An upper layer of Earth’s atmosphere recently collapsed in an unexpectedly large contraction, the sheer size of which has scientists scratching their heads, NASA announced. The layer of gas — called the thermosphere — is now rebounding again. This type of collapse is not rare, but its magnitude shocked scientists.
“This is the biggest contraction of the thermosphere in at least 43 years,” said John Emmert of the Naval Research Lab, lead author of a paper announcing the finding in the June 19 issue of the journal Geophysical Research Letters. “It’s a Space Age record.”
The collapse occurred during a period of relative solar inactivity — called a solar minimum from 2008 to 2009. These minimums are known to cool and contract the thermosphere, however, the recent collapse was two to three times greater than low solar activity could explain.
“Something is going on that we do not understand,” Emmert said.
Read More: Space.com