Date: Monday 23-January-2023
Speaker: Namrah Habib
Title: Modelling Dry Compositional Convection for Applications to Super-Earth and Sub-Neptune Exoplanet Atmospheres
Abstract: Representation of convection within 3D climate models, or General Circulation Models (GCMs), is a known source of uncertainty that affects the predicted climate and habitability of exoplanets. Convection occurs on length scales much smaller than most GCM studies resolve and is therefore parameterized. However, convection parameterizations are often tuned to Earth-based parameters or overly simplified. Additionally, in exoplanet’s with primarily H2/He atmospheres, convection can be inhibited by the greater density of atmospheric tracers compared to the background air. Previous studies have shown compositional gradients in H2/He atmospheres can cause the planetary deep atmospheric temperature to be 100s K hotter than what is conventionally predicted by a moist or dry adiabat. Hotter deep atmospheric temperatures would change our understanding of planetary interior chemistry, evolution, and habitability for terrestrial exoplanets. In this work, we aim to develop a fundamental understanding of how compositional gradients affect planetary atmospheres. We use Cloud Model 1 (CM1), a convection resolving model, to perform initial value problem testcases of non-condensing compositional convection for exoplanets with Earth-Air, H2, and CO2 atmospheres. Typically, atmospheric convection is assumed to mix the atmosphere to a global, neutrally stable atmospheric state that is only dependent on temperature. However, our CM1 simulations suggest that when there is compositional variation within planetary atmospheres, convection mixes the atmosphere to a neutrally stable state that is dependent on both the temperature and compositional profile within the atmosphere. We use our CM1 simulation results to formulate and validate a dry convective adjustment scheme for use in GCMs, which relies on an energy analysis, to determine the final adjusted atmospheric state. Overall, our convection scheme produces results that agree with our CM1 simulations and can easily be implemented in GCMs to improve modelling of compositional convection for super-Earth and sub-Neptune exoplanet atmospheres.
For further information contact PALS coordinators Quanzhi Ye at qye@umd.edu and Tad Komacek at tkomacek@umd.edu.
Date: Monday 06-February-2023
Speaker: Naomi Rowe-Gurney
Title: The Ice Giants from JWST
Abstract: The Ice Giants, Uranus and Neptune, are the least understood planets in our Solar System. They have only been visited once by flybys (in 1986 and 1989) by Voyager 2. The recently published 2023-2032 Decadal Strategy for Planetary Science and Astrobiology prioritized a flagship orbiter and probe to Uranus with the intent to “...transform our knowledge of ice giants in general and the Uranian system in particular”. By using remote sensing to probe their atmospheres, we can begin to understand their composition and complex weather systems in preparation for this future mission. Uranus and Neptune have been observed from ground- and space-based observatories in many wavelength bands. This talk will present post-Voyager infrared remote sensing observations of both planets and show how the James Webb Space Telescope (JWST) is advancing our understanding of ice giant atmospheres. NASA’s Spitzer Space Telescope was arguably the JWST's predecessor, and its Infrared Spectrometer (IRS) was used to observe the thermal emission (5 – 37 μm) of both Uranus and Neptune multiple times between 2004 and 2007. This disc-averaged thermal and chemical structure from Spitzer is our best characterization of ice giant thermal structure before the JWST Mid-Infrared Instrument (MIRI)'s resolved mid-infrared spectroscopy. This talk will outline the plans for the JWST Guaranteed Time Observations (GTO) and discuss the advancements that JWST gives with respect to Spitzer.
For further information contact PALS coordinators Quanzhi Ye at qye@umd.edu and Tad Komacek at tkomacek@umd.edu.
Date: Monday 13-February-2023
Speaker: Munazza Alam
Title: A Simple Static Disk Condensation Model to Connect Refractory Abundances in Ultra-hot Jupiters with Formation Location
Abstract: The enrichment or depletion of refractory and volatile elements in exoplanetary atmospheres is sensitive to formation location in the protoplanetary disk, planetesimal composition and size, total disk mass, and the surface density of solids in the disk. Whereas the chemistry of volatiles has long been the focus of disk modeling efforts, the abundance patterns of refractory species have been neglected because they condense into solids in exoplanets cooler than 2000 K. For ultra-hot Jupiters (T_eq >2000 K), however, refractories remain in gaseous form - thus also remaining in the observable part of the atmosphere. We present a simple static protoplanetary disk model for refractory elemental condensation sequences at distances between 0.01-0.50 AU, assuming chemical equilibrium at these radii. Refractory elements form interior to the water snowline (<3 AU), so the condensation sequences of these species can provide a detailed probe of atmospheric abundances for planets that formed within a few AU. The theoretical framework described here can be coupled with refractory abundance constraints from high-resolution cross-correlation spectroscopy observations of ultra-hot Jupiter atmospheres to provide a powerful tool for tracing the refractory condensation sequence of the hottest gas giants, constraining where and how these planets formed.
