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Way MJ, Ostberg C, Foley BJ, Gillmann C, Höning D, Lammer H, O’Rourke J, Persson M, Plesa AC, Salvador A, Scherf M, Weller M. Synergies Between Venus & Exoplanetary Observations: Venus and Its Extrasolar Siblings. SPACE SCIENCE REVIEWS 2023; 219:13. [PMID: 36785654 PMCID: PMC9911515 DOI: 10.1007/s11214-023-00953-3] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Figures] [Subscribe] [Scholar Register] [Received: 04/13/2022] [Accepted: 01/11/2023] [Indexed: 06/18/2023]
Abstract
Here we examine how our knowledge of present day Venus can inform terrestrial exoplanetary science and how exoplanetary science can inform our study of Venus. In a superficial way the contrasts in knowledge appear stark. We have been looking at Venus for millennia and studying it via telescopic observations for centuries. Spacecraft observations began with Mariner 2 in 1962 when we confirmed that Venus was a hothouse planet, rather than the tropical paradise science fiction pictured. As long as our level of exploration and understanding of Venus remains far below that of Mars, major questions will endure. On the other hand, exoplanetary science has grown leaps and bounds since the discovery of Pegasus 51b in 1995, not too long after the golden years of Venus spacecraft missions came to an end with the Magellan Mission in 1994. Multi-million to billion dollar/euro exoplanet focused spacecraft missions such as JWST, and its successors will be flown in the coming decades. At the same time, excitement about Venus exploration is blooming again with a number of confirmed and proposed missions in the coming decades from India, Russia, Japan, the European Space Agency (ESA) and the National Aeronautics and Space Administration (NASA). Here we review what is known and what we may discover tomorrow in complementary studies of Venus and its exoplanetary cousins.
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Affiliation(s)
- M. J. Way
- NASA Goddard Institute for Space Studies, 2880 Broadway, New York, NY 10025 USA
- Theoretical Astrophysics, Department of Physics and Astronomy, Uppsala University, Uppsala, Sweden
| | - Colby Ostberg
- Department of Earth and Planetary Sciences, University of California, Riverside, CA 92521 USA
| | - Bradford J. Foley
- Department of Geosciences, Pennsylvania State University, University Park, PA USA
| | - Cedric Gillmann
- Department of Earth, Environmental and Planetary Sciences, Rice University, Houston, TX 77005 USA
| | - Dennis Höning
- Potsdam Institute for Climate Impact Research, Potsdam, Germany
- Department of Earth Sciences, Vrije Universiteit Amsterdam, Amsterdam, The Netherlands
| | - Helmut Lammer
- Space Research Institute, Austrian Academy of Sciences, Schmiedlstr. 6, 8042 Graz, Austria
| | - Joseph O’Rourke
- School of Earth and Space Exploration, Arizona State University, Tempe, AZ USA
| | - Moa Persson
- Institut de Recherche en Astrophysique et Planétologie, Centre National de la Recherche Scientifique, Université Paul Sabatier – Toulouse III, Centre National d’Etudes Spatiales, Toulouse, France
| | | | - Arnaud Salvador
- Department of Astronomy and Planetary Science, Northern Arizona University, Box 6010, Flagstaff, AZ 86011 USA
- Habitability, Atmospheres, and Biosignatures Laboratory, University of Arizona, Tucson, AZ USA
- Lunar and Planetary Laboratory, University of Arizona, Tucson, AZ USA
| | - Manuel Scherf
- Space Research Institute, Austrian Academy of Sciences, Schmiedlstr. 6, 8042 Graz, Austria
- Institute of Physics, University of Graz, Graz, Austria
- Institute for Geodesy, Technical University, Graz, Austria
| | - Matthew Weller
- Lunar and Planetary Institute, 3600 Bay Area Blvd., Houston, TX 77058 USA
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Li C, Krohn J, Lippe M, Signorell R. How volatile components catalyze vapor nucleation. SCIENCE ADVANCES 2021; 7:eabd9954. [PMID: 33523884 PMCID: PMC7806218 DOI: 10.1126/sciadv.abd9954] [Citation(s) in RCA: 4] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Grants] [Track Full Text] [Download PDF] [Figures] [Subscribe] [Scholar Register] [Received: 07/24/2020] [Accepted: 11/16/2020] [Indexed: 06/12/2023]
Abstract
Gas phase nucleation is a ubiquitous phenomenon in planetary atmospheres and technical processes, yet our understanding of it is far from complete. In particular, the enhancement of nucleation by the addition of a more volatile, weakly interacting gaseous species to a nucleating vapor has escaped molecular-level experimental investigation. Here, we use a specially designed experiment to directly measure the chemical composition and the concentration of nucleating clusters in various binary CO2-containing vapors. Our analysis suggests that CO2 essentially catalyzes nucleation of the low vapor pressure component through the formation of transient, hetero-molecular clusters and thus provides alternative pathways for nucleation to proceed more efficiently. This work opens up new avenues for the quantitative assessment of nucleation mechanisms involving transient species in multicomponent vapors.
