Water vapor reservoir near star provides clue to how Earth’s oceans were filled
Water is everywhere on Earth, but nobody has ever been able to determine conclusively how it got here. Scientists know that the early Earth was far too hot to hold water or water vapor, but then, in relatively short geological time, the oceans appeared.
In a discovery that researchers say sheds important new light on that age-old question, a European team reported Thursday that it has found a very cold reservoir of water vapor in spacethat could explain where the water came from.
The region they discovered is at the outer reaches of a dusty disk surrounding a star 175 light-years away. The star and disk are in the early stages of forming planets, much as Earth was formed some 4.5 billion years ago.
The scientists’ conclusion from the new finding: Life-giving H2O was almost certainly delivered to Earth via comets and asteroids known to originate in these cold but water-filled zones, which were assumed to also be present when our solar system was forming.
“Our observations of this cold vapor indicates enough water exists in the disk to fill thousands of Earth oceans,” said astronomer Michiel Hogerheijde of Leiden Observatory in the Netherlands.
Hogerheijde is the lead author of a paper describing these findings in the Oct. 21 issue of the journal Science.
“Scientists have long suspected there were these reservoirs of cold water vapor hiding in the outer regions of planet-forming disks, but until now we’ve only found signs of water vapor in hot regions closer to the suns,” Hogerheijde said in an interview. “Since the comets and cold asteroids are formed in the outer reaches, this was a problem for the theory that comets delivered the water to Earth. But now we have the cold reservoir in the region where comets are formed, and so the theory gets considerably stronger.”
The logical extension, he said, is that water has also been delivered to some of the billions of exoplanets known to exist beyond our solar system, meaning there are likely to be many “ocean worlds” throughout the galaxies.