LOS ANGELES/NEW YORK, Oct 14: The 3D outer space thriller “Gravity” kept a tight grip on US and Canadian box offices over the weekend, eclipsing the debut of Somali pirate drama “Captain Phillips” in a battle between two Oscar hopefuls. “Gravity,” starring Sandra Bullock and George Clooney as astronauts stranded in space, held the top spot on movie charts for a second weekend, grabbing 44.3 million dollar in domestic ticket sales from Friday till yesterday. (agencies)