Paul Gilster posts:
In interstellar terms, a ‘fast’ mission is one that is measured in decades rather than millennia. Say for the sake of argument that we achieve this capability some time within the next 200 years. Can you imagine where we’ll be in terms of telescope technology by that time? It’s an intriguing question, because telescopes capable of not just imaging exoplanets but seeing them in great detail would allow us to choose our destinations wisely even while giving us voluminous data on the myriad worlds we choose not to visit. Will they also reduce our urge to make the trip?
Former NASA administrator Dan Goldin described the effects of a telescope something like this back in 1999 at a meeting of the American Astronomical Society. Although he didn’t have a specific telescope technology in mind, he was sure that by the mid-point of the 21st Century, we would be seeing exoplanets up close, an educational opportunity unlike any ever offered. Goldin’s classroom of this future era is one I’d like to visit, if his description is anywhere near the truth:
“When you look on the walls, you see a dozen maps detailing the features of Earth-like planets orbiting neighboring stars. Schoolchildren can study the geography, oceans, and continents of other planets and imagine their exotic environments, just as we studied the Earth and wondered about exotic sounding places like Banghok and Istanbul … or, in my case growing up in the Bronx, exotic far-away places like Brooklyn.”
Webster Cash, an astronomer whose Aragoscope concept recently won a Phase I award from the NASA Innovative Advanced Concepts program (see ‘Aragoscope’ Offers High Resolution Optics in Space), has also been deeply involved in starshades, in which a large occulter works with a telescope-bearing spacecraft tens of thousands of kilometers away. With the occulter blocking light from the parent star, direct imaging of exoplanets down to Earth size and below becomes possible, allowing us to make spectroscopic analyses of their atmospheres. Pool data from fifty such systems using interferometry and spectacular close-up images may one day be possible.
Image: The basic occulter concept, with telescope trailing the occulter and using it to separate planet light from the light of the parent star. Credit: Webster Cash.
Have a look at Cash’s New Worlds pages at the University of Colorado for more. And imagine what we might do with the ability to look at an exoplanet through a view as close as a hundred kilometers, studying its oceans and continents, its weather systems, the patterns of its vegetation and, who knows, its city lights. Our one limitation would be the orbital inclination of the planet, which would prevent us from mapping every area on the surface, but given the benefits, this seems like a small issue. We would have achieved what Dan Goldin described.
Seth Shostak, whose ideas we looked at yesterday in the context of SETI and political will, has also recently written on what large — maybe I should say ‘extreme’ — telescopes can do for us. In Forget Space Travel: Build This Telescope, which ran in the Huffington Post, Shostak talks about a telescope that could map exoplanets with the same kind of detail you get with Google Earth. To study planets within 100 light years, the instrument would require capabilities that outstrip those of Cash’s cluster of interferometrically communicating space telescopes:
At 100 light-years, something the size of a Honda Accord — which I propose as a standard imaging test object — subtends an angle of a half-trillionth of a second of arc. In case that number doesn’t speak to you, it’s roughly the apparent size of a cell nucleus on Pluto, as viewed from Earth.
You will not be stunned to hear that resolving something that minuscule requires a telescope with a honking size. At ordinary optical wavelengths, “honking” works out to a mirror 100 million miles across. You could nicely fit a reflector that large between the orbits of Mercury and Mars. Big, yes, but it would permit you to examine exoplanets in incredible detail.
Or, of course, you can do what Shostak is really getting at, which is to use interferometry to pool data from thousands of small mirrors in space spread out over 100 million miles, an array of the sort we are already building for radio observations and learning how to improve for optical and infrared work on Earth. Shostak discusses a system like this, which again is conceivable within the time-frame we are talking about for developing an actual interstellar probe, as a way to vanquish what he calls ‘the tyranny of distance.’ And, he adds, ‘You can forget deep space probes.’
I doubt we would do that, however, because we can hope that among the many worlds such a space-based array would reveal to us would be some that fire our imaginations and demand much closer study. The impulse to send robotic if not human crews will doubtless be fired by many of the exotic scenes we will observe. I wouldn’t consider this mammoth space array our only way of interacting with the galaxy, then, but an indispensable adjunct to our expansion into it.
Of course Shostak takes the long, sensor derived view of exploring the Universe, his life’s work is radio telescopes.
Gilster is correct that interferometry will be an adjunct to sending robotic probes to distant interstellar worlds, you can’t make money by just gawking at places.
Or can you?
I discovered Karl Schroeder’s work when I was researching brown dwarfs some years ago. Who knew that somebody was writing novels about civilizations around these dim objects? Permanence (Tor, 2003) was a real eye-opener, as were the deep-space cultures it described. Schroeder hooked me again with his latest book — he’s dealing with a preoccupation of mine, a human presence in the deep space regions between ourselves and the nearest stars, where resources are abundant and dark worlds move far from any sun. How to maintain such a society and allow it to grow into something like an empire? Karl explains the mechanism below. Science fiction fans, of which there are many on Centauri Dreams, will know Karl as the author of many other novels, including Ventus (2000), Lady of Mazes (2005) and Sun of Suns (2006).
by Karl Schroeder
My newest science fiction novel, Lockstep, has just finished its serialization in Analogmagazine, and Tor Books will have it on the bookshelves March 24. Reactions have been pretty favourable—except that I’ve managed to offend a small but vocal group of my readers. It seems that some people are outraged that I’ve written an SF story in which faster than light travel is impossible.
I did write Lockstep because I understood that it’s not actual starflight that interests most people—it’s the romance of a Star Trek or Star Wars-type interstellar civilization they want. Not the reality, but the fantasy. Even so, I misjudged the, well, the fervor with which some people cling to the belief that the lightspeed limit will just somehow, magically and handwavingly, get engineered around.
This is ironic, because the whole point of Lockstep was to find a way to have that Star Wars-like interstellar civilization in reality and not just fantasy. As an artist, I’m familiar with the power of creative constraint to generate ideas, and for Lockstep I put two constraints on myself: 1) No FTL or unknown science would be allowed in the novel. 2) The novel would contain a full-blown interstellar civilization exactly like those you find in books with FTL.
