A primary goal of the Habitable Worlds Observatory (HWO) is to detect and measure the abundance of biosignature molecules, such as water (H2O) and oxygen (O2), in the atmosphere of Earth analogs. This is expected to require deep spectroscopic observations lasting hundreds of hours per planet. In this context, it is essential to optimize the spectral resolution of the spectrograph to both maximize the number of planets that can be studied over the lifetime of the mission and also to reduce the risks of false detections. The purpose of this work is to provide a framework to explore the spectral resolution design trade-space for HWO. This framework must be valid and comparable across all spectral resolutions from low (R<100) to high resolutions (R>10,000), and account for the spectral correlation of the residual starlight (i.e., speckle noise chromaticity). Leveraging the concept of “template matching,” we develop a simulation toolkit based on the Python package EXOSIMS to compute the detection significance of planets and molecules. We then simulate observations of Earth analogs around 164 stars using representative mission parameters to explore the effects of the detector noise and the correlated speckle noise floor. Our findings suggest that a moderate- or high-resolution spectrograph (R>1000) will provide higher sensitivity to critical molecules compared with a low-resolution spectroscopy mode (e.g., R∼140). The correlated speckle noise may also entirely suppress our ability to detect biosignatures at low spectral resolutions. We conclude that a more comprehensive study, combined with detailed models of its stability and other sources of correlated noise, is necessary to fully explore the trade space of spectral resolution and detectability of key species.
\nThe factors that enable life to begin define the difference between an inhabited planet and one that is simply habitable. While used extensively in Origins, Worlds, and Life: A Decadal Strategy for Planetary Science and Astrobiology 2023–2032 (abbreviated \"OWL\" in this paper), the term origin of life is never mentioned in Pathways to Discovery in Astronomy and Astrophysics for the 2020s (notated as \"Astro2020\" in this paper). While the chapters on the search for life in the solar system in OWL treat the origin of life as a central concept, the exoplanet focused chapters of the OWL and Astro2020 reports mostly do not mention origin of life science, particularly with respect to how it intersects with biosignature identification and interpretation. To begin to fill this gap, we describe the set of conditions that are required for life to begin and suggest that they may be distinct from those that make an environment habitable. Finally, we present a putative list of origin of life processes that may be observable on exoplanets and outline the relevance of future planetary science and astrophysics missions to this topic. Given the complexity of detecting these conditions beyond the solar system, we argue that while looking for signs of the origin of life on exoplanets could be fruitful in determining which are worthy of further study, the concept is likely more appropriate for distinguishing true biosignatures from false positives. Ensuring that future facilities like the Large Interferometer For Exoplanets (LIFE) and the Habitable Worlds Observatory (HWO) can constrain origin of life conditions is necessary for life detection searches beyond the solar system.
", "doi": "10.3389/fspas.2025.1544426", "issn": "2296-987X", "publisher": "Frontiers Media SA", "publication": "Frontiers in Astronomy and Space Sciences", "publication_date": "2025-03-19", "volume": "12", "pages": "fspas.2025.1544426" }, { "id": "authors:wfhhj-5wb72", "collection": "authors", "collection_id": "wfhhj-5wb72", "cite_using_url": "https://authors.library.caltech.edu/records/wfhhj-5wb72", "type": "article", "title": "Short-term variation in Mars atmospheric methane concentrations driven by barometric pumping", "author": [ { "family_name": "Klusman", "given_name": "Ronald W." }, { "family_name": "Luo", "given_name": "Yangcheng", "orcid": "0000-0003-0983-3650", "clpid": "Luo-Yangcheng" }, { "family_name": "Chen", "given_name": "Pin", "orcid": "0000-0003-1195-9666", "clpid": "Chen-Pin" }, { "family_name": "Mischna", "given_name": "Michael A.", "orcid": "0000-0002-8022-5319", "clpid": "Mischna-Michael-A" }, { "family_name": "Yung", "given_name": "Yuk L.", "orcid": "0000-0002-4263-2562", "clpid": "Yung-Y-L" } ], "abstract": "Measurements of atmospheric methane by the Curiosity rover's SAM-TLS instrument are providing evidence of seasonality and diurnal variation in concentration. Given methane's short atmospheric lifetime relative to geological timescales, its presence implies a replenishing source, and the observed variation demands the proposition of a modulation mechanism. This paper focuses on the modulation mechanism on a diurnal scale, extending earlier modeling of seasonal variation. Our modeling shows that barometric pumping driven by both diurnal and seasonal variation of atmospheric pressure, along with possible adsorption and desorption of methane in the shallow subsurface driven by temperature and pressure change, can explain the variation in methane concentration. In the model, an active, continuous, steady-state deep source of methane is assumed, and carbon dioxide serves as the carrier gas for drawing methane and possible trace gaseous constituents into the atmosphere.
