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Styczinski MJ, Cooper ZS, Glaser DM, Lehmer O, Mierzejewski V, Tarnas J. Chapter 7: Assessing Habitability Beyond Earth. ASTROBIOLOGY 2024; 24:S143-S163. [PMID: 38498826 DOI: 10.1089/ast.2021.0097] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 03/20/2024]
Abstract
All known life on Earth inhabits environments that maintain conditions between certain extremes of temperature, chemical composition, energy availability, and so on (Chapter 6). Life may have emerged in similar environments elsewhere in the Solar System and beyond. The ongoing search for life elsewhere mainly focuses on those environments most likely to support life, now or in the past-that is, potentially habitable environments. Discussion of habitability is necessarily based on what we know about life on Earth, as it is our only example. This chapter gives an overview of the known and presumed requirements for life on Earth and discusses how these requirements can be used to assess the potential habitability of planetary bodies across the Solar System and beyond. We first consider the chemical requirements of life and potential feedback effects that the presence of life can have on habitable conditions, and then the planetary, stellar, and temporal requirements for habitability. We then review the state of knowledge on the potential habitability of bodies across the Solar System and exoplanets, with a particular focus on Mars, Venus, Europa, and Enceladus. While reviewing the case for the potential habitability of each body, we summarize the most prominent and impactful studies that have informed the perspective on where habitable environments are likely to be found.
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Affiliation(s)
- M J Styczinski
- University of Washington, Seattle, Washington, USA
- Jet Propulsion Laboratory, California Institute of Technology, Pasadena, California, USA
| | - Z S Cooper
- University of Washington, Seattle, Washington, USA
| | - D M Glaser
- School of Molecular Sciences, Arizona State University, Tempe, Arizona, USA
| | - O Lehmer
- NASA Ames Research Center, Moffett Field, California, USA
| | - V Mierzejewski
- School of Earth and Space Exploration, Arizona State University, Arizona, USA
| | - J Tarnas
- Jet Propulsion Laboratory, California Institute of Technology, Pasadena, California, USA
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Liquid water on cold exo-Earths via basal melting of ice sheets. Nat Commun 2022; 13:7521. [PMID: 36473880 PMCID: PMC9726705 DOI: 10.1038/s41467-022-35187-4] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/17/2022] [Accepted: 11/22/2022] [Indexed: 12/12/2022] Open
Abstract
Liquid water is a critical component of habitability. However, the production and stability of surficial liquid water can be challenging on planets outside the Habitable Zone and devoid of adequate greenhouse warming. On such cold, icy exo-Earths, basal melting of regional/global ice sheets by geothermal heat provides an alternative means of forming liquid water. Here, we model the thermophysical evolution of ice sheets to ascertain the geophysical conditions that allow liquid water to be produced and maintained at temperatures above the pressure-controlled freezing point of water ice on exo-Earths. We show that even with a modest, Moon-like geothermal heat flow, subglacial oceans of liquid water can form at the base of and within the ice sheets on exo-Earths. Furthermore, subglacial oceans may persist on exo-Earths for a prolonged period due to the billion-year half-lives of heat-producing elements responsible for geothermal heat. These subglacial oceans, often in contact with the planet's crust and shielded from the high energy radiation of their parent star by thick ice layers, may provide habitable conditions for an extended period.
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Olson S, Jansen MF, Abbot DS, Halevy I, Goldblatt C. The Effect of Ocean Salinity on Climate and Its Implications for Earth's Habitability. GEOPHYSICAL RESEARCH LETTERS 2022; 49:e2021GL095748. [PMID: 35864818 PMCID: PMC9286645 DOI: 10.1029/2021gl095748] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Download PDF] [Figures] [Subscribe] [Scholar Register] [Received: 11/01/2021] [Revised: 04/18/2022] [Accepted: 04/18/2022] [Indexed: 06/15/2023]
Abstract
The influence of atmospheric composition on the climates of present-day and early Earth has been studied extensively, but the role of ocean composition has received less attention. We use the ROCKE-3D ocean-atmosphere general circulation model to investigate the response of Earth's present-day and Archean climate system to low versus high ocean salinity. We find that saltier oceans yield warmer climates in large part due to changes in ocean dynamics. Increasing ocean salinity from 20 to 50 g/kg results in a 71% reduction in sea ice cover in our present-day Earth scenario. This same salinity change also halves the pCO2 threshold at which Snowball glaciation occurs in our Archean scenarios. In combination with higher levels of greenhouse gases such as CO2 and CH4, a saltier ocean may allow for a warm Archean Earth with only seasonal ice at the poles despite receiving ∼20% less energy from the Sun.
