Recursos de colección

Caltech Authors (155.447 recursos)

Repository of works by Caltech published authors.

Group = Keck Institute for Space Studies

Mostrando recursos 1 - 20 de 51

  1. Production of Sulfur Allotropes in Electron Irradiated Jupiter Trojans Ice Analogs

    Mahjoub, Ahmed; Poston, Michael J.; Blacksberg, Jordana; Eiler, John M.; Brown, Michael E.; Ehlmann, Bethany L.; Hodyss, Robert; Hand, Kevin P.; Carlson, Robert; Choukroun, Mathieu
    In this paper, we investigate sulfur chemistry in laboratory analogs of Jupiter Trojans and Kuiper Belt Objects (KBOs). Electron irradiation experiments of CH_3OH–NH_3–H_2O and H_2S–CH_3OH–NH_3–H_2O ices were conducted to better understand the chemical differences between primordial planetesimals inside and outside the sublimation line of H_2S. The main goal of this work is to test the chemical plausibility of the hypothesis correlating the color bimodality in Jupiter Trojans with sulfur chemistry in the incipient solar system. Temperature programmed desorption (TPD) of the irradiated mixtures allows the detection of small sulfur allotropes (S_3 and S_4) after the irradiation of H2S containing ice...

  2. Electronic environments of ferrous iron in rhyolitic and basaltic glasses at high pressure

    Solomatova, Natalia V.; Jackson, Jennifer M.; Sturhahn, Wolfgang; Rossman, George R.; Roskosz, Mathieu
    The physical properties of silicate melts within Earth's mantle affect the chemical and thermal evolution of its interior. Chemistry and coordination environments affect such properties. We have measured the hyperfine parameters of iron-bearing rhyolitic and basaltic glasses up to ~120 GPa and ~100 GPa, respectively, in a neon pressure medium using time domain synchrotron Mössbauer spectroscopy. The spectra for rhyolitic and basaltic glasses are well explained by three high-spin Fe^(2+)-like sites with distinct quadrupole splittings. Absence of detectable ferric iron was confirmed with optical absorption spectroscopy. The sites with relatively high and intermediate quadrupole splittings are likely a result of...

  3. Methane emissions from dairies in the Los Angeles Basin

    Viatte, Camille; Lauvaux, Thomas; Hedelius, Jacob K.; Parker, Harrison; Chen, Jia; Jones, Taylor; Franklin, Jonathan E.; Deng, Aijun J.; Gaudet, Brian; Verhulst, Kristal; Duren, Riley; Wunch, Debra; Roehl, Coleen; Dubey, Manvendra K.; Wofsy, Steven; Wennberg, Paul O.
    We estimate the amount of methane (CH_4) emitted by the largest dairies in the southern California region by combining measurements from four mobile solar-viewing ground-based spectrometers (EM27/SUN), in situ isotopic ^(13∕12)CH_4 measurements from a CRDS analyzer (Picarro), and a high-resolution atmospheric transport simulation with a Weather Research and Forecasting model in large-eddy simulation mode (WRF-LES). The remote sensing spectrometers measure the total column-averaged dry-air mole fractions of CH_4 and CO_2 (X_(CH)_4 and X_(CO)_2) in the near infrared region, providing information on total emissions of the dairies at Chino. Differences measured between the four EM27/SUN ranged from 0.2 to 22 ppb (part...

  4. Methane emissions from dairies in the Los Angeles Basin

    Viatte, Camille; Lauvaux, Thomas; Hedelius, Jacob K.; Parker, Harrison; Chen, Jia; Jones, Taylor; Franklin, Jonathan E.; Deng, Aijun J.; Gaudet, Brian; Verhulst, Kristal; Duren, Riley; Wunch, Debra; Roehl, Coleen; Dubey, Manvendra K.; Wofsy, Steven; Wennberg, Paul O.
    We estimate the amount of methane (CH_4) emitted by the largest dairies in the southern California region by combining measurements from four mobile solar-viewing ground-based spectrometers (EM27/SUN), in situ isotopic ^(13∕12)CH_4 measurements from a CRDS analyzer (Picarro), and a high-resolution atmospheric transport simulation with a Weather Research and Forecasting model in large-eddy simulation mode (WRF-LES). The remote sensing spectrometers measure the total column-averaged dry-air mole fractions of CH_4 and CO_2 (X_(CH)_4 and X_(CO)_2) in the near infrared region, providing information on total emissions of the dairies at Chino. Differences measured between the four EM27/SUN ranged from 0.2 to 22 ppb (part...

