What is the Significance of the C/O Ratio in Exoplanets?

A common question that has come up from search queries is How C/O ratio related to the exoplanets? Consider that after hydrogen and helium, carbon and oxygen are two of the most abundant elements in the Universe. That means that carbon and oxygen are amongst the most abundant elements in stars and planets.

It has been found that the carbon to oxygen ratio (the C/O ratio) in some exoplanets is different to the corresponding ratio in the host (parent) star. This means that the C/O ratio is in some way encoding information about the history of the planet, its formation and evolution. Even if the C/O ratios of the planet and its host star are not different, the planetary C/O ratio is a signature the physical and chemical composition and processes that pertained to the environment in which the planet formed. The catch is that unraveling this information from the C/O ratio and other measurable quantities is not easy. This is because the physics of the problem is highly complex, assumptions have to be made to simplify the problem, and one has to construct a model and compare it to the data. There are ambiguities in this process and the inferences made from the modeling. It is very much an active area of research.

Readers who have a suffiently advanced knowledge of physics are referred to a paper by Moses et al. (2013) which gives a good summary of the literature on the topic, and describes the results of a detailed investigation of modeling the C/O ration in giant planets.

Read more about exoplanet science in the book Exoplanets and Alien Solar Systems.

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File under: Exoplanet albedo; Different types of albedo; bond albedo; geometric albedo.