Oxygen controls on magmatism in rocky exoplanets

Area of Science:

• Planetary Science
• Geochemistry
• Exoplanetology

Background:

• Refractory oxygen is crucial for rocky exoplanet interiors, influencing core formation, mineralogy, and atmospheric composition.
• Oxygen fugacity (fO2) dictates the oxidation state of metals, affecting planetary differentiation.
• Previous studies focused on fO2's impact on metal valence, not directly on rock melting.

Purpose of the Study:

• To investigate the direct effect of oxygen fugacity (fO2) on the melting behavior of rocks.
• To understand how oxygen abundance influences magmatism and differentiation in exoplanets.

Main Methods:

• Performed melting experiments on synthetic iron-free basalt under varying oxygen fugacity (fO2) conditions.
• Simulated reducing (log fO2 = -11.5, -7) and oxidizing (log fO2 = -0.7) interior environments.
• Measured the liquidus temperature of the basalt at 1 atm pressure.

Main Results:

• Increasing oxygen fugacity (fO2) by 11 log units lowered the liquidus of iron-free basalt by 105 ± 10°C.
• This melting point depression is comparable to the effect of volatiles like H2O or CO2.
• Oxygen abundance directly impacts the conditions for magmatism, independent of iron or volatiles.

Conclusions:

• Refractory oxygen abundance is a key control on exoplanetary differentiation dynamics.
• Higher oxygen fugacity (fO2) promotes more extensive magmatism and volcanic outgassing.
• This has significant implications for understanding the evolution and atmospheric composition of rocky exoplanets.