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the dwarf planet ceres is known to host phyllosilicate minerals at its surface, but their distribution and origin have not previously been determined. we used the spectrometer onboard the dawn spacecraft to map their spatial distribution on the basis of diagnostic absorption features in the visible and near-infrared spectral range (0.25 to 5.0 micrometers). we found that magnesium- and ammonium-bearing minerals are ubiquitous across the surface. variations in the strength of the absorption features are spatially correlated and indicate considerable variability in the relative abundance of the phyllosilicates, although their composition is fairly uniform. these data, along with the distinctive spectral properties of ceres relative to other asteroids and carbonaceous meteorites, indicate that the phyllosilicates were formed endogenously by a globally widespread and extensive alteration process. | distribution of phyllosilicates on the surface of ceres |
we present an asymptotically and unconditionally stable numerical method to account for the momentum transfer between multiple species. momentum is conserved to machine precision. this implies that the asymptotic equilibrium corresponds to the velocity of the center of mass. aimed at studying dust dynamics, we implement this numerical method in the publicly available code fargo3d. to validate our implementation, we develop a test suite for an arbitrary number of species, based on analytical or exact solutions of problems related to perfect damping, damped sound waves, shocks, local and global gas-dust radial drift in a disk, and linear streaming instability. in particular, we obtain first-order steady-state solutions for the radial drift of multiple dust species in protoplanetary disks (ppds), in which the pressure gradient is not necessarily small. we additionally present nonlinear shearing-box simulations of the streaming instability and compare them with previous results obtained with lagrangian particles. we successfully validate our implementation by recovering the solutions from the test suite to second- and first-order accuracy in space and time, respectively. from this, we conclude that our scheme is suitable, and very robust, to study the self-consistent dynamics of several fluids. in particular, it can be used for solving the collisions between gas and dust in ppds, with any degree of coupling. | asymptotically stable numerical method for multispecies momentum transfer: gas and multifluid dust test suite and implementation in fargo3d |
the upper scorpius ob association is the nearest region of recent massive star formation and thus an important benchmark for investigations concerning stellar evolution and planet formation timescales. we present nine eclipsing binaries (ebs) in upper scorpius, three of which are newly reported here and all of which were discovered from k2 photometry. joint fitting of the eclipse photometry and radial velocities from newly acquired keck i/hires spectra yields precise masses and radii for those systems that are spectroscopically double-lined. the binary orbital periods in our sample range from 0.6 to 100 days, with total masses ranging from 0.2 to 8 m ⊙. at least 33% of the ebs reside in hierarchical multiples, including two triples and one quadruple. we use these ebs to develop an empirical mass-radius relation for pre-main-sequence stars and evaluate the predictions of widely used stellar evolutionary models. we report evidence for an age of 5-7 myr, which is self-consistent in the mass range of 0.3-5 m ⊙ and based on the fundamentally determined masses and radii of ebs. evolutionary models including the effects of magnetic fields imply an age of 9-10 myr. our results are consistent with previous studies that indicate that many models systematically underestimate the masses of low-mass stars by 20%-60% based on hertzsprung-russell diagram analyses. we also consider the dynamical states of several binaries and compare with expectations from tidal dissipation theories. finally, we identify rik 72 b as a long-period transiting brown dwarf (m = 59.2 ± 6.8 m jup, r = 3.10 ± 0.31 r jup, p ≈ 97.8 days) and an ideal benchmark for brown dwarf cooling models at 5-10 myr. | age determination in upper scorpius with eclipsing binaries |
the rosina mass spectrometer dfms on board esa's rosetta spacecraft detected the major isotopes of the noble gases argon, krypton, and xenon in the coma of comet 67p/churyumov-gerasimenko. earlier, it has been shown that xenon exhibits an isotopic composition distinct from anywhere else in the solar system. however, argon isotopes, within error, were shown to be consistent with solar isotope abundances. this discrepancy suggested an additional exotic component of xenon in comet 67p/churyumov-gerasimenko. here we show that also krypton exhibits an isotopic composition close to solar. furthermore, we found a depletion compared to solar of argon with respect to krypton and of krypton with respect to xenon, which is a necessity to postulate an addition of exotic xenon in the comet. | krypton isotopes and noble gas abundances in the coma of comet 67p/churyumov-gerasimenko |
