The Water in Our Solar System and on Earth is Older Than the Sun

Earth is known for its abundance of water. But where did that water come from in the first place and how did it get to our planet? Scientists have now discovered that much of our solar system's water probably originated as ice that first formed in interstellar space.

Water can be found throughout our solar system on icy comets and moons in addition to the shadowed basins of Mercury. Yet exactly how this water formed and got to these planetary bodies has long been cause for speculation. While the sun was surrounded by a protoplanetary disk in its youth from which the planets were born, it's been unclear whether the ice in this disk originated from the sun's own interstellar molecular cloud or if this water had been destroyed and reformed by the chemical reactions in the solar nebula.

In order to better understand the history of our solar system's ices, the scientists focused on hydrogen and its heavier isotope, deuterium. The difference in masses between isotopes causes subtle differences in their behavior during chemical reactions. This means that the ratio of hydrogen to deuterium in water molecules can tell scientists about the conditions under which the molecules formed.

The researchers created models that simulated a protoplanetary disk in which all the deuterium from space ice had already been eliminated by chemical processing and the system had to start over, producing ice with deuterium in it during a million-year period. In the end, the researchers found that the model couldn't produce the same ratios of deuterium to hydrogen that are found in meteorite samples. This means that at least some of the water in our solar system has an origin in interstellar space and predates our own sun.

"Our findings show that a significant fraction of our solar system's water, the most fundamental ingredient to fostering life, is older than the sun, which indicates that abundant, organic-rich interstellar ices should probably be found in all young planetary systems," said Conel Alexander, one of the researchers, in a news release.

The findings are published in the journal Science.