", "doi": "10.1016/j.icarus.2023.115810", "issn": "0019-1035", "publisher": "Elsevier", "publication": "Icarus", "publication_date": "2024-01-15", "volume": "408", "pages": "115810" }, { "id": "authors:z2vb2-6jv57", "collection": "authors", "collection_id": "z2vb2-6jv57", "cite_using_url": "https://resolver.caltech.edu/CaltechAUTHORS:20221220-736506000.3", "type": "article", "title": "Spectropolarimetry as a Means to Address Cloud Composition and Habitability for a Cloudy Exoplanetary Atmosphere in the Habitable Zone", "author": [ { "family_name": "West", "given_name": "Robert A.", "orcid": "0000-0002-4320-2599", "clpid": "West-Robert-A" }, { "family_name": "Dumont", "given_name": "Philip", "clpid": "Dumont-Philip" }, { "family_name": "Hu", "given_name": "Renyu", "orcid": "0000-0003-2215-8485", "clpid": "Hu-Renyu" }, { "family_name": "Natraj", "given_name": "Vijay", "orcid": "0000-0003-3154-9429", "clpid": "Natraj-Vijay" }, { "family_name": "Breckinridge", "given_name": "James B.", "orcid": "0000-0002-9488-098X", "clpid": "Breckinridge-James-B" }, { "family_name": "Chen", "given_name": "Pin", "clpid": "Chen-Pin" } ], "abstract": "In our solar system, the densely cloud-covered atmosphere of Venus stands out as an example of how polarimetry can be used to gain information on cloud composition and particle mean radius. With current interest running high on discovering and characterizing extrasolar planets in the habitable zone where water exists in the liquid state, making use of spectropolarimetric measurements of directly imaged exoplanets could provide key information unobtainable through other means. In principle, spectropolarimetric measurements can determine if acidity causes water activities in the clouds to be too low for life. To this end, we show that a spectropolarimeter measurement over the range 400\u20131000 nm would need to resolve linear polarization to a precision of about 1% or better for reflected starlight from an optically thick cloud-enshrouded exoplanet. We assess the likelihood of achieving this goal by simulating measurements from a notional spectropolarimeter as part of a starshade configuration for a large space telescope (a HabEx design, but for a 6 m diameter primary mirror). Our simulations include consideration of noise from a variety of sources. We provide guidance on limits that would need to be levied on instrumental polarization to address the science issues we discuss. For photon-limited noise, integration times would need to be of order 1 hr for a large radius (10 Earth radii) planet to more than 100 hr for smaller exoplanets depending on the star\u2013planet separation, planet radius, phase angle, and desired uncertainty. We discuss implications for surface chemistry and habitability.", "doi": "10.3847/1538-4357/ac9b42", "issn": "0004-637X", "publisher": "American Astronomical Society", "publication": "Astrophysical Journal", "publication_date": "2022-12-01", "series_number": "2", "volume": "940", "issue": "2", "pages": "Art. No. 183" }, { "id": "authors:y99cf-fkr11", "collection": "authors", "collection_id": "y99cf-fkr11", "cite_using_url": "https://authors.library.caltech.edu/records/y99cf-fkr11", "type": "article", "title": "Seasonality in Mars atmospheric methane driven by microseepage, barometric pumping, and adsorption", "author": [ { "family_name": "Klusman", "given_name": "Ronald W." }, { "family_name": "Luo", "given_name": "Yangcheng", "orcid": "0000-0003-0983-3650", "clpid": "Luo-Yangcheng" }, { "family_name": "Chen", "given_name": "Pin", "orcid": "0000-0003-1195-9666", "clpid": "Chen-Pin" }, { "family_name": "Yung", "given_name": "Yuk L.", "orcid": "0000-0002-4263-2562", "clpid": "Yung-Y-L" }, { "family_name": "Tallapragada", "given_name": "Sindhoora", "clpid": "Tallapragada-Sindhoora" } ], "abstract": "Measurements of atmospheric methane by the Curiosity rover's SAM-TLS instrument are providing evidence of seasonality with bimodal peaks in concentration. Given methane's short atmospheric lifetime relative to geological timescales, its presence implies a replenishing source, and the observed seasonality demands the proposition of a modulation mechanism. This paper focuses on the modulation mechanism. Our modeling study shows that barometric pumping driven by seasonal variation of atmospheric pressure, along with adsorption and desorption of methane in the shallow subsurface driven by temperature change, can explain the observed bimodal peaks in the seasonal variations of methane concentration. In the model, an active, continuous, steady-state deep source of methane is assumed, and carbon dioxide serves as the carrier gas for producing seasonal variation in the upper part of the sedimentary column for methane and other possible trace gaseous constituents. Our work also presents a comprehensive flow chart for modeling the microseepage of methane on Mars from first