the polarization state of electromagnetic radiation scattered by atmospheric particles such as aerosols, cloud droplets, or ice crystals contains much more information about the optical and microphysical properties than the total intensity alone. for this reason an increasing number of polarimetric observations are performed from space, from the ground and from aircraft. polarized radiative transfer models are required to interpret and analyse these measurements and to develop retrieval algorithms exploiting polarimetric observations. in the last years a large number of new codes have been developed, mostly for specific applications. benchmark results are available for specific cases, but not for more sophisticated scenarios including polarized surface reflection and multi-layer atmospheres. the international polarized radiative transfer (iprt) working group of the international radiation commission (irc) has initiated a model intercomparison project in order to fill this gap. this paper presents the results of the first phase a of the iprt project which includes ten test cases, from simple setups with only one layer and rayleigh scattering to rather sophisticated setups with a cloud embedded in a standard atmosphere above an ocean surface. all scenarios in the first phase a of the intercomparison project are for a one-dimensional plane-parallel model geometry. the commonly established benchmark results are available at the iprt website. | iprt polarized radiative transfer model intercomparison project - phase a |
absorption of high-energy radiation in planetary thermospheres is generally believed to lead to the formation of planetary winds. the resulting mass-loss rates can affect the evolution, particularly of small gas planets. we present 1d, spherically symmetric hydrodynamic simulations of the escaping atmospheres of 18 hot gas planets in the solar neighborhood. our sample only includes strongly irradiated planets, whose expanded atmospheres may be detectable via transit spectroscopy using current instrumentation. the simulations were performed with the pluto-cloudy interface, which couples a detailed photoionization and plasma simulation code with a general mhd code. we study the thermospheric escape and derive improved estimates for the planetary mass-loss rates. our simulations reproduce the temperature-pressure profile measured via sodium d absorption in hd 189733 b, but show still unexplained differences in the case of hd 209458 b. in contrast to general assumptions, we find that the gravitationally more tightly bound thermospheres of massive and compact planets, such as hat-p-2 b are hydrodynamically stable. compact planets dispose of the radiative energy input through hydrogen lyα and free-free emission. radiative cooling is also important in hd 189733 b, but it decreases toward smaller planets like gj 436 b. computing the planetary lyα absorption and emission signals from the simulations, we find that the strong and cool winds of smaller planets mainly cause strong lyα absorption but little emission. compact and massive planets with hot, stable thermospheres cause small absorption signals but are strong lyα emitters, possibly detectable with the current instrumentation. the absorption and emission signals provide a possible distinction between these two classes of thermospheres in hot gas planets. according to our results, wasp-80 and gj 3470 are currently the most promising targets for observational follow-up aimed at detecting atmospheric lyα absorption signals. simulated atmospheres are only available at the cds via anonymous ftp to http://cdsarc.u-strasbg.fr (ftp://130.79.128.5) or via http://cdsarc.u-strasbg.fr/viz-bin/qcat?j/a+a/586/a75 | simulating the escaping atmospheres of hot gas planets in the solar neighborhood |
observations of the warm neptune gj 436 b were performed with hst/stis at three different epochs (2012, 2013, 2014) in the stellar lyman-α line. they showed deep, repeated transits that were attributed to a giant exosphere of neutral hydrogen. the low radiation pressure from the m-dwarf host star was shown to play a major role in the dynamics of the escaping gas and its dispersion within a large volume around the planet. yet by itself it cannot explain the specific time-variable spectral features detected in each transit. here we investigate the combined role of radiative braking and stellar wind interactions using numerical simulations with the evaporating exoplanet code (eve) and we derive atmospheric and stellar properties through the direct comparison of simulated and observed spectra. the first epoch of