Author: Omar Abuassaf

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In our Solar System, there are numerous mean-motion resonances for the minor bodies and satellites, but there are no mean-motion resonances between the planets. The first mean-motion resonance in an extrasolar planetary system – the 2:1 resonance between two Jupiter-mass planets around the star GJ 876 – was discovered in 2001. Since then, an increasing number of pairs of planets in or near mean-motion resonances and resonant chains of three or more planets have been detected. I will discuss the dynamics of these systems and the constraints that they provide on the formation and dynamical evolution of planets. Topics will include high-order mean-motion resonances in the HD 202206 and nu Ophiuchi systems and the formation of resonant chains near the inner edge of protoplanetary disks.

 Venus, Earth’s twin, is not only the closest planet to us in the solar system, it the closest to Earth in mass, density and size and yet it evolved very differently than the Earth. Venus has an atmosphere that has 90 times the surface pressure as the Earth with a surface temperature of 460 C. Venus does not have a system of plate tectonics like the Earth which is one of the key reasons that Earth is a habitable planet. So how did two planets with roughly the same physical parameters evolve so differently? The NASA Magellan mission to Venus in the Early 1990’s used radar to image the planet’s surface through the optically opaque atmosphere at ~150 m resolution and showed that Venus has a young surface that had been volcanically resurfaced with the last 500 million years. As much a Magellan informed us about Venus it also left many key questions about Venus’s planetary evolution unanswered. Two missions to Venus, VERITAS by NASA, and EnVision by ESA in partnership with NASA, will return to Venus in the 2030’s with the goal of answering how these planet’s evolved so differently. The answer to this question will help inform how many Earth and Venus like planets are there in other solar systems. Radars play a key role on each mission and this talk will describe their role in these missions to Venus and how in combination with the other instruments hope to resolve one of the key mysteries in planetary science.  

Our knowledge of the satellite population in the solar system has grown rapidly in the past 100 years.
In the early 1900s almost every known moon was a regular satellite — the large, primordial bodies that formed with their parent planets.
The Voyager flybys fundamentally changed that picture by revealing numerous small inner satellites of the giant planets, bodies likely tied
to ring-system evolution and ongoing collisional processing near the planet. Beginning around 2000, wide-field CCD surveys (e.g. CFHT, Subaru) opened a third population regime: most new discoveries were irregular or outer satellites — dynamically distinct, highly inclined, often retrograde
objects whose origins are not native to the planet system but are best explained as captured heliocentric planetesimals from the early solar system. At JPL, we develop and maintain ephemerides for all known satellites. The orbital models range from simple precessing ellipses to full dynamical models that include tides, relativistic terms, satellite libration, and high order gravity field expansions. These models draw on data sets spanning more than a century of astrometric measurements, from early visual observations to modern spacecraft tracking. Ultimately, satellite ephemerides are not just navigation products needed to point a telescope or fly a spacecraft – they are scientific observables that encode the history and dynamics of entire planetary systems. Each orbit tells a story about its origin, its interactions, and its ongoing evolution.
We will review the current state of satellite ephemerides across the solar system and highlight some interesting dynamical puzzles.

Being able to image the ruptures of moderate earthquakes would significantly increase our observations towards comprehending earthquake source physics, fault properties and seismic hazards.

However, resolving their rupture characteristics remains challenging for conventional seismic networks due to limited station density. The emergence of Distributed Acoustic Sensing (DAS) offers a potential solution by providing dense and continuous measurements. In this study, we systematically evaluate the resolution capabilities of multi-fibre DAS networks for back-projection (BP) and demonstrate the feasibility of using DAS networks through both synthetic tests and analysis of a Mw 4.9 event in the Eastern California Shear Zone.

Furthermore, we propose a two-step inversion procedure that strategically integrates DAS with the conventional network. Our results suggest that strategically deployed multi-fibre DAS network can serve as the next generation of earthquake observation system and significantly enhance our understanding of earthquake rupture physics, as well as seismic risk preparedness.

