At a US-hosted climate summit launched on Earth Day, the Biden administration hopes to prove what it’s been saying for months: The US is back as a leader on climate action. And, in the wake of the Derek Chauvin trial, activists argue that increasingly militarized police shows that the US cannot solve its police brutality problems on its own. Also, a toaster-sized instrument on NASA’s Perseverance rover on Mars has taken the planet’s carbon dioxide atmosphere and has made oxygen with it.