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this paper reviews vlasov-based numerical methods used to model plasma in space physics and astrophysics. plasma consists of collectively behaving charged particles that form the major part of baryonic matter in the universe. many concepts ranging from our own planetary environment to the solar system and beyond can be understood in terms of kinetic plasma physics, represented by the vlasov equation. we introduce the physical basis for the vlasov system, and then outline the associated numerical methods that are typically used. a particular application of the vlasov system is vlasiator, the world's first global hybrid-vlasov simulation for the earth's magnetic domain, the magnetosphere. we introduce the design strategies for vlasiator and outline its numerical concepts ranging from solvers to coupling schemes. we review vlasiator's parallelisation methods and introduce the used high-performance computing (hpc) techniques. a short review of verification, validation and physical results is included. the purpose of the paper is to present the vlasov system and introduce an example implementation, and to illustrate that even with massive computational challenges, an accurate description of physics can be rewarding in itself and significantly advance our understanding. upcoming supercomputing resources are making similar efforts feasible in other fields as well, making our design options relevant for others facing similar challenges. | vlasov methods in space physics and astrophysics |
we present the first application of a bin-scheme microphysical and vertical transport model to determine the size distribution of titanium and silicate cloud particles in the atmospheres of hot jupiters. we predict particle size distributions from first principles for a grid of planets at four representative equatorial longitudes, and investigate how observed cloud properties depend on the atmospheric thermal structure and vertical mixing. the predicted size distributions are frequently bimodal and irregular in shape. there is a negative correlation between the total cloud mass and equilibrium temperature as well as a positive correlation between the total cloud mass and atmospheric mixing. the cloud properties on the east and west limbs show distinct differences that increase with increasing equilibrium temperature. cloud opacities are roughly constant across a broad wavelength range, with the exception of features in the mid-infrared. forward-scattering is found to be important across the same wavelength range. using the fully resolved size distribution of cloud particles as opposed to a mean particle size has a distinct impact on the resultant cloud opacities. the particle size that contributes the most to the cloud opacity depends strongly on the cloud particle size distribution. we predict that it is unlikely that silicate or titanium clouds are responsible for the optical rayleigh scattering slope seen in many hot jupiters. we suggest that cloud opacities in emission may serve as sensitive tracers of the thermal state of a planet’s deep interior through the existence or lack of a cold trap in the deep atmosphere. | formation of silicate and titanium clouds on hot jupiters |
transition disks with large dust cavities around young stars are promising targets for studying planet formation. previous studies have revealed the presence of gas cavities inside the dust cavities, hinting at recently formed, giant planets. however, many of these studies are biased toward the brightest disks in the nearby star-forming regions, and it is not possible to derive reliable statistics that can be compared with exoplanet populations. we present the analysis of 11 transition disks with large cavities (≥20 au radius) from a complete disk survey of the lupus star-forming region, using alma band 7 observations at 0.″3 (22-30 au radius) resolution of the 345 ghz continuum, 13co and c18o 3-2 observations, and the spectral energy distribution of each source. gas and dust surface density profiles are derived using the physical-chemical modeling code dali. this is the first study of transition disks of large cavities within a complete disk survey within a star-forming region. the dust cavity sizes range from 20 to 90 au radius, and in three cases, a gas cavity is resolved as well. the deep drops in gas density and large dust cavity sizes are consistent with clearing by giant planets. the fraction of transition disks with large cavities in lupus is ≳ 11 % , which is inconsistent with exoplanet population studies of giant planets at wide orbits. furthermore, we present a hypothesis of an evolutionary path for large massive disks evolving into transition disks with large cavities. | new insights into the nature of transition disks from a complete disk survey of the lupus star-forming region |
regional transport always plays a crucial role in the formation and dissipation of haze over the beijing-tianjin-hebei (bth) region. this study, conducted using pollution and meteorological observations and the weather research and forecasting model (wrf) coupled with the comprehensive air quality model with extensions (camx), investigated the possible meteorological causes for the occurrence of haze pollution and quantitatively assessed the pm2.5 transport contribution to haze episodes that occurred in beijing in january and july 2015. the results indicated that modeling system reproduced the spatial-temporal variation in pm2.5 concentrations in the bth region well. during the study period, haze episodes were primarily attributed to meteorological conditions such as planetary boundary layer height, relative humidity, wind vector, and temperature inversion, in the context of pollution emissions. analysis of surface pm2.5 transport showed that 62.89% of the surface pm2.5 in beijing was came from local emissions, with the remaining 23.69% and 13.42%, on average, originating from short- and long-range transport during the study period. the percentage of contribution varied with the evolutionary stage of the haze episodes, showing the joint influence of local emissions and regional transport on haze pollution in beijing. additionally, investigation of vertical pm2.5 transport identified the following three major pathways: a northwest-southeast pathway in january (at all layers below 1200 m, though it was stronger above 600 m), a southeast-northwest pathway in july (at all layers below 800 m), and a southwest-northeast pathway during both months (at a height of 200-1200 m). moreover, the magnitude of daily pm2.5 transport fluxes during the haze episodes was generally stronger than the corresponding monthly average. these results provide a scientific basis for strategic control of both multiple cities and provinces and in-depth knowledge of the mechanisms and sources of haze pollution in the bth region. | multiple perspectives for modeling regional pm2.5 transport across cities in the beijing-tianjin-hebei region during haze episodes |
the seasonal variability of black carbon (bc) aerosols in india is studied using high resolution (10 km) bc simulations conducted using the weather research and forecasting model coupled with chemistry. the model reproduces the observed seasonality of surface bc fairly well over most parts of india but fails to capture the seasonality in the himalayas and deviates from the observed bc magnitude at several sites. the errors in modeled bc are attributed to uncertainties in bc emissions and their diurnal cycle, planetary boundary layer height underestimation, and aerosol processes. model results show distinct but opposite seasonality of bc in the lower (lt) and free troposphere (ft) with bc showing winter maximum and summer minimum in the lt and vice versa in the ft. our analysis shows that bc seasonality is not driven by seasonality of the anthropogenic emissions but by changes in the regional meteorology through weakening of the horizontal transport and strengthening of the vertical transport of bc during summertime compared to winter. bc in both the lt and ft comes mostly from anthropogenic emissions followed by biomass burning emissions except during winter when long-distant sources become more important in the ft. bc in the ft is significantly affected by anthropogenic emissions from all parts of india. the source-receptor relationship changes seasonally, but the regional transport remains a significant contributor to bc loadings in the lt of india, highlighting the necessity of considering nonlocal sources along with local emissions when designing strategies for mitigating bc impacts on air quality. | what controls the seasonal cycle of black carbon aerosols in india? |
the growth of dust grains in protoplanetary disks is a necessary first step towards planet formation1. this growth has been inferred from observations of thermal dust emission2 towards mature protoplanetary systems (age >2 million years) with masses that are, on average, similar to neptune3. in contrast, the majority of confirmed exoplanets are heavier than neptune4. given that young protoplanetary disks are more massive than their mature counterparts, this suggests that planet formation starts early, but evidence for grain growth that is spatially and temporally coincident with a massive reservoir in young disks remains scarce. here, we report observations on a lack of emission of carbon monoxide isotopologues within the inner 15 au of a very young (age 100,000 years) disk around the solar-type protostar tmc1a. by using the absence of spatially resolved molecular line emission to infer the gas and dust content of the disk, we conclude that shielding by millimetre-size grains is responsible for the lack of emission. this suggests that grain growth and millimetre-size dust grains can be spatially and temporally coincident with a mass reservoir sufficient for giant planet formation. hence, planet formation starts during the earliest, embedded phases in the life of young stars. | evidence for the start of planet formation in a young circumstellar disk |
ribose is the central molecular subunit in rna, but the prebiotic origin of ribose remains unknown. we observed the formation of substantial quantities of ribose and a diversity of structurally related sugar molecules such as arabinose, xylose, and lyxose in the room-temperature organic residues of photo-processed interstellar ice analogs initially composed of h2o, ch3oh, and nh3. our results suggest that the generation of numerous sugar molecules, including the aldopentose ribose, may be possible from photochemical and thermal treatment of cosmic ices in the late stages of the solar nebula. our detection of ribose provides plausible insights into the chemical processes that could lead to formation of biologically relevant molecules in suitable planetary environments. | ribose and related sugars from ultraviolet irradiation of interstellar ice analogs |
quantifying the atmospheric mass loss during planet formation is crucial for understanding the origin and evolution of planetary atmospheres. we examine the contributions to atmospheric loss from both giant impacts and planetesimal accretion. giant impacts cause global motion of the ground. using analytic self-similar solutions and full numerical integrations we find (for isothermal atmospheres with adiabatic index γ = 5 / 3) that the local atmospheric mass loss fraction for ground velocities vg ≲ 0.25vesc is given by χloss =(1.71vg /vesc) 4.9 , where vesc is the escape velocity from the target. yet, the global atmospheric mass loss is a weaker function of the impactor velocity vimp and mass mimp and given by xloss ≃ 0.4 x + 1.4x2 - 0.8x3 (isothermal atmosphere) and xloss ≃ 0.4 x + 1.8x2 - 1.2x3 (adiabatic atmosphere), where x = (vimp m /vesc m) . atmospheric mass loss due to planetesimal impacts proceeds in two different regimes: (1) large enough impactors m≳√{ 2 }ρ0(πhr) 3 / 2 (25 km for the current earth), are able to eject all the atmosphere above the tangent plane of the impact site, which is h / 2 r of the whole atmosphere, where h, r and ρ0 are the atmospheric scale height, radius of the target, and its atmospheric density at the ground. (2) smaller impactors, but above m > 4 πρ0h3 (1 km for the current earth) are only able to eject a fraction of the atmospheric mass above the tangent plane. we find that the most efficient impactors (per unit impactor mass) for atmospheric loss are planetesimals just above that lower limit (2 km for the current earth). for impactor flux size distributions parametrized by a single power law, n (> r) ∝r - q + 1 , with differential power law index q, we find that for 1 < q < 3 the atmospheric mass loss proceeds in regime (1) whereas for q > 3 the mass loss is dominated by regime (2). impactors with m≲ 4 πρ0h3 are not able to eject any atmosphere. despite being bombarded by the same planetesimal population, we find that the current differences in earth's and venus' atmospheric masses can be explained by modest differences in their initial atmospheric masses and that the current atmosphere of the earth could have resulted from an equilibrium between atmospheric erosion and volatile delivery to the atmosphere from planetesimal impacts. we conclude that planetesimal impacts are likely to have played a major role in atmospheric mass loss over the formation history of the terrestrial planets. | atmospheric mass loss during planet formation: the importance of planetesimal impacts |
mass-radius relationships for water-rich rocky planets are usually calculated assuming most water is present in condensed (either liquid or solid) form. planet density estimates are then compared to these mass-radius relationships, even when these planets are more irradiated than the runaway greenhouse irradiation limit (around 1.1 times the insolation at earth for planets orbiting a sun-like star), for which water has been shown to be unstable in condensed form and would instead form a thick h2o-dominated atmosphere. here we use a 1-d radiative-convective inverse version of the lmd generic numerical climate model to derive new theoretical mass-radius relationships appropriate for water-rich rocky planets that are more irradiated than the runaway greenhouse irradiation limit, meaning planets endowed with a steam, water-dominated atmosphere. as a result of the runaway greenhouse radius inflation effect introduced in previous work, these new mass-radius relationships significantly differ from those traditionally used in the literature. for a given water-to-rock mass ratio, these new mass-radius relationships lead to planet bulk densities much lower than calculated when water is assumed to be in condensed form. in other words, using traditional mass-radius relationships for planets that are more irradiated than the runaway greenhouse irradiation limit tends to dramatically overestimate -possibly by several orders of magnitude- their bulk water content. in particular, this result applies to trappist-1 b, c, and d, which can accommodate a water mass fraction of at most 2, 0.3 and 0.08%, respectively, assuming planetary core with a terrestrial composition. in addition, we show that significant changes of mass-radius relationships (between planets less and more irradiated than the runaway greenhouse limit) can be used to remove bulk composition degeneracies in multiplanetary systems such as trappist-1. broadly speaking, our results demonstrate that non-h2/he-dominated atmospheres can have a first-order effect on the mass-radius relationships, even for rocky planets receiving moderate irradiation. finally, we provide an empirical formula for the h2o steam atmosphere thickness as a function of planet core gravity and radius, water content, and irradiation. this formula can easily be used to construct mass-radius relationships for any water-rich, rocky planet (i.e., with any kind of interior composition ranging from pure iron to pure silicate) more irradiated than the runaway greenhouse irradiation threshold. | revised mass-radius relationships for water-rich rocky planets more irradiated than the runaway greenhouse limit |
we present a combined observational and theoretical analysis to investigate the nature of plasma turbulence at kinetic scales in the earth’s magnetosheath. in the first decade of the kinetic range, just below the ion gyroscale, the turbulence was found to be similar to that in the upstream solar wind: predominantly anisotropic, low-frequency and kinetic alfvén in nature. a key difference, however, is that the magnetosheath ions are typically much hotter than the electrons, {t}{{i}}\gg {t}{{e}}, which, together with {β }{{i}}∼ 1, leads to a change in behavior in the second decade, close to electron scales. the turbulence here is characterized by an increased magnetic compressibility, following a mode we term the inertial kinetic alfvén wave, and a steeper spectrum of magnetic fluctuations, consistent with the prediction {e}b({k}\perp )\propto {k}\perp -11/3 that we obtain from a set of nonlinear equations. this regime of plasma turbulence may also be relevant for other astrophysical environments with {t}{{i}}\gg {t}{{e}}, such as the solar corona, hot accretion flows, and regions downstream of collisionless shocks. | nature of kinetic scale turbulence in the earth's magnetosheath |
the initial mass distribution in the solar nebula is a critical input to planet formation models that seek to reproduce today's solar system 1 . traditionally, constraints on the gas mass distribution are derived from observations of the dust emission from disks 2,3 , but this approach suffers from large uncertainties in dust opacity and gas-to-dust ratio 2 . on the other hand, previous observations of gas tracers only probe surface layers above the bulk mass reservoir 4 . here we present the first partially spatially resolved observations of the 13c18o j = 3-2 line emission in the closest protoplanetary disk, tw hydrae, a gas tracer that probes the bulk mass distribution. combining it with the c18o j = 3-2 emission and the previously detected hd j = 1-0 flux, we directly constrain the mid-plane temperature and optical depths of gas and dust emission. we report a gas mass distribution with radius, r, of 13 - 5 + 8 × ( r / 20 .5 au ) - 0.9 - 0.3 + 0.4 g cm-2 in the expected formation zone of gas and ice giants (5-21 au). we find that the mass ratio of total gas to millimetre-sized dust is 140 in this region, suggesting that at least 2.4m⊕ of dust aggregates have grown to centimetre sizes (and perhaps much larger). the radial distribution of gas mass is consistent with a self-similar viscous disk profile but much flatter than the posterior extrapolation of mass distribution in our own and extrasolar planetary systems. | mass inventory of the giant-planet formation zone in a solar nebula analogue |
the precursors to larger, biologically relevant molecules are detected throughout interstellar space, but determining the presence and properties of these molecules during planet formation requires observations of protoplanetary disks at high angular resolution and sensitivity. here, we present 0"3 observations of hc3n, ch3cn, and c-c3h2 in five protoplanetary disks observed as part of the molecules with alma at planet-forming scales (maps) large program. we robustly detect all molecules in four of the disks (gm aur, as 209, hd 163296, and mwc 480) with tentative detections of c-c3h2 and ch3cn in im lup. we observe a range of morphologies-central peaks, single or double rings-with no clear correlation in morphology between molecule or disk. emission is generally compact and on scales comparable with the millimeter dust continuum. we perform both disk-integrated and radially resolved rotational diagram analysis to derive column densities and rotational temperatures. the latter reveals 5-10 times more column density in the inner 50-100 au of the disks when compared with the disk-integrated analysis. we demonstrate that ch3cn originates from lower relative heights in the disks when compared with hc3n, in some cases directly tracing the disk midplane. finally, we find good agreement between the ratio of small to large nitriles in the outer disks and comets. our results indicate that the protoplanetary disks studied here are host to significant reservoirs of large organic molecules, and that this planet- and comet-building material can be chemically similar to that in our own solar system. this paper is part of the maps special issue of the astrophysical journal supplement. | molecules with alma at planet-forming scales (maps). ix. distribution and properties of the large organic molecules hc3n, ch3cn, and c-c3h2 |
