| Venus is a hot and dry planet where surface temperatures range from 660 to 740 K and water vapor in the sub-cloud atmosphere is present at ∼30 parts per million by volume. In contrast, Earth's average surface temperature is 288 K and its troposphere is much wetter with a water vapor content up to ∼4%. Even though these planets formed next to each other within the inner Solar System, they have very different characteristics. We might reasonably expect that both planets would have accumulated similar amounts of water during accretion. However, the extreme differences between the two planets leads us to the long standing question: has Venus always been dry, or did it lose its water over time?; If Venus had more water in the past as the high D/H ratio suggests, then hydrous minerals may have formed. This high ratio is indirect evidence that Venus had more water in the past. Irrefutable proof of greater water abundance in Venus' past could be obtained with the detection of hydrous minerals. However, thermodynamic models predict that hydrous minerals are unstable on Venus' surface and the decomposition rates are unknown. This thesis is the first experimental study that measures the decomposition rate of a hydrous mineral, specifically tremolite, with applications to Venus. My results show that once formed, tremolite will survive for billions of years at Venus' surface temperatures. Thus if Venus did indeed have more water in the past and hydrous minerals such as tremolite formed, the possibility remains that hydrous minerals could be detected on Venus today.; This thesis is composed of 4 journal articles. The first paper is a review of atmosphere-surface reactions predicted to occur on Venus and the remaining three cover the thermal decomposition kinetics of tremolite (Ca2Mg 5Si8O22(OH)2). Each of the tremolite decomposition papers has a different emphasis. The first focuses on the implications of the decomposition rate of tremolite for Venus, the second discusses the products, kinetic analysis and mechanism of tremolite decomposition and the last is about the slower decomposition rate of fluorine-bearing tremolite (fluor-tremolite is thermodynamically more stable than OH-tremolite). |
