Water is found throughout the Solar System. Not just on Earth, but on icy comets and moons, and in the shadowed basins of Mercury.
Water has been found included in mineral samples from meteorites, the Moon, and Mars.
The new study, published in the journal Science, found that a significant fraction of Earth’s water originated as ices that formed in interstellar space.
“This is an important step forward in our quest to find out if life exists on other planets. We know that water is vital for the evolution of life on Earth, but it was possible that Earth’s water originated in the specific conditions of the early Solar System, and that those circumstances might occur infrequently elsewhere,” said study senior author Prof Tim Harries of the University of Exeter.
“By identifying the ancient heritage of Earth’s water, we can see that the way in which our Solar System was formed will not be unique, and that extrasolar planets will form in environments with abundant water.”
To determine whether Earth’s water formed before, or during, the birth of the Sun, Prof Harries and his colleagues using sophisticated modeling techniques simulated the chemistry that went on as the Solar System formed.
They focused on the ratio of two slightly different varieties of water: the common kind and a heavier version called deuterium oxide, a form of water that contains a higher-than-normal proportion of the hydrogen isotopedeuterium.
Today, comets and Earth’s oceans hold particular ratios of heavy water – higher ratios than the Sun contains.
“We let the chemistry evolve for a million years – the typical lifetime of a planet-forming disk – and we found that chemical processes in the disk were inefficient at making heavy water throughout the Solar System,” said study first author Ilse Cleeves, a doctoral student at the University of Michigan.
The scientists found that up to 50 percent of Earth’s water, and 60 to 100 percent of the water in comets, came from the Sun’s birth environment, and thus roughly a million years older than the Sun itself.