principles.", "doi": "10.1016/j.icarus.2022.115079", "issn": "0019-1035", "publisher": "Elsevier", "publication": "Icarus", "publication_date": "2022-09-01", "volume": "383", "pages": "115079" }, { "id": "authors:3r7k7-y3x36", "collection": "authors", "collection_id": "3r7k7-y3x36", "cite_using_url": "https://resolver.caltech.edu/CaltechAUTHORS:20201117-100810486", "type": "article", "title": "Wavefront sensing and control in space-based coronagraph instruments using Zernike's phase-contrast method", "author": [ { "family_name": "Ruane", "given_name": "Garreth", "orcid": "0000-0003-4769-1665", "clpid": "Ruane-G-J" }, { "family_name": "Wallace", "given_name": "J. Kent", "orcid": "0000-0001-5299-6899", "clpid": "Wallace-J-K" }, { "family_name": "Steeves", "given_name": "John", "orcid": "0000-0002-2949-9314", "clpid": "Steeves-J-B" }, { "family_name": "Prada", "given_name": "Camilo Mejia", "clpid": "Prada-C-M" }, { "family_name": "Seo", "given_name": "Byoung-Joon", "clpid": "Seo-Byoung-Joon" }, { "family_name": "Bendek", "given_name": "Eduardo", "orcid": "0000-0002-9408-8925", "clpid": "Bendek-E-A" }, { "family_name": "Coker", "given_name": "Carl", "orcid": "0000-0002-9954-7887", "clpid": "Coker-C-T" }, { "family_name": "Chen", "given_name": "Pin", "clpid": "Chen-Pin" }, { "family_name": "Crill", "given_name": "Brendan", "orcid": "0000-0002-4650-8518", "clpid": "Crill-B-P" }, { "family_name": "Jewell", "given_name": "Jeff", "clpid": "Jewell-Jeffrey-B" }, { "family_name": "Kern", "given_name": "Brian", "clpid": "Kern-B-D" }, { "family_name": "Marx", "given_name": "David", "clpid": "Marx-D-S" }, { "family_name": "Poon", "given_name": "Phillip K.", "clpid": "Poon-Phillip-K" }, { "family_name": "Redding", "given_name": "David", "clpid": "Redding-D-C" }, { "family_name": "Riggs", "given_name": "A. J. Eldorado", "orcid": "0000-0002-0863-6228", "clpid": "Riggs-A-J-E" }, { "family_name": "Siegler", "given_name": "Nicholas", "clpid": "Siegler-N" }, { "family_name": "Zimmer", "given_name": "Robert", "clpid": "Zimmer-R-J" } ], "abstract": "Future space telescopes with coronagraph instruments will use a wavefront sensor (WFS) to measure and correct for phase errors and stabilize the stellar intensity in high-contrast images. The HabEx and LUVOIR mission concepts baseline a Zernike wavefront sensor (ZWFS), which uses Zernike's phase contrast method to convert phase in the pupil into intensity at the WFS detector. In preparation for these potential future missions, we experimentally demonstrate a ZWFS in a coronagraph instrument on the Decadal Survey Testbed in the High Contrast Imaging Testbed facility at NASA's Jet Propulsion Laboratory. We validate that the ZWFS can measure low- and mid-spatial frequency aberrations up to the control limit of the deformable mirror (DM), with surface height sensitivity as small as 1 pm, using a configuration similar to the HabEx and LUVOIR concepts. Furthermore, we demonstrate closed-loop control, resolving an individual DM actuator, with residuals consistent with theoretical models. In addition, we predict the expected performance of a ZWFS on future space telescopes using natural starlight from a variety of spectral types. The most challenging scenarios require \u223c1\u2009\u2009h of integration time to achieve picometer sensitivity. This timescale may be drastically reduced by using internal or external laser sources for sensing purposes. The experimental results and theoretical predictions presented here advance the WFS technology in the context of the next generation of space telescopes with coronagraph instruments.", "doi": "10.1117/1.jatis.6.4.045005", "issn": "2329-4124", "publisher": "Society of Photo-optical Instrumentation Engineers (SPIE)", "publication": "Journal of Astronomical Telescopes, Instruments, and Systems", "publication_date": "2020-11-09", "series_number": "4", "volume": "6", "issue": "4", "pages": "Art. No. 045005" }, { "id": "authors:h06h5-9k287", "collection": "authors", "collection_id": "h06h5-9k287", "cite_using_url": "https://resolver.caltech.edu/CaltechAUTHORS:20190304-082306585", "type": "article", "title": "Vector vortex coronagraphy for exoplanet detection with spatially variant diffractive waveplates", "author": [ { "family_name": "Serabyn", "given_name": "Eugene", "clpid": "Serabyn-E" }, { "family_name": "Mejia Prada", "given_name": "Camilo", "clpid": "Mejia-Prada-C" }, { "family_name": "Chen", "given_name": "Pin", "clpid": "Chen-Pin" }, { "family_name": "Mawet", "given_name": "Dimitri", "orcid": "0000-0002-8895-4735", "clpid": "Mawet-D" } ], "abstract": "Optical vortex coronagraphs have recently been deployed on most of the world's largest ground-based telescopes to assist in the search for faint exoplanets and dust emission near stars. These instruments typically make use of vector vortex phase masks, and at short near-infrared wavelengths, the phase masks tend to be spatially variant liquid-crystal-polymer-based diffractive waveplates. Optical vortex coronagraphs also hold great promise as a potential means of imaging terrestrial exoplanets in nearby solar systems with space-based telescopes, for which nearly ideal vortex phase masks will be needed. Here, we briefly