The next time you reach for a glass of water you might want to think about its primordial origins. A new study suggests that upwards of 50% of the Earth's water may be older thank the solar system itself. A recent experiment conducted by Ilse Cleeves at the University of Michigan may finally settle a debate about just how far back in galactic history our planet and our solar system's water formed.
There are two schools of though on the matter: (1) the molecules in comet ices and terrestrial oceans were born within the solar system itself, or (2) the water originated much earlier in the cold molecular cloud that generated the sun and its protoplanetary disk.
According to Cleeves, it's the latter; her simulation shows that between 30-50% came from the molecular cloud, making it roughly a million years older than the solar system. From the University of Michigan release:
To arrive at that estimate, Cleeves and Ted Bergin, a professor of astronomy, simulated the chemistry that went on as our solar system formed. They focused on the ratio of two slightly different varieties of water—the common kind and a heavier version. Today, comets and Earth's oceans hold particular ratios of heavy water—higher ratios than the sun contains.
“Chemistry tells us that Earth received a contribution of water from some source that was very cold—only tens of degrees above absolute zero, while the sun being substantially hotter has erased this deuterium, or heavy water, fingerprint,” Bergin said.
To start their solar system simulation, the scientists wound back the clock and zeroed out the heavy water. They hit "go" and waited to see if eons of solar system formation could lead to the ratios they see today on Earth and in comets.
"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," Cleeves said. "What this implies is if the planetary disk didn't make the water, it inherited it. Consequently, some fraction of the water in our solar system predates the sun."
One of the implications of this study is our sense of how much water — an important precursor for life — exists in the galaxy and in individual solar systems. This model suggests that other stellar systems also had access to the same ancient water reserves which were crucial for the development of life on Earth.
Water, therefore, may be quite abundant in the Milky Way and beyond.
“The implications of these findings are pretty exciting,” Cleeves said. “If water formation had been a local process that occurs in individual stellar systems, the amount of water and other important chemical ingredients necessary for the formation of life might vary from system to system. But because some of the chemically rich ices from the molecular cloud are directly inherited, young planetary systems have access to these important ingredients.”
To which Bergin added: "Based on our simulations and our growing astronomical understanding, the formation of water from hydrogen and oxygen atoms is a ubiquitous component of the early stages of stellar birth. It is this water, which we know from astronomical observations forms at only 10 degrees above absolute zero before the birth of the star, that is provided to nascent stellar systems everywhere."
Check out the entire study at Science: "The ancient heritage of water ice in the solar system." Supplementary info via University of Michigan.