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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: 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.