For further information contact PALS coordinators Quanzhi Ye at qye@umd.edu and Tad Komacek at tkomacek@umd.edu.
Date: Monday 20-February-2023
Speaker: Ben Hord
Title: Where Did They Come From, Where Will They Go: The Life and Death of Hot Jupiters
Abstract: Hot Jupiters are one of the biggest surprises of exoplanet science. The birth and evolution of such planets are unlike anything in the Solar System and they have challenged traditional theories of planet formation. A clue to unraveling this formation history comes from the fact that the vast majority of hot Jupiters lack nearby companion planets. By studying the handful of cases in which hot Juipters do possess nearby planets, we can distinguish between the possible mechanisms that form hot Jupiters. I will discuss my discovery of a new hot Jupiter companion planet – WASP-132 c – as well as emerging trends in the handful of hot Jupiter systems with this rare architecture. Furthermore, the death of hot Jupiters is poorly understood. Every hot Jupiter is doomed to inspiral into its host star, and I will present current and future work on directly observing this phenomenon to constrain hot Jupiter lifetimes. In this manner, I hope to provide further understanding on the two bookends of a hot Jupiter’s life.
For further information contact PALS coordinators Quanzhi Ye at qye@umd.edu and Tad Komacek at tkomacek@umd.edu.
Date: Monday 27-February-2023
Speaker: Yun Zhang
Title: Inferring the impact activation process of main-belt comets from their near-perihelion activity pattern
Abstract: Small bodies that contain volatile components hold valuable information about the evolution of the solar system and the origins of life on Earth, as well as be-ing of interest for resource exploration. In recent decades, dust emission driven by sublimation has been detected on several asteroids located in the main belt, known as main-belt comets (MBCs), which suggests the presence of buried ices in these bodies. Previous theoretical and numerical studies have predicted that main-belt objects may be able to retain subsurface water ice throughout their lifetime. These objects can exhibit comet-like activity when impacted by a small projectile that exposes the subsurface volatile ices of a local surface area. All of the MBCs discovered to date only show detectable activities near perihelion. Since the impact location and summer solstice are expected to be distributed randomly, the strongest activity of an impact-exposed area might not necessarily occur near perihelion. In this talk, I will discuss the observational features of MBCs, and present our investigation to explain this discrepancy and shed light on the detailed impact activation process.
For further information contact PALS coordinators Quanzhi Ye at qye@umd.edu and Tad Komacek at tkomacek@umd.edu.
Date: Thursday 02-March-2023
Speaker: Lili Alderson
Title: Into the IR: Exploring Exoplanet Atmospheres with Hubble and JWST
Abstract: TBD
For further information contact PALS coordinators Quanzhi Ye at qye@umd.edu and Tad Komacek at tkomacek@umd.edu.
Date: Monday 06-March-2023
Speaker: Adam Langeveld
Title: Investigating trends in transiting exoplanet atmospheres with high-resolution spectroscopy
Abstract: The alkali metal sodium (Na) is one of the most commonly detected chemical species in the upper atmospheres of giant exoplanets. The prevalence and strength of these detections presents an opportunity to search for trends and attempt to answer population-level questions on exoplanetary atmospheres. In this talk, I will report on a homogeneous survey of Na in a diverse sample of transiting exoplanets using high-resolution transmission spectroscopy. We use uniformly measured Na doublet line depths to constrain the atmospheric heights probed by Na observations across the sample. We assess an empirical trend describing the measured atmospheric heights as a function of the planetary bulk properties, and discuss measurements of atmospheric wind velocities. We also present initial results from the ongoing Exoplanets with Gemini Spectroscopy (ExoGemS) survey, which has acquired high-resolution transmission spectra of over 20 exoplanets using GRACES at the Gemini North Observatory. Surveys of this type highlight a promising avenue for using high-resolution transmission spectroscopy to further our understanding of how atmospheric characteristics vary over a diverse sample of exoplanets.
For further information contact PALS coordinators Quanzhi Ye at qye@umd.edu and Tad Komacek at tkomacek@umd.edu.
Date: Monday 27-March-2023
Speaker: Man-To Hui
Title: [POSTPONED] Recent Updates on Near-Sun Objects
Abstract: Near-Sun objects are a population of small solar system bodies characterised by extremely close distances to the Sun around perihelion within the orbit of Mercury. Their peculiar orbits inevitably pose often insurmountable challenges for discoveries and observations of these objects, hindering attempts to explore them and making them arguably the least studied population of small bodies in the solar system. However, the scarcity of near-Sun objects cannot be fully accounted for by the observational bias but is also suspected to be associated with physical mechanisms leading to their fragmentation that are probably not frequently seen elsewhere in the solar system. In this talk, I will highlight recent progress in studies of near-Sun objects and discuss how these can shed light on the understanding of this population.
