It’s interesting to consider, as Hector Socas-Navarro does in a new paper, the various markers a technological civilization might leave. Searching for biosignatures is one thing — we’re developing the tools to examine the atmospheres of planets around nearby stars for evidence of life — but how do we go about looking for astronomical evidence of a technological society, one found not by detection of a directed radio or laser beacon but by observation of the stars around us?
Various candidates have been suggested, the most famous being the Dyson sphere, in which an advanced civilization might choose to trap the energy output of its entire star, and we’re in the era of searches for such objects, as witness the Glimpsing Heat from Alien Technologies effort at Penn State. But there are many other suggestions, ranging from detecting antimatter used for power or propulsion, analyzing Fast Radio Bursts for evidence of manipulation as a propulsion system, and looking at depletion of metals in a stellar disk (asteroid mining).
Image: Astronomer Hector Socas-Navarro (Instituto de Astrofísica de Canarias). Credit: IAC.
What Socas-Navarro has in mind is a technology we have already begun to deploy and will presumably see in accelerated use. Delightfully, he has named his idea ‘the Clarke Exobelt’ (CEB) in a nod to the father of the communications satellite, an apt choice given that he defines the idea as the collection of objects, including non-functional ones, in geostationary and geosynchronous orbits around a planet. An astronomer at the Instituto de Astrofísica de Canarias, Socas-Navarro believes that because there is no natural ‘preference’ for this orbit, the detection of a population of objects within it would be highly suggestive of an artificial origin.
Published in The Astrophysical Journal, the paper has caught the eye of enough Centauri Dreams readers that I have five copies of it in my inbox. Seeing the Clarke name associated with it is enough to pique my interest — would that we had Sir Arthur’s own thoughts on the matter! Socas-Navarro points out that there is a certain economy in searching for Clarke Exobelt objects, in that current techniques to detect exoplanets and exomoons should also be able to detect a large enough cluster of technologies in geosynchronous orbits.
The paper, then, is a suggestion that we begin looking for this kind of technosignature amongst the other possibilities. The challenge is in the extrapolation, for to be detectable with our current and near-future technologies, such an Exobelt would have to be densely populated. Our own Clarke belt is relatively sparse, with two-thirds of existing satellites in low orbits. Socas-Navarro believes, however, that the realm of geostationary and geosynchronous satellites is destined to grow, and his simulations show that if it does, it will at some point become detectable:
The geostationary orbit, often named after Clarke, who explored its practical usefulness for communication purposes (Clarke 1945), is specially interesting because satellites placed there will remain static as seen from the ground reference frame. However, the available space in that orbit is limited. A moderately advanced civilization might eventually populate it with a relatively high density of objects, making it advisable (cheaper in a supply-and-demand sense) to use geosynchronous orbits when possible for those satellites whose requirements are less strict and allow for some degree of movement along the North-South direction on the sky. Over time, one might expect that societal needs would eventually drive an increase of object density in a band around the geostationary orbit, forming a CEB.
Using Earth’s current satellite population as a reference, the author creates a Clarke Exobelt model using as parameters radius, width, face-on opacity and inclination of the equatorial plane with respect to the plane of the sky (a CEB viewed edge-on would have an inclination of 90 degrees). The model excludes eccentric orbits and assumes all objects at the same orbital altitude. Using it, Socas-Navarro explores a Clarke Exobelt as it appears in the light curve of a star.
Our current Clarke belt would be orders of magnitude below the detection threshold for observers around other stars if they were using technologies similar to ours. Socas-Navarro argues that the Clarke belt around Earth is showing exponential growth, such that extrapolating it into the future would make it visible to other-world observers by the year 2200. The author considers this a reasonable extrapolation, though one highly dependent on future technology choices including, for example, space elevator systems, which could dramatically change access to these orbits and accelerate the emergence of a detectable signature.
As I read the Socas-Navarro paper, I was struck by its reliance on finding a civilization in a state of development close to our own. He is quite clear on this, saying his intention is “to explore the consequences of a direct extrapolation of our current trends,” acknowledging that even in our own near-future, we may take a different route in the population of our own Clarke belt.
Thus far, searches for technosignatures have assumed advanced technologies of the sort needed to dismantle planets and build Dyson spheres, although there is some discussion of atmospheric change through pollution or other civilizational activities. Despite the odds against finding a civilization just at the stage when it relied heavily on a Clarke Exobelt to maintain its essential services, the author thinks it prudent to keep our eyes open for this technosignature because of the deep uncertainties of forecasting what far more advanced cultures would do.
