Study: Trip around the sun may have altered comet water cycle

By Brooks Hays
A trip past the sun has appeared to alter the production processes of H2O and HDO on the surface of the comet Lovejoy. Photo by Damian Peach/NASA
A trip past the sun has appeared to alter the production processes of H2O and HDO on the surface of the comet Lovejoy. Photo by Damian Peach/NASA

Feb. 28 (UPI) -- Water production processes on Oort cloud comet C/2014 Q2, comet Lovejoy, may have been altered during the comet's closest approach to the sun, its perihelion.

Keck Observatory readings showed comet Lovejoy began producing two to three times more HDO, a heavier form of water.


Astronomers used Keck to monitor H2O and HDO production rates before and after Lovejoy's perihelion. HDO is a water molecule formed with deuterium, hydrogen atoms with a nucleus containing one proton and one neutron.

After its closest approach to the sun, H2O production on Lovejoy remained stable but HDO production increased, rising the water's D-to-H ratio and altering its chemical signature.

"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," Lucas Paganini, a researcher with the Goddard Center for Astrobiology, said in a news release.

Usually, when water processes are affected by solar energy, different water forms typically rise and fall in unison.

"If the D-to-H value changes with time, it would be misleading to assume that comets contributed only a small fraction of Earth's water compared to asteroids, especially, if these are based on a single measurement of the D-to-H value in cometary water," Paganini explained.


Because water typically features several thousand H2O atoms for every HDO atom, the level of HDO on comets is difficult to measure. However, Keck was able to measure HDO levels accurately because Lovejoy was so bright as a result of being so close to the sun. Researchers published their findings in the Astrophysical Journal Letters.

Scientists say solar radiation may have altered the chemical composition of surface water on Lovejoy, and there's a chance the comet has matured into a new phase of its lifecycle. It's also possible Lovejoy has long experienced D-to-H ratio fluctuations while astronomers and their instruments are only just now picking up on it.

"Comets can be quite active and sometimes quite dynamic, especially when they are in the inner solar system, closer to the sun," said Michael Mumma, director of the Goddard Center for Astrobiology. "The infrared technique provides a snapshot of the comet's output by measuring the production of H2O and HDO simultaneously. This is especially important because it eliminates many sources of systematic uncertainty."

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