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An arXiv preprint suggests that evidence of intelligent (or trashy) life could be found by looking for space junk:
Its author, Héctor Socas-Navarro, spends most of his time at the Canary Islands Institute of Astrophysics in Spain studying the sun. But he was struck by a weird side effect of the ring of active and retired satellites circling Earth: it's a little bit opaque. And the more satellites we throw up there, the more opaque it gets. He realized that if we—or any technologically advanced aliens out there—build enough satellites, they'll eventually become dense enough to leave a faint shadow around the planet when it passes in front of a star.
And that's awfully convenient given that one of the best ways we have of spotting alien planets is by staring at their stars and waiting for tiny dips in brightness as planets pass in front of them. Essentially, Socas-Navarro's new paper proposes, if aliens have put enough satellites into orbit around their planet, we'll be able to spot the faintly opaque bubble before and after we spot the brightness dip of the planet itself.
The scale of the endeavor would be a real challenge for the aliens, however, since this idea relies on between 10 billion and one trillion satellites. "It's like building the pyramids," Avi Loeb, an astronomer at Harvard University, told New Scientist. "Each building block is easy, but putting it together is the hard engineering task."
(Score: 4, Interesting) by Grishnakh on Thursday March 08 2018, @10:35PM (27 children)
Given the extreme distance, and how little light we really get from these stars (and how slight the dimming is from a full planet) there's got to be some limit to how feasible this really is. Sure, if the aliens have a bunch of big-ass space stations (like enough to hold billions of people) and solar collectors orbiting their planet we might be able to detect the difference between that and the planet, but if they're not quite that far along it doesn't seem like we'll see anything. This really seems a bit like looking for Dyson spheres; maybe not that extreme, but still like we're trying to spot aliens who are significantly more advanced than us.
(Score: 2, Interesting) by milsorgen on Thursday March 08 2018, @10:40PM (6 children)
Even if feasible I would assume that the timeframe a developing civilization would create large amounts of potentially dangerous debris would be a very short one. Either they would use their resources more effectively or they would come up with a way to remove the potential impactors from orbit. Thus leaving a very narrow window of time to hopefully observe another intelligent lifeform, I guess it boils down to how ubiquitous life is out there.
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(Score: 5, Insightful) by NotSanguine on Thursday March 08 2018, @11:38PM (5 children)
I'd go even farther than that. The issue isn't just the vast distances involved in seeking out such debris. Given the enormous time scales of the universe, should a civilization leave their space junk lying around, its' orbits would almost certainly (unless it was an incredibly large mass of junk) have decayed within a few million years, leaving nothing we could actually detect.
Consider the possibility that a species of dinosaur achieved sentience 75-100 million years ago. Even if they had a technological civilization, all traces of them would be completely eradicated (well, except possibly extremely long half-life artificial radioactive elements like P239) by now. Polymers would merely be carbon deposits. Any alloys would long ago have been degraded to their initial elements, any structures on the earth would have been completely destroyed/eroded away.
As such, if we can't definitively say (and we can't) whether or not there was a previous technological civilization *on the Earth*, the likelihood of discovering remnants of one around another star are vanishingly small.
No, no, you're not thinking; you're just being logical. --Niels Bohr
(Score: 0) by Anonymous Coward on Friday March 09 2018, @10:44AM (2 children)
We find footprints and even eggshells pretty regularly... Surely a technological civilization would leave artifacts more durable than that. Metal might corrode, but ceramic and glass should last over geological timescales, not to mention stone tools or fossilized bone tools, or the "footprints" of machinery. Now, if they were just sentient but only used that ability for social interaction had no technology, then of course we could only infer that if we found a skull.
(Score: 2) by maxwell demon on Friday March 09 2018, @12:00PM
The point is, they were so intelligent that they eventually came to the conclusion that littering the planet is a bad idea, so they collected all the artefacts in middle America, where they then destroyed them with a meteorite they directed towards earth for that purpose.
