It appears you don't have support to open PDFs in this web browser. To view this file, Open with your PDF reader
Abstract
For millennia, humanity has studied celestial objects through ground-based observations, including the Sun, planets, moons, and comets. Besides the orbits of these astronomical bodies, we have also observed space-based phenomena from the Earth, such as sunspots, solar eclipses, and aurorae. The emergence of space exploration and technological advancements in the mid-20th century enabled us to then directly probe the realm beyond our planet through in situ measurements. These innovations in direct, localized observations contributed significantly to addressing numerous questions related to the solar wind, planetary magnetospheres, and space weather. However, it was only around 20 years ago that the term Heliophysics was finally established to describe the interdisciplinary branch of science that connects the study of the Sun to its interactions throughout the solar system. This field was broadened to include the entire heliosphere, a vast region of space, influenced by the solar wind and the solar magnetic field, extending beyond the orbits of the outer planets. By framing our scientific approach to connect the solar corona, interplanetary medium, and geospace, we can gain a more cohesive understanding of the entire system.
Space-based technology for in situ measurements continues to advance, especially in studying the inner heliosphere, defined as the region extending from the Sun to the orbit of Jupiter. One example is the Parker Solar Probe (PSP) mission, which has traveled closer to the Sun than any previous spacecraft to study solar wind, solar activity, and the mechanisms that drive these phenomena. PSP includes a whole suite of instruments to examine the solar environment down to about 10 RS (solar radii) from the Sun. The mission primarily focuses on in situ measurements of the solar wind from intervals of quiescent conditions to large solar eruptive events. Another example is the Interior Exploration using Seismic Investigation, Geodesy and Heat Transport (InSight) mission on the surface of Mars to study the interior structure and seismic activity of the planet. The lander includes a magnetometer to provide the first surface magnetic field measurements on Mars. Additional magnetic field observations were later conducted by the Zhurong mission at 16 different locations on the Martian surface. This dissertation is dedicated to investigating these novel in situ measurements in different areas of Heliophysics, specifically focusing on the evolution of electrons and magnetic fields in the inner heliosphere. By analyzing spacecraft and lander measurements, along with numerical simulations, we investigate various environments between the Sun and Mars to connect different systems in the heliosphere for future studies.
We first aim to investigate the mechanisms that govern solar wind acceleration and energy balance near the Sun using PSP in situ measurements. These processes are theorized to be strongly influenced by the solar wind heat flux and ambipolar electric field, which can be studied through electron velocity distribution functions (eVDFs). While the electron core and halo populations of the eVDF are nearly isotropic, the strahl beam component is more anisotropic and typically magnetic field aligned. Due to the asymmetry and non-thermal nature of the electron strahl, this population mainly contributes to the overall heat flux in the near-Sun environment. The strahl beam can undergo adiabatic focusing by the solar magnetic field or pitch angle scattering due to Coulomb collisions and plasma wave instabilities. We can study the evolution of the electron strahl over a wide range of heliocentric distances under ambient solar wind conditions using the onboard Solar Probe ANalyzer-Electron (SPAN-E) instruments. Multiple calibration procedures are introduced to properly estimate various parameters of the solar wind electrons, such as electron density and temperature. As a proxy for strahl scattering, we fit to the beam distribution to obtain an angular strahl width and direction. We find the strahl beam to narrow with increasing electron energy. In addition, the strahl width is observed to vary with heliocentric distance, electron density, and electron collisional age. Our study suggests that close to the Sun, Coulomb collisions primarily scatter the strahl electrons, until whistler waves become the dominant mechanism above 30 RS from the Sun.