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Affiliation(s)
- Stephanie Olson
- Department of Earth, Atmospheric, and Planetary SciencePurdue UniversityWest LafayetteINUSA
| | - Malte F. Jansen
- Department of the Geophysical SciencesUniversity of ChicagoChicagoILUSA
| | - Dorian S. Abbot
- Department of the Geophysical SciencesUniversity of ChicagoChicagoILUSA
| | - Itay Halevy
- Department of Earth and Planetary SciencesWeizmann Institute of ScienceRehovotIsrael
| | - Colin Goldblatt
- School of Earth and Ocean SciencesUniversity of VictoriaVictoriaBCCanada
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Abstract
The current Martian climate is not habitable and far from Earth’s climate. At the same time that life spread on Earth (3 Gy ago), the Red Planet was possibly more similar to our Blue Planet. Our model includes a coupled model with dynamic ocean and atmosphere including a hydrological cycle and a simplified glacier mass flux scheme. We show that an ocean is stable in agreement with interpretations of the surface geological records. What was the nature of the Late Hesperian climate, warm and wet or cold and dry? Formulated this way the question leads to an apparent paradox since both options seem implausible. A warm and wet climate would have produced extensive fluvial erosion but few valley networks have been observed at the age of the Late Hesperian. A too cold climate would have kept any northern ocean frozen most of the time. A moderate cold climate would have transferred the water from the ocean to the land in the form of snow and ice. But this would prevent tsunami formation, for which there is some evidence. Here, we provide insights from numerical climate simulations in agreement with surface geological features to demonstrate that the Martian climate could have been both cold and wet. Using an advanced general circulation model (GCM), we demonstrate that an ocean can be stable, even if the Martian mean surface temperature is lower than 0 °C. Rainfall is moderate near the shorelines and in the ocean. The southern plateau is mostly covered by ice with a mean temperature below 0 °C and a glacier return flow back to the ocean. This climate is achieved with a 1-bar CO2-dominated atmosphere with 10% H2. Under this scenario of 3 Ga, the geologic evidence of a shoreline and tsunami deposits along the ocean/land dichotomy are compatible with ice sheets and glacial valleys in the southern highlands.
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Daher H, Arbic BK, Williams JG, Ansong JK, Boggs DH, Müller M, Schindelegger M, Austermann J, Cornuelle BD, Crawford EB, Fringer OB, Lau HCP, Lock SJ, Maloof AC, Menemenlis D, Mitrovica JX, Green JAM, Huber M. Long-Term Earth-Moon Evolution With High-Level Orbit and Ocean Tide Models. JOURNAL OF GEOPHYSICAL RESEARCH. PLANETS 2021; 126:e2021JE006875. [PMID: 35846556 PMCID: PMC9285098 DOI: 10.1029/2021je006875] [Citation(s) in RCA: 3] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 02/22/2021] [Revised: 08/26/2021] [Accepted: 09/14/2021] [Indexed: 05/25/2023]
Abstract
Tides and Earth-Moon system evolution are coupled over geological time. Tidal energy dissipation on Earth slows E a r t h ' s rotation rate, increases obliquity, lunar orbit semi-major axis and eccentricity, and decreases lunar inclination. Tidal and core-mantle boundary dissipation within the Moon decrease inclination, eccentricity and semi-major axis. Here we integrate the Earth-Moon system backwards for 4.5 Ga with orbital dynamics and explicit ocean tide models that are "high-level" (i.e., not idealized). To account for uncertain plate tectonic histories, we employ Monte Carlo simulations, with tidal energy dissipation rates (normalized relative to astronomical forcing parameters) randomly selected from ocean tide simulations with modern ocean basin geometry and with 55, 116, and 252 Ma reconstructed basin paleogeometries. The normalized dissipation rates depend upon basin geometry and E a r t h ' s rotation rate. Faster Earth rotation generally yields lower normalized dissipation rates. The Monte Carlo results provide a spread of possible early values for the Earth-Moon system parameters. Of consequence for ocean circulation and climate, absolute (un-normalized) ocean tidal energy dissipation rates on the early Earth may have exceeded t o d a y ' s rate due to a closer Moon. Prior to ∼ 3 Ga , evolution of inclination and eccentricity is dominated by tidal and core-mantle boundary dissipation within the Moon, which yield high lunar orbit inclinations in the early Earth-Moon system. A drawback for our results is that the semi-major axis does not collapse to near-zero values at 4.5 Ga, as indicated by most lunar formation models. Additional processes, missing from our current efforts, are discussed as topics for future investigation.