observations is difficult to interpret because of the lack of out-of-transit data. in contrast, the results of our simulations match the observations obtained in 2013 and 2014 well. the sharp early ingresses observed in these epochs come from the abrasion of the planetary coma by the stellar wind. spectra observed at later times during the transit can be produced by a dual exosphere of planetary neutrals (escaped from the upper atmosphere of the planet) and neutralized protons (created by charge-exchange with the stellar wind). we find similar properties at both epochs for the planetary escape rate (~2.5 × 108 g s-1), the stellar photoionization rate (~2 × 10-5 s-1), the stellar wind bulk velocity (~85 km s-1), and its kinetic dispersion velocity (~10 km s-1, corresponding to a kinetic temperature of 12 000 k). we also find high velocities for the escaping gas (~50-60 km s-1) that may indicate magnetohydrodynamic (mhd) waves that dissipate in the upper atmosphere and drive the planetary outflow. in 2014 the high density of the stellar wind (~3 × 103 cm-3) led to the formation of an exospheric tail that was mainly composed of neutralized protons and produced a stable absorption signature during and after the transit. the observations of gj 436 b allow for the first time to clearly separate the contributions of radiation pressure and stellar wind and to probe the regions of the exosphere shaped by each mechanism. the overall shape of the cloud, which is constant over time, is caused by the stability of the stellar emission and the planetary mass loss, while the local changes in the cloud structure can be interpreted as variations in the density of the stellar wind. | an evaporating planet in the wind: stellar wind interactions with the radiatively braked exosphere of gj 436 b |
compared to the earth, the exoplanet kepler-78b has a similar size (1.2 r⊕) and an orbital period a thousand times shorter (8.5 h). it is currently the smallest planet for which the mass, radius, and dayside brightness have all been measured. kepler-78b is an exemplar of the ultra-short-period (usp) planets, a category defined by the simple criterion porb < 1 day. we describe our fourier-based search of the kepler data that led to the discovery of kepler-78b, and review what has since been learned about the population of usp planets. they are about as common as hot jupiters, and they are almost always smaller than 2 r⊕. they are often members of compact multi-planet systems, although they tend to have relatively large period ratios and mutual inclinations. they might be the exposed rocky cores of "gas dwarfs," the planets between 2-4 r⊕ in size that are commonly found in somewhat wider orbits. | kepler-78 and the ultra-short-period planets |
we performed a comprehensive demographic study of the co extent relative to dust of the disk population in the lupus clouds in order to find indications of dust evolution and possible correlations with other disk properties. we increased the number of disks of the region with measured rco and rdust from observations with the atacama large millimeter/submillimeter array to 42, based on the gas emission in the 12co j = 2−1 rotational transition and large dust grains emission at ~0.89 mm. the co integrated emission map is modeled with an elliptical gaussian or nuker function, depending on the quantified residuals; the continuum is fit to a nuker profile from interferometric modeling. the co and dust sizes, namely the radii enclosing a certain fraction of the respective total flux (e.g., r68%), are inferred from the modeling. the co emission is more extended than the dust continuum, with a r68%co/r68%dust median value of 2.5, for the entire population and for a subsample with high completeness. six disks, around 15% of the lupus disk population, have a size ratio above 4. based on thermo-chemical modeling, this value can only be explained if the disk has undergone grain growth and radial drift. these disks do not have unusual properties, and their properties spread across the population's ranges of stellar mass (m⋆), disk mass (mdisk), co and dust sizes (rco, rdust), and mass accretion of the entire population. we searched for correlations between the size ratio and m⋆, mdisk, rco, and rdust: only a weak monotonic anticorrelation with the rdust is found, which would imply that dust evolution is more prominent in more compact dusty disks. the lack of strong correlations is remarkable: the sample covers a wide range of stellar and disk properties, and the majority of the disks have very similar size ratios. this result suggests that the bulk of the disk population may behave alike and be in a similar evolutionary stage, independent of the stellar and disk properties. these results should be further investigated, since the optical depth difference between co and dust continuum might play a major role in the observed size ratios of the population. lastly, we find a monotonic correlation between the co flux and the co size. the results for the majority of the disks are consistent with optically thick emission and an average co temperature of around 30 k; however, the exact value of the temperature is difficult to constrain. | measuring the ratio of the gas and dust emission radii of protoplanetary disks in the lupus star-forming region |