And we are improving the methods that might help us find such a Clarke Exobelt, even though they are not fine-tuned for such. Noting the difficulty of distinguishing between a CEB and a natural planetary ring system, the paper adds this:
While the similarity between a CEB and a ring system poses an initial difficulty, it also opens new opportunities. Existing interest in the physics of exorings and exomoons means that large efforts will be devoted in future photometric missions to examine rocky planet transits for evidence of such objects. This paper shows how future positive detections of orbital material may be further scrutinized for evidence of CEBs, making the search for moderately advanced technologies “piggyback” on such missions.
Thus we have a technosignature to add to our roster. One thing finding a CEB would imply is a still-functioning civilization — active maintenance would be required to keep objects in a crowded CEB within their proper orbits over long time-periods — which could not necessarily be said of a detected Dyson sphere, conceivably a relic of a long-dead culture. CEB detection is, as the author acknowledges, a ‘long shot.’ But having the widest range of technosignatures examined in the literature is only prudent. After all, who knows what we’ll find next?
The paper is Socas-Navarro, “Possible Photometric Signatures of Moderately Advanced Civilizations: The Clarke Exobelt.” The Astrophysical Journal Vol. 855, No. 2 (13 March 2018). Abstract / Preprint.
The premise of a dense CEB is suspect IMO. Exponential growth based on data that stops at 1738 satellites with a curve fit that doesn’t look right to me.
I am fairly sure that there is a limit to comsat density and that the trend of geosynchronous satellites is to larger ones, rather than increasing numbers. Because of the latency, we are moving to swarms of LEO satellites, and of course, ground-based fiberoptic cable.
As we expect that technological civs will most likely be millions of years in advance of us, premise requires that either we get very lucky finding a near equivalent civ to us, or that such satellites remain abandoned in orbit. Is that likely?
Clarke himself favored an orbital ring that coupled space elevators (The Fountains of Paradise, 3001: The final Odyssey). How wide would such a ring need to be to provide the necessary opacity?
The confluence of requirements – similar technology level civ, and the requirement for a dense CEB to meet their needs seem like a very long shot.
Why assume advanced aliens would necessarily build a Dyson sphere or anything like it? Maybe they could somehow regulate their star to keep it, perhaps even permanently, in their state of maximum efficiency.
What would the planets in a tidally locked system liked Trappist 1 look like? The belts would become further away from the planets as you progressed further out in the resonant chain, assuming that the whole system would eventualy be colonized and developed. Would the outer, cooler planets be easier to develop or the inner ones with more energy from the M Dwarf? Maybe we need to look for something that has been planned out for 1000’s of years, instead of our current treand of popularised communications.
We humans seem so prone to hero worship. A Dyson sphere has never been built nor even designed. The whole idea has never been evaluated – as far as I can find – in engineering terms. “Warp drive” is a fantasy from popular entertainment. The cold fact is that we have cluttered the orbital space around earth with junk. We talk about “terraforming” Mars while ignoring the decay of the cities on earth. Interstellar travel may be a impossible dream due to the density of density of particulate matter between the stars. Maybe I am getting old – actually, I have already – but so much of all this seems so horribly inane.
I’d just like to point out that the literal interpretation of the Dyson sphere as a solid shell of matter around a star is not at all what Dyson originally had in mind. Such “Dyson shells” have been examined in engineering terms, and found to be practically impossible—no existing or theorized material is strong enough to construct one, and there probably isn’t even enough mass in a solar system to construct one. Dyson himself responded to the idea by saying, “A solid shell or ring surrounding a star is mechanically impossible. The form of ‘biosphere’ which I envisaged consists of a loose collection or swarm of objects traveling on independent orbits around the star.”
Dyson’s actual proposal was that advanced civilization might build a loose swarm of solar power satellites orbiting a star to capture a percentage of its power output. There are no problems gradually building such a swarm, at least until you run out of building materials. This is the sort of megastructure that SETI researchers have in mind when they talk of glimpsing the heat signatures of advanced civilizations, not a solid “Dyson shell”.
>“Warp drive” is a fantasy from popular entertainment.
No serious studies into starflight (like Project Daedelus) propose we use “warp drive”. Talking about warp/jump/hyper drive is basically a strawman at this point. There are more than enough propulsion ideas based on real (not “reel”) physics to investigate and/or poke holes in!
> The cold fact is that we have cluttered the orbital space around earth with junk.
Space programs have of course left actual junk in orbit, from spent rocket stages and defunct satellites to stray bolts and flecks of paint, but most satellites have entirely worthwhile uses. Our space programs have greatly extended our knowledge both of space and the Earth we share. It’s safe to say that our modern lifestyle couldn’t continue without satellites. That’s pretty decent for “junk”.