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Affiliation(s)
- Chenxi Li
- School of Environmental Science and Engineering, Shanghai Jiao Tong University, Shanghai 200240, China
- Department of Chemistry and Applied Biosciences, Laboratory of Physical Chemistry, ETH Zürich, Vladimir-Prelog-Weg 2, CH-8093 Zürich, Switzerland
| | - Jan Krohn
- Department of Chemistry and Applied Biosciences, Laboratory of Physical Chemistry, ETH Zürich, Vladimir-Prelog-Weg 2, CH-8093 Zürich, Switzerland
| | - Martina Lippe
- Department of Chemistry and Applied Biosciences, Laboratory of Physical Chemistry, ETH Zürich, Vladimir-Prelog-Weg 2, CH-8093 Zürich, Switzerland
| | - Ruth Signorell
- Department of Chemistry and Applied Biosciences, Laboratory of Physical Chemistry, ETH Zürich, Vladimir-Prelog-Weg 2, CH-8093 Zürich, Switzerland.
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Ranjan S, Wordsworth R, Sasselov DD. Atmospheric Constraints on the Surface UV Environment of Mars at 3.9 Ga Relevant to Prebiotic Chemistry. ASTROBIOLOGY 2017; 17:687-708. [PMID: 28537771 DOI: 10.1089/ast.2016.1596] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/07/2023]
Abstract
Recent findings suggest that Mars may have been a clement environment for the emergence of life and may even have compared favorably to Earth in this regard. These findings have revived interest in the hypothesis that prebiotically important molecules or even nascent life may have formed on Mars and been transferred to Earth. UV light plays a key role in prebiotic chemistry. Characterizing the early martian surface UV environment is key to understanding how Mars compares to Earth as a venue for prebiotic chemistry. Here, we present two-stream, multilayer calculations of the UV surface radiance on Mars at 3.9 Ga to constrain the surface UV environment as a function of atmospheric state. We explore a wide range of atmospheric pressures, temperatures, and compositions that correspond to the diversity of martian atmospheric states consistent with available constraints. We include the effects of clouds and dust. We calculate dose rates to quantify the effect of different atmospheric states on UV-sensitive prebiotic chemistry. We find that, for normative clear-sky CO2-H2O atmospheres, the UV environment on young Mars is comparable to young Earth. This similarity is robust to moderate cloud cover; thick clouds (τcloud ≥ 100) are required to significantly affect the martian UV environment, because cloud absorption is degenerate with atmospheric CO2. On the other hand, absorption from SO2, H2S, and dust is nondegenerate with CO2, meaning that, if these constituents build up to significant levels, surface UV fluence can be suppressed. These absorbers have spectrally variable absorption, meaning that their presence affects prebiotic pathways in different ways. In particular, high SO2 environments may admit UV fluence that favors pathways conducive to abiogenesis over pathways unfavorable to it. However, better measurements of the spectral quantum yields of these pathways are required to evaluate this hypothesis definitively. Key Words: Radiative transfer-Origin of life-Mars-UV radiation-Prebiotic chemistry. Astrobiology 17, 687-708.
