Magnetic fields pervade astrophysical systems and strongly influence their dynamics. Because magnetic diffusion is usually much faster than system evolution, ancient fields cannot explain the present magnetization of planets, stars, and galaxies. Instead, self-sustaining dynamos, which convert fluid motion into magnetic energy, offer the most robust explanation. Numerical magnetohydrodynamic simulations are essential to understanding this phenomenon. This thesis uses numerical models of self-excited dynamos in two contexts: the interstellar medium (ISM) and the interiors of gas giant planets. First, I use 3D MHD simulations with the Pencil Code to study magnetic growth from irrotational, subsonic expansion flows, a simplified representation of supernova-driven motions in the ISM. These curl-free flows mimic stellar explosions and winds, drive turbulence, and seed magnetic amplification. The second part examines planetary dynamos. I outline the properties of planetary magnetic fields and their modeling through convection in spherical shells. Although many exoplanets are known, their magnetic fields remain difficult to detect, but may be observable through coherent radio emission with new low-frequency instruments. Using 3D dynamo simulations with the MagIC code, coupled to thermodynamic profiles from MESA-based evolution models, I study the magnetic evolution of cold gas giants. The models show a slow decline in field strength, a shift from multipolar to dipolar states, and clear evolutionary trends in dynamo behavior. I also investigate hot Jupiters, where strong irradiation alters convection and rotation. Most remain fast rotators, but massive, distant planets may enter different regimes. When heating is concentrated in outer layers, convection in the dynamo region weakens, reducing expected field strengths and helping explain the absence of confirmed detections in past radio surveys.

Interstellar objects are the ejected building blocks of other solar systems. As such, they enable the acquisition of otherwise inaccessible information about nascent extrasolar systems. The discovery of the third interstellar object, 3I/ATLAS, provides an opportunity to explore the properties of a small body from another solar system and to compare it to the small bodies in our own. To that end, we present spectrophotometric observations of 3I/ATLAS taken using the SuperNova Integral Field Spectrograph on the University of Hawaii 2.2-m telescope. Our data includes the earliest $\lambda\leq3800$ A spectrum of 3I/ATLAS, obtained $\sim$12.5 hours after the discovery announcement. Later spectra confirm previously reported cometary activity, including Ni and CN emission. The data show wavelength-varying spectral slopes ($S\approx($0\%-29\%)/1000 A, depending on wavelength range) throughout the pre-perihelion ($r_h=4.4$-$2.5$ au) approach of 3I/ATLAS. We perform synthetic photometry on our spectra and find 3I/ATLAS shows mostly stable color evolution over the period of our observations, with $g-r$ colors ranging from $\sim$0.69-0.75 mag, $r-i$ colors ranging from $\sim$0.26-0.30 mag, and $c-o$ colors ranging from $\sim$0.50-0.55 mag. Ongoing post-perihelion observations of 3I/ATLAS will provide further insight into its potentially extreme composition.

We study the effects of escaping cosmic rays (CRs) on the interstellar medium (ISM) around their source with spherically symmetric CR-hydrodynamical simulations taking into account the evolution of the CR energy spectrum, radiative cooling, and thermal conduction. We show how the escaping CRs accelerate and heat the ISM fluid depending on the CR diffusion coefficient. The CR heating effects are potentially responsible for the recent observations of the unexpected H$\alpha$ and [OIII]$\lambda$5007 lines in old supernova remnants. The implied gas outflow by CRs can be comparable to the Galactic star formation rate, compatible with the Galactic wind required for the metal-polluted halo gas and the production of eROSITA bubbles. Assuming a locally suppressed CR diffusion and a few nearby CR sources in the Local Bubble, we also propose alternative interpretations for the Galactic CR proton spectrum around the Earth measured with CALET, AMS02, and Voyager I.

