What happens if we discover Alpha Centauri simply does *not* have planets?

[PlutonianEmpire]

Inspired by multiple factors, really, including the recent thread on the same star system. And I couldn't figure out a better subforum to post this, so this is going here.

Anyways, lets say that over time, as our instruments and detection methods and techniques get better and better (within reason, of course), we eventually figure out that, short of actually going there to find out for sure, Alpha Centauri (Proxima included) simply does *not* have any planets whatsoever? (Dunno how much of a stretch this actually is...)

Then what? What happens next? Do we just sit here, assuming that we're not pretty much trapped here anyway as discussions here and elsewhere (off-site) seem to imply? Or do we try to figure out what we're going to do next?

As far as I can tell, the next 10 or 11 stars out after Alpha Centauri A, B, and C are M dwarves, which will almost certainly result in tidally-locked dystopias, an A star, and a brown dwarf. The nearest star that has a marginally better chance of supporting us is a K star about 10 light years away, which also happens to have its own exoplanet system; albeit gaseous.

So, yeah.

What do we do if Alpha Centauri turns out to be a disappointment in the exoplanet realm?

[Noclevername]

As far as I can tell, the next 10 or 11 stars out after Alpha Centauri A, B, and C are M dwarves, which will almost certainly result in tidally-locked dystopias, an A star, and a brown dwarf. The nearest star that has a marginally better chance of supporting us is a K star about 10 light years away, which also happens to have its own exoplanet system; albeit gaseous.

Exoplanets are unlikely to support us anyway, even the rare earthlike ones will probably need extensive terraforming, and a starship is just a long-wear space habitat with a big honkin' engine. If we can survive generations of the long journey to another star in a closed vessel, we can much more easily survive in vessels with sunlight and asteroids available. Planets will not be necessary at that point.

[Jens]

Plus, I'm not sure how much difference it would make. A centauri is like 4 light years away, right? That's pretty much just as close to infinity than 10 light years is. I think probably that if we can overcome the difficulties of reaching a star at 4 light years, we can probably get to one at 10 light years. Either way you need a ship that can last hundreds or thousands of years without any external power source.

[Noclevername]

Plus, I'm not sure how much difference it would make. A centauri is like 4 light years away, right? That's pretty much just as close to infinity than 10 light years is. I think probably that if we can overcome the difficulties of reaching a star at 4 light years, we can probably get to one at 10 light years. Either way you need a ship that can last hundreds or thousands of years without any external power source.

Well, it's not that simple. There's no "close to infinity"-- distances always matter. Going 2.5 times the interstellar distance is much more than 2.5 times as hard. It requires either a much greater amount of delta V and/or an even more massive increase in travel time (My math sucks, can someone help me out with the relevant calculations?), during which the ship has to be kept functional and life support has to be powered.

It's also many more generations in which the crew can get into trouble, lose knowledge or purpose, fragment socially, etc.

(Nitpick: A Centauri is not the abbreviation for Alpha Centauri.)

EDIT: There are several proposed starship concepts that use partial external power sources; beam riders, impact riders, fuel tracks, electrostatic ramjets, RAIR, etc.

[Selfsim]

Why beat around the bush ?

If the destination target is physically unreachable by humans, and meaningful remote interstellar probe communications over light year distances has never been shown to be practically feasible, (even in the slightest); why are we bothered at all when a remote 'Earth-like exoplanet' is detected ?

Having posed such an unpopular question as that, I suppose it would be reasonable to be 'bothered' if we received an intelligent signal from such an 'Earth-like exo-planet', but that is about the only reason I can think of which would be worthy of a somewhat raised eyebrow ... (??)

[Noclevername]

If the destination target is physically unreachable by humans, and meaningful remote interstellar probe communications over light year distances has never been shown to be practically feasible, (even in the slightest)

Neither claim is correct. What is your basis for these statements?

To clarify: Human starflight will not happen in the forseeable future, but the future will last a lot longer than we can foresee. There's nothing physically impossible about it. We know the physical parameters needed, they're massive, but not infinite.

As for communication, the only thing proven impossible at LY distances is detection of our normal, everyday Earthside communications-- commercial radio and TV transmissions.. A laser signal of sufficient strength could be detectable across interstellar distances.

[Jens]

Well, it's not that simple. There's no "close to infinity"-- distances always matter. Going 2.5 times the interstellar distance is much more than 2.5 times as hard.

That might be true, but I was thinking in terms of something like this: suppose you have to cross a one-mile freezing lake and a two-mile freezing lake. The effort won't be that much different, because, since you can't swim, you have to build yourself a boat, and once you have the boat, it will take you two hours instead of one hour. So I was thinking that if you travel 4 or 10 ly, still you are going to have to build a mother of a spaceship with a self-contained habitat that can last maybe thousands of years. So even if you have the same general speed, designing a habitat that can last for 2,000 years doesn't seem that much more difficult than one that can last for 1,000 years.