Numerical simulations of seismic wave propagation are crucial for investigating velocity structures and improving seismic hazard assessment. However, standard methods such as finite difference or finite element are computationally expensive. Recent studies have shown that a new class of machine learning models, called neural operators, can solve the elastodynamic wave equation orders of magnitude faster than conventional methods. Full waveform inversion is a prime beneficiary of the accelerated simulations. Neural operators, as end‐to‐end differentiable operators, combined with automatic differentiation, provide an alternative approach to the adjoint‐state method. State‐of‐the‐art optimization techniques built into PyTorch provide neural operators with greater flexibility to improve the optimization dynamics of full waveform inversion, thereby mitigating cycle‐skipping problems. We demonstrate the application of neural operators for full waveform inversion on real seismic data, using nodal transects collected across the San Gabriel, Chino, and San Bernardino basins in the Los Angeles metropolitan area. 

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Magnetopause magnetic reconnection during periods of northward interplanetary magnetic field (IMF) plays a key role in the entry of solar wind mass into the magnetosphere. The effects of reconnection can be observed in the low-altitude cusp, and the new NASA TRACERS mission is designed for this purpose. I will present a TRACERS-THEMIS conjunction near the peak of a geomagnetic storm after the IMF had turned northward. In the low-altitude cusp, TRACERS observed signatures consistent with lobe reconnection poleward of the cusp, including reversed ion dispersions and sunward convection. Concurrent THEMIS observations at the low-latitude magnetopause reveal the presence of a magnetosheath boundary layer (MSBL) and capture of magnetosheath plasma on magnetospheric field lines, both consistent with poleward-of-cusp reconnection. Global simulations of the event show that poleward-of-cusp reconnection was adding magnetic fields and plasma to the magnetosphere, and in the process moving the cusp poleward. The event also illustrates how the magnetosphere and cusp recover when the IMF turns northward after a storm has eroded the magnetopause inward and moved the cusp equatorward.

Jupiter’s moon Europa is a key target in the search for extraterrestrial life, but assessing its habitability via magnetic induction requires a well-grounded understanding of the plasma environment. At Europa, this task relies on magnetohydrodynamic (MHD) models that have been developed over many years. While powerful, these models are computationally expensive, with some codes requiring > 12 hours on a 2,000-core machine. Fitting spacecraft observations to MHD models demands many runs, resulting in a potentially days- or weeks-long process. This presents a major bottleneck for missions such as Europa Clipper and JUICE, potentially limiting their scientific return.
In this talk, I introduce a transformer-based surrogate for a state-of-the-art MHD model used to help characterize Europa’s subsurface ocean. The surrogate evaluates in milliseconds on a laptop rather than hours on a supercomputer, achieving a speed-up of approximately 40,000x while delivering high-fidelity, uncertainty-aware magnetic field predictions. This acceleration enables three new scientific pathways that are feasible with MHD alone: large-scale parameter surveys, simulation-based inference, and feature-importance analysis. These analyses are important as the environment is poorly constrained observationally. Overall, this approach represents a paradigm shift in the investigation of space plasmas and opens the door to a host of novel science investigations.

NASA science missions are often complex systems of systems, involving various stakeholders, including the United States’ Congress. To ensure a clear and concise communication of expectations, requirements, and constraints, NASA has adopted the Science Traceability Matrix (STM). STM provides a logical flow from the decadal survey to science goals and objectives, mission and instrument requirements, and data products. STM serves as a summary of what science will be achieved and how it will be achieved, with a clear definition of what mission success will look like. In this seminar, I will present the STM from the Parker Solar Probe (PSP), including requirements relating to the plasma instrument for which I am a co-investigator. I will describe how our team used the STM to map the mission’s top-level requirements to mission success criteria and helped to eliminate any single point of failure that could end the mission prematurely. I will then present my own research on magnetic switchbacks in the PSP magnetic and plasma observations and their role in solar wind acceleration and heating. I will conclude the seminar by discussing how my research on the temporal evolution of switchbacks in the solar wind led to a new STM, and helped to chart a multidisciplinary path to designing a ground-breaking science mission concept, titled Space Weather Investigation Frontier (SWIFT), with the potential to improve space weather forecasting lead times by up to 40%.

