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Planet Found in Habitable Zone Around Nearest Star (eso.org)
1187 points by Thorondor on Aug 24, 2016 | hide | past | web | favorite | 427 comments

The fun stuff is buried in footnote [4]:

> The actual suitability of this kind of planet to support water and Earth-like life is a matter of intense but mostly theoretical debate. Major concerns that count against the presence of life are related to the closeness of the star. For example gravitational forces probably lock the same side of the planet in perpetual daylight, while the other side is in perpetual night. The planet's atmosphere might also slowly be evaporating or have more complex chemistry than Earth’s due to stronger ultraviolet and X-ray radiation, especially during the first billion years of the star’s life. However, none of the arguments has been proven conclusively and they are unlikely to be settled without direct observational evidence and characterisation of the planet’s atmosphere. Similar factors apply to the planets recently found around TRAPPIST-1.

This is the first time I'm reading about this concept and I find it fascinating. If there was to be intelligent life on an eye ball like planet the cultural, mythological and theological aspects of having a thin habitable strip of land sandwiched between ice and fire would be captivating.

He was told that when approached the light would swiftly ascend to scorch him. Like the others, he was told to stay in the narrows, where both the light and the cold darkness were at a safe distance, but he set out on foot anyway. When he first encountered the Anteriorkies, Perimetus knew his defiance had paid off, and the Anteriorky leader gave Perimetus shelter from the angry light above...

This would pull me into the rest of the book. You just feed me images and a whole story to imagine. Thanks a lot.

I don't know any published books that use this as a trope, but it's a popular writing prompt on reddit: https://www.reddit.com/r/WritingPrompts/search?q=tidally&res...

This was a good one: https://www.reddit.com/r/WritingPrompts/comments/35mgnn/wp_a...

A similar concept was used in Jack of Shadows by Roger Zelazny, but with fantasy elements.


What are you quoting?

It's Mangeletti.

I'm imaging an age of discovery-esque expeditions to the center of the Solar Plane.

They'd likely have radically different definitions of poles. One hot enough to melt lead, one cold enough to freeze C02.

Check out Proxima by Stephen Baxter:


It's a Sci-fi book about life on Proxima Centauri and includes the idea you mentioned.

(Also a really good read!)

God damn it!

I have this annoying habit of impulsively buying books recommended on HN. Never been disappointed by one though. So thanks! :).

Until the 20th century, no human had been on either pole of Earth either.

But differences of temperature between Earth poles temperatures and those temperature differences in tidal-locked planets is much smaller

> They'd likely have radically different definitions of poles. One hot enough to melt lead, one cold enough to freeze C02.

Well, in a certain sense the West Pole and East Pole would exist in the manner you describe, but the behavior is not similar to that of the north and south poles. The stars will still rotate around the north-south axis, and east-west still won't affect that. It's not obvious that both phenomena should be called "poles".

> The stars will still rotate around the north-south axis, and east-west still won't affect that. It's not obvious that both phenomena should be called "poles".

Note that "north - south" poles already refers to two distinct phenomena, the axis of rotation and the axis of the magnetic field (these happen to be closely-enough aligned on Earth that the latter has historically been used as a proxy for the former, though this is by no means a universal feature of all planets.) The axis of orientation to the sun, for a tidelocked planet, seems no less plausibly described as "poles".

North and south magnetic poles are named after the north and south celestial poles because they seem to coincide. That doesn't apply to the solar poles.

People always make use of local geographic features when describing directions; river communities use "upstream" and "downstream" and island communities use "inland" (away from the sea). Those aren't termed poles (even though "inland" is defined by reference to a line perpendicular to the ground!), and while I agree that the axis of orientation to the sun is more pole-like than they are, it's still different enough that I don't see that it would necessarily be referred to in the same terms.

You don't have to look to rural tribes to find this behavior. In Manhattan, "North" and "South" usually are colloquially defined with respect to the orientation of the island, not the actual compass directions.

And here in the vicinity of Santa Cruz, and going up towards San Francisco, "north" and "south" are often defined by reference to the labels on a freeway, even when that freeway in fact runs east-west.

Doing that in the Bay Area can have some odd results, as (for example) there is a stretch of freeway that is simultaneously I-580W and I-80E (and vice versa). Naturally, it runs almost due North and South.

> North and south magnetic poles are named after the north and south celestial poles because they seem to coincide.

Sure, and that's why the axis-to-the-star probably wouldn't define "north" and "south" poles, but not a reason it doesn't make sense to call that the points where the surface intersects that axis through the planet "poles".

That all depends on how some not-particularly-advanced people feel about it when the terms are determined.

Having thought a bit more, I tend to think it's unlikely that both axes would be significant to the same people (and therefore that they are particularly unlikely to share terminology):

- One important aspect of east-west historically is that east is sunrise and west is sunset. This wouldn't matter to anyone on Tidelocked World, but it corresponds pretty well to the idea of having a Day Pole and a Night Pole. The Day Pole would be apparent to anyone who lived in an area where the sun was visible, and the Night Pole would be totally unapparent to everyone else; it is significant only in that the Day Pole is on the opposite side of the world.

- Historically, north is cold and south is hot. This would apply, I believe, only to the day side of Tidelocked World. It reinforces the idea of a Day Pole while doing nothing for the Night Pole (everything beyond the terminator should (?) be equally cold).

- North and south are also defined by reference to the stars, which rotate around the polar axis (this is the origin of the word "pole", and would definitively rule out a Sun Pole if "poles" had to be defined that way, which they don't). This would be apparent to everyone living in the night, but probably not to anyone in the day.

If you believe all that, then we have the sun as a navigational aid that guides us toward the hottest part of the world, and the stars as a navigational aid to indicate the North and South Poles, but no concept of a Night Pole, because that concept is useless on the night side and there are no local indicators for where it is. Day people would be likely to refer to "sunward" and "darkward" in the manner of islanders, and night people would likely refer to "north" and "south", but day people would be unlikely to recognize "north" and "south", and night people would be unlikely to recognize "lightward".

>everything beyond the terminator should (?) be equally cold

I don't think so. Winds, diffusion, conduction, refraction probably come into play.

Sure. How much variation do you expect as a function of distance from the terminator? Other sources of variation aren't really relevant.

It does occur to me that the Night Pole might be revealed by the shadow of the planet, if it has a moon.

> They'd likely have radically different definitions of poles. One hot enough to melt lead, one cold enough to freeze C02.

Think of the industrial applications! You'd have early metalworks near the hot pole, and when they'd finally figure out thermodynamics, I could imagine a planetary thermal engine created by bridging the hot and cold areas...

You could pretty easily imagine a planetary thermal engine on earth as well though - between the poles and the equator. In fact, we do have one. It's called "weather".

We haven't explored the bottoms of the oceans very well yet.

So that'd be more advanced than us I think.

Who says they have poles? Maybe they only have austrians and hungarians.

A Polandball planet would definitely have poles.

A song of fire and ice perhaps? That might explain their strange seasons.

There is an alternative explanation for their off seasons proposed in this April fools arxiv paper


The Three-Body Problem by Liu Cixin features a more extreme version.


Hard to imagine it being habitable when simple weather patterns would expose the thin strip to both extremes.

They say the star's gravity fixes one side of the planet toward the star, and that ice builds up on the other side. I suppose if the atmosphere had enough mass, and the balance was precarious enough, the far side could accumulate enough ice to flip toward the star and become the near side.

So there might be a season change every so often

I feel like adding mass on one side would only made the tidal locking stronger. Either way, you'd need some sort of massive energy input to make the planet spin up again.

It would be interesting to study given a specific level of ice build up how big of an asteroid would have to hit it at the perfect angle to make it flip?

You mean a cataclysmic planetary flood every so often. All that ice suddenly exposed to continual bright sunlight is going to melt fast.

Winter is Coming!

That's an awesome plausible theory. Must be happening somewhere in the universe for sure!

Is there any ballpark figure as to how broad (in degrees or km for an earth-sized planet) the habitable zone would be?

reminds me of the movie White Dwarf: http://www.imdb.com/title/tt0114926/

I imagine convection would give one of these planets crazy weather.

What a fascinating article! Thanks so much for sharing!

How such planet can protect its water from solar wind? There are probably different possibilities to get magnetosphere than Earth-Moon dynamo, but I don't know much about it.

The Moon isn't responsible for Earth's magnetosphere, rather our liquid iron core is.

Isn't it not that we have such a core, but that the core MOVES that creates it? If so, I can imagine the Moon playing a role in that.

That said "I can imagine" isn't terribly good science. Articles like https://en.wikipedia.org/wiki/Dynamo_theory don't make mention any role of the Moon, and googling around drowned out the actual question by talking about how the Moon might have once had a magnetosphere, along with articles about how smaller planets might be able to.

If so, I can imagine the Moon playing a role in that

It doesn't. The planet was spinning when it coalesced from a planetary nebula and conservation of angular momentum means it sped up as it coalesced. As the moon moves further away it _slows down_ the rotation of the planet.

I stay corrected on accepted theories.

