Molecular oxygen has never been detected on a comet before, although it has been observed in the atmospheres of icy moons orbiting Saturn and Jupiter. The discovery, may provide new clues about the conditions and environment where the Earth, Sun and solar system were born 4.6 billion years ago.
From September 2014 to March 2015, as 67P made its way closer to the Sun, researchers used a mass spectrometer on Rosetta to find out the molecules swirling around the comet and identify their chemical composition. They found on average that oxygen makes up 3.8% of the cloud relative to the most abundant substance, water.
It was not immediately clear where the oxygen came from. The researchers discovered that water and oxygen were often found together, an indication that similar processes could released both molecules.
The Rosetta space probe has been studying the comet for over a year and has detected an abundance of different gases pouring from its nucleus. Water vapour, carbon monoxide and carbon dioxide are the most prolific, with a rich array of other nitrogen, sulphur and carbon bearing species.
article reference:- nature.com