cometadata/datacite-titles-descriptions-related-identifiers huggingface dataset:
DOI: 10.48577/jpl.qqpn7w
title: A Statistical Estimation of the Occurrence of Extraterrestrial Intelligence in the Milky Way Galaxy

description: In the field of Astrobiology, the precise location, prevalence and age of potential extraterrestrial intelligence (ETI) have not been explicitly explored. Here, we address these inquiries using an empirical galactic simulation model to analyze the spatial-temporal variations and the prevalence of potential ETI within the Galaxy. This model estimates the occurrence of ETI, providing guidance on where to look for intelligent life in the Search for ETI (SETI) with a set of criteria, including well-established astrophysical properties of the Milky Way. Further, typically overlooked factors such as the process of abiogenesis, different evolutionary timescales and potential self-annihilation are incorporated to explore the growth propensity of ETI. We examine three major parameters: 1) the likelihood rate of abiogenesis (λA); 2) evolutionary timescales (Tevo); and 3) probability of self-annihilation of complex life (Pann). We found Pann to be the most influential parameter determining the quantity and age of galactic intelligent life. Our model simulation also identified a peak location for ETI at an annular region approximately 4 kpc from the Galactic center around 8 billion years (Gyrs), with complex life decreasing temporally and spatially from the peak point, asserting a high likelihood of intelligent life in the galactic inner disk. The simulated age distributions also suggest that most of the intelligent life in our galaxy are young, thus making observation or detection difficult.
DOI: 10.48577/jpl.fd3khw
title: The Dense Warm Ionized Medium in the Inner Galaxy

description: Context. Ionized interstellar gas is an important component of the interstellar medium and its lifecycle. The recent evidence for awidely distributed highly ionized warm interstellar gas with density intermediate between the warm ionized medium (WIM) andcompact Hii regions suggests that there is a major gap in our understanding of the interstellar gas.Aims. To investigate the properties of the dense warm ionized medium in the Milky Way using spectrally resolved SOFIA GREAT[N ii] 205 m fine-structure lines and Green Bank Telescope hydrogen radio recombination lines (RRL) data, supplemented by spectrallyunresolved Herschel PACS [N ii] 122m data, and spectrally resolved 12CO.Methods.We observed eight lines of sight LOS in the 20 &lt; l &lt; 30 region in the Galactic plane.We analyzed spectrally resolved linesof [N ii] at 205 m and RRL observations, along with the spectrally unresolved Herschel PACS 122 m emission, using excitation andradiative transfer models to determine the physical parameters of the dense warm ionized medium.We derive the kinetic temperature,and thermal and turbulent velocity dispersions from the [N ii] and RRL linewidths.Results. The regions with [N ii] 205 m emission are characterized by electron densities, n(e) 10 to 35 cm􀀀3, temperatures in therange 3400 to 8500 K, and nitrogen column densities, N(N+) 71016 to 31017 cm􀀀2. The ionized hydrogen column densitiesrange from 61020 to 1.71021 cm􀀀2 and the fractional nitrogen ion abundance, x(N+) 1.110􀀀4 to 3.010􀀀4, implying an enhancednitrogen abundance at a distance 4.3 kpc from the Galactic Center. The [N ii] 205 m emission lines coincide with CO emission,although often with an oset in velocity, which suggests that the dense warm ionized gas is located in, or near, star-forming regions,which themselves are associated with molecular gas.Conclusions. These dense ionized regions are found to contribute & 50% of the observed [C ii] intensity along these lines of sight.The kinetic temperatures we derive are too low to explain the presence of N+ resulting from electron collisional ionization and/orproton charge transfer of atomic nitrogen. Rather, these regions most likely are ionized by extreme ultraviolet (EUV) radiation fromnearby star-forming regions or as a result of EUV leakage through a clumpy and porous interstellar medium.
DOI: 10.48577/jpl.xdsccg
title: Interstellar Cloud Conditions Based on 63μm [OI] Emission and Absorption in W3

