CM – Up to half of the earth’s water can come from solar wind and space dust


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November 30, 2021

by Luke Daly, Martin R. Lee, Nick Timms, Phil Bland, The Conversation

Water is vital to life on earth, and some experts say that as part of a healthy lifestyle we should all drink about two liters every day. But where does our water come from beyond the tap?

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It flows from local rivers, reservoirs and aquifers. But where does this water come from? Over the course of geological time, the earth’s water circulates through living organisms, the atmosphere, rivers, oceans, the rocks beneath our feet, and even through the deep interior of the planet.

But what is before that? Where did the earth originally get its water from? Scientists have long searched for answers to this question.

We have studied tiny pieces of an asteroid to find out – and we believe that rains of protons from the sun all the time produce water on rocks and dust throughout the solar system could. In fact, up to half of the earth’s water could have been produced this way and got here with falling space dust.

We know that earth’s water probably came from space at the beginning of the history of our solar system. So what was the original delivery service that gave the earth its water?

Water-rich asteroids are currently the best candidates for the supply of water and carbon-hydrogen compounds that together make our beautiful habitable blue planets full of life.

However, water from asteroids contains a certain ratio of common hydrogen to a heavier species or isotope called deuterium. If all of the earth’s water was from asteroids, we would expect it to have the same ratio – but the earth’s water contains less deuterium, so there must be another water source in space with less deuterium as well.

The only thing we know in the solar system with a lot of hydrogen but a lower percentage of deuterium than the earth is the sun itself. This embarrasses us as it is difficult to see how the hydrogen is in the Earth’s water could come from the sun.

Back in 2011, the Japanese space agency (JAXA) sent the Hayabusa mission to take samples from the asteroid Itokawa and bring them back to Earth. In 2017 we were lucky enough to be able to match three extremely rare mineral particles from the sample, each about the width of a human hair.

Our goal was to examine the outer surfaces of these dust particles in a completely new way to see if they were affected by « space weathering ». This is a combination of processes known to affect all surfaces exposed in space, such as harmful galactic cosmic rays, micrometeorite impacts, solar radiation, and solar wind.

We worked in a huge team of experts from three continents and used a relatively new technique called atom probe tomography, which analyzes tiny samples at the atomic level. In this way we can measure the abundance and position of individual atoms and molecules in 3D.

Near the surface of the Itokawa particles we found a layer rich in hydroxide molecules (OH, contains an oxygen atom and a hydrogen atom) and above all Water (H₂O, contains two hydrogen atoms and one oxygen atom).

This discovery of water was very unexpected! For all we knew, these minerals from the asteroid should be bone dry.

The most likely source of the hydrogen atoms that will later be needed to form this water is the solar wind: hydrogen ions (atoms with missing electrons) released by the Sun stream through space and then settle in the surfaces of the dust particles.

We tested this theory in the laboratory by firing heavy hydrogen ions (deuterium) to simulate minerals like those in asteroids in the solar wind, and found found that these ions react with the mineral particles and steal oxygen atoms to produce hydroxide and water.

The water generated by the solar wind is a previously neglected reservoir in our solar system. Additionally, every vacuum in the world or rock in the entire galaxy could be home to a slowly renewed water resource powered by its suns.

This is fantastic news for future space exploration. This life-giving water resource could also potentially be broken down into hydrogen and oxygen to make rocket fuel.

As the Earth and its oceans formed, the solar system was teeming with objects ranging from asteroids miles wide to micrometer-sized dust particles. These objects have since fallen on our planet (and others).

Based on our tiny space-weathered grain, we estimated that one cubic meter of asteroid dust could contain up to 20 liters of water. With all the space dust that has fallen to Earth over the eons, a lot of water from the Sun (with less deuterium) would have arrived alongside the heavier water from larger asteroids.

We have calculated that an approximately 50:50 mixture of water-rich dust and asteroids is a perfect match for the isotopic composition of Earth’s water.

So while you are drinking your next glass of water, think about the strange thought that up to half of the earth’s water is drawn from the sun.

This article was republished by The Conversation under a Creative Commons license. Read the original article.

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