| With the explosion of exoplanetary discoveries, the question of planetary habitability is at the forefront, and generates many interesting and complex questions. One of those questions: Are planetary global magnetic fields necessary for the development of complex surface organics and the development of life? Does a global field protect planetary atmospheres? What detection signatures can be gleaned from a planet or moon with a global field as opposed to one without? We have a wealth of in situ magnetospheric data from Earth, as well as solar system planets and their moons from several vital satellite missions, such as the Voyager missions, the Pioneer missions, Galileo, Cassini, Messenger, MAVEN, and New Horizons. Due to the distances involved, it is not tenable to send satellites to obtain data at exoplanetary bodies, so we rely on simulations and using solar system data as analog environments to help set ground truth validation for the numerical work.;In this dissertation, I use a multifluid plasma model for gas giant magnetospheres to predict the potential dynamical consequences and detection signatures for giant exoplanets in a warm orbit (∼0.2 AU). I discuss the dynamics of plasma loss from an exomoon injected torus, and how the total mass flux out of the system is altered by increased stellar wind forcing as a function of orbital semi-major axis. Detection signatures for such a planet, including transit depth modifications due to plasma densities and radio emissions, show promise for further detecting and characterizing future systems. I also improve the multifluid model by implementing a full treatment of pressure anisotropy at Saturn, with a focus on the dynamics and structure of the magnetosphere. The improvements to the physics of the model generate more accurate system when compared to Cassini data; the anisotropic simulations show stronger current confinement of the Enceladus torus, consistent and well-structure flux interchange events, and global corotational convection that match more closely with the Cassini data than the isotropic model.;Turning from giant planets to terrestrial, I use a coupled one-dimensional photochemical and radiative-convective climate model to investigate the effects of M dwarf stellar flare activity on an Earth-like atmosphere for an unmagnetized planet in the nominal habitable zone. I find that EM-only activity - even to the level of some of the most active stars yet observed - is insufficient at the age of the universe to reduce the ozone column to the point that UV-C radiation can reach the surface. However, repeated proton events from frequent daily flare activity, which has been observed on several M dwarfs, can erode the ozone column by several orders of magnitude, allowing the surface of the planet to be bathed in UV-C, which is sterilizing and detrimental to the development of complex organic structures. The ability of a strong planetary magnetic field to deflect incoming stellar wind and flare-energized protons seems to be of import to maintain surface habitability.;I also use scaling laws to predict a potential atomic oxygen auroral signal from Proxima Centauri b, the detection of which would constrain the presence of an atmosphere and point to the presence of a magnetic field. The increased forcing from Proxima Centauri's stellar wind is expected to drive powerful emissions, orders of magnitude stronger than at Earth, and within easy reach of the next generation of observational telescopic instruments.;Magnetic fields do seem to be important for both detection and potential shielding of the atmosphere of exoplanets, but much work remains to be performed. Future observations combined with simulations validated against solar system star-planet interactions will likely provide answers to these questions, and perhaps lead to a focus on specific planetary targets for extensive investigation of astrobiological interest. |
