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persistent episodes of extreme weather in the northern hemisphere summer have been shown to be associated with the presence of high-amplitude quasi-stationary atmospheric rossby waves within a particular wavelength range (zonal wavenumber 6-8). the underlying mechanistic relationship involves the phenomenon of quasi-resonant amplification (qra) of synoptic-scale waves with that wavenumber range becoming trapped within an effective mid-latitude atmospheric waveguide. recent work suggests an increase in recent decades in the occurrence of qra-favorable conditions and associated extreme weather, possibly linked to amplified arctic warming and thus a climate change influence. here, we isolate a specific fingerprint in the zonal mean surface temperature profile that is associated with qra-favorable conditions. state-of-the-art (“cmip5”) historical climate model simulations subject to anthropogenic forcing display an increase in the projection of this fingerprint that is mirrored in multiple observational surface temperature datasets. both the models and observations suggest this signal has only recently emerged from the background noise of natural variability. | influence of anthropogenic climate change on planetary wave resonance and extreme weather events |
reconstructing the degree of warming during geological periods of elevated co2 provides a way of testing our understanding of the earth system and the accuracy of climate models. we present accurate estimates of tropical sea-surface temperatures (sst) and seawater chemistry during the eocene (56-34 ma before present, co2 >560 ppm). this latter dataset enables us to reinterpret a large amount of existing proxy data. we find that tropical sst are characterized by a modest warming in response to co2. coupling these data to a conservative estimate of high-latitude warming demonstrates that most climate simulations do not capture the degree of eocene polar amplification. | eocene greenhouse climate revealed by coupled clumped isotope-mg/ca thermometry |
in recent years, severe haze events often occurred in china, causing serious environmental problems. the mechanisms responsible for the haze formation, however, are still not well understood, hindering the forecast and mitigation of haze pollution. our study of the 2012-13 winter haze events in beijing shows that atmospheric water vapour plays a critical role in enhancing the heavy haze events. under weak solar radiation and stagnant moist meteorological conditions in winter, air pollutants and water vapour accumulate in a shallow planetary boundary layer (pbl). a positive feedback cycle is triggered resulting in the formation of heavy haze: (1) the dispersal of water vapour is constrained by the shallow pbl, leading to an increase in relative humidity (rh); (2) the high rh induces an increase of aerosol particle size by enhanced hygroscopic growth and multiphase reactions to increase particle size and mass, which results in (3) further dimming and decrease of pbl height, and thus further depressing of aerosol and water vapour in a very shallow pbl. this positive feedback constitutes a self-amplification mechanism in which water vapour leads to a trapping and massive increase of particulate matter in the near-surface air to which people are exposed with severe health hazards. | severe pollution in china amplified by atmospheric moisture |
a spherical harmonic model of the magnetic field of jupiter is obtained from vector magnetic field observations acquired by the juno spacecraft during its first nine polar orbits about the planet. observations acquired during eight of these orbits provide the first truly global coverage of jupiter's magnetic field with a coarse longitudinal separation of 45° between perijoves. the magnetic field is represented with a degree 20 spherical harmonic model for the planetary ("internal") field, combined with a simple model of the magnetodisc for the field ("external") due to distributed magnetospheric currents. partial solution of the underdetermined inverse problem using generalized inverse techniques yields a model ("juno reference model through perijove 9") of the planetary magnetic field with spherical harmonic coefficients well determined through degree and order 10, providing the first detailed view of a planetary dynamo beyond earth. | a new model of jupiter's magnetic field from juno's first nine orbits |
in the past few years, significant advances have been made in understanding the distributions of exoplanet populations and the architecture of planetary systems. we review the recent progress of planet statistics, with a focus on the inner ≲1-au region of planetary systems that has been fairly thoroughly surveyed by the kepler mission. we also discuss the theoretical implications of these statistical results for planet formation and dynamical evolution. | exoplanet statistics and theoretical implications |
recent analyses have shown that distant orbits within the scattered disk population of the kuiper belt exhibit an unexpected clustering in their respective arguments of perihelion. while several hypotheses have been put forward to explain this alignment, to date, a theoretical model that can successfully account for the observations remains elusive. in this work we show that the orbits of distant kuiper belt objects (kbos) cluster not only in argument of perihelion, but also in physical space. we demonstrate that the perihelion positions and orbital planes of the objects are tightly confined and that such a clustering has only a probability of 0.007% to be due to chance, thus requiring a dynamical origin. we find that the observed orbital alignment can be maintained by a distant eccentric planet with mass ≳10 m ⊕ whose orbit lies in approximately the same plane as those of the distant kbos, but whose perihelion is 180° away from the perihelia of the minor bodies. in addition to accounting for the observed orbital alignment, the existence of such a planet naturally explains the presence of high-perihelion sedna-like objects, as well as the known collection of high semimajor axis objects with inclinations between 60° and 150° whose origin was previously unclear. continued analysis of both distant and highly inclined outer solar system objects provides the opportunity for testing our hypothesis as well as further constraining the orbital elements and mass of the distant planet. | evidence for a distant giant planet in the solar system |
the earth is the only known planet where plate tectonics is active, and different studies have concluded that plate tectonics commenced at times from the early hadean to 700 ma. many arguments rely on proxies established on recent examples, such as paired metamorphic belts and magma geochemistry, and it can be difficult to establish the significance of such proxies in a hotter, older earth. there is the question of scale, and how the results of different case studies are put in a wider global context. we explore approaches that indicate when plate tectonics became the dominant global regime, in part by evaluating when the effects of plate tectonics were established globally, rather than the first sign of its existence regionally. the geological record reflects when the continental crust became rigid enough to facilitate plate tectonics, through the onset of dyke swarms and large sedimentary basins, from relatively high-pressure metamorphism and evidence for crustal thickening. paired metamorphic belts are a feature of destructive plate margins over the last 700 myr, but it is difficult to establish whether metamorphic events are associated spatially as well as temporally in older terrains. from 3.8-2.7 ga, suites of high th/nb (subduction-related on the modern earth) and low th/nb (non-subduction-related) magmas were generated at similar times in different locations, and there is a striking link between the geochemistry and the regional tectonic style. archaean cratons stabilised at different times in different areas from 3.1-2.5 ga, and the composition of juvenile continental crust changed from mafic to more intermediate compositions. xenon isotope data indicate that there was little recycling of volatiles before 3 ga. evidence for the juxtaposition of continental fragments back to ~2.8 ga, each with disparate histories highlights that fragments of crust were moving around laterally on the earth. the reduction in crustal growth at ~ 3 ga is attributed to an increase in the rates at which differentiated continental crust was destroyed, and that coupled with the other changes at the end of the archaean are taken to reflect the onset of plate tectonics as the dominant global regime. | frontiers -petrology/geochemistry and the onset of plate tectonics the evolution of the continental crust, and the onset of plate tectonics |
matter at extreme temperatures and pressures-commonly known as warm dense matter (wdm)-is ubiquitous throughout our universe and occurs in astrophysical objects such as giant planet interiors and brown dwarfs. moreover, wdm is very important for technological applications such as inertial confinement fusion and is realized in the laboratory using different techniques. a particularly important property for the understanding of wdm is given by its electronic density response to an external perturbation. such response properties are probed in x-ray thomson scattering (xrts) experiments and are central for the theoretical description of wdm. in this work, we give an overview of a number of recent developments in this field. to this end, we summarize the relevant theoretical background, covering the regime of linear response theory and nonlinear effects, the fully dynamic response and its static, time-independent limit, and the connection between density response properties and imaginary-time correlation functions (itcf). in addition, we introduce the most important numerical simulation techniques, including path-integral monte carlo simulations and different thermal density functional theory (dft) approaches. from a practical perspective, we present a variety of simulation results for different density response properties, covering the archetypal model of the uniform electron gas and realistic wdm systems such as hydrogen. moreover, we show how the concept of itcfs can be used to infer the temperature from xrts measurements of arbitrary complex systems without the need for any models or approximations. finally, we outline a strategy for future developments based on the close interplay between simulations and experiments. | electronic density response of warm dense matter |
plants are important in urban environments for removing pathogens and improving water quality. seagrass meadows are the most widespread coastal ecosystem on the planet. although these plants are known to be associated with natural biocide production, they have not been evaluated for their ability to remove microbiological contamination. using amplicon sequencing of the 16s ribosomal rna gene, we found that when seagrass meadows are present, there was a 50% reduction in the relative abundance of potential bacterial pathogens capable of causing disease in humans and marine organisms. moreover, field surveys of more than 8000 reef-building corals located adjacent to seagrass meadows showed twofold reductions in disease levels compared to corals at paired sites without adjacent seagrass meadows. these results highlight the importance of seagrass ecosystems to the health of humans and other organisms. | seagrass ecosystems reduce exposure to bacterial pathogens of humans, fishes, and invertebrates |
aerosols are common in the atmospheres of exoplanets across a wide swath of temperatures, masses and ages1-3. these aerosols strongly impact observations of transmitted, reflected and emitted light from exoplanets, obfuscating our understanding of exoplanet thermal structure and composition4-6. knowing the dominant aerosol composition would facilitate interpretations of exoplanet observations and theoretical understanding of their atmospheres. a variety of compositions have been proposed, including metal oxides and sulfides, iron, chromium, sulfur and hydrocarbons7-11. however, the relative contributions of these species to exoplanet aerosol opacity is unknown. here we show that the aerosol composition of giant exoplanets observed in transmission is dominated by silicates and hydrocarbons. by constraining an aerosol microphysics model with trends in giant exoplanet transmission spectra, we find that silicates dominate aerosol opacity above planetary equilibrium temperatures of 950 k due to low nucleation energy barriers and high elemental abundances, while hydrocarbon aerosols dominate below 950 k due to an increase in methane abundance. our results are robust to variations in planet gravity and atmospheric metallicity within the range of most giant transiting exoplanets. we predict that spectral signatures of condensed silicates in the mid-infrared are most prominent for hot (>1,600 k), low-gravity (<10 m s−2) objects. | aerosol composition of hot giant exoplanets dominated by silicates and hydrocarbon hazes |
iron formations (if) represent an iron-rich rock type that typifies many archaean and proterozoic supracrustal successions and are chemical archives of precambrian seawater chemistry and post-depositional iron cycling. given that if accumulated on the seafloor for over two billion years of earth's early history, changes in their chemical, mineralogical, and isotopic compositions offer a unique glimpse into environmental changes that took place on the evolving earth. perhaps one of the most significant events was the transition from an anoxic planet to one where oxygen was persistently present within the marine water column and atmosphere. linked to this progressive global oxygenation was the evolution of aerobic microbial metabolisms that fundamentally influenced continental weathering processes, the supply of nutrients to the oceans, and, ultimately, diversification of the biosphere and complex life forms. many of the key recent innovations in understanding if genesis are linked to geobiology, since biologically assisted fe(ii) oxidation, either directly through photoferrotrophy, or indirectly through oxygenic photosynthesis, provides a process for if deposition from mineral precursors. the abundance and isotope composition of fe(ii)-bearing minerals in if additionally suggests microbial fe(iii) reduction, a metabolism that is deeply rooted in the archaea and bacteria. linkages among geobiology, hydrothermal systems, and deposition of if have been traditionally overlooked, but now form a coherent model for this unique rock type. this paper reviews the defining features of if and their distribution through the neoarchaean and palaeoproterozoic. this paper is an update of previous reviews by bekker et al. (2010, 2014) that will improve the quantitative framework we use to interpret if deposition. in this work, we also discuss how recent discoveries have provided new insights into the processes underpinning the global rise in atmospheric oxygen and the geochemical evolution of the oceans. | iron formations: a global record of neoarchaean to palaeoproterozoic environmental history |
detecting ocean-floor seismic activity is crucial for our understanding of the interior structure and dynamic behavior of earth. however, 70% of the planet’s surface is covered by water, and seismometer coverage is limited to a handful of permanent ocean bottom stations. we show that existing telecommunication optical fiber cables can detect seismic events when combined with state-of-the-art frequency metrology techniques by using the fiber itself as the sensing element. we detected earthquakes over terrestrial and submarine links with lengths ranging from 75 to 535 kilometers and a geographical distance from the earthquake’s epicenter ranging from 25 to 18,500 kilometers. implementing a global seismic network for real-time detection of underwater earthquakes requires applying the proposed technique to the existing extensive submarine optical fiber network. | ultrastable laser interferometry for earthquake detection with terrestrial and submarine cables |
hydrogen is one of the possible alloying elements in the earth's core, but its siderophile (iron-loving) nature is debated. here we experimentally examined the partitioning of hydrogen between molten iron and silicate melt at 30-60 gigapascals and 3100-4600 kelvin. we find that hydrogen has a metal/silicate partition coefficient dh ≥ 29 and is therefore strongly siderophile at conditions of core formation. unless water was delivered only in the final stage of accretion, core formation scenarios suggest that 0.3-0.6 wt% h was incorporated into the core, leaving a relatively small residual h2o concentration in silicates. this amount of h explains 30-60% of the density deficit and sound velocity excess of the outer core relative to pure iron. our results also suggest that hydrogen may be an important constituent in the metallic cores of any terrestrial planet or moon having a mass in excess of ~10% of the earth. | experimental evidence for hydrogen incorporation into earth's core |
topology sheds new light on the emergence of unidirectional edge waves in a variety of physical systems, from condensed matter to artificial lattices. waves observed in geophysical flows are also robust to perturbations, which suggests a role for topology. we show a topological origin for two well-known equatorially trapped waves, the kelvin and yanai modes, owing to the breaking of time-reversal symmetry by earth’s rotation. the nontrivial structure of the bulk poincaré wave modes encoded through the first chern number of value 2 guarantees the existence of these waves. this invariant demonstrates that ocean and atmospheric waves share fundamental properties with topological insulators and that topology plays an unexpected role in earth’s climate system. | topological origin of equatorial waves |
despite the considerable reductions in primary and secondary air pollutants in china, surface ozone levels have increased in recent years. we report a trend of 3.3 ± 4.7 μg.m-3 year-1 in the annual mean maximum daily average ozone over an 8-h period (mda8 ozone) across china between 2015 and 2019. leveraging the kolmogorov-zurbenko filter method, we find that meteorology enhanced the ozone levels in beijing-tianjin-hebei (bth), the yangtze river delta (yrd), and the pearl river delta (prd) while the reduction of solar radiation and the planetary boundary layer height accelerated ozone decreases in the sichuan basin (scb) after 2017. solar radiation and temperature increases, together with the reduction in sea level pressure, were the main contributors to enhance ozone in the yrd. they also contributed to 32% of ozone increases in bth. weaker meridional wind, lower relative humidity, and higher temperature escalated ozone enhancement in the prd between 2016 and 2018. regarding precursor emissions, no2 long-term components showed a noticeable decline in all regions after 2017, partially due to the introduction of the most current action plan to reduce air pollutants over china in 2018. in contrast, the satellite-retrieved data suggest that voc concentrations did not change substantially in target regions during the study period. after 2017, however, vocs slightly increased in bth, the yrd, and the prd, which might be driven by temperature enhancements. overall, the impact of meteorology on ozone variations was dominant in the yrd, the prd, and the scb from 2015 to 2019. precursor emissions, however, played a leading role in ozone enhancement over the bth. we also found that bth and the yrd were in a transitional ozone formation regime while the prd and the scb tended to be more nox-sensitive. | a comprehensive investigation of surface ozone pollution in china, 2015-2019: separating the contributions from meteorology and precursor emissions |
