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The glow does not flicker like that of the waves: it is a pale, continuous, and uniform light that makes the night sea look like a field of snow. Scientists had been trying to capture it from space for years. The proof came when a round-the-world sailboat accidentally crossed the luminous waters and took the first photos.
An area of more than 100,000 km² of the ocean, the size of Iceland, glowed continuously for more than 40 nights south of Java, Indonesia, in 2019. The extremely rare phenomenon, known as milky sea, was captured by satellites and later confirmed by the crew of a sailboat that coincidentally crossed exactly that region of glowing waters, in an episode that helped science better understand this oceanic mystery.
The event occurred between the end of July and the beginning of September 2019, but was only detailed in a scientific study published in 2022, led by researcher Steven Miller from Colorado State University, USA. A clarification is needed right away: although the phenomenon is real and well documented, its exact cause is still not fully understood by science, and the explanations of what causes it remain largely in the realm of hypotheses.
What is the milky sea phenomenon
It is a phenomenon where vast areas of the ocean’s surface emit a pale, soft, continuous, and uniform light during the night, making the water look like an illuminated snowfield under a dark, moonless sky, according to researchers who study it.
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The most intriguing detail is that this glow does not depend on movement.
Unlike the more common bioluminescence, which lights up in flashes when the water is agitated by waves, boats, or swimming animals, the milky sea glows constantly and broadly, without needing to be disturbed.
It is this characteristic that makes it so different and so difficult to explain, intriguing navigators and scientists for a long time.
The gigantic glow south of Java
Specialized satellite sensors designed to capture low light detected, south of Java, a bright spot that extended over more than 100 thousand km², an area comparable to the size of Iceland, and remained active for more than 40 consecutive nights, one of the largest and longest-lasting records ever documented of the phenomenon.
What most caught the scientists’ attention was precisely the stability of the glow.
Instead of flickering on and off with the movement of the waters, the sea seemed to emit a constant light, spread over a huge area. This reinforced the idea that the milky sea is a distinct nature event, possibly linked to the activity of microorganisms on a gigantic scale, and not a simple reflection or optical illusion.
The proof came from a sailboat
The sailboat Ganesha, a private 16-meter yacht on a world tour, accidentally crossed the milky sea region on the night of August 2, 2019, and its crew captured photos of the glowing waters, without even knowing at the time what it was.
The vessel was sailing between Indonesia and the Cocos Islands when it encountered the spectacle.
It was only later that one of the crew members, Naomi McKinnon, learned from the press about the satellite detections and contacted the scientists to report the experience.
By crossing the sailboat’s route with orbital data, researcher Steven Miller confirmed that both had witnessed the same phenomenon.
It was the first time that a satellite observation was combined with a photographic record made on the sea surface at the same time, greatly increasing confidence in spatial measurements.
What can cause the glow
This is the part still shrouded in mystery, requiring caution.
The main hypothesis is that the glow is caused by a luminous bacterium called Vibrio harveyi, which would need to accumulate in colossal numbers, in the trillions, for their combined light to become visible even from space.
Even so, scientists themselves acknowledge that the composition, structure, and exact cause of the milky sea remain largely uncertain.
The mechanism behind this collective lighting would have a name: quorum sensing.
According to this hypothesis, the bacteria release signaling molecules into the water and, when they perceive that their population has reached an enormous density, they start to glow all together, creating the continuous light observed.
It is a fascinating explanation, but one that still needs to be better proven, as collecting samples of these rare events in the middle of the ocean is extremely difficult.
Why the bacteria would glow
If the cause is already uncertain, the function of the glow is even more speculative.
One of the hypotheses raised by researchers is that the light would serve to attract fish, which would end up ingesting the colonies of bacteria, and that, in the intestines of these animals, the microorganisms would find a nutrient-rich environment more protected than the open ocean, functioning as a strategy for survival and dispersion.
By this logic, glowing would not be a waste of energy, but an evolutionary investment: by becoming visible and attractive, the bacteria would ensure transport and shelter within other living beings.
It is worth noting, however, that this explanation is one of the possibilities studied, and not a certainty, being part of the set of open questions surrounding this phenomenon as rare as it is fascinating.
An ancient mystery seen from space
Although it seems new, the milky sea has accompanied humanity for a long time.
Reports from sailors about waters that glowed like milk have existed for centuries, but the first scientific confirmation by satellite only happened in 2005, when a luminous patch of about 15,400 km² was detected off the coast of Somalia and lasted three nights, paving the way for scientists to start hunting these events from space.
The phenomenon is extremely rare, occurring, on average, zero to two times a year worldwide, usually in tropical and subtropical waters, such as the northwest Indian Ocean and south of Java.
The 2019 case shows how satellite technology has transformed the way we study the oceans: a spectacle that once seemed like a navigation legend can now be monitored hundreds of kilometers away, in space.
The milky sea phenomenon south of Java is one of those reminders that the ocean still holds mysteries capable of challenging science and enchanting the imagination.
An area the size of an entire country glowing for weeks, likely thanks to microscopic bacteria, is the kind of natural wonder that links ancient sailors’ tales to the most advanced space observation technology.
Even though many questions remain unanswered, each new record brings researchers closer to understanding how invisible life can illuminate the sea on a scale that only increases our fascination with the planet.
And you, have you ever heard of the milky sea phenomenon? Can you imagine the feeling of being on a boat surrounded by waters that glow as far as the eye can see? Leave your comment, tell us what you think of this ocean mystery, and share the article with those who love science, nature, and the enigmas that still exist at the bottom of the sea.
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