Extraterrestrial EM induction was first carried out in the 1970s
by forming magnetic transfer functions for the Moon as the ratio of
magnetic fields observed at the surface (Apollo 12) to those observed in
distant orbit (Explorer 35). In March 2025, a similar analysis was
performed using the Lunar Magnetotelluric Sounder (LMS) on Blue Ghost
Mission 1 and the ARTEMIS spacecraft. In spite of nearly 90 deg arc
distance between these surface locations, the derived subsurface
conductivities are very similar. This sharply limits contemporary
temperatures under the western nearside of the Moon in spite of its past
history of widespread volcanism. The two-week surface mission recorded
surface electric and magnetic fields in the solar wind, magnetosheath, and
magnetotail, including an eclipse and sunset. Plasma properties correlate
well with ARTEMIS.

Mars’ lack of a global magnetic field led to low expectations for auroral phenomena on the planet, but MAVEN and Emirates Mars Mission observations have unexpectedly shown auroral activity to quite diverse in nature, dynamically varying and often global in scope. The image below shows three fundamentally different types of aurora on Mars. Ironically, Mars’ lack of a global field is actually responsible for most of the activity, which leads to a new perspective for non-magnetized objects in our solar system and beyond. Each of the three types of aurora is a tracer of a different important process involving the interaction between solar influences and the near-Mars magnetic and charged particle environment. The seminar will describe observations by MAVEN’s Imaging UltraViolet Spectrograph (IUVS) and the Emirates Mars UltraViolet Spectrometer (EMUS) and highlight the new insights they offer.

Space weather is the “weather” of the space environment driven by our active Sun—solar eruptions and changing solar wind conditions that can disturb Earth’s magnetic field and upper atmosphere, disrupt satellites and communications, degrade navigation and timing, increase radiation risk to astronauts, and induce electrical currents in long conductors on the ground. Over the past decade, U.S. preparedness for major space weather events has changed in two consequential ways: (1) the power sector began translating scientific risk into enforceable reliability practice when the Federal Energy Regulatory Commission (FERC) directed the North American Electric Reliability Corporation (NERC) to develop Reliability Standards to mitigate geomagnetic disturbance (GMD) impacts on the Bulk-Power System ; and (2) the United States adopted a coordinated, whole-of-government posture through the National Space Weather Strategy and Action Plan—now further advanced through a more recent federal implementation plan that builds on the 2015 foundation .

I will highlight key scientific and operational developments from the last few years, including NASA’s Space Weather Program role in advancing space weather observations, models, and applications that support prediction and tracking across the solar system. A central case study will be the May 2024 geomagnetic storm—first G5 (“severe”) storm in over two decades—now commonly referred to as the “Gannon storm,” and what it revealed about magnetosphere–ionosphere coupling, satellite impacts, and the pathways to societal consequences.

Finally, I will offer focused perspectives on high-impact risk areas—especially electric power grids—connecting space physics to practical resilience: where the key areas of uncertainty are, what “good enough” information looks like for operations, and how research, standards, and planning can converge to reduce national risk before the next extreme event.

Learn about ionizing radiation in the final frontier from UCLA Space Medicine Program Director Dr. Haig Aintablian and Radiation Oncology resident Dr. Nic Nelson. They will share a brief overview of modern space medicine and basic radiobiology before exploring the space radiation environment with its unique risks to astronaut health. They will then illustrate how researchers and mission planners are preparing for the next phase of human space exploration—interplanetary travel—by investigating different physical and biological countermeasures and applications in personalized medicine.

Solar radio bursts are signatures of nonthermal electron acceleration by energetic events such as flares and coronal mass ejections. The launches of Parker Solar Probe in 2018 and Solar Orbiter in 2020 have enabled new views of radio bursts from the vantage point of the inner heliosphere. In this talk, I will briefly discuss some of the top radio burst discoveries of the Parker-Orbiter era, with a focus on circular polarization observations made by Parker Solar Probe. I will describe the measurement of polarization using spacecraft antennas, show examples of circularly polarized Type II and Type III radio bursts, and discuss how polarization can serve as a remote diagnostic of radio burst source regions.