  5. Empirically Derived Sensitivity of Vegetation to Climate across Global Gradients of Temperature and Precipitation

    Quetin, Gregory R.; Swann, Abigail
    The natural composition of terrestrial ecosystems can be shaped by climate to take advantage of local environmental conditions. Ecosystem functioning (e.g., interaction between photosynthesis and temperature) can also acclimate to different climatological states. The combination of these two factors thus determines ecological–climate interactions. A global empirical map of the sensitivity of vegetation to climate is derived using the response of satellite-observed greenness to interannual variations in temperature and precipitation. Mechanisms constraining ecosystem functioning are inferred by analyzing how the sensitivity of vegetation to climate varies across climate space. Analysis yields empirical evidence for multiple physical and biological mediators of the...

  6. Methane Seepage on Mars: Where to Look and Why

    Oehler, Dorothy Z.; Etiope, Giuseppe
    Methane on Mars is a topic of special interest because of its potential association with microbial life. The variable detections of methane by the Curiosity rover, orbiters, and terrestrial telescopes, coupled with methane's short lifetime in the martian atmosphere, may imply an active gas source in the planet's subsurface, with migration and surface emission processes similar to those known on Earth as “gas seepage.” Here, we review the variety of subsurface processes that could result in methane seepage on Mars. Such methane could originate from abiotic chemical reactions, thermogenic alteration of abiotic or biotic organic matter, and ancient or extant...

  7. Easily fabricated ion source for characterizing mixtures of organic compounds by direct analysis in real time mass spectrometry

    Upton, Kathleen T.; Schilling, Katherine A.; Beauchamp, J. L.
    The increasing use of atmospheric pressure mass spectrometry has led to the development of many ambient ionization sources, for which sampling versatility and low cost are desired features. One such recent ambient ionization method is direct analysis in real time mass spectrometry (DART-MS), which has proven to be well suited to the analysis of native samples of both simple and complex natures. We describe a home-built DART source (EZ-DART) with versatile sampling capabilities, low power requirements, and low assembly cost which can be easily interfaced to mass spectrometers equipped with an atmospheric pressure inlet. The operating temperature range (22–250 °C)...

  8. Easily fabricated ion source for characterizing mixtures of organic compounds by direct analysis in real time mass spectrometry

    Upton, Kathleen T.; Schilling, Katherine A.; Beauchamp, J. L.
    The increasing use of atmospheric pressure mass spectrometry has led to the development of many ambient ionization sources, for which sampling versatility and low cost are desired features. One such recent ambient ionization method is direct analysis in real time mass spectrometry (DART-MS), which has proven to be well suited to the analysis of native samples of both simple and complex natures. We describe a home-built DART source (EZ-DART) with versatile sampling capabilities, low power requirements, and low assembly cost which can be easily interfaced to mass spectrometers equipped with an atmospheric pressure inlet. The operating temperature range (22–250 °C)...

  9. Emissions and topographic effects on column CO_2 (XCO_2) variations, with a focus on the Southern California Megacity

    Hedelius, Jacob K.; Feng, Sha; Roehl, Coleen M.; Wunch, Debra; Hillyard, Patrick W.; Podolske, James R.; Iraci, Laura T.; Patarasuk, Risa; Rao, Preeti; O'Keeffe, Darragh; Gurney, Kevin R.; Lauvaux, Thomas; Wennberg, Paul O.
    Within the California South Coast Air Basin (SoCAB), X_(CO)_2 varies significantly due to atmospheric dynamics and the nonuniform distribution of sources. X_(CO)_2 measurements within the basin have seasonal variation compared to the “background” due primarily to dynamics, or the origins of air masses coming into the basin. We observe basin-background differences that are in close agreement for three observing systems: Total Carbon Column Observing Network (TCCON) 2.3 ± 1.2 ppm, Orbiting Carbon Observatory-2 (OCO-2) 2.4 ± 1.5 ppm, and Greenhouse gases Observing Satellite 2.4 ± 1.6 ppm (errors are 1σ). We further observe persistent significant differences (∼0.9 ppm) in X_(CO)_2...