[Noclevername]

That might be true, but I was thinking in terms of something like this: suppose you have to cross a one-mile freezing lake and a two-mile freezing lake. The effort won't be that much different, because, since you can't swim, you have to build yourself a boat, and once you have the boat, it will take you two hours instead of one hour. So I was thinking that if you travel 4 or 10 ly, still you are going to have to build a mother of a spaceship with a self-contained habitat that can last maybe thousands of years. So even if you have the same general speed, designing a habitat that can last for 2,000 years doesn't seem that much more difficult than one that can last for 1,000 years.

If you can only row for one hour, it makes a big difference.

By the time it becomes remotely plausible to cross those distances, we will probably have had self-sustaining habitat communities at the edge of the Solar System for some time. So making the transition from that to a starship will be just a matter of gathering sufficient quantities of energy in a storable form (a several-mile ball of deuterium ice, for example), and stocking up on raw materials that can't be replenished in midflight. And building a big honkin' engine.

[swampyankee]

Why beat around the bush ?

If the destination target is physically unreachable by humans, and meaningful remote interstellar probe communications over light year distances has never been shown to be practically feasible, (even in the slightest); why are we bothered at all when a remote 'Earth-like exoplanet' is detected ?

Having posed such an unpopular question as that, I suppose it would be reasonable to be 'bothered' if we received an intelligent signal from such an 'Earth-like exo-planet', but that is about the only reason I can think of which would be worthy of a somewhat raised eyebrow ... (??)

The Voyager probes use 23 watt radios. I don't know what the gain on their antennas is, and, like telescope resolution, it's a function of diameter and wavelength, so a larger antenna using the same frequency won't be worse. When Voyager was closer -- at Jupiter -- it could transmit at 115 kilobyte/second. Jupiter is about 5 AU (8e-5 light years). A sufficiently powerful transmitter -- about 57 billion watts -- would give the same bit rate from Alpha Centauri. The most powerful transmitter I could find is about 50 megawatts, so it would take some work to build one of 57 gigawatts, but there's no reason -- except money -- it can't be done.

[Jeff Root]

I don't know enough about either the theory or the
specifics to say anything definitive, but I suspect that
you were comparing the power used by the Voyager
radio against the *effective* power in a transmitted
beam. 50 megawatts has to be way, way, way more
than the actual power supplied to the transmitter.

-- Jeff, in Minneapolis

[antoniseb]

Going back to the OP's question... Noclevername has already given something close to my answer, but I'd like to elaborate.

If Alpha Centuari has no planets, it probably does have asteroids and comets. Any probe we send, whether manned or not, will want resources when it arrives, such as light and easily accessed minerals... which will be available in the asteroids and comets. If it IS a manned mission, it seems likely it would be either a giant ship on a thousand-year voyage, in which case the residents on arrival wouldn't be thinking about changing lifestyle by moving to something so wild and unkempt as a planet (they might have storms and earthquakes and supervolcanos!)... or perhaps some collection of frozen embryos, waiting to be grown after arrival... again, no particular need for a planet-based culture after that.

If it isn't a manned mission, we'll probably send nano-factories that will make the most of what-ever is there for the purposes of manufacturing what we want-need for observations, communications, probes to yet other stars, and maybe habitats for future arrivals.

[NEOWatcher]

If you can only row for one hour, it makes a big difference.

But if the technology is to "push off" and coast, there's no difference.

No matter how you look at life support and human consumables, everything is going to have to be recycled, remanufactured, grown, etc. for either ship. There's probably loss in all these systems, but it's still a fraction of the increase.

Depending on the power source (independent of thrusting or whatever) might not scale up linearly.

[kzb]

In the unlikely event there are no planets whatsoever in the alpha-cent system, that will mean the planetary system formation theorists will have some more firm data to chew on. A negative result can be just as informative as a positive result in science.

[PlutonianEmpire]

I apologize for taking so long to answer. I really need to stop making new threads at times when I'm supposed to be going to bed.

Going back to the OP's question... Noclevername has already given something close to my answer, but I'd like to elaborate.

If Alpha Centuari has no planets, it probably does have asteroids and comets. Any probe we send, whether manned or not, will want resources when it arrives, such as light and easily accessed minerals... which will be available in the asteroids and comets. If it IS a manned mission, it seems likely it would be either a giant ship on a thousand-year voyage, in which case the residents on arrival wouldn't be thinking about changing lifestyle by moving to something so wild and unkempt as a planet (they might have storms and earthquakes and supervolcanos!)... or perhaps some collection of frozen embryos, waiting to be grown after arrival... again, no particular need for a planet-based culture after that.