Unfortunately they were still not intelligent enough to recognize the big error in their calculation, which led them to choose a much too big meteorite, causing their own extinction. ;-)
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(Score: 2) by NotSanguine on Friday March 09 2018, @04:54PM
Volcanism [wikipedia.org] (think the Siberian traps), plate tectonics, massive space rocks, and possibly even a large thermonuclear exchange could certainly obliterate just about any trace of a civilization over such long time scales.
Any of the major mass extinctions [worldatlas.com] (and conceivably others less massive) could have been caused by many things, even devastating nuclear exchanges. And over the time scales we're talking about (aside from, possibly, the Cretaceous), we'd likely be unable to identify such events.
Glass? Ceramics? Metal works? Given the geological processes at work, it's entirely possible (especially if a technological civilizations was concentrated on coastlines) that the ruins of such a civilization would be completely recycled via tectonic plate movements, with all evidence having been cycled through the Earth's mantle.
I'm not saying that such a thing happened, I'm merely suggesting that it could have, illustrating the difficulty in identifying the remains of a another hypothetical civilization around another star. Especially given the even longer time scales (10 billion years?) and vast distances involved.
Does that mean I think we shouldn't try? No. On the contrary, I think we should try to gather as much information about our universe as possible. Discovering such debris would be exciting, if incredibly unlikely.
No, no, you're not thinking; you're just being logical. --Niels Bohr
(Score: 2) by HiThere on Friday March 09 2018, @05:58PM (1 child)
The concentration of metals in ores is something that takes a long time. The dinosaurs isn't far enough back. Now if the trilobites had a technological civilization, I don't think we'd detect it unless they left traces on the moon, and we have explored enough there to rule that out...but the plausibility is quite low. The dinosaurs were (nearly?) evolved enough, but there were too many big ones for it to be plausible. (Just consider trying to fence out an apatosaurus.)
So I'm rather certain that we're the first technological civilization on Earth.
I guess I should have read the article, since people are talking about fragments and derelict civilizations, etc., but my first thought was that a topopolis should be rather detectable. The problem, though, is that it wouldn't be planet centric, but solar centric. Still, the inner rings would need to be as close as feasible to derive maximal energy/area from solar power, and that would mean it would need to be highly reflective to maintain a livable temperature inside. This should result in a sustained radiation spike in certain frequencies that would otherwise be hard to explain. There should also be certain effects in the heat spectrum...I don't want to say infra-red, because that's making assumptions about the habitable temperature of that lifeform. Still, it would obviously be easier to detect creatures that preferred a high temperature over those that preferred a lower temperature, unless the inner rings were automated.
I really doubt that a civilization that had been long in space would remain planet centric, so I have my doubts about their entire scenario. Still...if they *did* find one that way...well, I'd need to revise my thinking.
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(Score: 2) by HiThere on Friday March 09 2018, @06:08PM
1) We haven't explored the moon enough. I don't know how I left out that "n't".
2) Reading the article I see that they're proposing certain particular orbits, and only a very slight advance over our space capabilities. I find it hard to believe that this would be detectable, but they say they've calculated it, and certainly polished metallic objects are a lot more reflective than asteroids. I do think they're assuming that the targets would stay at approximately our level of space advancement for an extended period of time, however, and I find that implausible. We're going to either rise or fall, and soon. If we fall, we probably won't be able to get back up. If we rise, then I think the topopolis is more probable than dense clusters around the planets. (More probably, it will be something nobody's thought of.)
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(Score: 2) by bob_super on Thursday March 08 2018, @10:45PM (2 children)
Yep, it's completely stupid.
Don't mind me, i'm just jealous that I don't get to publish how we'll find alien civilizations by measuring how fast the CO2 goes up in their atmosphere.
Then my next publication will be looking for atmospheric nuclear explosions on exoplanets. Those would be pretty clear signs of life, right?
