A sea of ​​milk seen for the first time from space

For centuries, there has been written and verbal evidence of the existence of a phenomenon known as sea of ​​milk . It had never been photographed, until now.

For centuries, there has been written and verbal evidence of the existence of a phenomenon known as the sea of ​​milk. It had never been photographed until now: Earth observation satellites have collected images of a sea of ​​bioluminescent milk south of Java (Indonesia), with an extension of more than 100,000 km², and it has been confirmed later by sailors from a boat sailing the same night, the same sea.

What is this phenomenon due to? Is it just the reflection of the moon on the surface of the water? What relationship does it have with the search for life on planets beyond the solar system?

The sea of ​​milk in the great stories

In Jules Verne ‘s classic 20,000 Leagues Under the Sea you can read:

“The Nautilus, sailing on the surface of the water, found itself in the middle of a whitish sea that could be said to be milky. The strange effect was not due to moonbeams, for the moon had barely risen above the horizon yet. The whole sky, although illuminated by sidereal radiation, seemed black in contrast to the whiteness of the waters. Conseil could not believe his eyes and questioned me about the causes of the singular phenomenon. It is what is called a sea of ​​milk, I replied […]”.

The seas of milk, also mentioned by the writer Herman Melville in his work Moby Dick , have been sighted by dozens of sailors over the centuries, but until recently there was only written and verbal evidence of their existence.

A team led by researcher Steven Miller , from the Department of Atmospheric Science at Colorado State University (United States), has detected the phenomenon by analyzing satellite images taken south of the island of Java between July and September 2019. Some of the photographs show what could be a sea of ​​milk, a finding later confirmed by the Ganesha yacht crew.

On August 2, 2019, the yacht Ganesha (named after the Hindu god of wisdom and new beginnings) entered a stretch of sparkling water in the Indian Ocean region (between Lombok and the Cocos Islands) while moving in its course to circumnavigate the globe.

The crew observed a sea of ​​milk for about eight hours, between 9 at night and 5 in the morning, in an area of ​​more than 100,000 km² and recorded it both in the logbook and in emails sent to family and friends.

In a recent work , Steven Miller confirms this phenomenon based on interviews with crew members, digital photographs, video records of the yacht and satellite images.

How does the sea of ​​milk originate?

Although not proven, it is believed that the sea of ​​milk is due to a communication process between millions of luminescent bacteria ( Vibrio fischeri ) present in the ocean water called quorum sensing .

The discovery that bacteria can communicate with each other changed the perception of their behavior. They do this by secreting certain signal molecules into the environment, water in this case, some of them luminescent. This allows them to coordinate to perform actions together, as a population.

Not only fireflies shine

There are two natural processes capable of generating light: bioluminescence and biofluorescence .

  • Bioluminescence: is the process by which some animal species are capable of generating light through a chemical reaction (this is the case of bacteria).
  • Biofluorescence: is the process by which light of non-visible wavelengths is converted into light of visible wavelengths through the absorption/emission of photons.

There are many living beings capable of producing light, such as bacteria, fungi, protozoa, cnidarians, coelenterates, worms (annelids and nematodes), molluscs, cephalopods, crustaceans, insects, echinoderms and fish. Although perhaps the best-known bioluminescent animal is the firefly or glowworm, which is less and less abundant in nature.

Corals also emit light, but in this case it is fluorescence, that is, the conversion of ultraviolet light into visible light by a process of photon absorption and emission.

Fluorescence has also recently been demonstrated in almost all types of amphibians .

The light of extraterrestrial life

Many astronomers have been interested in this discovery as it could be a possible way to find life, both bioluminescent and biofluorescent, on other planets by observing the light emitted by their signals.

The researcher at Cornell University in Ithaca (United States) Lisa Kaltenegger explored in one of her studies the number of biofluorescent organisms that would be necessary to be able to observe their light from Earth using the next generation of giant telescopes such as the Extremely Large Telescope (Cerro Armazones, Chile), which is scheduled to start operating in 2027.

The sea of ​​milk, a phenomenon made into fiction by some writers and observed by dozens of sailors over the centuries, has finally been filmed thanks to technology and subsequently corroborated. Now, who knows if it will be observed beyond the solar system and what it will be able to discover for us.The Conversation

Francisco José Torcal Milla, Professor of the Department of Applied Physics, University of Zaragoza