Creativity under constraint is the best kind of creativity; it’s the kind that really may take us to the stars someday. In this case, by placing such mutually contradictory — even impossible — restrictions on myself, I was forced into a solution that, in hindsight, is obvious. It is simply this: everyone I know of who has thought about interstellar civilization has thought that the big problem to be solved is the problem of speed. The issue, though (as opposed to the problem), is how to travel to an interstellar destination, spend some time there, and return to the same home you left. Near-c travel solves this problem for you, but not for those you left at home. FTL solves the problem for both you and home, but with the caveat that it’s impossible. (Okay, okay, for the outraged among you: as far as we know. To put it more exactly, we can’t prove that FTL is impossible any more than we can prove that Santa Claus doesn’t exist. I’ll concede that.)
Read the rest here…
From Centauri Dreams:
Astronautics pioneer Robert H. Goddard is usually thought of in connection with liquid fuel rockets. It was his test flight of such a rocket in March of 1926 that demonstrated a principle he had been working on since patenting two concepts for future engines, one a liquid fuel design, the other a staged rocket using solid fuels. “A Method of Reaching Extreme Altitudes,” published in 1920, was a treatise published by the Smithsonian that developed the mathematics behind rocket flight, a report that discussed the possibility of a rocket reaching the Moon.
While Goddard’s work could be said to have anticipated many technologies subsequently developed by later engineers, the man was not without a visionary streak that went well beyond the near-term, expressing itself on at least one occasion on the subject of interstellar flight. Written in January of 1918, “The Ultimate Migration” was not a scientific paper but merely a set of notes, one that Goddard carefully tucked away from view, as seen in this excerpt from his later document “Material for an Autobiography” (1927):
“A manuscript I wrote on January 14, 1918 … and deposited in a friend’s safe … speculated as to the last migration of the human race, as consisting of a number of expeditions sent out into the regions of thickly distributed stars, taking in a condensed form all the knowledge of the race, using either atomic energy or hydrogen, oxygen and solar energy… [It] was contained in an inner envelope which suggested that the writing inside should be read only by an optimist.”
Optimism is, of course, standard currency in these pages, so it seems natural to reconsider Goddard’s ideas here. As to his caution, we might remember that the idea of a lunar mission discussed in “A Method of Reaching Extreme Altitudes” not long after would bring him ridicule from some elements in the press, who lectured him on the infeasibility of a rocket engine functioning in space without air to push against. It was Goddard, of course, who was right, but he was ever a cautious man, and his dislike of the press was, I suspect, not so much born out of this incident but simply confirmed by it.
In the event, Goddard’s manuscript remained sealed and was not published until 1972. What I hadn’t realized was that Goddard, on the same day he wrote the original manuscript, also wrote a condensed version that David Baker recently published for the British Interplanetary Society. It’s an interesting distillation of the rocket scientist’s thoughts that speculates on how we might use an asteroid or a small moon as the vehicle for a journey to another star. The ideal propulsion method would, in Goddard’s view, be through the control of what he called ‘intra-atomic energy.’
Image: Rocket pioneer Robert H. Goddard, whose notes on an interstellar future discuss human migration to the stars.
Atomic propulsion would allow journeys to the stars lasting thousands of years with the passengers living inside a generation ship, one in which, he noted, “the characteristics and natures of the passengers might change, with the succeeding generations.” We’ve made the same speculation here, wondering whether a crew living and dying inside an artificial world wouldn’t so adapt to the environment that it would eventually choose not to live on a planetary surface, no matter what it found in the destination solar system.
And if atomic energy could not be harnessed? In that case, Goddard speculated that humans could be placed in what we today would think of as suspended animation, the crew awakened at intervals of 10,000 years for a passage to the nearest stars, and intervals of a million years for greater distances. Goddard speculates on how an accurate clock could be built to ensure awakening, which he thought would be necessary for human intervention to steer the spacecraft if it came to be off its course. Suspended animation would involve huge changes to the body:
…will it be possible to reduce the protoplasm in the human body to the granular state, so that it can withstand the intense cold of interstellar space? It would probably be necessary to dessicate the body, more or less, before this state could be produced. Awakening may have to be done very slowly. It might be necessary to have people evolve, through a number of generations, for this purpose.
As to destinations, Goddard saw the ideal as a star like the Sun or, interestingly, a binary system with two suns like ours — perhaps he was thinking of the Alpha Centauri stars here. But that was only the beginning, for Goddard thought in terms of migration, not just exploration. His notes tell us that expeditions should be sent to all parts of the Milky Way, wherever new stars are thickly clustered. Each expedition should include “…all the knowledge, literature, art (in a condensed form), and description of tools, appliances, and processes, in as condensed, light, and indestructible a form as possible, so that a new civilisation could begin where the old ended.”
The notes end with the thought that if neither of these scenarios develops, it might still be possible to spread our species to the stars by sending human protoplasm, “…this protoplasm being of such a nature as to produce human beings eventually, by evolution.” Given that Goddard locked his manuscript away, it could have had no influence on Konstantin Tsiolkovsky’s essay “The Future of Earth and Mankind,” which in 1928 speculated that humans might travel on millennial voyages to the stars aboard the future equivalent of a Noah’s Ark.
Interstellar voyages lasting thousands of years would become a familiar trope of science fiction in the ensuing decades, but it is interesting to see how, at the dawn of liquid fuel rocketry, rocket pioneers were already thinking ahead to far-future implications of the technology. Goddard was writing at a time when estimates of the Sun’s lifetime gave our species just millions of years before its demise — a cooling Sun was a reason for future migration. We would later learn the Sun’s lifetime was much longer, but the migration of humans to the stars would retain its fascination for those who contemplate not only worldships but much faster journeys.
Goddard was obviously influenced by his contemporary J.D. Bernal with his The World, the Flesh and the Devil which predicted Man’s spread out into the Solar System and interstellar space with artificial worlds and hollowed out asteroids.
These worlds are needed because such journeys will take hundreds or perhaps thousands of years.
Of course that brings in natural evolution and what these people inside these places will become when they eventually reach their destinations and if they’ll actually have need of them.
