The Mar. 3 episode of The 100 -- titled "Thirteen" -- takes a trip back in time, right to the moment when a whole mess of nukes blew up the world. Even better, we get to see it all play out from the vantage point of the same space station that houses what remains of humanity when the show opens in Season 1.
Or is it? Last week's episode revealed that there was actually a thirteenth station in orbit called Polaris. It wasn't integrated into the Ark because it crashed and burned in the early days of the post-apocalypse.
This flashback -- and presumably others scattered throughout the coming episode -- should clear up some of the questions around Polaris, as well as the inciting events that brought about the end of the world.