In the following chapter, our focus shifts to large solar eruptive events observed by PSP, specifically Interplanetary Coronal Mass Ejections (ICMEs). ICMEs originate from the Sun as Coronal Mass Ejections (CMEs), large structures of coronal plasma and magnetic fields that travel through the interplanetary medium. These structures can interact with planetary environments to cause space weather phenomena, such as geomagnetic storms, potentially resulting in widespread disruptions to power systems and communication networks. Extensive research has been conducted using in situ instruments to study these events as they reach Earth or other planets. However, directly observing ICMEs close to the Sun will improve our understanding of their evolution and provide better constraints for numerical models. An example of such an event occurred on 05 September 2022 when PSP passed through a topologically complex, fast ICME near the Sun. Fortunately, this ICME did not impact Earth, but had the capacity to heavily affect geospace on a similar scale to the famous 1859 Carrington Event. PSP traveled through the flank and wake of the structure, collecting in situ measurements of the bulk plasma and magnetic field within 14 RS from the Sun. We observe classical ICME signatures compared to structures that reach 1 AU (astronomical unit) near Earth, along with two magnetic inversion line crossings. We also utilize remote-sensing observations from PSP, providing a novel visual perspective of the ICME close to the Sun. The event is modeled as two individual CMEs propagating from the Sun to achieve the best agreement with both in situ and coronagraph observations. In addition, a global reconfiguration of the Heliospheric Current Sheet (HCS) is identified after the eruption, suggesting that CMEs play a significant role in the evolution of the HCS. As the HCS extends across the heliosphere, these solar eruptions can therefore influence regions of space well beyond their direct travel path.
The manner in which solar wind and eruptive structures interact with other astronomical bodies depend on the presence of a global planetary magnetic field. This interaction can result in the formation of planetary magnetospheres, which may shield a planet from the substantial influx of particles and energy associated with ICMEs. While Mars currently does not possess an active geodynamo, it still exhibits an induced magnetosphere due to the solar wind and interplanetary magnetic field (IMF). However, an ancient dynamo may have existed in the past due to evidence of localized, remanent crustal magnetization, especially in the southern hemisphere. Thus, investigating these crustal fields may provide insight on the evolution of Martian magnetization. The final chapter of this dissertation analyzes the first in situ surface measurements of the Martian crustal magnetic field at the InSight and Zhurong landing sites. We model the Martian crustal magnetization with Monte Carlo simulations based on the altitude profile of crustal magnetic fields above each mission site. Our results provide improved constraints on magnetization coherence and depth scales near the surface below InSight and Zhurong. Furthermore, we develop new models of subsurface magnetization based on geological and topographic features to relate different regions of magnetization with distinct periods in Martian history. Our study suggests the occurrence of at least one magnetic polar field reversal in the past, along with evidence of a potential reactivation of a new dynamo (now extinct) following a weakened or dormant Martian geodynamo.
In each chapter, we utilize new in situ measurements conducted in different locations across the inner heliosphere. While the results and discussion in each section contribute to their respective sub-fields, it is also crucial to highlight their connection in future work. Understanding the mechanisms that control electron dynamics in the ambient solar wind is essential when studying electron physics within ICME structures. This research can then provide insight on ICME dynamics observed closer to the Sun, including their evolution and interactions with planetary environments. In the case of Mars, these interactions may have played a significant role in the climate evolution of the planet after the loss of its global magnetic field. Constraining the timing of the ancient Martian geodynamo through current and future measurements of crustal fields then becomes essential in better understanding this process. As our technological capabilities improve with time, novel in situ instrumentation could be extended to the outer heliosphere, further enhancing our knowledge of Heliophysics as an interconnected system.
You have requested "on-the-fly" machine translation of selected content from our databases. This functionality is provided solely for your convenience and is in no way intended to replace human translation. Show full disclaimer
Neither ProQuest nor its licensors make any representations or warranties with respect to the translations. The translations are automatically generated "AS IS" and "AS AVAILABLE" and are not retained in our systems. PROQUEST AND ITS LICENSORS SPECIFICALLY DISCLAIM ANY AND ALL EXPRESS OR IMPLIED WARRANTIES, INCLUDING WITHOUT LIMITATION, ANY WARRANTIES FOR AVAILABILITY, ACCURACY, TIMELINESS, COMPLETENESS, NON-INFRINGMENT, MERCHANTABILITY OR FITNESS FOR A PARTICULAR PURPOSE. Your use of the translations is subject to all use restrictions contained in your Electronic Products License Agreement and by using the translation functionality you agree to forgo any and all claims against ProQuest or its licensors for your use of the translation functionality and any output derived there from. Hide full disclaimer