Galileo, Cassini and Juno space missions have provided much data on gas giant magnetospheres. Here we examine the important commonalities of the two systems that also characterise the differences to the plasma environment of the inner planets. Both systems are fast rotators and have internal sources of magnetospheric material deep within the system. The internal sources means there must be a system for transport of material outward. Commonly, marginally stable interchange motions of flux tubes are invoked to provide diffusion on relatively small scales transverse to the field. This no doubt occurs near the source but processes like self-organisation may lead to more ordered motion at larger distances. A large distinction between Jupiter and Saturn systems is that the jovian planetary magnetic field is far from axially symmetric with respect to the planetary rotation axis whereas Saturn’s field is close to axially symmetric. However, despite this, the Saturn system does exhibit variable periodicities in plasma, radio, aurora and the external magnetic field around 10.7 hours. The external magnetic source was a surprise; the ubiquitous Saturn oscillations are still described as “mysterious”. No similar oscillations are recorded at Jupiter. We shall aim to remove some of the mystery and suggest that the dynamical effect of rotation has not been fully appreciated in either system.

Prediction serves as the ultimate test of our scientific understanding of geophysical systems. Accurate forecasting of near-Earth space environmental conditions is critical to radio communication, navigation, and space traffic management. Effective numerical prediction of the region’s conditions allows us to better protect important space assets and related systems in the event of natural hazards. My research group aims to advance the science and engineering of forecasting, as applied to the Earth’s atmosphere extending from the ground to geospace. Prediction of the constantly changing near-Earth space environmental conditions – affected by both space and terrestrial weather – is inherently challenging. Data assimilation provides a systematic approach to integrating observations with first-principles models, extending the predictive capability of numerical models by reducing uncertainties in drivers and preconditions and constraining model dynamics with observations. The data assimilation and ensemble-based probabilistic modeling framework can also be applied to the design of future missions and the targeting of observations to maximize scientific returns of observing systems. This seminar showcases some of the latest data assimilation research and outlines future plans, setting the stage a discussion on how we can work together to advance the next generation of predictive modeling and observational strategies.

The dynamics of glaciers and ice sheets influence rates of sea-level rise, freshwater supplies, and landscape evolution. Decades of research has highlighted key processes and connections between terrestrial ice, the climate, and the solid earth, but limited observations have allowed fundamental questions in glaciers dynamics to remain open. In this talk, we will explore some related questions: What is the viscosity of glacier ice and how does it depend on stress? Why does ice fracture? Building on these fundamental questions, we will highlight new efforts to support polar science and accelerate improvements in our ability to observe and model ice sheets. 

In this talk I am going to explore the interplay between tectonic and surface processes in shaping Cordilleran-type orogenic systems, having the Central Andes as the main study case. The Escoipe Canyon in NW Argentina cross cuts the fold-and-thrust belt of the Eastern Cordillera, which makes the transition from the Puna Plateau to the modern foreland region. A new dataset of multiple low-temperature thermochronometers records the history of orogenic building from rifting to foreland basin, and ultimately the thrust belt forming the present-day orographic barrier of the Central Andes. The apatite (U-Th)/He data, however, dates the last 10 myr of history after the main episode of shortening, and shows a westward trend of younger cooling ages, opposite to the regional cooling trend in the thrust belt. I will explore a hypothesis regarding climate and surface processes controlling rock exhumation in the canyon, and the impacts on orogenic evolution. Additionally to this data-driven study case, I will show some effects of orography in Cordilleran-type systems in the lithospheric scale using geodynamic models, and demonstrate that surface processes might affect strain distribution and lithospheric removal processes.

Climate change is stressing the American West’s century-old system of water storage and conveyance, through longer and more intense droughts and periods of exceptional rainfall and flooding. Nowhere are these challenges more acute than in California’s Central Valley, which produces 25% of the USA’s agricultural output on climatologically marginal farmland. Intense management of mountain discharge into the Central Valley, along with oversubscribed rights to surface water, have resulted in unchecked exploitation of the Valley’s groundwater resources and impeded initiatives to use occasional surface water surpluses for aquifer recharge.