This sort of negative attitude towards human endeavor seems to be chic these days, but I think it’s a lot more constructive to see both the positive and negative impacts of human activities and to plan ahead to see how we can minimize the latter.
>Maybe I am getting old – actually, I have already – but so much of all this seems so horribly inane.
There is nothing inane about discussing “blue sky” ideas like Dyson swarms and detecting alien civilizations. To be intellectually healthy, we need to be free to explore far-off possibilities instead of just confining ourselves to the immediate problems of everyday life. How many important scientists were inspired by concepts right out of science fiction, after all?
I’d just like to point out that the literal interpretation of the Dyson sphere as a solid shell of matter around a star is not at all what Dyson originally had in mind. Such “Dyson shells” have been examined in engineering terms, and found to be practically impossible—no existing or theorized material is strong enough to construct one, and there probably isn’t even enough mass in a solar system to construct one. Dyson himself responded to the idea by saying, “A solid shell or ring surrounding a star is mechanically impossible. The form of ‘biosphere’ which I envisaged consists of a loose collection or swarm of objects traveling on independent orbits around the star.”
Dyson’s actual proposal was that advanced civilization might build a loose swarm of solar power satellites orbiting a star to capture a percentage of its power output. There are no problems gradually building such a swarm, at least until you run out of building materials. This is the sort of megastructure that SETI researchers have in mind when they talk of glimpsing the heat signatures of advanced civilizations, not a solid “Dyson shell”.
No serious studies into starflight (like Project Daedelus) propose we use “warp drive”. Talking about warp/jump/hyper drive is basically a strawman at this point. There are more than enough propulsion ideas based on real (not “reel”) physics to investigate and/or poke holes in!
Space programs have of course left actual junk in orbit, from spent rocket stages and defunct satellites to stray bolts and flecks of paint, but most satellites have entirely worthwhile uses. Our space programs have greatly extended our knowledge both of space and the Earth we share. It’s safe to say that our modern lifestyle couldn’t continue without satellites. That’s pretty decent for “junk”.
This sort of negative attitude towards human endeavor seems to be chic these days, but I think it’s a lot more constructive to see both the positive and negative impacts of human activities and to plan ahead to see how we can minimize the latter.
There is nothing inane about discussing “blue sky” ideas like Dyson swarms and detecting alien civilizations. To be intellectually healthy, we need to be free to explore far-off possibilities instead of just confining ourselves to the immediate problems of everyday life. How many important scientists were inspired by concepts right out of science fiction, after all?
Beautifully said Mr Phoenix.
It’s futile to expect to solve all the problems here before going elsewhere. In fact, it’s unrealistic and childish. There’ll be no steady state civilization with living inhabitants in a viable environment. It won’t happen because solving problems generates conditions for further problems and environments change. Europeans didn’t perfect their homelands before setting out for other places, and that wasn’t due to some evil trait of Western white people; it’s true of every society that has expanded — and every one that hasn’t.
Fixing our cities before terraforming Mars is a childish, totalitarian demand however benevolent it sounds.
That is so plausible… good insight. It made me think about rearranging
E = m*c*c
to
m = E/c*c
is such a reversal possible? Any useful mass quantity would require a lot of energy of course
Do any physicists think we can one day capture starlight to synthesise needed elements? I guess plants do it, if chemical energy counts. Thinking outside my cage here, but I wonder what observable techno-signatures would such activity generate? I am thinking of Prizbylski’s star .. so strange
In a word—yes! Mass-energy equivalence does indeed work both ways. A small amount of mass can be converted into a LARGE amount of energy (per E = m * c^2). But you can also convert a large amount of energy into a tiny bit of matter. As you said, this takes a LOT of energy for only a tiny amount of created matter.
Surprisingly, we already have built energy-to-matter machines. Whenever we smash high-speed particles together in a particle accelerator like the LHC, some of the energy of the collision is transformed into a shower of other particles (which then show up on our detectors).
Well, yes and no. If you mean building up reservoirs of synthetic matter for building purposes etc. after we run out available matter in asteroids and planets, probably not. We can easily calculate how much mass we could produce this way, assuming we captured all the energy from the star an converted into to matter with 100% efficiency. Every second, the sun radiates 384.6 yottajoules of energy. Using M = E / C^2, we get about four thousand million metric tons of mass per second.
This sounds like a lot, but it only adds up to one Earth mass for every 35 million years of continuous operation. It would take 2000 years of continuous operation to equal the mass available in the asteroid belt alone, let alone what we could access by disassembling planets and moons. So it’s not much at all compared to the effort it takes. We’ve probably already used up all the available mass in the solar system building our Sun-enveloping machine, after all!
