<p dir="ltr">The climate and habitable potential of a planet is controlled in part by its orbital configuration, including its obliquity, eccentricity, rotation period, and separation from the host star. Recent studies have suggested the exoplanets with higher eccentricity or obliquity than Earth might be able to produce larger biospheres, potentially leading to "super-habitable" worlds. However, high-obliquity and high-eccentricity planets have also been shown to be susceptible to increased water loss, which would decrease the habitable lifetime.</p><p dir="ltr">I use ExoPlaSim, a 3D General Climate Model, to investigate the habitable lifetimes of a diverse range of possible orbital configurations by varying the planetary obliquity (0-90^o), eccentricity (0-0.4), rotation period (6-96 hr), and stellar constant (1350-1650 W/m²). I study each orbital parameter independently while also co-varying obliquity with eccentricity and rotation period for the entire range of stellar constants. I find that stellar constant is the primary control on atmospheric water vapor, but also that the planetary obliquity, eccentricity and rotation period can determine the escape regime. Increasing the obliquity or eccentricity can push the climate into the significant escape regime at lower stellar constants relative to low-obliquity or low-eccentricity planets. Increasing the rotation period at high obliquities maximizes the habitable lifetime of an exoplanet.</p>

The contemporary terrestrial atmosphere loses matter at a rate of around 100,000 tons per year. A major fraction of the net mass loss is constituted by ions, mainly H+ and O+, which escape from the Earth’s ionosphere in the polar regions. Previously, the outflow has only been measured at low altitudes, but to understand what fraction actually escapes and does not return, the measurements should be conducted far from the Earth. However, at large geocentric distances the outflowing ions are difficult to detect with conventional ion instruments on spacecraft, since the spacecraft electrostatic potential normally exceeds the equivalent energy of the ions. This also means that little is known about the ion outflow properties and distribution in space far from the Earth. In this thesis, we present a new method to measure the outflowing low-energy ions in those regions where they previously have been invisible. The method is based on the detection by electric field instruments of the large wake created behind a spacecraft in a flowing, low-energy plasma. Since ions with low energy will create a larger wake, the method is more sensitive to light ions, and our measured outflow is essentially the proton outflow. Applying this new method on data from the Cluster spacecraft, we have been able to make an extensive statistical study of ion outflows from 5 to 19 Earth radii in the magnetotail lobes. We show that cold proton outflows dominate in these large regions of the magnetosphere in both flux and density. Our outflow values of low-energy protons are close to those measured at low altitudes, which confirms that the ionospheric outflows continue far back in the tail and contribute significantly to the magnetospheric content. We also conclude that most of the ions are escaping and not returning, which improves previous estimates of the global outflow. The total loss of protons due to high-latitude escape is found to be on the order of 1026 protons/s.

Mars’ climate has undergone many massive changes over the course of it’s lifetime. In order toestablish how Mars lost the vast majority of its water, we must be able to understand how Marsis losing its atmosphere today. By understanding the current escape rates of H and D and theprocesses that control them, we can extrapolate back in time to model the escape rates under pastconditions. By using the Exospheric General Model (EGM) developed by researchers at LATMOS,Sorbonne University, I have simulated the density profiles and escape rates of H, D, related isotopesand particles due to collisions with hot oxygen particles in the Martian exosphere at the currentepoch at mean solar activity. By adding H and D to the model and implementing changes to theprogram between simulations, I have improved the accuracy of the escape rate of these particlesfrom Mars in the EGM. While my results for H, H2 and HD reflect what has been observed fromin-situ Martian Satellite, MAVEN, future work is needed to include the solar wind interaction for Din the model, as it has been shown to be significant and has been left out of this work.