  10. Emissions and topographic effects on column CO_2 (XCO_2) variations, with a focus on the Southern California Megacity

    Hedelius, Jacob K.; Feng, Sha; Roehl, Coleen M.; Wunch, Debra; Hillyard, Patrick W.; Podolske, James R.; Iraci, Laura T.; Patarasuk, Risa; Rao, Preeti; O'Keeffe, Darragh; Gurney, Kevin R.; Lauvaux, Thomas; Wennberg, Paul O.
    Within the California South Coast Air Basin (SoCAB), X_(CO)_2 varies significantly due to atmospheric dynamics and the nonuniform distribution of sources. X_(CO)_2 measurements within the basin have seasonal variation compared to the “background” due primarily to dynamics, or the origins of air masses coming into the basin. We observe basin-background differences that are in close agreement for three observing systems: Total Carbon Column Observing Network (TCCON) 2.3 ± 1.2 ppm, Orbiting Carbon Observatory-2 (OCO-2) 2.4 ± 1.5 ppm, and Greenhouse gases Observing Satellite 2.4 ± 1.6 ppm (errors are 1σ). We further observe persistent significant differences (∼0.9 ppm) in X_(CO)_2...

  11. Connecting active to passive fluorescence with photosynthesis: a method for evaluating remote sensing measurements of Chl fluorescence

    Magney, Troy S.; Frankenberg, Christian; Fisher, Joshua B.; Sun, Ying; North, Gretchen B.; Davis, Thomas S.; Kornfeld, Ari; Siebke, Katharina
    Recent advances in the retrieval of Chl fluorescence from space using passive methods (solar-induced Chl fluorescence, SIF) promise improved mapping of plant photosynthesis globally. However, unresolved issues related to the spatial, spectral, and temporal dynamics of vegetation fluorescence complicate our ability to interpret SIF measurements. We developed an instrument to measure leaf-level gas exchange simultaneously with pulse-amplitude modulation (PAM) and spectrally resolved fluorescence over the same field of view – allowing us to investigate the relationships between active and passive fluorescence with photosynthesis. Strongly correlated, slope-dependent relationships were observed between measured spectra across all wavelengths (Fλ, 670–850 nm) and PAM fluorescence parameters...

  12. Constraining the Origin of the Jupiter Trojans by In Situ Measurement of Volatiles, Minerals, and Ices

    Blacksberg, Jordana; Eiler, John M.
    As the KISS Trojans program comes to a close, we report here on our achievements in this venture that began with a KISS workshop in 2012, “In Situ Science and Instrumentation for Primitive Bodies”. The original workshop brought together a diverse group (see Appendix B) that set out to tackle an ambitious goal – to find a way to test predictions of dynamical models (such as the Nice model, named after the founding research group in Nice, France), that have recently led to a radically new understanding of solar system formation. We aimed to do so through interdisciplinary collaboration between...

  13. Exploration telepresence: A strategy for optimizing scientific research at remote space destinations

    Lester, Dan; Hodges, Kip; Anderson, Robert C.
    Modern telerobotic technologies offer astronaut scientists real-time presence on planetary surfaces without the risk and cost of putting them all the way there.

  14. ISS observations offer insights into plant function

    Stavros, Natasha; Schimel, David; Pavlick, Ryan; Serbin, Shawn; Swann, Abigail; Duncanson, Laura; Fisher, Joshua; Fassnacht, Fabian; Ustin, Susan; Dubayah, Ralph; Schweiger, Anna; Wennberg, Paul O.
    In 2018 technologies on the International Space Station will provide ~1 year of synchronous observations of ecosystem composition, structure and function. We discuss these instruments and how they can be used to constrain global models and improve our understanding of the current state of terrestrial ecosystems.

  15. Trajectory design of formation flying constellation for space-based solar power

    Goel, Ashish; Lee, Nicolas; Pellegrino, Sergio
    The concept of collecting solar power in space and transmitting it to the Earth using a microwave beam has appealed to the imagination of numerous researchers in the past. The Space Solar Power Initiative at Caltech is working towards turning this idea into reality, by developing the critical technologies necessary to make this an economically feasible solution. The proposed system comprises an array of ultralight, membrane-like deployable modules with high efficiency photovoltaics and microwave transmission antennas embedded in the structure. Each module is 60 m χ 60 m in size and in the final configuration, ∼2500 of these modules form...

