An examination of how the daily work of NASA's Mars Exploration Rovers was organized across three sites on two planets using local Mars time. In 2004, mission scientists and engineers working with NASA's Mars Exploration Rovers (MER) remotely operated two robots at different sites on Mars for ninety consecutive days. An unusual feature of this successful mission was that it operated on Mars time—the daily work was organized across three sites on two planets according to two Martian time zones. In Making Time on Mars , Zara Mirmalek shows that this involved more than a resetting of wristwatches; the team's struggle to synchronize with Mars time involved technological and communication breakdowns, informal workarounds, and extra work to support the technology that was intended to support people. Her account of how NASA created an entirely new temporality for the MER mission offers insights about the assumptions behind the organizational relationship between clock time and work. Mirmalek, herself a member of the mission team, offers an insider's view of the MER workplace and community. She describes the discord among MER's multiple temporalities and examines issues of professional identity that helped shape the experience of working according to Mars time. Considering time and work relationships through a multidisciplinary lens, Mirmalek shows how contemporary and historical human–technology relationships inform assumptions about the unalterability of clock time. She argues that the organizational connection between clock time and work, although still operational, is outdated.