I tried to find some discussion on this subject. I found this [1] quite recent paper (2016-03-31) that states that influence of Moon is necessary to maintain Earth's magnetosphere. Just food for thought. There are articles that quote this paper on the Web, but they have this suspicious date of 1st April (but paper was published day before) :)

[1] http://www.sciencedirect.com/science/article/pii/S0012821X16...

The moving core is created by radioactive material heating up the core and creating convection currents.

This. It important to note that there are SO many factors that we don't know that can prevent habitability (for Earth definitions of habitability). We will need detailed study of its atmosphere to really understand habitability, and even then there are many mechanisms (e.g. volcanism) that can produce false positive biosignatures. For all we know, this planet could still have a hydrogen atmosphere (i.e. more akin to a Hot Neptune). Still, this is a really exciting discovery and will prompt a lot of follow-up studies in the future to really understand the system.

There are so many potential reasons why life would be incapable of existing on a planet in the "Goldilocks Zone" that we can't even fathom. It could even come down to something as simple as the infinite potential variations in elemental composition for a given planet. Not to mention the sheer enormity of time required for something like abiogenesis to occur and those forms of life to evolve into something we could actually discover, even when the conditions are suitable.

We can't calculate those odds. We can't even start. It's like trying to calculate the likelihood that future AI will destroy humanity. We just can't know because it's so deeply theoretical.

For that reason, it seems absolutely absurd to me that someone would say with certainty that life exists elsewhere in the universe. We just can't know. The unlikelihood of its existence could be infinitely high and we might just be lottery winners. Who knows?

And frankly, I hope we're alone. I really don't want to share the universe. It would be so much nicer just to have it to ourselves. Let us do what we want, wherever we want, without interference until the heat death of everything.

Nobody says with certainty that life exists. But they do say the probability is so high that life in some form exists elsewhere, you might as well be certain.

As for not sharing the universe: what a depressing thought.

Why is that depressing? It's not like we would actually be ALONE. We have each other. We don't need Vulcans or whatever else to keep us company and suck up our resources.

When you put it that way, it doesn't actually matter. There's always going to be someone competing for resources. The only difference is whether they have hands or tentacles.

Another potential difference might be diet. Perhaps this other, tentacled species can't resist the taste of homo sapiens.

Nope, still true with us alone.

> For that reason, it seems absolutely absurd to me that someone would say with certainty that life exists elsewhere in the universe.

I'm not sure you have a conception of how truly BIG the universe is. In fact, according to current cosmological evidence, it is infinitely big.

But even if we confine our discussion to our Hubble Sphere, there is almost certainly life elsewhere in the universe. It's just that that life might be very, very far away.

My thoughts too. If we knew there were only 10,000 stars, it could seem likely that the chances of life existing are 1/50,000, and we happen to be lucky. But there are over 100 billion stars in the observable universe.

I think the law of large numbers applies here. The likelihood of life existing being high enough that we are the only ones, but low enough that our existence isn't winning some 1 in a googolplex chance just strikes me as an anthropocentric conceit.

The size of the universe is a large number, but the chance of life just forming from chaos is 1/(a large number). So the odds of life elsewhere in the universe is, roughly, a large number divided by another large number. The question is which large number is larger?

We don't know how difficult it is to create life. The universe is big, but the difficulty of creating life might be much bigger.

Thus. It is not certain that there is life elsewhere.

Just today we found the closest star to us to have a planet in the habitable zone.

The closest star. But, we struggle to observe it in any capacity. Indeed, only today we did. And that's nothing to say of the next closest star, or the next, or the next, ad (nearly) infinitum.

If planets in this zone aren't as rare as we think, life in the universe might also not be as rare as we think.

To me, the question is more "where," rather than "if."

The fact that life appeared on earth very shortly after it formed gives us a good indicator that Abiogenesis may not be that rare.

Something that's probably a lot more rare is favorable conditions over a long time period. It took a long time for life on planet earth to evolve into more complex forms.

I'm pretty sure we're not the only ones out there. But will mankind and our space neighbours exist long enough to facilitate communication?

Is every species that is competitive enough to subdue all other life on its planet doomed to disintegrate due to internal conflict?

There are over 100 billion _galaxies_ in the observable universe.

Here's one possibility: intelligent life is sufficiently rare yet the universe is sufficiently large that the universe contains a very large number (possibly even an infinite number) of intelligent civilisations, but they are all sufficiently distant from each other in space and/or time that the odds of any of them ever interacting with each other (or even knowing of each others' existence) is extremely low.

e.g. imagine a universe containing a million intelligent civilisations, but each of those intelligent civilisations is in a separate galaxy at least 100 million light years apart. If that is our universe, we might not encounter any of those other civilisations in the next million years. The odds of human extinction could easily be higher than the odds of having any contact with them.

Just see how that worked out for No Man's Sky...

Oh sure it's a particularly human conceit that that number be exactly 1. But it certainly might be that the number is low enough that it will be very very hard for us to ever detect or interact with other life.

the number of stars out there is more like 1,000,000,000,000,000,000,000 pieces, or 1 billion trillion in observable universe. which is just a subset of whole universe. pretty good chances for something out there. hopefully not as xenophobix as humans these days (and more advanced at the same time)

100 billion stars in our galaxy, not the observable universe.

Everyone always says this, but it seems to indicate more of an inability to grasp how much we don't know about other planets on your part than it does my inability to grasp how large the universe might be. It's entirely irrelevant if the universe is infinitely large if the probability of life arising is infinitely small.

If you think psychology is shoddy science wait until you hear some cosmology! The universe is very big so there MUST be life elsewhere. It just can't be otherwise!

Not quite. No one's publishing papers to that effect. What casual science fans and some popular scientists do posit is that the universe is so big, our solar system so average (as far as we know), so it's highly likely that life exists or has existed elsewhere.

The alternative is the anthropocentric view that the entire universe was created merely for our viewing pleasure on Earth.

Agreed with cmrdporcupine. The anthropocentric view is actually the idea that because life exists for us, it therefore isn't that special and is likely to have arisen somewhere else - we are anthropocentrically biased to think that life is more likely than it actually is because we ourselves experience it.

That's not really what anthropocentric means. Anthropocentric is that the human species, not just life, is special.

What you are talking about is "anthroexclusive", or something like that.

See my response to whom you agree with: https://news.ycombinator.com/item?id=12359111

Correct. The term I meant to use was anthropic bias.

Or that the universe is so diverse and complex that assuming that this same rather random event occurs in the exact same way multiple times in many places is also quite arrogant.

No one is claiming that a random event (?) occurs the exact same way. They just use statistics, based on some known factors and yes, a lot of guesses.

We know how stars form, how galaxies form, how solar systems form. We know the general consistency of the galaxies around us, and some systems in our same galaxy. It's not a big leap to assume that some percentage of them will be hospitable (for a time) for life, at least life as we know it.

I'd say the arrogant views are that the whole universe was created for us, or that life must be thoroughly plentiful throughout the universe. The least arrogant view is that it's somewhere in-between, but more importantly, to always adapt to the latest evidence.

Pulling probabilities out of your behind is not statistics. Currently we have an anecdote and you want to extrapolate from that. That's shoddy science.

Even further, we know very little about abiogenesis. And even if we did that would only explain the development of single cell prokaryotes. Eukaryotic cells are of immense complexity, we haven't found anything "between" prokaryotes and eukaryotes, and I haven't heard many good working theories for the explosion of them, and then beyond that multicellular organisms.

So to try to extrapolate that to the "inevitability" of complex life in the universe is like saying that your name will be spelled out in ASCII in the repeating digits of Pi somewhere. Maybe? Can you prove it? No?

I'm not a philosopher of science, or statistician. But the assumption that somewhere there are things "like us" seems to be both arrogant and very teleological -- an implication that the universe proceeds towards an order very similar to us. (Popular science fiction is infested with this kind of telelogical narrative.)

And contrary to arrogantly thinking earth-life is special and unique my argument is that we are just one of a rather infinite variety of "things" in the universe. Life is amazing and complex -- but so are the clouds of Jupiter.

> But the assumption that somewhere there are things "like us" seems to be both arrogant and very teleological

Well, "like us", inasmuch as an entity that is self-regulating, and capable of response to external stimuli. The most basic assumptions for life.

So yes, at some level it is arrogant to assume there's anything else like us. Your view is very nihilistic. But, until we know of other sentient species, it is all about us. We are, as far as we know, very lonely, ex-nihilio orphans in the vast universe. It's only arrogance to nothingness to posit there might be more life in the universe. It is not arrogant to humanity.

So, yes, we are in many ways better than clouds of Jupiter. But of course it is us making that claim. So what? Allow humanity some slack. If we have offended some unknown creator with our supposed insolence, perhaps it should make itself more easily known.

But, again, no one is claiming this is real science. It's just a fun thought experiment.

Not want to share? That's really dumb. If I have some things I use, I might not want to share them with someone else because then I can't use them.

But we make no use at all of 99.999999999999999999999% of the universe, so how does it hurt us if some other species do?

