ExoExplorers

Abstract: A major objective of the future Habitable Worlds Observatory (HWO) is to directly image and spectrally characterize at least 25 habitable worlds. Achieving this ambitious goal will depend on a myriad of factors, including the effectiveness of starlight suppression technology and the completeness of background calibration during post-processing. While coronagraphs are the favored starlight suppression technology for HWO, there is ongoing work to investigate the utility of a starshade complement operating in the ultraviolet (UV) spectrum. Although starshades are limited in the number of observations they can make due to fuel and reconfiguration time, their high throughput, high contrast, and broad spectral bandwidth make them a powerful characterization instrument. In this talk I will cover ongoing efforts to simulate and analyze Earth-like exoplanets using a starshade in the UV, accounting for varying orbital inclinations and phase angles as well as the presence of inhomogeneous exozodiacal dust distributions. Exozodiacal dust is likely to be one of the most significant sources of astrophysical noise when detecting terrestrial planets in the habitable zone, especially due to bright “clump”-like structures that result from disk-planet interaction. The first portion of this talk will focus on the data simulation pipeline, which builds on the Starshade Imaging Simulation Toolkit for Exoplanet Reconnaissance (SISTER). In the second portion of the talk I will introduce the analyses investigating the sensitivity of planet detection and characterization to the quality of exozodiacal dust removal. Finally, I will discuss how the introduced data and analyses pipelines will be used to inform the spectral retrieval capabilities of a starshade complement for HWO.

Abstract: Adaptive optics has enabled a wide range of scientific work in the last three decades, from the discovery of planetary systems to characterizing the supermassive black hole at the center of our galaxy. Continuous improvements in adaptive optics have kept us at the cutting edge of exoplanetary science. New developments improve the resolution and contrast needed to characterize exoplanets and their atmospheres through direct imaging and spectroscopy, allowing us to probe previously unobserved molecular species. This talk summarizes the facility adaptive optics upgrade on two Mauna Kea telescopes – Subaru and Keck – focusing on their swap to high-resolution deformable mirrors, a vital technology demonstration for future extremely large telescopes.

Abstract: In the JWST era and beyond, the search for signs of life on exoplanets is entering a new era where detection of atmospheric biosignatures may soon be possible. To maximize the application of this exciting opportunity, it is essential to identify many potential biosignatures and their specific environmental applicability. Many biosignature candidates, such as O2 and CH4, have significant potential false positives generated by abiotic processes. To address this issue, we propose the use of methylated gases as “capstone biosignatures”. The process of biomethylation, often an environmental detoxification mechanism, can utilize and subsequently volatilize a broad range of substrates including halogens, chalcogens, and metalloids (eg CH3Cl, CH3Br, CHBr3, CH3I, DMS, etc). Methylated gases are not produced as equilibrium products and have extremely limited pathways for abiotic production; therefore, they are signs of life with low ambiguity. Here we present simulations of flux-abundance relationships for a variety of methylated halogen gases such as CH3Cl, CH3I and CHBr3. Self-consistent simulations reveal that the presence of multiple methylated gases enhances individual buildup levels and lowers the threshold for photochemical runaway, increasing the potential detectability of methylated gas features and their application as remote biosignatures.

Abstract: The frequency of Earth-sized planets in the habitable zone is a key parameter in the design and success of future missions like the Habitable Worlds Observatory. Yet our estimates – and the Kepler sample that many are based on – are subject to change, as we learn more about the physical and statistical processes affecting planetary populations and our ability to study them. In this talk, I’ll introduce two recent investigations of Kepler’s Earth-sized planets, alongside ongoing efforts to expand our view beyond single-star, single-survey studies. In the first portion, I’ll describe how a population-level trend in atmospheric evolution helped identify the primordially rocky population of Earth-sized planets around Sun-like stars. In the second portion, I’ll explore how a decade of innovation has reshaped our understanding of Kepler’s M dwarfs and their Earth-sized planets. In both segments, I’ll provide our best estimates for the frequency of Earth-sized planets in the habitable zone, and their implications for the Habitable Worlds Observatory. Finally, I’ll discuss ongoing efforts to address open questions on this topic, like how we can move past Kepler’s limitations, and how our occurrence estimates are sensitive to Kepler’s unresolved stellar companions.

Abstract: We present the longest photometric monitoring of up to 1200-hours of the brown-dwarf binaries Luhman 16AB, documenting ±5% variability with periods under 10-hours. We show that short-period rotational modulation around 5-hour (k=1) and 2.5-hour (k=2) dominate the variability, where the planetary-scale waves model of k=1 and k=2 waves fit the lightcurve extremely well. We explain the difference in the narrowed range of k=2 periods compared to k=1 periods using models of zonal banding in Solar System giants (Jupiter and Saturn) and suggest that this difference arises from higher wind speed distribution at low latitudes compared to mid-to-high latitudes. Lastly, we show that Luhman 16 AB exhibits long-period ±5% variability with periods up to 100-hour - potentially coming from polar regions in the atmospheres? Our results are consistent with past GCMs, demonstrating that zonal-banding, latitude-dependent waves, and slowly varying atmospheric features could be present in Luhman 16 AB.

