Something very odd.
The Kepler telescope, which operated from 2009 to 2013, was designed to detect planets by the slight dimming they cause when they pass between us and their star.
Whatever's going on around KIC 8462852 - it's not just an exoplanet. The star is a bit under 1,500 light years away and bigger than the sun. Planets cause regular dips of about 1% in a star's brightness - even ones like Jupiter.
KIC 8462852 is dimming irregularly and by a lot more. 15 percent, 22 percent. And we don't know why. This would be normal for very young stars in the early stages of planet formation - but KIC 8462852 is a mature star.
But it's definitely surrounded by junk - and none of the 150,000 or so other stars studied by Kepler (which was damaged in 2013 and has yet to be repaired or replaced) have shown anything like this.
Which leaves two possible explanations, both of which fall into the "When you have eliminated the impossible" category.
The first is that by some coincidence we happened to look at it right (or 1,500 years after, given light speed) as another star swept through the oort cloud, creating a comet swarm. There's even a candidate star.
The second is...it's a Dyson sphere. Nobody is saying it is aliens, but for the first time we have a phenomenon where real scientists can say "Aliens" and not be laughed out of the room.
I'm not saying it's aliens. I'm saying there's a possibility, just a small one, that it's aliens. Enough of one that it might just be a good idea to tune a radio telescope that way and take a listen.
Just in case.