We investigate the microlensing detectability of extraterrestrial technosignatures originating from Dyson sphere \textendash like structures, such as Dyson Swarms surrounding primordial black holes (PBHs). These hypothetical swarms consist of stochastically varying, partially opaque structures that could modulate standard microlensing light curves through time-dependent transmission effects. We introduce a probabilistic framework that includes a stochastic transmission model governed by variable optical depth and random gap distributions. We perform a parameter scan and generate heatmaps of the optical transit duration. We study the infrared excess radiation and peak emission wavelength as complementary observational signatures. Additionally, we define and analyze the effective optical depth and the anomalous microlensing event rate for these stochastic structures. Our findings provide a new avenue for searching for extraterrestrial advanced civilizations by extending microlensing studies to include artificial, dynamic modulation signatures.

An instability among the giant planets' orbits can match many aspects of the Solar System's current orbital architecture. We explore the possibility that this dynamical instability was triggered by the close passage of a star or substellar object during the Sun's embedded cluster phase. We run N-body simulations starting with the giant planets in a resonant chain and an outer planetesimal disk, with a wide-enough planet-disk separation to preserve the planets' orbital stability for $>$100 Myr. We subject the system to a single flyby, testing a wide range in flyby mass, velocity and closest approach distance. We find a variety of outcomes, from flybys that over-excite the system (or strip the planets entirely) to flybys too weak to perturb the planets at all. An intermediate range of flybys triggers a dynamical instability that matches the present-day Solar System. Successful simulations -- that match the giant planets' orbits without over-exciting the cold classical Kuiper belt -- are characterized by the flyby of a substellar object ($3-30 M_{Jup}$) passing within 20 au of the Sun. We performed Monte Carlo simulations of the Sun's birth cluster phase, parameterized by the product of the stellar density $\eta$ and the cluster lifetime $T$. The balance between under- and over-excitation of the young Solar System is at $\eta T \approx 5 \times 10^4$~Myr pc$^{-3}$, in a range consistent with previous work. We find a probability of $\sim$1% that the Solar System's dynamical instability was triggered by a substellar flyby. The probability increases to $\sim$5% if the occurrence rate of free-floating planets and low-mass brown dwarfs is modestly higher than predicted by standard stellar initial mass functions.

Masses and radii of transiting brown dwarfs can be measured directly in contrast to isolated field brown dwarfs, whose mass and radius inferences are model dependent. Therefore, transiting brown dwarfs are a testbed for the interior and evolutionary models of brown dwarfs and giant exoplanets. We have developed atmospheric and evolutionary models for this emerging population. We show that intense stellar irradiation can cause a large enhancement in the radius of transiting brown dwarfs at all masses, especially if the incident flux exceeds $log_{10}(F/cgs)\ge$9 ($T_{\rm eq}\ge 1450$ K). Stellar irradiation can significantly alter rates of nuclear burning in irradiated brown dwarfs, making the Deuterium-burning and Hydrogen-burning minimum masses strong functions of incident stellar flux. We show that the D-burning and H-burning minimum masses can decrease by 16% and 13%, respectively, between isolated and strongly irradiated brown dwarfs ( $log_{10}(F/cgs)\ge$10 ($T_{\rm eq}\ge 2570$ K)). This shows that stellar irradiation has a larger impact on the planet-brown dwarf-star mass boundaries than metallicity or clouds. We show that metal cores or migration affect their evolution to a much lesser extent, whereas low mass highly irradiated old sources can help us test the physics of hot Jupiter radius anomaly. We fit the observed radii of 46 transiting brown dwarfs and show that our irradiated evolutionary models fit their radii better than models that ignore the host star, especially for highly irradiated objects. However, the measured radii of 10 objects are still inconsistent at $>3\sigma$ level, indicating residual gaps in our irradiated evolutionary model.

Astrochemistry is a well-established multidisciplinary field devoted to study molecules in space. While most astrochemists are oriented to observe molecules in the gas phase and reproduce their abundances by modeling the physical conditions of the medium, the microscopic dust particles wandering in the interstellar medium deserve the attention of a smaller community. Radiation and thermally-driven processes taking place in the bare dust, and particularly in dust particles covered by ice mantles, are mimicked in the laboratory. In addition to water, interstellar ice contains other simple species. In this Review we present our current knowledge on ice photochemistry and thermal processing that ultimately leads to formation of complex organic molecules (COMs). Numerous COMs are of astrobiological interest and match those present in comets and asteroids. Upon impact of these minor bodies, water and COMs were delivered to the earth and might have intervened in the first prebiotic reactions.