description: We investigate the origin of self-absorption in [O I] 63 μm line emission, which is very clearly seen in approximately half of the 12 Galactic giant molecular cloud (GMC)/H II regions observed. For this study, we observed velocity-resolved spectra of photon-dominated region (PDR) and H II region tracers, the [O I] 63 μm, [N II] 205 μm, and CO J = 5–4 and 8–7 lines, with the upGREAT instrument in the 4GREAT configuration on the NASA/DLR Stratospheric Observatory For Infrared Astronomy (SOFIA). To probe the origin of the [O I] absorption and line shape and what they tell us about the physical conditions, we focus on the W3 region, for which we obtained data for eight positions along a line near the H II region W3 A. We derive the foreground column density of low-excitation atomic oxygen to be in the range 2–7 × 1018 - cm 2. At the position of strongest [O I] emission and greatest absorbing column density, 24% of the oxygen in the PDR is in the form of lowexcitation atomic oxygen. We employ the Meudon PDR code to study the chemical and thermal structure of the PDR and to understand the large column density of neutral oxygen throughout the PDR. The reduction in the integrated intensity of the [O I] 63 μm emission is a factor of ;2–4 in directions with strong [O I] emission. The results from our sample, if general, would significantly impact the use of the [O I] 63 μm line as a tracer of massive star formation and could play a significant role in explaining the “63 μm [O I] deficit” seen in very luminous extragalactic sources.
DOI: 10.48577/jpl.xi0nvu
title: Probing Cosmic Reionization and Molecular Gas Growth with TIME

description: Line intensity mapping (LIM) provides a unique and powerful means to probe cosmic structures by measuring the aggregate line emission from all galaxies across redshift. The method is complementary to conventional galaxy redshift surveys that are object-based and demand exquisite point-source sensitivity. The Tomographic Ionized-carbon Mapping Experiment (TIME) will measure the star formation rate (SFR) during cosmic reionization by observing the redshifted [\ion{C}{ii}] 158\,$\mu$m line ($6 \la z \la 9$) in the LIM regime. TIME will simultaneously study the abundance of molecular gas during the era of peak star formation by observing the rotational CO lines emitted by galaxies at $0.5 \la z \la 2$. We present the modeling framework that predicts the constraining power of TIME on a number of observables, including the line luminosity function, and the auto- and cross-correlation power spectra, including synergies with external galaxy tracers. Based on an optimized survey strategy and fiducial model parameters informed by existing observations, we forecast constraints on physical quantities relevant to reionization and galaxy evolution, such as the escape fraction of ionizing photons during reionization, the faint-end slope of the galaxy luminosity function at high redshift, and the cosmic molecular gas density at cosmic noon. We discuss how these constraints can advance our understanding of cosmological galaxy evolution at the two distinct cosmic epochs for TIME, starting in 2021, and how they could be improved in future phases of the experiment.
DOI: 10.48577/jpl.rnfqap
title: ALMA Survey of Orion Planck Galactic Cold Clumps (ALMASOP): Detection of extremely high density compact structure of prestellar cores and multiple substructures within

description: Prestellar cores are self-gravitating dense and cold structures within molecular clouds where future stars are born. They are expected, at the stage of transitioning to the protostellar phase, to harbor centrally concentrateddense (sub)structures that will seed the formation of a new star or the binary/multiple stellar systems. Characterizing this critical stage of evolution is key to our understanding of star formation. In this work, we report thedetection of high density (sub)structures on the thousand-au scale in a sample of dense prestellar cores. Throughour recent ALMA observations towards the Orion molecular cloud, we have found five extremely dense prestellar cores, which have centrally concentrated regions 2000 au in size, and several 107 cm􀀀3 in average density. Masses of these centrally dense regions are in the range of 0.30 to 6.89 M. For the first time, our higher resolutionobservations (0.800 320 au) further reveal that one of the cores shows clear signatures of fragmentation;such individual substructures/fragments have sizes of 800 -1700 au, masses of 0.08 to 0.84 M, densities of2 􀀀 8 107 cm􀀀3, and separations of 1200 au. The substructures are massive enough (& 0:1 M) to formyoung stellar objects and are likely examples of the earliest stage of stellar embryos which can lead to widely ( 1200 au) separated multiple systems.
DOI: 10.48577/jpl.vlhq0i
title: Validation of SAGE III/ISS solar water vapor data with correlative satellite and balloon-borne measurements