Yes, because if we make it out there, I don't want to deal with having to get rid of the life there just so we can use the space. I am sure humanity will advance to use at least 50% of the space before our sun goes nova, if Moore's law is any indicator of technological advancement.

> so how does it hurt us if some other species do

Liu Cixin's The Dark Forest has an interesting take on this. Basically it's conceivable that the game-theoretically optimal policy is to kill any other sentient species you come across, even if it means you lose access to whatever resources they currently have. This argument falls apart at some point, because it's (presumably) not optimal for all humans to try to kill each other all the time, but it's an interesting idea nonetheless.

I found Blindsight/Echopraxia (released together as Firefall) a very interesting story on many levels, and it covers this kind of subject.

actually, the odd thing is how seemingly quickly abiogenesis seems to have occured on earth; few 100 million years give or take. This may mean that given proper planetary conditions, life just tends to happen rather easily - ie for a quite sizablle fraction of candidates at least. Or maybe that it's not going to happen at all unless it happens improbably quickly.

Basically we can't say a much about what the fraction of planets that develop life to planets that have conditions for developing life is based on just one example, but there's no apriori reason for particular pessimism about that number just yet.

Now how likely the conditions are to begin with is a different matter. They've certainly improved in the last decade, since planets at least seem to readily form and earth-sized things too, and apparently easily end up in orbits that could allow for water to exist etc. There's clearly a bunch of other potential conditions that may be necessary for abiogenesis -- untill we know more about how exactly it happens, we can't tell (and actually finding separate origins of life would greatly help in undestanding what that is)

I for one think it very likely this particular planet isn't habitable, because Proxima is such a lousy star, but it's certainly not ruled out. But also that microbes are likely reasonably common in the universe. Around a small fraction of the total number of stars, only some small percentage of what we'd consider candidates today based on their sizes and orbits -- but still that leaves immense numbers.

> ...until the heat death of everything.

If further climate outcomes continue to track Hansen's thus-far correct 35-year-old predictions [1], then we've already passed some kind of tipping point and "the heat death of everything" could potentially mean Venusian-style anthropogenic cooking of Earth in some worst-case scenarios, and mass population dislocations and mega-scale environmental disruptions in milder scenarios.

If it turns out that life as we know it is exceedingly rare (and I must admit that the more we find out about exoplanets, the more disconcerted I am while realizing that the hazy possible solution space to the Fermi Paradox is becoming rather uncomfortable as the resolution grows with each passing decade), then that would be truly a tragic outcome.

[1] https://tamino.wordpress.com/2016/08/16/crystal-serenity/

I believe GP was referring to the heat death of the universe [0], which might be paraphrased as the death of heat in the universe, rather than lifeforms on one planet dying when the environment becomes too hot for said lifeforms to survive.

[0] http://www.physlink.com/education/AskExperts/ae181.cfm

I should have been clearer; I trying to note the irony of saying "heat death of everything" could be a much shorter timeframe than we usually mean when we say that phrase, if Hansen's forecasts turn out correct.

Why you don't want to share the universe? I think it will be so nice to have a company in this vast universe!

Somehow we always feel that aliens would be always bad to humans, there might be good aliens also somewhere who might help us in solving our current diseases/share advance knowledge or even give us new resources!

>>It would be so much nicer just to have it to ourselves. Let us do what we want, wherever we want, without interference until the heat death of everything.

For all practical purposes we have it all for ourselves and we are doing nothing with it.

There is no serious investment in seeking a different home outside of earth.

Give us time, sheesh. We only figured out how to write a few thousand years ago. If we've been here for a billion years and we still haven't gone anywhere, then you may complain.

Yep, but even if it is not anything close to habitable (as it likely is not), it seems like we could learn a huge amount about about the habitability of red dwarf systems in general. https://en.wikipedia.org/wiki/Habitability_of_red_dwarf_syst...

There's life on Earth that thrives without atmosphere or sunlight. We should probably first develop a more complete, general framework for how carbon based chemical structures synthesize and transfer energy. It seems silly to narrow the search for alien life to "places that vaguely resemble Earth" when that criteria is already next to meaningless on Earth itself.

Life ... finds a way

I think the problem here isn't that life needs to find a way.

The universe is huge, really huge, so huge that even the distances to other planets in our solar system are so vast, that when you would consider the earth 1mm big, these distances would still cover thousands of kilometers. It's not possible to draw a liniarly scaled map of our solar system, so big is it.

Good news: life has plenty of space and probably also plenty of planets to find its way multiple times in the universe :)

Bad news: we probably won't find this life ):

Indeed. This is one of my favorite Wikipedia articles: https://en.wikipedia.org/wiki/Rare_Earth_hypothesis

>"Venus mean surface temperature is 735 K (462 °C; 863 °F) making Venus the hottest planet in the Solar System. Earth had a similar early atmosphere to Venus, but lost it in the giant impact event."

Ever since I saw it done in the new Universe series, a pet peeve of mine has been treating the giant impact hypothesis as some kind of established fact. Even the name on the wikipedia page includes the term "hypothesis": https://en.wikipedia.org/wiki/Giant-impact_hypothesis

The hubris surrounding the presentation of that particular hypothesis to the public is really, really awful. I actually stopped watching that new Universe series mid-episode after hearing it presented as fact (this was sometime in the first few episodes, maybe the first episode) and stopped reading this wikipedia page just now.

Also Proxima Centauri is a Flare Star. So it's light output can vary by +/- 8%. And this can change within a matter of weeks.

It is actually the most active flare star we know. https://www.ncbi.nlm.nih.gov/pmc/articles/PMC1063292/

Living at the twilight zone of such a planet would be a photographers nirvana. Golden hour every hour, for the rest of your life.

Traffic would be even worse because you can only "go around" so far before either cooking or freezing.

Perhaps they carpool.

when everything is golden, it ain't worth much

For example gravitational forces probably lock the same side of the planet in perpetual daylight, while the other side is in perpetual night.

Should I admit on HN to having watched a Vin Diesel film? Pitch Black, anyone?

If I remember right Pitch Black wasn't a tidally locked planet, but rather an _extended_ eclipsed caused by the other planets in their stellar system.

Astronomy nerdship aside, I loved Pitch Black. Such a good movie. I haven't watched any of the sequels, though.

The first game that they released, surprisingly for a movie to game adaptation, was also quite good.

That's because Vin Diesel is a gamer and didn't want games starting him to be run-of-the-mill movie tie/cash-ins, so he founded Tigon and tasked them with making good ones.

Fabulously geeky dude, I like his style.

Yes, Escape From Butcher Bay. A gem of game from the first-gen xbox era. Not sure if it holds up, but at the time it was a very high quality release.

I loved the sequel myself.

Pitch Black's planet situation reminded me of Nightfall (Asimov/Silverberg)[0], though there weren't six suns like in the book, and the occurrence of the "night" in the movie seemed to be shorter increments?

[0] - https://www.goodreads.com/book/show/99245.Nightfall

Planet rotation is 83 days [1]. So no, no perpetual days or nights on Proxima b.

[1] http://edition.cnn.com/2016/08/24/health/proxima-b-centauri-...

83 days is the star's rotation period.

Of course. Vin Diesel movies have their place and are fun. Pitch Black was great. Riddick is a good anti-hero.

You can transform that admission into geek credibility by referencing Asimov's Nightfall, on which Pitch Black was (loosely) based.

I'm trying to imagine what that might look like if you're on the surface of this thing looking up at the sky. The sun would be really close, comparatively, and even as a red dwarf, rather than main sequence like our sun, it must take up a huge portion of the sky. I would assume, if the planet is tidally-locked, that the sun would pretty much always be at the same point in the sky, when viewed from the same location?

Fun to think about, anyway.

We don't have to think about it. We can do the math.

The distance between the planet and the star is ˜7,000,000 km. The diameter of the star is roughly 1.5 * the diameter of Jupiter: 207525 km. The angular size of the star from the surface of the planet will be the arcsin of (207525 / 7*10ˆ6) or about 1.7 degrees.

This is a little bigger than three times the apparent size of the full moon or the sun from Earth.


Now we can factor in "always sunny" or "always dark" to our simulations of what aliens might look like (maybe even two races/species from the same planet?).

Well, "always dark" is waiting for us at the bottom of the ocean.

I'm almost certain I read an SF story with this premise. Two races on a tidally locked planet.

Even more interesting, if life does happen there, the imagination required to picture such life would be a fun exercise.

It's Always Sunny in Proxima b

Wow, amazing result. And talk about synchronicity - just last night I watched an interesting 2015 talk about the search for planets around Alpha Centauri using the radial velocity technique: https://www.youtube.com/watch?v=eieBXGpNYyE

The speaker even mentioned the previous incorrect HARPS announcement, which was later found to be an artefact due to the windowing function they used - a pretty embarrassing mistake. This new finding involves a completely different period: 11.2 days instead of the previous 3.24 day signal.

Also, link to the Nature paper for the lazy: http://www.eso.org/public/archives/releases/sciencepapers/es...

