Date: Monday 12-September-2022
Speaker: Maggie Thompson
Title: Terrestrial Exoplanet Atmospheres: From Outgassing Origins to Likely Observable Biosignatures
Abstract: Exoplanet science is now focusing on characterizing exoplanet atmospheres, including those of terrestrial-class, potentially habitable planets. My PhD research at the University of California, Santa Cruz has centered on two themes related to such atmospheres: (1) understanding their primordial compositions from an experimental cosmochemistry approach, and (2) evaluating the planetary context for observable biosignature gases.
The first theme is motivated because, at present, there is no first-principles understanding of how to connect a planet’s bulk composition to its initial atmospheric properties. Since terrestrial exoplanets likely form their atmospheres through outgassing, a novel step towards building such a theory is to assay meteorites, the left-over building blocks of planets, by heating them to measure their outgassed volatiles. I utilized multiple experimental techniques to determine the outgassing composition of primitive meteorite samples over a wide range of temperatures and pressures. I will present the results of these experiments in which I heated carbonaceous chondrite samples and measured by mass spectrometry the abundances of major released volatile species as a function of temperature in a high-vacuum environment. I also performed complementary bulk element analysis on the samples before and after the heating experiments to monitor outgassing of heavier elements. Currently, I am performing additional outgassing experiments using a novel technique consisting of a thermogravimetric analyzer coupled to a gas chromatograph on enstatite chondrite samples. I will discuss how my experimental results compare to thermochemical equilibrium models of chondrite outgassing and how these experiments can help improve atmospheric models, including the connection between bulk composition and early atmospheric properties.
For the second theme, I performed a comprehensive analysis of the necessary planetary conditions for atmospheric methane to be a compelling biosignature gas. Since methane is one of the only biosignatures that JWST can readily detect in terrestrial atmospheres, it is essential to understand methane biosignatures to contextualize these imminent observations. I will present my work on determining the necessary planetary context for methane to be a compelling biosignature, based on a combination of multiphase thermodynamic and atmospheric chemistry models. This work investigated methane’s various abiotic sources and determined when, under different conditions, they could be enhanced on other planets to result in false positives.
For further information contact PALS coordinators Tad Komacek and Quanzhi Ye at tkomacek@umd.edu and qye@umd.edu.
Date: Monday 19-September-2022
Speaker: Teddy Kareta
Title: Inner Solar System Blues: Thermal Alteration and Changing Activity on Near-Sun Asteroids and Dormant Comets
Abstract: The study of the remnant planetesimals of the Solar System -- the comets, asteroids, and so on -- is in part motivated by how they might retain information and properties from when they first coalesced during the epoch of planetary formation some Four-and-a-Half Billion years ago. However, the past twenty years have shown that many more populations of small bodies are active (losing mass) than previously recognized, and often in ways that are far from being clearly understood. In this talk, I will discuss a few recent and ongoing projects in which we have characterized the properties of meteor shower parent bodies and dormant comets with techniques ranging from telescopic observations to dynamical & compositional modeling to laboratory experiments heating meteorites to better understand the evolution of many inner Solar System small bodies. This multidisciplinary approach has proven highly successful in making inroads in understanding how the surfaces of these small objects are changed by their activity and orbit, but also in finding ways to "roll back the clock" on them and start to understand which of their modern properties are original -- and which ones document more recent processes. I will close this talk by connecting some of the questions explored here to our ability to understand the properties of Interstellar Objects -- small bodies which formed around other stars -- and to highlight some new areas of research that might stem from connecting the Solar System to exoplanet science a little more thoroughly.
For further information contact PALS coordinator Quanzhi Ye at qye@umd.edu.
Date: Monday 26-September-2022
Speaker: Oriel Humes
Title: Understanding Jupiter Trojans Across the Electromagnetic Spectrum
Abstract: The history of the Jupiter Trojans, a population of asteroids that orbit within Jupiter’s Lagrange regions, is intricately tied to the earliest history of the Solar System itself. With the recent launch of the Lucy mission, which will visit the Trojans for the first time in the next decade, this population of asteroids has come under intense investigation. However, the traditional tools of ground-based asteroid spectroscopy have revealed little about the origins of this mysterious population. In this talk, I will make the case for studying Jupiter Trojans across the electromagnetic spectrum, combining insights from ultraviolet, visible, near- and thermal infrared spectroscopy to illuminate the story of these unique asteroids.