We’d probably be better off mining mass from the Sun and attempting to synthesize heavier elements through nuclear fusion. The other problem is that when matter is created, equal amounts of particles and anti-particles are created, leaving the antimatter as a dangerous and explosive byproduct if all you want is raw materials.
Antimatter itself, however, is very much needed if your civilization makes large-scale use of antimatter. Scientists have proposed that we could build solar-powered antimatter farms around the sun to supply the needed antimatter, which would indeed convert captured solar energy into minute amounts of (anti)matter.
This idea is not new to science fiction writers. The earliest mention of creating desired matter out of energy I am aware of was in Philip Francis Nowlan’s 1928 novella Armageddon 2419 A.D. (the original Buck Rogers story!), in which the synthetic elements “inertron” and “ultron” are made by pulling “ultronic vibratons” out of the ether and building them up into atoms.
It would generate the same signatures as any other Dyson swarm type activity—infrared radiation from the waste heat emitted by the megastructure. Nothing is 100% efficient, unlike my thought experiment, and particle-antiparticle creation is notoriously inefficient.
I had not thought about colliders in that way. Thank you for giving this your attention. Its the sort of thing that would get too much “air-time” in my gob… now I can let it go :)
And I agree, there are better ways to get building materials. But anti-matter would be valued as you point out. I have to wonder if it is possible to set the dial to element 39 or whatever. I was thinking more about high-value elements being ‘on-demand’. A 3D-printer that produces an atom-for-atom replica would be nicer than all plastic. I remember fondly that Robot who cooked up a life-time supply of Kentucky whisky for Earl Holliman. There could be other uses too.
Also, i just read this (without understanding!) https://phys.org/news/2018-06-periodic-table.html
Perhaps SETI should include searching for “continents of stability” in its strategy. If we even would know one when we saw it
This is an interesting question. As far as I know, the answer appears to be no—all the methods we’ve used to transform energy to matter result in particle/antiparticle pairs of basic subatomic particles, like protons and antiprotons. Physicists have done this with particle accelerators and, a few years ago, an antimatter “gun” that creates positrons (the antimatter counterpart to electrons) by firing a laser pulse at a tiny gold disk.
This means the only element we can create is light hydrogen, by pairing one proton with one electron. Or, more usefully, we can pair one antiproton with one positron to produce a stable atom of anti-hydrogen. We would need to use nuclear fusion to create any elements with a higher atomic number. Incidentally, this is exactly how all elements heavier than hydrogen and helium formed in nature—nucleasynthesis inside stars and supernovae. But if we need to use fusion anyway, we should just mine hydrogen and helium from a star via “star lifting” and use it as feedstock for our reactors.
These forms of fusion would also be vastly more difficult than the reactions proposed for terrestrial power production—most are too difficult for current terrestrial reactors; the larger the nuclei you attempt to fuse, the harder it will be (due to greater electrostatic repulsion from the larger numbers of protons); and not all reactions will produce energy (creating elements heavier than iron consumes energy, which is why this only happens in supernovae).
Interestingly, this also means it would be quite difficult to create anti-elements heavier than hydrogen. We are unlikely to ever see anti-carbon, let alone anti-gold or anti-uranium.
We don’t need to create atoms from nothingness for that, just find some way to get them to hook up into the exactly chemical configurations we want. Outside of Star Trek’s replicators, we still don’t have a good idea how to do it though. :)
And we don’t know how Robbie did all that manufacturing behind the scenes. Perhaps he just built a hi-tech distillery. His response to Altaira when she requests him to place star sapphires on her next dress indicates he still has to crystallize them. Probably his real advantage is that he does all the hard work, tirelessly, without bothering his owners over the details.
That is an interesting article. Insofar as my limited knowledge goes, the authors are suggesting that there may be elements with atomic masses greater than 300 that are stable, and the the quarks within these atoms will not be bound into the triplets that make up protons and neutrons, making them a new form of “quark matter”. Alas, much of this is above my head like a cirrus cloud at this point.
I’d heard of the idea that there might be “islands of stability” in extremely heavy elements not yet discovered (the upper end of the known periodic table consists of unstable, radioactive elements), but the prediction that these nuclei will contain unbound quarks is entirely new to me.
I’m calling this selective data analysis regarding the satellite projections. However incomplete the UCS satellite database is, it has data going back to 1987. I extracted the data for GEO satellites and find a best fit is polynomial (R^2=0.999), not exponential(R^2 = 0.969). Does this make a difference?
The exponential projection for the year 2200 results in 2.1E12 satellites, whilst a polynomial results in just 32,000, a factor of 10^8 difference.