New regulation has sparked interest in better information on groundwater availability. Here at Scripps, our lab uses remotely sensed observations of Earth’s gravity and surface motion to infer the dynamics of the hydrological system that feeds the Central Valley aquifer. These techniques track the evolution of mountain water storage at various timescales, and they reveal how this stored water enters and flows through the Central Valley aquifer. Effective management of groundwater resources in the Central Valley will require adoption of data-informed policies, and our hope is that our insights into Central Valley hydrology will prove useful to this end.

50+ years after the Apollo missions, NASA will be sending astronauts back to the Moon. This time, the astronauts will land near the South Pole of the Moon. The Lunar Environment Monitoring Station (LEMS-A3) is one of the selected Artemis III Deployed Instruments. LEMS-A3 is built to operate independently of the Artemis III crew spacecraft, survive the lunar night and operate for at least two years. The LEMS-A3 payload is a set of astronaut-deployed seismometers, SeisLEMS, consisting of a broadband (BB) and short period (SP) instrument built by the University of Arizona and Silicon Audio Inc. Artemis astronauts will deploy and position LEMS-A3, and bury the BB and SP instruments into an astronaut dug-trench and borehole, respectively.
The BB and SP will continuously record ground motions at 100 samples per second (sps) and relay 15 sps data back to Earth once a month. The LEMS team will use the ground motions to detect and locate lunar seismic events including impact-driven, shallow, and deep moonquakes and iteratively backfill the events with 100 sps data. The proposed Artemis III landing sites all enable seismic surveys of the southern pole and farside of the Moon; geographic regions that have previously be unexplored with seismometers. Through seismic data interpretation we aim to catalog seismicity of the Moon, investigate the crustal and mantle structure of the south pole, determine the structure of the deep interior, and ascertain seismic hazards.
Although LEMS-A3 is designed as a stand-alone seismic station, it is possible that it may operate at the same time as other seismometers, e.g. the Farside Seismic Suite (FSS) and other future lunar missions equipped with seismometers. If FSS and LEMS-A3 are operational at the same time, more science may be accomplished through collaboration of the science teams and shared datasets.

The modern world teems with complex life—the animals, plants, fungi, seaweeds, and a dazzling array of single-celled organisms known as the protists. All of these are part of the eukaryotic clade, descended from a common ancestor that lived more than 1 billion years ago. In this talk, I will provide an overview of early eukaryote evolution and the environmental context in which they evolved.  I will present new research that sheds light on the habitats in which eukaryotes lived and how they might have survived the extreme “snowball Earth” glaciations that entombed the planet in ice 720–635 million years ago (Ma). Finally, I will highlight the outstanding questions that remain, including what drove their rise to dominance during the late Neoproterozoic Era (~600 Ma).

Statically stable density stratification is ubiquitous in geophysical flows. It tends to suppress vertical motions, leading to thin, sheared layers and highly anisotropic structures. This talk discusses recent progress in understanding stratified turbulence, including mixing efficiency and the role of intermittent events, and highlights open questions relevant to oceans and atmospheres.

Juno and Cassini have revealed that Jupiter and Saturn likely contain broad regions where heavy elements are mixed gradually, rather than being sharply separated. A major open question is how these composition gradients can survive for billions of years, even though the planets’ interiors are vigorously convecting.

In this talk, I’ll present numerical simulations that explore how convection mixes compositional gradients in a simplified model of a planet’s interior. I’ll show that rotation can play an important role in shaping the flow and can strongly influence how efficiently composition is mixed. Also, I will show that under certain conditions, the combined effects of temperature and composition cause the fluid to organize itself into stacked convective layers, remarkably similar to the layers that form in a latte. I’ll conclude by discussing the challenges for our understanding of convective mixing and what this means for giant planet interiors.