For further information contact PALS coordinator Quanzhi Ye at qye@umd.edu.
Date: Monday 3-October-2022
Speaker: Hayley Beltz
Title: (Ultra)Hot Jupiters, Magnetic Effects, and the Need for 3D Atmospheric Models
Abstract: High resolution spectroscopy (R~100,000) has opened the door to planetary atmospheric characterization at an unprecedented level. With this increase in resolution, more sophisticated models, specifically those in 3D, are necessary to utilize these spectra to their fullest potential. In this talk, I discuss my work on 3D atmospheric modeling of hot and Ultrahot Jupiters and how these planets are especially amenable to 3D modeling. I will specifically focus on our 3D model's unique implementation of magnetic drag and how it impacts the resulting atmospheric structure of Ultrahot Jupiters. Additionally, I will discuss how observables--namely phase curves and high resolution spectra---are influenced by 3D effects and our magnetic drag.
For further information contact PALS coordinator Tad Komacek at tkomacek@umd.edu.
Date: Monday 10-October-2022
Speaker: Yuna Grace Kwon
Title: On the dust of primitive small bodies in the solar system
Abstract: Of around 4000 extrasolar planetary systems discovered as of October 2022, a sizable fraction of nearby solar-type stars are surrounded by dusty disks, analogous to the solar system’s small body reservoirs. The dust therein plays a central role in sculpting planetary systems as a building block of planetesimals and as a feedstock for synthesising complex organic molecules and ice that could be significant on habitability. As a result, the locations and physical properties of the dust in these dust structures provide essential probes of the processes of the formation and subsequent dynamical evolution of planetary systems, with our solar system being a reference thanks to its highest-ever accessibility. Comets and comet-like primitive asteroids represent the best opportunity to explore this fundamental thrust because they preserve the least-altered planetesimal left from the formative epoch. In this talk, I will introduce my recent works using various ground-based telescopes seeking to understand the structural evolution of our solar system and some relevant works of Comet Interceptor.
For further information contact PALS coordinator Quanzhi Ye at qye@umd.edu.
Date: Monday 17-October-2022
Speaker: Victoria Hartwick
Title: Dusty Dune Worlds & ExoMars: How dust controls climate, alters habitability and cofounds easy spectral identification
Abstract: The dust cycle is the dominant driver of meteorology and climate on present-day Mars. Despite this, few studies have investigated the impact of dust interacting with incoming stellar radiation on the climate, habitability and potential spectral signature of Mars-like exo-land planets. Dust availability is positively correlated with increasing soil aridity and therefore dust has significant potential to modify dynamics on dry land planets. In this work, we use an advanced Mars general circulation model to study the coupling between radiatively active dust and land planet climate at different stellar heating rates or planetary orbits. We find that radiatively active dust can significantly modify land planet climate. At Earth orbit, dust with optical properties similar to present-day Mars warms the planetary surface above 273K and augments both the zonal mean circulation and the thermal tide, and in particular the semi-diurnal component. As dust accumulates, peak heating rises off the planetary surface and the most active regions of dust lifting shift from the summer to winter hemisphere. Simulated spectra are nearly featureless across all wavelengths. We find that in order to accurately assess the climate and habitability of land planets it is critical to carefully consider that potential atmospheric dust budget and its radiative impact.
For further information contact PALS coordinator Tad Komacek at tkomacek@umd.edu.
Date: Monday 24-October-2022
Speaker: Shuang Wang
Title: Equatorial Superrotation and Waves in the Atmosphere and Ocean of Tidally Locked Planets
Abstract: The phase curve observations of 1:1 tidally locked planets including hot Jupiters usually show an eastward shift, which is caused by atmospheric equatorial superrotation (i.e., west-to-east winds over the equator). The superrotation is due to the equator-ward momentum transports by stationary planetary waves. The planetary waves on tidally locked planets are dominated by wavenumber-1, stationary, off-equatorial Rossby waves and equatorial Kelvin waves, which are considered to be the Matsuno-Gill mode. However, the feedbacks of such a strong superrotation on the planetary waves are rarely studied. In this study, we solve the 1-layer shallow water equations analytically to get the wave patterns under a prescribed zonal flow, and find that the zonal flow can shift the phase of planetary waves. The degree of the phase shift is a monotonic but nonlinear function of the strength of the zonal flow, and the phase shift has two limits of -180 and 180 degrees. The two limits are constrained by the energy budget of the whole system. We also find a resonance between planetary waves and the zonal flow occurs when the speed of zonal flow approaches to the phase speed of the waves but with opposite sign. The resonance is also constrained by the energy budget of this system.
