The influence of the Venusian atmosphere on the impact crater record.

Enigmatic Venus has long been a subject of intense fascination. It has been called “Earth’s twin,” and yet it is encapsulated by an atmosphere of carbon dioxide and sulfurous gases that generates a surface pressure of 93 bars and cloud-level wind speeds of 100 m/s. The planet’s atmosphere protects its planet from asteroid impacts so effectively that only ~900 craters ranging in diameter from ~1.5 km to 270 km have formed on its ~800-Myr-old surface. However, the evolution of this “atmospheric shield” remains uncertain. It has been suggested that extensive volcanism has thickened the atmosphere. Alternatively, it has been postulated that solar wind stripping of ionospheric molecules has depleted the atmosphere to what it is today. However, the dominant mechanism that has driven the evolution of the Venusian atmosphere throughout the history of its current surface has remained largely unresolved in the literature. This work employs an in-house Fourth Order Runge-Kutta MATLAB® code (Horus Geb) to simulate the Venusian crater record with two asteroid population density models. The corresponding surface ages were determined to be 100 Myr and more credibly 800 Myr. Presented in this thesis is the first direct evidence that the evolution of the Venusian atmosphere has been dominated by “atmosphere thickening,” and consequently, the density of the atmosphere has increased over the history of its surface.