Volatiles on Mars

Compared to Earth’s atmosphere, Mars has a thin CO2-rich atmosphere with a surface pressure of about 700 Pa. When normalized to planetary mass (mass of Mars is 10.7% of that of Earth), the abundance of volatiles on Mars is about 0.07% to 6% of that on Earth (when CO2 in terrestrial carbonates is included). Is the depletion of volatiles on Mars a primary feature (because less volatiles accreted on Mars than on Earth), or a secondary feature (due to lower degree of degassing or due to gas escape to outer space)? In this contribution, I outline a simple model for volatile budgets of Mars, and implications for water on Mars.