Furthermore, we will show that there should also exist equatorial superrotation and planetary waves in the ocean. The waves are excited from heat source and wind stress, and they are in opposite phase. Both types of flows can transport eddy momentum to the equator, which can produce and maintain the oceanic superrotation. The oceanic superrotation can be found in analytical solutions and numerical simulations, and it may be observed on magma ocean planets by the telescope of JWST in the near future.
For further information contact PALS coordinator Tad Komacek at tkomacek@umd.edu.
Date: Monday 31-October-2022
Speaker: Guillame Chaverot
Title: First exploration of the entire runaway greenhouse transition with a 3D global climate model
Abstract: The new generation of telescopes will detect an increasing number of small, rocky, temperate exoplanets (e.g., PLATO, NIRPS, ExTrA) and characterize the best targets of them (e.g., JWST, RISTRETTO, HIRES, METIS). The runaway greenhouse is an important process for terrestrial planets, studied in particular to determine the inner limit of the habitable zone (HZ). This unstable state also distinguish two possible families of terrestrial atmospheres: atmospheres with habitable temperatures, and atmospheres with extreme temperatures and pressures - thus highly uninhabitable. Therefore, the understanding of the runaway greenhouse is pivotal to assess the possible evolution of terrestrial planets.
Using a 1D radiative-convective model, we have shown that a radiatively inactive gas like nitrogen (N2) strongly modifies the thermal emission of the atmosphere and the onset of the runaway greenhouse. We have also highlighted the importance of some physical processes too often relegated as second order (e.g. collisional broadening of water absorption lines). In the lineage of this effort, we use here a 3D global climate model, the Generic-PCM, to study the onset of the greenhouse effect for the same type of atmosphere. Our goal is to link these simulations at moderate temperature to the results obtained at high temperature (beyond the runaway greenhouse) for similar planets. This is necessary to draw a more detailed picture of this transition, taking into account all global climate processes. We also compare the results of 3D and 1D simulations, based on the findings of our previous study, to better understand the contribution of intrinsically three-dimensional processes such as clouds and large-scale atmospheric dynamics.
For further information contact PALS coordinator Tad Komacek at tkomacek@umd.edu.
Date: Monday 07-November-2022
Speaker: Mohammad Akhlaghi
Title: Carving out the low surface brightness astronomical signal
Abstract: Astronomical instrumentation has greatly advanced over the last 40 years: with digital detectors, space telescopes and +8m class ground-based telescopes for example. However, the signal-based detection paradigm is still the dominant method of low-level data analysis (for example from Petrosian or Kron in the 1970s, mostly through the implementation in SExtractor from the mid-1990s): detection, segmentation and measurements or catalog production. In this talk, after reviewing the major systematic biases regarding astronomical object detection and segmentation that is inherent to the signal-based paradigm, a fundamentally different "noise based" detection paradigm will be introduced for detecting signal that may have extremely low signal-to-noise ratios. With thresholds that are below the Sky value, and non-parametric expansion into noise, it is successfully able to detect very diffuse and irregularly shaped signal in noise (e.g., comets, nebulae, or galaxies) and improve the sky-level estimation by one order of magnitude see [1]. The software implementation of this method is called NoiseChisel (part of GNU Astronomy Utilities, or Gnuastro [2]). To define sub-structure over the detected signal, another software (Segment, also within Gnuastro) is in charge of Segmentation, finding true "clumps" over the NoiseChisel detections and using those to define "objects", see [3]. The talk will conclude with the application of NoiseChisel in several research projects and impact on science outputs.