While this does not invalidate the overall idea, it does cast doubt over a civ’s ability to create such a satellite ring. With exponential growth, in the year 2200, there would be 200 billion satellites placed in GEO. They are certainly not being launched by rockets from the planet at that rate! To put that number in perspective, current global shipping cargo tonnage is around 10^9 tonnes.
[Even using the truncated data 2002-2017, the exponential R^2=0.991 vs the polynomial R^2 = 0.999. The rate of satellite launches is at best rising linearly at around 34% per year, so that in 2200, there would be 245 launches, or 1 a day.]
We may do better with different technologies, e.g. space-based manufacturing or low-cost spaceplanes or reusable rockets, but I don’t see any way to justify the proposed satellite population over the next 200 years based on a small set of data and dubious extrapolation. ]
I have to agree with Alex Tolley. We would have to get a lucky find of a civilization that was near to our level of technological advancement. An ET civilization that was a million years more advanced than ours would have interstellar travel and very advanced satellites which would be few in number. Their space stations and satellites would have very advanced remote sensing capabilities. They could easily capture and collect all the old satellites and put them in a museum removing any dangerous space junk, so not much would be there to detect from Earth. This idea like the Dyson sphere is too trapped in the technology and zeitgeist of the past.
we’re developing the tools to examine the atmospheres of nearby stars for evidence of life
Do you mean exoplanet atmospheres?
Yes indeed. I think I’ll re-phrase that in the original text. Thanks.
Thanks, Paul, for such a nice review of my paper. It’s a very good summary and I feel honored to have it discussed in this forum. I have also read the responses and perhaps I can add some comments. First of all, I’d like to clarify that I’m not claiming that such crowded CEBs exist. I simply asked myself the question “could we observe the artificial satellite population of inhabited exoplanets? What is the minimum density required for observability?” This paper is my answer to that question. If one thinks that such CEBs don’t exist, then this is an interesting negative result. In that case we’d know we can’t detect them and that’s it, case closed, let’s move on. However, I don’t think that anybody can make that claim for sure. And, since we can’t be 100% sure that CEBs don’t exist and given that it doesn’t cost us anything, I don’t see any reason why we shouldn’t check the data and look for the signatures proposed in the paper. Furthermore, the 1e-4 filling factor result is for observations with current telescopes. It’s reasonable to assume that, in the future, we may have better capabilities and that number should decrease (we would be sensitive to less populated CEBs). Now I think about it perhaps I should have done the numbers for the JWST too but I wanted to keep the paper as “real” as possible. Twenty years ago we were finding the first exoplanets and we could only hope to detect hot jupiters. At that time, detecting Earth-like planets in habitable zone would have seemed pure utopia. Yet, here are we are twenty years later doing just that. I’d also like to mention that, while we are thinking in terms of our own satellites, we have no idea of what ETIs are doing with their orbital devices. A 1e-4 CEB could be the result of billions of satellites or it could be made of a bunch of cities, placed in geo orbits to facilitate supply and waste transportation to and from the surface via space elevators. Or it could be something completely different that we can’t even think of at this point. It’s virtually impossible to predict technology evolution over timescales of decades for our own species (even for someone like Arthur C Clarke), let alone for aliens with whom we share absolutely no common background. Thus, it is very risky to make absolute claims on technomarkers. Finally, regarding the data on current Earth satellites, it should be noted that publicly available databases are incomplete because they don’t include classified devices (which may constitute a significant fraction) and most don’t include decommissioned satellites. I cited my source in the paper, the compilation made by the UCS. It’s free and publicly accessible. In any case, it’s not a very important matter. I just included this in the paper as a request of the referee and we thought it was a good argument that our satellite population may be a factor to consider in the debate of active vs passive SETI. If (and that’s a big “if”, of course) we keep populating the Earth’s belt, we increase our chances of being detected. The 2200 extrapolation (rough as it may be) is based on an observer with our own current technology. Alien observers with better capabilities might be able to detect us before that.
Ok, sorry for the long post. I guess I have a lot of fun thinking and discussing about these issues
Best regards and kudos to the centauri-dreams.org crew for their very insightful and provocative articles, always fun to read
Hector
What a pleasure to have you join us, Dr. Socas-Navarro. Many thanks for these insights! I look forward to your next paper.
I have a suggestion for one. There are most likely(correct me if I am wrong)no stable Lagrange points anywhere in the TRAPPIST-1 system because all of the planets are all so closely packed together. By combining all of the current(and possibly the K2 campaign 19 data if there is still enough propellant to run it)and then stacking all of the data for every Lagrange point into one light curve, you might be able to build up the signal to a point where you can make a definitive detection.