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Affiliation(s)
- Sukrit Ranjan
- 1 Harvard-Smithsonian Center for Astrophysics , Cambridge, Massachusetts
| | - Robin Wordsworth
- 2 Harvard Paulson School of Engineering and Applied Sciences, Harvard University , Cambridge, Massachusetts
- 3 Department of Earth and Planetary Sciences, Harvard University , Cambridge, Massachusetts
| | - Dimitar D Sasselov
- 1 Harvard-Smithsonian Center for Astrophysics , Cambridge, Massachusetts
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Haqq-Misra J, Kopparapu RK, Batalha NE, Harman CE, Kasting JF. LIMIT CYCLES CAN REDUCE THE WIDTH OF THE HABITABLE ZONE. THE ASTROPHYSICAL JOURNAL 2016; 827:120. [PMID: 30116072 PMCID: PMC6090540 DOI: 10.3847/0004-637x/827/2/120] [Citation(s) in RCA: 84] [Impact Index Per Article: 10.5] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 11/18/2022]
Abstract
The liquid water habitable zone (HZ) describes the orbital distance at which a terrestrial planet can maintain above-freezing conditions through regulation by the carbonate-silicate cycle. Recent calculations have suggested that planets in the outer regions of the HZ cannot maintain stable, warm climates, but rather should oscillate between long, globally glaciated states and shorter periods of climatic warmth. Such conditions, similar to "Snowball Earth" episodes experienced on Earth, would be inimical to the development of complex land life, including intelligent life. Here, we build on previous studies with an updated energy balance climate model to calculate this "limit cycle" region of the HZ where such cycling would occur. We argue that an abiotic Earth would have a greater CO2 partial pressure than today because plants and other biota help to enhance the storage of CO2 in soil. When we tune our abiotic model accordingly, we find that limit cycles can occur but that previous calculations have overestimated their importance. For G stars like the Sun, limit cycles occur only for planets with CO2 outgassing rates less than that on modern Earth. For K- and M-star planets, limit cycles should not occur; however, M-star planets may be inhospitable to life for other reasons. Planets orbiting late G-type and early K-type stars retain the greatest potential for maintaining warm, stable conditions. Our results suggest that host star type, planetary volcanic activity, and seafloor weathering are all important factors in determining whether planets will be prone to limit cycling.
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Affiliation(s)
- Jacob Haqq-Misra
- Blue Marble Space Institute of Science, 1001 4th Avenue, Suite 3201, Seattle, WA 98154, USA
- NASA Astrobiology Institute's Virtual Planetary Laboratory, P.O. Box 351580, Seattle, WA 98195, USA
| | - Ravi Kumar Kopparapu
- Blue Marble Space Institute of Science, 1001 4th Avenue, Suite 3201, Seattle, WA 98154, USA
- NASA Astrobiology Institute's Virtual Planetary Laboratory, P.O. Box 351580, Seattle, WA 98195, USA
- NASA Goddard Space Flight Center, 8800 Greenbelt Road, Mail Stop 699.0, Building 34, Greenbelt, MD 20771, USA
- Department of Astronomy, University of Maryland, College Park, MD 20742, USA
| | - Natasha E Batalha
- NASA Astrobiology Institute's Virtual Planetary Laboratory, P.O. Box 351580, Seattle, WA 98195, USA
- Department of Astronomy and Astrophysics, The Pennsylvania State University, University Park, PA 16802, USA
- Center for Exoplanets and Habitable Worlds, The Pennsylvania State University, University Park, PA 16802, USA
| | - Chester E Harman
- NASA Astrobiology Institute's Virtual Planetary Laboratory, P.O. Box 351580, Seattle, WA 98195, USA
- Center for Exoplanets and Habitable Worlds, The Pennsylvania State University, University Park, PA 16802, USA
- Department of Geosciences, The Pennsylvania State University, University Park, PA 16802, USA
| | - James F Kasting
- NASA Astrobiology Institute's Virtual Planetary Laboratory, P.O. Box 351580, Seattle, WA 98195, USA
