New research has revealed the exact origin of mysterious Pacific Ocean “biotwan” sounds that were first detected during underwater surveys near the Mariana Trench in 2014. Researchers have finally pinpointed the source of the mysterious sounds coming from the deepest ocean basin. Described as “biotwan” sounds, the strange sounds sound a bit like sci-fi starships and are actually whale calls from Bryde’s whales (Balaenoptera edeniResearchers say whales may use calls to determine each other’s whereabouts, like a giant game of Marco Polo.

Scientists first discovered the unusual sounds in 2014, using underwater gliders to conduct an acoustic survey of the Mariana Trench, the world’s deepest ocean trench, which lies 2,400 kilometers south of Japan and has a maximum depth of 35,876 feet (10,935 meters).

The biotuang’s sound can be divided into two distinct parts: first, a low rumbling sound that echoes through the depths; second, a high-pitched metallic ringing that researchers liken to the sounds made by spaceships in Star Trek and Star Wars.

The sounds confused scientists at first, but in 2016, researchers discovered that the biotwang was likely a challenge from large baleen whales, such as blue whales (Balaenoptera musculus) or humpback whales (Megaptera novaeangliaeHowever, the sounds did not match any known whale sounds.

In a new study published Wednesday (September 18) in the journal Frontiers in Marine Science, researchers have finally managed to prove that Bryde’s whales make sounds, thanks in part to new artificial intelligence (AI) tools that combed through more than 200,000 hours of audio recordings that include a variety of ocean sounds.

Researchers suspected Bryde’s whales were behind the biotwang when they spotted 10 marine mammals swimming near the Mariana Islands and recorded nine of them making distinctive sounds.

“One time is an accident. Twice is a coincidence. Nine times — it’s definitely a Bryde’s whale,” lead study author Ann Allen, an oceanographer at the National Oceanographic and Atmospheric Administration’s (NOAA) Pacific Islands Fisheries Science Center, told Scientific American.

But to definitively prove that it was Bryde’s whales making the call, the team matched the occurrence of the sounds to the species’ migration patterns, which meant sorting through years of audio recordings made by monitoring stations in and around the Mariana Islands. They sped up the process by using artificial intelligence to convert the biotwang into images known as spectrograms, which can be easily distinguished from other noises using a machine learning algorithm.

The study also found that the biotwang could only be heard in the northwestern Pacific Ocean, even though Bryde’s whales roam a much wider area, suggesting that only a select population of whales were making the noise.

The data also showed an increase in biotwang calls in 2016, when warming ocean temperatures caused by El Niño led to an increase in Bryde’s whales visiting the area. It’s not yet known why these calls sound so strange, but researchers have guesses as to why they’re made.

“It’s possible they’re using biotungue as a communication call, like the ocean’s Marco Polo,” Allen told Popular Science, “but we need more information to say for sure.”