A decommissioned U.S. science satellite fell back to Earth but its precise re-entry time and location remained unknown, the U.S. space agency NASA said Saturday.

"The Upper Atmosphere Research Satellite fell back to Earth between 11:23 p.m. EDT Friday (0323 GMT Saturday) and 1:09 a.m. EDT (0509 GMT). The Joint Space Operations Center at Vandenberg Air Force Base in California said the satellite penetrated the atmosphere over the Pacific Ocean," said NASA.

The NASA stressed the risk to public safety or property is extremely small, adding that since the beginning of the Space Age in the late 1950s, there have been no confirmed reports of an injury resulting from re-entering space objects.

"Nor is there a record of significant property damage resulting from a satellite re-entry," NASA added.

The UARS satellite, launched in 1991 from a space shuttle, was the first multi-instrumented satellite to observe numerous chemical constituents of the atmosphere with a goal of better understanding atmospheric photochemistry and transport.