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“I started to take an interest in space and was looking for places where ions would be accelerated against surfaces,” Giapis said in a statement. “After looking at measurements made on Rosetta's comet, particularly regarding the energies of the water molecules hitting the comet, it all clicked. What I've been studying for years is happening right here on this comet.”
In a new paper, Giapis and his co-author and Caltech colleague Yunxi Yaos propose that the molecular oxygen at Comet 67P is not ancient, but is being produced right now by interactions within the comet’s nebulous aura, or coma, between water molecules coursing off the comet and particles streaming from the sun.
“We have shown experimentally that it is possible to form molecular oxygen dynamically on the surface of materials similar to those found on the comet,” said Yaos.
Here’s how it works: Water vapor molecules stream off the comet as it is heated by the sun. The water molecules become ionized, or charged, by ultraviolet light from the sun, and then the sun's wind blows the ionized water molecules back toward the comet. When the water molecules hit the comet's surface, which contains oxygen bound in materials such as rust and sand, the molecules pick up another oxygen atom from the surface and O2 is formed.
“This abiotic production mechanism is consistent with reported trends in the 67P coma,” the researchers write in their paper, “and raises awareness of the role of energetic negative ions,” not only in comets but other planetary bodies as well.
This oxygen-producing mechanism could be happening in a wide range of situations.