the detection of a wide range of substructures such as rings, cavities, and spirals has become a common outcome of high spatial resolution imaging of protoplanetary disks, both in the near-infrared scattered light and in the thermal millimetre continuum emission. the most frequent interpretation of their origin is the presence of planetary-mass companions perturbing the gas and dust distribution in the disk (perturbers), but so far the only bona fide detection has been the two giant planets carving the disk around pds 70. here, we present a sample of 15 protoplanetary disks showing substructures in sphere scattered-light images and a homogeneous derivation of planet detection limits in these systems. to obtain mass limits we rely on different post-formation luminosity models based on distinct formation conditions, which are critical in the first million years of evolution. we also estimate the mass of these perturbers through a hill radius prescription and a comparison to alma data. assuming that one single planet carves each substructure in scattered light, we find that more massive perturbers are needed to create gaps within cavities than rings, and that we might be close to a detection in the cavities of rx j1604.3-2130a, rx j1615.3-3255, sz cha, hd 135344b, and hd 34282. we reach typical mass limits in these cavities of 3-10 mjup. for planets in the gaps between rings, we find that the detection limits of sphere high-contrast imaging are about an order of magnitude away in mass, and that the gaps of pds 66 and hd 97048 seem to be the most promising structures for planet searches. the proposed presence of massive planets causing spiral features in hd 135344b and hd 36112 are also within sphere's reach assuming hot-start models. these results suggest that the current detection limits are able to detect hot-start planets in cavities, under the assumption that they are formed by a single perturber located at the centre of the cavity. more realistic planet mass constraints would help to clarify whether this is actually the case, which might indicate that perturbers are not the only way of creating substructures. | perturbers: sphere detection limits to planetary-mass companions in protoplanetary disks |
as host to two accreting planets, pds 70 provides a unique opportunity to probe the chemical complexity of atmosphere-forming material. we present alma band 6 observations of the pds 70 disk and report the first chemical inventory of the system. with a spatial resolution of 0"4-0"5 (~50 au), 12 species are detected, including co isotopologs and formaldehyde, small hydrocarbons, hcn and hco+ isotopologs, and s-bearing molecules. so and ch3oh are not detected. all lines show a large cavity at the center of the disk, indicative of the deep gap carved by the massive planets. the radial profiles of the line emission are compared to the (sub)millimeter continuum and infrared scattered light intensity profiles. different molecular transitions peak at different radii, revealing the complex interplay between density, temperature, and chemistry in setting molecular abundances. column densities and optical depth profiles are derived for all detected molecules, and upper limits obtained for the nondetections. excitation temperature is obtained for h2co. deuteration and nitrogen fractionation profiles from the hydrocyanide lines show radially increasing fractionation levels. comparison of the disk chemical inventory to grids of chemical models from the literature strongly suggests a disk molecular layer hosting a carbon-to-oxygen ratio c/o > 1, thus providing for the first time compelling evidence of planets actively accreting high c/o ratio gas at present time. | the chemical inventory of the planet-hosting disk pds 70 |
we report the detection of the first circumbinary planet (cbp) found by transiting exoplanet survey satellite (tess). the target, a known eclipsing binary, was observed in sectors 1 through 12 at 30 minute cadence and in sectors 4 through 12 at 2 minute cadence. it consists of two stars with masses of 1.1 m⊙ and 0.3 m⊙ on a slightly eccentric (0.16), 14.6 day orbit, producing prominent primary eclipses and shallow secondary eclipses. the planet has a radius of ∼6.9 r⊕ and was observed to make three transits across the primary star of roughly equal depths (∼0.2%) but different durations—a common signature of transiting cbps. its orbit is nearly circular (e ≈ 0.09) with an orbital period of 95.2 days. the orbital planes of the binary and the planet are aligned to within ∼1°. to obtain a complete solution for the system, we combined the tess photometry with existing ground-based radial-velocity observations in a numerical photometric-dynamical model. the system demonstrates the discovery potential of tess for cbps and provides further understanding of the formation and evolution of planets orbiting close binary stars. | toi-1338: tess' first transiting circumbinary planet |