From Centauri Dreams:
Jules Verne once had the notion of a comet grazing the Earth and carrying off a number of astounded people, whose adventures comprise the plot of the 1877 novel Off on a Comet. It’s a great yarn that was chosen by Hugo Gernsback to be reprinted as a serial in the first issues of his new magazine Amazing Stories back in 1926, but with a diameter of 2300 kilometers, Verne’s comet was much larger than anything we’ve actually observed. Comets tend to be small but they make up for it in volume, with an estimated 100 billion to several trillion thought to exist in the Oort Cloud. All that adds up to a total mass of several times the Earth’s.
Of course, coming up with mass estimates is, as with so much else about the Oort Cloud, a tricky business. Paul R. Weissman noted a probable error of about one order of magnitude when he produced the above estimate in 1983. What we are safe in saying is something that has caught Freeman Dyson’s attention: While most of the mass and volume in the galaxy is comprised of stars and planets, most of the area actually belongs to asteroids and comets. There’s a lot of real estate out there, and we’ll want to take advantage of it as we move into the outer Solar System and beyond.
Comets and Resources
Embedded with rock, dust and organic molecules, comets are composed of water ice as well as frozen gases like methane, carbon dioxide, carbon monoxide, ammonia and an assortment of compounds containing nitrogen, oxygen and sulfur. Porous and undifferentiated, these bodies are malleable enough to make them interesting from the standpoint of resource extraction. Richard P. Terra wrote about the possibilities in a 1991 article published in Analog:
This light fragile structure means that the resources present in the comet nuclei will be readily accessible to any human settlers. The porous mixture of dust and ice would offer little mechanical resistance, and the two components could easily be separated by the application of heat. Volatiles could be further refined through fractional distillation while the dust, which has a high content of iron and other ferrous metals, could easily be manipulated with magnetic fields.
Put a human infrastructure out in the realm of the comets, in other words, and resource extraction should be a workable proposition. Terra talks about colonies operating in the Oort Cloud but we can also consider it, as he does, a proving ground for even deeper space technologies aimed at crossing the gulf between the stars. Either way, as permanent settlements or as way stations offering resources on millennial journeys, comets should be plentiful given that the Oort Cloud may extend half the distance to Alpha Centauri. Terra goes on:
Little additional crushing or other mechanical processing of the dust would be necessary, and its fine, loose-grained structure would make it ideal for subsequent chemical processing and refining. Comet nuclei thus represent a vast reservoir of easily accessible materials: water, carbon dioxide, ammonia, methane, and a variety of metals and complex organics.
Energy by Starlight
Given that comets probably formed on the outer edges of the solar nebula, their early orbits would have been more or less in the same plane as the rest of the young system, but gravitational interactions with passing stars would have randomized their orbital inclinations, eventually producing a sphere of the kind Jan Oort first postulated back in 1950. Much of this is speculative, because we have little observational evidence to go on, but the major part of the cometary shell probably extends from 40,000 to 60,000 AU, while a projected inner Oort population extending from just beyond the Kuiper Belt out to 10,000 AU may have cometary orbits more or less in the plane of the ecliptic. Out past 10,000 AU the separation between comets is wide, perhaps about 20 AU, meaning that any communities that form out here will be incredibly isolated.
Image: An artist’s rendering of the Kuiper Belt and Oort Cloud. Credit: NASA/Donald K. Yeomans.
Whether humans can exploit cometary resources this far from home will depend on whether or not they can find sources of energy. In a paper called “Fastships and Nomads,” presented at the Conference on Interstellar Migration held at Los Alamos in 1983, Eric Jones and Ben Finney give a nod to non-renewable energy sources like deuterium, given that heavy elements like uranium will be hard to come by. Indeed, a typical comet, in Richard Terra’s figures, holds between 50,000 and 100,000 metric tons of deuterium, enough to power early settlement and mining.
But over the long haul, Jones and Finney are interested in keeping colonies alive through renewable resources, and that means starlight. The researchers talk about building vast mirrors using aluminum from comets, with each 1 MW mirror about the size of the continental United States. Now here’s a science fiction setting with punch, as the two describe it:
Although the mirrors would be tended by autonomous maintenance robots, the nomads would have to live nearby in case something went wrong… Although we could imagine that the several hundred people who could be supported by the resources of a single comet might live in a single habitat, the mirrors supporting that community would be spread across about 150,000 km. Trouble with a mirror or robot on the periphery of the mirror array would mean a long trip, several hours at least. It would make more sense if the community were dispersed in smaller groups so that trouble could be reached in a shorter time. There are also social reasons for expecting the nomad communities to be divided into smaller co-living groups.
Jones and Finney go on to point out that humans tend to work best in groups of about a dozen adults, whether in the form of hunter/gatherer bands, army platoons, bridge clubs or political cells. This observation of behavior leads them to speculate that bands of about 25 men, women and children would live together in a large habitat — think again of an O’Neill cylinder — built out of cometary materials, from which they would tend a mirror farm with the help of robots and computers. Each small group would tend a mirror farm perhaps 30,000 kilometers across.
The picture widens beyond this to include the need for larger communities that would occasionally come together, helping to avoid the genetic dangers of inbreeding and providing a larger social environment. Thus we might have about 500 individuals in clusters of 20 cometary bands which would stay in contact and periodically meet. Jones and Finney consider the band-tribe structure to be the smallest grouping that seems practical for any human community. Who would such a community attract — outcasts, dissidents, adventurers? And how would Oort Cloud settlers react to the possibility of going further still, to another star?
While by no means is this is a new theory, ( note the Jules Verne story ), it presents the scenario of the very slow spreading of intelligent biological life through-out the Galaxy ( see Slow Galactic Colonization, Zoo Hypothesis and the Fermi Paradox ).
Now here’s a thought; could a potential alien Oort Cloud civilization be the basis of the Ancient Astronaut Theory and the legends of the Sumerian Gods, the Anunnaki?
There’s no hard evidence of that of course, but there are Pluto-sized and larger objects in the Kuiper Belt glowing in the infrared, a sign that was said to represent a Dyson Sphere type civilisation.
Either these are natural objects such as Brown Dwarf stars, or potential alien civilisations whom don’t care whether they are detected in the infrared or not.
And that’s disturbing.
For about three hours on Wednesday, Voyager 1 had left the solar system — before a rewritten news release headline pulled it back in. Voyager 1, one of two spacecraft NASA launched in 1977 on a grand tour of the outer planets, is now nearly 11.5 billion miles from the Sun, speeding away at 38,000 miles per hour. In a paper accepted by the journal Geophysical Review Letters, William R. Webber of New Mexico State University and Frank B. McDonald of the University of Maryland reported that on Aug. 25 last year, the spacecraft observed a sudden change in the mix of cosmic rays hitting it.
