“The Ocean Planet” –Mystery of the Origin of Earth’s Water

"The Ocean Planet" --New Theory for Origin of Earth's Water

 

Science fiction writer and futurist, Arthur C Clarke once observed that our blue planet would have been more appropriately named “Ocean” rather than Earth. One of the unresolved mysteries of the planet is the origin of water –the driving force of all nature. A new study suggests that interstellar organic matter could produce an abundant supply of water by heating challenging recent research that terrestrial water was delivered by comets or meteorites from outside the “snow line” or “ice line” –the distance from the Sun where it is cold enough for compounds such as water, ammonia, methane, carbon dioxide, carbon monoxide to condense into solid ice.

“Until now, much less attention has been paid to organic matter, comparing to ices and silicates, even though there is an abundance inside the snow line” says planetary scientist Akira Kouchi at Hokkaido University. This new research offers an alternative to studies done, for example, by the Institute of Space Science in early 2019, indicating that, coinciding with the ‘Heavy Bombardment’ 3.8 billion years ago produced by the gravitational destabilization of the main asteroid belt, when billions of tons of carbonaceous chondrites reached Earth transporting in their fine matrices water and other volatile elements in form of hydrated minerals. Carbonaceous chondrites come from comets and asteroids that due to their size up to a hundred kilometers, never melted, or suffered internal chemical differentiation as planets did.

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Heating of Interstellar Organic Matter–The Source?

In the current study published in Scientific Reports, a group of scientists led by Akira Kouchi demonstrates that heating of the interstellar organic matter at high temperature could yield abundant water and oil. This suggests that water could be produced inside the snow line, without any contribution of comets or meteorites delivered from outside the snow line.

As a first step, the researchers made an analog of organic matter in interstellar molecular clouds using chemical reagents. To make the analog, they referred to analytical data of interstellar organics made by irradiating UV on a mixture containing H2O, CO, and NH3, which mimicked its natural synthetic process. Then, they gradually heated the organic matter analog from 24 to 400 ℃ under a pressured condition in a diamond anvil cell. The sample was uniform until 100 ℃, but was separated into two phases at 200 ℃. At approximately 350 ℃, the formation of water droplets became evident and the sizes of the droplets increased as the temperature rose. At 400 ℃, in addition to water droplets, black oil was produced.

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Petroleum of Ancient Earth

“Our results show that the interstellar organic matter inside the snow line is a potential source of water on the earth. Moreover, the abiotic oil formation we observed suggests more extensive sources of petroleum for the ancient Earth than previously thought,” says Kouchi. “Future analyses of organic matter in samples from the asteroid Ryugu, which the Japan’s asteroid explorer Hayabusa2 will bring back later this year, should advance our understanding of the origin of terrestrial water.”

Source: Hideyuki Nakano et al. Precometary organic matter: A hidden reservoir of water inside the snow line, Scientific Reports (2020). DOI: 10.1038/s41598-020-64815-6

The Daily Galaxy, Sam Cabot, via Hokkaido University and Nature