the double asteroid redirection test (dart) spacecraft successfully performed the first test of a kinetic impactor for asteroid deflection by impacting dimorphos, the secondary of near-earth binary asteroid (65803) didymos, and changing the orbital period of dimorphos. a change in orbital period of approximately 7 min was expected if the incident momentum from the dart spacecraft was directly transferred to the asteroid target in a perfectly inelastic collision1, but studies of the probable impact conditions and asteroid properties indicated that a considerable momentum enhancement (β) was possible2,3. in the years before impact, we used lightcurve observations to accurately determine the pre-impact orbit parameters of dimorphos with respect to didymos4-6. here we report the change in the orbital period of dimorphos as a result of the dart kinetic impact to be −33.0 ± 1.0 (3σ) min. using new earth-based lightcurve and radar observations, two independent approaches determined identical values for the change in the orbital period. this large orbit period change suggests that ejecta contributed a substantial amount of momentum to the asteroid beyond what the dart spacecraft carried. | orbital period change of dimorphos due to the dart kinetic impact |
global precipitation variations over the satellite era are reviewed using the global precipitation climatology project (gpcp) monthly, globally complete analyses, which integrate satellite and surface gauge information. mean planetary values are examined and compared, over ocean, with information from recent satellite programs and related estimates, with generally positive agreements, but with some indication of small underestimates for gpcp over the global ocean. variations during the satellite era in global precipitation are tied to enso events, with small increases during el ninos, and very noticeable decreases after major volcanic eruptions. no overall significant trend is noted in the global precipitation mean value, unlike that for surface temperature and atmospheric water vapor. however, there is a pattern of positive and negative trends across the planet with increases over tropical oceans and decreases over some middle latitude regions. these observed patterns are a result of a combination of inter-decadal variations and the effect of the global warming during the period. the results reviewed here indicate the value of such analyses as gpcp and the possible improvement in the information as the record lengthens and as new, more sophisticated and more accurate observations are included. | global precipitation: means, variations and trends during the satellite era (1979-2014) |
analysis suggests that to limit global temperature rise, we must slash emissions and invest now to protect, manage and restore ecosystems and land for the future. | nature-based solutions can help cool the planet — if we act now |
green water — terrestrial precipitation, evaporation and soil moisture — is fundamental to earth system dynamics and is now extensively perturbed by human pressures at continental to planetary scales. however, green water lacks explicit consideration in the existing planetary boundaries framework that demarcates a global safe operating space for humanity. in this perspective, we propose a green water planetary boundary and estimate its current status. the green water planetary boundary can be represented by the percentage of ice-free land area on which root-zone soil moisture deviates from holocene variability for any month of the year. provisional estimates of departures from holocene-like conditions, alongside evidence of widespread deterioration in earth system functioning, indicate that the green water planetary boundary is already transgressed. moving forward, research needs to address and account for the role of root-zone soil moisture for earth system resilience in view of ecohydrological, hydroclimatic and sociohydrological interactions. | a planetary boundary for green water |
total internal partition sums (tips) are reported for 166 isotopologues of 51 molecules important in planetary atmospheres. molecules 1 to 50 are taken from the hitran2016 list, and, in some cases, additional isotopologues are considered for some of the molecules. molecules 51-53 are c3h4, ch3, and cs2, respectively. tips are not reported for the o atom and cf4; thus, while there are 53 species in the list, data are reported for 51 molecules. the tips are determined by various methods from 1 k to a tmax that ensures the tips reported have converged. these data are provided with hitran2016 and a new version of the tips code is available in both fortran and python languages. | total internal partition sums for 166 isotopologues of 51 molecules important in planetary atmospheres: application to hitran2016 and beyond |
we present an approach for using machine learning to automatically discover the governing equations and unknown properties (in this case, masses) of real physical systems from observations. we train a 'graph neural network' to simulate the dynamics of our solar system's sun, planets, and large moons from 30 years of trajectory data. we then use symbolic regression to correctly infer an analytical expression for the force law implicitly learned by the neural network, which our results showed is equivalent to newton's law of gravitation. the key assumptions our method makes are translational and rotational equivariance, and newton's second and third laws of motion. it did not, however, require any assumptions about the masses of planets and moons or physical constants, but nonetheless, they, too, were accurately inferred with our method. naturally, the classical law of gravitation has been known since isaac newton, but our results demonstrate that our method can discover unknown laws and hidden properties from observed data. | rediscovering orbital mechanics with machine learning |
the earth formed by accretion of moon- to mars-size embryos coming from various heliocentric distances. the isotopic nature of these bodies is unknown. however, taking meteorites as a guide, most models assume that the earth must have formed from a heterogeneous assortment of embryos with distinct isotopic compositions. high-precision measurements, however, show that the earth, the moon and enstatite meteorites have almost indistinguishable isotopic compositions. models have been proposed that reconcile the earth-moon similarity with the inferred heterogeneous nature of earth-forming material, but these models either require specific geometries for the moon-forming impact or can explain only one aspect of the earth-moon similarity (that is, 17o). here i show that elements with distinct affinities for metal can be used to decipher the isotopic nature of the earth’s accreting material through time. i find that the mantle signatures of lithophile o, ca, ti and nd, moderately siderophile cr, ni and mo, and highly siderophile ru record different stages of the earth’s accretion; yet all those elements point to material that was isotopically most similar to enstatite meteorites. this isotopic similarity indicates that the material accreted by the earth always comprised a large fraction of enstatite-type impactors (about half were e-type in the first 60 per cent of the accretion and all of the impactors were e-type after that). accordingly, the giant impactor that formed the moon probably had an isotopic composition similar to that of the earth, hence relaxing the constraints on models of lunar formation. enstatite meteorites and the earth were formed from the same isotopic reservoir but they diverged in their chemical evolution owing to subsequent fractionation by nebular and planetary processes. | the isotopic nature of the earth’s accreting material through time |
the most abundant components of primitive meteorites (chondrites) are millimeter-sized glassy spherical chondrules formed by transient melting events in the solar protoplanetary disk. using pb-pb dates of 22 individual chondrules, we show that primary production of chondrules in the early solar system was restricted to the first million years after formation of the sun and that these existing chondrules were recycled for the remaining lifetime of the protoplanetary disk. this is consistent with a primary chondrule formation episode during the early high-mass accretion phase of the protoplanetary disk that transitions into a longer period of chondrule reworking. an abundance of chondrules at early times provides the precursor material required to drive the efficient and rapid formation of planetary objects via chondrule accretion. | early formation of planetary building blocks inferred from pb isotopic ages of chondrules |
the high-latitude regions of the northern hemisphere are a nexus for the interaction between land surface physical properties and their exchange of carbon and energy with the atmosphere. at these latitudes, two carbon pools of planetary significance - those of the permanently frozen soils (permafrost), and of the great expanse of boreal forest - are vulnerable to destabilization in the face of currently observed climatic warming, the speed and intensity of which are expected to increase with time. improved projections of future arctic and boreal ecosystem transformation require improved land surface models that integrate processes specific to these cold biomes. to this end, this study lays out relevant new parameterizations in the orchidee-mict land surface model. these describe the interactions between soil carbon, soil temperature and hydrology, and their resulting feedbacks on water and co2 fluxes, in addition to a recently developed fire module. outputs from orchidee-mict, when forced by two climate input datasets, are extensively evaluated against (i) temperature gradients between the atmosphere and deep soils, (ii) the hydrological components comprising the water balance of the largest high-latitude basins, and (iii) co2 flux and carbon stock observations. the model performance is good with respect to empirical data, despite a simulated excessive plant water stress and a positive land surface temperature bias. in addition, acute model sensitivity to the choice of input forcing data suggests that the calibration of model parameters is strongly forcing-dependent. overall, we suggest that this new model design is at the forefront of current efforts to reliably estimate future perturbations to the high-latitude terrestrial environment. | orchidee-mict (v8.4.1), a land surface model for the high latitudes: model description and validation |
the james webb space telescope (jwst) will offer the first opportunity to characterize terrestrial exoplanets with sufficient precision to identify high mean molecular weight atmospheres, and trappist-1's seven known transiting earth-sized planets are particularly favorable targets. to assist community preparations for jwst observations, we use simulations of plausible post-ocean-loss and habitable environments for the trappist-1 exoplanets, and test simulations of all bright object time-series spectroscopy modes and all mid-infrared instrument photometry filters to determine optimal observing strategies for atmospheric detection and characterization using both transmission and emission observations. we find that transmission spectroscopy with the near-infrared spectrograph prism is optimal for detecting terrestrial, co2-containing atmospheres, potentially in fewer than 10 transits for all seven trappist-1 planets, if they lack high-altitude aerosols. if the trappist-1 planets possess venus-like h2so4 aerosols, up to 12 times more transits may be required to detect an atmosphere. we present optimal instruments and observing modes for the detection of individual molecular species in a given terrestrial atmosphere and an observational strategy for discriminating between evolutionary states. we find that water may be prohibitively difficult to detect in both venus-like and habitable atmospheres, due to its presence lower in the atmosphere where transmission spectra are less sensitive. although the presence of biogenic o2 and o3 will be extremely challenging to detect, abiotically produced oxygen from past ocean loss may be detectable for all seven trappist-1 planets via o2-o2 collisionally induced absorption at 1.06 and 1.27 μm, or via nir o3 features for the outer three planets. our results constitute a suite of hypotheses on the nature and detectability of highly evolved terrestrial exoplanet atmospheres that may be tested with jwst. | the detectability and characterization of the trappist-1 exoplanet atmospheres with jwst |
the practical distinctions between asteroids and comets, viewed as products of accretion on either side of the snow line, are less clear-cut than previously understood. in this chapter, we discuss the numerous solar system populations which have physical and dynamical properties that conflict with any simple diagnosis of their nature and origin. studies of these so-called "continuum" or "transition objects", which include many of the most intriguing bodies in the solar system, have implications for a broad range of scientific topics from the demise of comets and the activation of asteroids to the production of interplanetary debris and the origin of the terrestrial planet volatiles. we present an overview of the current state of knowledge concerning the asteroid-comet continuum and discuss the numerous physical processes behind the activity shown by small bodies in the solar system. | the asteroid-comet continuum |
nitrogen availability is a pivotal control on terrestrial carbon sequestration and global climate change. historical and contemporary views assume that nitrogen enters earth’s land-surface ecosystems from the atmosphere. here we demonstrate that bedrock is a nitrogen source that rivals atmospheric nitrogen inputs across major sectors of the global terrestrial environment. evidence drawn from the planet’s nitrogen balance, geochemical proxies, and our spatial weathering model reveal that ~19 to 31 teragrams of nitrogen are mobilized from near-surface rocks annually. about 11 to 18 teragrams of this nitrogen are chemically weathered in situ, thereby increasing the unmanaged (preindustrial) terrestrial nitrogen balance from 8 to 26%. these findings provide a global perspective to reconcile earth’s nitrogen budget, with implications for nutrient-driven controls over the terrestrial carbon sink. | convergent evidence for widespread rock nitrogen sources in earth’s surface environment |
during the past three decades, the most rapid warming at the surface has occurred during the arctic winter. by analyzing daily era-interim data, it is found that the majority of the winter warming trend north of 70°n can be explained by the trend in the downward infrared radiation (ir). this downward ir trend can be attributed to an enhanced poleward flux of moisture and sensible heat into the arctic by poleward-propagating rossby waves, which increases the total column water and temperature within this region. this enhanced moisture flux is mostly due to changes in the planetary-scale atmospheric circulation rather than an increase in moisture in lower latitudes. the results of this study lead to the question of whether arctic amplification has mostly arisen through changes in the rossby wave response to greenhouse gas forcing and its impact on moisture transport into the arctic. | the role of downward infrared radiation in the recent arctic winter warming trend |
interplanetary coronal mass ejections (icmes) are large-scale heliospheric transients that originate from the sun. when an icme is sufficiently faster than the preceding solar wind, a shock wave develops ahead of the icme. the turbulent region between the shock and the icme is called the sheath region. icmes and their sheaths and shocks are all interesting structures from the fundamental plasma physics viewpoint. they are also key drivers of space weather disturbances in the heliosphere and planetary environments. icme-driven shock waves can accelerate charged particles to high energies. sheaths and icmes drive practically all intense geospace storms at the earth, and they can also affect dramatically the planetary radiation environments and atmospheres. this review focuses on the current understanding of observational signatures and properties of icmes and the associated sheath regions based on five decades of studies. in addition, we discuss modelling of icmes and many fundamental outstanding questions on their origin, evolution and effects, largely due to the limitations of single spacecraft observations of these macro-scale structures. we also present current understanding of space weather consequences of these large-scale solar wind structures, including effects at the other solar system planets and exoplanets. we specially emphasize the different origin, properties and consequences of the sheaths and icmes. | coronal mass ejections and their sheath regions in interplanetary space |
inside the epic quest to find life on the water-rich moons at the outer reaches of the solar systemwhere is the best place to find life beyond earth? we often look to mars as the most promising site in our solar system, but recent scientific missions have revealed that some of the most habitable real estate may actually lie farther away. beneath the frozen crusts of several of the small, ice-covered moons of jupiter and saturn lurk vast oceans that may have existed for as long as earth, and together may contain more than fifty times its total volume of liquid water. could there be organisms living in their depths? alien oceans reveals the science behind the thrilling quest to find out.kevin peter hand is one of today's leading nasa scientists, and his pioneering research has taken him on expeditions around the world. in this captivating account of scientific discovery, he brings together insights from planetary science, biology, and the adventures of scientists like himself to explain how we know that oceans exist within moons of the outer solar system, like europa, titan, and enceladus. he shows how the exploration of earth's oceans is informing our understanding of the potential habitability of these icy moons, and draws lessons from what we have learned about the origins of life on our own planet to consider how life could arise on these distant worlds.alien oceans describes what lies ahead in our search for life in our solar system and beyond, setting the stage for the transformative discoveries that may await us. | alien oceans. the search for life in the depths of space |