Cosmic rays are high-speed charged particles, mostly protons. Voyager 1’s instruments recorded nearly a doubling of cosmic rays from outside the solar system, while the intensity of cosmic rays that had been trapped in the outer solar system dropped by 90 percent.
The American Geophysical Union, publisher of the journal, sent out the news Wednesday morning: “Voyager 1 has left the solar system.” NASA officials, surprised, countered with a contrary statement from Edward C. Stone, the Voyager project scientist. “It is the consensus of the Voyager science team that Voyager 1 has not yet left the solar system or reached interstellar space,” Dr. Stone said. He said that the critical indicator would be a change in the direction of the magnetic field, not cosmic rays, for marking the outermost boundary of the solar system. In their paper, Dr. Webber and Dr. McDonald (who died only six days after Voyager observed the shift in cosmic rays) did not claim that Voyager 1 was in interstellar space, but had entered a part of the solar system they called the “heliocliff.” The geophysical union then sent out another e-mail with the same article but a milder headline: “Voyager 1 has entered a new region of space.”
Eventually Voyager 1 will leave the Solar System and there will be no dispute about it.
In the meantime, mainstream science will learn and post about the outer edges of the Solar System as Voyager 1 creeps along at .00002 lightspeed ( 37,500 mph ) .
Of course there are those in mainstream media and science who believe that mankind will never leave the Solar System because they proclaim that spacecraft will never be built that go faster than that.
Already the Pluto probe New Horizon traveling at 54,500 mph is breaking Voyager’s speed record and will probably leave the Solar System before Voyager does!
I’m certain in 100 years star probes will be launched toward Alpha Centauri and Tau Ceti that reach appreciable percentages of lightspeed bypassing all of our old interplanetary probes and perhaps in several centuries, mankind’s interstellar colonies will be picking up these old probes to study them, like old time capsules!
Hat tip to the Daily Grail.
Habitability is the measure of highest value in planet-hunting. But should it be?
Kepler and the other planet-finding missions have begun to bear fruit. We now know that most stars have planets, and that a surprising percentage will have Earth-sized worlds in their habitable zone–the region where things are not too hot and not too cold, where life can develop. Astronomers are justly fascinated by this region and what they can find there. We have the opportunity, in our lifetimes, to learn whether life exists outside our own solar system, and maybe even find out how common it is.
We have another opportunity, too–one less talked-about by astronomers but a common conversation among science fiction writers. For the first time in history, we may be able to identify worlds we could move to and live on.
As we think about this second possibility, it’s important to bear in mind that habitability and colonizability are not the same thing. Nobody seems to be doing this; I can’t find any term but habitability used to describe the exoplanets we’re finding. Whether a planet is habitable according to the current definition of the term has nothing to do with whether humans could settle there. So, the term applies to places that are vitally important for study; but it doesn’t necessarily apply to places we might want to go.Whether a planet is habitable according to the current definition of the term has nothing to do with whether humans could settle there.
To see the difference between habitability and colonizability, we can look at two very different planets: Gliese 581g and Alpha Centauri Bb. Neither of these is confirmed to exist, but we have enough data to be able to say a little about what they’re like if they do. Gliese 581g is a super-earth orbiting in the middle of its star’s habitable zone. This means liquid water could well form on its surface, which makes it a habitable world according to the current definition.
Centauri Bb, on the other hand, orbits very close to its star, and its surface temperature is likely high enough to render one half of it (it’s tidally locked to its sun, like our moon is to Earth) a magma sea. Alpha Centauri Bb is most definitely not habitable.
So Gliese 581g is habitable and Centauri Bb is not; but does this mean that 581g is more colonizable than Bb? Actually, no.
Because 581g is a super-earth, the gravity on its surface is going to be greater than Earth’s. Estimates vary, but the upper end of the range puts it at 1.7g. If you weigh 150 lbs on Earth, you’d weigh 255 lbs on 581g. This is with your current musculature; convert all your body fat to muscle and you might just be able to get around without having to use leg braces or a wheelchair. However, your cardiovascular system is going to be under a permanent strain on this world–and there’s no way to engineer your habitat to comfortably compensate.
On the other hand, Centauri Bb is about the same size as Earth. Its surface gravity is likely to be around the same. Since it’s tidally locked, half of its surface is indeed a lava hell–but the other hemisphere will be cooler, and potentially much cooler. I wouldn’t bet there’s any breathable atmosphere or open water there, but as a place to build sealed domes to live in, it’s not off the table.
Also consider that it’s easier to get stuff onto and off of the surface of Bb than the surface of a high-gravity super-earth. Add to that the very thick atmosphere that 581g is likely to have, and human subsistence on 581g–even if it’s a paradise for local life–is looking more and more awkward.
Doubtless 581g is a better candidate for life; but to me, Centauri Bb looks more colonizable.
A definition of colonizability
We’ve got a fairly good definition of what makes a planet habitable: stable temperatures suitable for the formation of liquid water. Is it possible to develop an equally satisfying (or more satisfying) definition of colonizability for a planet?
Yes–and here it is. Firstly, a colonizable world has to have an accessible surface. A super-earth with an incredibly thick atmosphere and a surface gravity of 3 or 4 gees just isn’t colonizable, however much life there may be on it.
Secondly, and more subtly, the right elements have to be accessible on the planet for it to be colonizable. This seems a bit puzzling at first, but what if Centauri Bb is the only planet in the Centauri system, and it has only trace elements of Nitrogen in its composition? It’s not going to matter how abundant everything else is. A planet like this–a star system like this–cannot support a colony of earthly life forms. Nitrogen is a critical component of biological life, at least our flavour of it.
In an article entitled “The Age of Substitutibility”, published in Science in 1978, H.E. Goeller and A.M. Weinberg proposed an artificial mineral they called Demandite. It comes in two forms. A molecule of industrial demandite would contain all the elements necessary for industrial manufacturing and construction, in the proportions that you’d get if you took, say, an average city and ground it up into a fine pulp. There’re about 20 elements in industrial demandite including carbon, iron, sodium, chlorine etc. Biological demandite, on the other hand, is made up almost entirely of just six elements: hydrogen, oxygen, carbon, nitrogen, phosphorus and sulfur. (If you ground up an entire ecosystem and looked at the proportions of these elements making it up, you could in fact find an existing molecule that has exactly the same proportions. It’s called cellulose.)