this chapter reviews accretion models for kuiper belt objects (kbos), discussing in particular the compatibility of the observed properties of the kbo population with the streaming instability paradigm. then it discusses how the dynamical structure of the kbo population, including the formation of its five subcomponents (cold, hot, resonant, scattered, and fossilized), can be quantitatively understood in the framework of the giant planet instability. we also establish the connections between the kbo population and the trojans of jupiter and neptune, the irregular satellites of all giant planets, the oort cloud and the d-type main belt asteroids. finally, we discuss the collisional evolution of the kbo population, arguing that the current size-frequency distribution below 100 km in size has been achieved as a collisional equilibrium in a few tens of myr inside the original massive trans-neptunian disk, possibly with the exception of the cold population subcomponent. | kuiper belt: formation and evolution |
we report helium absorption from the escaping atmosphere of toi 560.01 (hd 73583b), an r = 2.8r ⊕, p = 6.4 day mini-neptune orbiting a young (~600 myr) k dwarf. using keck/nirspec, we detect a signal with an average depth of 0.68% ± 0.08% in the line core. the absorption signal repeats during a partial transit obtained a month later, but is marginally stronger and bluer, perhaps reflecting changes in the stellar wind environment. ingress occurs on time, and egress occurs within 12 minutes of the white light egress, although absorption rises more gradually than it declines. this suggests that the outflow is slightly asymmetric and confined to regions close to the planet. the absorption signal also exhibits a slight 4 km s-1 redshift rather than the expected blueshift; this might be explained if the planet has a modest orbital eccentricity, although the radial velocity data disfavors such an explanation. we use xmm-newton observations to reconstruct the high-energy stellar spectrum and model the planet's outflow with 1d and 3d hydrodynamic simulations. we find that our models generally overpredict the measured magnitude of the absorption during transit, the size of the blueshift, or both. increasing the metallicity to 100× solar suppresses the signal, but the dependence of the predicted signal strength on metallicity is non-monotonic. decreasing the assumed stellar euv flux by a factor of three likewise suppresses the signal substantially. | escaping helium from toi 560.01, a young mini-neptune |
we detect lyα absorption from the escaping atmosphere of hd 63433c, a r = 2.67r ⊕, p = 20.5 day mini-neptune orbiting a young (440 myr) solar analog in the ursa major moving group. using hubble space telescope (hst)/space telescope imaging spectrograph, we measure a transit depth of 11.1 ± 1.5% in the blue wing and 8 ± 3% in the red. this signal is unlikely to be due to stellar variability, but should be confirmed by an upcoming second transit observation with hst. we do not detect lyα absorption from the inner planet, a smaller r = 2.15r ⊕ mini-neptune on a 7.1 day orbit. we use keck/nirspec to place an upper limit of 0.5% on helium absorption for both planets. we measure the host star's x-ray spectrum and mid-ultraviolet flux with xmm-newton, and model the outflow from both planets using a 3d hydrodynamic code. this model provides a reasonable match to the light curve in the blue wing of the lyα line and the helium nondetection for planet c, although it does not explain the tentative red wing absorption or reproduce the excess absorption spectrum in detail. its predictions of strong lyα and helium absorption from b are ruled out by the observations. this model predicts a much shorter mass-loss timescale for planet b, suggesting that b and c are fundamentally different: while the latter still retains its hydrogen/helium envelope, the former has likely lost its primordial atmosphere. | detection of ongoing mass loss from hd 63433c, a young mini-neptune |
stellar rotation periods are valuable both for constraining models of angular momentum loss and for understanding how magnetic features impact inferences of exoplanet parameters. building on our previous work in the northern hemisphere, we have used long-term, ground-based photometric monitoring from the mearth observatory to measure 234 rotation periods for nearby, southern hemisphere m dwarfs. notable examples include the exoplanet hosts gj 1132, lhs 1140, and proxima centauri. we find excellent agreement between our data and k2 photometry for the overlapping subset. among the sample of stars with the highest quality data sets, we recover periods in 66%; as the length of the data set increases, our recovery rate approaches 100%. the longest rotation periods we detect are around 140 days, which we suggest represent the periods that are reached when m dwarfs are as old as the local thick disk (about 9 gyr). | new rotation period measurements for m dwarfs in the southern hemisphere: an abundance of slowly rotating, fully convective stars |
active dark flows known as recurring slope lineae have been observed on the warmest slopes of equatorial mars. the morphology, composition and seasonality of the lineae suggest a role of liquid water in their formation. however, internal and atmospheric sources of water appear to be insufficient to sustain the observed slope activity. experimental evidence suggests that under the low atmospheric pressure at the surface of mars, gas can flow upwards through porous martian soil due to thermal creep under surface regions heated by the sun, and disturb small particles. here we present numerical simulations to demonstrate that such a dry process involving the pumping of rarefied gas in the martian soil due to temperature contrasts can explain the formation of the recurring slope lineae. in our simulations, solar irradiation followed by shadow significantly reduces the angle of repose due to the resulting temporary temperature gradients over shaded terrain, and leads to flow at intermediate slope angles. the simulated flow locations are consistent with observed recurring slope lineae that initiate in rough and bouldered terrains with local shadows over the soil. we suggest that this dry avalanche process can explain the formation of the recurring slope lineae on mars without requiring liquid water or co2 frost activity. | formation of recurring slope lineae on mars by rarefied gas-triggered granular flows |
in the present work sensitivity of weather research forecasting (wrf) model has been carried out using five planetary boundary layer (pbl) schemes - yonsei university scheme (ysu), mellor-yamada-janjić scheme (myj), aymmetric convective model version 2 (acm2), quasi normal scale elimination scheme (qnse), mellor-yamada-nakanishi-niino scheme (mynn) in different climatic zones over india namely tropical, temperate and arid for surface meteorological parameters, upper air variables and planetary boundary layer height during summer and winter season. the model outputs have been compared with observations through standard statistical measures. the aim is to study the relative performance of these schemes, selecting the best option climatic zone-wise and thereby minimizing uncertainty in model predictions. wrf model performance evaluation shows better agreement for temperature and relative humidity compared to wind speed. overall for india, acm2, qnse show good performance for temperature and relative humidity whereas acm2, mynn show better performance for wind speed though these may vary for different climatic zones. geopotential height and wind over 850 hpa is well simulated by acm2 and mynn over india. for pbl height acm2, mynn and myj works best for chennai, new delhi and kolkata respectively during summer period. however, for winter period myj works best for chennai while, qnse works best for new delhi and kolkata. considering all meteorological parameters together, it is seen that for arid zone acm2, qnse and myj schemes work reasonably well. for temperate zone, acm2, qnse and mynn schemes show better results. for tropical zone all pbl schemes work closely. hence, depending on the application, parameter and climate zone, this study provides suitable recommendations for choosing pbl schemes appropriately for each zone and parameter separately for the indian region. | sensitivity of wrf model estimates to various pbl parameterizations in different climatic zones over india |
the planetary camera and spectrograph (pcs) for the extremely large telescope (elt) will be dedicated to detecting and characterising nearby exoplanets with sizes from sub-neptune to earth-size in the neighbourhood of the sun. this goal is achieved by a combination of extreme adaptive optics (xao), coronagraphy and spectroscopy. pcs will allow us not only to take images, but also to look for biosignatures such as molecular oxygen in the exoplanets' atmospheres. this article describes the pcs primary science goals, the instrument concept and the research and development activities that will be carried out over the coming years. | pcs — a roadmap for exoearth imaging with the elt |
ex lup is a low-mass pre-main-sequence star that occasionally shows accretion-related outbursts. here, we present jwst/miri medium-resolution spectroscopy obtained for ex lup 14 yr after its powerful outburst. ex lup is now in quiescence and displays a class ii spectrum. we detect a forest of emission lines from molecules previously identified in infrared spectra of classical t tauri disks: h2o, oh, h2, hcn, c2h2, and co2. the detection of organic molecules demonstrates that they are back after disappearing during the large outburst. spectral lines from water and oh are for the first time deblended and will provide a much-improved characterization of their distribution and density in the inner disk. the spectrum also shows broad emission bands from warm, submicron-size amorphous silicate grains at 10 and 18 μm. during the outburst, in 2008, crystalline forsterite grains were annealed in the inner disk within 1 au, but their spectral signatures in the 10 μm silicate band later disappeared. with jwst we rediscovered these crystals via their 19.0, 20.0, and 23.5 μm emission, the strength of which implies that the particles are at ~3 au from the star. this suggests that crystalline grains formed in 2008 were transported outwards and now approach the water snowline, where they may be incorporated into planetesimals. containing several key tracers of planetesimal and planet formation, ex lup is an ideal laboratory to study the effects of variable luminosity on the planet-forming material and may provide an explanation for the observed high crystalline fraction in solar system comets. | jwst/miri spectroscopy of the disk of the young eruptive star ex lup in quiescence |
mass-independent isotopic anomalies define two cosmochemically distinct regions: the carbonaceous and non-carbonaceous meteorites1, implying that the non-carbonaceous (terrestrial) and carbonaceous (jovian) reservoirs were kept separate during and after planet formation. the formation of jupiter is widely invoked to explain this compositional dichotomy by acting as an effective barrier between the two reservoirs2. jupiter's solid kernel possibly grew to 20 earth masses (m⊕?) in 1 myr from the accretion of submetre-sized objects (`pebbles'), followed by slower accretion via planetesimals. subsequent gas envelope contraction led to jupiter's formation as a gas giant3. here, we use dynamical simulations to show that the growth of jupiter from pebble accretion is not fast enough to be responsible for the inferred separation of the terrestrial and jovian reservoirs. we propose instead that the dichotomy was caused by a pressure maximum in the disk near jupiter's location, which created a ringed structure such as those detected by alma4. one or multiple such—potentially mobile—long-lived pressure maxima almost completely prevented pebbles from the jovian region reaching the terrestrial zone, maintaining a compositional partition between the two regions. we thus suggest that our young solar system's protoplanetary disk developed at least one and probably multiple rings, which potentially triggered the formation of the giant planets. | the partitioning of the inner and outer solar system by a structured protoplanetary disk |
with the discovery of planets beyond our solar system 25 years ago, exoplanet research has expanded dramatically, with new state-of-the-art ground-based and space-based missions dedicated to their discovery and characterisation. with more than 3,500 exoplanets now known, the complexity of the discovery techniques, observations and physical characterisation have grown exponentially. this handbook ties all these avenues of research together across a broad range of exoplanet science. planet formation, exoplanet interiors and atmospheres, and habitability are discussed, providing in-depth coverage of our knowledge to date. comprehensively updated from the first edition, it includes instrumental and observational developments, in-depth treatment of the new kepler mission results and hot jupiter atmospheric studies, and major updates on models of exoplanet formation. with extensive references to the research literature and appendices covering all individual exoplanet discoveries, it is a valuable reference to this exciting field for both incoming and established researchers. | the exoplanet handbook |
the transiting exoplanet survey satellite (tess) will provide high-precision time series photometry for millions of stars with at least a half-hour cadence. of particular interest are the circular regions of 12° radius centred around the ecliptic poles that will be observed continuously for a full year. spectroscopic stellar parameters are desirable to characterize and select suitable targets for tess, whether they are focused on exploring exoplanets, stellar astrophysics or galactic archaeology. here, we present spectroscopic stellar parameters (teff, log g, [fe/h], v sin i, vmicro) for about 16 000 dwarf and subgiant stars in tess' southern continuous viewing zone. for almost all the stars, we also present bayesian estimates of stellar properties including distance, extinction, mass, radius and age using theoretical isochrones. stellar surface gravity and radius are made available for an additional set of roughly 8500 red giants. all our target stars are in the range 10 < v < 13.1. among them, we identify and list 227 stars belonging to the large magellanic cloud. the data were taken using the high efficiency and resolution multi-element spectrograph (hermes; r ∼ 28 000) at the anglo-australian telescope as part of the tess-hermes survey. comparing our results with the tess input catalogue (tic) shows that the tic is generally efficient in separating dwarfs and giants, but it has flagged more than 100 cool dwarfs (teff < 4800 k) as giants, which ought to be high-priority targets for the exoplanet search. the catalogue can be accessed via http://www.physics.usyd.edu.au/tess-hermes/, or at mikulski archive for space telescopes (mast). | the tess-hermes survey data release 1: high-resolution spectroscopy of the tess southern continuous viewing zone |
the response of the indian summer monsoon (ism) circulation and precipitation to middle east dust aerosols on sub-seasonal timescales is studied using observations and the weather research and forecasting model coupled with online chemistry (wrf-chem). satellite data show that the ism rainfall in coastal southwest india, central and northern india, and pakistan is closely associated with the middle east dust aerosols. the physical mechanism behind this dust-ism rainfall connection is examined through ensemble simulations with and without dust emissions. each ensemble includes 16 members with various physical and chemical schemes to consider the model uncertainties in parameterizing short-wave radiation, the planetary boundary layer, and aerosol chemical mixing rules. experiments show that dust aerosols increase rainfall by about 0.44 mm day-1 (~10 % of the climatology) in coastal southwest india, central and northern india, and north pakistan, a pattern consistent with the observed relationship. the ensemble mean rainfall response over india shows a much stronger spatial correlation with the observed rainfall response than any other ensemble members. the largest modeling uncertainties are from the boundary layer schemes, followed by short-wave radiation schemes. in wrf-chem, the dust aerosol optical depth (aod) over the middle east shows the strongest correlation with the ism rainfall response when dust aod leads rainfall response by about 11 days. further analyses show that increased ism rainfall is related to enhanced southwesterly monsoon flow and moisture transport from the arabian sea to the indian subcontinent, which are associated with the development of an anomalous low-pressure system over the arabian sea, the southern arabian peninsula, and the iranian plateau due to dust-induced heating in the troposphere. the dust-induced heating in the mid-upper troposphere is mainly located in the iranian plateau rather than the tibetan plateau. this study demonstrates a thermodynamic mechanism that links remote desert dust emissions in the middle east to ism circulation and precipitation variability on sub-seasonal timescales, which may have implications for ism rainfall forecasts. | consistent response of indian summer monsoon to middle east dust in observations and simulations |
planetesimals may form from the gravitational collapse of dense particle clumps initiated by the streaming instability. we use simulations of aerodynamically coupled gas-particle mixtures to investigate whether the properties of planetesimals formed in this way depend upon the sizes of the particles that participate in the instability. based on three high-resolution simulations that span a range of dimensionless stopping times 6× {10}-3≤slant τ ≤slant 2, no statistically significant differences in the initial planetesimal mass function are found. the mass functions are fit by a power law, {dn}/{{dm}}p\propto {m}p-p, with p = 1.5-1.7 and errors of {{δ }}p≈ 0.1. comparing the particle density fields prior to collapse, we find that the high-wavenumber power spectra are similarly indistinguishable, though the large-scale geometry of structures induced via the streaming instability is significantly different between all three cases. we interpret the results as evidence for a near-universal slope to the mass function, arising from the small-scale structure of streaming-induced turbulence. | evidence for universality in the initial planetesimal mass function |