for 2 years, the insight lander has been recording seismic data on mars that are vital to constrain the structure and thermochemical state of the planet. we used observations of direct (p and s) and surface-reflected (pp, ppp, ss, and sss) body-wave phases from eight low-frequency marsquakes to constrain the interior structure to a depth of 800 kilometers. we found a structure compatible with a low-velocity zone associated with a thermal lithosphere much thicker than on earth that is possibly related to a weak s-wave shadow zone at teleseismic distances. by combining the seismic constraints with geodynamic models, we predict that, relative to the primitive mantle, the crust is more enriched in heat-producing elements by a factor of 13 to 20. this enrichment is greater than suggested by gamma-ray surface mapping and has a moderate-to-elevated surface heat flow. | upper mantle structure of mars from insight seismic data |
the planetary boundary layer (pbl) governs the vertical transport of mass, momentum, and moisture between the surface and the free atmosphere, and thus the determination of pbl height (blh) is recognized as crucial for air quality, weather, and climate analysis. although reanalysis products can provide important insight into the global view of blh in a seamless way, the blh observed in situ on a global scale remains poorly understood due to the lack of high-resolution (1 or 2 s) radiosonde measurements. the present study attempts to establish a near-global blh climatology at synoptic times (00:00 and 12:00 utc) and in the daytime using high-resolution radiosonde measurements over 300 radiosonde sites worldwide for the period 2012 to 2019, which is then compared against the blhs obtained from four reanalysis datasets, including era5, merra-2, jra-55, and ncep-2. the variations in daytime blh exhibit large spatial and temporal dependence, and as a result the blh maxima are generally discerned over the regions such as the western united states and western china, in which the balloon launch times mostly correspond to the afternoon. the diurnal variations in blh are revealed with a peak at 17:00 local solar time (lst). the most promising reanalysis product is era5, which underestimates blh by around 130 m as compared to radiosondes released during daytime. in addition, merra-2 is a well-established product and has an underestimation of around 160 m. jra-55 and ncep-2 might produce considerable additional uncertainties, with a much larger underestimation of up to 400 m. the largest bias in the reanalysis data appears over the western united states and western china, and it might be attributed to the maximal blh in the afternoon when the pbl has risen. statistical analyses further indicate that the biases of reanalysis blh products are positively associated with orographic complexity, as well as the occurrence of static instability. to our best knowledge, this study presents the first near-global view of high-resolution radiosonde-derived boundary layer height and provides a quantitative assessment of the four frequently used reanalysis products. | investigation of near-global daytime boundary layer height using high-resolution radiosondes: first results and comparison with era5, merra-2, jra-55, and ncep-2 reanalyses |
szent-győrgi called water the "matrix of life" and claimed that there was no life without it. this statement is true, as far as we know, on our planet, but it is not clear whether it must hold throughout the cosmos. to evaluate that question requires a close consideration of the many varied and subtle roles that water plays in living cells—a consideration that must be free of both an assumed essentialism that gives water an almost mystical life-giving agency and a traditional tendency to see it as a merely passive solvent. water is a participant in the "life of the cell," and here i describe some of the features of that active agency. water's value for molecular biology comes from both the structural and dynamic characteristics of its status as a complex, structured liquid as well as its nature as a polar, protic, and amphoteric reagent. any discussion of water as life's matrix must, however, begin with an acknowledgment that our understanding of it as both a liquid and a solvent is still incomplete. | water is an active matrix of life for cell and molecular biology |
bathymetry mapping forms the basis of understanding physical, economic, and ecological processes in the vastly biodiverse coastal fringes of our planet which are subjected to constant anthropogenic pressure. here, we pair recent advances in cloud computing using the geospatial platform of the google earth engine (gee) with optical remote sensing technology using the open sentinel-2 archive, obtaining low-cost in situ collected data to develop an empirical preprocessing workflow for estimating satellite-derived bathymetry (sdb). the workflow implements widely used and well-established algorithms, including cloud, atmospheric, and sun glint corrections, image composition and radiometric normalisation to address intra- and inter-image interferences before training, and validation of four sdb algorithms in three sites of the aegean sea in the eastern mediterranean. best accuracy values for training and validation were r2 = 0.79, rmse = 1.39 m, and r2 = 0.9, rmse = 1.67 m, respectively. the increased accuracy highlights the importance of the radiometric normalisation given spatially independent calibration and validation datasets. spatial error maps reveal over-prediction over low-reflectance and very shallow seabeds, and under-prediction over high-reflectance (<6 m) and optically deep bottoms (>17 m). we provide access to the developed code, allowing users to map bathymetry by customising the time range based on the field data acquisition dates and the optical conditions of their study area. | estimating satellite-derived bathymetry (sdb) with the google earth engine and sentinel-2 |
chondrules are millimeter-sized spherules that dominate primitive meteorites (chondrites) originating from the asteroid belt. the incorporation of chondrules into asteroidal bodies must be an important step in planet formation, but the mechanism is not understood. we show that the main growth of asteroids can result from gas drag-assisted accretion of chondrules. the largest planetesimals of a population with a characteristic radius of 100 km undergo runaway accretion of chondrules within ~3 my, forming planetary embryos up to mars's size along with smaller asteroids whose size distribution matches that of main belt asteroids. the aerodynamical accretion leads to size sorting of chondrules consistent with chondrites. accretion of millimeter-sized chondrules and ice particles drives the growth of planetesimals beyond the ice line as well, but the growth time increases above the disc lifetime outside of 25 au. the contribution of direct planetesimal accretion to the growth of both asteroids and kuiper belt objects is minor. in contrast, planetesimal accretion and chondrule accretion play more equal roles in the formation of moon-sized embryos in the terrestrial planet formation region. these embryos are isolated from each other and accrete planetesimals only at a low rate. however, the continued accretion of chondrules destabilizes the oligarchic configuration and leads to the formation of mars-sized embryos and terrestrial planets by a combination of direct chondrule accretion and giant impacts. | growth of asteroids, planetary embryos, and kuiper belt objects by chondrule accretion |
high-resolution spectroscopy (r ≥ 25,000) has recently emerged as one of the leading methods for detecting atomic and molecular species in the atmospheres of exoplanets. however, it has so far been lacking a robust method for extracting quantitative constraints on the temperature structure and molecular/atomic abundances. in this work, we present a novel bayesian atmospheric retrieval framework applicable to high-resolution cross-correlation spectroscopy (hrccs) that relies on the cross-correlation between data and models to extract the planetary spectral signal. we successfully test the framework on simulated data and show that it can correctly determine bayesian credibility intervals on atmospheric temperatures and abundances, allowing for a quantitative exploration of the inherent degeneracies. furthermore, our new framework permits us to trivially combine and explore the synergies between hrccs and low-resolution spectroscopy to maximally leverage the information contained within each. this framework also allows us to quantitatively assess the impact of molecular line opacities at high resolution. we apply the framework to vlt crires k-band spectra of hd 209458 b and hd 189733 b and retrieve abundant carbon monoxide but subsolar abundances for water, which are largely invariant under different model assumptions. this confirms previous analysis of these data sets, but is possibly at odds with detections of h2o at different wavelengths and spectral resolutions. the framework presented here is the first step toward a true synergy between space observatories and ground-based high-resolution observations. | retrieving temperatures and abundances of exoplanet atmospheres with high-resolution cross-correlation spectroscopy |
evidence from palaeoclimatology suggests that abrupt northern hemisphere cold events are linked to weakening of the atlantic meridional overturning circulation (amoc)1, potentially by excess inputs of fresh water2. but these insights—often derived from model runs under preindustrial conditions—may not apply to the modern era with our rapid emissions of greenhouse gases. if they do, then a weakened amoc, as in 1975-1998, should have led to northern hemisphere cooling. here we show that, instead, the amoc minimum was a period of rapid surface warming. more generally, in the presence of greenhouse-gas heating, the amoc's dominant role changed from transporting surface heat northwards, warming europe and north america, to storing heat in the deeper atlantic, buffering surface warming for the planet as a whole. during an accelerating phase from the mid-1990s to the early 2000s, the amoc stored about half of excess heat globally, contributing to the global-warming slowdown. by contrast, since mooring observations began3-5 in 2004, the amoc and oceanic heat uptake have weakened. our results, based on several independent indices, show that amoc changes since the 1940s are best explained by multidecadal variability6, rather than an anthropogenically forced trend. leading indicators in the subpolar north atlantic today suggest that the current amoc decline is ending. we expect a prolonged amoc minimum, probably lasting about two decades. if prior patterns hold, the resulting low levels of oceanic heat uptake will manifest as a period of rapid global surface warming. | global surface warming enhanced by weak atlantic overturning circulation |
the juno spacecraft has measured jupiter's low-order, even gravitational moments, j2-j8, to an unprecedented precision, providing important constraints on the density profile and core mass of the planet. here we report on a selection of interior models based on ab initio computer simulations of hydrogen-helium mixtures. we demonstrate that a dilute core, expanded to a significant fraction of the planet's radius, is helpful in reconciling the calculated jn with juno's observations. although model predictions are strongly affected by the chosen equation of state, the prediction of an enrichment of z in the deep, metallic envelope over that in the shallow, molecular envelope holds. we estimate jupiter's core to contain a 7-25 earth mass of heavy elements. we discuss the current difficulties in reconciling measured jn with the equations of state and with theory for formation and evolution of the planet. | comparing jupiter interior structure models to juno gravity measurements and the role of a dilute core |
several small dense exoplanets are now known, inviting comparisons to earth and venus. such comparisons require translating their masses and sizes to composition models of evolved multi-layer interior planets. such theoretical models rely on our understanding of the earth’s interior, as well as independently derived equations of state, but so far have not involved direct extrapolations from earth’s seismic model: the preliminary reference earth model (prem). to facilitate more detailed compositional comparisons between small exoplanets and the earth, we derive here a semi-empirical mass-radius relation for two-layer rocky planets based on prem, \frac{r}{{r}\oplus }=(1.07-0.21\cdot {cmf})\cdot {≤ft(\frac{m}{{m}\oplus }\right)}1/3.7, where cmf stands for core mass fraction. it is applicable to 1 ∼ 8 m⊕ and a cmf of 0.0 ∼ 0.4. applying this formula to earth and venus and several known small exoplanets with radii and masses measured to better than ∼30% precision gives a cmf fit of 0.26 ± 0.07. | mass-radius relation for rocky planets based on prem |
under the paris agreement, 195 nations have committed to holding the increase in the global average temperature to well below 2 °c above pre-industrial levels and to strive to limit the increase to 1.5 °c (ref. 1). it is noted that this requires "a balance between anthropogenic emissions by sources and removals by sinks of greenhouse gases in the second half of the century"1. this either calls for zero greenhouse gas (ghg) emissions or a balance between positive and negative emissions (ne)2,3. roadmaps and socio-economic scenarios compatible with a 2 °c or 1.5 °c goal depend upon ne via bioenergy with carbon capture and storage (beccs) to balance remaining ghg emissions4-7. however, large-scale deployment of beccs would imply significant impacts on many earth system components besides atmospheric co2 concentrations8,9. here we explore the feasibility of ne via beccs from dedicated plantations and potential trade-offs with planetary boundaries (pbs)10,11 for multiple socio-economic pathways. we show that while large-scale beccs is intended to lower the pressure on the pb for climate change, it would most likely steer the earth system closer to the pb for freshwater use and lead to further transgression of the pbs for land-system change, biosphere integrity and biogeochemical flows. | biomass-based negative emissions difficult to reconcile with planetary boundaries |
large impacts provide a mechanism for resurfacing planets through mixing near-surface rocks with deeper material. central peaks are formed from the dynamic uplift of rocks during crater formation. as crater size increases, central peaks transition to peak rings. without samples, debate surrounds the mechanics of peak-ring formation and their depth of origin. chicxulub is the only known impact structure on earth with an unequivocal peak ring, but it is buried and only accessible through drilling. expedition 364 sampled the chicxulub peak ring, which we found was formed from uplifted, fractured, shocked, felsic basement rocks. the peak-ring rocks are cross-cut by dikes and shear zones and have an unusually low density and seismic velocity. large impacts therefore generate vertical fluxes and increase porosity in planetary crust. | the formation of peak rings in large impact craters |
postprocessing ensemble weather predictions to correct systematic errors has become a standard practice in research and operations. however, only a few recent studies have focused on ensemble postprocessing of wind gust forecasts, despite its importance for severe weather warnings. here, we provide a comprehensive review and systematic comparison of eight statistical and machine learning methods for probabilistic wind gust forecasting via ensemble postprocessing that can be divided in three groups: state-of-the-art postprocessing techniques from statistics [ensemble model output statistics (emos), member-by-member postprocessing, isotonic distributional regression], established machine learning methods (gradient-boosting extended emos, quantile regression forests), and neural network–based approaches (distributional regression network, bernstein quantile network, histogram estimation network). the methods are systematically compared using 6 years of data from a high-resolution, convection-permitting ensemble prediction system that was run operationally at the german weather service, and hourly observations at 175 surface weather stations in germany. while all postprocessing methods yield calibrated forecasts and are able to correct the systematic errors of the raw ensemble predictions, incorporating information from additional meteorological predictor variables beyond wind gusts leads to significant improvements in forecast skill. in particular, we propose a flexible framework of locally adaptive neural networks with different probabilistic forecast types as output, which not only significantly outperform all benchmark postprocessing methods but also learn physically consistent relations associated with the diurnal cycle, especially the evening transition of the planetary boundary layer. | machine learning methods for postprocessing ensemble forecasts of wind gusts: a systematic comparison |
recent deployments of cubesat imagers by companies such as planet may advance hydrological remote sensing by providing an unprecedented combination of high temporal and high spatial resolution imagery at the global scale. with approximately 170 cubesats orbiting at full operational capacity, the planet cubesat constellation currently offers an average revisit time of <1 day for the arctic and near-daily revisit time globally at 3 m spatial resolution. such data have numerous potential applications for water resource monitoring, hydrologic modeling and hydrologic research. here we evaluate planet cubesat imaging capabilities and potential scientific utility for surface water studies in the yukon flats, a large sub-arctic wetland in north central alaska. we find that surface water areas delineated from planet imagery have a normalized root mean square error (nrmse) of <11% and geolocation accuracy of <10 m as compared with manual delineations from high resolution (0.3–0.5 m) worldview-2/3 panchromatic satellite imagery. for a 625 km2 subarea of the yukon flats, our time series analysis reveals that roughly one quarter of 268 lakes analyzed responded to changes in yukon river discharge over the period 23 june–1 october 2016, one half steadily contracted, and one quarter remained unchanged. the spatial pattern of observed lake changes is heterogeneous. while connections to yukon river control the hydrologically connected lakes, the behavior of other lakes is complex, likely driven by a combination of intricate flow paths, underlying geology and permafrost. limitations of planet cubesat imagery include a lack of an automated cloud mask, geolocation inaccuracies, and inconsistent radiometric calibration across multiple platforms. although these challenges must be addressed before planet cubesat imagery can achieve its full potential for large-scale hydrologic research, we conclude that cubesat imagery offers a powerful new tool for the study and monitoring of dynamic surface water bodies. | tracking dynamic northern surface water changes with high-frequency planet cubesat imagery |
