Devil Comet’s Water Matches Earth, Strengthening Theory of Cosmic Origins

“Devil” comet water looks surprisingly like the water on Earth, researchers say. The discovery bolsters the notion that water was delivered to our planet by comets smashing into the young Earth, which helped prepare the stage for life to arise, the team reported Aug. 8 in the journal Nature Astronomy. “Our new findings provide the best evidence that the hydrogen originally in Halley's comet was used in the formation of Earth's water,” said Martin Cordiner, a NASA molecular astrophysicist who led the study, in a statement.

Why the Devil Comet Discovery Matters

According to Space, the astronomers found the signatures when they aimed their instruments at a comet known as 12P/Pons-Brooks (also known as the "Devil Comet") and looked."In the end, we were able to identify a repeated carbon (C) atom emission line with a very high enrichment ([C]/[H] abundance) of about 7 times the standard value of the universe," the astronomers wrote in the paper.

Comet 12P/Pons-Brooks is a Halley-type comet with a period between 20 and 200 years.
The researchers also analysed the ratio between deuterium (a neutron-loaded version of the hydrogen atom) and common hydrogen (D/H) — a “chemical fingerprint” that may be used to follow the water's lineage — in the water of Comet 12P/Pons-Brooks, found in ALMA and IRTF data.

How Scientists Mapped the Comet's Water

They found that the comet's water is “practically indistinguishable” from the water on Earth. This is especially intriguing, since prior estimates of the water on Halley-type comets feature distinct D/H ratios, which have cast severe doubts on the notion of comets bringing water to Earth. But now this new discovery helps to solidify it.

The ALMA observations of Comet 12P/Pons-Brooks represent the first time that the boundaries of water in any comet have been mapped like this. The team analysed both regular water (H2O) and “heavy” water (HDO), which contains deuterium. They also studied gases in the comet to get a better idea of what it's made of.