Vol. 625
In section 1. Letters

Terrestrial deuterium-to-hydrogen ratio in water in hyperactive comets

by D. C. Lis et al. 2019, A&A, 625, L5

Contrary to the other planets of the solar system, the surface of the Earth is dominated by liquid water. The origin of this water is unclear, which has motivated the investigation of extraterrestrial sources. For that, the deuterium-to-protium ratio (D/H) is a good indicator. Deuterium and protium are two stable isotopes of hydrogen, and a source for the water filling our oceans should have a similar D/H value. Up to now, comets had been thought to be inconsistent with the ratio measured on Earth. This conclusion was a result of measurements from four comets: Halley, Hyakutake, Hale–Bopp, and 67P/Churyumov–Gerasimenko. This new study by Lis et al. tells us that the hyperactive comet 46P/Wirtanen presents a D/H value in its outgassed water, during periods of hyperactivity that is similar to that of the Earth. The authors observed this comet with the GREAT spectrometer aboard the Stratospheric Observatory for Infrared Astronomy (SOFIA). They argue that the hyperactivity requires an additional source of water vapor, which would explain the different D/H value. They assume that these results could hold for any hyperactive comets, making them potential sources for our oceans.