The unexpectedly large radii of transiting hot Jupiters have led to many proposals for the physical mechanisms responsible for heating their interiors. While it has been shown that hot Jupiters reinflate as their host stars brighten due to heating deep in planetary interiors, young hot Jupiters also exhibit signs of delayed cooling possibly related to heating closer to their surfaces. To investigate this tension, we enhance our previously published hot Jupiter thermal evolution model by adding a parameter that allows for both deep heating and delayed cooling. We fit our thermal evolution models to a homogeneous, physically self-consistent catalog of accurate and precise hot Jupiter system properties in a hierarchical Bayesian framework. We find that hot Jupiters' interior cooling rates are reduced on average by 95\%--98\% compared to simpler anomalous heating models. The most plausible explanation for this inference is substantial shallow heating just below their radiative--convective boundaries that enables reinflation with much less deep heating. Shallow heating by Ohmic dissipation and/or temperature advection are therefore important components of accurate models of hot Jupiter atmospheres, especially in circulation models. If hot Jupiters are inflated primarily by shallow heating as we propose, then we predict that their observed phase curve offsets should increase with temperature in the range $T_{\text{eq}}~\lesssim1500~\text{K}$, peak in the range $1500~\text{K}~\lesssim~T_{\text{eq}}~\lesssim~1800~\text{K}$, and decrease in the range $T_{\text{eq}}~\gtrsim~1800~\text{K}$.

From 01- to 15-Aug-2025 UT, the SPHEREx spacecraft observed interstellar object 3I/ATLAS. Using $R = 40$-$130$ spectrophotometry at $\lambda = 0.7$-$5\mu$m, light curves, spectra, and imaging of 3I were obtained. From these, robust detections of water gas emission at $2.7$-$2.8\,\mu\mathrm{m}$ and CO$_2$ gas at $4.23$-$4.27\,\mu$m plus tentative detections of $^{13}$CO$_2$ and CO gas were found. A slightly extended H$_2$O coma was detected, and a huge CO$_2$ atmosphere extending out to at least $4.2\times10^{5}\,$km was discovered. Gas production rates for H$_2$O, $^{12}$CO$_2$, $^{13}$CO$_2$, and CO were $Q_{\mathrm{gas}} = 3.2\times10^{26} \pm 20\%$, $1.6\times10^{27} \pm 10\%$, $1.3\times10^{25} \pm 25\%$, and $1.0\times10^{26} \pm 25\%$, respectively. Co-addition of all $\lambda = 1.0$-$1.5\,\mu$m scattered light continuum images produced a high SNR image consistent with an unresolved source. The scattered light lightcurve showed $\lesssim 15\%$ variability over the observation period. The absolute brightness of 3I at $1.0$-$1.5\,\mu$m is consistent with a < 2.5\,km radius nucleus surrounded by a 100 times brighter coma. The $1.5$-$4.0\,\mu$m continuum structure shows a strong feature commensurate with water ice absorption seen in KBOs and distant comets. The observed cometary behavior of 3I, including its preponderance of CO$_2$ emission, lack of CO output, small size, and predominance of large icy chunks of material in a flux-dominant coma is reminiscent of the behavior of short period comet 103P/Hartley 2, target of the NASA Deep Impact extended mission in 2010 and a ``hyperactive comet'' near the end of its outgassing lifetime. This correspondence places 3I closer to barely- or non-active 1I/Oumuamua than primitive, ice rich 2I/Borisov, suggesting that ISOs are often highly thermally processed before ejection into the ISM.

A key question in astronomy is how ubiquitous Earth-like rocky planets are. The formation of terrestrial planets in our solar system was strongly influenced by the radioactive decay heat of short-lived radionuclides (SLRs), particularly $^{26}$Al, likely delivered from nearby supernovae. However, current models struggle to reproduce the abundance of SLRs inferred from meteorite analysis without destroying the protosolar disk. We propose the `immersion' mechanism, where cosmic-ray nucleosynthesis in a supernova shockwave reproduces estimated SLR abundances at a supernova distance ($\sim$1 pc), preserving the disk. We estimate that solar-mass stars in star clusters typically experience at least one such supernova within 1 pc, supporting the feasibility of this scenario. This suggests solar-system-like SLR abundances and terrestrial planet formation are more common than previously thought.