- Center for Exoplanets and Habitable Worlds, The Pennsylvania State University, University Park, PA 16802, USA
- Department of Geosciences, The Pennsylvania State University, University Park, PA 16802, USA
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Rushby AJ, Claire MW, Osborn H, Watson AJ. Habitable zone lifetimes of exoplanets around main sequence stars. ASTROBIOLOGY 2013; 13:833-849. [PMID: 24047111 DOI: 10.1089/ast.2012.0938] [Citation(s) in RCA: 12] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/02/2023]
Abstract
The potential habitability of newly discovered exoplanets is initially assessed by determining whether their orbits fall within the circumstellar habitable zone of their star. However, the habitable zone (HZ) is not static in time or space, and its boundaries migrate outward at a rate proportional to the increase in luminosity of a star undergoing stellar evolution, possibly including or excluding planets over the course of the star's main sequence lifetime. We describe the time that a planet spends within the HZ as its "habitable zone lifetime." The HZ lifetime of a planet has strong astrobiological implications and is especially important when considering the evolution of complex life, which is likely to require a longer residence time within the HZ. Here, we present results from a simple model built to investigate the evolution of the "classic" HZ over time, while also providing estimates for the evolution of stellar luminosity over time in order to develop a "hybrid" HZ model. These models return estimates for the HZ lifetimes of Earth and 7 confirmed HZ exoplanets and 27 unconfirmed Kepler candidates. The HZ lifetime for Earth ranges between 6.29 and 7.79×10⁹ years (Gyr). The 7 exoplanets fall in a range between ∼1 and 54.72 Gyr, while the 27 Kepler candidate planets' HZ lifetimes range between 0.43 and 18.8 Gyr. Our results show that exoplanet HD 85512b is no longer within the HZ, assuming it has an Earth analog atmosphere. The HZ lifetime should be considered in future models of planetary habitability as setting an upper limit on the lifetime of any potential exoplanetary biosphere, and also for identifying planets of high astrobiological potential for continued observational or modeling campaigns.
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Affiliation(s)
- Andrew J Rushby
- 1 School of Environmental Sciences, University of East Anglia , Norwich, UK
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van Berk W, Fu Y, Ilger JM. Reproducing early Martian atmospheric carbon dioxide partial pressure by modeling the formation of Mg-Fe-Ca carbonate identified in the Comanche rock outcrops on Mars. ACTA ACUST UNITED AC 2012. [DOI: 10.1029/2012je004173] [Citation(s) in RCA: 14] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/10/2022]
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Vincendon M, Pilorget C, Gondet B, Murchie S, Bibring JP. New near-IR observations of mesospheric CO2and H2O clouds on Mars. ACTA ACUST UNITED AC 2011. [DOI: 10.1029/2011je003827] [Citation(s) in RCA: 56] [Impact Index Per Article: 4.3] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/09/2022]
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van Berk W, Fu Y. Reproducing hydrogeochemical conditions triggering the formation of carbonate and phyllosilicate alteration mineral assemblages on Mars (Nili Fossae region). ACTA ACUST UNITED AC 2011. [DOI: 10.1029/2011je003886] [Citation(s) in RCA: 15] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/09/2022]