How about looking for radio waves originating from exoplanets, hoping that they would be modulated in ways similar to ours? Yep, that'd be totally dumb! Can I publish that?
(Score: 4, Insightful) by Grishnakh on Thursday March 08 2018, @11:10PM (1 child)
The radio modulation thing isn't *that* dumb; there's really only a few ways to modulate radio transmissions after all (amplitude and frequency being the main two). The problem is that as radio technology progresses, at least in our experience, it becomes lower-power and the modulation for more complex, making it look essentially like random noise from a distance. In short, if aliens were trying to detect *US* by our radio transmissions, they only had a relatively short window in which to do so, the time from when we first started seriously publicly broadcasting, up until we moved to digital spread-spectrum schemes. If they tried to detect us by our emanations today, they most likely wouldn't notice us. And if our technology progression is typical, that means that we're very unlikely to detect anyone who's at least as advanced as us; we'd only be able to detect them if their earlier signals (from when they were as advanced as us in the 1950s-60s) happen to hit our antennae when we were listening. It doesn't help that even those higher-power transmissions are likely to be very difficult to detect over such a distance, since they weren't meant to be detected by far-away aliens, but only used terrestrially.
Basically, SETI would make more sense if there were some aliens out there intentionally broadcasting very strong radio signals with the goal of being detected by us. That's not a great assumption.
(Score: 2) by Immerman on Friday March 09 2018, @02:31AM
What about polarization - either linear or radial?
But yeah, even that only pushes it up to possible modulations... though I honestly don't know if anyone is seriously looking at polarization at all. Heck, for all I know the interstellar medium might destroy polarization, which could actually be an advantage for a security- or obscurity-minded species.
(Score: 3, Interesting) by fyngyrz on Thursday March 08 2018, @10:56PM (11 children)
Here's the thing: Aperture synthesis. [wikipedia.org]
On earth, there are pretty obvious limits to this, although, still outright amazing.
Once telescopes are established in space... those limits move way, way down the line. The people to whom this is available to will see (even more) amazing things.
My guess: most likely, the space version of this will be entirely practical within 100 years or so, once we get resource development, manufacturing and robotics established "out there."
(Score: 2) by Grishnakh on Thursday March 08 2018, @11:22PM (7 children)
Here's a question for astrophysicists:
Would there be any significant advantage to locating a telescope (or array of them) in interstellar space, outside the heliosphere? Is being inside the heliosphere limiting what we can see, the way that being inside our planet's atmosphere does?
(Score: 3, Informative) by takyon on Thursday March 08 2018, @11:43PM (6 children)
It's probably not even worth thinking about.
The closest idea to that being considered right now is probably FOCAL:
https://en.wikipedia.org/wiki/FOCAL_(spacecraft) [wikipedia.org]
https://www.airspacemag.com/daily-planet/ultimate-space-telescope-would-use-sun-lens-180962499/ [airspacemag.com]
https://www.centauri-dreams.org/2006/08/18/the-focal-mission-to-the-suns-gravity-lens/ [centauri-dreams.org]
https://arxiv.org/abs/1604.06351 [arxiv.org]
Using the Sun as a gravitational lens by putting a telescope ~600 AU away would have a vastly greater effect on what we can observe than moving out of the heliosphere.
The next milestone after that would be sending a starchip or other craft to another star system, such as Proxima/Alpha Centauri.
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(Score: 2) by Grishnakh on Friday March 09 2018, @01:26AM (5 children)
FOCAL looks like it would require a telescope well outside the heliosphere, as it needs to be about 600AU, and the heliosphere seems to be about 120AU according to my quick Wikipedia research, so that's sorta doing what I suggested, but of course for a very different reason. One big problem with it, however, is that it can only look in one direction (toward the Sun), so if you want to see anything else, you have to move the telescope.