I think that, while Dr. Socas-Navarro’s thesis is a “hit or miss” one, such searches are worthwhile. I doubt whether such ETI activity–building CEBs–can be mathematically predicted one way or another, because space exploration, like wars, runs on “gusts of emotion,” and space exploitation (and exploitation of planet-synchronous orbits in particular) proceeds along lines of profitability for communications of numerous kinds, defense communications and observation needs, and utility for meteorological observation, and:
All of this is, I know, human-centric, but any other civilizations that would utilize such orbits must, in at least some cultural and/or economic ways, be similar to our own, regardless of their peoples’ physical forms. Even for our own future, some–and not just Arthur C. Clarke in his novel, “The Fountains of Paradise”–have predicted that an artificial ring system, either solid or consisting of space colonies and various utility spacecraft, may eventually be built around the Earth at (or closely “straddling”) the geosynchronous altitude. In “Cosmos” (the book as well as the television series), Carl Sagan mused upon (and showed in an illustration) the possibility that we may find such rings around the planets of some advanced civilizations. Also:
In concert with space elevator “spokes” from the planetary surface, such rings could also provide, in addition to structural stability for the elevators, a means to easily leave and reach the planets with minimal expenditure of energy. A lunatron-type electromagnetic launcher running along the outer edge of such a ring could enable rocket-less departures and arrivals (for the latter, the carriage could match velocities with an arriving vehicle and effect a docking, then electromagnetically brake both to an “at rest” condition with respect to the ring). If we can conceive of such uses for planet-synchronous orbits, someone older and more accomplished may have done so, so *not* looking for signatures of such things just because we haven’t (yet!) utilized our Clarke Belt so extensively would be self-defeating.
Another thought: It could be useful, to give us an idea of what we might see around a distant exoplanet (at least in terms of the light curves, if not actual images), if our solar system probes looked at the Earth from various distances, at the appropriate wavelengths to detect our own Clarke Belt. This is already done routinely to calibrate the probes’ cameras and instruments (as well as to add more navigation fixes for plotting accurate trajectories, particularly for probes that utilize Earth flybys to either gain or lose [solar] orbital energy, as needed), and:
At certain ranges and phase angles (Sun-Clarke Belt-spacecraft), the spacecraft should detect “sparkles,” especially in forward-scattered sunlight, when the Sun is behind–or nearly so–the Earth, from the spacecraft’s viewpoint. (Jupiter’s gossamer ring was televised by the Voyagers in this way–an irregularity [intensity drop] in Pioneer 11’s Jovian radiation belt data suggested that a ring might be there, but in forward-scattered sunlight, the very “fine-particled” ring couldn’t be seen; even the Hubble Telescope has to “look hard” to see it.) As well:
The Clarke Belt satellites’ sparkles might not be visible in photographs taken by the deep space probes, but by using binning techniques to collect the photon “hits” on their cameras’ CCD detectors, plotted light reflection curves, plotted with respect to the changing phase angle, should show some sign of the sparkles (especially if an occulting disc, as in a spacecraft’s coronograph, was used to block out the Earth on one side or the other, leaving part of the Clarke Belt in view [at the right distance, the disc would cover the entire Earth, leaving both sides of the Clarke Belt in view]). Many if not most views of exoplanets can, at some time, utilize the forward-scattered light of their stars (unless the planes of the planets’ orbits are nearly “in plan view, from the north or south” from our point of view).
Good point, take a look at the early views of the rings of Saturn.
Early Views of Saturn: Galileo and Huygens over Two Saturn Years.
http://planetaryweather.blogspot.com/2013/03/early-views-of-saturn-galileo-and.html?m=1
4.bp.blogspot.com/-BIfJhYi9hHk/UVC3JCw26PI/AAAAAAAABXo/j21MiU0R4lk/s1600/huygens_phases1.gif
Thank you, and for posting those; I had seen Galileo’s drawings (he likened what he saw around Saturn to ears), but not Huygens’. Had Uranus’ rings been edge-on at the time of the 1977 stellar occultation which revealed their presence, the ring plane’s tilt with respect to the planet’s apparent motion across the star could easily have resulted in light “dips” on only one side of the planet–and possibly only due to one or two of the densest rings–which would have made them look like moons (or clumped clouds of debris) instead of rings. Our own Clarke Belt should also look asymmetrical, because the geosynchronous satellites aren’t distributed evenly, like a sparse ring.
One extreme idea to reduce AGW is to put sunshades between the Earth and the sun. It might, therefore, be worth looking for such an object by other means than transits. As the shade would be at the L1 Lagrange point between the planet and the star, this would seem likely an artificial object. It might be dark as it converts the star’s energy for planetary use, or simply reflective, allowing for visual detection.
