The article calculates that solar-radiation reducing shields for earth-sized exoplanets (like some propose for mitigating climate change) will be detectable by the next generation of astronomical telescopes.
I'm confused... Does this mean we are looking for life sufficiently intelligent to build these radiation-reducing shields? Or are we looking for natural shields (i.e., a moon?) that might make a planet naturally resistant to climate change?
The L1 point is a saddle point in the local effective potential: it is therefore not stable enough for an object to stay there without station-keeping.
So yes, the goal here would indeed be to detect life capable of creating large structures and keeping them actively in orbit. There is some tongue-in-cheekness to this sort of research, but as the abstract notes, also some seriousness. The tongue-in-cheekness is that we're nowhere near being able to build something this large between Earth and the Sun; as the abstract notes, it has to be around as large as the Earth in order to usefully eclipse the Sun; that's a very very large structure, and we're certainly able to get into space right now: and yet we have no prospects even in the next many thousand years for engineering anything at that scale, unless folks are right about an impending technological singularity.
The seriousness, on the other hand, comes from one consideration: blotting out the Sun is probably easier than fleeing to nearby star-systems. It's very hard to say exactly how much energy it takes to flee to a nearby star-system, but a lower limit for the technology that I can presently envision is maybe 10^20 J of kinetic energy; my imagination might not be very good though, but I think that's reasonably conservative. Now the solar power irradiating a disk-that-blots-out-the-Sun is known to be 10^17 W or so. So the claim is, to even harvest the level of energy that is required to try and scout out neighboring star systems, one needs Sun-blotting scales of energy-harvesting technology; the length scale could maybe be smaller by a couple orders of magnitude to scout, but one can imagine that the energy needs of billions of entities fleeing their home planet would be several orders of magnitude larger, too.
> blotting out the Sun is probably easier than fleeing to nearby star-systems
If we want to later use the sun-blotter as a solar panel to power our interstellar exploits, then yeah.
If we just want to make the Earth a little cooler, we'd be far better off seeding the stratosphere with some dust, creating a mini 'nuclear winter' / 'Krakatoa effect' in a controllable way.
Presumably this would detect both, but I think they are operating on the assumption that the shield would be just enough to shield the planet and that finding a moon sitting in L1 orbit that also has that shape would be unlikely. I didn't read the whole thing yet, but maybe they cover this.
As with a lot of stuff in space, we assume a lot to be unlikely until we find out that it's not :)