massive stars, at least ∼10 times more massive than the sun, have two key properties that make them the main drivers of evolution of star clusters, galaxies, and the universe as a whole. on the one hand, the outer layers of massive stars are so hot that they produce most of the ionizing ultraviolet radiation of galaxies; in fact, the first massive stars helped to re-ionize the universe after its dark ages. another important property of massive stars are the strong stellar winds and outflows they produce. this mass loss, and finally the explosion of a massive star as a supernova or a gamma-ray burst, provide a significant input of mechanical and radiative energy into the interstellar space. these two properties together make massive stars one of the most important cosmic engines: they trigger the star formation and enrich the interstellar medium with heavy elements, that ultimately leads to formation of earth-like rocky planets and the development of complex life. the study of massive star winds is thus a truly multidisciplinary field and has a wide impact on different areas of astronomy. in recent years observational and theoretical evidences have been growing that these winds are not smooth and homogeneous as previously assumed, but rather populated by dense "clumps". the presence of these structures dramatically affects the mass loss rates derived from the study of stellar winds. clump properties in isolated stars are nowadays inferred mostly through indirect methods (i.e., spectroscopic observations of line profiles in various wavelength regimes, and their analysis based on tailored, inhomogeneous wind models). the limited characterization of the clump physical properties (mass, size) obtained so far have led to large uncertainties in the mass loss rates from massive stars. such uncertainties limit our understanding of the role of massive star winds in galactic and cosmic evolution. supergiant high mass x-ray binaries (sgxbs) are among the brightest x-ray sources in the sky. a large number of them consist of a neutron star accreting from the wind of a massive companion and producing a powerful x-ray source. the characteristics of the stellar wind together with the complex interactions between the compact object and the donor star determine the observed x-ray output from all these systems. consequently, the use of sgxbs for studies of massive stars is only possible when the physics of the stellar winds, the compact objects, and accretion mechanisms are combined together and confronted with observations. this detailed review summarises the current knowledge on the theory and observations of winds from massive stars, as well as on observations and accretion processes in wind-fed high mass x-ray binaries. the aim is to combine in the near future all available theoretical diagnostics and observational measurements to achieve a unified picture of massive star winds in isolated objects and in binary systems. | towards a unified view of inhomogeneous stellar winds in isolated supergiant stars and supergiant high mass x-ray binaries |
air pollution simulations critically depend on the quality of the underlying meteorology. in phase 2 of the air quality model evaluation international initiative (aqmeii-2), thirteen modeling groups from europe and four groups from north america operating eight different regional coupled chemistry and meteorology models participated in a coordinated model evaluation exercise. each group simulated the year 2010 for a domain covering either europe or north america or both. here were present an operational analysis of model performance with respect to key meteorological variables relevant for atmospheric chemistry processes and air quality. these parameters include temperature and wind speed at the surface and in the vertical profile, incoming solar radiation at the ground, precipitation, and planetary boundary layer heights. a similar analysis was performed during aqmeii phase 1 (vautard et al., 2012) for offline air quality models not directly coupled to the meteorological model core as the model systems investigated here. similar to phase 1, we found significant overpredictions of 10-m wind speeds by most models, more pronounced during night than during daytime. the seasonal evolution of temperature was well captured with monthly mean biases below 2 k over all domains. solar incoming radiation, precipitation and pbl heights, on the other hand, showed significant spread between models and observations suggesting that major challenges still remain in the simulation of meteorological parameters relevant for air quality and for chemistry-climate interactions at the regional scale. | comparative analysis of meteorological performance of coupled chemistry-meteorology models in the context of aqmeii phase 2 |
