THE EVOLUTIONARY ROLE OF PROLONGED VOLCANISM ON THE FORMATION AND CHANGES OF THE MARTIAN ATMOSPHERE

For billions of years, Mars has been a carrier of powerful volcanic activity. Volcanism provided the initial formation of the atmosphere and hydrosphere and continues to influence the dynamics of the modern gas composition and the activity of mantle plumes. The Earth is characterized by plate tectonics, which provides an exchange of volatile substances between the atmosphere and the mantle. The absence of plate movement on Mars led to the accumulation of magma in one place, and to the formation of huge shield volcanoes. Such a concentrated release of energy and mass had global consequences for the atmosphere, since each large eruption was able to throw into the air an amount of gases sufficient to temporarily change the climatic regime of the entire planet. In the early historical period, intensive degassing of the primary mantle occurred; this led to the creation of a dense atmosphere of CO2 and H2O. Martian volcanoes also emitted other gases. For example, the ratio of deuterium to hydrogen (D/H) on Mars is 5–6 times higher than on Earth; this indicates a selective loss of light hydrogen to space over billions of years. Similarly, volcanic nitrogen helped explain the observed 15N/14N ratio. The evolution of ideal gases, in particular xenon Xe, suggests that most of the atmospheric distribution of gaseous constituents occurred within the first few hundred million years of the planet's history. It was long believed that on Mars, as on Earth, the main sulfur-containing gas was sulfur dioxide SO2. However, new modeling, taking into account the oxidation state of the Martian mantle, shows that Mars emitted mainly reduced forms of sulfur: hydrogen sulfide H2S, sulfur S2, and the powerful greenhouse gas sulfur hexafluoride SF6. It retains heat thousands of times more effectively than CO2. The presence of SF6 on Mars also explains the existence of liquid water 3–4 billion years ago without the need to assume unrealistically high concentrations of CO2. The results of the InSight mission and modern orbital observations have shown that Mars remains a geologically active planet.