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Unleash a bit of it, and suddenly all water on Earth transforms to ice-nine and freezes solid.
Ice-nine was a satirical invention, but an abrupt, disastrous phase transition is a possibility.
If humans were to survive a long time and spread through the galaxy, then the total number of people who will ever live might number in the trillions.
By pure odds, it's unlikely that we would be among the very first hundredth of a percent of all those people.
For a real chill, look to the Kuiper belt, a zone just beyond Neptune that contains roughly 100,000 ice-balls more than 50 miles in diameter.
Once a day or so, you would see a bright flash appear, briefly outshine everything else, then vanish.
Before the cataclysmal event, such a double star might be almost completely undetectable, so we'd likely have no advance notice if one is lurking nearby.
Once the burst begins, however, there would be no missing its fury.
But with big asteroids, it doesn't matter much where they land.
Objects more than a half-mile wide—which strike Earth every 250,000 years or so—would touch off firestorms followed by global cooling from dust kicked up by the impact.