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Lammer H, Selsis F, Chassefière E, Breuer D, Griessmeier JM, Kulikov YN, Erkaev NV, Khodachenko ML, Biernat HK, Leblanc F, Kallio E, Lundin R, Westall F, Bauer SJ, Beichman C, Danchi W, Eiroa C, Fridlund M, Gröller H, Hanslmeier A, Hausleitner W, Henning T, Herbst T, Kaltenegger L, Léger A, Leitzinger M, Lichtenegger HIM, Liseau R, Lunine J, Motschmann U, Odert P, Paresce F, Parnell J, Penny A, Quirrenbach A, Rauer H, Röttgering H, Schneider J, Spohn T, Stadelmann A, Stangl G, Stam D, Tinetti G, White GJ. Geophysical and atmospheric evolution of habitable planets. ASTROBIOLOGY 2010; 10:45-68. [PMID: 20307182 DOI: 10.1089/ast.2009.0368] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/29/2023]
Abstract
The evolution of Earth-like habitable planets is a complex process that depends on the geodynamical and geophysical environments. In particular, it is necessary that plate tectonics remain active over billions of years. These geophysically active environments are strongly coupled to a planet's host star parameters, such as mass, luminosity and activity, orbit location of the habitable zone, and the planet's initial water inventory. Depending on the host star's radiation and particle flux evolution, the composition in the thermosphere, and the availability of an active magnetic dynamo, the atmospheres of Earth-like planets within their habitable zones are differently affected due to thermal and nonthermal escape processes. For some planets, strong atmospheric escape could even effect the stability of the atmosphere.
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Affiliation(s)
- Helmut Lammer
- Space Research Institute, Austrian Academy of Sciences, Graz, Austria.
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Stability against freezing of aqueous solutions on early Mars. Nature 2009; 459:401-4. [DOI: 10.1038/nature07978] [Citation(s) in RCA: 102] [Impact Index Per Article: 6.8] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/19/2008] [Accepted: 03/16/2009] [Indexed: 11/08/2022]
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Segura TL, Toon OB, Colaprete A. Modeling the environmental effects of moderate-sized impacts on Mars. ACTA ACUST UNITED AC 2008. [DOI: 10.1029/2008je003147] [Citation(s) in RCA: 104] [Impact Index Per Article: 6.5] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/10/2022]
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Montmessin F, Gondet B, Bibring JP, Langevin Y, Drossart P, Forget F, Fouchet T. Hyperspectral imaging of convective CO2ice clouds in the equatorial mesosphere of Mars. ACTA ACUST UNITED AC 2007. [DOI: 10.1029/2007je002944] [Citation(s) in RCA: 65] [Impact Index Per Article: 3.8] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/09/2022]
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Määttänen A, Vehkamäki H, Lauri A, Napari I, Kulmala M. Two-component heterogeneous nucleation kinetics and an application to Mars. J Chem Phys 2007; 127:134710. [PMID: 17919046 DOI: 10.1063/1.2770737] [Citation(s) in RCA: 26] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/15/2022] Open
Abstract
We develop a two-component heterogeneous nucleation model that includes exact calculation of the Stauffer-type [D. Stauffer, J. Aerosol Sci. 7, 319 (1976)] steady-state kinetic prefactor using the correct heterogeneous Zeldovich factor for a heterogeneous two-component system. The model, and a simplified version of it, is tested by comparing its predictions to experimental data for water-n-propanol nucleating on silver particles. The model is then applied to water-carbon dioxide system in Martian conditions, which has not been modeled before. Using the ideal mixture assumption, the model shows theoretical possibilities for two-component nucleation adjacent to the initial stages of one-component water nucleation, especially with small water vapor amounts. The numbers of carbon dioxide molecules in the critical cluster are small in the case of large water amounts (up to 300 ppm) in the gas phase, but larger when there is very little water vapor (1 ppm).
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Affiliation(s)
- Anni Määttänen
- Division of Atmospheric Sciences, Department of Physical Sciences, University of Helsinki, 00014 Helsinki, Finland.