we reevaluate the systematics and geologic setting of terrestrial, lunar, martian, and asteroidal "impactites" resulting from single or multiple impacts. for impactites derived from silicate rocks and sediments, we propose a unified and updated system of progressive shock metamorphism. "shock-metamorphosed rocks" occur as lithic clasts or melt particles in proximal impactites at impact craters, and rarely in distal impactites. they represent a wide range of metamorphism, typically ranging from unshocked to shock melted. as the degree of shock metamorphism, at a given shock pressure, depends primarily on the mineralogical composition and the porosity of a rock or sediment sample, different shock classification systems are required for different types of planetary rocks and sediments. we define shock classification systems for eight rock and sediment classes which are assigned to three major groups of rocks and sediments (1) crystalline rocks with classes f, m, a, and u; (2) chondritic rocks (class c); and (3) sedimentary rocks and sediments with classes sr, se, and re. the abbreviations stand for felsic (f), mafic (m), anorthositic (a), ultramafic (u), sedimentary rocks (sr), unconsolidated sediments (se), and regoliths (re). in each class, the progressive stages of shock metamorphism are denominated s1 to sx. these progressive shock stages are introduced as: s1-s7 for f, s1-s7 for m, s1-s6 for a, s1-s7 for u, s1-s7 for c, s1-s7 for sr, s1-s5 for se, and s1-s6 for re. s1 stands for "unshocked" and sx (variable between s5 and s7) stands for "whole rock melting." we propose a sequence of symbols characterizing the degree of shock metamorphism of a sample, i.e., f-s1 to f-s7 with the option to add the tabulated pressure ranges (in gpa) in parentheses. | shock metamorphism of planetary silicate rocks and sediments: proposal for an updated classification system |
the climate is a forced, dissipative, nonlinear, complex, and heterogeneous system that is out of thermodynamic equilibrium. the system exhibits natural variability on many scales of motion, in time as well as space, and it is subject to various external forcings, natural as well as anthropogenic. this review covers the observational evidence on climate phenomena and the governing equations of planetary-scale flow and presents the key concept of a hierarchy of models for use in the climate sciences. recent advances in the application of dynamical systems theory, on the one hand, and nonequilibrium statistical physics, on the other hand, are brought together for the first time and shown to complement each other in helping understand and predict the system's behavior. these complementary points of view permit a self-consistent handling of subgrid-scale phenomena as stochastic processes, as well as a unified handling of natural climate variability and forced climate change, along with a treatment of the crucial issues of climate sensitivity, response, and predictability. | the physics of climate variability and climate change |
determining the architecture of multi-planetary systems is one of the cornerstones of understanding planet formation and evolution. resonant systems are especially important as the fragility of their orbital configuration ensures that no significant scattering or collisional event has taken place since the earliest formation phase when the parent protoplanetary disc was still present. in this context, toi-178 has been the subject of particular attention since the first tess observations hinted at the possible presence of a near 2:3:3 resonant chain. here we report the results of observations from cheops, espresso, ngts, and speculoos with the aim of deciphering the peculiar orbital architecture of the system. we show that toi-178 harbours at least six planets in the super-earth to mini-neptune regimes, with radii ranging from 1.152−0.070+0.073 to 2.87−0.13+0.14 earth radii and periods of 1.91, 3.24, 6.56, 9.96, 15.23, and 20.71 days. all planets but the innermost one form a 2:4:6:9:12 chain of laplace resonances, and the planetary densities show important variations from planet to planet, jumping from 1.02−0.23+0.28 to 0.177−0.061+0.055 times the earth's density between planets c and d. using bayesian interior structure retrieval models, we show that the amount of gas in the planets does not vary in a monotonous way, contrary to what one would expect from simple formation and evolution models and unlike other known systems in a chain of laplace resonances. the brightness of toi-178 (h = 8.76 mag, j = 9.37 mag, v = 11.95 mag) allows for a precise characterisation of its orbital architecture as well as of the physical nature of the six presently known transiting planets it harbours. the peculiar orbital configuration and the diversity in average density among the planets in the system will enable the study of interior planetary structures and atmospheric evolution, providing important clues on the formation of super-earths and mini-neptunes. | six transiting planets and a chain of laplace resonances in toi-178 |
we use an end-to-end model of planet formation, thermodynamic evolution, and atmospheric escape to investigate how the statistical imprints of evaporation depend on the bulk composition of planetary cores (rocky versus icy). we find that the population-wide imprints like the location of the “evaporation valley” in the distance-radius plane and the corresponding bimodal radius distribution clearly differ depending on the bulk composition of the cores. comparison with the observed position of the valley suggests that close-in low-mass kepler planets have a predominantly earth-like rocky composition. combined with the excess of period ratios outside of mmr, this suggests that low-mass kepler planets formed inside of the water iceline but were still undergoing orbital migration. the core radius becomes visible for planets losing all primordial h/he. for planets in this “triangle of evaporation” in the distance-radius plane, the degeneracy in composition is reduced. in the observed planetary mass-mean density diagram, we identify a trend to more volatile-rich compositions with an increasing radius (r/r ⊕ ≲ 1.6 rocky; 1.6-3.0 ices, and/or h/he ≳3: h/he). the mass-density diagram contains important information about formation and evolution. its characteristic broken v-shape reveals the transitions from solid planets to low-mass core-dominated planets with h/he and finally to gas-dominated giants. evaporation causes the density and orbital distance to be anticorrelated for low-mass planets in contrast to giants, where closer-in planets are less dense, likely due to inflation. the temporal evolution of the statistical properties reported here will be of interest for the plato 2.0 mission, which will observe the temporal dimension. | compositional imprints in density-distance-time: a rocky composition for close-in low-mass exoplanets from the location of the valley of evaporation |
remanent magnetization in geological samples may record the past intensity and direction of planetary magnetic fields. traditionally, this magnetization is analyzed through measurements of the net magnetic moment of bulk millimeter to centimeter sized samples. however, geological samples are often mineralogically and texturally heterogeneous at submillimeter scales, with only a fraction of the ferromagnetic grains carrying the remanent magnetization of interest. therefore, characterizing this magnetization in such cases requires a technique capable of imaging magnetic fields at fine spatial scales and with high sensitivity. to address this challenge, we developed a new instrument, based on nitrogen-vacancy centers in diamond, which enables direct imaging of magnetic fields due to both remanent and induced magnetization, as well as optical imaging, of room-temperature geological samples with spatial resolution approaching the optical diffraction limit. we describe the operating principles of this device, which we call the quantum diamond microscope (qdm), and report its optimized image-area-normalized magnetic field sensitivity (20 µtṡµm/hz1/2), spatial resolution (5 µm), and field of view (4 mm), as well as trade-offs between these parameters. we also perform an absolute magnetic field calibration for the device in different modes of operation, including three-axis (vector) and single-axis (projective) magnetic field imaging. finally, we use the qdm to obtain magnetic images of several terrestrial and meteoritic rock samples, demonstrating its ability to resolve spatially distinct populations of ferromagnetic carriers. | micrometer-scale magnetic imaging of geological samples using a quantum diamond microscope |
extreme variability of the winter- and spring-time stratospheric polar vortex has been shown to affect extratropical tropospheric weather. therefore, reducing stratospheric forecast error may be one way to improve the skill of tropospheric weather forecasts. in this review, the basis for this idea is examined. a range of studies of different stratospheric extreme vortex events shows that they can be skilfully forecasted beyond 5 days and into the sub-seasonal range (0-30 days) in some cases. separate studies show that typical errors in forecasting a stratospheric extreme vortex event can alter tropospheric forecast skill by 5-7% in the extratropics on sub-seasonal time-scales. thus understanding what limits stratospheric predictability is of significant interest to operational forecasting centres. both limitations in forecasting tropospheric planetary waves and stratospheric model biases have been shown to be important in this context. | the predictability of the extratropical stratosphere on monthly time-scales and its impact on the skill of tropospheric forecasts |
the climate of early mars remains a topic of intense debate. ancient terrains preserve landscapes consistent with stream channels, lake basins and possibly even oceans, and thus the presence of liquid water flowing on the martian surface 4 billion years ago. however, despite the geological evidence, determining how long climatic conditions supporting liquid water lasted remains uncertain. climate models have struggled to generate sufficiently warm surface conditions given the faint young sun—even assuming a denser early atmosphere. a warm climate could have potentially been sustained by supplementing atmospheric co2 and h2o warming with either secondary greenhouse gases or clouds. alternatively, the martian climate could have been predominantly cold and icy, with transient warming episodes triggered by meteoritic impacts, volcanic eruptions, methane bursts or limit cycles. here, we argue that a warm and semi-arid climate capable of producing rain is most consistent with the geological and climatological evidence. | the geological and climatological case for a warmer and wetter early mars |
basaltic eruptions are the most common form of volcanism on earth and planetary bodies. the low viscosity of basaltic magmas inhibits fragmentation, which favours effusive and lava-fountaining activity, yet highly explosive, hazardous basaltic eruptions occur. the processes that promote fragmentation of basaltic magma remain unclear and are subject to debate. here we used a numerical conduit model to show that a rapid magma ascent during explosive eruptions produces a large undercooling. in situ experiments revealed that undercooling drives exceptionally rapid (in minutes) crystallization, which induces a step change in viscosity that triggers magma fragmentation. the experimentally produced textures are consistent with basaltic plinian eruption products. we applied a numerical model to investigate basaltic magma fragmentation over a wide parameter space and found that all basaltic volcanoes have the potential to produce highly explosive eruptions. the critical requirements are initial magma temperatures lower than 1,100 °c to reach a syn-eruptive crystal content of over 30 vol%, and thus a magma viscosity around 105 pa s, which our results suggest is the minimum viscosity required for the fragmentation of fast ascending basaltic magmas. these temperature, crystal content and viscosity requirements reveal how typically effusive basaltic volcanoes can produce unexpected highly explosive and hazardous eruptions. | magma fragmentation in highly explosive basaltic eruptions induced by rapid crystallization |
we have reconstructed longitude-latitude maps of column dust optical depth (cdod) for martian year (my) 34 (5 may 2017- 23 march 2019), using observations by the mars climate sounder (mcs) aboard nasa's mars reconnaissance orbiter spacecraft. our methodology works by gridding a combination of standard (v5.2) and novel (v5.3.2) estimates of cdod from mcs limb observations, using an improved "iterative weighted binning." in this work, we have produced four gridded cdod maps per sol, at different mars universal times. together with the seasonal and daily variability, the use of several maps per sol also allows us to explore the diurnal variability of cdod in the mcs dataset, which is shown to be particularly strong during the my 34 equinoctial global dust event (gde). in order to understand whether the diurnal variability of cdod has a physical explanation, and examine the impact of the my 34 gde on some aspects of the atmospheric circulation, we have carried out numerical simulations with the "laboratoire de météorologie dynamique" mars global climate model. we show that the model is able to account for at least part of the observed cdod diurnal variability. this is particularly true in the southern hemisphere where a strong diurnal wave at the time of the gde is able to displace dust horizontally as well as vertically. the simulations also clearly show the impact of the my 34 gde on the mean meridional circulation and the super-rotating equatorial jet, similarly to the effects of the equinoctial gde in my 25. | martian year 34 column dust climatology from mars climate sounder observations: reconstructed maps and model simulations |
the composition of the lower mantle--comprising 56% of earth's volume--remains poorly constrained. among the major elements, mg/si ratios ranging from ~0.9-1.1, such as in rocky solar-system building blocks (or chondrites), to ~1.2-1.3, such as in upper-mantle rocks (or pyrolite), have been proposed. geophysical evidence for subducted lithosphere deep in the mantle has been interpreted in terms of efficient mixing, and thus homogenous mg/si across most of the mantle. however, previous models did not consider the effects of variable mg/si on the viscosity and mixing efficiency of lower-mantle rocks. here, we use geodynamic models to show that large-scale heterogeneity associated with a 20-fold change in viscosity, such as due to the dominance of intrinsically strong (mg, fe)sio3-bridgmanite in low-mg/si domains, is sufficient to prevent efficient mantle mixing, even on large scales. models predict that intrinsically strong domains stabilize mantle convection patterns, and coherently persist at depths of about 1,000-2,200 km up to the present-day, separated by relatively narrow up-/downwelling conduits of pyrolitic material. the stable manifestation of such bridgmanite-enriched ancient mantle structures (beams) may reconcile the geographical fixity of deep-rooted mantle upwelling centres, and geophysical changes in seismic-tomography patterns, radial viscosity, rising plumes and sinking slabs near 1,000 km depth. moreover, these ancient structures may provide a reservoir to host primordial geochemical signatures. | persistence of strong silica-enriched domains in the earth's lower mantle |
nine transiting earth-sized planets have recently been discovered around nearby late-m dwarfs, including the trappist-1 planets and two planets discovered by the mearth survey, gj 1132b and lhs 1140b. these planets are the smallest known planets that may have atmospheres amenable to detection with the james webb space telescope (jwst). we present model thermal emission and transmission spectra for each planet, varying composition and surface pressure of the atmosphere. we base elemental compositions on those of earth, titan, and venus and calculate the molecular compositions assuming chemical equilibrium, which can strongly depend on temperature. both thermal emission and transmission spectra are sensitive to the atmospheric composition; thermal emission spectra are sensitive to surface pressure and temperature. we predict the observability of each planet’s atmosphere with jwst. gj 1132b and trappist-1b are excellent targets for emission spectroscopy with jwst/miri, requiring fewer than 10 eclipse observations. emission photometry for trappist-1c requires 5-15 eclipses; lhs 1140b and trappist-1d, trappist-1e, and trappist-1f, which could possibly have surface liquid water, may be accessible with photometry. seven of the nine planets are strong candidates for transmission spectroscopy measurements with jwst, although the number of transits required depends strongly on the planets’ actual masses. using the measured masses, fewer than 20 transits are required for a 5σ detection of spectral features for gj 1132b and six of the trappist-1 planets. dedicated campaigns to measure the atmospheres of these nine planets will allow us, for the first time, to probe formation and evolution processes of terrestrial planetary atmospheres beyond our solar system. | observing the atmospheres of known temperate earth-sized planets with jwst |
with no analogues in the solar system, the discovery of thousands of exoplanets with masses and radii intermediate between earth and neptune was one of the big surprises of exoplanet science. these super-earths and sub-neptunes probably represent the most common outcome of planet formation1,2. mass and radius measurements indicate a diversity in bulk composition much wider than for gas giants3; however, direct spectroscopic detections of molecular absorption and constraints on the gas mixing ratios have largely remained limited to planets more massive than neptune4-6. here we analyse a combined hubble/spitzer space telescope dataset of 12 transits and 20 eclipses of the sub-neptune exoplanet gj 3470 b, whose mass of 12.6 m⊕ places it near the halfway point between previously studied neptune-like exoplanets (22-23 m⊕)5-7 and exoplanets known to have rocky densities (7 m⊕)8. obtained over many years, our dataset provides a robust detection of water absorption (>5σ) and a thermal emission detection from the lowest irradiated planet to date. we reveal a low-metallicity, hydrogen-dominated atmosphere similar to that of a gas giant, but strongly depleted in methane gas. the low metallicity (o/h = 0.2-18.0) sets important constraints on the potential planet formation processes at low masses as well as the subsequent accretion of solids. the low methane abundance indicates that methane is destroyed much more efficiently than previously predicted, suggesting that the ch4/co transition curve has to be revisited for close-in planets. finally, we also find a sharp drop in the cloud opacity at 2-3 µm, characteristic of mie scattering, which enables narrow constraints on the cloud particle size and makes gj 3470 b a key target for mid-infrared characterization with the james webb space telescope. | a sub-neptune exoplanet with a low-metallicity methane-depleted atmosphere and mie-scattering clouds |
