Who would have guessed that Earth鈥檚 oceans are older than the sun? Much of the water on our planet and around the solar system started out as tiny grains of ice floating in interstellar space. The discovery provides important clues about not only the make-up of our solar system, but also what planets around other stars might be like.
鈥淲ater is an essential ingredient that pretty much all known forms of life on Earth need to flourish,鈥� says at the University of Michigan in Ann Arbor. 鈥淭o understand where water came from tells us a little bit about how common life is in the universe.鈥�
All water in the solar system 鈥� whether on planets, in comets or meteorites, or icy moons like Europa 鈥� contains a certain amount of deuterium 鈥� an isotope of hydrogen that has an extra neutron attached.
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Ripped apart
Ice found between stars is even more deuterium-rich, so it was long suspected that it was the source of our solar system鈥檚 heavy water. But the young solar system was so violent and full of radiation that any incoming ice should have been ripped apart, recombining later into water 鈥� according to this picture.
But when Cleeves and her collaborators built a model of the early sun, they found that this explanation didn鈥檛 stand up. After their model scrapped all of the interstellar ice, they found that oxygen was being locked up in frozen carbon monoxide. And there wasn鈥檛 enough ionised, deuterium-rich hydrogen being produced either. In short, the nascent solar system wouldn鈥檛 have had the ingredients for water with the high levels of deuterium we see.
Instead, interstellar ice must have made its way into planets, moons and comets intact. Cleeves and her colleagues calculate that as much as half the water in Earth鈥檚 oceans and possibly all of the water found in comets came from this ancient source.
Ice isn鈥檛 the only thing out there in interstellar space 鈥� there鈥檚 also organic material, says , a planetary scientist at the University of Chicago. If this interstellar stuff went into the formation of our solar system鈥檚 planets, then it probably forms part of planets around other stars too 鈥� boosting the chances that many planetary systems formed with the raw ingredients for life.
鈥淚t provides the opportunity for organic materials, and the things that are important to the formation of life, to at least be accessible to all planets out there,鈥� says Ciesla. 鈥淲hether or not it forms into aliens and little green men and women is a whole other story.鈥�
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