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Affiliation(s)
- Houraa Daher
- Department of Climate and Space Sciences and EngineeringUniversity of MichiganAnn ArborMIUSA
- Rosenstiel School for Marine and Atmospheric ScienceUniversity of MiamiMiamiFLUSA
| | - Brian K. Arbic
- Department of Earth and Environmental SciencesUniversity of MichiganAnn ArborMIUSA
- Institut des Géosciences de L'Environnement (IGE)GrenobleFrance
- Laboratoire des Etudes en Géophysique et Océanographie Spatiale (LEGOS)ToulouseFrance
| | - James G. Williams
- Jet Propulsion LaboratoryCalifornia Institute of TechnologyPasadenaCAUSA
| | - Joseph K. Ansong
- Department of Earth and Environmental SciencesUniversity of MichiganAnn ArborMIUSA
- Department of MathematicsUniversity of GhanaAccraGhana
| | - Dale H. Boggs
- Jet Propulsion LaboratoryCalifornia Institute of TechnologyPasadenaCAUSA
| | | | | | | | - Bruce D. Cornuelle
- Scripps Institution of OceanographyUniversity of CaliforniaLa JollaCAUSA
| | - Eliana B. Crawford
- Department of Earth and Environmental SciencesUniversity of MichiganAnn ArborMIUSA
- Swift NavigationSan FranciscoCAUSA
- Department of PhysicsKenyon CollegeGambierOHUSA
| | - Oliver B. Fringer
- Department of Civil and Environmental EngineeringStanford UniversityStanfordCAUSA
| | - Harriet C. P. Lau
- Department of Earth and Planetary SciencesUniversity of CaliforniaBerkeleyCAUSA
- Department of Earth and Planetary SciencesHarvard UniversityCambridgeMAUSA
| | - Simon J. Lock
- Division of Geological and Planetary SciencesCalifornia Institute of TechnologyPasadenaCAUSA
| | - Adam C. Maloof
- Department of GeosciencesPrinceton UniversityPrincetonNJUSA
| | | | - Jerry X. Mitrovica
- Department of Earth and Planetary SciencesHarvard UniversityCambridgeMAUSA
| | | | - Matthew Huber
- Department of Earth, Atmospheric, and Planetary SciencesPurdue UniversityWest LafayetteINUSA
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Studholme JHP, Markina MY, Gulev SK. Role of Surface Gravity Waves in Aquaplanet Ocean Climates. JOURNAL OF ADVANCES IN MODELING EARTH SYSTEMS 2021; 13:e2020MS002202. [PMID: 34221241 PMCID: PMC8244083 DOI: 10.1029/2020ms002202] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Grants] [Track Full Text] [Download PDF] [Figures] [Subscribe] [Scholar Register] [Received: 06/17/2020] [Revised: 05/10/2021] [Accepted: 05/10/2021] [Indexed: 06/13/2023]
Abstract
We present a set of idealized numerical experiments of a solstitial aquaplanet ocean and examine the thermodynamic and dynamic implications of surface gravity waves (SGWs) upon its mean state. The aquaplanet's oceanic circulation is dominated by an equatorial zonal jet and four Ekman driven meridional overturning circulation (MOC) cells aligned with the westerly atmospheric jet streams and easterly trade winds in both hemispheres. Including SGW parameterization (representing modulations of air-sea momentum fluxes, Langmuir circulation, and Stokes-Coriolis force) increases mixed layer vertical momentum diffusivity by ∼40% and dampens surface momentum fluxes by ∼4%. The correspondingly dampened MOC impacts the oceanic density structure to 1 km depth by lessening the large-scale advective transports of heat and salt, freshening the equatorial latitudes (where evaporation minus precipitation [E - P] is negative) and increasing salinity in the subtropics (where E - P is positive) by ∼1%. The midlatitude pycnocline in both hemispheres is deepened by the inclusion of SGWs. Including SGWs into the aquaplanet ocean model acts to increase mixed layer depth by ∼10% (up to 20% in the wintertime in midlatitudes), decrease vertical shear in the upper 200 m and alter local midlatitude buoyancy frequency. Generally, the impacts of SGWs upon the aquaplanet ocean are found to be consistent across cooler and warmer climates. We suggest that the implications of these simulations could be relevant to understanding future projections of SGW climate, exoplanetary oceans, and the dynamics of the Southern Ocean mixed layer.