this paper uses observations of dusty debris discs, including a growing number of gas detections in these systems, to test our understanding of the origin and evolution of this gaseous component. it is assumed that all debris discs with icy planetesimals create second generation co, c and o gas at some level, and the aim of this paper is to predict that level and assess its observability. we present a new semi-analytical equivalent of the numerical model of kral et al. allowing application to large numbers of systems. that model assumes co is produced from volatile-rich solid bodies at a rate that can be predicted from the debris discs fractional luminosity. co photodissociates rapidly into c and o that then evolve by viscous spreading. this model provides a good qualitative explanation of all current observations, with a few exceptional systems that likely have primordial gas. the radial location of the debris and stellar luminosity explain some non-detections, e.g. close-in debris (like hd 172555) is too warm to retain co, while high stellar luminosities (like η tel) result in short co lifetimes. we list the most promising targets for gas detections, predicting >15 co detections and >30 c i detections with alma, and tens of c ii and o i detections with future far-ir missions. we find that co, c i, c ii and o i gas should be modelled in non-lte for most stars, and that co, c i and o i lines will be optically thick for the most gas-rich systems. finally, we find that radiation pressure, which can blow out c i around early-type stars, can be suppressed by self-shielding. | predictions for the secondary co, c and o gas content of debris discs from the destruction of volatile-rich planetesimals |
radial substructures in circumstellar discs are now routinely observed by atacama large millimeter/submillimeter array. there is also growing evidence that disc winds drive accretion in such discs. we show through 2d (axisymmetric) simulations that rings and gaps develop naturally in magnetically coupled disc-wind systems on the scale of tens of au, where ambipolar diffusion (ad) is the dominant non-ideal magnetohydrodynamic effect. in simulations where the magnetic field and matter are moderately coupled, the disc remains relatively laminar with the radial electric current steepened by ad into a thin layer near the mid-plane. the toroidal magnetic field sharply reverses polarity in this layer, generating a large magnetic torque that drives fast accretion, which drags the poloidal field into a highly pinched radial configuration. the reconnection of this pinched field creates magnetic loops where the net poloidal magnetic flux (and thus the accretion rate) is reduced, yielding dense rings. neighbouring regions with stronger poloidal magnetic fields accrete faster, forming gaps. in better magnetically coupled simulations, the so-called avalanche accretion streams develop continuously near the disc surface, rendering the disc-wind system more chaotic. nevertheless, prominent rings and gaps are still produced, at least in part, by reconnection, which again enables the segregation of the poloidal field and the disc material similar to the more diffusive discs. however, the reconnection is now driven by the non-linear growth of magnetorotational instability channel flows. the formation of rings and gaps in rapidly accreting yet laminar discs has interesting implications for dust settling and trapping, grain growth, and planet formation. | the formation of rings and gaps in magnetically coupled disc-wind systems: ambipolar diffusion and reconnection |
the recent discovery of three earth-sized, potentially habitable planets around a nearby cool star, trappist-1, has provided three key targets for the upcoming james webb space telescope (jwst). depending on their atmospheric characteristics and precise orbit configurations, it is possible that any of the three planets may be in the liquid water habitable zone, meaning that they may be capable of supporting life. we find that present-day earth levels of ozone, if present, would be detectable if jwst observes 60 transits for innermost planet 1b and 30 transits for 1c and 1d. | habitable worlds with jwst: transit spectroscopy of the trappist-1 system? |
this paper presents the atmospheric characterization of three large, gaseous planets: wasp-127 b, wasp-79 b, and wasp-62 b. we analyzed spectroscopic data obtained with the g141 grism (1.088-1.68 μm) of the wide field camera 3 on board the hubble space telescope using the iraclis pipeline and the taurex3 retrieval code, both of which are publicly available. for wasp-127 b, which is the least dense planet discovered so far and is located in the short-period neptune desert, our retrieval results found strong water absorption corresponding to an abundance of log(h2o) = -2.71 ${}_{-1.05}^{+0.78}$ and absorption compatible with an iron hydride abundance of log(feh) = $-{5.25}_{-1.10}^{+0.88}$ , with an extended cloudy atmosphere. we also detected water vapor in the atmospheres of wasp-79 b and wasp-62 b, with best-fit models indicating the presence of iron hydride, too. we used the atmospheric detectability index as well as bayesian log evidence to quantify the strength of the detection and compared our results to the hot jupiter population study by tsiaras et al. while all the planets studied here are suitable targets for characterization with upcoming facilities such as the james webb space telescope and ariel, wasp-127 b is of particular interest due to its low density, and a thorough atmospheric study would develop our understanding of planet formation and migration. * ares: ariel retrieval of exoplanets school. | ares. ii. characterizing the hot jupiters wasp-127 b, wasp-79 b, and wasp-62b with the hubble space telescope |
solar coronal mass ejections (cmes) and flares have a statistically well-defined relationship, with more energetic x-ray flares corresponding to faster and more massive cmes. how this relationship extends to more magnetically active stars is a subject of open research. here we study the most probable stellar cme candidates associated with flares captured in the literature to date, all of which were observed on magnetically active stars. we use a simple cme model to derive masses and kinetic energies from observed quantities and transform associated flare data to the geostationary operational environmental satellite 1-8 å band. derived cme masses range from ∼1015 to 1022 g. associated flare x-ray energies range from 1031 to 1037 erg. stellar cme masses as a function of associated flare energy generally lie along or below the extrapolated mean for solar events. in contrast, cme kinetic energies lie below the analogous solar extrapolation by roughly 2 orders of magnitude, indicating approximate parity between flare x-ray and cme kinetic energies. these results suggest that the cmes associated with very energetic flares on active stars are more limited in terms of the ejecta velocity than the ejecta mass, possibly because of the restraining influence of strong overlying magnetic fields and stellar wind drag. lower cme kinetic energies and velocities present a more optimistic scenario for the effects of cme impacts on exoplanets in close proximity to active stellar hosts. | the stellar cme-flare relation: what do historic observations reveal? |
lakes existed on mars later than 3.6 billion years ago, according to sedimentary evidence for deltaic deposition. the observed fluviolacustrine deposits suggest that individual lake-forming climates persisted for at least several thousand years (assuming dilute flow). but the lake watersheds’ little-weathered soils indicate a largely dry climate history, with intermittent runoff events. here we show that these observational constraints, although inconsistent with many previously proposed triggers for lake-forming climates, are consistent with a methane burst scenario. in this scenario, chaotic transitions in mean obliquity drive latitudinal shifts in temperature and ice loading that destabilize methane clathrate. using numerical simulations, we find that outgassed methane can build up to atmospheric levels sufficient for lake-forming climates, if methane clathrate initially occupies more than 4% of the total volume in which it is thermodynamically stable. such occupancy fractions are consistent with methane production by water-rock reactions due to hydrothermal circulation on early mars. we further estimate that photochemical destruction of atmospheric methane curtails the duration of individual lake-forming climates to less than a million years, consistent with observations. we conclude that methane bursts represent a potential pathway for intermittent excursions to a warm, wet climate state on early mars. | methane bursts as a trigger for intermittent lake-forming climates on post-noachian mars |
exoplanet catalogs produced by surveys suffer from a lack of completeness (not every planet is detected) and less than perfect reliability (not every planet in the catalog is a true planet), particularly near the survey's detection limit. exoplanet occurrence rate studies based on such a catalog must be corrected for completeness and reliability. the final kepler data release, dr25, features a uniformly vetted planet candidate catalog and data products that facilitate corrections. we present a new probabilistic approach to the characterization of kepler completeness and reliability, making full use of the kepler dr25 products. we illustrate the impact of completeness and reliability corrections with a poisson-likelihood occurrence rate method, using a recent stellar properties catalog that incorporates gaia stellar radii and essentially uniform treatment of the stellar population. correcting for reliability has a significant impact: the exoplanet occurrence rate for orbital period and radius within 20% of earth's around gk dwarf stars, corrected for reliability, is ${0.015}_{-0.007}^{+0.011}$ , whereas not correcting results in ${0.034}_{-0.012}^{+0.018}$ —correcting for reliability reduces this occurrence rate by more than a factor of two. we further show that using gaia-based versus dr25 stellar properties impacts the same occurrence rate by a factor of two. we critically examine the the dr25 catalog and the assumptions behind our occurrence rate method. we propose several ways in which confidence in both the kepler catalog and occurrence rate calculations can be improved. this work provides an example of how the community can use the dr25 completeness and reliability products. | a probabilistic approach to kepler completeness and reliability for exoplanet occurrence rates |
the final architecture of planetary systems depends on the extraction of angular momentum and mass-loss processes of the discs in which they form. theoretical studies proposed that magnetohydrodynamic winds launched from the discs (mhd disc winds) could govern accretion and disc dispersal. in this work, we revisit the observed disc demographics in the framework of mhd disc winds, combining analytical solutions of disc evolution and a disc population synthesis approach. we show that mhd disc winds alone can account for both disc dispersal and accretion properties. the decline of disc fraction over time is reproduced by assuming that the initial accretion time-scale (a generalization of the viscous time-scale) varies from disc to disc and that the decline of the magnetic field strength is slower than that of the gas. the correlation between accretion rate and disc mass, and the dispersion of the data around the mean trend as observed in lupus, is then naturally reproduced. the model also accounts for the rapidity of the disc dispersal. this paves the way for planet formation models in the paradigm of wind-driven accretion. | mhd disc winds can reproduce fast disc dispersal and the correlation between accretion rate and disc mass in lupus |
we present stellar rotation periods for late k- and early m-dwarf members of the 4 gyr old open cluster m67 as calibrators for gyrochronology and tests of stellar spin-down models. using gaia edr3 astrometry for cluster membership and pan-starrs (ps1) photometry for binary identification, we build this set of rotation periods from a campaign of monitoring m67 with the canada-france-hawaii telescope's megaprime wide-field imager. we identify 1807 members of m67, of which 294 are candidate single members with significant rotation period detections. moreover, we fit a polynomial to the period versus color-derived effective temperature sequence observed in our data. we find that the rotation of very cool dwarfs can be explained by simple solid-body spin-down between 2.7 and 4 gyr. we compare this rotational sequence to the predictions of gyrochronological models and find that the best match is skumanich-like spin-down, p rot ∝ t 0.62, applied to the sequence of ruprecht 147. this suggests that, for spectral types k7-m0 with near-solar metallicity, once a star resumes spinning down, a simple skumanich-like relation is sufficient to describe their rotation evolution, at least through the age of m67. additionally, for stars in the range m1-m3, our data show that spin-down must have resumed prior to the age of m67, in conflict with the predictions of the latest spin-down models. | a 4 gyr m-dwarf gyrochrone from cfht/megaprime monitoring of the open cluster m67 |
water, the most abundant volatile in earth’s interior, preserves the young surface of our planet by catalysing mantle convection, lubricating plate tectonics and feeding arc volcanism. since planetary accretion, water has been exchanged between the hydrosphere and the geosphere, but its depth distribution in the mantle remains elusive. water drastically reduces the strength of olivine and this effect can be exploited to estimate the water content of olivine from the mechanical response of the asthenosphere to stress perturbations such as the ones following large earthquakes. here, we exploit the sensitivity to water of the strength of olivine, the weakest and most abundant mineral in the upper mantle, and observations of the exceptionally large (moment magnitude 8.6) 2012 indian ocean earthquake to constrain the stratification of water content in the upper mantle. taking into account a wide range of temperature conditions and the transient creep of olivine, we explain the transient deformation in the aftermath of the earthquake that was recorded by continuous geodetic stations along sumatra as the result of water- and stress-activated creep of olivine. this implies a minimum water content of about 0.01 per cent by weight—or 1,600 h atoms per million si atoms—in the asthenosphere (the part of the upper mantle below the lithosphere). the earthquake ruptured conjugate faults down to great depths, compatible with dry olivine in the oceanic lithosphere. we attribute the steep rheological contrast to dehydration across the lithosphere-asthenosphere boundary, presumably by buoyant melt migration to form the oceanic crust. | upper-mantle water stratification inferred from observations of the 2012 indian ocean earthquake |
recent measurements of the volatile composition of the coma of comet 67p/churyumov-gerasimenko (hereafter 67p) allow constraints to be set on the origin of volatile elements (water, carbon, nitrogen, noble gases) in inner planets' atmospheres. analyses by the rosina mass spectrometry system onboard the rosetta spacecraft indicate that 67p ice has a d/h ratio three times that of the ocean value (altwegg et al., 2015) and contains significant amounts of n2, co, co2, and importantly, argon (balsiger et al., 2015). here we establish a model of cometary composition based on literature data and the rosina measurements. from mass balance calculations, and provided that 67p is representative of the cometary ice reservoir, we conclude that the contribution of cometary volatiles to the earth's inventory was minor for water (≤1%), carbon (≤1%), and nitrogen species (a few % at most). however, cometary contributions to the terrestrial atmosphere may have been significant for the noble gases. they could have taken place towards the end of the main building stages of the earth, after the moon-forming impact and during either a late veneer episode or, more probably, the terrestrial late heavy bombardment around 4.0-3.8 billion years (ga) ago. contributions from the outer solar system via cometary bodies could account for the dichotomy of the noble gas isotope compositions, in particular xenon, between the mantle and the atmosphere. a mass balance based on 36ar and organics suggests that the amount of prebiotic material delivered by comets could have been quite considerable - equivalent to the present-day mass of the biosphere. on mars, several of the isotopic signatures of surface volatiles (notably the high d/h ratios) are clearly indicative of atmospheric escape processes. nevertheless, we suggest that cometary contributions after the major atmospheric escape events, e.g., during a martian late heavy bombardment towards the end of the noachian era, could account for the martian elemental c/n/36ar ratios, solar-like krypton isotope composition and high 15n/14n ratios. taken together, these observations are consistent with the volatiles of earth and mars being trapped initially from the nebular gas and local accreting material, then progressively added to by contributions from wet bodies from increasing heliocentric distances. overall, no unified scenario can account for all of the characteristics of the inner planet atmospheres. advances in this domain will require precise analysis of the elemental and isotopic compositions of comets and therefore await a cometary sample return mission. | origins of volatile elements (h, c, n, noble gases) on earth and mars in light of recent results from the rosetta cometary mission |
in this work we investigate the impact of calculating non-equilibrium chemical abundances consistently with the temperature structure for the atmospheres of highly-irradiated, close-in gas giant exoplanets. chemical kinetics models have been widely used in the literature to investigate the chemical compositions of hot jupiter atmospheres which are expected to be driven away from chemical equilibrium via processes such as vertical mixing and photochemistry. all of these models have so far used pressure-temperature (p-t) profiles as fixed model input. this results in a decoupling of the chemistry from the radiative and thermal properties of the atmosphere, despite the fact that in nature they are intricately linked. we use a one-dimensional radiative-convective equilibrium model, atmo, which includes a sophisticated chemistry scheme to calculate p-t profiles which are fully consistent with non-equilibrium chemical abundances, including vertical mixing and photochemistry. our primary conclusion is that, in cases of strong chemical disequilibrium, consistent calculations can lead to differences in the p-t profile of up to 100 k compared to the p-t profile derived assuming chemical equilibrium. this temperature change can, in turn, have important consequences for the chemical abundances themselves as well as for the simulated emission spectra. in particular, we find that performing the chemical kinetics calculation consistently can reduce the overall impact of non-equilibrium chemistry on the observable emission spectrum of hot jupiters. simulated observations derived from non-consistent models could thus yield the wrong interpretation. we show that this behaviour is due to the non-consistent models violating the energy budget balance of the atmosphere. | the effects of consistent chemical kinetics calculations on the pressure-temperature profiles and emission spectra of hot jupiters |
we combine analytical understanding of resonant dynamics in two-planet systems with machine-learning techniques to train a model capable of robustly classifying stability in compact multiplanet systems over long timescales of 109 orbits. our stability of planetary orbital configurations klassifier (spock) predicts stability using physically motivated summary statistics measured in integrations of the first 104 orbits, thus achieving speed-ups of up to 105 over full simulations. this computationally opens up the stability-constrained characterization of multiplanet systems. our model, trained on ∼100,000 three-planet systems sampled at discrete resonances, generalizes both to a sample spanning a continuous period-ratio range, as well as to a large five-planet sample with qualitatively different configurations to our training dataset. our approach significantly outperforms previous methods based on systems' angular momentum deficit, chaos indicators, and parametrized fits to numerical integrations. we use spock to constrain the free eccentricities between the inner and outer pairs of planets in the kepler-431 system of three approximately earth-sized planets to both be below 0.05. our stability analysis provides significantly stronger eccentricity constraints than currently achievable through either radial velocity or transit-duration measurements for small planets and within a factor of a few of systems that exhibit transit-timing variations (ttvs). given that current exoplanet-detection strategies now rarely allow for strong ttv constraints [s. hadden, t. barclay, m. j. payne, m. j. holman, astrophys. j. 158, 146 (2019)], spock enables a powerful complementary method for precisely characterizing compact multiplanet systems. we publicly release spock for community use. | predicting the long-term stability of compact multiplanet systems |