a key stage in planet formation is the evolution of a gaseous and magnetized solar nebula. however, the lifetime of the nebular magnetic field and nebula are poorly constrained. we present paleomagnetic analyses of volcanic angrites demonstrating that they formed in a near-zero magnetic field (<0.6 microtesla) at 4563.5 ± 0.1 million years ago, ~3.8 million years after solar system formation. this indicates that the solar nebula field, and likely the nebular gas, had dispersed by this time. this sets the time scale for formation of the gas giants and planet migration. furthermore, it supports formation of chondrules after 4563.5 million years ago by non-nebular processes like planetesimal collisions. the core dynamo on the angrite parent body did not initiate until about 4 to 11 million years after solar system formation. | lifetime of the solar nebula constrained by meteorite paleomagnetism |
delhi, india, is the second most populated city in the world and routinely experiences some of the highest particulate matter concentrations of any megacity on the planet, posing acute challenges to public health (world health organization, 2018). however, the current understanding of the sources and dynamics of pm pollution in delhi is limited. measurements at the delhi aerosol supersite (das) provide long-term chemical characterization of ambient submicron aerosol in delhi, with near-continuous online measurements of aerosol composition. here we report on source apportionment based on positive matrix factorization (pmf), conducted on 15 months of highly time-resolved speciated submicron non-refractory pm1 (nr-pm1) between january 2017 and march 2018. we report on seasonal variability across four seasons of 2017 and interannual variability using data from the two winters and springs of 2017 and 2018. we show that a modified tracer-based organic component analysis provides an opportunity for a real-time source apportionment approach for organics in delhi. phase equilibrium modeling of aerosols using the extended aerosol inorganics model (e-aim) predicts equilibrium gas-phase concentrations and allows evaluation of the importance of the ventilation coefficient (vc) and temperature in controlling primary and secondary organic aerosol. we also find that primary aerosol dominates severe air pollution episodes, and secondary aerosol dominates seasonal averages. | sources and atmospheric dynamics of organic aerosol in new delhi, india: insights from receptor modeling |
the nature and evolution of earth's crust during the hadean and eoarchean is largely unknown owing to a paucity of material preserved from this period. however, clues may be found in the chemical composition of refractory minerals that initially grew in primordial material but were subsequently incorporated into younger rocks and sediment during lithospheric reworking. here we report hf isotopic data in 3.9 to 1.8 billion year old detrital zircon from modern stream sediment samples from west greenland, which document successive reworking of felsic hadean-to-eoarchean crust during subsequent periods of magmatism. combined with global zircon hf data, we show a planetary shift towards, on average, more juvenile hf values 3.2 to 3.0 billion years ago. this crustal rejuvenation was coincident with peak mantle potential temperatures that imply greater degrees of mantle melting and injection of hot mafic-ultramafic magmas into older hadean-to-eoarchean felsic crust at this time. given the repeated recognition of felsic hadean-to-eoarchean diluted signatures, ancient crust appears to have acted as buoyant life-rafts with enhanced preservation-potential that facilitated later rapid crustal growth during the meso-and-neoarchean. | widespread reworking of hadean-to-eoarchean continents during earth's thermal peak |
astrophysical ices are exposed to different radiation fields including photons, electrons and ions. the latter stem from interstellar cosmic rays (cr), the solar and stellar winds, shock waves or are trapped in the magnetospheres of giant planets. we briefly discuss the physics of energy deposition by ion ir radiation in condensed matter and experimental methods to study the induced effects. we then present results on radiation effects such as sputtering, amorphisation and compaction, dissociation of molecules, formation of new molecular species after radiolysis and by implantation of ions. the formation and radio-resistance of organic molecules, related to the question of the initial conditions for the emergence of life, are briefly discussed. this review is not meant to be comprehensive, but rather focusses on recent findings, with special emphasis on experiments with heavy multiply charged ion beams. these experiments aim in particular at simulating the effects of crs on icy grains in dense molecular clouds, and on the formation of molecules on icy bodies in the solar system. | modification of ices by cosmic rays and solar wind |