Thirdly, there must be a manageable flow of energy at the surface. The place can be hot or cold, but it has to be possible for us to move heat around. You can’t really do that at the surface of Venus, for instance; it’s 800 degrees everywhere on the ground so your air conditioning spends an insane amount of energy just overcoming this thermal inertia. Access to a gradient of temperature or energy is what makes physical work possible.
Obviously things like surface pressure, stellar intensity, distance from Earth etc. play big parts, but these are the main three factors that I can see. It should be instantly obvious that they have almost nothing to do with how far the planet is from its primary. There is no ‘colonizable zone’ similar to a ‘habitable zone’ around any given star. The judgment has to be made on a world by world basis.
Note that by this definition, Mars is marginally colonizable. Why? Not because of its temperature or low air pressure, but because it’s very low in Nitrogen, at least at the surface. The combination of Mars and Ceres may make a colonizable unit, if Ceres has a good supply of Nitrogen in its makeup–and this idea of combo environments being colonizable complicates the picture. We’re unlikely to be able to detect an object the size of Ceres around Alpha Centauri, so long-distance elimination of a system as a candidate for colonizability is going to be difficult. Conversely, if we can detect the presence of all the elements necessary for life and industry on a roughly Earth-sized planet, regardless of whether it’s in its star’s habitable zone, we may have a candidate for colonizability.
The colonizability of an accessible planet with a good temperature gradient can be rated according to how well its composition matches the compositions of industrial and biological demandite. We can get very precise with this scale, and we probably should. It, and not habitability, is the true measure of which worlds we might wish to visit.
To sum up, I’m proposing that we add a second measure to the existing scale of habitability when studying exoplanets. The habitability of a planet actually says nothing about how attractive it might be for us to visit. Colonizability is the missing metric for judging the value of planets around other stars.
This raises the ethical question of at which point do we as a race change the environment of an alien world’s biology in order to suit our needs?
Do we engage in biological genicide to seed a planet with Earth-life, or do we adapt ourselves to suit the exoplanet’s environment?
Or do we move on to another planet that is more “colonizable” as Schroeder suggests and totally build a habitat from scratch?
Hat tip to Centauri Dreams.
From Centauri Dreams:
Building Structures That Last
A sense of that futurity pervaded our recent sessions at the Tennessee Valley Interstellar Workshop in Huntsville. Several speakers alluded to instances in human history where people looked well beyond their own generation, a natural thought for a conference discussing technologies that might take decades if not centuries to achieve. We talked about a solar power project that might take 35 years, or perhaps 50 (much more about this in coming days).
The theme became explicit when educator and blogger Mike Mongo talked about getting interstellar issues across to the public, referring to vast projects like the pyramids and the great cathedrals of Europe. Cathedrals are a fascinating study in their own right, and it’s worth pausing on them as we ponder long-term notions. Although they’re often considered classic instances of people building for a remote future, some cathedrals were built surprisingly quickly. Anyone who has stood in awe at the magnificent lines of Chartres southwest of Paris is surprised to learn that it came together in less than 60 years (the main structure in a scant 26), though keep in mind that this was partly a reconstruction of an earlier structure that dated back to 1145.
Image: The great cathedral at Chartres.
With unstinting public support, such things could happen even with the engineering of the day, creating what historians now view as the high point of French Gothic art. Each cathedral, of course, tells its own tale. Salisbury Cathedral was completed except for its spire in 45 years. Other cathedrals took longer. Notre Dame in Paris was the work of a century, as was Lincoln Cathedral, while the record for cathedral construction surely belongs to Cologne, where the foundation stone was laid in 1248. By the time of the Reformation 300 years later, the roof was still unfinished, and later turmoil pushed the completion of the cathedral all the way into the 19th Century, with many stops and starts along the way.
Remember, too, that the cathedral builders lived at a time when the average lifespan was in the 30s. The 15-year old boy who started working on the foundation of a cathedral might have hoped to see its consecration but he surely knew the odds didn’t favor it. Humans are remarkably good at this kind of thing, even if the frenetic pace and short-term focus of our times makes us forget it. Robert Kennedy pointed out to me at the conference that the Dutch dike system has been maintained for over 500 years, and can actually be traced back as far as the 9th Century. The idea of technology-building across generations is hardly something new to our civilization.
The ‘long result’ context is an interesting one in which to place our interstellar thinking. Naturally we’d like to make things happen faster than the 4000-year plus journeys I talked about on Friday with worldships, though my guess is that as the species becomes truly spacefaring and begins to differentiate, we’ll see colonies aboard O’Neill-class cylinders holding thousands, many of the colonists being people who will spend less and less time on a planetary surface. At some point, it would be entirely natural to see one of these groups decide to head into the interstellar deep. They would be, after all, taking their world with them, a world that was already home.
Evolutionary Change in Space
Gerald Driggers is a retired engineer and current science fiction author who worked with Gerald O’Neill in the 1970s. I see him as worldship material because he has chosen for the last seventeen years to live on a boat, saying “It was the closest thing I could get to a space ship.” Driggers believes we can begin our interstellar work by getting humans to Mars, where they will be faced with many of the challenges that will attend much longer-term missions. We must, after all, build a system-wide infrastructure, mastering the complexities of power generation and resource extraction on entirely new scales, before we can truly hope to go interstellar.
And what happens to humans as they begin working in extreme environments? Evolution doesn’t stop when we leave the planet, as Freeman Dyson is so fond of pointing out. These are changes that should be beneficial, says Driggers. “Evolutionary steps toward becoming interstellar voyagers reduce the chances for human failures on these journeys. We’re going to change, and we will continue to change as we look toward longer voyages. The first humans to arrive around another star system probably won’t be like anybody in the audience today.” Responding to evolutionary change, Martians may make the best designers and builders of interstellar craft.
Image: Gerald Driggers discussing a near-term infrastructure that will one day support interstellar missions.