If you mean the previous claim of there being an Alpha Centauri Bb planet, later retracted, then this new finding involves a completely different star, not just a different period.

This is around Proxima Centauri, the previous one was around Alpha Centauri B. Proxima is a really really small red dwarf, just 12.3% the mass of sun, while Alpha Centauri B is a K-type star, ie somewhat smaller than sun but not that much; around 90% of Sun's mass (And there's also Alpha Centauri A, 10% more massive than the sun). We're not even 100% sure that Proxima is part of the Alpha Centauri system, though I gather it's considered highly likely - it's pretty distant from the Alpha Centauri system, some 15 000 AU (1 AU = distance between Sun and Earth), almost a quarter of a light year.

Yes, realized this and was editing my comment to reflect that but you beat me to it :). They did mention a previous signal from 2013, which got me confused with the spurious signal the SETI lecture mentioned.

heh, as you say; apparently there was a previous signal; reading the article about the find at centauri dreams, http://www.centauri-dreams.org/?p=36210 - and it does mention a pre-2016 Doppler signal with a period of 11.2 days around specifically Proxima, that was unconfirmed, and that this mission was to investigate that more closely. "The HARPS Pale Red Dot campaign was created to confirm or refute this 11.2-day signal"

I'm just not sure if that's what the speaker in your video was talking about, of if the embarrasing mistake that was actually announced was the Alpha Centauri Bb planet (or maybe there were other candidates I didn't hear about); I'm gonna watch the lecture you linked and see. Thx for an interesting link, btw!

If the period is 11.2 days, seems like there is a high chance that it is tidally locked to the star. If that's the case, that side is probably pretty roasting hot, the other quite cool. But maybe life near the edge is OK. Probably some interesting weather patterns there as well.

Probably some interesting weather patterns there as well.

If by "interesting" you mean constant hurricane force convective flows going 24/7 between a scorching hell and frozen wastelands.

Before there was soil, or sky, or any green thing, there was only the gaping abyss of Ginnungagap. This chaos of perfect silence and darkness lay between the homeland of elemental fire, Muspelheim, and the homeland of elemental ice, Niflheim.


Perhaps it could be "the chaos of perfect silence," because the wind noises generated would render any unprotected human ears deaf within minutes?

Hmmm. We can generate heat and light using electricity, and we can generate electricity using windmills. Could we perhaps inhabit the dark side of a planet like this by building really sturdy windmills to harness those constant winds and then building an insulated, heated, artificially lit structure to grow plants and live in?

We can build thermal powerplants on the edge and live off the temperature gradient. Either use Seebeck effect or just steam turbines.

I can only see geothermal energy working effectively

...constant hurricane force convective flows going 24/7 between a scorching hell and frozen wastelands.

Seems like this would allow surface habitation some way onto the bright side. Wind at the surface would be blowing from cold to hot, with the return at some altitude.

> If by "interesting" you mean constant hurricane force convective flows going 24/7 between a scorching hell and frozen wastelands.

Hey, at least it's a short walk between cooking your food and icing your drink!

Its a really really tiny star; quite small even as M-dwarfs go. So its habitable zone cannot but be where it could tidally lock the planet. Now, maybe some other resonances are possible, perhaps if there are other bigger planets around it helps (and I think they didn't exclude something up to a size of Neptune at about 1AU or beyond); don't know how the orbital mechanics of all this work out.

But there were various modelling attempts to see how a tidal lock affects the climate, and it may not be a dealbreaker; not too thick an atmosphere could effectively transport that heat around, at least so that it doesn't risk freezing the atmosphere on the dark side and making it uninhabitable. But its just modelling so..

Maybe even more problematic is that a tidal lock could imply no internal dynamo, and so no protective magnetic field, and Proxima flares quite a lot, so it could have totally eroded its atmosphere and sterilized the surface with UV etc. Plus Proxima was much much hotter early on; would that period have permanently made the planet uninhabitable?

We just know so very little about habitability of M-dwarfs, and particullary the really small ones; we'll just have to find out,

Before we took a close look with probes, we thought Mars had lichens living on it, to explain its color variations or some such; there's no reason to think we have any more clue about M-dwarf planets than we had about mars then, for we have yet so study any.

Good thing one just happens to be in our backyard :D Though realistically, perhaps it turns out easier to study more distant M-dwarf planets, because this one seems not to transit from our perspective. And I think we could study the spectra and hence atmospheric composition of transiting planets sooner than we can hope for direct imaging of them. Not perfectly sure though.

Why would a tidal lock imply no internal dynamo?

well, you need rotation to create a dynamo, and these rotate rather slowly; once per orbit only. Now, it does seem this is still quite fast enough to produce a dynamo, but still the issue is whether it can still be strong enough to create a sufficient magnetosphere to save the atmosphere from completely eroding away, given both how close and how active Proxima Cent. is . Here's a paper that tries to see how much atmosphere planets in habitable zones around red dwarfs could lose given the activity of the star and the magnetosphere they could produce: - http://arxiv.org/abs/1204.0275 . I guess its quite possible various other models have different takes on it, but anyhow that's the worry. I hope we'll see such modelling work done for Proxima Cent. b soon.

> We just know so wery little about habitability of M-dwarfs

s/M-dwarfs/planets around any star/

Well we just know so very little about planets around any star, excluding 8 planets circling around one out of ~1,000,000,000,000,000,000,000 stars in the observable universe.

yeah, kinda true -- though there's a great deal of extra uncertainty about M-dwarfs in particular in comparison to more sun-like stars, just because we did have this one example to study of that.

But on the other hand, we see all kinds of planet types around all kinds of different stars that pose similar problems (say superearth habitability), so even that only applies to questions about planets more similar so some of the types we can find in our own solar system.

There are other tidal locking modes than 1:1, like mercury has a 3:2 lock. Is that a possibility here?

The weather is likely rough on the surface, but there could be plenty of good conditions for life under ground/water.

Just in time for the third book in Liu Cixin's space opera ("Remembrance of Earth's Past") to be released in english next month: https://www.goodreads.com/book/show/25451264-death-s-end

Previously on HN: https://duckduckgo.com/?q=site%3Anews.ycombinator.com+cixin+... https://hn.algolia.com/?query=Cixin%20Liu&sort=byPopularity&...

And recently published Proxima about settlers on a planet around Proxima Cent. https://www.amazon.com/Proxima-Stephen-Baxter/dp/045146771X

Finished Ultima a couple of weeks ago, didn't know it was the second in a series. I'm looking forward to reading Proxima when I can get to it on my list.

I got an early release of this, and it is fantastic.

Waiting eagerly.

Oh, what timing! I just finished the second book a couple of days ago. I had no idea the next book was coming out soon.

After reading the first one I pre-ordered both the 2nd in paperback and the 3rd in hardcover, so they'd arrive at about the same time. It felt sort of clever at the time, but I guess I won't do very much that weekend...

Keep in mind that at best it would take maybe 1,000 years with current technology to get there with a probe or human-supporting ship. It would be highly unpopular however as it involves exploding nuclear bombs behind the craft to get it there that fast--that and it would probably cost trillions to build the thing.

There's a $100 million effort to develop tiny spacecraft that are accelerated to 10%-20% the speed of light with ground-based lasers: https://en.wikipedia.org/wiki/Breakthrough_Starshot

Today at 2:55 EST Philip Lubin, who is involved with the Starshot project, will present some work on the study he is doing for NASA investigating the feasibility of this.

You can watch it live here: http://livestream.com/viewnow/NIAC2016

The craziest thing to me is that if we sent a generational spaceship there that was expected to take 1,000 years, it seems likely that better technology would allow the next generation of spaceships to get there much faster. So by the time the 1,000 year spaceship arrived, there would already be people there!

This is a known paradox, I forget what it's called though. The concept is that it's arguable that any long-term space travel is pointless because there will always be a faster ship surpassing it as the originating civilization improves its technology, and so on for that faster ship. So, it's irrational to ever launch anything...

Apple has adopted a similar philosophy with their MacBook Pro line of computers.

I haven't laughed so much in days. Thank you.

This is known as the incessant obsolescence postulate: http://arxiv.org/abs/1101.1066

>>This is a known paradox >>So, it's irrational to ever launch anything...

That faster ship just won't appear out of the blue.

You need to launch slower ones to get to the faster ones.

Its like the original inventor of the car opting not to build it because someday there would be a Ferrari.

Improving the speed of a 1000-year ship may only require improvements in propulsion or structure (lighter ships). There are nearby incentives to create better propulsion and structure. We do not necessarily have to launch a 1000-year ship to create a 500-year ship.

But you don't have to send your people 1000 years away.

Yup -- This is precisely the answer to the question, so it thus remains an unresolvable paradox.

Seems like you'd reach a point where it becomes worth it even with continuous improvement. If the speed of light really is a speed limit, then you'll get to a point where the maximum theoretical improvement is still some small amount. If there's a way to go faster than light, then you'll get to a point where it only takes two seconds to get to your destination.