If it isn't a manned mission, we'll probably send nano-factories that will make the most of what-ever is there for the purposes of manufacturing what we want-need for observations, communications, probes to yet other stars, and maybe habitats for future arrivals.

Hmm, I got an interesting idea when I finished reading this, that even if Alpha Centauri had no planets, it might make for a useful "pit stop" for a manned mission to a more distant system, such as, collecting resources from whatever asteroids or comets that Alpha Cen may have lying around, and using their resources to aid in the continuation of the voyage.

Might that have any feasibility at all, depending on the travelers' (manned or not) final destination?

In the unlikely event there are no planets whatsoever in the alpha-cent system, that will mean the planetary system formation theorists will have some more firm data to chew on. A negative result can be just as informative as a positive result in science.

That's true.

[potoole]

As I understand (probably wrongly so) Alphas 'A' and 'B' orbit a center of gravity, which would be located between the two sun-like stars. (I think)

Proxima is a distant small star that probably orbits that same center of gravity. In effect (maybe?) it orbits the two larger stars. Perhaps, there are planets orbiting the two larger stars in the same manner as Proxima. Planets that could be somewhere in between Proxima and Alphas 'A' and 'B', and such planets would be receiving energy from both large stars.

Perhaps there is a goldilocks zone at a certain distance from the center of gravity.

Just my thoughts
PO'T

[Noclevername]

Hmm, I got an interesting idea when I finished reading this, that even if Alpha Centauri had no planets, it might make for a useful "pit stop" for a manned mission to a more distant system, such as, collecting resources from whatever asteroids or comets that Alpha Cen may have lying around, and using their resources to aid in the continuation of the voyage.

Might that have any feasibility at all, depending on the travelers' (manned or not) final destination?

Probably not, the majority of starship designs will require a signifigant existing infrastructure to launch-- so it's basically one start, and if you're lucky, one stop. (Unlucky means no stop.) If you make a "pit stop", it will be for the rest of your life-- and if the crew and their descendents can survive at Alpha Centauri long enough to build up a launching industry, they'll probably be so settled-in that they won't bother to build it or to continue with the rest of the trip.

Also, most of the nearby stars in the direction beyond AC are not suitable for Earthlike planets. If that's what you're looking for, then another part of the sky would make a better destination.

[Noclevername]

As I understand (probably wrongly so) Alphas 'A' and 'B' orbit a center of gravity, which would be located between the two sun-like stars. (I think)

Proxima is a distant small star that probably orbits that same center of gravity. In effect (maybe?) it orbits the two larger stars. Perhaps, there are planets orbiting the two larger stars in the same manner as Proxima. Planets that could be somewhere in between Proxima and Alphas 'A' and 'B', and such planets would be receiving energy from both large stars.

Perhaps there is a goldilocks zone at a certain distance from the center of gravity.

Just my thoughts
PO'T

A and B are 85 AU apart, so there are two GL zones-- one for each star. Proxima, not so much.

[Solfe]

A and B are 85 AU apart, so there are two GL zones-- one for each star. Proxima, not so much.

Is the distance to Alpha Centauri measured from the center point of the system to the center point of our Solar System?

[Hornblower]

Proxima and the AB pair are in orbit around the overall barycenter of all three, which according to my estimate is roughly 1/20 of the way from AB to Proxima. That distance is several times the separation of A and B. I will show the math if anyone has any question about my reasoning.

[potoole]

Proxima and the AB pair are in orbit around the overall barycenter of all three, which according to my estimate is roughly 1/20 of the way from AB to Proxima. That distance is several times the separation of A and B. I will show the math if anyone has any question about my reasoning.

Would there be such a thing as a goldilocks zone in this mess?

How far is proxima from A and/or B?

[Noclevername]

Would there be such a thing as a goldilocks zone in this mess?

The A Goldilocks zone would be 1.25 AU from A, B's Goldilocks zone would be 7/10 of 1 AU from B. Proxima, being a small red dwarf flare star, is unlikely to have a livable world, but if it did, it would be somewhere between 0.023–0.054 AU away.

How far is proxima from A and/or B?

0.123 LY, or about 738 trillion miles.

[potoole]

The A Goldilocks zone would be 1.25 AU from A, B's Goldilocks zone would be 7/10 of 1 AU from B. Proxima, being a small red dwarf flare star, is unlikely to have a livable world, but if it did, it would be somewhere between 0.023–0.054 AU away.

