkies and quite different from what I would've expected you to say.

So you feel that, there really is ZERO reason to go to space, other than the wonder? Perhaps you are correct, but that is certainly not what I've been led to believe.

 . . . might have to go pilfer the "Prospecting the Solar System" thread for some links or quotes . . .

[Green Baron]

 

11 minutes ago, Diche Bach said:

So you feel that, there really is ZERO reason to go to space, other than the wonder? Perhaps you are correct, but that is certainly not what I've been led to believe.

Eh ? What makes you think that ? I didn't even imply that.

Prospecting asteroids or other planets is a foolish idea because what you can get and what it takes to obtain that is grossly divergent, it'll probably never be worth the effort.

 

Going to space is a necessity if we want to learn more about our neighbourhood (Mars, close asteroids). I fully support that. But i am a little reserved as to what is technologically achievable.

Edited November 7, 2017 by Green Baron