If you look at what the God of Thunder is holding, you’ll notice that it is not his trusty hammer Mjolnir, but instead a ridiculously big axe (not unlike the one that Thor carried in Marvel’s line of Ultimate comics).
Maybe Thor: Ragnarok will provide an answer when it comes out later this year.
Obviously we’re extremely thrilled just to have the tease of Rocket and Thor together in one piece of concept art, but there’s another interesting element to this shot as well.