the relationship between aerosol optical depth (aod) and pm2.5 is often investigated in order to obtain surface pm2.5 from satellite observation of aod with a broad area coverage. however, various factors could affect the aod-pm2.5 regressions. using both ground and satellite observations in beijing from 2011 to 2015, this study analyzes the influential factors including the aerosol type, relative humidity (rh), planetary boundary layer height (pblh), wind speed and direction, and the vertical structure of aerosol distribution. the ratio of pm2.5 to aod, which is defined as η, and the square of their correlation coefficient (r2) have been examined. it shows that η varies from 54.32 to 183.14, 87.32 to 104.79, 95.13 to 163.52, and 1.23 to 235.08 µg m-3 with aerosol type in spring, summer, fall, and winter, respectively. η is smaller for scattering-dominant aerosols than for absorbing-dominant aerosols, and smaller for coarse-mode aerosols than for fine-mode aerosols. both rh and pblh affect the η value significantly. the higher the rh, the smaller the η, and the higher the pblh, the smaller the η. for aod and pm2.5 data with the correction of rh and pblh compared to those without, r2 of monthly averaged pm2.5 and aod at 14:00 lt increases from 0.63 to 0.76, and r2 of multi-year averaged pm2.5 and aod by time of day increases from 0.01 to 0.93, 0.24 to 0.84, 0.85 to 0.91, and 0.84 to 0.93 in four seasons respectively. wind direction is a key factor for the transport and spatial-temporal distribution of aerosols originated from different sources with distinctive physicochemical characteristics. similar to the variation in aod and pm2.5, η also decreases with the increasing surface wind speed, indicating that the contribution of surface pm2.5 concentrations to aod decreases with surface wind speed. the vertical structure of aerosol exhibits a remarkable change with seasons, with most particles concentrated within about 500 m in summer and within 150 m in winter. compared to the aod of the whole atmosphere, aod below 500 m has a better correlation with pm2.5, for which r2 is 0.77. this study suggests that all the above influential factors should be considered when we investigate the aod-pm2.5 relationships. | analysis of influential factors for the relationship between pm2.5 and aod in beijing |
observations of the mars upper atmosphere made from the mars atmosphere and volatile evolution (maven) spacecraft have been used to determine the loss rates of gas from the upper atmosphere to space for a complete mars year (16 nov 2014 - 3 oct 2016). loss rates for h and o are sufficient to remove ∼2-3 kg/s to space. by itself, this loss would be significant over the history of the planet. in addition, loss rates would have been greater early in history due to the enhanced solar euv and more-active sun. integrated loss, based on current processes whose escape rates in the past are adjusted according to expected solar evolution, would have been as much as 0.8 bar co2 or 23 m global equivalent layer of h2o; these losses are likely to be lower limits due to the nature of the extrapolation of loss rates to the earliest times. combined with the lack of surface or subsurface reservoirs for co2 that could hold remnants of an early, thick atmosphere, these results suggest that loss of gas to space has been the dominant process responsible for changing the climate of mars from an early, warmer environment to the cold, dry one that we see today. | loss of the martian atmosphere to space: present-day loss rates determined from maven observations and integrated loss through time |
the nasa ames stereo pipeline is a suite of free and open source automated geodesy and stereogrammetry tools designed for processing stereo images captured from satellites (around earth and other planets), robotic rovers, aerial cameras, and historical images, with and without accurate camera pose information. it produces cartographic products, including digital terrain models, ortho-projected images, 3-d models, and bundle-adjusted networks of cameras. ames stereo pipeline's data products are suitable for science analysis, mission planning, and public outreach. | the ames stereo pipeline: nasa's open source software for deriving and processing terrain data |
we present whfast, a fast and accurate implementation of a wisdom-holman symplectic integrator for long-term orbit integrations of planetary systems. whfast is significantly faster and conserves energy better than all other wisdom-holman integrators tested. we achieve this by significantly improving the kepler solver and ensuring numerical stability of coordinate transformations to and from jacobi coordinates. these refinements allow us to remove the linear secular trend in the energy error that is present in other implementations. for small enough timesteps, we achieve brouwer's law, i.e. the energy error is dominated by an unbiased random walk due to floating-point round-off errors. we implement symplectic correctors up to order 11 that significantly reduce the energy error. we also implement a symplectic tangent map for the variational equations. this allows us to efficiently calculate two widely used chaos indicators the lyapunov characteristic number and the mean exponential growth factor of nearby orbits. whfast is freely available as a flexible c package, as a shared library, and as an easy-to-use python module. | whfast: a fast and unbiased implementation of a symplectic wisdom-holman integrator for long-term gravitational simulations |
in mechanical fault diagnosis, most traditional methods for signal processing attempt to suppress or cancel noise imbedded in vibration signals for extracting weak fault characteristics, whereas stochastic resonance (sr), as a potential tool for signal processing, is able to utilize the noise to enhance fault characteristics. the classical bistable sr (cbsr), as one of the most widely used sr methods, however, has the disadvantage of inherent output saturation. the output saturation not only reduces the output signal-to-noise ratio (snr) but also limits the enhancement capability for fault characteristics. to overcome this shortcoming, a novel method is proposed to extract the fault characteristics, where a piecewise bistable potential model is established. simulated signals are used to illustrate the effectiveness of the proposed method, and the results show that the method is able to extract weak fault characteristics and has good enhancement performance and anti-noise capability. finally, the method is applied to fault diagnosis of bearings and planetary gearboxes, respectively. the diagnosis results demonstrate that the proposed method can obtain larger output snr, higher spectrum peaks at fault characteristic frequencies and therefore larger recognizable degree than the cbsr method. | an adaptive unsaturated bistable stochastic resonance method and its application in mechanical fault diagnosis |
we present one of the most precise emission spectra of an exoplanet observed so far. we combine five secondary eclipses of the hot jupiter wasp-18b (t day ∼ 2900 k) that we secured between 1.1 and 1.7 μm with the wide field camera 3 instrument on board the hubble space telescope. our extracted spectrum (s/n = 50, r ∼ 40) does not exhibit clearly identifiable molecular features but is poorly matched by a blackbody spectrum. we complement this data with previously published spitzer/infrared array camera observations of this target and interpret the combined spectrum by computing a grid of self-consistent, 1d forward models, varying the composition and energy budget. at these high temperatures, we find there are important contributions to the overall opacity from h- ions, as well as the removal of major molecules by thermal dissociation (including water), and thermal ionization of metals. these effects were omitted in previous spectral retrievals for very hot gas giants, and we argue that they must be included to properly interpret the spectra of these objects. we infer a new metallicity and c/o ratio for wasp-18b, and find them well constrained to be solar ([m/h] = -0.01 ± 0.35, c/o < 0.85 at 3σ confidence level), unlike previous work but in line with expectations for giant planets. the best-fitting self-consistent temperature-pressure profiles are inverted, resulting in an emission feature at 4.5 μm seen in the spitzer photometry. these results further strengthen the evidence that the family of very hot gas giant exoplanets commonly exhibit thermal inversions. | h- opacity and water dissociation in the dayside atmosphere of the very hot gas giant wasp-18b |
space weathering refers to alteration that occurs in the space environment with time. lunar samples, and to some extent meteorites, have provided a benchmark for understanding the processes and products of space weathering. lunar soils are derived principally from local materials but have accumulated a range of optically active opaque particles (oaopq) that include nanophase metallic iron on/in rims formed on individual grains (imparting a red slope to visible and near-infrared reflectance) and larger iron particles (which darken across all wavelengths) such as are often found within the interior of recycled grains. space weathering of other anhydrous silicate bodies, such as mercury and some asteroids, produces different forms and relative abundance of oaopq particles depending on the particular environment. if the development of oaopq particles is minimized (such as at vesta), contamination by exogenic material and regolith mixing become the dominant space weathering processes. volatile-rich bodies and those composed of abundant hydrous minerals (dwarf planet ceres, many dark asteroids, and outer solar system satellites) are affected by space weathering processes differently than the silicate bodies of the inner solar system. however, the space weathering products of these bodies are currently poorly understood and the physics and chemistry of space weathering processes in different environments are areas of active research. | space weathering on airless bodies |
traditional cooling systems consume tremendous amounts of energy and thus aggravate the greenhouse effect1,2. passive radiative cooling, dissipating an object's heat through an atmospheric transparency window (8-13 μm) to outer space without any energy consumption, has attracted much attention3-9. the unique feature of radiative cooling lies in the high emissivity in the atmospheric transparency window through which heat can be dissipated to the universe. therefore, for achieving high cooling performance, the design and fabrication of selective emitters, with emission strongly dominant in the transparency window, is of essential importance, as such spectral selection suppresses parasitic absorption from the surrounding thermal radiation. recently, various materials and structures with tailored spectrum responses have been investigated to achieve the effect of daytime radiative cooling6-8,10-15. however, most of the radiative cooling materials reported possess broad-band absorption/emission covering the whole mid-infrared wavelength11-15. here we demonstrate that a hierarchically designed polymer nanofibre-based film, produced by a scalable electrostatic spinning process, enables selective mid-infrared emission, effective sunlight reflection and therefore excellent all-day radiative cooling performance. specifically, the c-o-c (1,260-1,110 cm-1) and c-oh (1,239-1,030 cm-1) bonding endows the selective emissivity of 78% in 8-13 μm wavelength range, and the design of nanofibres with a controlled diameter allows for a high reflectivity of 96.3% in 0.3-2.5 μm wavelength range. as a result, we observe ~3 °c cooling improvement of this selective thermal emitter as compared to that of a non-selective emitter at night, and 5 °c sub-ambient cooling under sunlight. the impact of this hierarchically designed selective thermal emitter on alleviating global warming and temperature regulating an earth-like planet is also analysed, with a significant advantage demonstrated. with its excellent cooling performance and a scalable process, this hierarchically designed selective thermal emitter opens a new pathway towards large-scale applications of all-day radiative cooling materials. | scalable and hierarchically designed polymer film as a selective thermal emitter for high-performance all-day radiative cooling |
in this work, we performed a systematic study of the symmergent gravity (sg) in a black hole (bh) environment. being an emergent gravity model in which gravity emerges to restore the gauge symmetries and stabilize the higgs boson mass in a way giving a holographic ultraviolet (uv) completion of the underlying quantum field theory, the sg involves the general relativity (gr) plus quadratic-curvature term with a loop-induced coupling c0 being proportional to the boson-fermion number difference. we investigated c0 and other quantities by utilizing the various bhs observations. in this regard, we investigated particle dynamics, obtained keplerian frequencies describing the harmonic oscillations, and determined quasi periodic oscillations (qpos) about such orbits by using the relativistic precession (rp), warped disk (wd), and epicyclic resonant (er) models. we also analyse the bh shadow and determine constraints on the loop parameter c0 from the event horizon telescope (eht) data for both the static observers and observers co-moving with the cosmological expansion. we explored the weak deflection angle by considering the effect of finite distance and studied the resulting einstein rings. we conclude the work by giving an overall discussion of the quasiperiodic oscillations, shadow cast, and weak deflection angle, with a mention of future prospects concerning other possible investigations of the sg. we also study weak deflection angle and planetary perihelion shift and determined bounds on the sg parameters. furthermore, we compute shadow radius for both static and co-moving observers near and far from the symmergent bh and revealed the sensitivity of these observers to the model parameters. we conclude the work by giving an overall discussion and giving future prospects concerning other possible analyses of the sg. | quasiperiodic oscillations, weak field lensing and shadow cast around black holes in symmergent gravity |
the earth's inner core grows by the freezing of liquid iron at its surface. the point in history at which this process initiated marks a step-change in the thermal evolution of the planet. recent computational and experimental studies have presented radically differing estimates of the thermal conductivity of the earth's core, resulting in estimates of the timing of inner-core nucleation ranging from less than half a billion to nearly two billion years ago. recent inner-core nucleation (high thermal conductivity) requires high outer-core temperatures in the early earth that complicate models of thermal evolution. the nucleation of the core leads to a different convective regime and potentially different magnetic field structures that produce an observable signal in the palaeomagnetic record and allow the date of inner-core nucleation to be estimated directly. previous studies searching for this signature have been hampered by the paucity of palaeomagnetic intensity measurements, by the lack of an effective means of assessing their reliability, and by shorter-timescale geomagnetic variations. here we examine results from an expanded precambrian database of palaeomagnetic intensity measurements selected using a new set of reliability criteria. our analysis provides intensity-based support for the dominant dipolarity of the time-averaged precambrian field, a crucial requirement for palaeomagnetic reconstructions of continents. we also present firm evidence for the existence of very long-term variations in geomagnetic strength. the most prominent and robust transition in the record is an increase in both average field strength and variability that is observed to occur between a billion and 1.5 billion years ago. this observation is most readily explained by the nucleation of the inner core occurring during this interval; the timing would tend to favour a modest value of core thermal conductivity and supports a simple thermal evolution model for the earth. | palaeomagnetic field intensity variations suggest mesoproterozoic inner-core nucleation |
comets are pristine, volatile-rich objects formed beyond the orbits of the gas giants and, thus, thought to preserve a record of the primordial molecular cloud material parental to our solar system. we use magnesium and chromium isotopes to show that a class of pristine chondrites, the metal-rich carbonaceous chondrites, has a signature distinct from most inner solar system planets and asteroids. this signature is consistent with that predicted for unprocessed primordial molecular cloud material, suggesting that—similar to comets—metal-rich carbonaceous chondrites are samples of asteroids that accreted in the outer solar system. therefore, these objects may provide a direct window into the formation history of the outer solar system. | isotopic evidence for primordial molecular cloud material in metal-rich carbonaceous chondrites |
the double asteroid redirection test (dart) is a planetary defense mission, designed to demonstrate the kinetic impactor technique on (65803) didymos i dimorphos, the secondary of the (65803) didymos system. dart has four level 1 requirements to meet in order to declare mission success: (1) impact dimorphos between 2022 september 25 and october 2, (2) cause at least a 73 s change in its binary orbit period via the impact, (3) measure the change in binary period to an uncertainty of 7.3 s or less, and (4) measure the momentum transfer efficiency (β) of the impact and characterize the resulting effects of the impact. the data necessary to achieve these requirements will be obtained and analyzed by the dart investigation team. we discuss the rationales for the data to be gathered, the analyses to be undertaken, and how mission success will be achieved. | the double asteroid redirection test (dart): planetary defense investigations and requirements |
we present the first dedicated γ -ray analysis of jupiter, using 12 years of data from the fermi telescope. we find no robust evidence of γ -ray emission, and set upper limits of ∼10-9 gev cm-2 s-1 on the jovian γ -ray flux. we point out that jupiter is an advantageous dark matter (dm) target due to its large surface area (compared with other solar system planets), and cool core temperature (compared with the sun). these properties allow jupiter to both capture and retain lighter dm, providing a complementary probe of sub-gev dm. we therefore identify and perform a new search for dm-sourced γ -rays in jupiter, where dm annihilates to long-lived particles, which can escape the jovian surface and decay into γ rays. we consequently constrain dm-proton scattering cross sections as low as about 10-40 cm2 , showing jupiter is up to 10 orders of magnitude more sensitive than direct detection. this sensitivity is reached under the assumption that the mediator decay length is sufficient to escape jupiter, and the equilibrium between dm capture and annihilation; sensitivities can be lower depending on the dm model. our work motivates follow-up studies with upcoming mev telescopes such as amego and e-astrogam. | first analysis of jupiter in gamma rays and a new search for dark matter |
earth observation, aiming at monitoring the state of planet earth using remote sensing data, is critical for improving our daily lives and living environment. with a growing number of satellites in orbit, an increasing number of datasets with diverse sensors and research domains are being published to facilitate the research of the remote sensing community. in this paper, we present a comprehensive review of more than 400 publicly published datasets, including applications like land use/cover, change/disaster monitoring, scene understanding, agriculture, climate change, and weather forecasting. we systematically analyze these earth observation datasets with respect to five aspects volume, bibliometric analysis, resolution distributions, research domains, and the correlation between datasets. based on the dataset attributes, we propose to measure, rank, and select datasets to build a new benchmark for model evaluation. furthermore, a new platform for earth observation, termed earthnets, is released as a means of achieving a fair and consistent evaluation of deep learning methods on remote sensing data. earthnets supports standard dataset libraries and cutting-edge deep learning models to bridge the gap between the remote sensing and machine learning communities. based on this platform, extensive deep learning methods are evaluated on the new benchmark. the insightful results are beneficial to future research. the platform and dataset collections are publicly available at https://earthnets.github.io/. | earthnets: empowering ai in earth observation |