  16. Lunarport: A proposed Lunar-resource station to expand deep-space travel horizons

    Gat, Ilana; Talon, Thibaud
    Deep-space travel is limited by the costly voyage to leave Earth's atmosphere and gravitational pull. The volume of propellants per unit mass of the payload required for that segment constrains the payload size and payload destination. To circumvent that limitation, this paper presents the feasibility of a refueling station using Lunar resources, called Lunarport. On Earth's moon, an unmanned station will robotically mine, produce, and store fuel and oxidizer from water ice at the poles. A first-stage-like rocket, called the Lunar Resupply Shuttle (LRS), stationed there and propelled with mined resources, will launch and dock with a passing payload-carrying rocket....

  17. Lunarport: A proposed Lunar-resource station to expand deep-space travel horizons

    Gat, Ilana; Talon, Thibaud
    Deep-space travel is limited by the costly voyage to leave Earth's atmosphere and gravitational pull. The volume of propellants per unit mass of the payload required for that segment constrains the payload size and payload destination. To circumvent that limitation, this paper presents the feasibility of a refueling station using Lunar resources, called Lunarport. On Earth's moon, an unmanned station will robotically mine, produce, and store fuel and oxidizer from water ice at the poles. A first-stage-like rocket, called the Lunar Resupply Shuttle (LRS), stationed there and propelled with mined resources, will launch and dock with a passing payload-carrying rocket....

  18. Visible to near-infrared MSL/Mastcam multispectral imaging: Initial results from select high-interest science targets within Gale Crater, Mars

    Wellington, Danika F.; Bell, James F., III; Johnson, Jeffrey R.; Kinch, Kjartan M.; Rice, Melissa S.; Godber, Austin; Ehlmann, Bethany L.; Fraeman, Abigail A.; Hardgrove, Craig
    The Mastcam CCD cameras on the Mars Science Laboratory Curiosity Rover each use an 8-position filter wheel in acquiring up to 1600 × 1200 pixel images. The filter set includes a broadband near-infrared cutoff filter for RGB Bayer imaging on each camera and 12 narrow-band geology filters distributed between the two cameras, spanning the wavelength range 445–1013 nm. This wavelength region includes the relatively broad charge-transfer and crystal-field absorption bands that are most commonly due to the presence of iron-bearing minerals. To identify such spectral features, sequences of images taken with identical pointings through different filters have been calibrated to...

  19. High Efficiency UV/Optical/NIR Detectors for Large Aperture Telescopes and UV Explorer Missions: Development of and Field Observations with Delta-doped Arrays

    Nikzad, Shouleh; Jewell, April D.; Hoenk, Michael E.; Jones, Todd; Hennessy, John; Goodsall, Tim; Carver, Alexander; Shapiro, Charles; Cheng, Samuel R.; Hamden, Erika; Kyne, Gillian; Martin, D. Christopher; Schiminovich, David; Scowen, Paul; France, Kevin; McCandliss, Stephan; Lupu, Roxana E.
    A number of exciting concepts are under development for Flagship, Probe class, Explorer class, and Suborbital class NASA missions in the ultraviolet/optical spectral ranges. These missions will depend on high performance silicon detector arrays being delivered affordably and in high numbers. In a focused effort we have advanced delta-doping technology to high throughput and high yield wafer-scale processing, encompassing a multitude of state-of-the-art silicon-based detector formats and designs. As part of this technology advancement and in preparation for upcoming missions, we have embarked on a number of field observations, instrument integrations, and independent evaluations of delta-doped arrays. In this paper,...

  20. Aerosol scattering effects on water vapor retrievals over the Los Angeles Basin

    Zeng, Zhao-Cheng; Zhang, Qiong; Natraj, Vijay; Margolis, Jack S.; Shia, Run-Lie; Newman, Sally; Fu, Dejian; Pongetti, Thomas J.; Wong, Kam W.; Sander, Stanley P.; Wennberg, Paul O.; Yung, Yuk L.
    In this study, we propose a novel approach to describe the scattering effects of atmospheric aerosols in a complex urban environment using water vapor (H_2O) slant column measurements in the near infrared. This approach is demonstrated using measurements from the California Laboratory for Atmospheric Remote Sensing Fourier Transform Spectrometer on the top of Mt. Wilson, California, and a two-stream-exact single scattering (2S-ESS) radiative transfer (RT) model. From the spectral measurements, we retrieve H_2O slant column density (SCD) using 15 different absorption bands between 4000 and 8000 cm^(−1). Due to the wavelength dependence of aerosol scattering, large variations in H_2O SCD retrievals...

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