@conference_item {CaltechAUTHORS_https://authors.library.caltech.edu/id/eprint/97746, title ="Constraining the formation of interstellar methanol using isotopologues", author = "Wilkins, Olivia and Carroll, Brandon", pages = "PHYS-0322", month = "August", year = "2019", url = "https://resolver.caltech.edu/CaltechAUTHORS:20190812-083216758", note = "© 2019 American Chemical Society.", revision_no = "10", abstract = "The formation of so-called complex mols. in the early stages of star formation has implications not only for how we decipher the evolution of planetary systems but also how we understand the evolution of mols. themselves. Interstellar complex mols., which are simple by terrestrial stds. with only six or more atoms, are key precursors to the rich chem. diversity found in comets and meteorites and on planetary bodies. Isotopologues have proven useful in other areas of chem., for instance in pinning down formation mechanisms of mols. in synthetic org. chem., but there has been relatively little work done using isotopologues to understand how interstellar mols. form. Isotopologues have been used, however, in constraining the formation of compds. such as Me cyanide (CH_3CN) and methanol (CH_3OH) in the Orion Kleinmann-Low nebula (Orion KL). Previous low-spatial-resoln. studies of methanol in Orion KL have been inconclusive, and thus we have obtained high-resoln. imaging data of deuterated methanol (CH_2DOH, CH_3OD) toward Orion KL with the Atacama Large Millimeter/submillimeter Array (ALMA). These data show the distribution of deuterated methanol on spatial scales commensurate with local star formation. Comparing ratios of CH_2DOH and CH_3OD with ^(13)CH_3OH, we aim to assess how methanol chem. varies across the nebula and det. observationally whether the compd. is formed predominantly on the surfaces of icy dust grains as predicted by lab. expts. and computational models. Moreover, mol. clouds also contain relatively acidic compds., such as water, that can prompt spontaneous hydrogen/deuterium exchange on the oxygen atom in methanol. Thus, we will also explore the persistence of deuterium in methanol across the nebula by assessing how the relative abundances of CH_2DOH and CHOD change. Using these results, we can better constrain both the formation and reactivity of methanol in star-forming regions, a first step in understanding how even more complex chem.-perhaps even prebiotic chem.-evolved over the history of the universe.", } @conference_item {CaltechAUTHORS_https://authors.library.caltech.edu/id/eprint/97742, title ="Direct detection of water in the thermal emission spectra of hot jupiters", author = "Buzard, Cam and Piskorz, Danielle", pages = "PHYS-0660", month = "August", year = "2019", url = "https://resolver.caltech.edu/CaltechAUTHORS:20190812-081918332", note = "© 2019 American Chemical Society.", revision_no = "11", abstract = "Over the past nearly 30 years, over 3500 planets have been discovered orbiting stars other than the Sun. The discovery of these other worlds has revolutionized the field of planetary science from studying the few and distinct planets within the solar system to studying planetary populations in a statistical sense. With this vast new data, we can ask and begin to answer questions about planetary formation and evolution, and what it means for a planet to be habitable. Water is a key component of these answers. Because liq. water is crucial to life on Earth, it has become a std. of whether an exoplanet has the potential to sustain life. Gaseous water in the atmospheres of planets, specifically gas giant planets, can provide a clue to their formation and evolutionary history. Here, we describe a technique that we have pioneered to directly detect the thermal emission from hot Jupiters, gaseous Jupiter-sized planets that orbit their stars in only 3-5 day periods. Historically, hot Jupiters have been assumed to form at large orbital radii, like where our Jupiter exists today, and then migrate in to their current positions. More recent theories have suggested that it may actually be possible for\nhot Jupiters to have formed in their current orbits. An atm. carbon-to-oxygen (C/O) ratio, obtained from relative measurements of a carbon bearing species, most likely CO or CH_4, and water, could