Even without the speed limit, you can expect to reach this point. Let's say your technology gets 10% faster every 25-year generation, you should launch a 200-year trip but not a 250-year one. We'll probably keep improving at that pace or better for a few iterations at least, but eventually space travel will be a stable technology, speed improvements will be rare and incremental, and 1000-year journeys will be justified.

Right, barring time travel, once you can make the voyage at all, you'll always reach a point where it makes sense to depart on it. If you invent technology that takes a million years to arrive, then you have a maximum deadline of a million years. Past that point, even instantaneous travel won't be worth waiting for, if your goal is simply to get there as early as possible.

> So, it's irrational to ever launch anything...

Sounds like the interstellar version of Zeno's paradox.

On a tangent with this topic, you guys should treat yourselves with a short sci-fi story named "The road not taken".

I just finished reading the entire novel series that Turtledove spun out of that short story concept. It's really good, well-researched and imaginative.

But technology that would be able to send spaceships significantly faster would probably cost significantly more, so it might not be worth pursuing given the cost.

Moore's law never stopped anyone from making chips with current technology.

Or maybe they'd rendezvous and bring them "up to speed" so to speak ?

it would be better to just 'seed' the tiny starshot spacecraft with human embryos that could litter the planet and then develop on arrival.

Right because human babies let alone embryos do so well on their own.

that's why we also send self-replicating nanobots along with them.

For their extensive experience in child rearing.

no problem, we train them with a convolutional neural net w/ examples from earth to provide for them. should suffice until about an age of 7 after which they'll just continue to use the nanobots to provide raw materials.

See James P. Hogan's Voyage from Yesteryear. It involves a post-scarcity civilization seeded in much the way you suggest.


Adults from later, faster spacecrafts could raise the babies.

Why wouldn't they just bring their own? Or make some?

we'll also send send self-replicating nanobots

If you're limiting it to generational ships then there isn't much improvement to be made, we can still only accelerate at ~1G. The only variable is how long that acceleration can be maintained.

Maybe there could be a kind of factory-ship that was built to be self-improving, so during those 1000 years it would improve itself and increase it's speed.

After we build the laser it might not cost that much more just to keep a constant stream of these guys going to the planet relaying their information back along the stream. Effectively giving us a streaming feed of what's happening on the planet.

A single probe in orbit could obviously do this but with this idea there's no way to slow down.

There's a way to slow down:


>The lightsail is built in two sections, an outer doughtnut- shaped ring, and an inner circular section 30 km in diameter. This 30 km payload section of the sail has a mass of 71 metric tons, including a science payload of 26 metric tons. The remaining, ring-shaped "decel" stage has the mass of 714 metric tons, or ten times the smaller payload "stage". The central payload section of the sail is detached from the larger stage and turned around so that its reflecting surface faces the reflecting surface of the ring-shaped portion (see Fig. 4). At a time 4.3 years earlier, the laser power from the solar system was upgraded to 26 TW (there are 37 years to get ready for this increase in power). The stronger laser beam travels across the space to the larger ring sail. The increased power raises the acceleration of the ring sail to 0.2 m/s2 , and it continues to gain speed. The light reflected from the ring sail is focused onto the smaller sail, now some distance behind. The light rebounds from the 30-km sail, giving it a momentum push opposite to its velocity, and slowing it down. Since the smaller sail is 1/10 the mass of the larger one, its deceleration rate is 2.0 m/s2 , or 0.2 g. The light flux on the smaller sail has increased considerably, but it is only two-thirds of the maximum light flux that the sail can handle.

This is from the same people who announced the "Breakthrough Message", an open competiton with a $1 million dollar prize pool, whose details were "to be announced soon". [1]

The press release was made in July 2015, and there has been no communication about it since then. I'm not sure how seriously to take this group.

[1] http://www.breakthroughinitiatives.org/Initiative/2

Unless "The Moties" send one here, first :-)

Yet another comment plugging a story involving some novel interplanetary travel (this one involving a species from a red dwarf): https://en.wikipedia.org/wiki/The_Mote_in_God%27s_Eye

This should be the top comment! Not the guy poo pooing on the idea of checking out this planet.

(ignore what I said here)

Also at 10% the speed of light the probe zips by the planet in a fraction of a second. There's no slowing down in this scenario.

You can slow down - just that the probe won't remain intact. But perhaps that isn't necessary for the probe to be useful. We can also use these space probes to do geological and atmospheric surveys of the planet when they arrive.

Simply: we slam the probe into the planet, a few milliseconds after it transmits the final images. One gram going at 20% of the speed of light has kinetic energy that bears comparison to the Hiroshima bomb.

At a steep angle of entry, the huge entry glow will give a reading of the atmospheric molecular makeup. And if we can ionize some of the crust, massive space telescopes can get a spectroscopic measurement of the composition, four light years away.

Let's hope any alien race living there doesn't have the same idea and send a few probes to smash in to Earth.

That would be like Christopher Columbus, mid-Atlantic crossing, encountering a gunpowder-equipped Mayan navy going off to conquer Europe. Not likely.

now that's a way to say Hi to a foreign species! there isn't high chance this wouldn't be considered as an act of hostility, and if they would check our history of our current world, they would probably just decide to erase this dangerous species from the face of the universe for greater common good.

I think we both know humanity's interstellar destiny is to become the murderous alien invaders we've faced down in so many movies.

There are ideas for slowing them down and even returning them back to Earth, at least in principle:


Nothing that could be implemented in any foreseeable future though.

Could they carry mini solar sails to slow down? Solar parachutes if you will.

Or if we sent them in single file several seconds apart they could each relay what they see to the ones behind them and then back to us. Effective oh giving us a long exposure.

The laser is only on each device for 10 minutes. And there are 1,000 of them. So the hope is that at laest 1 in 1,000 will make it.

if even a tiny fraction of those 1000 tiny probes hit that planet at 20% of speed of light, could that pose a problem? it sounds like a shotgun approach, not so figuratively, using pellets loaded with plutonium.

The probes would each be only a few grams, so they'd have about 10^13 J of relativistic kinetic energy, or a half kilotons of TNT equivalent. This can be compared with the 15 kilotons for the (small, by modern standard) Little Boy atomic bomb. So it's probably noticeable for any inhabitants in the area, depending on how the energy is dissipated in the atmosphere, but still quite small on the scale of a planet.

It should be noted that meteors explode with Hiroshima-like force fairly regularly within Earth's atmosphere, on the order of once a decade or so. It happens high up enough that nobody notices beyond an occasional light show. The meteor explosion which hurt a bunch of people in Chelyabinsk a few years back was about 500 kilotons.

And so many of those people were injured because they went to a window to see the spectacle, not knowing about the shock wave that was coming.

It made me realize that the civil defense films we watched in the '50s weren't so misguided after all:


Indeed, that's pretty much what "duck and cover" was all about. There was even a school teacher in Chelyabinsk who apparently remembered her Cold War drills and had her students take cover, saving them from injury.

cool, good to know that raining down a bunch of probes in this manner would most likely be a pretty light show. still i wonder about the plutonium aspect of this?

it might be prudent to first consult with the legal experts and diplomats of the Galactic Council, to clear this type of activity with them first, minimize interpretation of this probing as a hostile interstellar act.

I don't think the plutonium would be enough to have any real effect, although it might irritate the inhabitants if there are any. Certainly, we've put far more plutonium into Earth's atmosphere by blowing up thousands of nuclear bombs in it, and we survived.

Clearing it with the Galactic Council definitely sounds like a good idea. Do you have their phone number handy? I seem to have deleted their contact info by accident.

>>So it's probably noticeable for any inhabitants in the area

An intelligent civilization with a 1000 year head start whose presence was just proven by device that arrived at 10% the speed of light would pretty much scare any government on earth.

I would assume it would scare the aliens there too.

This is the coolest project I've heard about in a while. Thanks for sharing!

I wonder what it would be like to be the Nth generation of guys-that-left-in-2016 finally arriving and be greeted by the descendants of the FTL guys that arrived 800 years before you.

This is the plot of at least one Star Trek: Enterprise episode.

Which one? I Netflix'ed my way through that whole show a couple years ago and didn't see any like that.

It does sound a little bit like "Space Seed" from TOS though, except I don't remember that ship having a particular destination. There was another TOS episode where they find a stray asteroid that turns out to actually be a generation ship inside. And there was some TNG episode where they find a ship with some 20th-century Earthers in cryogenic storage because they had just died of medical ailments. But I don't remember any ENT episodes like this, just some talk about "slow" Earth ships traveling at only Warp 1.5 or so, so that people lived their whole lives on them while on long-term trading missions (their helmsman came from one of these ships).

I'm pretty sure you're wrong and it was an episode of 'The Next Generation, although I've no idea what the title of the episode was... [0]

[0] I've watched the episode only once (I'm not a Trekkie :) ), but if I remember correctly a synopsis of the plot was that decades (at least...) ago an automated ship containing Klingons in cryogenic suspension was launched to colonise a distant planet; in the time following the launch of that ship, the Federation reached and colonised that planet using faster ships, unaware that the Klingon ship was on the way...

