Scientists Finally Solved the Mystery of the ‘Golden Orb’ Found 2 Miles Under the Sea

A viral deep sea mystery took more than two years to solve because the ocean still hides life in forms scientists barely recognize.

Two miles below the Gulf of Alaska, in darkness, cold, and crushing pressure, a remotely operated vehicle came upon a smooth golden dome stuck to a rock. It had a small tear near its side. It looked biological, but weird, almost like an egg from the Alien franchise.

For more than two years, no one could say exactly what it was.

Now scientists at NOAA and the Smithsonian National Museum of Natural History have identified the mystery thing. The so-called “golden orb” was not an egg case, nor was it a sponge, a microbial mat, or anything alien. It was the leftover base of a giant deep-sea anemone called Relicanthus daphneae — a strange, rarely seen animal with long pinkish tentacles that can trail through the dark like living ribbons.

In a new study, researchers report that the orb was a remnant cuticle, a kind of secreted outer layer, left behind by the animal after it died, moved, or perhaps reproduced in a way scientists still do not fully understand.

A Golden Thing in the Dark

The object entered the world’s imagination on August 30, 2023, during NOAA’s Seascape Alaska 5 expedition. The NOAA Ship Okeanos Explorer had sent its remotely operated vehicle, Deep Discoverer, down to an unnamed volcanic feature southwest of Walker Seamount.

At 3,250 meters down, the vehicle’s lights swept over exposed basalt cobbles and small glass sponges. Then the golden dome appeared.

It was about four inches across, stuck to the rock, and oddly smooth. Scientists watching the livestream debated what they were seeing in real time. Maybe it was an egg case or a dead sponge. Maybe something had crawled out of the hole.

The team collected it with a suction sampler and sent it to the Smithsonian, where it entered the slow machinery of science: microscopes, specimen comparison, DNA extraction, genome sequencing, and the good ol’ scientific method.

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Allen Collins, a NOAA Fisheries zoologist and director of the National Systematics Laboratory, initially expected the analysis to be routine.

“We work on hundreds of different samples and I suspected that our routine processes would clarify the mystery,” Collins said in NOAA’s statement. “But this turned into a special case that required focused efforts and expertise of several different individuals. This was a complex mystery that required morphological, genetic, deep-sea and bioinformatics expertise to solve.”

The orb did not contain obvious animal parts. It had no mouth, gut, muscles, or any clear body plan for that matter. Under the microscope, it looked instead like a loose mass of fibers covered by a smooth, layered surface.

But the surface carried the first clue.

The Stinging Cells Gave It Away

The researchers found the orb’s surface packed with spirocysts, a kind of sticky stinging cell found only in a group of cnidarians called hexacorals. This group includes sea anemones, stony corals, and black corals.

That narrowed the search. The golden object had come from a cnidarian.

A second clue came from an older specimen. In 2021, scientists aboard the Schmidt Ocean Institute’s Falkor had collected a similar golden, flaky material from a seamount near Howland and Baker Islands in the central Pacific. At the time, it too had been mistaken for a sponge or microbial biofilm.

The two specimens looked alike. Under the microscope, their stinging cells looked alike. Then genetics tightened the case.

At first, routine DNA barcoding failed. The orb had become home to many microscopic organisms, and their DNA confused the result. So, the team turned to deeper whole-genome sequencing. This time, the signal became clearer. Both the Alaska orb and the Pacific specimen contained DNA from Relicanthus daphneae. Their mitochondrial genomes were almost identical to each other and very close to a known Relicanthus reference genome.

The “golden orb” was therefore not a new monster. It was the remains of a known, but still poorly understood, giant anemone.

Relicanthus daphneae has a body that may reach about 30 centimeters across. Its tentacles can stretch for meters. Some reports describe tentacles up to six or seven feet long. They are usually pink, purple, or reddish, and can detach when the animal is disturbed.

It lives in deep water, often near hydrothermal vent fields or on exposed rocks where currents can carry prey into its tentacles. The new paper places confirmed records between roughly 1,667 and 3,948 meters deep, with evidence that the species may be widely distributed across the world’s oceans.

A Golden Robe

The researchers argue that the golden mass was likely the cuticle from the anemone’s base. In many animals, cuticle means an outer layer. For some sea anemones, especially deep-sea species, such layers can help anchor or protect the body.

In Relicanthus, the cuticle seems to sit beneath the animal, hidden while the anemone is alive. That may explain why no one had recognized it before.

The team examined a Relicanthus specimen from the Southern Ocean collected near hydrothermal vents. It had loose pieces of thin, layered cuticle attached to it. One layer was golden, so bingo! The pattern on the cuticle matched the underside of the animal’s base.

The anemone uses this cellular base to anchor its massive body to the rocky ocean floor. Sometimes, an anemone moves to a new home or simply sheds its base. The tough, golden footprint stays behind, waiting to confuse the next robotic explorer.

A Tiny Ecosystem on a Dead Anemone

The orb was not alone. In fact, it had become a habitat.

When the team sequenced all the DNA in the specimen, they found a community of microbes living in and around the cuticle. Some belonged to groups known for processing nitrogen. Others were typical of deep-sea sediments and seafloor biofilms. Many appeared to be poorly known or possibly undescribed microbial lineages.

In simpler terms, the dead anemone base had become a tiny recycling station on the seafloor.

As bacteria and archaea broke down nitrogen-rich animal tissue, other microbes may have converted the chemical leftovers into new forms. The researchers describe the decaying cuticle as a possible micro-scale biogeochemical reactor — a small patch where biological remains feed chemistry, and chemistry feeds life.

That may sound like a minor detail. It is not.

The deep sea covers most of the planet’s habitable space, but it remains sparsely explored. A single odd object, collected because it looked strange on camera, turned out to teach us a few new things about this submerged alien-like world.

Had the orb looked less golden, scientists might have ignored it.

“So often in deep ocean exploration, we find these captivating mysteries, like the ‘golden orb’,” CAPT William Mowitt, acting director of NOAA Ocean Exploration, said in NOAA’s statement. “With advanced techniques like DNA sequencing, we are able to solve more and more of them. This is why we keep exploring — to unlock the secrets of the deep and better understand how the ocean and its resources can drive economic growth, strengthen our national security, and sustain our planet.”

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The findings have appeared in the preprint server bioRxiv.