clue us in to where in the protoplanetary disk the planet formed. We will describe how we have used our technique to detect water in hot Jupiter atmospheres and our current approaches to try to simultaneously detect a carbon-bearing species. With these detections made in the same atm., we will be able to constrain the hot Jupiter's C/O ratio and est. where in the disk it formed. Furthermore, our technique promises to be particularly well adaptable for future studies of smaller, terrestrial, habitable zone planets. Water is a key component of planetary atmospheres and our detection of water in hot Jupiters paves the way for future studies of planetary formation and habitability alike.", } @conference_item {CaltechAUTHORS_https://authors.library.caltech.edu/id/eprint/97740, title ="Molecular snow lines in protoplanetary disks", author = "Blake, Geoffrey A. and Anderson, Dana", pages = "PHYS-0383", month = "August", year = "2019", url = "https://resolver.caltech.edu/CaltechAUTHORS:20190812-081229325", note = "© 2019 American Chemical Society.", revision_no = "10", abstract = "Compared to the Sun and to the gas+dust compn. of the interstellar medium from which the solar system formed, the Carbon and Nitrogen content of the bulk silicate Earth (mantle+hydrosphere+atm.) is reduced by several orders of magnitude, relative to Silicon. Evidence from primitive bodies as a function of distance from the Sun suggests that at least part of this depletion must occur early in the process of planetesimal assembly. With pioneering IR and (sub)mm observations such as those enabled by ground-based 8-10m class telescopes (and in future the James Webb Space Telescope) and the Atacama Large Millimeter Array (ALMA), we can now examine the principal volatile reservoirs of gas rich disks as a function position within the disk and evolutionary state. Key to these studies is the concept of condensation fronts, or 'snow lines,' in disks - locations at which key volatiles such as water, carbon monoxide, or nitrogen first condense from the gas. This talk will review the observational characterization of snow lines in protoplanetary disks via both gas and dust tracers, esp. recent ALMA observations, and highlight links to theor. investigations that are needed to tie the observational results to the delivery of volatiles to planetary surfaces in the habitable zones around Sun-like stars.", } @conference_item {CaltechAUTHORS_https://authors.library.caltech.edu/id/eprint/97741, title ="TeraHertz time domain spectroscopy (THz TDS) of molecular ices", author = "Blake, Geoffrey A. and Ioppolo, Sergio", pages = "PHYS-0605", month = "August", year = "2019", url = "https://resolver.caltech.edu/CaltechAUTHORS:20190812-081652853", note = "© 2019 American Chemical Society.", revision_no = "10", abstract = "In mol. clouds and protoplanetary disks, water-dominated ices comprise the bulk of the condensible CNO-elements that can ultimately be delivered to planetary surfaces. Such ices have long been studied by IR spectroscopy, but in the very densest cloud cores or in the disks around young stars such studies are exceedingly difficult. Yet, any grains warm enough to emit at mid-IR wavelengths are too hot to retain icy mantles. We have developed a coherent TeraHertz (THz) time domain instrument that can measure the optical consts. of solid materials and mol. ices from temps. of 10-300 K. Such an instrument probes the intermol. degrees of freedom in ices, and provides the possibility of studying the dominant org. and volatile reservoirs in forming planetary systems with instruments such as the HIgh Resoln. Mid-IR Spectrometer (HIRMES) onboard the Stratospheric Observatory for IR Astronomy (SOFIA). In our latest generation instrument, we have implemented a single shot multi-channel detection system that permits the entire THz waveform to be detected with each laser pulse, resulting in an approach that can study thin samples down into the several to several tens of monolayer regime. We will report on THz TDS studies of single component and mixed ices of relevance to star- and planetformation, with a view toward upcoming studies with SOFIA and the James Webb Space Telescope (JWST).", } @conference_item {CaltechAUTHORS_https://authors.library.caltech.edu/id/eprint/97783, title ="Towards elusive hybrid perovskite carrier dynamics through ultrafast THz spectroscopy: Influence of quantum confinement and charge transport layers", author = "Virgil, Kyle and Atwater, Harry", pages = "ENFL-0227", month = "August", year = "2019", url = "https://resolver.caltech.edu/CaltechAUTHORS:20190812-133101846", note = "© 2019 American Chemical Society.", revision_no = "9", abstract = "Development of solar cells which are simultaneously cheap, stable, scalable, and highly efficient is crit. to realizing the vision of globally accessible renewable energy dependence. Over the past decade, hybrid org.