0.123 LY, or about 738 trillion miles.

Noclevername
"Proxima and the AB pair are in orbit around the overall barycenter of all three, which according to my estimate is roughly 1/20 of the way from AB to Proxima. That distance is several times the separation of A and B. I will show the math if anyone has any question about my reasoning. "
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Could there be a planet, or planets, orbiting that barycenter, which is 1/20 of the distance from AB to Proxima? Rather than orbiting any of the individual stars.
PO'T

[Noclevername]

Noclevername
"Proxima and the AB pair are in orbit around the overall barycenter of all three, which according to my estimate is roughly 1/20 of the way from AB to Proxima. That distance is several times the separation of A and B. I will show the math if anyone has any question about my reasoning. "
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Could there be a planet, or planets, orbiting that barycenter, which is 1/20 of the distance from AB to Proxima? Rather than orbiting any of the individual stars.
PO'T

I think not, too gravitationally unstable at that distance, but if there were it would be nowhere near any goldilocks zone. About 37 trillion miles from the nearest star.

[potoole]

I think not, too gravitationally unstable at that distance, but if there were it would be nowhere near any goldilocks zone. About 37 trillion miles from the nearest star.

Thank you
PO'T

[Hornblower]

Noclevername
"Proxima and the AB pair are in orbit around the overall barycenter of all three, which according to my estimate is roughly 1/20 of the way from AB to Proxima. That distance is several times the separation of A and B. I will show the math if anyone has any question about my reasoning. "
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Could there be a planet, or planets, orbiting that barycenter, which is 1/20 of the distance from AB to Proxima? Rather than orbiting any of the individual stars.
PO'T

Please be careful with quotes. You somehow attributed one of my posts to Noclevername.

[potoole]

Please be careful with quotes. You somehow attributed one of my posts to Noclevername.

My apologies, and thank you for the information.

PO'T

[Romanus]

Nothing significant will happen, IMO.

1.) A light-year is a light-year; going 20 in a reasonable amount of time with feasible technology won't be much harder than going one. We'd be no less "trapped" with planets at Alpha Centauri than without; the time, effort, technology, and money necessary are godlike and far beyond the horizon.
2.) Alpha Centauri has never been the sine qua non of exoplanet studies.

As far as I can tell, the next 10 or 11 stars out after Alpha Centauri A, B, and C are M dwarves, which will almost certainly result in tidally-locked dystopias, an A star, and a brown dwarf. The nearest star that has a marginally better chance of supporting us is a K star about 10 light years away, which also happens to have its own exoplanet system; albeit gaseous.

3.) If we've learned anything in the 20 years since the first exoplanets were found, it's that we shouldn't second-guess what we haven't discovered yet.

[wd40]

Wouldn't it be fun if it turned out that those poor deluded souls who believe that the stars are only light-days away were right after all

eg

http://astronomyinformation.org/index1.htm

http://fixedearth.com/Redshift%20Fraud.htm

http://archive.org/details/DeLaboreSolis

http://ncse.com/cej/2/2/moon-spencer-small-universe

and that Voyager suddenly reported back to us that its coming up on Alpha Centauri 10,000 years too soon, something like in "The Truman Show"!

[cjameshuff]

Well, it's not that simple. There's no "close to infinity"-- distances always matter. Going 2.5 times the interstellar distance is much more than 2.5 times as hard. It requires either a much greater amount of delta V and/or an even more massive increase in travel time (My math sucks, can someone help me out with the relevant calculations?), during which the ship has to be kept functional and life support has to be powered.

Except it isn't more than 2.5 times as hard, or even 2.5 times as hard. It doesn't require any more delta-v, the same delta-v gives a trip time that's only about 2.5 times as long...a bit less because the acceleration and deceleration periods are a smaller portion of the trip. You're almost certainly going to have a highly self-sustaining habitat on the spacecraft, extending the travel time by 2.5 times only requires perhaps a minor increase in some supplies that are imperfectly recycled. Difficulty is likely to be almost independent of distance, except for the most extreme cases.

[cjameshuff]

The Voyager probes use 23 watt radios. I don't know what the gain on their antennas is, and, like telescope resolution, it's a function of diameter and wavelength, so a larger antenna using the same frequency won't be worse. When Voyager was closer -- at Jupiter -- it could transmit at 115 kilobyte/second. Jupiter is about 5 AU (8e-5 light years). A sufficiently powerful transmitter -- about 57 billion watts -- would give the same bit rate from Alpha Centauri. The most powerful transmitter I could find is about 50 megawatts, so it would take some work to build one of 57 gigawatts, but there's no reason -- except money -- it can't be done.

Difficult, but not impractical, and taking some severely conservative approximations. The Voyager antenna is 3.66 m in diameter. Parabolic antenna gain scales with the square of linear dimensions. Arecibo is 305 m in diameter. Taking your 57 GW figure for a Voyager-sized dish and adjusting for an Arecibo-sized dish, I get 8.2 MW.

And that's doing it the hard way, with a direct radio link. Relay stations would allow you to reduce power further or operate at higher bandwidth, and laser communication would allow considerable further improvements. The only thing keeping us from constructing an interstellar communications link with present-day technology is the difficulty of putting hardware at the far end.