Oxygen Gas From Comets

Rosetta was a European Space Agency (ESA) Mission, launched in 2004 with the goal of capturing comet 67P/Churyumov-Gerasimenko in 2014 and to accompany it into the interior solar system. Onboard was an instrument known as ROSINA (Rosetta Orbiter Sensor for Ion and Neutral Analysis) which combined two mass mass spectrometers to study the composition of  the comet's corona.
In 2015, researchers from the Center for Space and Habitability (CSH) at the University of Bern analysed the comet's gases and made an unexpected discovery, traces of molecular oxygen (O_2(g)) were detected! It turned out that molecular oxygen was the fourth most abundant gas in the comet's atmosphere after water, carbon monoxide and carbon dioxide!
Where did this molecular oxygen come from? Surely if it was formed very early, at about the same time as the Solar System, it would have reacted with other substances by now because molecular oxygen is very reactive. We could expect compounds containing oxygen like carbon dioxide and water, but not molecular oxygen.
This puzzle was only solved in 2017.

Caltech Professor Konstantinos P. Giapis studies chemical reactions involving high-speed ions colliding with semiconductor surfaces as a means to create faster computer chips and larger digital memories for computers and phones. He thought the same thing was happening in the comet.

First, as the comet is heated by the sun, water vapor is released from the icy comet..
Next, ultraviolet light from the sun causes the water molecules to become ionised.
Then the ionized water molecules are pushed back towards the surface of the comet by the sun's wind.
After that the ionized water molecules hit oxygen containing compounds on the surface of the comet like rust and sand.
Finally the molecules pick up another oxygen atom from these surfaces to form molecular oxygen.

This gives us a possible mechanism by which molecular oxygen could be produced in space without the need for living things, and, could change the way we search for signs of life on planets beyond our solar system.


Reference
California Institute of Technology. "Chemical engineer explains oxygen mystery on comets." ScienceDaily. ScienceDaily, 8 May 2017. .

Further Reading:
Pure Substances and Mixtures

Elements and Compounds

Molecular Formula

Molecular Formula for Covalent Compounds

Physical and Chemical Changes

Mass and Moles in a Chemical Reaction

Mass Spectroscopy for Isotopes

Mass Spectroscopy for Structural Determination


Suggested study Questions:

1.  Which of the following are pure substances?
   • molecular oxygen
   • water
   • carbon monoxide
   • carbon dioxide
   • rust
2.  Which of the following substances are mixtures?
   • molecular oxygen
   • water
   • carbon monoxide
   • carbon dioxide
   • rust
3. Which of the following substances are elements?
   • molecular oxygen
   • water
   • carbon monoxide
   • carbon dioxide
   • rust
4. Which of the following substances are compounds?
   • molecular oxygen
   • water
   • carbon monoxide
   • carbon dioxide
   • rust
5.  Write the molecular formula for each of the following:
   • molecular oxygen
   • water
   • carbon monoxide
   • carbon dioxide
6.  Write chemical equation for the first reaction that occurs on the comet's surface.
7.  Explain how a water molecule could be ionized.
8.  Explain why molecular oxygen is considered to be a reactive molecule. 
9.  Assume that a comet has a mass of 10¹⁴ kg and that it is composed only of water. Calculate the maximum mass of molecular oxygen that could be formed if the entire comet was vaporized.
10.  Explain how a mass spectrometer can be used to identify elements and compounds in space.