Earth's Water is Older Than the Sun
And why that makes alien life a lot more likely.
Image: Davide Restivo
Astronomers have discovered that much of the water on Earth—and the solar system—predates the Sun.
Not only is that an insane thing to think about, it's a breakthrough that suggests water is abundant in other planetary systems as well.
We've known for a while that the water on Earth is very old, but this latest finding suggests it's almost unfathomably old. The finding fuels speculation that the processes and materials that led to life on Earth may be a common paradigm throughout the universe.
Researchers arrived at their results by creating a detailed computer simulation of the early solar system:
"While we can't go back in time to see the the Sun and solar system at its formation," Ilsedore Cleeves, a researcher at the University of Michigan who made the discovery, told me. "The wonderful thing about the vastness of the galaxy is that we can observe many other young Sun-like stars that are currently forming or have recently formed."
"By studying these astrophysical objects using high power telescopes and numerical techniques, we can use this information to model the protoplanetary disk environment in great detail," she said.
The specific variable that Cleeves and her colleagues, who published a paper on the finding in the journal Science, honed in on was 'heavy water' interstellar ice in the protoplanetary disk. Heavy water contains deuterium—a hydrogen isotope—in the place of a normal hydrogen atom. It forms at temperatures hovering just above absolute zero, and was widespread during the birth of the solar system, judging by samples originating from that period.
"Earth's oceans, meteorites, and comets all show high levels of heavy water (HDO) to light water (H2O) as compared to the number of deuterium to hydrogen atoms in the universe," Cleeves explained. "Putting together our current knowledge of disk energetic processes, I simulated how much heavy water we'd expect to form under within the protoplanetary disk environment."
The question was whether the high deuterium levels found in those samples was "inherited" from the pre-existing environment of interstellar gas, or whether it was created by chemical reactions in the accreting protoplanetary disks.
"The short answer was that disks did not synthesize heavy water in abundance, and so could not have been the original source of our water," Cleeves said. "This work implies that much of the solar system's water ice was inherited from the original birth environment of the Sun in very dark, cold interstellar gas."
In other words, much of the water that flows on Earth is older than the planet itself, as well as its host star. Its a mindboggling notion, especially when extended to other exoplanets and stars.
Water may be inherently seeded into solar systems across the universe, and so might other essential organic compounds. Indeed, that's where Cleeves is taking her research next.
"We will follow up this work by looking at what else may have been delivered along with the water ice," she said. "Interstellar ices are extremely chemically rich blends of many different species, with abundant carbon-bearing ices, including simple organics—it will be interesting to see what else made it into the solar system too."
Co-author and cosmochemist Conel Alexander also emphasized the astrobiological potential of discovery.
"Primitive meteorites and at least one comet contain deuterium-rich organic matter," he told me. "As with the water, there is an ongoing debate about whether the organic matter formed in the presolar molecular cloud or in the solar system. We are planning a second paper to look into this issue."
Let's hope the next paper adds even more weight to the theory that habitable conditions abound across the universe, nurturing alien biodiversity on countless other worlds.