But as with the satellites argument, it does require that the civ be in the highly unlikely technology stage only a little advanced than ourselves.
Why would such things only be expected from a slightly more advanced (than humanity) civilization? The Pyramids, the Great Wall of China, and many other ancient structures are still here. Such in-space structures, assuming that they became obsolete (which might or might not be the case), could remain there as monuments to the societies’ past achievements, or because they were re-purposed by later generations, or because removing them would be difficult and leaving them “abandoned in place” causes no problems to the current generations.
If a civ solves it GW problem (assuming they had one) they would dismantle the structure. The problem with this sort of geoengineering fix is that it can only solve part of the problem. Acidifying the oceans, lakes and rivers while the planet has its insolation decreased is not a long term solution. If it is, then it would result in an impoverished biosphere. It might look like Giedi Prime.
OTOH, if the biosphere collapses, and with it the civ, then maybe the shield would remain as a “monument”.
Even though Lagrange points are attractors, a swarm solar shield would lose its structure unless maintained. That may be OK if it is designed as a cloud, rather than a thin shield. A monolithic shield would drift in orientation. That may be OK if it remains in place and all we want is to observe it.
It would be easier and cheaper to just turn a big shield edge-on to the star (in case it might be needed again in their future), with a long cable or thin structure (with a mass at its far end) attached to the shield’s edge to give it passive, gravity gradient orientation in the edge-on attitude. If it rotated slowly around its long, star-pointing axis for any reason, it wouldn’t change the tiny amount of starlight that the edge of the shield would block. Such an often-unused structure could even carry stellar observation instruments to give its makers’ planet early warning of stellar coronal mass ejections, as do our Sun/Earth L1 spacecraft.
Luc Arnold also has some thoughts on the subject:
http://www.obs-hp.fr/~larnold/homepage.html
Talk about running out of materials…
The World Is Running Out of Sand | The New Yorker
https://www.newyorker.com/magazine/2017/05/29/the-world-is-running-out-of-sand
May 29, 2017 – It’s one of our most widely used natural resources, but it’s scarcer than you think. … A report said that sand and gravel mining “greatly exceeds natural renewal rates.”. … Natural aggregate is the world’s second most heavily exploited natural resource, after water, and for …
The World is Running Out of Sand | Science | Smithsonian
https://www.smithsonianmag.com/science…/world-facing-global-sand-crisis-1809648…
Sep 8, 2017 – The World is Running Out of Sand. The little-known exploitation of this seemingly infinite resource could wreak political and environmental …
Why the world is running out of sand – Business Insider
http://www.businessinsider.com/world-running-out-sand-resources-concrete-2018-6
6 days ago – Well, enjoy them now, because we’re using up sand at such an … The world is running out of sand — and there’s a black market for it now.
World running out of sand, making it the black market’s hot commodity …
https://www.rt.com/business/430000-sand-lack-black-market/
13 hours ago – A global shortage of sand is prompting black-market gangs to steal large amounts from rivers and beaches. Scientists are warning that the …
People here have very good instincts…
Another mineral that’s becoming scarce is the particular sort of stone that is used to make the handles of the sliding discs that are used in the ice game called curling–apparently it’s found only in Scotland, and it’s been almost all used up.
This sand shortage could, perhaps ironically, bring asteroid mining to fruition more quickly. Stony or–even better–“rubble pile” silicate asteroids could provide sand (and those with iron/nickel/cobalt [fine natural steel] and rare earth metals mixed in would be “additional value added” bodies). I suspect, though, that a new industry of on-Earth sand production may arise, using larger and improved ultrasonic RATs (Rock Abrasion Tools) to convert demolished abandoned and disused concrete buildings and structures into sand-like concrete powder of various particle sizes.
Sands that are suitable for concrete and industrial processes are the result of erosion. Asteroidal rock would be unsuitable. One might as well try to process rocks on Earth. It will be interesting if suitable sands can be found on Mars for local requirements, or whether they too are unsuitable.
Today’s technology is tomorrows Junk. A warp drive could be come a reality in the distant future. Lets see where we are ten years from now with the FTL for there could be some surprising breakthroughs with the FTL
Would the diameter of the exo-belt be detectable instead of just its existence? If, so it gives a pretty good estimate of the planets rotation rate.