The nominal habitable zone for exoplanets orbiting M dwarfs lies close to the host star, making dynamical considerations especially important. One consequence of this proximity is the expectation of spin synchronization, with implications for atmospheric circulation. Several mechanisms can maintain non-zero obliquities over long timescales in compact multi-planet systems, including capture into Cassini State 2 (CS2) and other forms of secular spin-orbit coupling; such pathways are plausible in the orbital architectures of close-in M-dwarf planets. In this study, we search for transit duration variations (TDVs) consistent with the nodal precession rates predicted by Laplace-Lagrange secular theory in compact M-dwarf multi-planet systems. Our sample includes 23 exoplanets orbiting 12 stars. We compare recent, high-precision transit durations obtained from JWST white-light curves with measurements published at the discovery epoch and afterward. The resulting transit duration variation ranges from seconds to minutes, and we fit a linear trend to duration versus time for each planet. All systems are consistent with flat (no TDV) at the 3{\sigma} level. The strongest candidate is TRAPPIST-1d, whose fitted slope differs from zero with 2.2{\sigma} confidence. We calculate the expected TDV signals predicted by secular precession and compare them to the observed limits. Our null detection is consistent with the low-impact-parameter regime, where theoretical TDVs are only a few seconds per decade and below our sensitivity. Higher-impact-parameter configurations predict substantially larger TDVs and are disfavored: under uniformly distributed geometries, at least half of the allowed configurations would be excluded.

Icy planetesimals are likely to supply volatiles to terrestrial planets and serve as building blocks of icy bodies in the outer Solar System. Samples from the C-type asteroid Ryugu, collected by the Hayabusa-2 spacecraft, indicate a low-temperature history with aqueous alteration and organic materials. In contrast, iron meteorites with isotopic ratios similar to carbonaceous chondrites suggest exposure to higher temperatures. These findings imply that the thermal evolution of icy planetesimals is highly diverse. Since direct exploration provides only localized data, understanding this diversity requires comparing observational results with model calculations incorporating key evolutionary processes. We develop a model including radial growth, impact heating, water phase changes, aqueous alteration, and structural differentiation, to re-evaluate the thermal evolution of icy planetesimals during the first 100 Myr after CAI formation. The model considers final radius (10-1000 km), growth onset (1.0 or 2.0 Myr after CAI), growth duration (0.4 or 4.0 Myr), and growth mode (linear or runaway). Our results show that larger planetesimals generally reach higher temperatures, but growth timing and mode significantly affect thermal evolution. Early accretion leads to higher temperatures, with some bodies reaching the Fe-FeS eutectic (1250 K), while delayed or prolonged growth reduces heating. Our results show that the constituent materials of Ryugu, which kept below 40 degC, likely formed near the surface of a hydrated mineral layer. This is possible even in planetesimals several hundred kilometers in size due to efficient heat transport via convection. If accretion begins 2.0 Myr after CAI and completes in 0.4 Myr, a wide region in such a body could yield Ryugu's material.

The launch of the James Webb Space Telescope (JWST) has delivered high-quality atmospheric observations and expanded the known chemical inventory of exoplanetary atmospheres, opening new avenues for atmospheric chemistry modeling to interpret these data. Here, we present XODIAC, a fast, GPU-accelerated, one-dimensional photochemical model with a built-in equilibrium chemistry solver, an updated thermochemical database, and three chemical reaction networks. This framework enables comparative atmospheric chemistry studies, including the newly developed XODIAC-2025 network, a state-of-the-art C-H-O-N-P-S-Metals network, linking 594 species through 7,720 reactions. The other two are existing, publicly available C-H-O-N-S and C-H-O-N-S-Metals networks, from the established photochemical models VULCAN and ARGO, respectively, which are commonly used in the community. The XODIAC model has been rigorously benchmarked on the well-studied hot Jupiter HD 189733 b, with results compared against these two models. Benchmarking shows excellent agreement and demonstrates that, when the same chemical network and initial conditions are used, the numerical scheme for solving atmospheric chemistry does not significantly affect the results. We also revisited the atmospheric chemistry of HD 189733 b and performed a comparative analysis across the three networks. Sulfur chemistry shows the least variation across networks, carbon chemistry shows slightly more, and phosphorus chemistry varies the most, primarily due to the introduction of unique PHO and PN pathways comprising 390 reactions in the XODIAC-2025 network. These findings highlight XODIAC's capability to advance exoplanetary atmospheric chemistry and provide a robust framework for comparative exoplanetology.

