Thor to prepare for a possible big event as the Black Winter showed him a vision of a dark future. Which has Thanos holding Mjolnir with the Infinity Stones attached to the hammer in one hand and a demonic black gauntlet in the the other arm. Behind Thanos are zombie versions of all of the heroes of the Marvel Universe.

He took off the Mjolnir to and put it in Broxton, Oklahoma to test a theory.