description: Since June 2017, the Stratospheric Aerosol and Gas Experiment III instrument on the International Space Station (SAGE III/ISS) has been providing vertical profiles of upper tropospheric to stratospheric water vapor (WV) retrieved from solar occultation transmission measurements. The goal of this paper is to evaluate the publicly released SAGE III/ISS beta version 5.1 WV retrieval through intercomparison with independent satellite- and balloon-based measurements, and to present recommendations for SAGE III/ISS data quality screening criteria. Overall, we find that SAGE III/ISS provides high quality water vapor measurements. Low quality profiles are predominately due to retrieval instabilities in the upper stratosphere that cause step-like changes in the profile, and aerosol/cloud-related interferences (below ~20 km). Above 35 km, the retrieved uncertainty and noise in the data rapidly grow with increasing altitude due to relatively low extinction signal from water vapor. Below the tropopause, retrieved uncertainty increases with decreasing altitude due to enhanced molecular scattering and aerosol extinction. After screening low-quality data using the procedures described herein, SAGE III/ISS WV is shown to be in good agreement with independent satellite and balloon-based measurements. From 20 – 40 km, SAGE III/ISS WV v5.1 data exhibit a bias of 0.0 to -0.5 ppmv (~10 %) relative to the independent data, depending on the instrument and altitude. Despite its status as a beta version, the level of SAGE III/ISS WV agreement with independent data is similar to previous SAGE instruments, and therefore the data are suitable for scientific studies of stratospheric water vapor.
DOI: 10.48577/jpl.wkfaw1
title: When image correlation is needed: unravelling the complex dynamics of a slow-moving landslide in the tropics with dense radar and optical time series.

description: Slow-moving landslides exhibit persistent but non-uniform motion at low rates which makes them25 exceptional natural laboratories to study the mechanisms that control the dynamics of unstable26 hillslopes. Here we leverage 4.5+ years of satellite-based radar and optical remote sensing data to27 quantify the kinematics of a slow-moving landslide in the tropical rural environment of the Kivu Rift,28 with unprecedented high spatial and temporal resolution. We measure landslide motion using sub29pixel image correlation methods and invert these data into dense time series that capture weekly to30 multi-year changes in landslide kinematics. We cross-validate and compare our satellite-based results31 with very-high-resolution Unoccupied Aircraft System topographic datasets, and explore how rainfall,32 simulated pore-water pressure, and nearby earthquakes control the overall landslide behaviour. The33 landslide exhibited seasonal and multi-year velocity variations that varied across the landslide34 kinematic units. While rainfall-induced changes in pore-water pressure exerts a primary control on35 the landslide motion, these alone cannot explain the observed variability in landslide behaviour. We36 suggest instead that the observed landslide kinematics result from internal landslide dynamics, such37 as extension, compression, material redistribution, and interactions within and between kinematic38 units. Our study provides, a rare, detailed overview of the deformation pattern of a landslide located39 in a tropical environment. In addition, our work highlights the viability of sub-pixel image correlation40 with long time series of radar-amplitude data to quantify surface deformation in tropical41 environments where optical data is limited by persistent cloud cover and emphasize the importance42 of exploiting synergies between multiple types of data to capture the complex kinematic pattern of43 landslides.
DOI: 10.48577/jpl.5zxsjo
title: Study of Antarctic blowing snow storms using MODIS and CALIOP observations with a machine learning model

description: As a common phenomenon over Antarctica, blowing snow (BLSN), especially the large BLSN storms, play an important role in the Antarctic surface mass balance, radiation budget and planetary boundary processes. This paper presents the work on BLSN storm identification and analysis with observations from the Moderate Resolution Imaging Spectroradiometer (MODIS) onboard the Aqua satellite. Spectral analysis shows that BLSN identification is feasible with MODIS daytime data. A random forest machine learning model is developed and observations from the Cloud-Aerosol Lidar with Orthogonal Polarization (CALIOP) are used for training. Model performance results show that machine-learning based classification can achieve over 90% overall accuracy when classifying MODIS pixels into cloud, clear and BLSN categories. The machine learning model is applied to MODIS observations during the month of October 2009 for BLSN storm analysis. Results show that the size of BLSN storms has a large spectrum and can reach hundreds of thousands km2. The MODIS based BLSN storm frequency map extends the CALIPSO coverage limit from 820S to the South Pole. A BLSN storm belt, which extends from the South Pole region to the coastal area between 1300E and 1600E along the Transantarctic Mountains, provides a potential pathway of snow transport. These results are important in improving the understanding of BLSN impact on Antarctic surface mass balance and boundary layer processes.
DOI: 10.48577/jpl.aii8mc
title: Earth-like habitable environments in the subsurface of Mars