the galilean moons play major roles in the giant magnetosphere of jupiter. at the same time, the magnetospheric particles and fields affect the moons. the impact of magnetospheric ions on the moons' atmospheres supplies clouds of escaping neutral atoms that populate a substantial fraction of their orbits. at the same time, ionization of atoms in the neutral cloud is the primary source of magnetospheric plasma. the stability of this feedback loop depends on the plasma/moon-atmosphere interaction. the purpose of this review is to describe the physical processes that shape the space environment around the two innermost galilean moons—io and europa—and to show their impact from the planet jupiter out into interplanetary space. | the space environment of io and europa |
anthropogenic heat (ah) emissions from human activities caused by urbanization can affect the city environment. based on the energy consumption and the gridded demographic data, the spatial distribution of ah emission over the yangtze river delta (yrd) region is estimated. meanwhile, a new method for the ah parameterization is developed in the wrf/chem model, which incorporates the gridded ah emission data with the seasonal and diurnal variations into the simulations. by running this upgraded wrf/chem for 2 typical months in 2010, the impacts of ah on the meteorology and air quality over the yrd region are studied. the results show that the ah fluxes over the yrd have been growing in recent decades. in 2010, the annual-mean values of ah over shanghai, jiangsu and zhejiang are 14.46, 2.61 and 1.63 w m-2, respectively, with the high value of 113.5 w m-2 occurring in the urban areas of shanghai. these ah emissions can significantly change the urban heat island and urban-breeze circulations in the cities of the yrd region. in shanghai, 2 m air temperature increases by 1.6 °c in january and 1.4 °c in july, the pblh (planetary boundary layer height) rises up by 140 m in january and 160 m in july, and 10 m wind speed is enhanced by 0.7 m s-1 in january and 0.5 m s-1 in july, with a higher increment at night. the enhanced vertical movement can transport more moisture to higher levels, which causes the decrease in water vapor at ground level and the increase in the upper pbl (planetary boundary layer), and thereby induces the accumulative precipitation to increase by 15-30 % over the megacities in july. the adding of ah can impact the spatial and vertical distributions of the simulated pollutants as well. the concentrations of primary air pollutants decrease near the surface and increase at the upper levels, due mainly to the increases in pblh, surface wind speed and upward air vertical movement. but surface o3 concentrations increase in the urban areas, with maximum changes of 2.5 ppb in january and 4 ppb in july. chemical direct (the rising up of air temperature directly accelerates surface o3 formation) and indirect (the decrease in nox at the ground results in the increase in surface o3) effects can play a significant role in o3 changes over this region. the meteorology and air pollution predictions in and around large urban areas are highly sensitive to the anthropogenic heat inputs, suggesting that ah should be considered in the climate and air quality assessments. | modeling of the anthropogenic heat flux and its effect on regional meteorology and air quality over the yangtze river delta region, china |
during recent winters, hazes often occurred in beijing, causing major environmental problems. to understand the causes of this "beijing haze", a haze episode (from oct. 21 to oct. 31, 2013) in beijing was analyzed. during the episode, the daily mean concentration of fine particulate matter (pm2.5) reached a peak value of 270 μg/m3 on oct. 28, 2013, and rapidly decreased to 50 μg/m3 the next day (oct. 29, 2013). this strong variability provided a good opportunity to study the causes of a "beijing haze". two numerical models were applied for this study. the first model is a chemical/dynamical regional model (wrf-chem). this model is mainly used to study the effects that weather conditions have on pm2.5 concentrations in the beijing region. the results show that the presence of high air pressure in northwest beijing (nw-high) generally produced strong northwest winds with clean upwind air. as a result, the nw-high played an important role in cleaning beijing's pm. however, the nw-high's cleaning effect did not occur in every situation. when there was low air pressure in southeast beijing (se-low) accompanied by an nw-high, an air convergent zone appeared in beijing. the pollutants became sandwiched, producing high pm2.5 concentrations in the beijing region. the second model used in this study is a box model, which is applied to estimate some crucial parameters associated with the budget of pm2.5 in the beijing region. under calm winds, the calculations show that continuous local emissions rapidly accumulate pollutants. the pm2.5 concentrations reached 150 μg/m3 and 250 μg/m3 within one (1) day and two (2) days, respectively. without horizontal dilution, this estimate can be considered as an upper time limit (the fastest time) for the occurrences of haze events in the beijing region. the wind speed (wsb) is calculated for the balance between the continuous emissions and atmospheric clean processes. the results show that the wsb is strongly dependent on the planetary boundary layer (pbl) height and the wind direction. under se-low weather conditions, the wsb is 2 m/s with a higher pbl height (700 m). however, under lower pbl heights, the wsb rapidly increases, reaching 4.5 m/s and 7.0 m/s with pbl heights of 300 m and 200 m, respectively. in contrast, under nw-high weather conditions, the wsb reduces to 2.5 m/s and 4.0 m/s. these results suggest that when the prevailing wind in beijing is a northwest wind (with wind speeds of >4 m/s), particulate matter (pm) begins to decrease. | a budget analysis of the formation of haze in beijing |
we present exo-transmit, a software package to calculate exoplanet transmission spectra for planets of varied composition. the code is designed to generate spectra of planets with a wide range of atmospheric composition, temperature, surface gravity, and size, and is therefore applicable to exoplanets ranging in mass and size from hot jupiters down to rocky super-earths. spectra can be generated with or without clouds or hazes with options to (1) include an optically thick cloud deck at a user-specified atmospheric pressure or (2) to augment the nominal rayleigh scattering by a user-specified factor. the exo-transmit code is written in c and is extremely easy to use. typically the user will only need to edit parameters in a single user input file in order to run the code for a planet of their choosing. exo-transmit is available publicly on github with open-source licensing at https://github.com/elizakempton/exo_transmit. | exo-transmit: an open-source code for calculating transmission spectra for exoplanet atmospheres of varied composition |
earth's climate, mantle, and core interact over geologic time scales. climate influences whether plate tectonics can take place on a planet, with cool climates being favorable for plate tectonics because they enhance stresses in the lithosphere, suppress plate boundary annealing, and promote hydration and weakening of the lithosphere. plate tectonics plays a vital role in the long-term carbon cycle, which helps to maintain a temperate climate. plate tectonics provides long-term cooling of the core, which is vital for generating a magnetic field, and the magnetic field is capable of shielding atmospheric volatiles from the solar wind. coupling between climate, mantle, and core can potentially explain the divergent evolution of earth and venus. as venus lies too close to the sun for liquid water to exist, there is no long-term carbon cycle and thus an extremely hot climate. therefore, plate tectonics cannot operate and a long-lived core dynamo cannot be sustained due to insufficient core cooling. on planets within the habitable zone where liquid water is possible, a wide range of evolutionary scenarios can take place depending on initial atmospheric composition, bulk volatile content, or the timing of when plate tectonics initiates, among other factors. many of these evolutionary trajectories would render the planet uninhabitable. however, there is still significant uncertainty over the nature of the coupling between climate, mantle, and core. future work is needed to constrain potential evolutionary scenarios and the likelihood of an earth-like evolution. | whole planet coupling between climate, mantle, and core: implications for rocky planet evolution |
southern west greenland contains some of the best-studied and best-preserved magmatic eoarchean rocks on earth, and these provide an excellent vantage point from which to view long-standing questions regarding the growth of the earliest continental crust. in order to address the questions surrounding early crustal growth and complementary mantle depletion, we present laser ablation split stream (lass) analyses of the u-pb and hf isotope compositions of zircon from eleven samples of the least-altered meta-igneous rocks from the itsaq (amîtsoq) gneisses of the isukasia and nuuk regions of southern west greenland. this analytical technique allows a less ambiguous approach to determining the age and hf isotope composition of complicated zircon. results corroborate previous findings that eoarchean zircon from the itsaq gneiss (∼3.85 ga to ∼3.63 ga) were derived from a broadly chondritic source. in contrast to the sm-nd whole rock isotope record for southern west greenland, the zircon lu-hf isotope record provides no evidence for early mantle depletion, nor does it suggest the presence of crust older than ∼3.85 ga in greenland. utilizing lass u-pb and hf data from the greenland zircons studied here, we demonstrate the importance of focusing on the magmatic (rather than detrital) zircon record to more confidently understand early crustal growth and mantle depletion. we compare the greenland hf isotope data with other eoarchean magmatic complexes such as the acasta gneiss complex, nuvvuagittuq greenstone belt, and the gneissic complexes of southern africa, and all lack zircons with suprachondritic hf isotope compositions. in total, these data suggest only a very modest volume of crust was produced during (or survived from) the hadean and earliest eoarchean. there remains no record of planet-scale early earth mantle depletion in the hf isotope record prior to 3.8 ga. | using the magmatic record to constrain the growth of continental crust-the eoarchean zircon hf record of greenland |
this book on multiscale seismic tomography, written by one of the leaders in the field, is suitable for undergraduate and graduate students, researchers, and professionals in earth and planetary sciences who need to broaden their horizons about seismotectonics, volcanism, and interior structure and dynamics of the earth and moon. it describes the state-of-the-art in seismic tomography, with emphasis on the new findings obtained by applying tomographic methods in local, regional, and global scales for understanding the generating mechanism of large and great earthquakes such as the 2011 tohoku-oki earthquake (mw 9.0), crustal and upper mantle structure, origin of active arc volcanoes and intraplate volcanoes including hotspots, heterogeneous structure of subduction zones, fate of subducting slabs, origin of mantle plumes, mantle convection, and deep earth dynamics. the first lunar tomography and its implications for the mechanism of deep moonquakes and lunar evolution are also introduced. | multiscale seismic tomography |
we present results from a quantitative spectroscopic analysis conducted on archival keck/hires high-resolution spectra from the california-kepler survey (cks) sample of transiting planetary host stars identified from the kepler mission. the spectroscopic analysis was based on a carefully selected set of fe i and fe ii lines, resulting in precise values for the stellar parameters of effective temperature (teff) and surface gravity (log g). combining the stellar parameters with gaia dr2 parallaxes and precise distances, we derived both stellar and planetary radii for our sample, with a median internal uncertainty of 2.8% in the stellar radii and 3.7% in the planetary radii. an investigation into the distribution of planetary radii confirmed the bimodal nature of this distribution for the small-radius planets found in previous studies, with peaks at ∼1.47 ± 0.05 and ∼2.72 ± 0.10 r⊕ with a gap at ∼1.9 r⊕. previous studies that modeled planetary formation that is dominated by photoevaporation predicted this bimodal radii distribution and the presence of a radius gap, or photoevaporation valley. our results are in overall agreement with these models, as well as core powered mass-loss models. the high internal precision achieved here in the derived planetary radii clearly reveal the presence of a slope in the photoevaporation valley for the cks sample, indicating that the position of the radius gap decreases with orbital period; this decrease was fit by a power law of the form rpl ∝ p-0.11, which is consistent with both photoevaporation and core powered mass-loss models of planet formation, with earth-like core compositions. | a spectroscopic analysis of the california-kepler survey sample. i. stellar parameters, planetary radii, and a slope in the radius gap |
theoretical models of stellar evolution predict that most of the lithium inside a star is destroyed as the star becomes a red giant. however, observations reveal that about 1% of red giants are peculiarly rich in lithium, often exceeding the amount in the interstellar medium or predicted from the big bang. with only about 150 lithium-rich giants discovered in the past four decades, and no distinguishing properties other than lithium enhancement, the origin of lithium-rich giant stars is one of the oldest problems in stellar astrophysics. here we report the discovery of 2330 low-mass (1-3 m ⊙) lithium-rich giant stars, which we argue are consistent with internal lithium production that is driven by tidal spin-up by a binary companion. our sample reveals that most lithium-rich giants have helium-burning cores ({80}-6+7 % ), and that the frequency of lithium-rich giants rises with increasing stellar metallicity. we find that while planet accretion may explain some lithium-rich giants, it cannot account for the majority that have helium-burning cores. we rule out most other proposed explanations for the origin of lithium-rich giants. our analysis shows that giants remain lithium-rich for only about two million years. a prediction from this lithium depletion timescale is that most lithium-rich giants with a helium-burning core have a binary companion. | tidal interactions between binary stars can drive lithium production in low-mass red giants |
evidence of star-planet interactions in the form of planet-modulated chromospheric emission has been noted for a number of hot jupiters. magnetic star-planet interactions involve the release of energy stored in the stellar and planetary magnetic fields. these signals thus offer indirect detections of exoplanetary magnetic fields. here, we report the derivation of the magnetic field strengths of four hot jupiter systems, using the power observed in calcium uc(ii) k emission modulated by magnetic star-planet interactions. by approximating the fractional energy released in the calcium uc(ii) k line, we find that the surface magnetic field values for the hot jupiters in our sample range from 20 g to 120 g, around 10-100 times larger than the values predicted by dynamo scaling laws for planets with rotation periods of around 2-4 days. however, these values are in agreement with scaling laws relating the magnetic field strength to the internal heat flux in giant planets. large planetary magnetic field strengths may produce observable electron cyclotron maser radio emission by preventing the maser from being quenched by the planet's ionosphere. intensive radio monitoring of hot jupiter systems will help to confirm these field values and inform the generation mechanism of magnetic fields in this important class of exoplanets. | magnetic field strengths of hot jupiters from signals of star-planet interactions |
the prevalence of substructures in ∼1-10 myr old protoplanetary disks, which are often linked to planet formation, has raised the question of how early such features form and, as a corollary, how early planet formation begins. here we present observations of seven protostellar disks (aged ∼ 0.1-1 myr) from the very large array/atacama large millimeter/submillimeter array nascent disk and multiplicity survey of orion protostars (vandam: orion) that show clear substructures, thereby demonstrating that these features can form early in the lifetimes of disks. we use simple analytic models as well as detailed radiative transfer modeling to characterize their structure. in particular we show that at least four of the sources have relatively massive envelopes, indicating that they are particularly young, likely the youngest disks with substructures known to date. several of these disks also have emission from an inner disk that is offset from the center of the ring structure. given the size of the cleared-out regions of the disk, it is unclear, however, whether these features are related to planet formation, or rather if they are signposts of close-separation binary formation at early times. | the vla/alma nascent disk and multiplicity (vandam) survey of orion protostars. iii. substructures in protostellar disks |
we performed a stereo-photogrammetric (spg) analysis of more than 1500 rosetta/osiris nac images of comet 67p/churyumov-gerasimenko (67p). the images with pixel scales in the range 0.2-3.0 m/pixel were acquired between august 2014 and february 2016. we finally derived a global high-resolution 3d description of 67p's surface, the spg shap7 shape model. it consists of about 44 million facets (1-1.5 m horizontal sampling) and a typical vertical accuracy at the decimeter scale. although some images were taken after perihelion, the spg shap7 shape model can be considered a pre-periheliondescription and replaces the previous spg shap4s shape model. from the new shape model, some measures for 67p with very low 3σ uncertainties can be retrieved: 18.56 km3 ± 0.02 km3 for the volume and 537.8 kg/m3 ± 0.7 kg/m3 for the mean density assuming a mass value of 9.982 × 1012 kg. | the global meter-level shape model of comet 67p/churyumov-gerasimenko |
