Remember the Ozone hole? The satellite that spotted it just caused a space junk scare

South Korean authorities warned locals to avoid falling space junk, which probably splashed down harmlessly

A defunct weather-monitoring satellite came crashing back to Earth over the weekend, and reentered the atmosphere over the Bering Sea, the US Department of Defense confirmed on Monday.

Launched in 1984, the spacecraft was part of NASA's Earth Radiation Budget Experiment (ERBE) mission, and studied how the Sun impacts Earth's climate. The 5,400-pound device (2,449 kg) was designed to operate for two years, but continued to record data until it was finally retired after a series of hardware failures in 2005.

After spending nearly four decades in space, the dead satellite plummeted back to Earth on 8 January at 1104 EST (1604 UTC). Most of the components were destroyed by the heat and friction of reentry, but South Korea's Ministry of Science and ICT nonetheless warned residents to watch for falling chunks of satellite.

Officials later said the satellite was "believed to have passed over the Korean Peninsula, and no special damage has been reported so far," according to Bloomberg. 

The ERBE-sat measured how much solar energy the Earth absorbed and emitted back to outer space, and analysed chemical compounds in the stratosphere. The craft helped confirm the breakdown of Earth's ozone layer, a protective part of the atmosphere that absorbs most of the Sun's harmful ultraviolet rays.

"The Stratospheric Aerosol and Gas Experiment II (SAGE II) on the [ERB satellite] ... collected important data that confirmed the ozone layer was declining on a global scale," NASA said. "That data helped shape the international Montreal Protocol Agreement, resulting in a dramatic decrease around the globe in the use of ozone-destroying chlorofluorocarbons. Today, SAGE III on the International Space Station collects data on the health of the ozone layer."

The agreement came into effect in 1989 and urged countries to stop producing substances containing chlorofluorocarbons, that were often found in refrigerant gases and used as propellants in aerosol sprays, since the molecules readily interacted with ozone. The chemical reactions slowly depleted the ozone layer, leaving a giant hole over Antarctica. 

Fortunately, the ozone layer has bounced back and is on track to making a full recovery, according to a study backed by the United Nations presented at this year's American Meteorological Society's 103rd annual meeting. "If current policies remain in place, the ozone layer is expected to recover to 1980 values (before the appearance of the ozone hole) by around 2066 over the Antarctic, by 2045 over the Arctic and by 2040 for the rest of the world," according to the UN's World Meteorological Organization. ®