Arizonans see UFO, NASA says it's a balloon

NASA officials say it wasn't an alien spacecraft people in Arizona and New Mexico spotted floating far above them in the clear blue sky, just a giant research balloon.

Federal Aviation Administration spokesman Ian Gregor says he got calls about the object all afternoon Monday, according to the Arizona Republic newspaper.

Bill Stepp of NASA's Columbia Scientific Balloon Facility in Palestine, Texas, says the mysterious flying orb was a 4,000-pound (1,814-kilogram) NASA research balloon used to measure gamma ray emissions.

Stepp says the balloon usually floats at 130,000 feet (nearly 40,000 meters) and can be seen for many miles on a clear day.