During their formative stages, giant planets are fed by infalling material sourced from the background circumstellar disk. Due to conservation of angular momentum, the incoming gas and dust collects into a circumplanetary disk that processes the material before it reaches the central planet itself. This work investigates the complex vertical structure of these circumplanetary disks and calculates their radiative signatures. A self-consistent numerical model of the temperature and density structure of the circumplanetary environment reveals that circumplanetary disks are thick and hot, with aspect ratios $H/R\sim0.1-0.25$ and temperatures approaching that of the central planet. The disk geometry has a significant impact on the radiative signatures, allowing future observations to determine critical system parameters. The resulting disks are gravitationally stable and viscosity is sufficient to drive the necessary disk accretion. However, sufficiently rapid mass accretion can trigger a thermal instability, which sets an upper limit on the mass accretion rate. This paper shows how the radiative signatures depend on the properties of the planetary system and discuss how the system parameters can be constrained by future observations.

The challenge of constraining both the inner and the outer orbits in multiple stars has resulted in a growing abyss between the rich theoretical and the sparse observational studies of von Zeipel-Kozai-Lidov (ZKL) oscillations in stellar systems. Here we solve for the full orbital architecture of the bright intermediate-mass nearby system Lambda Ophiuchi based on astrometric measurements of the outer orbit (period of 129 years) compiled in the Sixth Catalog of Orbits of Visual Binary Stars and new VLTI/GRAVITY interferometric measurements that are used to determine the inner orbit (period of 42 days). The orbits are retrograde and misaligned by either $88.5\pm1.9^o$ or $113.5\pm1.9^o$, which in either case results in the inner binary currently undergoing ZKL oscillations. While pure Newtonian point source evolution would have predicted the stars in the inner binary to have merged long ago, in reality the eccentricity oscillations are significantly modulated by general relativistic, tidal and rotational bulge precession. We show that due to the effect of ``slaved'' precession the dynamics can still be solved semi-analytically. We find that the (currently unknown) inclination angles between the stellar spins axes and the inner orbital axis play a very important role in the amplitude of the ZKL oscillations, which is at a minimum $\Delta e = e_{\mathrm{max}} - e_{\mathrm{min}} \simeq 0.15$ and could be as high as $\Delta e \simeq 0.70$. We argue that currently feasible spectroscopic and interferometric observations could allow for a complete and unique dynamical solution for this system.

The heavy element content of giant exoplanets, inferred from structure models based on their radius and mass, often exceeds predictions based on classical core accretion. Pebble drift, coupled with volatile evaporation, has been proposed as a possible remedy to this with the level of heavy element enrichment a planet can accrete, as well as its atmospheric composition, being strongly dependent on where in the disc it is forming. We use a planet formation model which simulates the evolution of the protoplanetary disc, accounting for pebble growth, drift and evaporation, and the formation of planets from pebble and gas accretion. The growth and migration of planetary embryos is simulated in 10 different protoplanetary discs which have their chemical compositions matched to the host stars of the planets which we aim to reproduce, providing a more realistic model of their growth than previous studies. The heavy element content of giant exoplanets is used to infer their formation location and thus make a prediction of their atmospheric abundances. We focus here on giants more massive than Saturn, as we expect that their heavy element content is dominated by their envelope rather than their core. The heavy element content of 9 out of the 10 planets simulated is successfully matched to their observed values. Our simulations predict formation in the inner disc regions, where the majority of the volatiles have already evaporated and can thus be accreted onto the planet via the gas. As the majority of the planetary heavy element content originates from water vapour accretion, our simulations predict a high atmospheric O/H ratio in combination with a low atmospheric C/O ratio, in general agreement with observations. For certain planets, namely WASP-84b, these properties may be observable in the near future, offering a method of testing the constraints made on the planet's formation.

