First icy star-disc hints at source of Earth's water
For the first time, astronomers have found a planet-forming disc around a star that is awash with frozen water. The discovery adds credence to the idea that Earth got its water from comets – especially as the disc seems to contain enough water to fill Earth's oceans thousands of times over.
Hot water vapour has previously been detected in the inner part of the planet-forming discs of nascent, alien solar systems. But this is too close to the central star to be incorporated into the forming planets.
By contrast, the new observations are of water in the form of ice grains, which can exist only in the frigid outer reaches of a planet-forming disc. It is there that they can ultimately coalesce into planets and comets.
Before planets form, the disc of material surrounding young stars is mostly gas. Astronomers can probe the contents of that gas by analysing the spectra of the light it emits. Earlier observations had found organic materials like carbon monoxide and cyanide in such discs, but because Earth's own atmosphere is so damp, it interferes with the detection of alien water from the ground.