Scientists in Germany are baffled after a large underwater observatory apparently vanished from the seabed.
The two environmental sensors, which weigh around 350kg (770lb) in total and were installed into a restricted area of the sea, stopped transmitting data on 21 August.
The radio silence was initially thought to be due to a transmission error, but a closer inspection with divers found the equipment had in fact disappeared.
All that was left of the station was a shredded cable that once connected the €300,000 (£270,000) sensors to land.
A professor working with the Helmholtz Centre for Ocean Research Kiel (GEOMAR), the owners of the observatory, said the marine data it collected was “downright priceless”, before appealing for any tips.
“At first we tried to find the devices with our own research and other diving applications. So far without success,” Dr Hermann Bange said.
“That’s why we would be very happy for any hints.”
GEOMAR has so far ruled out the possibility of marine animals, water currents or storms from removing the observatory, due to it being “extremely massive”.
“I need to stress that neither aliens, the Russian Navy nor a torpedo attack can be made responsible for the missing observatory!” Mr Bange told Sky News on Friday.
He added that the “most likely scenario” was that a fisherman had accidentally caught the sensors in a trawler net.
A team of divers and a ship with sonar equipment have since been deployed to search for the missing sensors, and local police are involved.
The station, which was installed into an area of Eckernförde Bay in Kiel, northern Germany, was used to collect monthly data that would monitor the ecosystem of the Baltic Sea.
Because of this data collection, Mr Bange says, the company “will try to get the observatory back up and running as soon as possible”.