Interstellar objects such as 1I/'Oumuamua and 2I/Borisov offer a unique window into the formation and evolution of other star systems, yet the tracking and analysis of their trajectories remain limited to specialized research institutions. Existing interstellar and solar system datasets are large, complex, and difficult to navigate, reducing accessibility for developers, researchers, and enthusiasts. To address this, we present The Interstellar Signature: a computational framework for open-source interstellar tracking, implemented through a web-based platform. Interstellar Signature bridges raw astronomical data and an intuitive, developer-friendly interface. The framework integrates live data streams from public repositories and APIs with physics-based simulation methods to model and visualize the motion of interstellar and solar system objects in real time. The platform supports interactive visualizations, comparative orbital analysis, and modular tools that allow users to explore and extend the system for research, experimentation, or development. As an open-source project, the framework encourages collaboration and hands-on engagement with complex datasets. It exists within NexusCosmos, an ecosystem envisioned as a "Linux for the space race," aimed at democratizing access to space science tools and data. By transforming large datasets into visual, interactive, and customizable simulations, Interstellar Signature expands participation in interstellar research and observation. Future extensions will add AI-driven trajectory prediction, anomaly detection, and advanced visualization. By combining open-source accessibility with computational rigor, this framework lowers the barrier to interstellar analysis and serves as a step toward bridging professional astronomy and public scientific engagement.

We report resolution of a halo of X-ray line emission surrounding the Zero Age Main Sequence (ZAMS) G8.5V star HD 61005 by Chandra ACIS-S. Located only 36.4 pc distant, HD 61005 is young (approx. 100 Myr), x-ray bright (300 times Solar), observed with nearly edge-on geometry, and surrounded by Local Interstellar Medium (LISM) material denser than in the environ of the Sun. HD 61005 is known to harbor large amounts of circumstellar dust in a dense ecliptic plane full of mm-sized particles plus attached, extended wing like structures full of micron sized particles, which are evidence for a strong LISM-dust disk interaction. These properties aided our ability to resolve the 220 au wide astrosphere of HD61005, the first ever observed for a main sequence G-star. The observed x-ray emission morphology is roughly spherical, as expected for an astrospheric structure dominated by the host star. The Chandra spectrum of HD 61005 is a combination of a hard stellar coronal emission (T=8 MK) at Lx = 6 x10e29 erg per sec, plus an extended halo contribution at Lx = 1x10e29 erg per sec dominated by charge exchange (CXE) lines, such as those of OVIII and NeIX. The Chandra CXE x-ray morphology does not track the planar dust morphology but does extend out roughly to where the base of the dust wings begins. We present a toy model of x-ray emission produced by stellar wind (SW)-LISM CXE interactions, similar to the state of the young Sun when it was approximately 100 Myrs old (Guinan and Engle 2007), and transiting through an approximately 1000 times denser part of the interstellar medium (ISM) such as a Giant Molecular Cloud (Stern 2003, Opher and Loeb 2024).

Short-period exoplanets may exhibit orbital precession driven by several different processes, including tidal interactions with their host stars and secular interactions with additional planets. This motion manifests as periodic shifts in the timing between transits which may be detectable via high-precision and long-baseline transit- and occultation-timing measurements. Detecting precession and attributing it to a particular process may constrain the tidal responses of planets and point to the presence of otherwise undetected perturbers. However, over relatively short timescales, orbital decay driven by the same tidal interactions can induce transit-timing signals similar to the precession signal, and distinguishing between the two processes requires robust assessment of the model statistics. In this context, occultation observations can help distinguish the two signals, but determining the precision and scheduling of observations sufficient to meaningfully contribute can be complicated. In this study, we expand on earlier work focused on searches for tidal decay to map out simple metrics that facilitate detection of precession and how to distinguish it from tidal decay. We discuss properties for a short-period exoplanet system that can maximize the likelihood for detecting such signals and prospects for contributions from citizen-science observations.