For further information contact PALS coordinators Quanzhi Ye at qye@umd.edu and Tad Komacek at tkomacek@umd.edu.
Date: Monday 10-April-2023
Speaker: Karl Battams
Title: Phaethon and the Geminids: New Insights from NASA's Heliophysics Fleet
Abstract: The Geminids are one of the most prominent terrestrial meteor showers, occurring in mid-December every year, and are one of a very small number of meteor showers not associated with a comet. Instead, the Geminid parent is widely believed to be near-Sun asteroid 3200/Phaethon, which itself was only discovered in 1983. Much remains unknown or unclear about the collective Geminid-Phaethon system, including the massively disruptive event (or events) that led to the formation of the Geminids, their evolution over the proposed 2kyr since their formation, as well as the properties of Phaethon itself and its behavior at perihelion. Ground-based observations of this system have remained largely confined to studies of Earth-encountering Geminids, and observations of an inactive Phaethon at substantial distances from its 0.14au perihelion. In recent years, however, a surprising source of information about this enigmatic system has come from the NASA and ESA heliophysics space fleet, with direct observations of both the Geminids and Phaethon itself at their perihelion points. In this seminar, I will discuss the breadth of observations, insights, and surprises revealed from analyses of SOHO, STEREO, and Parker Solar Probe data, including some of the questions they have answered and the many more that they have raised.
For further information contact PALS coordinators Quanzhi Ye at qye@umd.edu and Tad Komacek at tkomacek@umd.edu.
Date: Monday 17-April-2023
Speaker: Leah Dodson
Title: Looking Up: A Molecular Perspective at Astronomical Complexity
Abstract: The new molecules astronomers are discovering in space keep astrochemists on their toes! Many of the molecules observed in astrophysical objects are totally outlandish by traditional perspectives: long linear unsaturated carbon chains, metals in surprising charge states, and strained ring structures have all challenged chemists to think beyond terrestrial conventions in explaining how these molecules form and react, and where they fit into the overall cycle of planetary and stellar evolution. The challenge to laboratory astrochemists like us is to study this exotic chemistry under the relevant physical conditions—most importantly the low temperatures of space. In this talk I will explain the lengths we go to to study chemical reactions at temperatures down to 10 K. Come hear about all of the exceptions to the rules (lies) you were taught in your introductory chemistry courses!
For further information contact PALS coordinators Quanzhi Ye at qye@umd.edu and Tad Komacek at tkomacek@umd.edu.
Date: Monday 24-April-2023
Speaker: Callie Hood
Title: The Promise and Challenge of Brown Dwarf Retrievals at Medium Spectral Resolution
Abstract: Brown dwarf spectra offer vital testbeds for our understanding of the chemical and physical processes that sculpt substellar atmospheres. Atmospheric retrieval approaches have been successfully applied to a number of low-resolution (R≈100) spectra of L, T, and Y dwarfs, yielding constraints on the abundances of chemical species and temperature structures of these atmospheres. Medium-resolution (R≈1E3) spectra of brown dwarfs offer significant additional insight, as molecular features are more easily disentangled from one another and the thermal structure of the upper atmosphere is more readily probed. First, I will discuss my recently submitted publication in which we apply a GPU-version of the CHIMERA retrieval framework to a high signal-to-noise, medium-resolution (R≈6000) FIRE spectrum of a T9 dwarf from 0.85-2.5 microns. At 60x higher spectral resolution than previous brown dwarf retrievals, a number of novel challenges arise, which we explore. For example, we examine the strong effect of different line lists on our retrieved molecular abundances, in particular for CH4. We compare these retrieval results to those obtained for a R≈100 spectrum of the same object, revealing how constraints on atmospheric abundances improve by an order of magnitude or more (depending on the species) with increased spectral resolution. Next, I will present preliminary results from the application of this retrieval framework to JWST NIRSpec/G395H observations of a T8 dwarf with R~2700 over 2.87–5.14 microns. Together, these projects illustrate the power of retrievals on high-quality, medium-resolution spectra to precisely constrain the atmospheric properties of substellar atmospheres.
For further information contact PALS coordinators Quanzhi Ye at qye@umd.edu and Tad Komacek at tkomacek@umd.edu.