james webb space telescope (jwst) transmission and emission spectra will provide invaluable glimpses of transiting exoplanet atmospheres, including possible biosignatures. this promising science from jwst, however, will require exquisite precision and understanding of systematic errors that can impact the time series of planets crossing in front of and behind their host stars. here, we provide estimates of the random noise sources affecting jwst near-infrared camera (nircam) time-series data on the integration-to-integration level. we find that 1/f noise can limit the precision of grism time series for two groups (230-1000 ppm depending on the extraction method and extraction parameters), but will average down like the square root of n frames/reads. the current nircam grism time-series mode is especially affected by 1/f noise because its grismr dispersion direction is parallel to the detector fast-read direction, but could be alleviated in the grismc direction. care should be taken to include as many frames as possible per visit to reduce this 1/f noise source: thus, we recommend the smallest detector subarray sizes one can tolerate, four output channels, and readout modes that minimize the number of skipped frames (rapid or bright2). we also describe a covariance-weighting scheme that can significantly lower the contributions from 1/f noise as compared to sum extraction. we evaluate the noise introduced by pre-amplifier offsets, random telegraph noise, and high dark current resistor capacitor (rc) pixels and find that these are correctable below 10 ppm once background subtraction and pixel masking are performed. we explore systematic error sources in a companion paper. | jwst noise floor. i. random error sources in jwst nircam time series |
magnetic flux ropes are characterized by coherently twisted magnetic field lines, which are ubiquitous in magnetized plasmas. as the core structure of various eruptive phenomena in the solar atmosphere, flux ropes hold the key to understanding the physical mechanisms of solar eruptions, which impact the heliosphere and planetary atmospheres. the strongést disturbances in the earth&'s space environments are often associated with large-scale flux ropes from the sun colliding with the earth&'s magnetosphere, leading to adverse, sometimes catastrophic, space-weather effects. however, it remains elusive as to how a flux rope forms and evolves toward eruption, and how it is structured and embedded in the ambient field. the present paper addresses these important questions by reviewing current understandings of coronal flux ropes from an observer&'s perspective, with an emphasis on their structures and nascent evolution toward solar eruptions, as achieved by combining observations of both remote sensing and in-situ detection with modeling and simulation. this paper highlights an initiation mechanism for coronal mass ejections (cmes) in which plasmoids in current sheets coalesce into a 'seed&' flux rope whose subsequent evolution into a cme is consistent with the standard model, thereby bridging the gap between microscale and macroscale dynamics. | magnetic flux ropes in the solar corona: structure and evolution toward eruption |
we present the discovery and characterisation of two transiting planets observed by the transiting exoplanet survey satellite (tess) orbiting the nearby (d⋆ ≈ 22 pc), bright (j ≈ 9 mag) m3.5 dwarf ltt 3780 (toi-732). we confirm both planets and their association with ltt 3780 via ground-based photometry and determine their masses using precise radial velocities measured with the carmenes spectrograph. precise stellar parameters determined from carmenes high-resolution spectra confirm that ltt 3780 is a mid-m dwarf with an effective temperature of teff = 3360 ± 51 k, a surface gravity of log g⋆ = 4.81 ± 0.04 (cgs), and an iron abundance of [fe/h] = 0.09 ± 0.16 dex, with an inferred mass of m⋆ = 0.379 ± 0.016m⊙ and a radius of r⋆ = 0.382 ± 0.012r⊙. the ultra-short-period planet ltt 3780 b (pb = 0.77 d) with a radius of 1.35-0.06+0.06 r⊕, a mass of 2.34-0.23+0.24 m⊕, and a bulk density of 5.24-0.81+0.94 g cm-3 joins the population of earth-size planets with rocky, terrestrial composition. the outer planet, ltt 3780 c, with an orbital period of 12.25 d, radius of 2.42-0.10+0.10 r⊕, mass of 6.29-0.61+0.63 m⊕, and mean density of 2.45-0.37+0.44 g cm-3 belongs to the population of dense sub-neptunes. with the two planets located on opposite sides of the radius gap, this planetary system is anexcellent target for testing planetary formation, evolution, and atmospheric models. in particular, ltt 3780 c is an ideal object for atmospheric studies with the james webb space telescope (jwst). | the carmenes search for exoplanets around m dwarfs. two planets on opposite sides of the radius gap transiting the nearby m dwarf ltt 3780 |
we introduce zeus, a well-tested python implementation of the ensemble slice sampling (ess) method for bayesian parameter inference. ess is a novel markov chain monte carlo (mcmc) algorithm specifically designed to tackle the computational challenges posed by modern astronomical and cosmological analyses. in particular, the method requires only minimal hand-tuning of 1-2 hyperparameters that are often trivial to set; its performance is insensitive to linear correlations and it can scale up to 1000s of cpus without any extra effort. furthermore, its locally adaptive nature allows to sample efficiently even when strong non-linear correlations are present. lastly, the method achieves a high performance even in strongly multimodal distributions in high dimensions. compared to emcee, a popular mcmc sampler, zeus performs 9 and 29 times better in a cosmological and an exoplanet application, respectively. | zeus: a python implementation of ensemble slice sampling for efficient bayesian parameter inference |
we present results from a set of simulations using a fully coupled three-dimensional (3d) chemistry-radiation-hydrodynamics model and investigate the effect of transport of chemical species by the large-scale atmospheric flow in hot jupiter atmospheres. we coupled a flexible chemical kinetics scheme to the met office unified model, which enables the study of the interaction of chemistry, radiative transfer, and fluid dynamics. we used a newly-released "reduced" chemical network, comprising 30 chemical species, that was specifically developed for its application in 3d atmosphere models. we simulated the atmospheres of the well-studied hot jupiters hd 209458b and hd 189733b which both have dayside-nightside temperature contrasts of several hundred kelvin and superrotating equatorial jets. we find qualitatively quite different chemical structures between the two planets, particularly for methane (ch4), when advection of chemical species is included. our results show that consideration of 3d chemical transport is vital in understanding the chemical composition of hot jupiter atmospheres. three-dimensional mixing leads to significant changes in the abundances of absorbing gas-phase species compared with what would be expected by assuming local chemical equilibrium, or from models including 1d - and even 2d - chemical mixing. we find that ch4, carbon dioxide (co2), and ammonia (nh3) are particularly interesting as 3d mixing of these species leads to prominent signatures of out-of-equilibrium chemistry in the transmission and emission spectra, which are detectable with near-future instruments. | implications of three-dimensional chemical transport in hot jupiter atmospheres: results from a consistently coupled chemistry-radiation-hydrodynamics model |
the kepler mission revealed a class of planets known as "super-puffs," with masses only a few times larger than earth's but radii larger than neptune, giving them very low mean densities. all three of the known planets orbiting the young solar-type star kepler 51 are super-puffs. the kepler 51 system thereby provides an opportunity for a comparative study of the structures and atmospheres of this mysterious class of planets, which may provide clues about their formation and evolution. we observed two transits each of kepler 51b and 51d with the wide field camera 3 (wfc3) on the hubble space telescope. combining new wfc3 transit times with reanalyzed kepler data and updated stellar parameters, we confirmed that all three planets have densities lower than 0.1 g cm-3. we measured the wfc3 transmission spectra to be featureless between 1.15 and 1.63 μm, ruling out any variations greater than 0.6 scale heights (assuming a h/he-dominated atmosphere), thus showing no significant water absorption features. we interpreted the flat spectra as the result of a high-altitude aerosol layer (pressure <3 mbar) on each planet. adding this new result to the collection of flat spectra that have been observed for other sub-neptune planets, we find support for one of the two hypotheses introduced by crossfield & kreidberg, that planets with cooler equilibrium temperatures have more high-altitude aerosols. we strongly disfavor their other hypothesis that the h/he mass fraction drives the appearance of large-amplitude transmission features. | the featureless transmission spectra of two super-puff planets |
the young massive jupiters discovered with high-contrast imaging1-4 provide a unique opportunity to study the formation and early evolution of gas giant planets. a key question is to what extent gravitational energy from accreted gas contributes to the internal energy of a newly formed planet. this has led to a range of formation scenarios from `cold' to `hot' start models5-8. for a planet of a given mass, these initial conditions govern its subsequent evolution in luminosity and radius. except for upper limits from radial velocity studies9,10, disk modelling11 and dynamical instability arguments12, no mass measurements of young planets are yet available to distinguish between these different models. here, we report on the detection of the astrometric motion of beta pictoris, the 21-myr-old host star of an archetypical directly imaged gas giant planet, around the system's centre of mass. subtracting the highly accurate hipparcos13,14 and gaia15,16 proper motion from the internal 3 yr hipparcos astrometric data reveals the reflex motion of the star, giving a model-independent planet mass of 11 ± 2 jupiter masses. this is consistent with scenarios in which the planet is formed in a high-entropy state as assumed by hot start models. the ongoing data collection by gaia will soon lead to mass measurements of other young gas giants and form a great asset to further constrain early-evolution scenarios. | the mass of the young planet beta pictoris b through the astrometric motion of its host star |
organic compounds occur in some chondritic meteorites, and their signatures on solar system bodies have been sought for decades. spectral signatures of organics have not been unambiguously identified on the surfaces of asteroids, whereas they have been detected on cometary nuclei. data returned by the visible and infrared mapping spectrometer on board the dawn spacecraft show a clear detection of an organic absorption feature at 3.4 micrometers on dwarf planet ceres. this signature is characteristic of aliphatic organic matter and is mainly localized on a broad region of ~1000 square kilometers close to the ~50-kilometer ernutet crater. the combined presence on ceres of ammonia-bearing hydrated minerals, water ice, carbonates, salts, and organic material indicates a very complex chemical environment, suggesting favorable environments to prebiotic chemistry. | localized aliphatic organic material on the surface of ceres |
we present observations by the mars atmosphere and volatile evolution (maven) mission of a substantial plume-like distribution of escaping ions from the martian atmosphere, organized by the upstream solar wind convection electric field. from a case study of maven particle-and-field data during one spacecraft orbit, we identified three escaping planetary ion populations: plume fluxes mainly along the upstream electric field over the north pole region of the mars-sun-electric field (mse) coordinate system, antisunward ion fluxes in the tail region, and much weaker upstream pickup ion fluxes. a statistical study of o+ fluxes using 3 month maven data shows that the plume is a constant structure with strong fluxes widely distributed in the mse northern hemisphere, which constitutes an important planetary ion escape channel. the escape rate through the plume is estimated to be ~30% of the tailward escape and ~23% of the total escape for > 25 ev o+ ions. | strong plume fluxes at mars observed by maven: an important planetary ion escape channel |
the design and construction of carmenes has been presented at previous spie conferences. it is a next-generation radial-velocity instrument at the 3.5m telescope of the calar alto observatory, which was built by a consortium of eleven spanish and german institutions. carmenes consists of two separate échelle spectrographs covering the wavelength range from 0.52 to 1.71μm at a spec-tral resolution of r < 80,000, fed by fibers from the cassegrain focus of the telescope. carmenes saw "first light" on nov 9, 2015. during the commissioning and initial operation phases, we established basic performance data such as throughput and spectral resolution. we found that our hollow-cathode lamps are suitable for precise wavelength calibration, but their spectra contain a number of lines of neon or argon that are so bright that the lamps cannot be used in simultaneous exposures with stars. we have therefore adopted a calibration procedure that uses simultaneous star / fabry pérot etalon exposures in combination with a cross-calibration between the etalons and hollow-cathode lamps during daytime. with this strategy it has been possible to achieve 1-2 m/s precision in the visible and 5-10 m/s precision in the near-ir; further improvements are expected from ongoing work on temperature control, calibration procedures and data reduction. comparing the rv precision achieved in different wavelength bands, we find a "sweet spot" between 0.7 and 0.8μm, where deep tio bands provide rich rv information in mid-m dwarfs. this is in contrast to our pre-survey models, which predicted comparatively better performance in the near-ir around 1μm, and explains in part why our near-ir rvs do not reach the same precision level as those taken with the visible spectrograph. we are now conducting a large survey of 340 nearby m dwarfs (with an average distance of only 12pc), with the goal of finding terrestrial planets in their habitable zones. we have detected the signatures of several previously known or suspected planets and also discovered several new planets. we find that the radial velocity periodograms of many m dwarfs show several significant peaks. the development of robust methods to distinguish planet signatures from activity-induced radial velocity jitter is therefore among our priorities. due to its large wavelength coverage, the carmenes survey is generating a unique data set for studies of m star atmospheres, rotation, and activity. the spectra cover important diagnostic lines for activity (h alpha, na i d1 and d2, and the ca ii infrared triplet), as well as feh lines, from which the magnetic field can be inferred. correlating the time series of these features with each other, and with wavelength-dependent radial velocities, provides excellent handles for the discrimination between planetary companions and stellar radial velocity jitter. these data are also generating new insight into the physical properties of m dwarf atmospheres, and the impact of activity and flares on the habitability of m star planets. | carmenes: high-resolution spectra and precise radial velocities in the red and infrared |
the perihelion of mercury’s orbit precesses due to perturbations from other solar system bodies, solar quadrupole moment (j 2), and relativistic gravitational effects that are proportional to linear combinations of the parametrized post-newtonian parameters β and γ. the orbits and masses of the solar system bodies are quite well known, and thus the uncertainty in recovering the precession rate of mercury’s perihelion is dominated by the uncertainties in the parameters j 2, β, and γ. separating the effects due to these parameters is challenging since the secular precession rate has a linear dependence on each parameter. here we use an analysis of radiometric range measurements to the messenger (mercury surface, space environment, geochemistry, and ranging) spacecraft in orbit about mercury to estimate the precession of mercury’s perihelion. we show that the messenger ranging data allow us to measure not only the secular precession rate of mercury’s perihelion with substantially improved accuracy, but also the periodic perturbation in the argument of perihelion sensitive to β and γ. when combined with the γ estimate from a shapiro delay experiment from the cassini mission, we can decouple the effects due to β and j 2 and estimate both parameters, yielding (β -1)=(-2.7+/- 3.9)× {10}-5 and j 2 = (2.25 ± 0.09) × 10-7. we also estimate the total precession rate of mercury’s perihelion as 575.3100 ± 0.0015″/century and provide estimated contributions and uncertainties due to various perturbing effects. | precession of mercury’s perihelion from ranging to the messenger spacecraft |
au mic is a young planetary system with a resolved debris disc showing signs of planet formation and two transiting warm neptunes near mean-motion resonances. here we analyse three transits of au mic b observed with the characterising exoplanet satellite (cheops), supplemented with sector 1 and 27 transiting exoplanet survey satellite (tess) photometry, and the all-sky automated survey from the ground. the refined orbital period of au mic b is 8.462995 ± 0.000003 d, whereas the stellar rotational period is prot = 4.8367 ± 0.0006 d. the two periods indicate a 7:4 spin-orbit commensurability at a precision of 0.1%. therefore, all transits are observed in front of one of the four possible stellar central longitudes. this is strongly supported by the observation that the same complex star-spot pattern is seen in the second and third cheops visits that were separated by four orbits (and seven stellar rotations). using a bootstrap analysis we find that flares and star spots reduce the accuracy of transit parameters by up to 10% in the planet-to-star radius ratio and the accuracy on transit time by 3-4 min. nevertheless, occulted stellar spot features independently confirm the presence of transit timing variations (ttvs) with an amplitude of at least 4 min. we find that the outer companion, au mic c, may cause the observed ttvs. | the changing face of au mic b: stellar spots, spin-orbit commensurability, and transit timing variations as seen by cheops and tess |
this paper describes the 2020 release of the geisa database (gestion et etude des informations spectroscopiques atmosphériques: management and study of atmospheric spectroscopic information), developed and maintained at lmd since 1974. geisa is the reference database for several current or planned thermal and short-wave infrared (tir and swir) space missions iasi (infrared atmospheric sounding interferometer), iasi-ng (iasi new generation), microcarb (carbon dioxide monitoring mission), merlin (methane remote sensing lidar mission). it is actually a compilation of three databases: the "line parameters database", the "cross-section sub-database" and the "microphysical and optical properties of atmospheric aerosols sub-database". the new edition concerns only the line parameters dataset, with significant updates and additions implemented using the best available spectroscopic data. the geisa-2020 line parameters database involves 58 molecules (145 isotopic species) and contains 6,746,987 entries, in the spectral range from 10-6 to 35877 cm-1. in this version, 23 molecules have been updated (with 10 new isotopic species) and 6 new molecules have been added (hono, cofcl, ch3f, ch3i, ruo4, h2c3h2 (isomer of c3h4)) corresponding to 15 isotopic species. the compilation can be accessed through the aeris data and services center for the atmosphere website (https://geisa.aeris-data.fr/). based on four examples (h2o, o3, o2 and sf6), this paper also shows how the lmd in house validation algorithm sparte (spectroscopic parameters and radiative transfer evaluation) helps to evaluate, correct, reject or defer the input of new spectroscopic data into geisa and this, thanks to iterations with researchers from different communities (spectroscopy, radiative transfer). | the 2020 edition of the geisa spectroscopic database |