The crew of the Enterprise [D] has to try to figure out how to stop the Klingon ship from introducing the Federation colonists on the planet to the magic of orbital bombardment (a casus belli) without destroying the Klingon ship (a casus belli).

I think you're mixing up some details of that episode. The closest episode I can think of that matches that is "The Ensigns of Command", which involves a colony of humans that were isolated and underdeveloped due to interference from the planet's radiation. The colony was on a planet that technically belonged to the "Sheliak", a mysterious race the Federation had limited contact with, but who had decided to begin colonizing the planet and gave the Federation a short time span to remove the humans before they would eradicate them.

I looked it up, and the title of the episode was "The Emissary" [S2E20] (although, yes, either I remembered a few details incorrectly or the Wikipedia synopsis of the plot is incomplete).

... are you sure?

There's one episode where they visit a colony established decades previous by a warp 1 or warp 2 ship, but they don't beat the colonists to the planet.

no shortage of fiction covering that scenario...

Since we're pretty sure FTL is pure fiction and not possible in reality, that likely won't be an issue. Just because we don't know everything, doesn't mean we don't know anything.

We are, by no means, sure of that. There are numerous theoretical possibilities that fit current theory. Not least of which is the Alcubierre Drive: https://en.wikipedia.org/wiki/Alcubierre_drive

Mathmatically compatible with GR (which is known to be incomplete) doesn't mean possible in reality, in fact, read your own source, it makes that clear..

> Although the metric proposed by Alcubierre is mathematically valid (in that the proposal is consistent with the Einstein field equations), it may not be physically meaningful, in which case a drive will not be possible.

That drive is nothing more than speculative science fiction.

Are there really numerous possibilities? I know about Alcubierre, what are the others?

Alcubierre's drive is a solution to Einstein's field equations which simply means the math checks out in theory for warp drive.

The resulting practical problem is that the energy requirements necessary for the solution are far greater than what we can feasibly achieve now or in the future (exotic matter's existence notwithstanding).

But the fact that a physicist was able to derive this metric (energy requirements aside) is significant. Given the history of science, I would not discount the possibility that someone else will come along in the future with another solution which lowers the energy requirements to something feasible. But we can't predict this.

But isn't it amazing that the math checks out at all? I find it inspiring...

I'm not so sure the energy requirements are all that high. Alcubierre suggested that the sort of exotic matter needed would actually be fairly easy to create. NASA's been running experiments hoping to measure it with inconclusive results:


> In 2012, a NASA laboratory announced that they had constructed an interferometer that they claim will detect the spatial distortions produced by the expanding and contracting spacetime of the Alcubierre metric. The work has been described in Warp Field Mechanics 101, a NASA paper by Harold Sonny White.[5][6] Alcubierre has expressed skepticism about the experiment, saying "from my understanding there is no way it can be done, probably not for centuries if at all".

> In 2013, the Jet Propulsion Laboratory published results of a 19.6-second warp field from early Alcubierre-drive tests under vacuum conditions.[33] Results have been reported as "inconclusive".[34]

Wormholes are another. There's some debate whether or not the idea of creatable wormholes really exists in our physical models. But the idea of existing shortcuts through space time certainly does.

Wormholes aren't known to exist; they're theoretical implications of some math, not known things. It's entirely possible they don't exist at all.

Hence the "in our models".

No, but if we leave today with a trip time of 1000 years and in 100 years we invent a way to travel .2c, then the people on the ship with the new tech will arrive in 120 years instead of 1000. Don't need FTL tech to make generation ships a silly prospect.

The other thing you guys are missing is relativistic time dilation: get the ship moving fast enough and time will pass more slowly inside the ship than outside. The ship may take a century or two to get to the destination, but only a few years will have passed for the travelers.

You have to go really, really fast to get 100:1 time dilation (like, 99.99% c) -- probably fast enough to make interstellar travel hazardous in a "collide with a hydrogen atom, it hurts" kind of way.

Also, the energies involved are absurd.

They will still arrive after the faster ship.

Pretty sure? I'm pretty sure we don't know near enough to make any type of guess on that.

Your mistaken, and this opinion is what the second sentence was for; just because we don't know everything doesn't mean we don't know anything. FTL is likely not physically possible. That's not to say it's impossible, just that it's not likely given the vast number of things we do know about physics.

Maybe you'd get a nice little tech upgrade when you got there. And I'd hope that we'd at least develop some form of suspended animation to make things bearable.

To be honest, assuming, you get there safely I'd rather be in suspected animation on the slow ship than the fast one. I'd get all the heroism and send-offs of a pioneer, I'd have my name etched on a monument somewhere, I'd have the thrill of exploring something totally new. All that, except when I arrive all the brutal, dangerous, boring work of establishing a self-sufficient biome will already be done and I can jump immediately into the "boldly go where no one has gone before" part.

They'd just get picked up along the way.

Well, they can stop at the spaceship on their way back and then... I don't know

It's not quite that bad. Have you heard of fission-fragment rockets? Highly feasible, and travel times to Alpha Centauri on the order of decades, not millennia. Baffles me that no one talks about them.


Someone mentioned them in this discussion ~30 minutes before you posted.

Where? I'm ctrl-f-ing here and seeing nothing older than my comment.

OK, the previous ref was for nuclear pulse propulsion, which I'm sure you consider completely different.

They are extremely different. One is a highly impractical idea from the 1940s, and the other is a relatively recent and promising design that continues to be refined.

What's exactly impractical about a nuclear pulse drive - conventionally launched and activated outside the atmosphere? We know how to build that stuff safely to account for launch failures, it has been done with RTGs many times already.

Actually the 1000 year number comes from Project Orion in the 1940ties and 50ties.


An updated design from the 80ties calculated a time of 100 years:


And a nuclear fusion design is calculated to achieve 12% of light speed, thereby reducing time to reach the fourth nearest sun system in 46 years.


So there are concepts that could make unmanned interstellar travel possible, even within a humans life span, it's just that it costs so much and the incentive is pretty low compared to the incentive countries had for getting objects into space. (primarily military incentives - get spy satellites and nuclear warheads into space to not fall back behind adversaries)

I believe that given a strong enough incentive humans could do it, no matter what current consensus is telling us.

Humans set out to work on reaching outer space without even having a design on how this could be achieved and we did it anyway.

At current rates, it would be 137 thousand years.


50ties - Fifty-ties -- Fifties - 50s / 50's

Thanks, English is not my native language. So what is correct, 50s or 50's?

Yeah, I figured, no worries. Your English is excellent, apart from this little oddity. Either way to put the 's' is fine, really, but I think with the apostrophe (50's) is more common.

Thanks a lot! Very kind of you.

Yeah, I smiled when I read "Just over four light-years" as if just around the corner kind of thing.

It might be just around the corner in space travel time, but those are quite a few light years still.

Also no one knows how to shield a spaceship from the interstellar medium https://en.wikipedia.org/wiki/Interstellar_travel#Interstell... over such distance.

Fission fragment rockets are well within current technology and can achieve delta-vs of 0.1c at reasonable payload fractions, getting us there in ~ 40yr.

Edit: Nuclear pulse propulsion is good for about half that (80yr, not 1000).

How does it slow down?

It doesn't hence its going to be used for flyby missions and not orbit/capture missions.

Many missions to the outer planets are flybys since we can't have enough fuel to actually slow down.

just curious but how would you even capture any usable signals when passing a planet at 20% lightspeed?

Well if you think about it we are capturing useful signals that move at relativistic speeds all the time.

Many galaxies we see are moving at very high speeds due to the expansion of the universe hence the doppler shift and we can take both optical and radio images of them.

I'm not an RF/Optical engineer but I would think that it would be possible to capture and send some data back to earth even its minimal it's still might be better than nothing / what we can get from earth/our solar system, at the end we only might have to account for the doppler shift.

IIRC there have been also other tricks like deploying very large sails and using them as drag chutes or using some mechanical trickery and deploying a very small probe by literally like having it on some pendulum and some other weird stuff so you would transfer most of the momentum it has to the probe and you'll release it with considerably less momentum than the rest of the spacecraft.

The planet itself could slow the probe down quite rapidly. ;)

Would it be possible to drop a payload that would enter orbit?

The payload would need to slow down to be captured by the planet just the same. Normally you could try aerobraking and the like, but we are talking about relativistic speeds here.

To get better closeup pictures, if possible, aim the probe for the planet and live stream picture home all the way to impact.

Although I'm not sure these probes are at all steerable, either autonomously or remotely.

Highly unlikely, the mass of the probes will be on the order of several grams at most, and, depending on the trajectory relative to the planet, steering could require an equally impractical amount of fuel as slowing down would.

Livestream at 20% of light speed?

There may not be any significant atmosphere for aerobraking. This likely would not be known until long after the probe arrived.

We'd also have limited knowledge of the system itself. Without more accurate data about its objects and their orbits, it'd be almost impossible to plan out orbit insertions even assuming we come up with a means of slowing a probe from relativistic speeds.