Slightly off-topic, but interesting: about exomoons around giant planets:
https://arxiv.org/abs/1805.03370
The METI art project created by artist Trevor Paglen called The Last Pictures, which was launched in 2012 attached to the EchoStar 16 comsat, was placed into geosynchronous orbit because it will last for millions of years that far out into space, thus increasing the chances that it will remain preserved and be found one day.
https://centauri-dreams.org/2013/01/18/the-last-pictures-contemporary-pessimism-and-hope-for-the-future/
To quote from the above:
Paglen became fascinated by the fact that these comsats might be among the last bits of evidence that humanity ever existed. The artist imagined an advanced alien intelligence arriving in the Sol system in some remote future time and encountering this “man-made ring of Saturn forged from aluminum and silicon spacecraft hulls.”
…
When EchoStar XVI approaches the end of its initial career as a comsat around the year 2027, ground controllers will command the satellite to fire its thrusters. This event will move EchoStar XVI several hundred kilometers further away from Earth into what is known as a “graveyard” or supersynchronous orbit. Here is where many past geosynchronous comsats “go to die”, to use a phrase. This realm for the older, obsolete satellites gives the next generations of comsats the important room they need to function in the relatively narrow and highly prized technology zone far above our planet and the civilization which is quite dependent on these machines.
Once EchoStar XVI and its attached artifact reach their second home in space and the comsat is subsequently shut down, that is when this satellite and its atypical cargo begin their next tasks — as keepers of perhaps one of the final messages to future humanity, or beings from other worlds, or to the vast and unaware Universe far beyond Earth’s geosynchronous realm.
Unless comsat technology remains viable or we give up being a space faring/using civ, then I think such satellites will be removed, rher than left parked. They would constitute a hazard for spacecraft, even if relatively few are built. Salvage crews or garbage collection seems their most likely fate if we develop our solar system economy.
I discuss that possibility in my article. Paglen’s view is that humanity won’t last, so these comsats will be among the few remaining examples of our civilization.
I do not share his opinion as I think he was speaking to a very specific demographic which gets off on such attitudes, just so long as they don’t end up being a statistic.
https://en.m.wikipedia.org/wiki/Against_a_Dark_Background
The Late Iain M Banks, in the linked-to book above, wrote of the earth-like planet Golter having a glitter-ring (I think it was called) of sats, habs etc that even cast a pale light… ever the vivid storyteller he was; that image has been foremost in my mind since reading anything about this concept of a Clarke Exobelt.
I cannot speak for other planets, but in the far future the Moon shall approach Earth until it is torn apart by our world’s mass, creating a new ring of debris. This may be a problem for any artificial objects in the vicinity.
https://www.space.com/3373-earth-moon-destined-disintegrate.html
But, Seriously, Where Are the Aliens?
Humanity may be as few as 10 years away from discovering evidence of extraterrestrial life. Once we do, it will only deepen the mystery of where alien intelligence might be hiding.
Derek Thompson
June 22, 2018
https://www.theatlantic.com/technology/archive/2018/06/but-seriously-where-is-everybody/563498/
Alien Life Vs Earthly Assumptions: The Fermi Paradox Stands Firm.
By Hontas Farmer | June 26th 2018 11:56 PM
Assuming that alien life has to be like life on Earth is the safest way to scientifically search for evidence of it. A recent paper on the arXiv by a research team from Oxford is likely to cause headaches for SETI. In short it shouldn’t since the Oxford team has made a basic error in the midst of a masterful application of statistical analysis.
When searching for the truly unknown one must assume as little as possible. In theoretical physics the hall mark of a good theory is one in which the most testable implications follow from the fewest assumptions and adjustable parameters. Such is true of most areas of science. So too must this be true of astrobiology and searches for intelligent life.
In a paper “Dissolving the Fermi Paradox” (arXiv:1806.02404v1) Anders Sandberg, Eric Drexler and Toby Ord of Oxford Universities Future of Humanity Institute demonstrate the danger of assuming too much and doing so by implication. Their mathematical techniques are intriguing and look sound on first reading.
I have not done a full review where I attempt to recreate their results, yet. The goal of this blog is to get the rest of the media to hold their horses in reporting on this. Implicit in their analysis is a reliance on work done in search of extraterrestrial intelligence which believe it or not tends towards the conservative.
Full article here:
http://www.science20.com/hontas_farmer/alien_life_vs_earthly_assumptions_the_fermi_paradox_stands_firm-233004
To quote:
Given the sheer distances involved it does not seem reasonable to claim that we are the ONLY intelligence that is likely to exist. Once we have had time for signals to reach us from that entire area, which would have a radius of about 4500 light years and hear nothing THEN we can say we may be the only ones. Until then we really don’t know and at best we can speak in terms of bounding values and probabilities (even then being most optimistic we could perhaps know with only just slightly better than coin toss level confidence one way or the other).
In short I would advise caution about putting too much stock in any finding that is so final and certain on this question. The paper that stimulated this blog is well done, but the conclusion reached is a big leap based on our limited information.