-inorg. perovskite materials have experienced a meteoric rise in research efforts which continue to demonstrate the promise of perovskite technol. in all these areas. We still lack, however, a detailed understanding of the fundamental charge carrier dynamics and photogenerated charge transport behavior in these materials with respect to quantum confinement and solar cell interfaces. Ultrafast terahertz (THz, or far-IR) spectroscopy provides a time-resolved, non-invasive probe of the collective carrier dynamics and lattice vibrations in semiconductors, both from sub-bandgap and photoexcited absorption as well as from THz emission. We discuss comprehensive THz investigations in benchmark hybrid perovskite systems that will allow for the extn. of crucial material parameters such as carrier mobility, permittivity, photocond., and lattice-coupling to intimately assess the influence of 2D architectures and electron/hole transport layers. Characterization in this manner offers vital insights to guide the rapid development of perovskite solar cells and strengthens our foundational knowledge of hybrid perovskite materials. Furthermore, cohesively optimizing perovskite potential through diverse scientific frontiers is necessary to achieve the revolutionary energy technol. of our future.", } @conference_item {CaltechAUTHORS_https://authors.library.caltech.edu/id/eprint/97743, title ="Towards single shot multidimensional terahertz spectroscopy of hydrogen-bonded liquids", author = "Mead, Griffin and Lin, Haw-Wei", pages = "PHYS-0250", month = "August", year = "2019", url = "https://resolver.caltech.edu/CaltechAUTHORS:20190812-082223585", note = "© 2019 American Chemical Society.", revision_no = "10", abstract = "Two-dimensional terahertz-terahertz-Raman (TTR) spectroscopy provides a direct probe of low energy, thermally excited intra- and inter-mol. modes of liqs. at room temp., as well as information on the modes' anharmonicities. However, the need to use two delay stages to sample the TTR response results in datasets that take tens of hours to acquire, thus limiting our ability to explore chem. and thermodn. space. To combat this difficulty, we present a single shot TTR spectrometer which, by replacing one delay line with a reflective echelon, allows tens of picoseconds of mol. dynamics to be captured in milliseconds, as opposed to the minutes previosuly required. We present a series of TTR results on room temp. liqs. highlighting the capabilities of the instrument and areas for improvement.", } @conference_item {CaltechAUTHORS_https://authors.library.caltech.edu/id/eprint/99737, title ="The Co-Evolution of Mars’ Atmosphere and Massive South Polar CO₂ Ice Deposit", author = "Ingersoll, A. P. and Ehlmann, B. L.", pages = "Art. No. 6008", month = "July", year = "2019", url = "https://resolver.caltech.edu/CaltechAUTHORS:20191107-124404583", note = "NASA’s NPP, NESSF, and MFRP programs supported this work. Part of this work was performed at the Jet Propulsion Laboratory, Cali-fornia Institute of Technology, under a contract with NASA. Government support acknowledged. Copyright 2019, All Rights Reserved.", revision_no = "11", abstract = "A Massive CO₂ Ice Deposit (MCID) that rivals the mass of Mars’ current, 96% CO₂ atmosphere was recently discovered to overlie part of Mars’ southern H₂O cap [1]. The MCID is layered: a top layer of 1-10 m of CO₂, the Residual South Polar Cap (RSPC) [2], is underlain by ~10-20 m of H₂O ice, followed by up to three 100s-meter-thick layers of CO2 ice, separated by two layers of ~20-40 m of H₂O ice [3] (Fig. 1). Previous studies invoked orbital cycles to explain the layering, assuming the H₂O ice insulates