description: In Earth’s deep continental subsurface, where groundwaters are often isolated for &gt;10^6-10^9 years, energy released by radionuclides within rock produces oxidants and reductants that drive metabolisms of non-photosynthetic microorganisms. Similar processes could support past and present life in the martian subsurface. Sulfate-reducing microorganisms are common in Earth’s deep subsurface, often using hydrogen derived directly from radiolysis of pore water and sulfate derived from oxidation of rock-matrix-hosted sulfides by radiolytically-derived oxidants. Radiolysis thus produces redox energy to support a deep biosphere in groundwaters isolated from surface substrate input for millions to billions of years on Earth. Here we demonstrate that radiolysis by itself could produce sufficient redox energy to sustain a habitable environment in the subsurface of present-day Mars, one in which Earth-like microorganisms could survive wherever groundwater exists. We show that the source localities for many martian meteorites are capable of producing sufficient redox nutrients to sustain up to millions of sulfate-reducing microbial cells per kg rock via radiolysis alone, comparable to cell densities observed in many regions of Earth’s deep subsurface. Additionally, we calculate variability in supportable sulfate-reducing cell densities between the martian meteorite source regions. Our results demonstrate that martian subsurface groundwaters, where present, would largely be habitable by sulfate-reducing bacteria from a redox energy perspective via radiolysis alone.
DOI: 10.48577/jpl.pqcq5x
title: Forced Oscillatory Motion of Trapped Counter-Propagating Solitons

description: Both the group velocity and phase velocity of two co-propagating solitons can be synchronized by a Kerr-effect mediated interaction, causing what is known as soliton trapping. Trapping can occur when solitons travel through single-pass optical fibers or when circulating in optical resonators. Here, we demonstrate and theoretically explain a new manifestation of soliton trapping that occurs between counter-propagating solitons in microresonators. When counter-pumping a microresonator using slightly detuned pump frequencies and in the presence of backscattering, the group velocities of clockwise and counter-clockwise solitons undergo periodic modulation instead of being locked to a constant velocity. Upon emission from the microcavity, the solitons feature a relative oscillatory motion having an amplitude that can be larger than the soliton pulse width. This relative motion introduces a sideband fine structure into the optical spectrum of the counter-propagating solitons. Our results highlight the significance of coherent pumping in determining soliton dynamics within microresonators and add a new dimension to the physics of soliton trapping.
DOI: 10.48577/jpl.pucvsj
title: Cloudy atmospheres on directly imaged exoplanets: the need for accurate particulate representation in photopolarimetric simulations

description: Missions like the upcoming Roman Space Telescope and its follow-on missions, Habitable Exoplanet Observatory (HabEx) and the Large UV/Optical/IR Surveyor (LUVOIR), will provide direct imaging observations of stellar light reflected by exoplanets with successively closer orbits. The synergistic use of ground-based polarimeters like Gemini Planet Imager and Very Large Telescope/Spectro-Polarimetric High-contrast Exoplanet Research instrument (SPHERE) would allow us to characterize cloudy exoplanet atmospheres using spectropolarimetric direct imaging. We present an extension of our semianalytic 3D radiative transfer modeling framework for brown dwarfs to include stellar light reflected by exoplanets with cloudy atmospheres. Using Mie theory to compute scattering by cloud and haze consisting of spherical particles, we show that the currently widespread use of approximations like the scalar Two-Term Henyey–Greenstein or the vector Henyey–Greenstein Rayleigh (HGR) composite result in a blurring of the phase-dependent features of exoplanet lightcurves, causing a 10%–39% loss of sensitivity to atmospheric parameters in an average measurement for signal-to-noise ratios (S/Ns) between 5 and 500. The HGR approximation creates the misleading impression that clouds are as polarizing as Rayleigh scatterers, regardless of their droplet size. This not only causes significant errors in the scientific interpretation of polarimetric measurements, but also results in a negligible sensitivity of HGR simulations to polarization measurements at the S/Ns considered, whereas Mie simulations show a 10%–30% gain in parametric sensitivity through the addition of polarimetry.
DOI: 10.48577/jpl.ghay3r
title: Inferring Planetary Complexity using Epsilon Machines: A Novel Approach to Agnostic Biosignatures

