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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: 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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