summarize the optical vortex coronagraph, foreseen performance requirements for terrestrial exoplanet imaging detection, the obstacles to nearly ideal diffractive-waveplate-based vortex phase masks, and recent broadband performance demonstrations.", "doi": "10.1364/josab.36.000d13", "issn": "0740-3224", "publisher": "Optical Society of America", "publication": "Journal of the Optical Society of America B", "publication_date": "2019-05-01", "series_number": "5", "volume": "36", "issue": "5", "pages": "D13-D19" }, { "id": "authors:6d6dk-78554", "collection": "authors", "collection_id": "6d6dk-78554", "cite_using_url": "https://resolver.caltech.edu/CaltechAUTHORS:20180925-073151228", "type": "article", "title": "Methane on Mars and Habitability: Challenges and Responses", "author": [ { "family_name": "Yung", "given_name": "Yuk L.", "orcid": "0000-0002-4263-2562", "clpid": "Yung-Y-L" }, { "family_name": "Chen", "given_name": "Pin", "clpid": "Chen-Pin" }, { "family_name": "Nealson", "given_name": "Kenneth", "orcid": "0000-0001-5189-3732", "clpid": "Nealson-K-H" }, { "family_name": "Atreya", "given_name": "Sushil", "orcid": "0000-0002-1972-1815", "clpid": "Atreya-S-K" }, { "family_name": "Beckett", "given_name": "Patrick", "clpid": "Beckett-P" }, { "family_name": "Blank", "given_name": "Jennifer G.", "clpid": "Blank-J-G" }, { "family_name": "Ehlmann", "given_name": "Bethany", "orcid": "0000-0002-2745-3240", "clpid": "Ehlmann-B-L" }, { "family_name": "Eiler", "given_name": "John", "clpid": "Eiler-J-M" }, { "family_name": "Etiope", "given_name": "Giuseppe", "clpid": "Etiope-G" }, { "family_name": "Ferry", "given_name": "James G.", "clpid": "Ferry-J-G" }, { "family_name": "Forget", "given_name": "Fran\u00e7ois", "clpid": "Forget-F" }, { "family_name": "Gao", "given_name": "Peter", "orcid": "0000-0002-8518-9601", "clpid": "Gao-Peter" }, { "family_name": "Hu", "given_name": "Renyu", "orcid": "0000-0003-2215-8485", "clpid": "Hu-Renyu" }, { "family_name": "Kleinb\u00f6hl", "given_name": "Armin", "clpid": "Kleinb\u00f6hl-A" }, { "family_name": "Klusman", "given_name": "Ronald", "clpid": "Klusman-" }, { "family_name": "Lef\u00e8vre", "given_name": "Franck", "clpid": "Lef\u00e8vre-F" }, { "family_name": "Miller", "given_name": "Charles", "orcid": "0000-0002-9380-4838", "clpid": "Miller-C-E" }, { "family_name": "Mischna", "given_name": "Michael", "orcid": "0000-0002-8022-5319", "clpid": "Mischna-M-A" }, { "family_name": "Mumma", "given_name": "Michael", "clpid": "Mumma-M-J" }, { "family_name": "Newman", "given_name": "Sally", "orcid": "0000-0003-0710-995X", "clpid": "Newman-S" }, { "family_name": "Oehler", "given_name": "Dorothy", "clpid": "Oehler-D-Z" }, { "family_name": "Okumura", "given_name": "Mitchio", "orcid": "0000-0001-6874-1137", "clpid": "Okumura-M" }, { "family_name": "Oremland", "given_name": "Ronald", "clpid": "Oremland-R-S" }, { "family_name": "Orphan", "given_name": "Victoria", "orcid": "0000-0002-5374-6178", "clpid": "Orphan-V-J" }, { "family_name": "Popa", "given_name": "Radu", "clpid": "Popa-R" }, { "family_name": "Russell", "given_name": "Michael", "clpid": "Russell-M-J" }, { "family_name": "Shen", "given_name": "Linhan", "orcid": "0000-0003-3871-655X", "clpid": "Shen-Linhan" }, { "family_name": "Sherwood Lollar", "given_name": "Barbara", "clpid": "Sherwood-Lollar-B" }, { "family_name": "Staehle", "given_name": "Robert", "clpid": "Staehle-R-L" }, { "family_name": "Stamenkovi\u0107", "given_name": "Vlada", "orcid": "0000-0003-2416-3683", "clpid": "Stamenkovi\u0107-V" }, { "family_name": "Stolper", "given_name": "Daniel", "orcid": "0000-0003-3299-3177", "clpid": "Stolper-D-A" }, { "family_name": "Templeton", "given_name": "Alexis", "clpid": "Templeton-A" }, { "family_name": "Vandaele", "given_name": "Ann C.", "clpid": "Vandaele-A-C" }, { "family_name": "Viscardy", "given_name": "S\u00e9bastien", "clpid": "Viscardy-S" }, { "family_name": "Webster", "given_name": "Christopher R.", "clpid": "Webster-C-R" }, { "family_name": "Wennberg", "given_name": "Paul O.", "orcid": "0000-0002-6126-3854", "clpid": "Wennberg-P-O" }, { "family_name": "Wong", "given_name": "Michael L.", "clpid": "Wong-Michael-L" }, { "family_name": "Worden", "given_name": "John", "orcid": "0000-0003-0257-9549", "clpid": "Worden-J-R" } ], "abstract": "Recent measurements of methane (CH_4) by the Mars Science Laboratory (MSL) now confront us with robust data that demand interpretation. Thus far, the MSL data have revealed a baseline level of CH_4 (\u223c0.4 parts per billion by volume [ppbv]), with seasonal variations, as well as greatly enhanced spikes of CH_4 with peak abundances of \u223c7\u2009ppbv. What do these CH_4 revelations with drastically different abundances and temporal signatures represent in terms of interior geochemical processes, or is martian CH_4 a biosignature? Discerning how CH_4 generation occurs on Mars may shed light on the potential habitability of Mars. There is no evidence of life on the surface of Mars today, but microbes might reside beneath the surface. In this case, the carbon flux represented by CH_4 would serve as a link between a putative subterranean biosphere on Mars and what we can measure above the surface. Alternatively, CH_4 records modern geochemical activity. Here we ask the fundamental question: how active is Mars, geochemically and/or biologically? In this article, we examine geological, geochemical, and biogeochemical processes related to our overarching question. The martian atmosphere and surface are an overwhelmingly oxidizing environment, and life requires pairing of electron donors and electron acceptors, that is, redox gradients, as an essential source of energy. Therefore, a fundamental and critical question regarding the possibility of life on Mars is, \"Where can we find redox gradients as energy sources for life on Mars?