As for sending a starship to another star system, I don't see how that really helps much. It would let you see stuff in that system close-up, obviously, but if you want to observe lots of star systems, or even galaxies, I don't see how it's really any better than doing it right here. It'll help if you really want to see some star system that's nearby, and closer to Alpha Centauri than here (like something on the other side of it), but that's probably only a handful of systems that are close enough to AC to really make a difference; with farther systems, you're not getting that much closer.
I was just wondering if the effects of the heliosphere were causing any issues with long-range observation and if there'd be a significant difference in interstellar space. I'm not sure we know that very well at this point though, since we've only barely penetrated that region, and only with very old spacecraft that, I believe, no longer even have functional cameras. You're probably right though: it's probably insignificant.
(Score: 2) by takyon on Friday March 09 2018, @02:24AM (1 child)
It would be cool to stick a huge ground telescope on a moon of Planet Nine (700+ AU away). Assuming they both exist.
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(Score: 2) by All Your Lawn Are Belong To Us on Friday March 09 2018, @03:26PM
You'll get your data! In about four days....
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(Score: 2) by All Your Lawn Are Belong To Us on Friday March 09 2018, @03:49PM (2 children)
That is about the distance of the heliopause, if we haven't moved the cheese again on the Voyager data [xkcd.com]. (Actually, no, the second heliopause announcement seems to have been a PR agent error [arstechnica.com]). But at lunch the other day we were talking about Voyager which got me to look up that the Voyagers are 141 and 117 AU's away currently - since Voyager 1's heliopause was measured about 116 AU's, makes me wonder when we'll hear about Voyager 2.
It also mades me wonder what the travel time for a dedicated mission to 600 AU's would be. Speed is variable to thrust, of course, and the Voyagers had a different mission, but 40 years to 140 AU.... At Voyager 1's heliopause recession speed of 17 km/s (the fastest so far per Wikipedia) by my calculations shows 167 years to 600 AU. Talk about your long-range mission planning!
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(Score: 1) by Grishnakh on Friday March 09 2018, @04:25PM (1 child)
Yeah, you'd really need a more powerful rocket for a decent mission to 600AU. I also wonder what the transmission delay would be, and how much trouble they'd have maintaining radio communication over that distance.
(Score: 3, Interesting) by All Your Lawn Are Belong To Us on Friday March 09 2018, @05:20PM
600 AU is 3.46 light-days - so a full week for a roundtrip signal. Signal degradation in free space is interesting. We're already getting signal from Voyager past the heliosphere and NASA said they could still run radio communications for another couple of decades with Voyager, alignment thrust issues notwithstanding... I wonder if there is anything out there that would significantly degrade the signal? I think I remember reading our current uplink signal is 17.5 kW. Again if I remember right we're receiving something like -123dB strength from Voyager on Earth; its radios are 23 watts at 8 GHz. (The 144 MHz radio I have in my car can do 50 W at that frequency, but I think 23W @ 8 is pretty screaming in terrestrial terms).
It's a bandwidth tradeoff, though. Higher data rates require more power. Voyager does between 160 bits per second and 1.4 kbps.
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(Score: 1) by Ethanol-fueled on Friday March 09 2018, @02:03AM
Wonder if there's a way to utilize an array plus degree of backscatter to look for space junk. Backscatter would make sense to detect reflected radiation from a sensor or irregulary-shaped target (asteroid belt or space junk) in motion with respect to each other, but from the perspective of a single sensor or closely-spaced group of sensors, the return reflections are interpreted as attenuation rather than a high-backscatter target.
(Score: 2) by HiThere on Friday March 09 2018, @06:18PM (1 child)
Aperture synthesis is great for refining focus, but it doesn't do much for collecting additional photons. That's strictly dependent of reception area (and, of course, sensitivity). If what you need is a clearer image, then aperture synthesis is the best way to go. If the signal's too weak to read, you need a larger or more sensitive detector.
