Scientists have for the first time detected oxygen on a comet, a finding that could upend theories about how the solar system was formed.
Reporting their findings in the journal Nature on Wednesday, an international team said that they detected "a lot" of molecular oxygen in the cloud of gas, or coma, surrounding the nucleus of comet 67P/Churyumov-Gerasimenko.
While molecular oxygen has been found in Jupiter and Saturn, it's never been found on a comet. The neutral gas comas of most comets are composed largely of water, carbon monoxide and carbon dioxide.
"It is the most surprising discovery we have made so far in 67P because oxygen was not among the molecules suspected in a cometary comas," Kathrin Altwegg, one of the co-authors on the paper from the University of Bern, told reporters during a press conference Tuesday. "The first time we saw it I think we all went a little bit into denial because it was not expected to be found in a comet," she said. "Molecular oxygen is very reactive. There was a lot of hydrogen around when the solar system was formed. Everybody and all models showed that molecular oxygen would react with the hydrogen and would no longer be present as molecular oxygen."