\" Hence, regardless of the pathway that generates CH_4 on Mars, the presence of CH_4, a reduced species in an oxidant-rich environment, suggests the possibility of redox gradients supporting life and habitability on Mars. Recent missions such as ExoMars Trace Gas Orbiter may provide mapping of the global distribution of CH_4. To discriminate between abiotic and biotic sources of CH_4 on Mars, future studies should use a series of diagnostic geochemical analyses, preferably performed below the ground or at the ground/atmosphere interface, including measurements of CH_4 isotopes, methane/ethane ratios, H_2 gas concentration, and species such as acetic acid. Advances in the fields of Mars exploration and instrumentation will be driven, augmented, and supported by an improved understanding of atmospheric chemistry and dynamics, deep subsurface biogeochemistry, astrobiology, planetary geology, and geophysics. Future Mars exploration programs will have to expand the integration of complementary areas of expertise to generate synergistic and innovative ideas to realize breakthroughs in advancing our understanding of the potential of life and habitable conditions having existed on Mars. In this spirit, we conducted a set of interdisciplinary workshops. From this series has emerged a vision of technological, theoretical, and methodological innovations to explore the martian subsurface and to enhance spatial tracking of key volatiles, such as CH_4.", "doi": "10.1089/ast.2018.1917", "pmcid": "PMC6205098", "issn": "1557-8070", "publisher": "Mary Ann Liebert", "publication": "Astrobiology", "publication_date": "2018-10", "series_number": "10", "volume": "18", "issue": "10", "pages": "1221-1242" }, { "id": "authors:9d0e8-4f789", "collection": "authors", "collection_id": "9d0e8-4f789", "cite_using_url": "https://resolver.caltech.edu/CaltechAUTHORS:20120503-150855437", "type": "article", "title": "Information Content of Exoplanetary Transit Spectra: An Initial Look", "author": [ { "family_name": "Line", "given_name": "Michael R.", "orcid": "0000-0002-2338-476X", "clpid": "Line-M-R" }, { "family_name": "Zhang", "given_name": "Xi", "clpid": "Zhang-Xi" }, { "family_name": "Vasisht", "given_name": "Gautam", "orcid": "0000-0002-1871-6264", "clpid": "Vasisht-G" }, { "family_name": "Natraj", "given_name": "Vijay", "orcid": "0000-0003-3154-9429", "clpid": "Natraj-V" }, { "family_name": "Chen", "given_name": "Pin", "clpid": "Chen-Pin" }, { "family_name": "Yung", "given_name": "Yuk L.", "orcid": "0000-0002-4263-2562", "clpid": "Yung-Y-L" } ], "abstract": "It has been shown that spectroscopy of transiting extrasolar planets can potentially provide a wealth of information about their atmospheres. Herein, we set up the inverse problem in spectroscopic retrieval. We use nonlinear optimal estimation to retrieve the atmospheric state (pioneered for Earth sounding by Rodgers). The formulation quantifies the degrees of freedom and information content of the spectrum with respect to geophysical parameters; herein, we focus specifically on temperature and composition. First, we apply the technique to synthetic near-infrared spectra and explore the influence of spectral signal-to-noise ratio and resolution (the two important parameters when designing a future instrument) on the information content of the data. As expected, we find that the number of retrievable parameters increases with increasing signal-to-noise ratio and resolution, although the gains quickly level off for large values. Second, we apply the methods to the previously studied dayside near-infrared emission spectrum of HD 189733b and compare the results of our retrieval with those obtained by others.", "doi": "10.1088/0004-637X/749/1/93", "issn": "0004-637X", "publisher": "American Astronomical Society", "publication": "Astrophysical Journal", "publication_date": "2012-04-10", "series_number": "1", "volume": "749", "issue": "1", "pages": "93" }, { "id": "authors:swedk-ndz07", "collection": "authors", "collection_id": "swedk-ndz07", "cite_using_url": "https://resolver.caltech.edu/CaltechAUTHORS:20140822-083020182", "type": "article", "title": "Thermochemical and Photochemical Kinetics in Cooler Hydrogen-dominated Extrasolar Planets: A Methane-poor GJ436b?", "author": [ { "family_name": "Line", "given_name": "Michael R.", "orcid": "0000-0002-2338-476X", "clpid": "Line-M-R" }, { "family_name": "Vasisht", "given_name": "Gautam", "orcid": "0000-0002-1871-6264", "clpid": "Vasisht-G" }, { "family_name": "Chen", "given_name": "Pin", "clpid": "Chen-Pin" }, { "family_name": "Angerhausen", "given_name": "D.", "clpid": "Angerhausen-D" }, { "family_name": "Yung", "given_name": "Yuk