What I think would be (eventually) great is a couple of 5 mile diameter mirrors at opposite point of Neptune's orbit. But that's not going to happen *this* decade. (For best results you need three mirrors, and the third should be inside Mercury's orbit, when measured by projection onto the orbital plane, but as far above it as the diameter of Neptune's orbit. That way when you synthesize the aperature you get a real 3-D image.)
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(Score: 2) by fyngyrz on Friday March 09 2018, @10:29PM
Or, if you can keep the sensor noise down, more time.
They're pushing photon counting [gigajot.tech] now, so there's that to look forward to. Once you're down to counting actual photons, as opposed to random electrons wobbling off the sides of a collection well, all you need are counters. Given enough time, signal will emerge from the noise. Noise is random; it averages out. Signal is not, and does not. As long as there is some signal. And generally speaking, in cases like this, there is.
You can get astonishingly good astro images using nothing but a DSLR with multiple exposures and image stacking+post-shooting-alignment to push the noise down. I do a bit of that myself. Magnitude 10 and even dimmer objects are easily captured at reasonable ISOs with the most mundane equipment.
(Score: 2) by JoeMerchant on Thursday March 08 2018, @11:08PM (2 children)
The whole space-elevator concept would lead to a visible ring, if practical. Chemical rockets, not so much (unless they have very little gravity.)
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(Score: 1) by Ethanol-fueled on Friday March 09 2018, @02:05AM (1 child)
The space-elevator concept is to space enthusiasts as Yakub or Xenu are to religious people. Let that comparison sink in for a moment.
(Score: 4, Insightful) by Immerman on Friday March 09 2018, @02:54AM
Only on Earth, and only the beanstalk variety. Earth-based "beanstalk" space elevators are so far at the extreme edge of feasability that they look increasingly unlikely to ever be possible - Carbon nanotubes, which we have good reason to suspect are approaching the physical limits of tensile strength, have only barely the strength-to-weight ratio to make it possible, theoretically. And no engineer worthy of the name would even consider building such a structure with safety margins measured in single-digit percentages.
On the moon though,and many other planet(oids) it's a whole different ballgame - existing bulk carbon fiber cable is more than strong enough to do the job with a decent safety margin. Even Mars wouldn't need much advancement in material science - If the population eer get
And of course, there are many, many other concepts that fall under the umbrella of "space elevator" : fountains, tumbling cables/wheels, etc, etc, etc - many of which are quite feasible with existing technology, even here on Earth. They just mostly have such outlandish up-front costs or concepts that they're unlikely to get built until space-travel becomes far more routine, and additional incremental cost savings are desired beyond what fully-reusable rockets could deliver. But, assuming civilization doesn't collapse in the next few centuries, nor lose interest in space, that seems rather inevitable.
It's rather like the difference between automobiles and rail - autos (rockets) are FAR more cost effective in low-traffic / low infrastructure use-cases, but rail is unquestionably vastly superior when it comes to efficiently moving large volumes of freight on a regular basis.
(Score: 2) by frojack on Friday March 09 2018, @07:58AM (1 child)
No they wouldn't. Aliens significantly more advanced than us would have learned long ago how to deorbit their space junk and recycle it.
And no advance society is going to have billions of individuals living on space stations. We are planetary animals. Perfectly adapted to our planets.
Advanced societies would learn to take care of their planet rather than moving onto space stations.
If you put ALL the space junk we've ever launched on a football field it wouldn't even cover half.
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(Score: 1, Insightful) by Anonymous Coward on Friday March 09 2018, @10:51AM
We are really only perfectly adapted to live in the African savanna. But we live in lots of other places too - so much so that most of humanity isn't actually properly adapted to live there any more.
While any civilization with sufficient technology will no doubt have certain factions who prefer to live on planets, just as we have some people who prefer to live in the middle of nowhere and hunt for food, someone will decide to live in space if it is possible to do so. Their children will consider it home and find it completely natural. And given the disparity in living space and resources, their descendants will outnumber the planet-bound by a billion to one.