Mars explorer MAVEN entered the Red Planet’s orbit late Sunday night, beginning a yearlong journey during which scientists hope to discover what happened to the Martian atmosphere. Mission managers at NASA’s Goddard Space Flight Center in Greenbelt, Md., received confirmation of MAVEN’s arrival at about 10:25 p.m. E.T. — about a half-hour after it began slowing down from more than 10,000 m.p.h.