observations of exoplanet atmospheres have shown that aerosols, like in the solar system, are common across a variety of temperatures and planet types. the formation and distribution of these aerosols are inextricably intertwined with the composition and thermal structure of the atmosphere. at the same time, these aerosols also interfere with our probes of atmospheric composition and thermal structure, and thus a better understanding of aerosols lead to a better understanding of exoplanet atmospheres as a whole. here we review the current state of knowledge of exoplanet aerosols as determined from observations, modeling, and laboratory experiments. measurements of the transmission spectra, dayside emission, and phase curves of transiting exoplanets, as well as the emission spectrum and light curves of directly imaged exoplanets and brown dwarfs have shown that aerosols are distributed inhomogeneously in exoplanet atmospheres, with aerosol distributions varying significantly with planet equilibrium temperature and gravity. parameterized and microphysical models predict that these aerosols are likely composed of oxidized minerals like silicates for the hottest exoplanets, while at lower temperatures the dominant aerosols may be composed of alkali salts and sulfides. particles originating from photochemical processes are also likely at low temperatures, though their formation process is highly complex, as revealed by laboratory work. in the years to come, new ground and space based observatories will have the capability to assess the composition of exoplanet aerosols, while new modeling and laboratory efforts will improve upon our picture of aerosol formation and dynamics. | aerosols in exoplanet atmospheres |
we present the most detailed data-driven exploration of cloud opacity in a substellar object to-date. we have tested over 60 combinations of cloud composition and structure, particle-size distribution, scattering model, and gas phase composition assumptions against archival 1-15 μm spectroscopy for the unusually red l4.5 dwarf 2massw j2224438-015852 using the brewster retrieval framework. we find that, within our framework, a model that includes enstatite and quartz cloud layers at shallow pressures, combined with a deep iron cloud deck fits the data best. this model assumes a hansen distribution for particle sizes for each cloud, and mie scattering. we retrieved particle effective radii of $\log _{10} a {\rm (\mu m)} = -1.41^{+0.18}_{-0.17}$ for enstatite, $-0.44^{+0.04}_{-0.20}$ for quartz, and $-0.77^{+0.05}_{-0.06}$ for iron. our inferred cloud column densities suggest ${\rm (mg/si)} = 0.69^{+0.06}_{-0.08}$ if there are no other sinks for magnesium or silicon. models that include forsterite alongside, or in place of, these cloud species are strongly rejected in favour of the above combination. we estimate a radius of 0.75 ± 0.02 rjup, which is considerably smaller than predicted by evolutionary models for a field age object with the luminosity of 2m2224-0158. models which assume vertically constant gas fractions are consistently preferred over models that assume thermochemical equilibrium. from our retrieved gas fractions, we infer ${\rm [m/h]} = +0.38^{+0.07}_{-0.06}$ and ${\rm c/o} = 0.83^{+0.06}_{-0.07}$. both these values are towards the upper end of the stellar distribution in the solar neighbourhood, and are mutually consistent in this context. a composition towards the extremes of the local distribution is consistent with this target being an outlier in the ultracool dwarf population. | cloud busting: enstatite and quartz clouds in the atmosphere of 2m2224-0158 |
determining whether plate tectonics or some other mode of planetary dynamics operated in the early archean is one of the most contentious and debated areas of earth sciences today. the paleo- mesoarchean dome-and-basin structures of the eastern pilbara craton are widely used as an example of an early archean terrane supposedly unlike any produced by plate tectonics in the current mode of active-lid plate tectonics on earth. in contrast, we produce a synthesis of the structural, magmatic and sedimentological development of the eastern pilbara craton from 3600 to 2800 ma, and through comparative tectonic analysis, show that the craton developed following a typical orogenic sequence from an immature oceanic arc-dominated accretionary orogen, with the oldest rocks of the craton represented by slabs of primitive circa 3590 ma gabbro - anorthosite - ultramafic rocks, and 3522-3426 ma oceanic crust and overlying dominantly hydrothermal deep-water cherts imbricated in thrust piles and giant recumbent nappes. these were intruded by juvenile arc magmas including gabbros, diorites, and ttg suites, most of which intruded as sills into structurally favorable sites between 3484 and 3416 ma. these oceanic crust and overlying sedimentary litho-tectonic assemblages of gabbro/ basalt/ komatiite/ chert, and ttg-diorite-dominated plutonic rocks were deformed into imbricate and antiformal thrust stacks intruded by suites of sheet-like ttg magmas during late regional shortening-related deformation at 3318-3290 ma, then soon-after, folded by upright folds during continued contractional deformation. the intrusive style, compositions, and relationships to structures suggest that the late magmatic suites represent a massive slab-failure magmatic event similar to those formed during arc accretion and slab failure events in the north and south american cordilleras, and older orogens of all ages. late-orogenic shortening deformed these sheet intrusions into large domal structures, synchronous with or soon-after late- to post-orogenic cross-cutting steep-walled circa 3274-3223 ma plutons vertically intruded the cores of some of the domes, forming nested plutons akin to the cretaceous sierra crest suite of the sierra nevada batholith, and deformed equivalents in phanerozoic orogens. in a much younger magmatic event, a wide swath of the craton was affected by circa 2851-2831 monzogranite intrusions, after which the magmatic events of the archean of the eastern pilbara were terminated by the circa 2772 ma black range dolerite dike swarm, that preserves evidence for rapid apw drift during its intrusion. the eastern pilbara represents only a very small preserved paleo-mesoarchean crustal remnant, measuring a mere 200 × 200 km2, yet has been frequently used to model the presumed tectonic behavior of the entire planet for much of the archean. in this synthesis, we show that the scale of the craton renders its significance in this literature greatly exaggerated. the eastern pilbara is only 1/3 the size of just the sierra nevada batholith. considering the entire eastern, central and western pilbara belts, the scale and tectonic zonation of lithotectonic assemblages is remarkably similar to that of the california section of the north american cordillera, from arc root (eastern pilbara. cf. sierra nevada), to fore-arc overlap basin (de gray basin, cf. great central valley sequence), to an accretionary complex (western pilbara, cf. franciscan). the duration of different magmatic and deformational events, confined to three main pulses in 300 ma, including about six total magmatic suites over 500 ma, is similar to that of different pulses and/or accretionary events in the western american cordilleran examples, such as the peri-gondwanan famatinian (cambro-ordovician) and pampean (cambrian) arcs which were later affected by permian and mesozoic intrusives from the peruvian coastal batholith, and form part of the present day active andean margin of south america. from this analysis, we firmly conclude from four degrees of similarity of the full data set of field, structural, temporal, and compositional data that the evolution of the craton is readily and rather simply explained by the plate tectonic paradigm. thus there is no scientific justification to suggest that the geological characteristics of the eastern pilbara require any different imaginative or fantastic type of planetary heat loss mode during the interval of its formation from 3600 to 2800 ma. the eastern pilbara is simply an exceptionally well-preserved small fragment of a poly-phase root of a continental margin accretionary orogen that evolved from accretion and magmatism from some of earth oldest telescoped oceans and included arcs, in a regime of accretionary-style plate tectonics. comparison with other well-preserved eo-mesoarchean terranes shows a common trait, that of derivation from immature introceanic accretionary orogens, building earth's first continents. | archean dome-and-basin style structures form during growth and death of intraoceanic and continental margin arcs in accretionary orogens |
double planetary gear sets (dpgss) are widely applied to high power and high torque mechanical transmission systems due to the high loading capacity, steady transmission, and high transmission efficiency. most previous works studied the planetary bearing vibration characteristics without the gear excitations. this work establishes a dynamic model for a dpgs containing all components (sun gear, ring gear, carrier, inner planet, outer planet, planetary bearing roller, and planetary bearing cage). the components' excitations in this work are more comprehensive than the reported references. the proposed model considers the planetary bearing roller and cage dynamics. moreover, the gear interactions, planetary gear-bearing-carrier interactions, and roller-cage interactions are contained in the proposed model. the vibrations of planetary bearing roller, planet, carrier, and planetary bearing cage are analyzed. the effect of sun gear rotation speed on the planetary bearing contact force, planetary bearing roller-cage impact force, and vibrations of planetary bearing parts are studied. the simulated and experimental results are compared to prove the correctness of proposed model. moreover, the results from proposed model and model without the cage are compared to show the advantage of proposed model. | a dynamic model for the planetary bearings in a double planetary gear set |
static compression experiments over 4 mbar are rare, yet critical for developing accurate fundamental physics and chemistry models, relevant to a range of topics including modeling planetary interiors. here we show that focused ion beam crafted toroidal single-crystal diamond anvils with 9.0 μm culets are capable of producing pressures over 5 mbar. the toroidal surface prevents gasket outflow and provides a means to stabilize the central culet. we have reached a maximum pressure of 6.15 mbar using re as in situ pressure marker, a pressure regime typically accessed only by double-stage diamond anvils and dynamic compression platforms. optimizing single-crystal diamond anvil design is key for extending the pressure range over which studies can be performed in the diamond anvil cell. | single crystal toroidal diamond anvils for high pressure experiments beyond 5 megabar |
the university of california, san diego (ucsd) time-dependent three-dimensional (3-d) reconstruction technique provides volumetric maps of density, velocity, and solar surface extrapolated magnetic fields by iteratively fitting our kinematic 3-d model to interplanetary scintillation (ips) observations. while we currently use data from the institute for space-earth environmental research (isee), japan, we have also integrated this system adding data from worldwide ips stations (wipss) network groups to increase both spatial and temporal coverage when these data are available. some of these stations, especially the low frequency array (lofar), centered in the netherlands, currently operate in "campaign" mode only during periods of interest when the parker solar probe (psp) makes close passes to the sun. the ucsd 3-d iterative reconstruction technique is unique in its ability to yield a low-resolution seamless extension of density and velocity parameters measured in situ, going outward into the surrounding interplanetary medium at the resolution of the volumetric data. we here present analyses using archival data sets from both isee, lofar, and bsa3 (pushchino, russia), mostly during psp close passes of the sun. these analyses provide the location of all inner planets from mercury to mars, and the spacecraft psp, bepicolombo, and solar orbiter in the 3-d reconstructed volumes and can show the heliospheric structures that reach them as in-situ predictions of the structures present and forecasts of these parameters in near real time compared with near-earth data sets. | interplanetary scintillation (ips) analyses during lofar campaign mode periods that include the first three parker solar probe close passes of the sun |
the dynamical and thermodynamical importance of gravity waves was initially recognized in the atmosphere of earth. extensive studies over recent decades demonstrated that gravity waves exist in atmospheres of other planets, similarly play a significant role in the vertical coupling of atmospheric layers and, thus, must be included in numerical general circulation models. since the spatial scales of gravity waves are smaller than the typical spatial resolution of most models, atmospheric forcing produced by them must be parameterized. this paper presents a review of gravity waves in planetary atmospheres, outlines their main characteristics and forcing mechanisms, and summarizes approaches to capturing gravity wave effects in numerical models. the main goal of this review is to bridge research communities studying atmospheres of earth and other planets. | gravity waves in planetary atmospheres: their effects and parameterization in global circulation models |
we use the robo-ao survey of kepler planetary candidate host stars, the largest adaptive optics survey yet performed, to measure the recovery rate of close stellar binaries in gaia dr2. we find that gaia recovers binaries down to 1″ at magnitude contrasts as large as six; closer systems are not resolved, regardless of secondary brightness. gaia dr2 binary detection does not have a strong dependence on the orientation of the stellar pairs. we find 177 nearby stars to kepler planetary candidate host stars in gaia dr2 that were not detected in the robo-ao survey, almost all of which are faint (g > 20) the remainder were largely targets observed by robo-ao in poor conditions. if the primary star is the host, the impact on the radii estimates of planet candidates in these systems is likely minimal; many of these faint stars, however, could be faint eclipsing binaries that are the source of a false positive planetary transit signal. with robo-ao and gaia combined, we find that 18.7 ± 0.7% of kepler planet candidate hosts have nearby stars within 4″. we also find 36 nearby stars in gaia dr2 around 35 planetary candidate host stars detected with k2. the nearby star fraction rate for k2 planetary candidates is significantly lower than that for the primary kepler mission. the binary recovery rate of gaia will improve initial radius estimates of future transiting exoplanet survey satellite planet candidates significantly; however, ground-based high-resolution follow-up observations are still needed for precise characterization and confirmation. the sensitivity of gaia to closely separated binaries is expected to improve in later data releases. | measuring the recoverability of close binaries in gaia dr2 with the robo-ao kepler survey |
the zinc (zn) stable isotope system has great potential for tracing planetary formation and differentiation processes due to its chalcophile, lithophile and moderately volatile character. as an initial approach, the terrestrial mantle, and by inference, the bulk silicate earth (bse), have previously been suggested to have an average δ66zn value of ∼+0.28‰ (relative to jmc 3-0749l) primarily based on oceanic basalts. nevertheless, data for mantle peridotites are relatively scarce and it remains unclear whether zn isotopes are fractionated during mantle melting. to address this issue, we report high-precision (±0.04‰; 2sd) zn isotope data for well-characterized peridotites (n = 47) from cratonic and orogenic settings, as well as their mineral separates. basalts including mid-ocean ridge basalts (morb) and ocean island basalts (oib) were also measured to avoid inter-laboratory bias. the morb analyzed have homogeneous δ66zn values of +0.28 ± 0.03‰ (here and throughout the text, errors are given as 2sd), similar to those of oib obtained in this study and in the literature (+0.31 ± 0.09‰). excluding the metasomatized peridotites that exhibit a wide δ66zn range of -0.44‰ to +0.42‰, the non-metasomatized peridotites have relatively uniform δ66zn value of +0.18 ± 0.06‰, which is lighter than both morb and oib. this difference suggests a small but detectable zn isotope fractionation (∼0.1‰) during mantle partial melting. the magnitude of inter-mineral fractionation between olivine and pyroxene is, on average, close to zero, but spinels are always isotopically heavier than coexisting olivines (δ66znspl-ol = +0.12 ± 0.07‰) due to the stiffer zn-o bonds in spinel than silicate minerals (ol, opx and cpx). zinc concentrations in spinels are 11-88 times higher than those in silicate minerals, and our modelling suggests that spinel consumption during mantle melting plays a key role in generating high zn concentrations and heavy zn isotopic compositions of morb. therefore, preferential melting of spinel in the peridotites may account for the zn isotopic difference between spinel peridotites and basalts. by contrast, the absence of zn isotope fractionation between silicate minerals suggests that zn isotopes are not significantly fractionated during partial melting of spinel-free garnet-facies mantle. if the studied non-metasomatized peridotites represent the refractory upper mantle, mass balance calculation shows that the depleted morb mantle (dmm) has a δ66zn value of +0.20 ± 0.05‰ (2sd), which is lighter than the primitive upper mantle (pum) estimated in previous studies (+0.28 ± 0.05‰, 2sd, chen et al., 2013b; +0.30 ± 0.07‰, 2sd, doucet et al., 2016). this indicates that the earth's upper mantle has a heterogeneous zn isotopic composition vertically, which is probably due to shallow mantle melting processes. | zinc isotope fractionation during mantle melting and constraints on the zn isotope composition of earth's upper mantle |
outflows driven by large-scale magnetic fields likely play an important role in the evolution and dispersal of protoplanetary disks and in setting the conditions for planet formation. we extend our 2d-axisymmetric nonideal mhd model of these outflows by incorporating radiative transfer and simplified thermochemistry, with the dual aims of exploring how heating influences wind launching and illustrating how such models can be tested through observations of diagnostic spectral lines. our model disks launch magnetocentrifugal outflows primarily through magnetic tension forces, so the mass-loss rate increases only moderately when thermochemical effects are switched on. for typical field strengths, thermochemical and irradiation heating are more important than magnetic dissipation. we furthermore find that the entrained vertical magnetic flux diffuses out of the disk on secular timescales as a result of nonideal mhd. through postprocessing line radiative transfer, we demonstrate that spectral line intensities and moment-1 maps of atomic oxygen, the hcn molecule, and other species show potentially observable differences between a model with a magnetically driven outflow and one with a weaker, photoevaporative outflow. in particular, the line shapes and velocity asymmetries in the moment-1 maps could enable the identification of outflows emanating from the disk surface. | global hydromagnetic simulations of protoplanetary disks with stellar irradiation and simplified thermochemistry |
