Honestly, he just destroys the planet. The last time we saw Thanos he was completely enraged and planned to kill the 616 universe. Here he's just tossed on a plan and asked to do one of two things, destroy it or take it over in 5 days, since Thanos is peeved and isn't much of a fan of dominating a single planet, why wouldn't he just immediately slam his fist into the ground and destroy the planet?