Even if your probe had the computing power to run orbital mechanics calculations, there's no guarantee that it'd be in a position to actually make it work when it got there. Of course, that's ignoring the mass constraints involved.

But that doesn't discount the value of even 'just' flyby missions. The scientific benefit would be, literally, incalculable. And the data could help with followup missions, assuming we develop a drive system that could get there and slow down.

The StarShot probes are going to be about a gram. Not much weight to make a primary probe AND a payload.

slowing down from that kind of velocity is serious business. you're talking about braking from 75000km/s to ~8km/s and not blowing up in a spectacular explosion.

I just died laughing. I'm reading all the inspiring comments on how we actually could get there, and could totally see myself being on an engineering team that builds this thing, and 100 billion dollars later you ask that question and we all go: "Oh... oh crap." On a constructive note -- does anyone have a list / book of generally smart people getting sidelined by such things?

There's a book called It Looked Good On Paper full of things a bit like that, albeit on a smaller scale.

This comment left me flabbergasted. Great thinking.

What about orbiting the planet and using the lasers when the craft is orbiting towards us in blasts to slow it down gradually?

Magsails would work.

If you're going to use magsails to slow it down, why not use a magsail to get it there? The trip is basically symmetrical.

I suppose it's possible that the laser could produce a much more stable and precise trajectory, while a magsail would just slow it's descent towards or accelerate it away from the sun. But I think it's more likely to be a case of the materials science and energy density being in favor of the laser method over sails.

What if we used lasers to send a fleet of laser ships with powerful one-time-use chemical lasers, then the front set of laser ships fired the same kind of beam back at the rearmost ship to to slow it down?

> If you're going to use magsails to slow it down, why not use a magsail to get it there? The trip is basically symmetrical.

If you launch a strong magnet in interstellar space, it will slow down relatively to plasma by deflecting charged particles.

In order to speed up, you need to spend energy.

The symmetry is broken between accelerating and slowing down relatively to interstellar plasma (Edit: or solar wind).

Ah, I had neglected the effects of interstellar plasma.

I assumed the magsail operated in a similar fashion to a solar sail, depending on the solar wind. If the destination's solar wind was sufficient to slow us down, I expected that the Sun's solar wind would be sufficient to speed us up.

Thanks for the explanation!

Imagine the political implications of choosing who will go onto that ship, as well (assuming the intent is to colonize the world and fill it up with humans)

Telephone sanitisers.

A poet.

This is a (likely) reference to Contact (1997), with Jodie Foster.

Some celestial event. No - no words. No words to describe it. Poetry! They should've sent a poet. So beautiful. So beautiful... I had no idea.

Only the richest, elites. I say we ship them immediately! /s

Let's get real, they wouldn't go anyway. It's too good for them here where they have people to do things for them.

> Only the richest, elites.

Would they actually want to go? If we are talking about a 1000 year voyage, and not assuming a major breakthrough in cryogenics or longevity, signing up for that trip means you are going to spend the rest of your life on that ship, mostly outside but near our solar system.

I don't see that being particularly enticing to rich elites.

I don't remember were I read this so cannot properly give credit, but I saw an interesting variation on the generation ship.

The conventional approach is to send a large crew, whose job is to operate the ship, reproduce, and raise their kids to take their place, generation after generation until the ship arrives and they become colonists.

The variation would be to start with a much smaller crew and large collection of frozen embryos. You make use of the embryos when you arrive to build up the population to full colony size.

The advantage of this approach is that since there are fewer people during the trip, you have more capacity for supplies. You can better equip the ship to deal with unforeseen problems.

For instance, suppose taking the embryo approach, you can get it down to a crew of 6. You'll have 12 when the crew is overlapping with their kids. Call it 18 if the crew's parents have not yet died when the crew has their kids.

Suppose each crew member needs 3000 calories per day. Then on a 1000 year voyage, you need 18 people x 3000 calories/person/day x 365.2422 days/year x 1000 years = 19.7 billion calories.

I have a protein bar by my desk at the moment. It is 190 calories, and is about 125 mm x 30m x 20mm = 75000 mm^3. So, 19.7 billion calories x 1 bar/190 calories x 75000 mm^3/bar gives a volume of 7.8 x 10^12 mm^3. Stored in a cubic storage container, this would require a container with an interior length, width, and height of 19.8 m.

The "small active crew, everyone else a frozen embryo" generation ship could start out with enough food on board to last the entire voyage, and so would not need to raise food onboard. That alone should greatly simplify things, and greatly improve the chances of making it. Of course they probably would still grow food, but now it would be for added variety and flavor, not a necessity.

(I'm not going to do the calculation to see if they could start with enough water for the whole trip. Water is very bulky and we use a lot of it, so my totally uneducated guess is that it would take too much space. However, I believe that efficient water recycling in a closed environment is something we know how to do very well, and so water should not be a problem).

The problem is that these people are going to be living out their entire lives on the ship. While you can maintain genetic viability by supplementing from frozen stock. Maintaining a viable culture and a society that the caretakers will actually want to live in is another thing. Forcing anyone to live a culturally and socially impoverished life is cruel.

I would suspect you would want to have at least 10-20 people in each 5 year age bracket. Then people will have a fighting chance at developing their own social lives and maybe even their own culture.

That's a lot of generations of inbreeding before the approx three descendant females of childbearing age get to unfreeze the embryos and start widening the gene pool though, assuming they're up for the task of being the surrogate mother for dozens of other people's kids...

tbh I think storing enough food for the journey is going to be the least of all problems

You could do a mix of crew replacement by breeding and crew replacement by reviving frozen embryos to keep the genetic diversity up.

Or maybe an all female crew that does crew replacement either using frozen sperm or frozen embryos, and selects for female replacements.

When the ship arrives and it is time to start the colony, I don't think you'd try to grow to thousands of people quickly. I think you'd want to go slow early to make sure you understand your new environment. Maybe 12 years out, the crew switches from 1:1 replacement to 3:1. Sticking with 6 as the main crew, plus possibly up to 6 of the crew's parents still alive, plus 18 kids. I think you'd want to spend a few years based on the ship studying the planet and conducting research expeditions to figure out if the planet really is suitable for colonization and figure out dangers that unmanned probes and study from Earth may have missed. When that is done, the kids should be 18 or so, and you can start the colony with them and with their grandparents, with the main crew staying with the ship to provide support. That would give 18-24 people on planet attempting to live there, but not needing to be self-supporting yet because of the ship.

In a few years, the colony population should start naturally growing. If the babies do OK, people can be encouraged to have bigger families, with one or two per family being from the frozen embryos and the rest produced the old fashioned way.

> tbh I think storing enough food for the journey is going to be the least of all problems

Yeah, there will be a lot of problems.

Many of the hard ones will not even be technical. For instance, you'd want to have some way to stop from happening something that happened to a colony in Larry Niven's "Known Space" universe. When the colony ship arrived the crew decided to set up the colony so that the crew was the ruling class and the colonists essentially serfs.

The ship in that Niven story wasn't a generation ship. Crew and colonists were cryogenically suspended for the trip, with the crew being automatically revived when the ship arrived. I supposed one advantage of the traditional generation ship is that it has some protection against that scenario because during the trip everyone is crew.

There's no reason they have to wait to arrive to start using the embryos.

I think you're conflating a few things here:

1.) A probe and a human spaceship are vastly different problems. Since all a probe really needs is electricity to sustain itself, you could get away with a tiny payload and some long lasting radioactive energy source, light sails or even sending the energy from earth's orbit. Such a thing would be either slow and cheap or fast (a few percent of light speed) and expensive, but not both at the same time and I doubt it would be in the trillion dollar range whatever you do.

2.) I completely agree that sending humans would currently not be feasible within a single nation's budget and the technology for that is still at the very least decades out (cryogenics, EM shielding, better propulsion systems, using mass from cheaper solar system bodies than earth etc.).

3.) 1000 years is what we'd need with conventional current technology. The theoretical limit for a nuclear impulse propulsion drive is 20% of light speed if you want to break or 40% for a fly-by.

Well using laser propulsion, we might be able to get a very lightweight probe up to 1/4 c using technology that isn't too far off.[0]

Coincidentally, the group working on this will be presenting some of their most recent work on this at 2:55 EST today. You can watch that live here[2].

[0] http://www.deepspace.ucsb.edu/projects/directed-energy-inter... [1]https://www.nasa.gov/sites/default/files/atoms/files/2016_sy... [2]http://livestream.com/viewnow/NIAC2016

Don't forget that halfway there you have to turn it around and start slowing down.

The bigger deal is, How do you deal with the ablation problem at those speeds? Given the likely density of H in interstellar space, erosion is your primary problem.

Add the Broussard ramscoop, magnetically deflect the atoms into an accelerator and expel them to add to your propulsion.

What about a solar sail mixed[1] with, ion engine[2] and nuclear powered[3]? With all those things combined, you would constantly be accelerating for many years.