a stunning range of substructures in the dust of protoplanetary disks is routinely observed across a range of wavelengths. these gaps, rings and spirals are highly indicative of a population of unseen planets, hinting at the possibility of current observational facilities being able to capture planet-formation in action. over the last decade, our understanding of the influence of a young planet on the dynamical structure of its parental disk has progressed significantly, revealing a host of potentially observable features which would betray the presence of a deeply embedded planet. in concert, recent observations have shown that subtle perturbations in the kinematic structure of protoplanetary disks are found in multiple sources, potentially the characteristic disturbances associated with embedded planets. in this work, we review the theoretical background of planet-disk interactions, focusing on the kinematical features, and the current methodologies used to observe these interactions in spatially and spectrally resolved observations. we discuss the potential pit falls of such kinematical detections of planets, providing best-practices for imaging and analysing interferometric data, along with a set of criteria to use as a benchmark for any claimed detection of embedded planets. we finish with a discussion on the current state of simulations in regard to planet-disk interactions, highlighting areas of particular interest and future directions which will provide the most significant impact in our search for embedded planets. this work is the culmination of the 'visualizing the kinematics of planet formation' workshop, held in october 2019 at the center for computational astrophysics at the flatiron institute in new york city. | visualizing the kinematics of planet formation |
thermal protection systems are a critical component of planetary exploration, enabling probes to enter the atmosphere and perform in-situ measurements. the aero-thermal conditions encountered during entry are destination and vehicle dependent, ranging from relatively benign conditions at mars and titan, to extreme conditions at venus and jupiter. the thermal protection system is a single-point-of-failure for both entry probe and aerocapture missions, and hence must be qualified using ground tests to ensure mission success. the high density carbon-phenolic which was used in the galileo and the pioneer venus missions is no longer available due to the lack of the manufacturing base for its raw materials. to address the need for venus and outer planet missions, nasa has developed the heatshield for extreme environment entry technology (heeet). the present study uses the aerocapture mission analysis tool (amat) to perform a comparative study of the thermal protection system requirements for various planetary destinations and the applicability of heeet for future entry and aerocapture missions. the heat rate and stagnation pressure for aerocapture is significantly less compared to probe entry. the large heat loads during aerocapture present a challenge, but heeet is capable of sustaining large heat loads within a reasonable tps mass fraction. | thermal protection system requirements for future planetary entry and aerocapture missions |
in this proceedings, we study the possible gravitational impact of primordial black holes (pbhs) or dark matter (dm) clumps on gnss satellite orbits and gravimeter measurements. it provides a preliminary step to the future exhaustive statistical analysis over 28 years of gravimeter and gnss data to get constraints over the density of asteroid-mass pbh and dm clumps inside the solar system. such constraints would be the first to be obtained by direct observation on a terrestrial scale. | observing dark matter clumps and asteroid-mass primordial black holes in the solar system with gravimeters and gnss networks |
we determine the observability in transmission of inhomogeneous cloud cover on the limbs of hot jupiters through post-processing a general circulation model to include cloud distributions computed using a cloud microphysics model. we find that both the east and west limbs often form clouds, but that the different properties of these clouds enhance the limb-to-limb differences compared to the clear case. using the james webb space telescope, it should be possible to detect the presence of cloud inhomogeneities by comparing the shape of the transit light curve at multiple wavelengths because inhomogeneous clouds impart a characteristic, wavelength-dependent signature. this method is statistically robust even with limited wavelength coverage, uncertainty on limb-darkening coefficients, and imprecise transit times. we predict that the short-wavelength slope varies strongly with temperature. the hot limbs of the hottest planets form higher-altitude clouds composed of smaller particles, leading to a strong rayleigh slope. the near-infrared spectral features of clouds are almost always detectable, even when no spectral slope is visible in the optical. in some of our models a spectral window between 5 and 9 μm can be used to probe through the clouds and detect chemical spectral features. our cloud particle size distributions are not lognormal and differ from species to species. using the area- or mass-weighted particle size significantly alters the relative strength of the cloud spectral features compared to using the predicted size distribution. finally, the cloud content of a given planet is sensitive to a species’ desorption energy and contact angle, two parameters that could be constrained experimentally in the future. | transit signatures of inhomogeneous clouds on hot jupiters: insights from microphysical cloud modeling |
to determine the origin of the spiral structure observed in the dust continuum emission of elias 2-27 we analyze multiwavelength continuum alma data with a resolution of ~0"2 (~23 au) at 0.89, 1.3, and 3.3 mm. we also study the kinematics of the disk with 13co and c18o alma observations in the j = 3-2 transition. the spiral arm morphology is recovered at all wavelengths in the dust continuum observations, where we measure contrast and spectral index variations along the spiral arms and detect subtle dust-trapping signatures. we determine that the emission from the midplane is cold and interpret the optical depth results as signatures of a disk mass higher than previous constraints. from the gas data, we search for deviations from keplerian motion and trace the morphology of the emitting surfaces and the velocity profiles. we find an azimuthally varying emission layer height in the system, large-scale emission surrounding the disk, and strong perturbations in the channel maps, colocated with the spirals. additionally, we develop multigrain dust and gas hydrodynamical simulations of a gravitationally unstable disk and compare them to the observations. given the large-scale emission and highly perturbed gas structure, together with the comparison of continuum observations to theoretical predictions, we propose infall-triggered gravitational instabilities as the origin for the observed spiral structure. | spiral arms and a massive dust disk with non-keplerian kinematics: possible evidence for gravitational instability in the disk of elias 2-27 |
following paper i we investigate the properties of atmospheres that form around small protoplanets embedded in a protoplanetary disc by conducting hydrodynamical simulations. these are now extended to three dimensions, employing a spherical grid centred on the planet. compression of gas is shown to reduce rotational motions. contrasting the 2d case, no clear boundary demarcates bound atmospheric gas from disc material; instead, we find an open system where gas enters the bondi sphere at high latitudes and leaves through the mid-plane regions, or, vice versa, when the disc gas rotates sub-keplerian. the simulations do not converge to a time-independent solution; instead, the atmosphere is characterized by a time-varying velocity field. of particular interest is the time-scale to replenish the atmosphere by nebular gas, treplenish. it is shown that the replenishment rate, matm/treplenish, can be understood in terms of a modified bondi accretion rate, ∼r_bondi^2ρ _gasv_bondi, where vbondi is set by the keplerian shear or the magnitude of the sub-keplerian motion of the gas, whichever is larger. in the inner disc, the atmosphere of embedded protoplanets replenishes on a time-scale that is shorter than the kelvin-helmholtz contraction (or cooling) time-scale. as a result, atmospheric gas can no longer contract and the growth of these atmospheres terminates. future work must confirm whether these findings continue to apply when the (thermodynamical) idealizations employed in this study are relaxed. but if shown to be broadly applicable, replenishment of atmospheric gas provides a natural explanation for the preponderance of gas-rich but rock-dominant planets like super-earths and mini-neptunes. | hydrodynamics of embedded planets' first atmospheres - ii. a rapid recycling of atmospheric gas |
constraining turbulence in disks is key towards understanding their evolution through the transport of angular momentum. until now measurements of high turbulence have remained elusive and methods for estimating turbulence relay mostly on complex radiative transfer models of the data. using the disk emission from im lup, a source proposed to be undergoing magneto-rotational instabilities (mri) and possibly have high turbulence values in the upper disk layers, we present a new way of directly measuring turbulence without need of radiative transfer or thermochemical models. through the characterization of the cn and c$_2$h emission in im lup, we aim to connect the information on the vertical and thermal structure of a particular disk region to derive turbulence at that location. by using an optically thin tracer it is possible to directly measure turbulence from the non-thermal broadening of the line. the vertical layers of the cn and c$_2$h emission are traced directly from the channel maps using alfahor. by comparing their position to that of optically thick co observations we are able to characterize the kinetic temperature of the emitting region. using a simple parametric model of the line intensity with discminer we accurately measure the emission linewidth and separate the thermal and non-thermal components. assuming that the non-thermal component is fully turbulent, we are able to directly estimate the turbulent motions at the studied radial and vertical location of cn emission. im lup shows high turbulence of mach 0.4-0.6 at $z/r \sim$ 0.25. considering previous estimates of low turbulence near the midplane, this may indicate a vertical gradient in the disk turbulence, which is a key prediction of mri studies. cn and c$_2$h are both emitting from a localized upper disk region at $z/r =$0.2-0.3, in agreement with thermochemical models. | high turbulence in the im lup protoplanetary disk: direct observational constraints from cn and c$_2$h emission |
the metallicity of exoplanet systems serves as a critical diagnostic of planet formation mechanisms. previous studies have demonstrated the planet-metallicity correlation for large planets ({{r}p} ≥slant 4 {{r}e}); however, a correlation has not been found for smaller planets. with a sample of 406 kepler objects of interest whose stellar properties are determined spectroscopically, we reveal a universal planet-metallicity correlation: not only gas-giant planets (3.9 {{r}e} \lt {{r}p} ≤slant 22.0 {{r}e}) but also gas-dwarf (1.7 {{r}e} \lt {{r}p} ≤slant 3.9 {{r}e}) and terrestrial planets ({{r}p} ≤slant 1.7 {{r}e}) occur more frequently in metal-rich stars. the planet occurrence rates of gas-giant planets, gas-dwarf planets, and terrestrial planets are 9.30-3.04+5.62, 2.03-0.26+0.29, and 1.72-0.17+0.19 times higher for metal-rich stars than for metal-poor stars, respectively. | revealing a universal planet-metallicity correlation for planets of different sizes around solar-type stars |
this work describes the update of no along with the incorporation of no2 and n2o to the hitemp database. where appropriate, the hitran line lists for the same molecules have also been updated. this work brings the current number of molecules provided by hitemp to seven. the initial line lists originating from ab initio and semi-empirical methods for each molecule have been carefully validated against available observations and, where necessary, adjustments have been made to match observations. we anticipate this work will be applied to a variety of high-temperature environments including astronomical applications, combustion monitoring, and non-local thermodynamic equilibrium conditions. | spectroscopic line parameters of no, no2, and n2o for the hitemp database |
a primary goal of exoplanet characterization is to use a planet's current composition to understand how that planet formed. for example, the c/o ratio has long been recognized as carrying important information on the chemistry of volatile species. refractory elements, like fe, mg, and si, are usually not considered in this conversation because they condense into solids like fe(s) or mgsio3 and would be removed from the observable, gaseous atmosphere in exoplanets cooler than about 2000 k. however, planets hotter than about 2000 k, called ultra-hot jupiters (uhjs), are warm enough to largely avoid the condensation of refractory species. in this paper, we explore the insight that the measurement of refractory abundances can provide into a planet's origins. through refractory-to-volatile elemental abundance ratios, we can estimate a planet's atmospheric rock-to-ice fraction and constrain planet formation and migration scenarios. we first relate a planet's present-day refractory-to-volatile ratio to its rock-to-ice ratio from formation using various compositional models for the rocky and icy components of the protoplanetary disk. we discuss potential confounding factors like the sequestration of heavy metals in the core and condensation. we then show such a measurement using atmospheric retrievals of the low-resolution uv-ir transmission spectrum of wasp-121b with petra, from which we estimate a refractory-to-volatile ratio of 5.0 ${}_{-2.7}^{+6.0}\,\times $ solar and a rock-to-ice ratio greater than 2/3. this result is consistent with significant atmospheric enrichment by rocky planetismals. lastly, we discuss the rich future potential for measuring refractory-to-volatile ratios in uhjs with the arrival of the james webb space telescope and by combining observations at low and high resolution. | a new window into planet formation and migration: refractory-to-volatile elemental ratios in ultra-hot jupiters |
we investigate possible chemical conditions on a canonical hycean world, focusing on the present and primordial molecular composition of the atmosphere, and the inventory of bioessential elements for the origin and sustenance of life in the ocean. traditionally, the search for life on exoplanets has been predominantly focused on rocky exoplanets. the recently proposed hycean worlds have the potential to significantly expand and accelerate the search for life elsewhere. hycean worlds are a class of habitable sub-neptunes with planet-wide oceans and h2-rich atmospheres. their broad range of possible sizes and temperatures lead to a wide habitable zone and high potential for discovery and atmospheric characterization using transit spectroscopy. over a dozen candidate hycean planets are already known to be transiting nearby m dwarfs, making them promising targets for atmospheric characterization with the james webb space telescope (jwst). in this work, we investigate possible chemical conditions on a canonical hycean world, focusing on (a) the present and primordial molecular composition of the atmosphere, and (b) the inventory of bioessential elements for the origin and sustenance of life in the ocean. based on photochemical and kinetic modeling for a range of conditions, we discuss the possible chemical evolution and observable present-day composition of its atmosphere. in particular, for reduced primordial conditions the early atmospheric evolution passes through a phase that is rich in organic molecules that could provide important feedstock for prebiotic chemistry. we investigate avenues for delivering bioessential metals to the ocean, considering the challenging lack of weathering from a rocky surface and the ocean separated from the rocky core by a thick icy mantle. based on ocean depths from internal structure modelling and elemental estimates for the early earth's oceans, we estimate the requirements for bioessential metals in such a planet. we find that the requirements can be met for plausible assumptions about impact history and atmospheric sedimentation, and supplemented by other steady state sources. we discuss the observational prospects for atmospheric characterisation of hycean worlds with jwst and future directions of this new paradigm in the search for life on exoplanets. | chemical conditions on hycean worlds |
in this paper, we study how gaseous dynamical friction (df) affects the motion of fly-by stellar-mass black holes (sbhs) embedded in active galactic nucleus (agn) discs. we perform three-body integrations of the interaction of two co-planar sbhs in nearby, initially circular orbits around the supermassive black hole. we find that df can facilitate the formation of gravitationally bound near-keplerian binaries in agn discs, and we delineate the discrete ranges of impact parameters and agn disc parameters for which such captures occur. we also report trends in the bound binaries' eccentricity and sense of rotation (prograde or retrograde with respect to the background agn disc) as a function of the impact parameter of the initial encounter. while based on an approximate description of gaseous friction, our results suggest that binary formation in agn discs should be common and may produce both prograde and retrograde, as well as both circular and eccentric binaries. | gas dynamical friction as a binary formation mechanism in agn discs |
aerocapture is a maneuver which uses aerodynamic drag to slow down a spacecraft in a single pass through the atmosphere. all planetary orbiters to date have used propulsive orbit insertion. aerocapture is a promising alternative, especially for small satellite missions and missions to the ice giants. the large {\delta}v requirement makes it practically impossible for small satellites to enter low circular orbits. aerocapture can enable insertion of low-cost satellites into circular orbits around mars and venus. for ice giant missions, aerocapture can enable orbit insertion from fast arrival trajectories which are impractical with propulsive insertion. by utilizing the atmospheric drag to impart the {\delta}v, aerocapture can offer significant propellant mass and cost savings for a wide range of planetary missions. the present study analyzes the performance benefit offered by aerocapture for a set of design reference missions and their applications to future solar system exploration from venus to neptune. the estimated performance benefit for aerocapture in terms of delivered mass increase are: venus (92%), earth (108%), mars (17%), and titan (614%), uranus (35%), and neptune (43%). at uranus and neptune, aerocapture is a mission enabling technology for orbit insertion from fast arrival interplanetary trajectories. | performance benefit of aerocapture for the design reference mission set |
thanks to the muse integral field spectrograph on the vlt, extragalactic distance measurements with the [o iii] 5007 a planetary nebula luminosity function (pnlf) are now possible out to approx. 40 mpc. here we analyze the vlt/muse data for 20 galaxies from the eso public archive to identify the systems' planetary nebulae (pne) and determine their pnlf distances. three of the galaxies do not contain enough pne for a robust measure of the pnlf, and the results for one other system are compromised by the galaxy's internal extinction. however, we obtain robust pnlf distances for the remaining 16 galaxies, two of which are isolated and beyond 30 mpc in a relatively unperturbed hubble flow. from these data, we derive a hubble constant of 74.2 +/- 7.2 (stat) +/-3.7 (sys) km/s/mpc, a value that is very similar to that found from other quality indicators (e.g., cepheids, the tip of the red giant branch, and surface brightness fluctuations). at present, the uncertainty is dominated by the small number of suitable galaxies in the eso archival and their less than ideal observing conditions and calibrations. based on our experience with these systems, we identify the observational requirements necessary for the pnlf to yield a competitive value for h0 that is independent of the sn ia distance scale, and help resolve the current tension in the hubble constant. | towards precision cosmology with improved pnlf distances using vlt-muse ii. a test sample from archival data |
