A dead NASA Upper Atmosphere Research satellite fell on Earth on Saturday, but it is not known where the crashed remains are.

It is reported to be the biggest crash of a NASA satellite since 1979, and NASA experts insist the debris fell in the Pacific Ocean.

The data about dead satellites like UARS are gathered by ground-based radars and optical sensors located at 25 sites worldwide.

One of the ways you find out a satellite is no longer in orbit is you have sensors in the Space Surveillance Network go look for it, and if they don’t find it then it has re-entered, says Nick Johnson chief orbital debris scientist at NASA's Johnson Space Center in Houston, Texas.

The satellite, which weighs 5,897 kilograms, was sent into orbit aboard a space shuttle mission to study ozone and other chemicals in the Earth's atmosphere.

“NASA's decommissioned Upper Atmosphere Research Satellite (UARS) fell back to Earth between 11:23 p.m. EDT Friday, Sept. 23 and 1:09 a.m. Sept. 24, 20 years and nine days after its launch on a 14-year mission that produced some of the first long-term records of chemicals in the atmosphere, said NASA in a statement on Saturday.

NASA said that the re-entry time and the location impact of the fallen debris have not been determined yet.

NASA and the Joint Space Operations will continue to investigate the fall of the UARS.

Space NASA International Space Station Earth