Abstract: XUV-driven photoevaporation is a leading hypothesis on the astrophysical processes that sculpt the observed distribution of short-period planetary radii. In recent years, direct evidence of atmospheric escape has been detected via in-transit transmission of the metastable He triplet near 10830 Å. Dozens of planets have been probed with this tracer, mostly as single-epoch snapshots. Since the stellar XUV that underlies planetary mass-loss is time-variable, it is necessary to understand the outflows’ responses to changes in the incident flux. Here, we report results from an ongoing longitudinal study to characterize the time-variability of WASP-69b’s atmospheric outflow. In August and September 2023, we obtained contemporaneous metastable He data from Palomar/WIRC along with X-ray and mid-UV data from the Swift Observatory. Together, these data lead to a comprehensive characterization of WASP-69b’s hydrodynamical state in the epoch of observation. By comparison to archival metastable He data and archival high-energy data from XMM-Newton, we assess the time variability of WASP-69b’s mass-loss rate on timescales commensurate with typical stellar activity cycles.

Abstract: The present-day orbital architecture of planetary systems is a fossil record of the system's formation history. While transit surveys have provided us with numerous planetary systems, it is unable to determine the mass of a planet, its orbital eccentricity, and whether the system harbors planets with inclinations large enough to preclude them from transiting. Where the transit method falls short, radial velocity follow-up demonstrates its strength. In this presentation, I will share the system architectures revealed by the TESS-Keck Survey: a significant radial velocity follow-up effort aimed at measuring the masses and orbital properties of 86 TESS Objects of Interest. My work represents the largest uniform analysis of TESS-discovered planets to date, resulting in mass and orbital constraints for 127 planets. This includes 12 non-transiting companions and precise constraints on orbital eccentricity, which are crucial for accurate dynamical modeling of these systems. Additionally, I will highlight the importance of complimenting primary survey instruments, such as Keck/HIRES, with instruments of comparatively lower precision. This synergy leads to fuller phase space coverage, resulting in more precise measurements of critical orbital parameters, such as eccentricity.The present-day orbital architecture of planetary systems is a fossil record of the system's formation history. While transit surveys have provided us with numerous planetary systems, it is unable to determine the mass of a planet, its orbital eccentricity, and whether the system harbors planets with inclinations large enough to preclude them from transiting. Where the transit method falls short, radial velocity follow-up demonstrates its strength.

Abstract: The last decade of exoplanet exploration has a population of 1-3 RE short-period planets, with peaks in the population at sub-Neptune and super-Earth radii, and a “radius valley” in between. Based on bulk composition alone, the nature of these planets has remained elusive, but atmospheric observations offer a new window to explore their compositional diversity. The JWST COMPASS survey (Compositions of Mini-Planet Atmospheres for Statistical Study) will obtain transmission spectra of 11 such planets using JWST NIRSpec/G395H, building a critical link between atmospheric characterisation and planetary demographics. In this talk, I will present results from the first multi-planet system observed by the COMPASS program, with the 2.8–5.2μm transmission spectrum of the ~870K, 1.7RE super-Earth TOI-836b. We find that transmission spectra from two visits are consistent with one another, and that by combining both visits, we can narrow in on the potential metallicity and cloud properties of the planet. I will also compare TOI-836b to its exterior sibling planet, the sub-Neptune TOI-836c, and the wider implications for this radius valley straddling system. This work provides insight into planning future observations of high metallicity planets around bright host stars, given the noise properties of our data.

Abstract: Transit timing variations (TTVs) are ubiquitous in exoplanet transit datasets, with Kepler alone containing ~2,000 periodic TTVs. However, these TTVs are often ambiguous from a model selection perspective, as it is difficult to determine the physical cause of a TTV, be it another planet, a moon, or stellar activity. Currently, careful considerations must be taken, on a case-by-case basis, using computationally expensive N-body simulations, in order to determine the cause of an observed TTV signal. In this talk, we will discuss our work building TTV model selection techniques, through investigations of the orbital landscape of exoplanet TTVs. Specifically, we will focus our discussion on two primary areas: the exomoon corridor and the exoplanet edge. The exomoon corridor ranges from two-to-four times the orbital period of the transiting planet, and is where we expect a pile-up (~50%) of exomoon induced TTVs near the Nyquist period due to aliasing caused by undersampling. We will share our results from searching the exomoon corridor for moon-like TTVs and our follow-up analysis of one of these systems. We will also present our finding that perturbing planets are not expected to induce a TTV with an observed dominant period less than half their own orbital period. This “exoplanet edge” is the manifestation of an observational alias of the true TTV period. The presence of an anomalous dominant TTV period, in a two-planet system, that falls below the exoplanet edge would demonstrate that there exists additional mass in the system, besides the two known exoplanets. Finally, we identify a number of two-planet systems, in Kepler data, that don't lie on the exoplanet edge, and discuss several possible explanations for additional mass in the system.

Abstract: Water must condense into ice clouds in the coldest brown dwarfs and exoplanets. When they form, these icy clouds change the emergent spectra, temperature structure, and albedo of the substellar atmosphere. The properties of clouds are governed by complex microphysics but these complexities are often not captured by the simpler parameterized cloud models used in climate models or retrieval models. To accurately interpret the exquisite details JWST observations show of ultra-cool substellar objects, we need to be prepared to efficiently generate atmospheric models without compromising the accuracy of the cloud’s morphology and optical properties, both of which significantly impact the observables. In this talk, I will discuss how we combine microphysical cloud modeling and 1D climate modeling with the goal of incorporating insights from microphysical models into a self-consistent, parameterized cloud model. I will highlight the differences we see in the observables between the current water cloud prescription and those with our new microphysically informed water clouds. The improvements discussed here will be used towards analyzing JWST observations of ultra-cool substellar worlds including WISE 0855, the coldest known brown dwarf.