the activity of the sun alternates between a solar minimum and a solar maximum, the former corresponding to a period of "quieter" status of the heliosphere. during solar minimum, it is in principle more straightforward to follow eruptive events and solar wind structures from their birth at the sun throughout their interplanetary journey. in this paper, we report analysis of the origin, evolution, and heliospheric impact of a series of solar transient events that took place during the second half of august 2018, that is, in the midst of the late declining phase of solar cycle 24. in particular, we focus on two successive coronal mass ejections (cmes) and a following high-speed stream (hss) on their way toward earth and mars. we find that the first cme impacted both planets, whilst the second caused a strong magnetic storm at earth and went on to miss mars, which nevertheless experienced space weather effects from the stream interacting region preceding the hss. analysis of remote-sensing and in-situ data supported by heliospheric modeling suggests that cme-hss interaction resulted in the second cme rotating and deflecting in interplanetary space, highlighting that accurately reproducing the ambient solar wind is crucial even during "simpler" solar minimum periods. lastly, we discuss the upstream solar wind conditions and transient structures responsible for driving space weather effects at earth and mars. | cme evolution in the structured heliosphere and effects at earth and mars during solar minimum |
while dust disks around optically visible, class ii protostars are found to be vertically thin, when and how dust settles to the midplane are unclear. as part of the atacama large millimeter/submillimeter array large program, early planet formation in embedded disks, we analyze the edge-on, embedded, class i protostar iras 04302+2247, also nicknamed the "butterfly star." with a resolution of 0.″05 (8 au), the 1.3 mm continuum shows an asymmetry along the minor axis that is evidence of an optically thick and geometrically thick disk viewed nearly edge-on. there is no evidence of rings and gaps, which could be due to the lack of radial substructure or the highly inclined and optically thick view. with 0.″1 (16 au) resolution, we resolve the 2d snow surfaces, i.e., the boundary region between freeze-out and sublimation, for 12co j = 2-1, 13co j = 2-1, c18o j = 2-1, h 2co j = 30,3-20,2, and so j = 65-54, and constrain the co midplane snow line to ~130 au. we find keplerian rotation around a protostar of 1.6 ± 0.4 m ⊙ using c18o. through forward ray-tracing using radmc-3d, we find that the dust scale height is ~6 au at a radius of 100 au from the central star and is comparable to the gas pressure scale height. the results suggest that the dust of this class i source has yet to vertically settle significantly. | early planet formation in embedded disks (edisk). ii. limited dust settling and prominent snow surfaces in the edge-on class i disk iras 04302+2247 |
antarctic snowfall consists of frequent clear-sky precipitation and heavier falls from intrusions of maritime airmasses associated with amplified planetary waves. we investigate the importance of different precipitation events using the output of the racmo2 model. extreme precipitation events consisting of the largest 10% of daily totals are shown to contribute more than 40% of the total annual precipitation across much of the continent, with some areas receiving in excess of 60% of the total from these events. the greatest contribution of extreme precipitation events to the annual total is in the coastal areas and especially on the ice shelves, with the amery ice shelf receiving 50% of its annual precipitation in less than the 10 days of heaviest precipitation. for the continent as a whole, 70% of the variance of the annual precipitation is explained by variability in precipitation from extreme precipitation events, with this figure rising to over 90% in some areas. | the dominant role of extreme precipitation events in antarctic snowfall variability |
the chemical composition of stars hosting small exoplanets (with radii less than four earth radii) appears to be more diverse than that of gas-giant hosts, which tend to be metal-rich. this implies that small, including earth-size, planets may have readily formed at earlier epochs in the universe's history when metals were more scarce. we report kepler spacecraft observations of kepler-444, a metal-poor sun-like star from the old population of the galactic thick disk and the host to a compact system of five transiting planets with sizes between those of mercury and venus. we validate this system as a true five-planet system orbiting the target star and provide a detailed characterization of its planetary and orbital parameters based on an analysis of the transit photometry. kepler-444 is the densest star with detected solar-like oscillations. we use asteroseismology to directly measure a precise age of 11.2 ± 1.0 gyr for the host star, indicating that kepler-444 formed when the universe was less than 20% of its current age and making it the oldest known system of terrestrial-size planets. we thus show that earth-size planets have formed throughout most of the universe's 13.8 billion year history, leaving open the possibility for the existence of ancient life in the galaxy. the age of kepler-444 not only suggests that thick-disk stars were among the hosts to the first galactic planets, but may also help to pinpoint the beginning of the era of planet formation. | an ancient extrasolar system with five sub-earth-size planets |
the admitted, conventional scenario to explain the complex spectral evolution of brown dwarfs (bds) since their first detection 20 years ago has always been the key role played by micron-size condensates, called “dust” or “clouds,” in their atmosphere. this scenario, however, faces major problems, in particular the j-band brightening and the resurgence of feh absorption at the l to t transition, and a physical first-principle understanding of this transition is lacking. in this letter, we propose a new, completely different explanation for bd and extrasolar giant planet (egp) spectral evolution, without the need to invoke clouds. we show that, due to the slowness of the co/ch4 and n2/nh3 chemical reactions, brown dwarf (l and t, respectively) and egp atmospheres are subject to a thermo-chemical instability similar in nature to the fingering or chemical convective instability present in earth oceans and at the earth core/mantle boundary. the induced small-scale turbulent energy transport reduces the temperature gradient in the atmosphere, explaining the observed increase in near-infrared j-h and j-k colors of l dwarfs and hot egps, while a warming up of the deep atmosphere along the l to t transition, as the co/ch4 instability vanishes, naturally solves the two aforementioned puzzles, and provides a physical explanation of the l to t transition. this new picture leads to a drastic revision of our understanding of bd and egp atmospheres and their evolution. | cloudless atmospheres for l/t dwarfs and extrasolar giant planets |
the sun is the only star whose surface can be directly resolved at high resolution, and therefore constitutes an excellent test case to explore the physical origin of stellar radial-velocity (rv) variability. we present harps observations of sunlight scattered off the bright asteroid 4/vesta, from which we deduced the sun's activity-driven rv variations. in parallel, the helioseismic and magnetic imager instrument on board the solar dynamics observatory provided us with simultaneous high spatial resolution magnetograms, dopplergrams and continuum images of the sun in the fe i 6173 å line. we determine the rv modulation arising from the suppression of granular blueshift in magnetized regions and the flux imbalance induced by dark spots and bright faculae. the rms velocity amplitudes of these contributions are 2.40 and 0.41 m s-1, respectively, which confirms that the inhibition of convection is the dominant source of activity-induced rv variations at play, in accordance with previous studies. we find the doppler imbalances of spot and plage regions to be only weakly anticorrelated. light curves can thus only give incomplete predictions of convective blueshift suppression. we must instead seek proxies that track the plage coverage on the visible stellar hemisphere directly. the chromospheric flux index r^' }_{hk} derived from the harps spectra performs poorly in this respect, possibly because of the differences in limb brightening/darkening in the chromosphere and photosphere. we also find that the activity-driven rv variations of the sun are strongly correlated with its full-disc magnetic flux density, which may become a useful proxy for activity-related rv noise. | the sun as a planet-host star: proxies from sdo images for harps radial-velocity variations |
we report the detection of water absorption features in the day side spectrum of the first-known hot jupiter, 51 peg b, confirming the star-planet system to be a double-lined spectroscopic binary. we use high-resolution (r≈ 100,000), 3.2 μ {{m}} spectra taken with crires/vlt to trace the radial-velocity shift of the water features in the planet’s day side atmosphere during 4 hr of its 4.23 day orbit after superior conjunction. we detect the signature of molecular absorption by water at a significance of 5.6σ at a systemic velocity of {v}{sys}=-33+/- 2 km s-1, coincident with the 51 peg host star, with a corresponding orbital velocity {k}{{p}}={133}-3.5+4.3 km s-1. this translates directly to a planet mass of {m}{{p}}={0.476}-0.031+0.032 {m}{{j}}, placing it at the transition boundary between jovian and neptunian worlds. we determine upper and lower limits on the orbital inclination of the system of 70^\circ < i< 82\buildrel{\circ}\over{.} 2. we also provide an updated orbital solution for 51 peg b, using an extensive set of 639 stellar radial velocities measured between 1994 and 2013, finding no significant evidence of an eccentric orbit. we find no evidence of significant absorption or emission from other major carbon-bearing molecules of the planet, including methane and carbon dioxide. the atmosphere is non-inverted in the temperature-pressure region probed by these observations. the deepest absorption lines reach an observed relative contrast of 0.9× {10}-3 with respect to the host star continuum flux at an angular separation of 3 milliarcseconds. this work is consistent with a previous tentative report of k-band molecular absorption for 51 peg b by brogi et al. | discovery of water at high spectral resolution in the atmosphere of 51 peg b |
we carried out a systematic study of full-orbit phase curves for known transiting systems in the northern ecliptic sky that were observed during year 2 of the tess primary mission. we applied the same methodology for target selection, data processing, and light-curve fitting as we did in our year 1 study. out of the 15 transiting systems selected for analysis, seven-hat-p-7, kelt-1, kelt-9, kelt-16, kelt-20, kepler-13a, and wasp-12-show statistically significant secondary eclipses and day-night atmospheric brightness modulations. small eastward dayside hot-spot offsets were measured for kelt-9b and wasp-12b. kelt-1, kepler-13a, and wasp-12 show additional phase-curve variability attributed to the tidal distortion of the host star; the amplitudes of these signals are consistent with theoretical predictions. we combined occultation measurements from tess and spitzer to compute dayside brightness temperatures, tess-band geometric albedos, bond albedos, and phase integrals for several systems. the new albedo values solidify the previously reported trend between dayside temperature and geometric albedo for planets with 1500 k < tday < 3000 k. for kepler-13ab, we carried out an atmospheric retrieval of the full secondary eclipse spectrum, which revealed a noninverted temperature-pressure profile, significant h2o and k absorption in the near-infrared, evidence for strong optical atmospheric opacity due to sodium, and a confirmation of the high geometric albedo inferred from our simpler analysis. we explore the implications of the phase integrals (ratios of bond to geometric albedos) for understanding exoplanet clouds. we also report updated transit ephemerides for all of the systems studied in this work. | visible-light phase curves from the second year of the tess primary mission |
binary evolution theory predicts that the second common envelope (ce) ejection can produce low-mass (0.32-0.36 msun) subdwarf b (sdb) stars inside ultrashort-orbital-period binary systems, as their helium cores are ignited under nondegenerate conditions. with the orbital decay driven by gravitational-wave (gw) radiation, the minimum orbital periods of detached sdb binaries could be as short as ~20 minutes. however, only four sdb binaries with orbital periods below an hour have been reported so far, while none of them has an orbital period approaching the above theoretical limit. here we report the discovery of a 20.5-minute-orbital-period ellipsoidal binary, tmts j052610.43+593445.1, in which the visible star is being tidally deformed by an invisible carbon-oxygen white dwarf (wd) companion. the visible component is inferred to be an sdb star with a mass of ~0.33 msun, approaching that of helium-ignition limit, although a he-core wd cannot be completely ruled out. in particular, the radius of this low-mass sdb star is only 0.066 rsun, about seven earth radii, possibly representing the most compact nondegenerate star ever known. such a system provides a key clue to map the binary evolution scheme from the second ce ejection to the formation of am cvn stars having a helium-star donor, and it will also serve as a crucial verification binary of space-borne gw detectors in the future. | a seven-earth-radius helium-burning star inside a 20.5-min detached binary |
the samarium-146 (146sm)-neodymium-142 (142nd) short-lived decay system (half-life of 103 million years) is a powerful tracer of the early mantle-crust evolution of planetary bodies. however, an increased 142nd/144nd in modern terrestrial rocks relative to chondrite meteorites has been proposed to be caused by nucleosynthetic anomalies, obscuring early earth’s differentiation history. we use stepwise dissolution of primitive chondrites to quantify nucleosynthetic contributions on the composition of chondrites. after correction for nucleosynthetic anomalies, earth and the silicate parts of differentiated planetesimals contain resolved excesses of 142nd relative to chondrites. we conclude that only collisional erosion of primordial crusts can explain such compositions. this process associated with planetary accretion must have produced substantial loss of incompatible elements, including long-term heat-producing elements such as uranium, thorium, and potassium. | earth’s composition was modified by collisional erosion |
life on planet earth is under siege. we are now in an uncharted territory. for several decades, scientists have consistently warned of a future marked by extreme climatic conditions because of escalating global temperatures caused by ongoing human activities that release harmful greenhouse gasses into the atmosphere. unfortunately, time is up. we are seeing the manifestation of those predictions as an alarming and unprecedented succession of climate records are broken, causing profoundly distressing scenes of suffering to unfold. we are entering an unfamiliar domain regarding our climate crisis, a situation no one has ever witnessed firsthand in the history of humanity. in the present report, we display a diverse set of vital signs of the planet and the potential drivers of climate change and climate-related responses first presented by ripple and wolf and colleagues (2020), who declared a climate emergency, now with more than 15,000 scientist signatories. the trends reveal new all-time climate-related records and deeply concerning patterns of climate-related disasters. at the same time, we report minimal progress by humanity in combating climate change. given these distressing developments, our goal is to communicate climate facts and policy recommendations to scientists, policymakers, and the public. it is the moral duty of us scientists and our institutions to clearly alert humanity of any potential existential threat and to show leadership in taking action. this report is part of our series of concise and easily accessible yearly updates on the state of the climate crisis. | the 2023 state of the climate report: entering uncharted territory |
massive and water-rich planets should be ubiquitous in the universe. many of these worlds are expected to be subject to important irradiation from their host star, and display supercritical water layers surrounded by extended steam atmospheres. irradiated ocean planets with such inflated hydrospheres have been recently shown to be good candidates for matching the mass-radius distribution of sub-neptunes. here we describe a model that computes a realistic structure for water-rich planets by combining an interior model with an updated equation of state (eos) for water, and an atmospheric model that takes into account radiative transfer. we find that the use of inappropriate eoss can lead to the overestimation of the planetary radius by up to ~10%, depending on the planet size and composition. our model has been applied to the gj 9827 system as a test case and indicates earth- or venus-like interiors for planets b and c, respectively. planet d could be an irradiated ocean planet with a water mass fraction (wmf) of ~20% ± 10%. we also provide fits for the mass-radius relationships, allowing one to directly retrieve a wide range of planetary compositions, without the requirement to run the model. our calculations finally suggest that highly irradiated planets lost their h/he content through atmospheric loss processes, and that the leftover material led to either super-earths or sub-neptunes, depending on the wmf. | mass-radius relationships for irradiated ocean planets |
palatini f(r) gravity is probably the simplest extension of general relativity (gr) and the simplest realization of a metric-affine theory. it has the same number of degrees of freedom as gr and, in vacuum, it is straightforwardly mapped into gr with a cosmological constant. the mapping between gr and palatini f(r) inside matter is possible but at the expense of reinterpreting the meaning of the matter fields. the physical meaning and consequences of such mapping will depend on the physical context. here, we consider three such cases within the weak field limit: solar system dynamics, planetary internal dynamics (seismology), and galaxies. after revising our previous results on the solar system and earth’s seismology, we consider here the possibility of f(r) palatini as a dark matter candidate. for any f(r) that admits a polynomial approximation in the weak field limit, we show here, using sparc data and a recent method that we proposed, that the theory cannot be used to replace dark matter in galaxies. we also show that the same result applies to the eddington-inspired born-infeld gravity. differently from the metric f(r) case, the rotation curve data are sufficient for this conclusion. | palatini f(r) gravity tests in weak field limit: solar system, seismology and galaxies |
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