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.