Get it right on Mars, in other words, and we get it right elsewhere and learn the basics of infrastructure building all the way to the Kuiper Belt, with active lunar settlements and plentiful activity among the asteroids. Along the way we adapt, we change. Driggers’ worst-case scenario has Martian settlements delayed until the mid-22nd Century, but he is hopeful that the date can be moved up and the infrastructure begun.
All of which brings me back to something Mike Mongo talked about. We are not going to the stars ourselves, but we can inspire and train people who will solve many of the technical problems going forward, just as they train the next generation. One of these generations will one day train the crew of the first human interstellar mission, or if we settle on robotics, the controllers who will manage our first probes. Placing ourselves in the context of the long result acknowledges our obligation to future generations as we begin putting foundation stones in place.
This is not the first time Paul Gilster and others have compared building interstellar ships and matching infrastructure to building pyramids and cathedrals. Both were long range projects in the human past that required multi-generational planning, money, political will and many generations of workers who never saw the end result.
Now, whether interstellar ships will be multi-generation, fast, slow or whatever in the end, they will result from human cultural biases and will be unique in this region of space.
In the end, they will be the result of many generations of human genius.
I couldn’t resist posting this today after reading it at Centauri Dreams. It’s extremely mainstream, by which the papers Paul Gilster discusses uses geological travel times for interstellar travel and the effects on the Fermi Paradox.
But he talks about the “zoo” hypothesis for our supposed lack of contact with ETIs ( no discussion of UFOs what-so-ever of course ) and I find that fascinating:
Many explanations for the Fermi paradox exist, but Hair and Hedman want to look at the possibility that starflight is so long and difficult that it takes vast amounts of time (measured in geologic epochs) to colonize on the galactic scale. Given that scenario, large voids within the colonized regions may still persist and remain uninhabited. If the Earth were located inside one of these voids we would not be aware of the extraterrestrial expansion. A second possibility is that starflight is so hard to achieve that other civilizations have simply not had time to reach us despite having, by some calculations, as much as 5 billion years to have done so (the latter figure comes from Charles Lineweaver, and I’ll have more to say about it in a moment).
Image: A detailed view of part of the disc of the spiral galaxy NGC 4565. Have technological civilizations had time enough to spread through an entire galaxy, and if so, would they be detectable? Credit: ESA/NASA.
The authors work with an algorithm that allows modeling of the expansion from the original star, running through iterations that allow emigration patterns to be analyzed in light of these prospects. It turns out that in 250 iterations, covering 250,000 years, a civilization most likely to emigrate will travel about 500 light years, for a rate of expansion that is approximately one-fourth of the maximum travel speed of one percent of the speed of light, the conservative figure chosen for this investigation. A civilization would spread through the galaxy in less than 50 million years.
These are striking numbers. Given five billion years to work with, the first civilization to develop starfaring capabilities could have colonized the Milky Way not one but 100 times. The idea that it takes billions of years to accomplish a galaxy-wide expansion fails the test of this modeling. Moreover, the idea of voids inside colonized space fails to explain the Fermi paradox as well:
…while interior voids exist at lower values of c initially, most large interior voids become colonized after long periods regardless of the cardinal value chosen, leaving behind only relatively small voids. In an examination of several 250 Kyr models with a wide range of parameters, the largest interior void encountered was roughly 30 light years in diameter. Since humans have been broadcasting radio since the early 20th century and actively listening to radio signals from space since 1960 (Time 1960), it is highly unlikely that the Earth is located in a void large enough to remain undiscovered to the present day. It follows that the second explanation of Fermi’s Paradox (Landis 1998) is not supported by the model presented.
There are mitigating factors that can slow down what the authors call the ‘explosively exponential nature’ of expansion, in which a parent colony produces daughter colonies and the daughters continue to do the same ad infinitum. The paper’s model suggests that intense competition for new worlds can spring up in the expanding wavefront of colonization. At the same time, moving into interior voids to fill them with colonies slows the outward expansion. But even models set up to reduce competition between colonies present the same result: Fermi’s lunchtime calculations seem to be valid, and the fact that we do not see evidence of other civilizations suggests that this kind of galactic expansion has not yet taken place.
Temporal Dispersion into the Galaxy
I can’t discuss Hair and Hedman’s work without reference to Hair’s earlier paper on the expansion of extraterrestrial civilizations over time. Tom had sent me this one in 2011 and I worked it into the Centauri Dreams queue before getting sidetracked by preparations for the 100 Year Starship symposium in Orlando. If I had been on the ball, I would have run an analysis of Tom’s paper at the time, but the delay gives me the opportunity to consider the two papers together, which turns out to work because they are a natural fit.
For you can see that Hair’s spatial analysis goes hand in glove with the question of why an extraterrestrial intelligence might avoid making its presence known. Given that models of expansion point to a galaxy that can be colonized many times over before humans ever emerged on our planet, let’s take up a classic answer to the Fermi paradox, that the ‘zoo hypothesis’ is in effect, a policy of non-interference in local affairs for whatever reason. Initially compelling, the idea seems to break down under close examination, given that it only takes one civilization to act contrary to it.
But there is one plausible scenario that allows the zoo hypothesis to work: The influence of a particularly distinguished civilization. Call it the first civilization. What sort of temporal head start would this first civilization have over later arrivals?
Hair uses Monte Carlo simulations, drawing on the work of Charles Lineweaver and the latter’s estimate that planets began forming approximately 9.3 billion years ago. Using Earth as a model and assuming that life emerged here about 600 million years after formation, we get an estimate of 8.7 billion years ago for the appearance of the first life in the Milky Way. Factoring in how long it took for complex land-dwelling organisms to evolve (3.7 billion years), Lineweaver concludes that the conditions necessary to support intelligent life in the universe could have been present for at least 5.0 billion years. At some point in that 5 billion years, if other intelligent species exist, the first civilization arose. Hair’s modeling goes to work on how long this civilization would have had to itself before other intelligence emerged. The question thus has Fermi implications:
…even if this ﬁrst grand civilization is long gone . . . could their initial legacy live on in the form of a passed down tradition? Beyond this, it does not even have to be the ﬁrst civilization, but simply the ﬁrst to spread its doctrine and control over a large volume of the galaxy. If just one civilization gained this hegemony in the distant past, it could form an unbroken chain of taboo against rapacious colonization in favour of non-interference in those civilizations that follow. The uniformity of motive concept previously mentioned would become moot in such a situation.