hera is a planetary defense mission under development in the space safety and security program of the european space agency for launch in 2024 october. it will rendezvous in late 2026 december with the binary asteroid (65803) didymos and in particular its moon, dimorphos, which will be impacted by nasa's dart spacecraft on 2022 september 26 as the first asteroid deflection test. the main goals of hera are the detailed characterization of the physical properties of didymos and dimorphos and of the crater made by the dart mission, as well as measurement of the momentum transfer efficiency resulting from dart's impact. the data from the hera spacecraft and its two cubesats will also provide significant insights into asteroid science and the evolutionary history of our solar system. hera will perform the first rendezvous with a binary asteroid and provide new measurements, such as radar sounding of an asteroid interior, which will allow models in planetary science to be tested. hera will thus provide a crucial element in the global effort to avert future asteroid impacts at the same time as providing world-leading science. | the esa hera mission: detailed characterization of the dart impact outcome and of the binary asteroid (65803) didymos |
black carbon (bc) has been identified to play a critical role in aerosol-planetary boundary layer (pbl) interaction and further deterioration of near-surface air pollution in megacities, which has been referred to as the "dome effect". however, the impacts of key factors that influence this effect, such as the vertical distribution and aging processes of bc, as well as the underlying land surface, have not been quantitatively explored yet. here, based on available in situ measurements of meteorology and atmospheric aerosols together with the meteorology-chemistry online coupled model wrf-chem, we conduct a set of parallel simulations to quantify the roles of these factors in influencing the bc dome effect and surface haze pollution. furthermore, we discuss the main implications of the results to air pollution mitigation in china. we found that the impact of bc on the pbl is very sensitive to the altitude of aerosol layer. the upper-level bc, especially that near the capping inversion, is more essential in suppressing the pbl height and weakening the turbulent mixing. the dome effect of bc tends to be significantly intensified as bc mixed with scattering aerosols during winter haze events, resulting in a decrease in pbl height by more than 15 %. in addition, the dome effect is more substantial (up to 15 %) in rural areas than that in the urban areas with the same bc loading, indicating an unexpected regional impact of such an effect to air quality in countryside. this study indicates that china's regional air pollution would greatly benefit from bc emission reductions, especially those from elevated sources from chimneys and also domestic combustion in rural areas, through weakening the aerosol-boundary layer interactions that are triggered by bc. | dome effect of black carbon and its key influencing factors: a one-dimensional modelling study |
the online coupled weather research and forecasting-chemistry (wrf-chem) model was applied to simulate a haze event that happened in january 2010 in the north china plain (ncp), and was validated against various types of measurements. the evaluations indicate that wrf-chem provides reliable simulations for the 2010 haze event in the ncp. this haze event was mainly caused by high emissions of air pollutants in the ncp and stable weather conditions in winter. secondary inorganic aerosols also played an important role and cloud chemistry had important contributions. air pollutants outside beijing contributed about 64.5 % to the pm2.5 levels in beijing during this haze event, and most of them are from south hebei, tianjin city, shandong and henan provinces. in addition, aerosol feedback has important impacts on surface temperature, relative humidity (rh) and wind speeds, and these meteorological variables affect aerosol distribution and formation in turn. in shijiazhuang, planetary boundary layer (pbl) decreased about 278.2 m and pm2.5 increased more than 20 µg m-3 due to aerosol feedback. it was also shown that black carbon (bc) absorption has significant impacts on meteorology and air quality changes, indicating more attention should be paid to bc from both air pollution control and climate change perspectives. | modeling study of the 2010 regional haze event in the north china plain |
being an effective methodology to adaptatively decompose a multi-component signal into a series of amplitude-modulated-frequency-modulated (amfm) sub-signals with limited bandwidth, the variational mode decomposition (vmd) has received increasing attention in the diagnosis of rolling element bearings. in implementing vmd, an optimal determination of decomposition parameters, including the mode number and bandwidth control parameter, is the pivotal starting point. however, in practical engineering, heavy background noise, abnormal impulses and vibration interferences from other internal components, often bring great challenges in selecting mode number and bandwidth control parameter. these issues may lead to the performance degradation of vmd for bearing fault diagnosis. therefore, a fault information-guided vmd (fivmd) method is proposed in this paper for extracting the weak bearing repetitive transient. to minimize the effects of background noise and/or interferences from other components, two nested statistical models based on the fault cyclic information, incorporated with the statistical threshold at a specific significance level, are used to approximately determine the mode number. then the ratio of fault characteristic amplitude (rfca) is defined and utilized to identify the optimal bandwidth control parameter, through which the maximum fault information is extracted. finally, comparisons with the original vmd, empirical mode decomposition (emd) and local mean decomposition (lmd) are conducted using both simulation and experimental datasets. successful fault diagnosis of rolling element bearings under complicated operating conditions, including early bearing fault signals in run-to-failure test datasets, signals with impulsive noise and planet bearing signals, demonstrates that the proposed fivmd is a superior approach in extracting weak bearing repetitive transients. | a fault information-guided variational mode decomposition (fivmd) method for rolling element bearings diagnosis |
the fraction of the incoming solar energy scattered by earth back to space is referred to as the planetary albedo. this reflected energy is a fundamental component of the earth's energy balance, and the processes that govern its magnitude, distribution, and variability shape earth's climate and climate change. we review our understanding of earth's albedo as it has progressed to the current time and provide a global perspective of our understanding of the processes that define it. joint analyses of surface solar flux data that are a complicated mix of measurements and model calculations with top-of-atmosphere (toa) flux measurements from current orbiting satellites yield a number of surprising results including (i) the northern and southern hemispheres (nh, sh) reflect the same amount of sunlight within 0.2 w m-2. this symmetry is achieved by increased reflection from sh clouds offsetting precisely the greater reflection from the nh land masses. (ii) the albedo of earth appears to be highly buffered on hemispheric and global scales as highlighted by both the hemispheric symmetry and a remarkably small interannual variability of reflected solar flux ( 0.2% of the annual mean flux). we show how clouds provide the necessary degrees of freedom to modulate the earth's albedo setting the hemispheric symmetry. we also show that current climate models lack this same degree of hemispheric symmetry and regulation by clouds. the relevance of this hemispheric symmetry to the heat transport across the equator is discussed. | the albedo of earth |
humanoid robots that can autonomously operate in diverse environments have the potential to help address labour shortages in factories, assist elderly at homes, and colonize new planets. while classical controllers for humanoid robots have shown impressive results in a number of settings, they are challenging to generalize and adapt to new environments. here, we present a fully learning-based approach for real-world humanoid locomotion. our controller is a causal transformer that takes the history of proprioceptive observations and actions as input and predicts the next action. we hypothesize that the observation-action history contains useful information about the world that a powerful transformer model can use to adapt its behavior in-context, without updating its weights. we train our model with large-scale model-free reinforcement learning on an ensemble of randomized environments in simulation and deploy it to the real world zero-shot. our controller can walk over various outdoor terrains, is robust to external disturbances, and can adapt in context. | real-world humanoid locomotion with reinforcement learning |
the cassini-huygens mission has transformed our understanding of titan from a hazy veiled moon to a place surprisingly like the earth, with terrestrial physical processes such as wind, rainfall, and erosion shaping the landscape albeit with entirely different chemistry and temperatures. dragonfly, a single element mission which fits within the new frontiers cost cap will arrive at titan in 2034, and perform in-situ investigations of the organic materials on the surface. however, its detailed investigations will be limited to region within its short flight range. the big gaps in our understanding of titan global topography, climate, and upper atmospheric chemistry which can only investigated from an orbiter around titan will remain to be addressed by a future orbiter mission. due to the challenges of attaining orbit, past titan orbiter concepts have been beyond the new frontiers cost cap. the present study explores the use of drag modulation aerocapture for a titan orbiter which fits within new frontiers. the study shows how a dragonfly-like lander, and a titan orbiter which each individually fit within the new frontiers cost cap, when combined together can provide the science data return equivalent to a flagship-class mission. | adept drag modulation aerocapture: applications for future titan exploration |
the growth of a planetary core by pebble accretion stops at the so-called pebble isolation mass, when the core generates a pressure bump that traps drifting pebbles outside its orbit. the value of the pebble isolation mass is crucial in determining the final planet mass. if the isolation mass is very low, gas accretion is protracted and the planet remains at a few earth masses with a mainly solid composition. for higher values of the pebble isolation mass, the planet might be able to accrete gas from the protoplanetary disc and grow into a gas giant. previous works have determined a scaling of the pebble isolation mass with cube of the disc aspect ratio. here, we expand on previous measurements and explore the dependency of the pebble isolation mass on all relevant parameters of the protoplanetary disc. we use 3d hydrodynamical simulations to measure the pebble isolation mass and derive a simple scaling law that captures the dependence on the local disc structure and the turbulent viscosity parameter α. we find that small pebbles, coupled to the gas, with stokes number τf < 0.005 can drift through the partial gap at pebble isolation mass. however, as the planetary mass increases, particles must be decreasingly smaller to penetrate the pressure bump. turbulent diffusion of particles, however, can lead to an increase of the pebble isolation mass by a factor of two, depending on the strength of the background viscosity and on the pebble size. we finally explore the implications of the new scaling law of the pebble isolation mass on the formation of planetary systems by numerically integrating the growth and migration pathways of planets in evolving protoplanetary discs. compared to models neglecting the dependence of the pebble isolation mass on the α-viscosity, our models including this effect result in higher core masses for giant planets. these higher core masses are more similar to the core masses of the giant planets in the solar system. | pebble-isolation mass: scaling law and implications for the formation of super-earths and gas giants |
we applied a global 3-d chemical transport model (geos-chem) to examine the variations in the frequency and intensity in severe winter haze days (swhds) in beijing-tianjin-hebei (bth) from 1985 to 2017 and quantified the roles of changes in anthropogenic emissions and/or meteorological parameters. observed swhds were defined as the days with daily mean pm2.5 concentration exceeding 150 µg m-3, and simulated swhds were identified by using the same threshold but with adjustment on the basis of simulation biases. comparisons between the simulated swhds and those obtained from the observed pm2.5 concentrations and atmospheric visibility showed that the model can capture the spatial and temporal variations in swhds in china; the correlation coefficient between the simulated and observed swhds is 0.98 at 161 grids in china. from 1985 to 2017, with changes in both anthropogenic emissions and meteorological parameters, the simulated frequency (total severe haze days in winter) and intensity (pm2.5 concentration averaged over severe haze days in winter) of swhds in bth showed increasing trends of 4.5 d per decade and 13.5 µg m-3 per decade, respectively. the simulated frequency exhibited fluctuations from 1985 to 2017, with a sudden decrease from 1992 to 2001 (29 to 10 d) and a rapid growth from 2003 to 2012 (16 to 47 d). the sensitivity simulations indicated that variations in meteorological parameters played a dominant role during 1992-2001, while variations in both emissions and meteorological parameters were important for the simulated frequency trend during 2003-2012 (simulated trends were 27.3 and 12.5 d per decade owing to changes in emissions alone and changes in meteorology alone, respectively). the simulated intensity showed a steady increase from 1985 to 2017, which was driven by changes in both emissions and meteorology. process analysis on all swhds during 1985-2017 indicated that transport was the most important process for the formation of swhds in bth with a relative contribution of 65.3 %, followed by chemistry (17.6 %), cloud processes (-7.5 %), dry deposition (-6.4 %), and planetary boundary layer (pbl) mixing (3.2 %). further examination showed that swhds exhibited large interannual variations in frequency and intensity, which were mainly driven by changes in meteorology. the results of this study have important implications for the control of swhds in bth. | severe winter haze days in the beijing-tianjin-hebei region from 1985 to 2017 and the roles of anthropogenic emissions and meteorology |
laboratory experiments indicate that direct growth of silicate grains via mutual collisions can only produce particles up to roughly millimeters in size. on the other hand, recent simulations of the streaming instability have shown that mm/cm-sized particles require an excessively high metallicity for dense filaments to emerge. using a numerical algorithm for stiff mutual drag force, we perform simulations of small particles with significantly higher resolutions and longer simulation times than in previous investigations. we find that particles of dimensionless stopping time τs = 10-2 and 10-3 - representing cm- and mm-sized particles interior of the water ice line - concentrate themselves via the streaming instability at a solid abundance of a few percent. we thus revise a previously published critical solid abundance curve for the regime of τs ≪ 1. the solid density in the concentrated regions reaches values higher than the roche density, indicating that direct collapse of particles down to mm sizes into planetesimals is possible. our results hence bridge the gap in particle size between direct dust growth limited by bouncing and the streaming instability. | concentrating small particles in protoplanetary disks through the streaming instability |
