Early this morning, as space shuttle Discovery was in preparations for returning to Earth, members of the crew noticed an object floating away from the shuttle into space. Most likely, the object broke free from the shuttle during maneuvers to position the orbiter for re-entry. Commander Mark E. Kelly also noticed what he called a "bump" sticking out from the side of the shuttle's tail rudder.
NASA is reviewing photos and video of both anomalies before allowing the shuttle to land, and the crew may re-deploy the robotic arm so that the camera mounted on the arm can get a better look to verify that Discovery is safe for landing.
At this point, it seems likely to me that landing will be delayed by at least a day in order to ensure the safety of the astronauts and the shuttle. In a worst case scenario, the crew will return to the International Space Station and dock while awaiting pickup by the emergency backup shuttle, which has been a part of every mission since the return-to-flight after the Columbia accident.