How Clouds of Ancient Space Water Filled Earth's Oceans

Water is a fundamental requirement for life on Earth, but where did it come from? Was it present when the planet was formed or did it arrive later through comets and asteroids? A recent study published in the journal Nature proposes that water was created slowly over time in vast clouds of gas and dust between stars, predating the sun and solar system.

Incorporating the water directly from the cold interstellar medium before the formation of a star, the water was unchanged and was integrated from the protoplanetary disk - a dense layer of dust and gas that orbits newborn stars, and from which planets and small bodies like comets emerge. The water was also drawn into comets "relatively unchanged."

Several origins theories for water in solar systems have been suggested, including the hot nebular theory, where the heat in a protoplanetary disk around a natal star would break down water and other molecules, which form afresh as things start to cool. However, when water emerges at relatively warm temperatures in a protoplanetary disk, it will not look like the water found on comets and asteroids, which act as time capsules, preserving the state of matter in the early solar system. Specifically, water made in the disk would not have enough deuterium, an isotope of hydrogen, which contains one neutron and one proton in its nucleus, rather than a single proton as in typical hydrogen.

An alternative theory proposes that water forms at cold temperatures on the surface of dust grains in vast clouds in the interstellar medium. This deep chill changes the dynamics of water formation, so that more deuterium is incorporated in place of typical hydrogen atoms in H2O molecules, more closely resembling the hydrogen-to-deuterium ratio seen in asteroids and comets. The surface of dust grains is the only place where you can efficiently form large amounts of water with deuterium in it.

Although this explanation worked in theory, the new paper is the first time that scientists have found evidence that water from the interstellar medium can survive the intense heat during the formation of a protoplanetary disk. The researchers used the European Southern Observatory's Atacama Large Millimeter/submillimeter Array, a radio telescope in Chile, to observe the protoplanetary disk around the young star V883 Orionis, about 1,300 light-years away from Earth in the constellation Orion.

Radio telescopes such as this one can detect the signal of water molecules in the gas phase, but dense dust found in protoplanetary disks very close to young stars often turns water into ice, which sticks to grains in ways telescopes cannot observe. However, V883 Orionis is not a typical young star – it's been shining brighter than normal due to material from the protoplanetary disk falling onto the star. This increased intensity warmed ice on dust grains farther out than usual, allowing researchers to detect the signal of deuterium-enriched water in the disk. That signature of that level of deuterium gives you your smoking gun, explains John Tobin, an astronomer studying star formation at the National Radio Astronomy Observatory and lead author of the paper.

This discovery suggests that Earth's oceans and rivers are, at a molecular level, older than the sun itself. Tobin is eager to explore the findings further, wanting to observe more systems to verify if the discovery was just a fluke. Water chemistry may be somehow altered later in the development of planets, comets, and asteroids, as they smash together in a protoplanetary disk. Tobin has identified several other candidates that are in the Orion star-forming region, adding that you just need to find something that has a disk around it.

Conclusion

The origin of Earth's water has long been a mystery,