L.", "orcid": "0000-0002-4263-2562", "clpid": "Yung-Y-L" } ], "abstract": "We introduce a thermochemical kinetics and photochemical model. We use high-temperature bidirectional reaction rates for important H, C, O, and N reactions (most importantly for CH_4 to CO interconversion), allowing us to attain thermochemical equilibrium, deep in an atmosphere, purely kinetically. This allows the chemical modeling of an entire atmosphere, from deep-atmosphere thermochemical equilibrium to the photochemically dominated regime. We use our model to explore the atmospheric chemistry of cooler (T_(eff) < 10^3 K) extrasolar giant planets. In particular, we choose to model the nearby hot-Neptune GJ436b, the only planet in this temperature regime for which spectroscopic measurements and estimates of chemical abundances now exist. Recent Spitzer measurements with retrieval have shown that methane is driven strongly out of equilibrium and is deeply depleted on the day side of GJ436b, whereas quenched carbon monoxide is abundant. This is surprising because GJ436b is cooler than many of the heavily irradiated hot Jovians and thermally favorable for CH_4, and thus requires an efficient mechanism for destroying it. We include realistic estimates of ultraviolet flux from the parent dM star GJ436, to bound the direct photolysis and photosensitized depletion of CH_4. While our models indicate fairly rich disequilibrium conditions are likely in cooler exoplanets over a range of planetary metallicities, we are unable to generate the conditions for substantial CH_4 destruction. One possibility is an anomalous source of abundant H atoms between 0.01 and 1 bars (which attack CH_4), but we cannot as yet identify an efficient means to produce these hot atoms.", "doi": "10.1088/0004-637X/738/1/32", "issn": "0004-637X", "publisher": "American Astronomical Society", "publication": "Astrophysical Journal", "publication_date": "2011-09-01", "series_number": "1", "volume": "738", "issue": "1", "pages": "Art. No. 32" }, { "id": "authors:0a1rv-jc534", "collection": "authors", "collection_id": "0a1rv-jc534", "cite_using_url": "https://resolver.caltech.edu/CaltechAUTHORS:20091021-113138246", "type": "article", "title": "Water, Methane, and Carbon Dioxide Present in the Dayside Spectrum of the Exoplanet HD 209458b", "author": [ { "family_name": "Swain", "given_name": "M. R.", "orcid": "0000-0002-0919-4468", "clpid": "Swain-M-R" }, { "family_name": "Tinetti", "given_name": "G.", "clpid": "Tinetti-G" }, { "family_name": "Vasisht", "given_name": "G.", "orcid": "0000-0002-1871-6264", "clpid": "Vasisht-G" }, { "family_name": "Deroo", "given_name": "P.", "clpid": "Deroo-P" }, { "family_name": "Griffith", "given_name": "C.", "clpid": "Griffith-C" }, { "family_name": "Bouwman", "given_name": "J.", "clpid": "Bouwman-J" }, { "family_name": "Chen", "given_name": "Pin", "clpid": "Chen-Pin" }, { "family_name": "Yung", "given_name": "Y.", "orcid": "0000-0002-4263-2562", "clpid": "Yung-Y-L" }, { "family_name": "Burrows", "given_name": "A. S.", "orcid": "0000-0002-3099-5024", "clpid": "Burrows-A-S" }, { "family_name": "Brown", "given_name": "L. R.", "clpid": "Brown-L-R" }, { "family_name": "Matthews", "given_name": "J.", "clpid": "Matthews-J" }, { "family_name": "Rowe", "given_name": "J. F.", "orcid": "0000-0002-5904-1865", "clpid": "Rowe-J-F" }, { "family_name": "Kuschnig", "given_name": "R.", "clpid": "Kuschnig-R" }, { "family_name": "Angerhausen", "given_name": "D.", "clpid": "Angerhausen-D" } ], "abstract": "Using the NICMOS instrument on the Hubble Space Telescope, we have measured the dayside spectrum of HD 209458b between 1.5 and 2.5 \u03bcm. The emergent spectrum is dominated by features due to the presence of methane (CH_4) and water vapor (H_2O), with smaller contributions from carbon dioxide (CO_2). Combining this near-infrared spectrum with existing mid-infrared measurements shows the existence of a temperature inversion and confirms the interpretation of previous photometry measurements. We find a family of plausible solutions for the molecular abundance and detailed temperature profile. Observationally resolving the ambiguity between abundance and temperature requires either (1) improved wavelength coverage or spectral resolution of the dayside emission spectrum or (2) a transmission spectrum where abundance determinations are less sensitive to the temperature structure.", "doi": "10.1088/0004-637X/704/2/1616", "issn": "0004-637X", "publisher": "American Astronomical Society", "publication": "Astrophysical Journal", "publication_date": "2009-10-20", "series_number": "2", "volume": "704", "issue": "2", "pages": "1616-1621" }, { "id": "authors:sramy-3he35", "collection": "authors", "collection_id": "sramy-3he35", "cite_using_url": "https://resolver.caltech.edu/CaltechAUTHORS:SWAapjl09", "type": "article", "title": "Molecular Signatures in the Near-Infrared Dayside Spectrum of HD 189733b", "author": [ { "family_name": "Swain", "given_name": "M. R.", "orcid": "0000-0002-0919-4468", "clpid": "Swain-M-R" }, { "family_name": "Vasisht", "given_name": "G.", "orcid": "0000-0002-1871-6264", "clpid": "Vasisht-G" }, { "family_name": "Tinetti", "given_name": "G.", "clpid": "Tinetti-G" }, { "family_name": "Bouwman", "given_name": "J.", "clpid": "Bouwman-J" }, { "family_name": "Chen", "given_name": "Pin", "clpid": "Chen-Pin" }, { "family_name": "Yung", "given_name": "Y.", "orcid": "0000-0002-4263-2562", "clpid": "Yung-Y-L" }, { "family_name": "Deming", "given_name": "D.", "orcid": "0000-0001-5727-4094", "clpid": "Deming-D" }, { "family_name": "Deroo", "given_name": "P.", "clpid": "Deroo-P" } ], "abstract": "We have measured the dayside spectrum of HD 189733b between 1.5 and 2.5 \u03bcm using the NICMOS instrument on the Hubble Space Telescope. The emergent spectrum contains significant modulation, which we attribute to the presence of molecular bands seen in absorption. We find that water (H2O), carbon monoxide (CO), and carbon dioxide (CO2) are needed to explain the observations, and we are able to estimate the mixing ratios for these molecules. We also find temperature decreases with altitude in the ~0.01 < P< ~1 bar region of the dayside near-infrared photosphere and set an upper limit to the dayside abundance of methane (CH4) at these pressures.", "doi": "10.1088/0004-637X/690/2/L114", "issn": "2041-8205", "publisher": "American Astronomical Society", "publication": "Astrophysical Journal Letters", "publication_date": "2009-01-10", "series_number": "2", "volume": "690", "issue": "2", "pages": "L114-L117" }, { "id": "authors:2k7g2-gz531", "collection": "authors", "collection_id": "2k7g2-gz531", "cite_using_url": "https://resolver.caltech.edu/CaltechAUTHORS:20120914-103111591", "type": "article", "title": "Submillimeter-Wave Measurements and Analysis of the Ground and \u03bd2 = 1 States of Water", "author": [ { "family_name": "Chen", "given_name": "Pin", "clpid": "Chen-Pin" }, { "family_name": "Pearson", "given_name": "J. C.", "clpid": "Pearson-J-C" }, { "family_name": "Pickett", "given_name": "Herbert M.", "clpid": "Pickett-H-M" }, { "family_name": "Matsuura", "given_name": "Shuji", "orcid": "0000-0002-5698-9634", "clpid": "Matsuura-Shuji" }, { "family_name": "Blake", "given_name": "Geoffrey A.", "orcid": "0000-0003-0787-1610", "clpid": "Blake-G-A" } ], "abstract": "In order to facilitate further studies of water in the interstellar medium, the envelopes of late-type stars, jets, and shocked regions, the frequencies of 17 newly measured H_2 ^(16)O transitions between 0.841 and 1.575 THz are reported. A complete update of the available water line frequencies and a detailed calculation of unmeasured rotational transitions and transition intensities as a function of temperature are presented for the ground and \u03bd_2 = 1 state levels below 3000 cm^(-1) of excitation energy. The new terahertz transitions were measured with a recently developed laser difference frequency spectrometer. Six of these transitions arise from the \u03bd_2 = 1 state, and the other 11 are in the ground state; all have lower state energies from 700 to 1750 cm^(-1) and should be accessible to Stratospheric Observatory For Infrared Astronomy (SOFIA) through the atmosphere. The transitions near 0.850 THz are accessible from the ground with existing receivers. Observations of the newly measured \u03bd_2 = 1 state transitions, which include the 1_(1, 1)-0_(0, 0) fundamental at 1.2057 THz and five other very low J transitions, should provide valuable insights into role played by the \u03bd2 = 1 state in the cooling dynamics of jets, shocks, masers, and strongly infrared-pumped regions. The line list is presented to assist in the planning of observational campaigns with the Far-Infrared Space Telescope (FIRST) and other proposed space missions with which a full suite of water observations can be carried out.", "doi": "10.1086/313377", "issn": "0067-0049", "publisher": "American Astronomical Society", "publication": "Astrophysical Journal Supplement Series", "publication_date": "2000-05", "series_number": "1", "volume": "128", "issue": "1", "pages": "371-385" }, { "id": "authors:y09ty-0hy87", "collection": "authors", "collection_id": "y09ty-0hy87", "cite_using_url": "https://resolver.caltech.edu/CaltechAUTHORS:20120913-144928826", "type": "article", "title": "A tunable cavity-locked diode laser source for terahertz photomixing", "author": [ { "family_name": "Matsuura", "given_name": "Shuji", "orcid": "0000-0002-5698-9634", "clpid": "Matsuura-Shuji" }, { "family_name": "Chen", "given_name": "Pin", "clpid": "Chen-Pin" }, { "family_name": "Blake", "given_name": "Geoffrey A.", "orcid": "0000-0003-0787-1610", "clpid": "Blake-G-A" }, { "family_name": "Pearson", "given_name": "John C.", "clpid": "Pearson-J-C" }, { "family_name": "Pickett", "given_name": "Herbert M.", "clpid": "Pickett-H-M" } ], "abstract": "An all solid-state approach to the precise frequency synthesis and control of widely tunable terahertz radiation by differencing continuous-wave diode lasers at 850 nm is reported in this paper. The difference frequency is synthesized by three fiber-coupled external-cavity laser diodes. Two of the lasers are Pound-Drever-Hall locked to different orders of a Fabry-Perot (FP) cavity, and the third is