Thus the Zoo Hypothesis begins to look a bit more plausible if we have each subsequent civilization emerging into a galaxy monitored by a vastly more ancient predecessor who has established the basic rules for interaction between intelligent species. The details of Hair’s modeling are found in the paper, but the conclusions are startling, at least to me:
The time between the emergence of the ﬁrst civilization within the Milky Way and all subsequent civilizations could be enormous. The Monte Carlo data show that even using a crowded galaxy scenario the ﬁrst few inter-arrival times are similar in length to geologic epochs on Earth. Just what could a civilization do with a ten million, one hundred million, or half billion year head start (Kardashev 1964)? If, for example, civilizations uniformly arise within the Galactic Habitable Zone, then on these timescales the ﬁrst civilization would be able to reach the solar system of the second civilization long before it evolved even travelling at a very modest fraction of light speed (Bracewell 1974, 1982; Freitas 1980). What impact would the arrival of the ﬁrst civilization have on the future evolution of the second civilization? Would the second civilization even be allowed to evolve? Attempting to answer these questions leads to one of two basic conclusions, the ﬁrst is that we are alone in the Galaxy and thus no one has passed this way, and the second is that we are not alone in the Galaxy and someone has passed this way and then deliberately left us alone.
The zoo hypothesis indeed. A galactic model of non-interference is a tough sell because of the assumed diversity between cultures emerging on a vast array of worlds over time. But Hair’s ‘modified zoo hypothesis’ has great appeal. It assumes that the oldest civilization in the galaxy has a 100 million year head start, allowing it to become hugely influential in monitoring or perhaps controlling emerging civilizations. We would thus be talking about the possibility of evolving similar cultural standards with regard to contact as civilizations follow the lead of this assumed first intelligence when expanding into the galaxy. It’s an answer to Fermi that holds out hope we are not alone, and I’ll count that as still another encouraging thought on the day the world didn’t end.
I have a problem with this simply because of the economics involved; what is the motivation for ETIs to expand into the Universe to begin with?
Like, are they like humans in the sense that we go because “it’s there?”
Or are there more practical impulses involved like “can we make money” on these endeavors?
A commentor to this particular post wrote that before we colonize ( if we ever do ) the Moon, Mars and other planets in this Solar System ( and perhaps the closer stars ) that it’ll be cheaper to shoot small probes with micro cameras to these places ( NASA is already proposing sending tele-operated probes to the Lunar surface instead of astronauts ) and sell virtual reality tours. Expanded versions of Google Earth and Google Mars!
In other words, it’s cheaper to build Universes that have Star Trek and upload your mind into it than actually building such things as star-ships!
Could this be an answer to the Fermi Paradox?
Given the “big bang” of exoplanet discoveries over the past decade, I predict that there is a reasonable chance a habitable planet will be found orbiting the nearest star to our sun, the Alpha Centauri system. Traveling at just five percent the speed of light, a starship could get there in 80 years.
One Earth-sized planet has already been found at Alpha Centauri, but it is a molten blob that’s far too hot for life as we know it to survive.
The eventual discovery of a nearby livable world will turbo-boost interest and ignite discussions about sending an artificially intelligent probe to investigate any hypothetical life forms there.
But no nation will be capable of paying the freight for such a mission. Building a single starship would be orders of magnitude more expensive than the Apollo moon missions. And, the science goals alone could not justify the cost/benefit of undertaking such a gigaproject. Past megaprojects, such as Apollo and the Manhattan Project, could be justified by their promise of military supremacy, energy independence, support of the high tech industry or international prestige. The almost altruistic “we boldly go for all mankind” would probably stop an interstellar mission in its tracks.
The enormous risk and cost for starship development aside, future nations would also be preoccupied with competing gigaprojects that promise shorter term and directly useful solutions — such as fusion power plants, solar power satellites, or even fabrication of a subatomic black hole. However, the discovery of an extraterrestrial civilization at Alpha Centauri could spur an international space race to directly contact them and possibly have access to far advanced alien technology. (Except that it would take far advanced technology to get there in the first place!)
Microsystem technologist Frederik Ceyssens proposes that there should be a grassroots effort to privately organize and finance an interstellar mission. This idea would likely be received with delight at Star Trek conventions everywhere.
What’s the motivation for coughing up donations for an interstellar mission? Ceyssens says the single inspiring goal would be to establish a second home planet for humanity and the rest of Earth’s life forms by the end of the millennium. Such a project might be called “Ark II.”
“It could be our privilege to be able to lay the foundation of a something of unfathomable proportions,” Ceyssens writes.
He envisions establishing an international network of non-governmental organizations focused on private and public fundraising for interstellar exploration. The effort would be a vastly scaled up version of the World Wildlife Fund for Nature.
“Existing space advocacy organizations such as the Planetary Society or the British Interplanetary Society could play a central role in establishing the initiative, and gain increased momentum,” Ceyssens says. He proposes establishing a Noble foundation or a government wealth fund that can be fed with regular donations over, literally, an estimated 300 years it would take to have the bucks and technology to build a space ark.
ANALYSIS: Uniting the Planet for a Journey to Another Star
This slow and steady approach would avoid having a single generation make huge donations to the cause. Each consecutive generation would contribute some intellectual and material resources. A parallel can be found in the construction of the great cathedrals in late medieval Europe. An incentive might be that one of the distance descendants of each of the biggest donors is guaranteed a seat on the colonization express.
Unlike the British colonies in the great Age of Discovery, it is impractical to think of another star system as an outpost colony that can trade with Imperial Earth. There is no financial potential to investors.
Comparing an interstellar voyage to building cathederals because it could be a multi-generation project is a valid point, although it doesn’t seem to take into account advancing technology in robotics and rocket propulsion that can shorten the time needed to construct such a mission.
Actually, I wouldn’t be a bit surprised if another Earth-type world was discovered at Alpha Centauri, an interstellar mission would be mounted by the end of the 21st Century by a James Cameron-type and it wouldn’t take 80 years to get there either!
Hat tip to Graham Hancock.com.