free-electron lasers produce extremely brief, coherent, and bright laser-like photon pulses that allow to image matter at atomic resolution and at timescales faster than the characteristic atomic motions. in pulses of about 50 femtoseconds duration they provide as many photons as one gets in 1 s from modern storage ring synchrotron radiation facilities. flash, the free-electron laser at desy in hamburg was the first fel in the xuv/soft x-ray spectral range, started operation as a user facility in summer 2005, and was for almost 5 years the only short wavelength fel facility worldwide. hence, most of the technological developments as well as the scientific experiments performed by the user community were new and unique as outlined below. flash was driving fel science and technology and paved the way for many new ideas. because of using a linear accelerator in superconducting rf technology flash combines the extreme peak brightness characteristic for fels with very high average brightness. it also was the prototype for the european xfel located in the hamburg metropolitan area, which started user operation in summer 2017. the present review provides an overview of the progress made with accelerator science and technology at flash for the production of stable beams of well characterized electron pulses, reduction of the pulse jitter to the femtosecond level, generation of ultra-short photon pulses, adequate synchronization of the machine parameters with the experiment, and demonstrating advanced fel schemes using variable gap undulators. much of this was done in the very exciting early days of fel science when it was even not clear if the fel concept could be realized for x-rays. the development and the operation of the flash user facility is described, as well as the techniques developed to make use of the new type of x-ray beams including photon beam diagnostics and damage studies of the optical elements. the review emphasizes breakthrough experiments which demonstrated that many of the ideas collected in the world-wide discussion of the scientific case of free-electron lasers could indeed be realized and they often produced unexpected results. the first experiment on coulomb explosion of xe clusters performed in 2002 was a clear demonstration of the feasibility of experiments with free-electron laser beams and opened a lively discussion in the atom, molecular and optical physics community (amo). time resolved single-shot single-particle imaging, summarized in the slogan "take movies instead of pictures", was one of the most popular science drivers for the construction of free-electron x-ray lasers. as a first step in this direction experiments using a highly focused beam of flash demonstrated that pictures of 2 dimensional objects could be reconstructed from single-shot single-particle diffraction patterns. explosion dynamics of nano-size particles hit by an intense fel pulse were studied. this method, called "diffraction before destruction", is now very successfully applied with hard x-rays and, to a large extent, solves the radiation damage problem in structural biology. a long term goal is to determine the 3 dimensional structure of a large molecule from a single-shot diffraction pattern. along these lines the 3d architecture of free ag nanoparticles could be determined from one diffraction pattern only using soft x-rays from flash. to understand light-matter interactions in this new parameter space a number of pioneering amo experiments have been performed including non-linear interactions in atoms, molecules and clusters. multiphoton photoionization processes in the presence of intense optical fields have been studied, as well as photo-absorption of xuv photon energies on molecular ions important for astrophysics. the nature of formation and breaking of molecular bonds was investigated in vuv pump-vuv probe experiments using a reaction microscope and a specific delay line. as an example the process of ultrafast isomerization of acetylene molecules c2h2 triggered by single photon excitation has been studied. the structural changes during the isomerization process were visualized and an isomerization time of 52 +/- 15 fs was found. clusters of variable size, which can be produced routinely, allow distinguish between inter- and intra-atomic effects and are considered model systems for the investigation of light-matter interactions in multi-atom objects. as an example such experimental studies provided instructive data for benchmarking theoretical models describing cluster ionization in intense short-wavelength laser pulses. the combination of single-shot single-particle imaging for determination of the cluster size with spectroscopy was crucial for success of these experiments. the investigations could later be extended to very large xe clusters providing new insights into the nanoplasma formation and explosion dynamics of such large systems from early on, studies of high energy density plasmas and warm dense matter have been one of the most prominent research fields in building the scientific case for x-ray free-electron lasers. a good understanding of this complex regime between cold solids and hot dilute plasmas is important for high pressure studies, applied materials studies, inertial fusion, and planetary interiors. with the first observation of saturable absorption of an l-shell transition in aluminum and pioneering studies of warm dense hydrogen flash kicked off research of matter in extreme conditions with free-electron lasers. in condensed matter experiments the emphasis is not so much on the peak power of the fel beam and extreme focusing, but on beam properties like polarization and pulse duration. the sample has to stay intact in the beam over hours and the number of photons per pulse impinging on the sample has to be limited to avoid space charge effects. after demonstrating the possibility to record single-shot resonant magnetic scattering images with fels the first time-resolved demagnetization study using a pump-probe approach with an ir-pump pulse and an xuv probe pulse to record a resonant magnetic scattering pattern as a function of pump-probe delay was also performed at flash. free-electron lasers offer the possibility to extend the well-established x-ray spectroscopic techniques for the investigation of the static electronic structure of matter to probing the evolution of the electronic structure in the time domain after controlled excitation. at flash first time resolved core level photoemission (tr-xps) experiments have been performed which are element specific and provide information on the dynamics of the local charge state around a specific center. using 198 ev photons in a surface study at ir single crystals it was possible to separate surface and bulk contributions in the ir 4f levels with sufficient instrumental resolution. time and angular resolved photoelectron spectroscopy (tr-arpes) is a very powerful tool to study non-equilibrium electron dynamics of condensed matter systems, since it offers the possibility to follow the dynamics of the full band structure of a material. in another pioneering experiment the photo-induced dynamics of the mott insulator 1t-tas2 was studied at flash by investigating the dynamics of the ta 4f photoemission. the formation of a commensurate charge density wave (ccdw) leads to a splitting of the ta 4f level which decreases first on a sub-picosecond time scale due to electronic melting of the ccdw and afterwards on a picosecond lifetime due to electron-phonon coupling. this leads to transfer of energy from the electronic system to the lattice and a partial melting of the periodic lattice distortions accompanying the periodic charge arrangement in the ccdw phase. in materials science x-ray absorption and emission spectroscopy are among the most powerful spectroscopies to study the electronic structure of matter. the wavelength of the radiation is scanned over certain element specific resonances which at flash 1 can only be done by scanning the electron energy. this is time consuming and makes the experiments difficult. nevertheless, the first time-resolved x-ray emission spectroscopy (xes) experiment was done at flash 1 in order to study non-thermal melting of a silicon sample. from a comparison of the observed valence electronic structure at different times after the photoexcitation it became clear that in the melting process in the first few ps a non-equilibrium low density liquid state is reached. the existence of such a metastable low density liquid state had been postulated for many systems that show tetragonal bonding in the crystalline phase like water for example, but spectroscopically the time-resolved silicon xes data taken at flash verified its existence for the first time. flash 2 has tunable undulators and it was demonstrated that scanning of the wavelength is very easy there. | 10 years of pioneering x-ray science at the free-electron laser flash at desy |
the pluto system was recently explored by nasa’s new horizons spacecraft, making closest approach on 14 july 2015. pluto’s surface displays diverse landforms, terrain ages, albedos, colors, and composition gradients. evidence is found for a water-ice crust, geologically young surface units, surface ice convection, wind streaks, volatile transport, and glacial flow. pluto’s atmosphere is highly extended, with trace hydrocarbons, a global haze layer, and a surface pressure near 10 microbars. pluto’s diverse surface geology and long-term activity raise fundamental questions about how small planets remain active many billions of years after formation. pluto’s large moon charon displays tectonics and evidence for a heterogeneous crustal composition; its north pole displays puzzling dark terrain. small satellites hydra and nix have higher albedos than expected. | the pluto system: initial results from its exploration by new horizons |
we have produced a multiannual climatology of airborne dust from martian year 24-31 using multiple datasets of retrieved or estimated column optical depths. the datasets are based on observations of the martian atmosphere from april 1999 to july 2013 made by different orbiting instruments: the thermal emission spectrometer (tes) aboard mars global surveyor, the thermal emission imaging system (themis) aboard mars odyssey, and the mars climate sounder (mcs) aboard mars reconnaissance orbiter (mro). the procedure we have adopted consists of gridding the available retrievals of column dust optical depth (cdod) from tes and themis nadir observations, as well as the estimates of this quantity from mcs limb observations. our gridding method calculates averages and uncertainties on a regularly spaced spatio-temporal grid, using an iterative procedure that is weighted in space, time, and retrieval quality. the lack of observations at certain times and locations introduces missing grid points in the maps, which therefore may result in irregularly gridded (i.e. incomplete) fields. in order to evaluate the strengths and weaknesses of the resulting gridded maps, we compare with independent observations of cdod by pancam cameras and mini-tes spectrometers aboard the mars exploration rovers "spirit" and "opportunity", by the surface stereo imager aboard the phoenix lander, and by the compact reconnaissance imaging spectrometer for mars aboard mro. we have statistically analyzed the irregularly gridded maps to provide an overview of the dust climatology on mars over eight years, specifically in relation to its interseasonal and interannual variability, in addition to provide a basis for instrument intercomparison. finally, we have produced regularly gridded maps of cdod by spatially interpolating the irregularly gridded maps using a kriging method. these complete maps are used as dust scenarios in the mars climate database (mcd) version 5, and are useful in many modeling applications. the two datasets for the eight available martian years are publicly available and distributed with open access on the mcd website. | eight-year climatology of dust optical depth on mars |
the masses and radii of exoplanets are fundamental quantities needed for their characterisation. studying the different populations of exoplanets is important for understanding the demographics of the different planetary types, which can then be linked to planetary formation and evolution. we present an updated exoplanet catalogue based on reliable, robust, and, as much as possible accurate mass and radius measurements of transiting planets up to 120 m⊕. the resulting mass-radius (m-r) diagram shows two distinct populations, corresponding to rocky and volatile-rich exoplanets which overlap in both mass and radius. the rocky exoplanet population shows a relatively small density variability and ends at mass of ~25 m⊕, possibly indicating the maximum core mass that can be formed. we use the composition line of pure water to separate the two populations, and infer two new empirical m-r relations based on this data: m = (0.9 ± 0.06) r(3.45±0.12) for the rocky population, and m = (1.74 ± 0.38) r(1.58±0.10) for the volatile-rich population. while our results for the two regimes are in agreement with previous studies, the new m-r relations better match the population in the transition region from rocky to volatile-rich exoplanets, which correspond to a mass range of 5-25 m⊕, and a radius range of 2-3 r⊕. | revisited mass-radius relations for exoplanets below 120 m⊕ |
chemical disequilibrium in planetary atmospheres has been proposed as a generalized method for detecting life on exoplanets through remote spectroscopy. among solar system planets with substantial atmospheres, the modern earth has the largest thermodynamic chemical disequilibrium due to the presence of life. however, how this disequilibrium changed over time and, in particular, the biogenic disequilibria maintained in the anoxic archean or less oxic proterozoic eons are unknown. we calculate the atmosphere-ocean disequilibrium in the precambrian using conservative proxy- and model-based estimates of early atmospheric and oceanic compositions. we omit crustal solids because subsurface composition is not detectable on exoplanets, unlike above-surface volatiles. we find that (i) disequilibrium increased through time in step with the rise of oxygen; (ii) both the proterozoic and phanerozoic may have had remotely detectable biogenic disequilibria due to the coexistence of o$_{2}$, n$_{2}$, and liquid water; and (iii) the archean had a biogenic disequilibrium caused by the coexistence of n$_2$, ch$_4$, co$_2$, and liquid water, which, for an exoplanet twin, may be remotely detectable. on the basis of this disequilibrium, we argue that the simultaneous detection of abundant ch$_{4}$ and co$_{2}$ in a habitable exoplanet's atmosphere is a potential biosignature. specifically, we show that methane mixing ratios greater than 0.001 are potentially biogenic, whereas those exceeding 0.01 are likely biogenic due to the difficulty in maintaining large abiotic methane fluxes to support high methane levels in anoxic atmospheres. biogenicity would be strengthened by the absence of abundant co, which should not coexist in a biological scenario. | disequilibrium biosignatures over earth history and implications for detecting exoplanet life |
the second workshop on extreme precision radial velocities defined circa 2015 the state of the art doppler precision and identified the critical path challenges for reaching 10 cm s-1 measurement precision. the presentations and discussion of key issues for instrumentation and data analysis and the workshop recommendations for achieving this bold precision are summarized here. beginning with the high accuracy radial velocity planet searcher spectrograph, technological advances for precision radial velocity (rv) measurements have focused on building extremely stable instruments. to reach still higher precision, future spectrometers will need to improve upon the state of the art, producing even higher fidelity spectra. this should be possible with improved environmental control, greater stability in the illumination of the spectrometer optics, better detectors, more precise wavelength calibration, and broader bandwidth spectra. key data analysis challenges for the precision rv community include distinguishing center of mass (com) keplerian motion from photospheric velocities (time correlated noise) and the proper treatment of telluric contamination. success here is coupled to the instrument design, but also requires the implementation of robust statistical and modeling techniques. com velocities produce doppler shifts that affect every line identically, while photospheric velocities produce line profile asymmetries with wavelength and temporal dependencies that are different from keplerian signals. exoplanets are an important subfield of astronomy and there has been an impressive rate of discovery over the past two decades. however, higher precision rv measurements are required to serve as a discovery technique for potentially habitable worlds, to confirm and characterize detections from transit missions, and to provide mass measurements for other space-based missions. the future of exoplanet science has very different trajectories depending on the precision that can ultimately be achieved with doppler measurements. | state of the field: extreme precision radial velocities |
the composition of a planet’s atmosphere is determined by its formation, evolution, and present-day insolation. a planet’s spectrum therefore may hold clues on its origins. we present a “chain” of models, linking the formation of a planet to its observable present-day spectrum. the chain links include (1) the planet’s formation and migration, (2) its long-term thermodynamic evolution, (3) a variety of disk chemistry models, (4) a non-gray atmospheric model, and (5) a radiometric model to obtain simulated spectroscopic observations with james webb space telescope and ariel. in our standard chemistry model the inner disk is depleted in refractory carbon as in the solar system and in white dwarfs polluted by extrasolar planetesimals. our main findings are: (1) envelope enrichment by planetesimal impacts during formation dominates the final planetary atmospheric composition of hot jupiters. we investigate two, under this finding, prototypical formation pathways: a formation inside or outside the water iceline, called “dry” and “wet” planets, respectively. (2) both the “dry” and “wet” planets are oxygen-rich (c/o < 1) due to the oxygen-rich nature of the solid building blocks. the “dry” planet’s c/o ratio is <0.2 for standard carbon depletion, while the “wet” planet has typical c/o values between 0.1 and 0.5 depending mainly on the clathrate formation efficiency. only non-standard disk chemistries without carbon depletion lead to carbon-rich c/o ratios >1 for the “dry” planet. (3) while we consistently find c/o ratios <1, they still vary significantly. to link a formation history to a specific c/o, a better understanding of the disk chemistry is thus needed. | the imprint of exoplanet formation history on observable present-day spectra of hot jupiters |
the insight (interior exploration using seismic investigations, geodesy and heat transport) mission landed in elysium planitia on mars on 26 november 2018 and fully deployed its seismometer by the end of february 2019. the mission aims to detect, characterize and locate seismic activity on mars, and to further constrain the internal structure, composition and dynamics of the planet. here, we present seismometer data recorded until 30 september 2019, which reveal that mars is seismically active. we identify 174 marsquakes, comprising two distinct populations: 150 small-magnitude, high-frequency events with waves propagating at crustal depths and 24 low-frequency, subcrustal events of magnitude mw 3-4 with waves propagating at various depths in the mantle. these marsquakes have spectral characteristics similar to the seismicity observed on the earth and moon. we determine that two of the largest detected marsquakes were located near the cerberus fossae fracture system. from the recorded seismicity, we constrain attenuation in the crust and mantle, and find indications of a potential low-s-wave-velocity layer in the upper mantle. | the seismicity of mars |
here we review how environmental context can be used to interpret whether o2 is a biosignature in extrasolar planetary observations. this paper builds on the overview of current biosignature research discussed in schwieterman et al. (2017), and provides an in-depth, interdisciplinary example of biosignature identification and observation that serves as a basis for the development of the general framework for biosignature assessment described in catling et al., (2017). o2 is a potentially strong biosignature that was originally thought to be an unambiguous indicator for life at high-abundance. we describe the coevolution of life with the early earth's environment, and how the interplay of sources and sinks in the planetary environment may have resulted in suppression of o2 release into the atmosphere for several billion years, a false negative for biologically generated o2. false positives may also be possible, with recent research showing potential mechanisms in exoplanet environments that may generate relatively high abundances of atmospheric o2 without a biosphere being present. these studies suggest that planetary characteristics that may enhance false negatives should be considered when selecting targets for biosignature searches. similarly our ability to interpret o2 observed in an exoplanetary atmosphere is also crucially dependent on environmental context to rule out false positive mechanisms. we describe future photometric, spectroscopic and time-dependent observations of o2 and the planetary environment that could increase our confidence that any observed o2 is a biosignature, and help discriminate it from potential false positives. by observing and understanding o2 in its planetary context we can increase our confidence in the remote detection of life, and provide a model for biosignature development for other proposed biosignatures. | exoplanet biosignatures: understanding oxygen as a biosignature in the context of its environment |