[1] http://www.planetary.org/explore/projects/lightsail-solar-sa... [2] http://www.nasa.gov/centers/glenn/about/fs21grc.html [3] https://en.wikipedia.org/wiki/Radioisotope_thermoelectric_ge...

I'm interested in NASA's work on the Alcubierre drive [1]. Still likely to require much more energy than we'll be able to produce in the near future, but 100 years ago we were just getting a firm handle on the basic mechanics of flight.

[1] http://ntrs.nasa.gov/archive/nasa/casi.ntrs.nasa.gov/2011001...

The Alcubierre drive is just a solution to the equations of general relativity that most probably can not be achieved in practice. Sure, maybe one day we will have drives like that, but we do not have any idea currently that even remotely resembles a warp drive permitted by the laws of nature.

That would require us to create matter with a negative energy density, which has never been detected and is likely impossible.

Still fiction; it relies on magic, i.e. things not known to actually exist.

Magic operates in ways we don't understand. I think we understand negative energy density, we just don't know if it's possible in reality.

> Magic operates in ways we don't understand.

Witches would disagree. :)

> I think we understand negative energy density, we just don't know if it's possible in reality.

Exactly as in magic. When you propose things are possible if only X material with some magical property necessary for thing to work, that's speculative fiction. Especially when those constructs only make sense mathematically. Math isn't physics, but physics is math, there's an important implication there.

According to Niel DeGrasse Tyson, you could send a tiny, pocket-sized payload and get it there in only a few decades. So if we just want a couple snapshots and not the sort of thing we typically send to orbit planets, it could be done in a reasonable amount of time.

Why would it be unpopular? On the scale of the space involved, any "pollution" would be literally inconsequential.

On the cost, I agree and think we have much bigger fish to fry on our own planet than to spend huge sums to discover what is in all likelihood a barren rock.

Frying every piece of electronics on the ground below the ship when you fire it up, and every satellite visible above the horizon, would be bad PR.

You could potentially boost it far away from Earth by more conventional means before turning on the nukes, but suddenly it becomes a far larger and more difficult thing.

Oh please.

Any interstellar ship like this is not going to be built on Earth's surface, it's going to be constructed in space somewhere. Building a craft that large on the surface is far more difficult than just assembling it in zero-g from components, since the stresses of leaving the gravity well through the atmosphere on a large object are huge.

The point is, not only does it need to be built in space, but it needs to be built (or moved) pretty far away from Earth before you light it up. You can't just build it in Earth orbit. And even that would be well beyond modern capabilities. A ground-launched Orion could be built now, but constructing an interstellar ship in solar orbit will require a lot more work on space access.

A ground-launched Orion could be built now, but it'd make a mess when it launches, and it'd probably be much too small for a useful interstellar mission anyway, because of that scaling problem I mentioned. The stresses are just too high, and it's pointless because you don't need a ship that rugged in space, only for transiting planetary atmospheres.

I don't think we have the capability now to build a sufficiently large ship on the ground anyway, even if we decided to say "screw it, we don't care if it's wasteful to massively overbuild this thing"; our materials science probably isn't up to the task. So we need to learn to build things in space anyway.

No, we don't really have this capability right now. But we need to assume we'll have it when we need it, and we need to work towards it, and not try any kind of missions requiring it until we do. Thinking about interstellar missions right now is really putting the cart before the horse; we haven't even gotten manned missions beyond the Moon, and even those were pretty simple (walk around, hit some golf balls, drive a rover around), not anything involving real work such as building a habitat or serious excavation or mining.

This is why I think all this talk about going to Mars is silly too; we need to be concentrating on closer things, like near-Earth asteroid retrieval and prospecting, and building a Moon base, and figuring out how to mine materials and build larger ships offworld. We need a bigger ship to go to Mars, not some little tin can that you can stick on top of a rocket; something the size of the ISS would be good, because the crew will have to be trapped in it for months, and they need stuff for landing on the surface and doing real work there. You can't do all that with something the size of the lunar modules we launched on the Saturn V.

Just build it in space.

Maybe wait for space elevators?

Didn't Project Orion determine that it's theoretically feasible to accelerate to not-insignificant fractions of c using NPP? If your journey could average even 0.05c, you can potentially make it within a human lifespan.

I thought the issues were:

  - navigation at any non-trivial fraction of *c* (not running into something that would obliterate the vessel)
  - slowing down and actually arriving where you wanted to and not overshooting it or stopping .5 LY away

About slowing down, it's pretty predictable. The idea is even to run the ship in constant acceleration.

I don't think you'll want to actually navigate that ship. It's a point and go task. But if needed, you rotate the ship and keep accelerating. But I have no idea on how much you'd be able to fix your route after you discovered it is wrong.

I think the main issues are how do we make a ship where people can live for decades? And how do we launch it from the ground?

I think speed is only one part of it you'd be dead from radiation over such a long period of time unless you were surrounded by lead.

Proxima Centauri is 4ly away. New Horizons (the Pluto Probe) was travelling at 15.73km/second (just over 34,000/mph)

You're looking at closer to 75,000 years - not 1,000 years - to reach Proxima Centauri.


Did actual maths. Closer to 75,000 not 100,000.

This whole conversation reminds me of Europeans who have never been to the states thinking of flying over for a week, renting a car and visiting the Florida Keys, Times Square, the grand Canyon and Disneyland.

At 34k MPH it would take 75 Millenia to reach our literal stellar next door neighbor.

Makes the blood boil how vast and empty space really is, when you think about it

As you mention - comprehending how large/small countries are is tough for some people. Planet-size differences even more so. Many probably don't realize how big the sun is! Then you have to comprehend that on a galactic scale - our sun is really, really tiny [0].

We exist on a tiny spec of dust; inside of a solar system that is no larger than a tiny spec of dust; inside of a galaxy that is no larger than a tiny spec of dust; inside a supercluster that is only a tiny spec of dust.

[0] http://i.imgur.com/DUzDo3k.gifv

Every time I try to comprehend the sun as it actually is -- its size and composition -- I end up completely boggled and unnerved. A vast and uncaring ball of plasma, mostly hydrogen, supporting billions of years of fusion reactions, so big that the orbit of the planet I live on causes only the slightest wobble in its position; it's no wonder the ancients worshiped the sun. There's nothing about it I can begin to grasp except by analogy.

Ill just leave THIS here for you


Thanks to you, and to the GP. I do enjoy the analogies! I think the absolutely brain-crushing thing about objects of astronomic magnitude is trying to reverse the log-transform we use to make sense of them. For me it produces a sense of vertigo, like standing at the top of a cliff.

Okay. . . (humbly slinks away with tail between his legs)

that video totally blows my mind, i must have watched it a dozen times.

Yeah, it's pretty damn epic.

I did some rough estimation on a map recently and decided that driving from Seattle to Miami was only slightly shorter than from Paris to China.

This is a bloody big country.

New Horizons is a traditional design with chemical propultion. Ion drives should hit ~5.5x that speed fairly easily. (http://www.extremetech.com/extreme/144296-nasas-next-ion-dri...)

A larger issue is RTG's are not useful on a very long long timescale.

ITER style fusion is likely the best power source for such missions and should hit ~1-10% of light speed fairly easily. But, building something that large is a major issue.

On the upside, we have already gone 18.1 light hours, 4.2 light years is not an unreasonable jump.

~5.5x that speed is still about 13,636~ years. Much better but still not very realistic....

18.1 lighthours is 3/4ths of 1 lightday. Which is 1/1533 of 4.2 lightyears or in other words: 0.06% of the way there. Going the remaining 99.94% is a massive jump!

Can you link to more information?

Not the best link but here's something to chew on:


>However, despite these advantages in fuel-efficiency and specific impulse, the most sophisticated NTP concept has a maximum specific impulse of 5000 seconds (50 kN·s/kg). Using nuclear engines driven by fission or fusion, NASA scientists estimate it would could take a spaceship only 90 days to get to Mars when the planet was at “opposition” – i.e. as close as 55,000,000 km from Earth.

> But adjusted for a one-way journey to Proxima Centauri, a nuclear rocket would still take centuries to accelerate to the point where it was flying a fraction of the speed of light. It would then require several decades of travel time, followed by many more centuries of deceleration before reaching it destination. All told, were still talking about 1000 years before it reaches its destination. Good for interplanetary missions, not so good for interstellar ones.

There's talk of other drive systems being able to pull it off but this is the only one that actually has been tested but never built to scale.

He's probably thinking of Freeman Dyson's Project Orion: https://en.wikipedia.org/wiki/Project_Orion_(nuclear_propuls...

http://breakthroughinitiatives.org/Initiative/3 http://www.spaceflightinsider.com/missions/stephen-hawking-r...

It says the probe would be able to get there in about 20 years, travelling at 20% the speed of light, that's around 37,200mps.

There's going to be a relativistic effect, I think 20 years from our perspective will be slightly shorter from the probes point of view?

I'm reminded of the books Illium and Olympos by Dan Simmons.

I've read them--- how and why are you reminded of them by this story?

I was referring to the comment I replied to.

<Obligatory flamewar-starting "Em Drive" comment>

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