description: We present a new approach to exoplanet assessment using techniques from complexity science. The majority of life detection schemes rely upon biochemical signatures and planetary context. However, it is increasingly recognized that extraterrestrial life could be very different to life on Earth. Therefore, we explore a novel, agnostic approach that focusses on temporal variability of light reflected or emitted by a planet, and the hypothesis that the presence of life correlates with complexity. We use a technique known as epsilon machine reconstruction to compute the ‘statistical complexity’, a measure of the minimal model size for time series data. We show that statistical complexity is an effective measure of the complexity of planetary features. Increasing levels of qualitative planetary complexity correlate with increases in the linear sum of statistical complexity and Shannon entropy rate, demonstrating that our approach can identify planets with the richest dynamics, and possibly even the presence of life.
DOI: 10.48577/jpl.qt3rc9
title: New fault slip distribution for the 2010 Mw 7.2 El Mayor Cucapah earthquake based on realistic 3D finite element inversions of coseismic displacements using space geodetic data

description: In this work we investigate the 4 April, 2010, Mw 7.2 El Mayor-Cucapah (EMC) earthquake. Existing studies modeled the EMC area as an elastic half-space in a homogeneous or vertically layered structure, which, along with differences in data and inversion methodologies, led to considerable variability in the resultant fault slip models. To investigate the EMC earthquake more realistically, we first examine how published coseismic fault slip models have approached the problem and what are their findings, then we select the optimal geometry and slip of one most recent and comprehensive coseismic fault slip model, obtained through analytical inversions, and adapt them in a three-dimensional finite element numerical environment where we assess the effectsof topography and material heterogeneities. Numerically optimized slip models are obtained viajoint inversion of GPS, interferometric synthetic aperture radar and subpixel offset datasets. We find the effect of topography to be negligible while the inclusion of material heterogeneities enhances the slip at depth, as might be expected where the medium has higher rigidity, and better fits the displacements at both near and far field, especially around the Salton Sea area. The match with geodetic data is significantly improved when the fault slip is increased at the fault planes close to the epicenter and deeper at the southernmost plane, with respect to the slip of the chosen analytical model. Our findings suggest that this earthquake was associated with a higher and more spatially concentrated slip than previously thought implying a greater stress drop at depth.
DOI: 10.48577/jpl.tphnnq
title: The NANOGrav 12.5-Year Data Set: Monitoring Interstellar Scattering Delays

description: We extract interstellar scintillation parameters for pulsars observed by the NANOGrav radio pulsar timingprogram. Dynamic spectra for the observing epochs of each pulsar were used to obtain estimates of scintillationtimescales, scintillation bandwidths, and the corresponding scattering delays using a stretching algorithm toaccount for frequency-dependent scaling. We were able to measure scintillation bandwidths for 28 pulsars at1500 MHz and 15 pulsars at 820 MHz. We examine scaling behavior for 17 pulsars and find indices rangingfrom -0:7 to -3:6. We were also able to measure scintillation timescales for six pulsars at 1500 MHz and sevenpulsars at 820 MHz. There is fair agreement between our scattering delay measurements and electron-densitymodel predictions for most pulsars, with some significant outliers likely resulting from frequency channel resolutionlimits outside of this range. We derive interstellar scattering-based transverse velocities assuming ascattering screen halfway between the pulsar and earth. We also calculate the location of the scattering screensassuming proper motion and interstellar scattering-derived transverse velocities are equal. We find no correlationsbetween variations in scattering delay and either variations in dispersion measure or flux density. For mostof the pulsars for which scattering delays were measurable, we find that time of arrival uncertainties for a given epoch are larger than our scattering delay measurements, indicating that variable scattering delays are currentlysubdominant in our overall noise budget but are important for achieving precisions of tens of ns or less.