offset-frequency locked to the second of the cavity-locked lasers using a tunable microwave oscillator. The first cavity-locked laser and the offset-locked laser produce the difference frequency, whose value is accurately determined by the sum of an integer multiple of the free spectral range of the FP cavity and the offset frequency. The dual-frequency 850-nm output of the three laser system is amplified to 500 mW through two-frequency injection seeding of a single semiconductor tapered optical amplifier. As proof of precision frequency synthesis and control of tunability, the difference frequency is converted into a terahertz wave by optical-heterodyne photomixing in low-temperature-grown GaAs and used for the spectroscopy of simple molecules. The 3-dB spectral power bandwidth of the terahertz radiation is routinely observed to be \u227e1 MHz. A simple, but highly accurate, method of obtaining an absolute frequency calibration is proposed and an absolute calibration of 10^(-7) demonstrated using the known frequencies of carbon monoxide lines between 0.23-1.27 THz.", "doi": "10.1109/22.826836", "issn": "0018-9480", "publisher": "IEEE", "publication": "IEEE Transactions on Microwave Theory and Techniques", "publication_date": "2000-03", "series_number": "3", "volume": "48", "issue": "3", "pages": "380-387" }, { "id": "authors:np11r-ge035", "collection": "authors", "collection_id": "np11r-ge035", "cite_using_url": "https://resolver.caltech.edu/CaltechAUTHORS:20120919-094928326", "type": "article", "title": "Simultaneous Amplification of Terahertz Difference Frequencies by an Injection-Seeded Semiconductor Laser Amplifier at 850 nm", "author": [ { "family_name": "Matsuura", "given_name": "Shuji", "orcid": "0000-0002-5698-9634", "clpid": "Matsuura-Shuji" }, { "family_name": "Chen", "given_name": "Pin", "clpid": "Chen-Pin" }, { "family_name": "Blake", "given_name": "Geoffrey A.", "orcid": "0000-0003-0787-1610", "clpid": "Blake-G-A" }, { "family_name": "Pearson", "given_name": "J. C.", "clpid": "Pearson-J-C" }, { "family_name": "Pickett", "given_name": "Herbert M.", "clpid": "Pickett-H-M" } ], "abstract": "Two-frequency operation of an 850 nm semiconductor optical amplifier was achieved by simultaneously injection seeding it with two diode lasers. The two frequencies could be independently amplified without strong interference when they were separated by more than 10 GHz, and the spectral purity was preserved by the amplification process. At frequency differences below 10 GHz, unbalanced two-frequency output was observed, which can be explained by a two-mode interaction driven by the refractive index modulation at the beat frequency. The laser system is\nsuitable for the difference-frequency generation of coherent terahertz radiation in ultra-fast photoconductors or nonlinear optical media.", "doi": "10.1023/A:1022676407601", "issn": "0195-9271", "publisher": "Plenum Publishing Corporation", "publication": "International Journal of Infrared and Millimeter Waves", "publication_date": "1998-06", "series_number": "6", "volume": "19", "issue": "6", "pages": "849-858" }, { "id": "authors:jky49-r5857", "collection": "authors", "collection_id": "jky49-r5857", "cite_using_url": "https://resolver.caltech.edu/CaltechAUTHORS:CHEapl97", "type": "article", "title": "Spectroscopic applications and frequency locking of THz photomixing with distributed-Bragg-reflector diode lasers in low-temperature-grown GaAs", "author": [ { "family_name": "Chen", "given_name": "Pin", "clpid": "Chen-Pin" }, { "family_name": "Blake", "given_name": "Geoffrey A.", "orcid": "0000-0003-0787-1610", "clpid": "Blake-G-A" }, { "family_name": "Gaidas", "given_name": "M. C.", "clpid": "Gaidis-M-C" }, { "family_name": "Brown", "given_name": "E. R.", "clpid": "Brown-E-R" }, { "family_name": "McIntosh", "given_name": "K. A.", "clpid": "McIntosh-K-A" }, { "family_name": "Chou", "given_name": "S. Y.", "clpid": "Chou-S-Y" }, { "family_name": "Nathan", "given_name": "M. I.", "clpid": "Nathan-M-I" }, { "family_name": "Williamson", "given_name": "F.", "clpid": "Williamson-F" } ], "abstract": "A compact, narrow-linewidth, tunable source of THz radiation has been developed for spectroscopy and other high-resolution applications. Distributed-Bragg-reflector (DBR) diode lasers at 850 nm are used to pump a low-temperature-grown GaAs photomixer. Resonant optical feedback is employed to stabilize the center frequencies and narrow the linewidths of the DBR lasers. The heterodyne linewidth full-width at half-maximum of two optically locked DBR lasers is 50 kHz on the 20 ms time scale and 2 MHz over 10 s; free-running DBR lasers have linewidths of 40 and 90 MHz on such time scales. This instrument has been used to obtain rotational spectra of acetonitrile (CH3CN) at 313 GHz. Detection limits of 1 \u00d7 10^\u20134 Hz^1/2 (noise/total power) have been achieved, with the noise floor dominated by the detector's noise equivalent power.", "doi": "10.1063/1.119845", "issn": "0003-6951", "publisher": "American Institute of Physics", "publication": "Applied Physics Letters", "publication_date": "1997-09-22", "series_number": "12", "volume": "71", "issue": "12", "pages": "1601-1603" } ]