Planets exhibit extraordinary diversity in physical properties and orbital architectures, spanning more than four orders of magnitude in mass, separation, and age. Interpreting this landscape is challenging as observational biases and orbital migration obscure the pathways of planet formation and evolution across both space and time. While the full picture remains incomplete, a story is emerging for gas giants from radial velocity surveys probing planetary systems from the inside out and high-contrast imaging from the outside in. These complementary approaches are converging at intermediate scales, enabling a more continuous view of giant planet populations. I will present results from recent ground- and space-based efforts to constrain how giant planets assemble and evolve, focusing on accretion disks, population demographics, orbital eccentricities, and stellar spin–orbit misalignments. Together, these are informing the processes of gas accretion, angular momentum exchange, and dynamical evolution that shape planetary systems. I will also highlight how upcoming astrometric discoveries from Gaia—which is expected to reveal thousands of giant planets at intermediate separations later this year—will help bridge the gap between inner and outer planet populations and clarify how giant planets form and interact over time.

In its travel through the Milky Way, the Sun traverses a variety of Galactic
environments, including dense interstellar clouds. Astronomical effects on
Earth’s past climate have been limited to 10,000-year scales variations in
Earth’s orbital parameters while our recent studies suggest that
longer-term climate shifts that occur every few million year may be linked
to compression of the heliosphere (the “cocoon” formed by the solar wind)
when the Sun crosses dense clouds as it travels through the Milky Way.
During such periods Earth was exposed to increased radiation and large
amounts of hydrogen, potentially altering its climate. These events are
consistent with independent 60Fe records indicating nearby astrophysical
encounters at ~2–3 and ~6–7 million years ago (Ma), as well as 10Be
anomalies near ~10 Ma that may reflect prolonged exposure to enhanced
radiation during a cold cloud crossing.  A convergence of recent advances
across astronomy, space physics, and paleoclimate creates an unprecedented
opportunity to rigorously test this hypothesis. We now have high-precision
astrometry from the Gaia mission that allows one to reconstruct the Sun’s
trajectory through the Galaxy and to identify, with remarkable accuracy,
the interstellar structures it has encountered over the past ~10 Ma. Major
theoretical and modeling advances now enable quantitative predictions of
how the heliosphere evolved during these encounters. In this talk I will
discuss our recent work that show that during such periods, Earth was
exposed to increased radiation and large amounts of hydrogen. I will
discuss our preliminary results that show that the increase in hydrogen
augmented mesospheric water vapor, leading to increased formation of both
polar mesospheric clouds and polar stratospheric clouds. The amount of
radiation that Earth experiences from such events depends on the duration
of the crossing and the amount of compression of the heliosphere, with
implications for Earth’s climate. I will discuss our results as well that
indicate that high temporal 10Be signal in ocean records and ice cores can
distinguish between alternative scenarios such as supernova explosions and
cold cloud crossings.

The 2028 Summer Olympics will be held in Los Angeles from July 14–30, making Los Angeles only the third city(after London and Paris)to host the Summer Games three times. Los Angeles is an attractive Olympic venue not only because of its mild climate and global tourist appeal, but also because of its remarkable physical setting: a major coastal metropolis situated adjacent to actively deforming mountain ranges rising to elevations above 10,000 feet. This unique geological context provides an exceptional opportunity to connect a globally watched sporting event with public understanding of how Earth systems operate.
The geology of the Los Angeles region is far more dynamic and diverse than that of other Summer Olympic host cities. The convergence of intense public interest in the Olympics with an unusually compelling natural setting creates a rare opportunity for large-scale informal STEM education focused on Earth science and natural history. Leveraging this moment could engage audiences ranging from K–12 students to lifelong learners, both locally and worldwide. We refer to this proposed effort as the LA2028 GeOlympics.

This initiative aims to capitalize on global attention surrounding the 2028 Games by providing accessible, place-based explanations of the geological history of the Los Angeles region, particularly around Olympic venues, and by illustrating how tectonics, climate, and surface processes have shaped this iconic landscape. Achieving this goal will require coordinated collaboration among the region’s extensive educational and cultural infrastructure, including 14 college and university geology departments, 19 community colleges, approximately 2,000 K–12 schools, 136 museums, hundreds of environmental organizations, and a broad range of media outlets. This presentation outlines the vision for LA2028 GeOlympics, discusses organizational and funding needs, and explores pathways for collaboration with the LA28 Organizing Committee to transform the Olympics into a powerful platform for Earth science education.