and seals in the CO₂, allowing it to survive periods of high obliquity [3,4]. We also model that orbital cycles [5] drive the MCID’s development, but instead assume the MCID is in continuous vapor contact with the atmosphere rather than sealed. Pervasive meter-scale polygonal patterning and km-scale collapse pits observed on the sub-RSPC H₂O layer [1,3] are consistent with it being fractured and permeable to CO₂ mass flux. Using currently observed optical properties of martian polar CO₂ ice deposits [6], our model demonstrates that the present MCID is a remnant of larger CO₂ ice deposits laid down during epochs of decreasing obliquity that are eroded, liberating a residual lag layer of H₂O ice, when obliquity increases. With these assumptions, our energy balance model ex-plains why only the south polar cap hosts an MCID, why the RSPC exists, and the observed MCID stratigraphy. We use our model to calculate Mars’ pressure history and the age of the MCID.", } @conference_item {CaltechAUTHORS_https://authors.library.caltech.edu/id/eprint/94951, title ="Observational constraints on the distribution and temperature dependence of H_2O_2 on the surface of Europa", author = "Trumbo, S. K. and Brown, M. E.", journal = "EPSC Abstracts", pages = "Art. No. EPSC2018-203-1", month = "September", year = "2018", url = "https://resolver.caltech.edu/CaltechAUTHORS:20190424-155510319", note = "© Author(s) 2018. \n\nS. K. Trumbo is supported through a NASA Earth and Space Sciences Fellowship (NESSF). K. de Kleer is supported via the 51 Pegasi b Fellowship Program.", revision_no = "13", abstract = "We use Keck NIRSPEC to investigate the geographic distribution of hydrogen peroxide, a potentially biologically important oxidant, on the surface of Europa. Contrary to expectation, we see the highest abundances at low latitudes, potentially correlated with geologically young chaos terrain. We also use NASA IRTF SpeX spectra of Europa before and after eclipse to investigate the extent to which temperature controls equilibrium hydrogen peroxide concentrations on the surface. During eclipse, Europa's surface temperature falls 10-20 K. If temperature were a significant control on peroxide concentrations, then the hydrogen peroxide band strengths should be different pre- and post-eclipse. Ultimately, these investigations will help further our understanding of the surface, and perhaps subsurface, composition of Europa.", } @conference_item {CaltechAUTHORS_https://authors.library.caltech.edu/id/eprint/90775, title ="Tracing the origins of nitrogen bearing organics toward Orion KL with ALMA", author = "Carroll, Brandon and Blake, Geoffrey", pages = "PHYS-560", month = "August", year = "2018", url = "https://resolver.caltech.edu/CaltechAUTHORS:20181108-161250799", note = "© 2018 American Chemical Society.", revision_no = "9", abstract = "A comprehensive anal. of a broadband 1.2 THz wide spectral survey of the Orion Kleinmann-Low nebula (Orion-KL) has shown that nitrogen bearing complex orgs. trace systematically hotter gas than O-bearing orgs. toward this source. The origin of this O/N dichotomy remains a mystery. If complex mols. originate from grain surfaces, N-bearing species may be more difficult to remove from grain surfaces than O-bearing orgs. Theor. studies, however, have shown that hot (T=300 K) gas phase chem. can produce high abundances of N-bearing orgs. while suppressing the formation of Obearing complex mols. Measurement of gradients in isotopic fractionation at spatial scales commensurate with the\nforces driving this chem. can distinguish these distinct formation pathways. Isotopic fractionation is a relatively common tool in astrochem., however until recently it has not been possible to measure fractionation at high angular resoln. The Atacama Large Millimeter/Submillimeter Array (ALMA) combines the sensitivity and angular resoln. required for these measurements, and represents a new method of approaching observational astrochem. We have obtained extremely high angular resoln. observations of Me cyanide (CH3CN) using the ALMA toward Orion KL. By simultaneously imaging 13CH3CN and CH2DCN we map the temp. structure and D/H ratio of CH3CN. We will present the results of these observations and discuss their implications for the formation of