Date: Monday 01-May-2023
Speaker: Esteban Wright
Title: Ricochets and Stranding Boulders on Rubble Pile Asteroids
Abstract: Many asteroids are ‘rubble piles’, conglomerations of weakly gravitationally bounded material with a wide span of grain sizes present on their surfaces. Impacts, spin-out events, and seismic activity can produce a population of gravitational bound objects in orbit that can impact the surface at low velocity and a distribution of impact angles. First, we present low velocity, oblique impacts of spherical projectiles into several monodisperse granular substrates. With high speed video and fluorescent markers on the projectiles we track projectile trajectory and spin during impact. We estimate constraints on projectile radius, velocity, and impact angle that would allow projectiles on asteroids to ricochet or roll away from the initial impact site. We perform experiments of ricocheting impactors, with fixed impact velocity and angle, into granular media with different mean grain size. We find that hydro-static-like, drag-like and lift-like forces, used in empirical impact force laws are sensitive to mean grain size, with the lift coefficient being the most sensitive. Second, we consider how a subsurface seismic pulse affects the surface of an asteroid distant from the impact site. Using dry polydisperse gravel mixture, we film and track the ejecta launched by a single upward propagating pressure pulse. We find ejecta trajectories are independent of particle size, and collisions primarily take place upon landing, where smaller particles are scattered off larger particles, a process dubbed ‘ballistic sorting’. These projects illustrate that surface size distribution should be considered in future impact models on granular asteroid surfaces and that a single strong pulse is an additional mechanism for stranding previously buried boulders on the surface.
For further information contact PALS coordinators Quanzhi Ye at qye@umd.edu and Tad Komacek at tkomacek@umd.edu.
Date: Monday 08-May-2023
Speaker: Man-To Hui
Title: Recent Updates on Near-Sun Objects
Abstract: Near-Sun objects are a population of small solar system bodies characterised by extremely close distances to the Sun around perihelion within the orbit of Mercury. Their peculiar orbits inevitably pose often insurmountable challenges for discoveries and observations of these objects, hindering attempts to explore them and making them arguably the least studied population of small bodies in the solar system. However, the scarcity of near-Sun objects cannot be fully accounted for by the observational bias but is also suspected to be associated with physical mechanisms leading to their fragmentation that are probably not frequently seen elsewhere in the solar system. In this talk, I will highlight recent progress in studies of near-Sun objects and discuss how these can shed light on the understanding of this population.
For further information contact PALS coordinators Quanzhi Ye at qye@umd.edu and Tad Komacek at tkomacek@umd.edu.
Date: Monday 15-May-2023
Speaker: Richard Wainscoat
Title: The discovery of `Oumuamua - an insider's perspective
Abstract: In October 2017, the Pan-STARRS1 telescope on Haleakala, Hawaii, discovered the first interstellar object. It moved rapidly away from Earth, and was only easy to observe for one lunation, producing a worldwide frenzy of observations, including telescopes on Maunakea. I will describe how we realized that this object had a hyperbolic orbit, and some of our early efforts to characterize it, and the challenges that we encountered. As `Oumuamua departed from the Sun, it accelerated slightly, showing non-gravitational motion. This small acceleration was evident in published astrometry, producing a difficult waiting period to publish this while we continued to observe `Oumuamua as it departed using HST. Most likely, the acceleration is caused by low-level cometary activity, probably involving larger grains. Prospects for discovery of more interstellar objects will also be discussed.
For further information contact PALS coordinators Quanzhi Ye at qye@umd.edu and Tad Komacek at tkomacek@umd.edu.
Date: Monday 24-July-2023
Speaker: Nathan Mayne (Exeter)
Title: Exoplanet Climates in 3D: challenges & opportunities
Abstract: Planetary climates are tricky requiring a range of model complexities to understand, interpret and predict observations. Simple models aid our understanding of the key mechanisms but can provide seemingly robust inferences which are actually dependent on the physical ingredients or assumptions (e.g., 1D versus 3D), whereas higher complexity models are more resource intensive and dependent on a larger number of input parameters. Our progress in understanding the Earth's climate, and that of its neighbouring solar system planets, a relatively small number of well observed cases, is helping us accelerate our understanding of the vast (overwhelming?) diversity of exoplanets. In turn, studies of exoplanets are benefitting the understanding of our own changing climate. One lesson from Earth climate research is clear, a range of approaches and perspectives is vital to make progress.
In this talk I will detail the research undertaken by our team at the University of Exeter employing, predominantly, 3D climate models across a range of complexities to try to unravel the interactions between chemistry, radiative transfer, dynamics and biology in planetary climates. I will focus on simulations of gas giant exoplanets, including clouds and chemical kinetics, compared to observations from JWST, and simulations of terrestrial planets, connecting the Early Earth with potentially habitable candidates. Additionally, I will briefly describe the knowledge transfer with Earth climate research through a co-development framework with the UK Met Office. Finally, I will mention the context of our work within the recent exoplanet Model Intercomparison Projects of the CUISINES framework.
For further information contact PALS coordinators Quanzhi Ye at qye@umd.edu and Tad Komacek at tkomacek@umd.edu.
