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takyon [soylentnews.org] writes:

The C/2014 Q2 (Lovejoy) [wikipedia.org] comet has been found to release more semiheavy water [nasa.gov] following its closest approach with the Sun:

The team focused on Lovejoy's water, simultaneously measuring the release of H₂O along with production of a heavier form of water, HDO. Water molecules consist of two hydrogen atoms and one oxygen atom. A hydrogen atom has one proton, but when it also includes a neutron, that heavier hydrogen isotope is called deuterium, or the "D" in HDO. From these measurements, the researchers calculated the D-to-H ratio – a chemical fingerprint that provides clues about exactly where comets (or asteroids) formed within the cloud of material that surrounded the young sun in the early days of the solar system. Researchers also use the D-to-H value to try to understand how much of Earth's water may have come from comets versus asteroids.

The scientists compared their findings from the Keck observations with another team's observations made before the comet reached perihelion, using both space- and ground-based telescopes, and found an unexpected difference: After perihelion, the output of HDO was two to three times higher, while the output of H₂O remained essentially constant. This meant that the D-to-H ratio was two to three times higher than the values reported earlier.

"The change we saw with this comet is surprising, and highlights the need for repeated measurements of D-to-H in comets at different positions in their orbits to understand all the implications," said Lucas Paganini, a researcher with the Goddard Center for Astrobiology and lead author of the study, available online in the Astrophysical Journal Letters [doi.org] [DOI: 10.3847/2041-8213/aa5cb3].

Semiheavy water [wikipedia.org].

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