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Khodachenko ML, Ribas I, Lammer H, Griessmeier JM, Leitner M, Selsis F, Eiroa C, Hanslmeier A, Biernat HK, Farrugia CJ, Rucker HO. Coronal mass ejection (CME) activity of low mass M stars as an important factor for the habitability of terrestrial exoplanets. I. CME impact on expected magnetospheres of Earth-like exoplanets in close-in habitable zones. ASTROBIOLOGY 2007; 7:167-84. [PMID: 17407406 DOI: 10.1089/ast.2006.0127] [Citation(s) in RCA: 19] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/14/2023]
Abstract
Low mass M- and K-type stars are much more numerous in the solar neighborhood than solar-like G-type stars. Therefore, some of them may appear as interesting candidates for the target star lists of terrestrial exoplanet (i.e., planets with mass, radius, and internal parameters identical to Earth) search programs like Darwin (ESA) or the Terrestrial Planet Finder Coronagraph/Inferometer (NASA). The higher level of stellar activity of low mass M stars, as compared to solar-like G stars, as well as the closer orbital distances of their habitable zones (HZs), means that terrestrial-type exoplanets within HZs of these stars are more influenced by stellar activity than one would expect for a planet in an HZ of a solar-like star. Here we examine the influences of stellar coronal mass ejection (CME) activity on planetary environments and the role CMEs may play in the definition of habitability criterion for the terrestrial type exoplanets near M stars. We pay attention to the fact that exoplanets within HZs that are in close proximity to low mass M stars may become tidally locked, which, in turn, can result in relatively weak intrinsic planetary magnetic moments. Taking into account existing observational data and models that involve the Sun and related hypothetical parameters of extrasolar CMEs (density, velocity, size, and occurrence rate), we show that Earth-like exoplanets within close-in HZs should experience a continuous CME exposure over long periods of time. This fact, together with small magnetic moments of tidally locked exoplanets, may result in little or no magnetospheric protection of planetary atmospheres from a dense flow of CME plasma. Magnetospheric standoff distances of weakly magnetized Earth-like exoplanets at orbital distances <or=0.1 AU can be shrunk, under the action of CMEs, to altitudes of about 1,000 km above the planetary surface. Such compressed magnetospheres may have crucial consequences for atmospheric erosion processes.
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Colaprete A, Barnes JR, Haberle RM, Hollingsworth JL, Kieffer HH, Titus TN. Albedo of the south pole on Mars determined by topographic forcing of atmosphere dynamics. Nature 2005; 435:184-8. [PMID: 15889086 DOI: 10.1038/nature03561] [Citation(s) in RCA: 58] [Impact Index Per Article: 3.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/25/2004] [Accepted: 03/10/2005] [Indexed: 11/09/2022]
Abstract
The nature of the martian south polar cap has remained enigmatic since the first spacecraft observations. In particular, the presence of a perennial carbon dioxide ice cap, the formation of a vast area of black 'slab ice' known as the Cryptic region and the asymmetric springtime retreat of the cap have eluded explanation. Here we present observations and climate modelling that indicate the south pole of Mars is characterized by two distinct regional climates that are the result of dynamical forcing by the largest southern impact basins, Argyre and Hellas. The style of surface frost deposition is controlled by these regional climates. In the cold and stormy conditions that exist poleward of 60 degrees S and extend 180 degrees in longitude west from the Mountains of Mitchel (approximately 30 degrees W), surface frost accumulation is dominated by precipitation. In the opposite hemisphere, the polar atmosphere is relatively warm and clear and frost accumulation is dominated by direct vapour deposition. It is the differences in these deposition styles that determine the cap albedo.
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Affiliation(s)
- Anthony Colaprete
- NASA Ames Research Center, Space Science Division, Moffett Field, Mountain View, California 94035, USA.
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Colaprete A. Formation of convective carbon dioxide clouds near the south pole of Mars. ACTA ACUST UNITED AC 2003. [DOI: 10.1029/2003je002053] [Citation(s) in RCA: 38] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/10/2022]
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