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Affiliation(s)
| | - Margarita Y. Markina
- Shirshov Institute of OceanologyRussian Academy of ScienceMoscowRussia
- Present affiliation: University of OxfordOxfordUK
| | - Sergey K. Gulev
- Shirshov Institute of OceanologyRussian Academy of ScienceMoscowRussia
- Lomonosov Moscow State UniversityMoscowRussia
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Boutle IA, Joshi M, Lambert FH, Mayne NJ, Lyster D, Manners J, Ridgway R, Kohary K. Mineral dust increases the habitability of terrestrial planets but confounds biomarker detection. Nat Commun 2020; 11:2731. [PMID: 32518292 PMCID: PMC7283277 DOI: 10.1038/s41467-020-16543-8] [Citation(s) in RCA: 12] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/09/2019] [Accepted: 05/05/2020] [Indexed: 11/09/2022] Open
Abstract
Identification of habitable planets beyond our solar system is a key goal of current and future space missions. Yet habitability depends not only on the stellar irradiance, but equally on constituent parts of the planetary atmosphere. Here we show, for the first time, that radiatively active mineral dust will have a significant impact on the habitability of Earth-like exoplanets. On tidally-locked planets, dust cools the day-side and warms the night-side, significantly widening the habitable zone. Independent of orbital configuration, we suggest that airborne dust can postpone planetary water loss at the inner edge of the habitable zone, through a feedback involving decreasing ocean coverage and increased dust loading. The inclusion of dust significantly obscures key biomarker gases (e.g. ozone, methane) in simulated transmission spectra, implying an important influence on the interpretation of observations. We demonstrate that future observational and theoretical studies of terrestrial exoplanets must consider the effect of dust. In this study, the authors investigate in the influence of atmospheric dust on the habitability of exoplanets. They find that atmospheric dust may postpone planetary water loss; for tidally locked planets in particular, dust can significantly widen the habitable zone by cooling the day side and warming the night side.
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Affiliation(s)
- Ian A Boutle
- College of Engineering, Mathematics and Physical Sciences, University of Exeter, Exeter, EX4 4QL, UK. .,Met Office, FitzRoy Road, Exeter, EX1 3PB, UK.
| | - Manoj Joshi
- School of Environmental Sciences, University of East Anglia, Norwich, NR4 7TJ, UK
| | - F Hugo Lambert
- College of Engineering, Mathematics and Physical Sciences, University of Exeter, Exeter, EX4 4QL, UK
| | - Nathan J Mayne
- College of Engineering, Mathematics and Physical Sciences, University of Exeter, Exeter, EX4 4QL, UK
| | - Duncan Lyster
- College of Engineering, Mathematics and Physical Sciences, University of Exeter, Exeter, EX4 4QL, UK
| | - James Manners
- College of Engineering, Mathematics and Physical Sciences, University of Exeter, Exeter, EX4 4QL, UK.,Met Office, FitzRoy Road, Exeter, EX1 3PB, UK
| | - Robert Ridgway
- College of Engineering, Mathematics and Physical Sciences, University of Exeter, Exeter, EX4 4QL, UK
| | - Krisztian Kohary
- College of Engineering, Mathematics and Physical Sciences, University of Exeter, Exeter, EX4 4QL, UK
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9
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Clouds will Likely Prevent the Detection of Water Vapor in JWST Transmission Spectra of Terrestrial Exoplanets. ACTA ACUST UNITED AC 2020. [DOI: 10.3847/2041-8213/ab6200] [Citation(s) in RCA: 33] [Impact Index Per Article: 8.3] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/18/2022]
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Impact of Clouds and Hazes on the Simulated JWST Transmission Spectra of Habitable Zone Planets in the TRAPPIST-1 System. ACTA ACUST UNITED AC 2019. [DOI: 10.3847/1538-4357/ab5862] [Citation(s) in RCA: 59] [Impact Index Per Article: 11.8] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/07/2023]
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11
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Habitability and Spectroscopic Observability of Warm M-dwarf Exoplanets Evaluated with a 3D Chemistry-Climate Model. ACTA ACUST UNITED AC 2019. [DOI: 10.3847/1538-4357/ab4f7e] [Citation(s) in RCA: 32] [Impact Index Per Article: 6.4] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/18/2022]