From Centauri Dreams:
Stretch out your time horizons and interstellar travel gets a bit easier. If 4.3 light years seems too immense a distance to reach Alpha Centauri, we can wait about 28,000 years, when the distance between us will have closed to 3.2 light years. As it turns out, Alpha Centauri is moving in a galactic orbit far different from the Sun’s. As we weave through the Milky Way in coming millennia, we’re in the midst of a close pass from a stellar system that will never be this close again. A few million years ago Alpha Centauri would not have been visible to the naked eye.
The great galactic pinball machine is in constant motion. Epsilon Indi, a slightly orange star about an eighth as luminous as the Sun and orbited by a pair of brown dwarfs, is currently 11.8 light years out, but it’s moving 90 kilometers per second relative to the Sun. In about 17,000 years, it will close to 10.6 light years before beginning to recede. Project Ozma target Tau Ceti, now 11.9 light years from our system, has a highly eccentric galactic orbit that, on its current inbound leg, will take it to within the same 10.6 light years if we can wait the necessary 43,000 years.
And here’s an interesting one I almost forgot to list, though its close pass may be the most intriguing of all. Gliese 710 is currently 64 light years away in the constellation Serpens. We have to wait a bit on this one, but the orange star, now at magnitude 9.7, will in 1.4 million years move within 50,000 AU of the Sun. That puts it close enough that it should interact with the Oort Cloud, perhaps perturbing comets there or sending comets from its own cometary cloud into our system. In any case, what a close-in target for future interstellar explorers!
I’m pulling all this from Erik Anderson’s new book Vistas of Many Worlds, whose subtitle — ‘A Journey Through Space and Time’ — is a bit deceptive, for the book actually contains four journeys. The first takes us on a tour of ten stars within 20 light years of the Sun, with full-page artwork on every other page and finder charts that diagram the stars in each illustration. The second tour moves through time and traces the stars of an evolving Earth through text and images. Itinerary three is a montage of scenes from known exoplanets, while the fourth tour takes us through a sequence of young Earth-like worlds as they develop.
Anderson’s text is absorbing — he’s a good writer with a knack for hitting the right note — but the artwork steals the show on many of these pages, for he’s been meticulous at recreating the sky as it would appear from other star systems. It becomes easy to track the Sun against the background of alien constellations. Thus a spectacular view of the pulsar planet PSR B1257+12 C shows our Sun lost among the brighter stars Canopus and Spica, with Rigel and Betelgeuse also prominent. The gorgeous sky above an icy ocean on a planet circling Delta Pavonis shows the Sun between Alpha Centauri and Eta Cassiopeiae. Stellar motion over time and the perspectives thus created from worlds much like our own are a major theme of this book.
From Epsilon Eridani, as seen in the image below, the Sun is a bright orb seen through the protoplanetary disk at about the 4 o’clock position below the bright central star.
Image: The nearby orange dwarf star Epsilon Eridani reveals its circumstellar debris disks in this close-up perspective. Epsilon Eridani is only several hundred million years old and perhaps resembles the state of our own solar system during its early, formative years. Credit: Erik Anderson.
Vistas of Many Worlds assumes a basic background in astronomical concepts, but I think even younger readers will be caught up in the wonder of imagined scenes around planets we’re now discovering, which is why I’m buying a copy for my star-crazed grandson for Christmas. He’ll enjoy the movement through time as well as space. In one memorable scene, Anderson depicts a flock of ancient birds flying through a mountain pass 4.8 million years ago. At that time, the star Theta Columbae, today 720 light years away, was just seven light years out, outshining Venus and dominating the sunset skies of Anderson’s imagined landscape.
And what mysteries does the future hold? The end of the interglacial period is depicted in a scene Anderson sets 50,000 years from now, showing a futuristic observation station on the west coast of an ice-choked Canada. The frigid landscape and starfield above set the author speculating on how our descendants will see their options:
Will the inhabitants of a re-glaciating Earth seek refuge elsewhere? Alpha Centauri, our nearest celestial neighbor, has in all this time migrated out of the southern skies to the celestial equator, where it can be sighted from locations throughout the entire globe. It seems to beckon humanity to the stars.
And there, tagged by the star-finder chart and brightly shining on the facing image, is the Alpha Centauri system, now moving inexorably farther from our Sun but still a major marker in the night sky. Planet hunter Greg Laughlin has often commented on how satisfying it is that we have this intriguing stellar duo with accompanying red dwarf so relatively near to us as we begin the great exoplanet detection effort. We’re beginning to answer the question of planets around Alpha Centauri, though much work lies ahead. Perhaps some of that work will be accomplished by scientists who, in their younger years, were energized by the text and images of books like this one.
What I find facinating is a comment by a reader ( kzb ) of this post concerning the Fermi Paradox:
One frequently-seen explanation of the Fermi paradox is that interstellar travel is just too difficult: the distances are so great that no intelligent species has ever cracked the problem.
This article highlights an argument against this outlook. One scale-length towards the galactic centre, and the space density of stellar systems is 2.7 times what it is around here. Two scale lengths in and the density is 7.4 times greater. The scale-length of our galaxy is around only 2.1-3kpc according to recent literature.
Intelligent species that evolve in the inner galactic disk will not have the same problem that we have. Over galactic timescales, encounters between stellar systems within 1 light-year will not be uncommon.
I think you can see what I am saying, and I think this is one aspect of the FP discussion that is poorly represented currently.
And Erik Anderson’s response:
@ kzb: I give an overview of the Fermi Paradox on page 110 and I didn’t miss your point. It was definitely articulated by Edward Teller, whom I explicitly quote: “…as far as our Galaxy is concerned, we are living somewhere in the sticks, far removed from the metropolitan area of the Galactic center.”
Of course this precludes the explanations that there is no such thing as speedy interstellar travel ( be they anti-matter or warp drives ) and UFOs are really just mass hallucinations.
However Anderson’s book is novel in its’ treatment of interstellar exploration over vast timescales and that closer to the Galactic Center, possible advanced civilizations could have stellar cultures due to faster stellar movements and much shorter distances between stars. And I find that novel in an Olaf Stapledon kind of way!
That and the fact as we are discovering using the Kepler and HARP interstellar telescopes multiple star systems that have their own solar systems and many of them could have intelligent life lends credence to Mr. Anderson’s themes.
So I might treat myself to an early Christmas present by purchasing Anderson’s book!