Bad weather in Florida and a mysterious object floating near the U.S. space shuttle have combined to delay the orbiter's landing by at least one day.

Cargo bay of Space Shuttle Atlantis is surveyed by video cameras after an object that may have accidentally flown out of the cargo bay was spotted flying outside the shuttle

The six astronauts aboard the shuttle Atlantis were stowing gear in preparation for Wednesday's return to Earth when mission controllers in Houston told them they would remain aloft until at least Thursday.

They told the crew that rain and strong crosswinds at the Florida landing site would make touch down risky. That forecast alone would have been enough to keep them in orbit, but ground controllers also gave a second reason. The shuttle's camera captured a small object floating alongside Atlantis that worries shuttle program manager Wayne Hale. He says the space agency wants to make sure it is not a vital piece of the shuttle needed for landing or a lost segment of orbiter's fragile heat shield that must endure searing temperatures during re-entry into the atmosphere.

"Now the question is, what is it? Is it something benign or is it something more critical that we should pay attention to," said Wayne Hale.

The Atlantis astronauts will scan the shuttle's surface with a camera at the end of a long robot arm over the next several hours. Hale says the most likely possibility is a plastic separator or shim that came loose from between the ceramic tiles, but which would be of no consequence to the flight. A surface inspection earlier in the mission showed the shim sticking out.

"We're taking it very seriously," he said. "We're going to go out and make sure we know what's going on to the best of our ability and make sure we are safe to land before we commit to that incredible journey through the atmosphere."

The U.S. space agency is taking no chances over shuttle safety after the loss of the orbiter Columbia in 2003. A piece of launch debris punctured the shuttle's wing, allowing superheated atmospheric gases to penetrate upon re-entry. This caused the shuttle's disintegration and the deaths of seven astronauts.

Hale says if an inspection finds that the mysterious floating object is a critical part of the shuttle necessary for landing, Atlantis can return to the International Space Station until another shuttle flies up to rescue its crew. That is an emergency standby procedure developed as a result of the Columbia disaster.

Atlantis had departed from the station Sunday after a mission that resumed construction of the outpost for the first time since the Columbia accident.