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12
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Del Genio AD, Kiang NY, Way MJ, Amundsen DS, Sohl LE, Fujii Y, Chandler M, Aleinov I, Colose CM, Guzewich SD, Kelley M. Albedos, Equilibrium Temperatures, and Surface Temperatures of Habitable Planets. THE ASTROPHYSICAL JOURNAL 2019; 884:75. [PMID: 33100349 PMCID: PMC7580787 DOI: 10.3847/1538-4357/ab3be8] [Citation(s) in RCA: 10] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 11/18/2022]
Abstract
The potential habitability of known exoplanets is often categorized by a nominal equilibrium temperature assuming a Bond albedo of either ∼0.3, similar to Earth, or 0. As an indicator of habitability, this leaves much to be desired, because albedos of other planets can be very different, and because surface temperature exceeds equilibrium temperature due to the atmospheric greenhouse effect. We use an ensemble of general circulation model simulations to show that for a range of habitable planets, much of the variability of Bond albedo, equilibrium temperature and even surface temperature can be predicted with useful accuracy from incident stellar flux and stellar temperature, two known parameters for every confirmed exoplanet. Earth's Bond albedo is near the minimum possible for habitable planets orbiting G stars, because of increasing contributions from clouds and sea ice/snow at higher and lower instellations, respectively. For habitable M star planets, Bond albedo is usually lower than Earth's because of near-IR H2O absorption, except at high instellation where clouds are important. We apply relationships derived from this behavior to several known exoplanets to derive zeroth-order estimates of their potential habitability. More expansive multivariate statistical models that include currently non-observable parameters show that greenhouse gas variations produce significant variance in albedo and surface temperature, while increasing length of day and land fraction decrease surface temperature; insights for other parameters are limited by our sampling. We discuss how emerging information from global climate models might resolve some degeneracies and help focus scarce observing resources on the most promising planets.
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Affiliation(s)
- Anthony D Del Genio
- NASA Goddard Institute for Space Studies, 2880 Broadway, New York, NY 10025, USA
| | - Nancy Y Kiang
- NASA Goddard Institute for Space Studies, 2880 Broadway, New York, NY 10025, USA
| | - Michael J Way
- NASA Goddard Institute for Space Studies, 2880 Broadway, New York, NY 10025, USA
| | - David S Amundsen
- NASA Goddard Institute for Space Studies, 2880 Broadway, New York, NY 10025, USA
- Department of Applied Physics and Applied Mathematics, Columbia University, New York, NY 10027, USA
| | - Linda E Sohl
- NASA Goddard Institute for Space Studies, 2880 Broadway, New York, NY 10025, USA
- Center for Climate Systems Research, Columbia University, New York, NY 10027, USA
| | - Yuka Fujii
- Earth-Life Science Institute, Tokyo Institute of Technology, Ookayama, Meguro, Tokyo 152-8550, Japan
| | - Mark Chandler
- NASA Goddard Institute for Space Studies, 2880 Broadway, New York, NY 10025, USA
- Center for Climate Systems Research, Columbia University, New York, NY 10027, USA
| | - Igor Aleinov
- NASA Goddard Institute for Space Studies, 2880 Broadway, New York, NY 10025, USA
- Center for Climate Systems Research, Columbia University, New York, NY 10027, USA
| | - Christopher M Colose
- NASA Postdoctoral Program, Goddard Institute for Space Studies, New York, NY 10025, USA
| | | | - Maxwell Kelley
- NASA Goddard Institute for Space Studies, 2880 Broadway, New York, NY 10025, USA
- SciSpace LLC, 2880 Broadway, New York, NY 10025, USA
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14
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Ocean Dynamics and the Inner Edge of the Habitable Zone for Tidally Locked Terrestrial Planets. ACTA ACUST UNITED AC 2019. [DOI: 10.3847/1538-4357/aaf1a8] [Citation(s) in RCA: 44] [Impact Index Per Article: 8.8] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/18/2022]
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