N-bearing orgs. in the interstellar medium.", } @conference_item {CaltechAUTHORS_https://authors.library.caltech.edu/id/eprint/87830, title ="Atmospheric chemistry on Venus: An overview of unresolved issues", author = "Mills, Franklin and Marcq, Emmanuel", pages = "PHYS-631", month = "March", year = "2018", url = "https://resolver.caltech.edu/CaltechAUTHORS:20180713-125059321", note = "© 2018 American Chemical Society.", revision_no = "11", abstract = "Venus' atm. is 96.5% CO_2 and 3.5% N_2 with trace abundances of SO_2, OCS, H_2O, HCl, HF, and HBr, as well as their\nphotochem. and lightning-induced products. The global clouds are composed at least partly of concd. sulfuric acid. The\nsurface pressure is 90 atm and surface temps. exceed 700 K. Atm. chem. transitions from ion chem. through\nphotochem. to thermal equil. chem. with heterogeneous chem. likely throughout the atm. Three major chem. cycles have\nbeen identified: the carbon dioxide, sulfur oxidn., and polysulfur cycles. The carbon dioxide cycle includes CO_2\nphotolysis, transport of a significant fraction of CO and O to the night side, prodn. of O_2, and conversion of CO and O_2 to\nCO_2, possibly via chlorine catalyzed pathways. The sulfur oxidn. cycle comprises transport upward of OCS, SO_2, and\nH_2O, oxidn. to H_2SO_4, condensation to form the global 30-km thick cloud layers, and sulfuric acid rain. The polysulfur\ncycle involves the upward transport of OCS and SO_2, disproportionation and prodn. of S_x (x=2-8), and downward\ntransport of S_x to react with CO and SO_3. There is solid evidence for the carbon dioxide and sulfur oxidn. cycles; the\npolysulfur cycle is more speculative but plausible. Alternatively, sulfur chem. on Venus has been conceptually divided\ninto fast and slow atm. cycles and a geol. cycle. Recent work (Parkinson et al, PSS, 2015) suggests the ternary SO_2-H_2O-H_2SO_4 system may bifurcate depending on the relative abundances of H_2O and SO_2. Despite this general\nunderstanding, five decades of spacecraft, and 200 years of observation, numerous significant unresolved issues remain.\nOne is the means by which CO_2 is stabilized over geol. time - models predict O_2 abundances a factor of ten larger than\nthe observational upper limit. Another is the lack of consistency among models of the chem. and microphysics in\ndifferent regions, esp. in the cloud layers, where the mixing ratios of many important trace species change by orders of\nmagnitude within several vertical scale heights, and at the surface. A third is the mechanism(s) creating an inversion\nlayer in SO_2 abundances in the mesosphere. This talk presents an overview of our current understanding and key\nunresolved issues.", } @conference_item {CaltechAUTHORS_https://authors.library.caltech.edu/id/eprint/86149, title ="Measurements of the thermo-chemical evolution of the planet-forming region in disks", author = "Banzatti, Andrea and Pontoppidan, Klaus", pages = "PHYS-260", month = "August", year = "2017", url = "https://resolver.caltech.edu/CaltechAUTHORS:20180501-081642894", note = "© 2017 American Chemical Society.", revision_no = "12", abstract = "I will present a large ongoing effort to measure the evolving thermo-chem. structure of planet-forming disks\nat 0.05-10 au. The main component of this work is high-resoln. spectroscopy (R ∼ 700-100,000) of mol. gas\nemission at IR wavelengths (2.9-35 um), from a suite of telescopes on the ground and in space (Spitzer, VLT,\nKeck, IRTF). This technique provides spatial information about mol. gas in inner disk regions unreachable by\nALMA. Large surveys of spectrally-resolved IR emission from disks give us measurements of: 1) the location\nand excitation temp. of CO, H2O, and OH in the 0.05-10 au region, 2) the thermo-chem. evolution of mol.\ngas, including simple org. mols. (HCN and C2H2), during planet formation, 3) the evolving chem. of inner\ndisks that are being dried-up from water. In addn., we are now combining these surveys to high-resoln. optical\nspectroscopy, to study the products of mol. photo-dissocn., and to multi-wavelength dust tracers, to\ncharacterize the interplay between dust grains and mol. gas in evolving disks. I will conclude with future\nprospects for mol. inventories in evolving planet-forming disk with JWST.", }