[1] https://doi.org/10.1088/0067-0049/220/1/1 [2] https://www.gnu.org/software/gnuastro [3] https://arxiv.org/abs/1909.11230
For further information contact PALS coordinator Quanzhi Ye at qye@umd.edu.
Date: Monday 14-November-2022
Speaker: Qasim Afghan
Title: Structural Analysis of Long Period Comet Dust Tails using the Finson-Probstein Model
Abstract: Long period comets (LPCs), originating from the Oort Cloud, are highly unprocessed bodies that provide insight into the conditions present in the early Solar System. By analysing comet dust tails, characteristics of the parent comet body and the heliospheric conditions it experiences during its perihelion passage can be ascertained. Using images taken by the amateur astronomer community, these dust tails are analysed using the Finson-Probstein model. This modelled dust tail structure is then projected and overlaid onto the comet image to directly compare and identify similarities and discrepancies between the model and the image. Using the novel analysis method of mapping the image onto dust grain beta vs ejection time parameter space[1], tail structures can be more easily identified, analysed and tracked over time. This talk will focus on two specific comets, C/2020 F3 (NEOWISE) and C/2014 Q1 (PanSTARRS). Comet NEOWISE (C/2020 F3) displayed a highly structured dust tail, exhibiting the most prominent dust tail features visible from Earth since Comet McNaught (C/2006 P1) in the Southern Hemisphere and Comet Hale-Bopp (C/1995 O1) in the Northern Hemisphere. Fine-scale dust tail structures are identified and characterised to create a ‘profile’ of the comet’s dust tail. This is then compared with similar structures seen in other cometary dust tails, providing explanations on how these structures form and the shared characteristics of LPCs as a population. The first identification of a ‘dust tail gap’, a region of low dust number density, was identified in amateur images of the dust tail of long period comet C/2014 Q1 (PanSTARRS) . This gap presented itself as a wedge-shaped region devoid of dust in the middle of the dust tail. This dust-sparse area corresponds to the comet’s perihelion, when the comet should be at its most active. This dust tail ‘gap’ is analysed and parameterized, and the results used to investigate the origins of this peculiar structure.
[1] Price, Oliver, Geraint H. Jones, Jeff Morrill, Mathew Owens, Karl Battams, Huw Morgan, Miloslav Drückmuller, and Sebastian Deiries. 2019. "Fine-Scale Structure In Cometary Dust Tails I: Analysis Of Striae In Comet C/2006 P1 (Mcnaught) Through Temporal Mapping". Icarus 319: 540-557. doi:10.1016/j.icarus.2018.09.013.
For further information contact PALS coordinator Quanzhi Ye at qye@umd.edu.
Date: Monday 28-November-2022
Speaker: Xian Shi
Title: Boulder ejection and mobilisation on comet 67P observed by Rosetta/OSIRIS
Abstract: With an unprecedented resolution, OSIRIS cameras on board ESA’s Rosetta mission witnessed a diversity of dust activity during over two years’ rendezvous with comet 67P/Churyumov-Gerasimenko. These observations show, besides nominal ‘jets’ and spontaneous outbursts, also ejections of boulders that are aggregates decimetres to metres in size. In this talk, I will introduce observations of various forms of boulder activity on 67P, and our investigation to explain possible underlying mechanisms. We found that such activity could be a significant part of the resurfacing process of the nucleus and contributes to the redistribution of icy materials.
For further information contact PALS coordinator Quanzhi Ye at qye@umd.edu.
Date: Monday 05-December-2022
Speaker: Yoonyoung Kim
Title: Active asteroids observed by Hubble Space Telescope
Abstract: Active asteroids show transient cometary activity, driven by a range of processes (sublimation, impacts, rotational breakup, and combinations of these processes). A sub-set, called main-belt comets, may be driven by sublimation and so could be useful for tracing the present-day distribution of asteroid ice. In this talk, I will introduce Hubble Space Telescope observations of newly discovered objects. I combine the high-resolution optical data with a Monte Carlo dust dynamics model to quantify the nature of the dust coma and underlying nucleus source, then determine the cause of the activity (sublimation or something else). This is important to better constrain the intrinsic ice content in the main belt.
For further information contact PALS coordinator Quanzhi Ye at qye@umd.edu.