this study offers an overview of the low-frequency (i.e., monthly to seasonal) evolution, dynamics, predictability, and surface impacts of a rare southern hemisphere (sh) stratospheric warming that occurred in austral spring 2019. between late august and mid-september 2019, the stratospheric circumpolar westerly jet weakened rapidly, and antarctic stratospheric temperatures rose dramatically. the deceleration of the vortex at 10 hpa was as drastic as that of the first-ever-observed major sudden stratospheric warming in the sh during 2002, while the mean antarctic warming over the course of spring 2019 broke the previous record of 2002 by ∼50% in the midstratosphere. this event was preceded by a poleward shift of the sh polar night jet in the uppermost stratosphere in early winter, which was then followed by record-strong planetary wave-1 activity propagating upward from the troposphere in august that acted to dramatically weaken the polar vortex throughout the depth of the stratosphere. the weakened vortex winds and elevated temperatures moved downward to the surface from mid-october to december, promoting a record strong swing of the southern annular mode (sam) to its negative phase. this record-negative sam appeared to be a primary driver of the extreme hot and dry conditions over subtropical eastern australia that accompanied the severe wildfires that occurred in late spring 2019. state-of-the-art dynamical seasonal forecast systems skillfully predicted the significant vortex weakening of spring 2019 and subsequent development of negative sam from as early as late july. | the 2019 southern hemisphere stratospheric polar vortex weakening and its impacts |
large igneous province (lip) eruptions are increasingly considered to have driven mass extinction events throughout the phanerozoic; however, uncertainties in radiometric age dating of lip materials, along with difficulty in accurate age dating of sedimentary rocks that record the environmental and biological history of our planet, create inherent uncertainties in any linkage. as such, there is interest in using geochemical proxies to fingerprint periods of major volcanism in the sedimentary record (termed here lip marks). the use of sedimentary mercury (hg) contents has been suggested to be the best tool to accomplish this goal, and recent work is reviewed here. studies to-date show that most extinction events, ocean anoxic events, and other environmental crises through the phanerozoic have an associated sedimentary hg anomaly. it remains unclear though if each hg anomaly is truly a signature of massive volcanism, or if it is controlled by local or regional processes. as hg has a strong affinity to organic matter (om), normalisation with total organic carbon (toc) has been used to assess anomalies. the measurement of toc has been fraught with error throughout many studies, leaving some claimed hg/toc anomalies questionable. normalisation by other elements that can affect hg sequestration, such as al and s, are less common but warrant further investigation. stable isotope systematics of hg have helped to further clarify the origin of hg spikes, and clearly show that not all hg anomalies are directly related to volcanism. although a promising tool, the hg proxy requires more refinement to accurately understand the nuances of an hg anomaly in the rock record. | mercury as a proxy for volcanic emissions in the geologic record |
planetary science research involves analysing vast amounts of remote sensing data, which are often costly and time-consuming to annotate and process. one of the essential tasks in this field is geological mapping, which requires identifying and outlining regions of interest in planetary images, including geological features and landforms. however, manually labelling these images is a complex and challenging task that requires significant domain expertise and effort. to expedite this endeavour, we propose the use of knowledge distillation using the recently introduced cutting-edge segment anything (sam) model. we demonstrate the effectiveness of this prompt-based foundation model for rapid annotation and quick adaptability to a prime use case of mapping planetary skylights. our work reveals that with a small set of annotations obtained with the right prompts from the model and subsequently training a specialised domain decoder, we can achieve satisfactory semantic segmentation on this task. key results indicate that the use of knowledge distillation can significantly reduce the effort required by domain experts for manual annotation and improve the efficiency of image segmentation tasks. this approach has the potential to accelerate extra-terrestrial discovery by automatically detecting and segmenting martian landforms. | knowledge distillation with segment anything (sam) model for planetary geological mapping |
biomass burning is a major source of atmospheric brown carbon (brc), and through its absorption of uv/vis radiation, it can play an important role in the planetary radiative balance and atmospheric photochemistry. the considerable uncertainty of brc impacts is associated with its poorly constrained sources, transformations, and atmospheric lifetime. here we report laboratory experiments that examined changes in the optical properties of the water-soluble (ws) brc fraction of laboratory-generated biomass burning particles from hardwood pyrolysis. effects of direct uvb photolysis and oh oxidation in the aqueous phase on molecular-weight-separated brc were studied. results indicated that the majority of low-molecular-weight (mw) brc (<400 da) was rapidly photobleached by both direct photolysis and oh oxidation on an atmospheric timescale of approximately 1 h. high mw brc (≥400 da) underwent initial photoenhancement up to ∼15 h, followed by slow photobleaching over ∼10 h. the laboratory experiments were supported by observations from ambient brc samples that were collected during the fire seasons in greece. these samples, containing freshly emitted to aged biomass burning aerosol, were analyzed for both water- and methanol-soluble brc. consistent with the laboratory experiments, high-mw brc dominated the total light absorption at 365 nm for both methanol and water-soluble fractions of ambient samples with atmospheric transport times of 1 to 68 h. these ambient observations indicate that overall, biomass burning brc across all molecular weights has an atmospheric lifetime of 15 to 28 h, consistent with estimates from previous field studies - although the brc associated with the high-mw fraction remains relatively stable and is responsible for light absorption properties of brc throughout most of its atmospheric lifetime. for ambient samples of aged (>10 h) biomass burning emissions, poor linear correlations were found between light absorptivity and levoglucosan, consistent with other studies suggesting a short atmospheric lifetime for levoglucosan. however, a much stronger correlation between light absorptivity and total hydrous sugars was observed, suggesting that they may serve as more robust tracers for aged biomass burning emissions. overall, the results from this study suggest that robust model estimates of brc radiative impacts require consideration of the atmospheric aging of brc and the stability of high-mw brc. | atmospheric evolution of molecular-weight-separated brown carbon from biomass burning |
some active asteroids have been proposed to be formed as a result of impact events1. because active asteroids are generally discovered by chance only after their tails have fully formed, the process of how impact ejecta evolve into a tail has, to our knowledge, not been directly observed. the double asteroid redirection test (dart) mission of nasa2, in addition to having successfully changed the orbital period of dimorphos3, demonstrated the activation process of an asteroid resulting from an impact under precisely known conditions. here we report the observations of the dart impact ejecta with the hubble space telescope from impact time t + 15 min to t + 18.5 days at spatial resolutions of around 2.1 km per pixel. our observations reveal the complex evolution of the ejecta, which are first dominated by the gravitational interaction between the didymos binary system and the ejected dust and subsequently by solar radiation pressure. the lowest-speed ejecta dispersed through a sustained tail that had a consistent morphology with previously observed asteroid tails thought to be produced by an impact4,5. the evolution of the ejecta after the controlled impact experiment of dart thus provides a framework for understanding the fundamental mechanisms that act on asteroids disrupted by a natural impact1,6. | ejecta from the dart-produced active asteroid dimorphos |
the earth's thermosphere and ionosphere (ti) are characterized by perpetual variability as integral parts of the atmosphere system, with intermittent disturbances from solar and geomagnetic forcing. this review examines how the ti variability is affected by processes originating from the lower atmosphere and implications for quantifying and forecasting the ti. this aspect of the ti variability has been increasingly appreciated in recent years from both observational and numerical studies, especially during the last extended solar minimum. this review focuses on the role of atmospheric waves, including tides, planetary waves, gravity waves, and acoustic waves, which become increasingly significant as they propagate from their source region to the upper atmosphere. recent studies have led to better understanding of how these waves directly or indirectly affect ti wind, temperature, and compositional structures; the circulation pattern; neutral and ion species transport; and ionospheric wind dynamo. the variability of these waves on daily to interannual scales has been found to significantly impact the ti variability. several outstanding questions and challenges have been highlighted: (i) large, seemingly stochastic, day-to-day variability of tides in the ti; (ii) control of model error in the ti region by the lower atmosphere; and (iii) the increasing importance of processes with shorter spatial and temporal scales at higher altitudes. addressing these challenges requires model capabilities to assimilate observations of both lower and upper atmosphere and higher model resolution to capture complex interactions among processes over a broad range of scales and extended altitudes. | variability and predictability of the space environment as related to lower atmosphere forcing |
we propose a novel method for testing gravity models using seismic data from earth. by imposing observational constraints on earth's moment of inertia and mass, we rigorously limit the gravitational models' parameters within a $2\sigma$ accuracy. our method constrains the parameters governing additional terms to the general relativity lagrangian to the following ranges: $-2\times10^9\lesssim\beta\lesssim 10^9 \text{m}^2$ for palatini $f(r)$ gravity, $-8\times10^9\lesssim\epsilon\lesssim 4\times 10^9 \text{m}^2$ for eddington-inspired born-infeld gravity, and $-10^{-3}\lesssim\upsilon\lesssim10^{-3}$ for degenerate higher-order scalar-tensor theories. we also discuss potential avenues to enhance the proposed method, aiming to impose even tighter constraints on gravity models. | earthquakes as probing tools for gravity theories |
the ability to model surface processes and to couple them to both subsurface and atmospheric regimes has proven invaluable to research in the earth and planetary sciences. however, creating a new model typically demands a very large investment of time, and modifying an existing model to address a new problem typically means the new work is constrained to its detriment by model adaptations for a different problem. landlab is an open-source software framework explicitly designed to accelerate the development of new process models by providing (1) a set of tools and existing grid structures - including both regular and irregular grids - to make it faster and easier to develop new process components, or numerical implementations of physical processes; (2) a suite of stable, modular, and interoperable process components that can be combined to create an integrated model; and (3) a set of tools for data input, output, manipulation, and visualization. a set of example models built with these components is also provided. landlab's structure makes it ideal not only for fully developed modelling applications but also for model prototyping and classroom use. because of its modular nature, it can also act as a platform for model intercomparison and epistemic uncertainty and sensitivity analyses. landlab exposes a standardized model interoperability interface, and is able to couple to third-party models and software. landlab also offers tools to allow the creation of cellular automata, and allows native coupling of such models to more traditional continuous differential equation-based modules. we illustrate the principles of component coupling in landlab using a model of landform evolution, a cellular ecohydrologic model, and a flood-wave routing model. | creative computing with landlab: an open-source toolkit for building, coupling, and exploring two-dimensional numerical models of earth-surface dynamics |
as we approach the james webb space telescope (jwst) era, several studies have emerged that aim to (1) characterize how the instruments will perform and (2) determine what atmospheric spectral features could theoretically be detected using transmission and emission spectroscopy. to some degree, all these studies have relied on modeling of jwst’s theoretical instrument noise. with under two years left until launch, it is imperative that the exoplanet community begins to digest and integrate these studies into their observing plans, as well as think about how to leverage the hubble space telescope (hst) to optimize jwst observations. to encourage this and to allow all members of the community access to jwst & hst noise simulations, we present here an open-source python package and online interface for creating observation simulations of all observatory-supported timeseries spectroscopy modes. this noise simulator, called pandexo, relies on some aspects of space telescope science institute’s exposure time calculator, pandeia. we describe pandexo and the formalism for computing noise sources for jwst. then we benchmark pandexo's performance against each instrument team’s independently written noise simulator for jwst, and previous observations for hst. we find that pandexo is within 10% agreement for hst/wfc3 and for all jwst instruments. | pandexo: a community tool for transiting exoplanet science with jwst & hst |
several planetary satellites apparently have subsurface seas that are of great interest for, among other reasons, their possible habitability. the geologically diverse saturnian satellite enceladus vigorously vents liquid water and vapor from fractures within a south polar depression and thus must have a liquid reservoir or active melting. however, the extent and location of any subsurface liquid region is not directly observable. we use measurements of control points across the surface of enceladus accumulated over seven years of spacecraft observations to determine the satellite's precise rotation state, finding a forced physical libration of 0.120 ± 0.014° (2σ). this value is too large to be consistent with enceladus's core being rigidly connected to its surface, and thus implies the presence of a global ocean rather than a localized polar sea. the maintenance of a global ocean within enceladus is problematic according to many thermal models and so may constrain satellite properties or require a surprisingly dissipative saturn. | enceladus's measured physical libration requires a global subsurface ocean |
the earth climate system is out of energy balance, and heat has accumulated continuously over the past decades, warming the ocean, the land, the cryosphere, and the atmosphere. according to the sixth assessment report by working group i of the intergovernmental panel on climate change, this planetary warming over multiple decades is human-driven and results in unprecedented and committed changes to the earth system, with adverse impacts for ecosystems and human systems. the earth heat inventory provides a measure of the earth energy imbalance (eei) and allows for quantifying how much heat has accumulated in the earth system, as well as where the heat is stored. here we show that the earth system has continued to accumulate heat, with 381±61 zj accumulated from 1971 to 2020. this is equivalent to a heating rate (i.e., the eei) of 0.48±0.1 w m-2. the majority, about 89 %, of this heat is stored in the ocean, followed by about 6 % on land, 1 % in the atmosphere, and about 4 % available for melting the cryosphere. over the most recent period (2006-2020), the eei amounts to 0.76±0.2 w m-2. the earth energy imbalance is the most fundamental global climate indicator that the scientific community and the public can use as the measure of how well the world is doing in the task of bringing anthropogenic climate change under control. moreover, this indicator is highly complementary to other established ones like global mean surface temperature as it represents a robust measure of the rate of climate change and its future commitment. we call for an implementation of the earth energy imbalance into the paris agreement's global stocktake based on best available science. the earth heat inventory in this study, updated from von schuckmann et al. (2020), is underpinned by worldwide multidisciplinary collaboration and demonstrates the critical importance of concerted international efforts for climate change monitoring and community-based recommendations and we also call for urgently needed actions for enabling continuity, archiving, rescuing, and calibrating efforts to assure improved and long-term monitoring capacity of the global climate observing system. the data for the earth heat inventory are publicly available, and more details are provided in table 4. | heat stored in the earth system 1960-2020: where does the energy go? |
the enigmatic ediacara biota (571 million to 541 million years ago) represents the first macroscopic complex organisms in the geological record and may hold the key to our understanding of the origin of animals. ediacaran macrofossils are as “strange as life on another planet” and have evaded taxonomic classification, with interpretations ranging from marine animals or giant single-celled protists to terrestrial lichens. here, we show that lipid biomarkers extracted from organically preserved ediacaran macrofossils unambiguously clarify their phylogeny. dickinsonia and its relatives solely produced cholesteroids, a hallmark of animals. our results make these iconic members of the ediacara biota the oldest confirmed macroscopic animals in the rock record, indicating that the appearance of the ediacara biota was indeed a prelude to the cambrian explosion of animal life. | ancient steroids establish the ediacaran fossil dickinsonia as one of the earliest animals |
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