we review the results of an extensive campaign to determine the physical, geological, and dynamical properties of asteroid (101955) bennu. this investigation provides information on the orbit, shape, mass, rotation state, radar response, photometric, spectroscopic, thermal, regolith, and environmental properties of bennu. we combine these data with cosmochemical and dynamical models to develop a hypothetical timeline for bennu's formation and evolution. we infer that bennu is an ancient object that has witnessed over 4.5 gyr of solar system history. its chemistry and mineralogy were established within the first 10 myr of the solar system. it likely originated as a discrete asteroid in the inner main belt approximately 0.7-2 gyr ago as a fragment from the catastrophic disruption of a large (approximately 100-km), carbonaceous asteroid. it was delivered to near-earth space via a combination of yarkovsky-induced drift and interaction with giant-planet resonances. during its journey, yorp processes and planetary close encounters modified bennu's spin state, potentially reshaping and resurfacing the asteroid. we also review work on bennu's future dynamical evolution and constrain its ultimate fate. it is one of the most potentially hazardous asteroids with an approximately 1-in-2700 chance of impacting the earth in the late 22nd century. it will most likely end its dynamical life by falling into the sun. the highest probability for a planetary impact is with venus, followed by the earth. there is a chance that bennu will be ejected from the inner solar system after a close encounter with jupiter. osiris-rex will return samples from the surface of this intriguing asteroid in september 2023. | the osiris-rex target asteroid (101955) bennu: constraints on its physical, geological, and dynamical nature from astronomical observations |
in the search for a record of eustatic sea level change on glacial-interglacial timescales, the seychelles ranks as one of the best places on the planet to study. owing to its location with respect to the former margins of northern hemisphere ice sheets that wax and wane on orbital cycles, the local-or relative-sea level history is predicted to lie within a few meters of the globally averaged eustatic signal during the last interglacial period. we have surveyed and dated last interglacial fossil corals to ascertain peak sea level and hence infer maximum retreat of polar ice sheets during this time interval. we observe a pattern of gradually rising sea level in the seychelles between ∼129 and 125 thousand years ago (ka), with peak eustatic sea level attained after 125 ka at 7.6 ± 1.7 m higher than present. after accounting for thermal expansion and loss of mountain glaciers, this sea-level budget would require ∼5-8 m of polar ice sheet contribution, relative to today's volume, of which only ∼2 m came from the greenland ice sheet. this result clearly identifies the antarctic ice sheet as a significant source of melt water, most likely derived from one of the unstable, marine-based sectors in the west and/or east antarctic ice sheet. furthermore, the establishment of a +5.9 ± 1.7 m eustatic sea level position by 128.6 ± 0.8 ka would require that partial ais collapse was coincident with the onset of the sea level highstand. | tropical tales of polar ice: evidence of last interglacial polar ice sheet retreat recorded by fossil reefs of the granitic seychelles islands |
water scarcity is rapidly spreading across the planet, threatening the population across the five continents and calling for global sustainable solutions. water reclamation is the most ecological approach for supplying clean drinking water. however, current water purification technologies are seldom sustainable, due to high-energy consumption and negative environmental footprint. here, we review the cutting-edge technologies based on protein nanofibrils as water purification agents and we highlight the benefits of this green, efficient and affordable solution to alleviate the global water crisis. we discuss the different protein nanofibrils agents available and analyze them in terms of performance, range of applicability and sustainability. we underline the unique opportunity of designing protein nanofibrils for efficient water purification starting from food waste, as well as cattle, agricultural or dairy industry byproducts, allowing simultaneous environmental, economic and social benefits and we present a case analysis, including a detailed life cycle assessment, to establish their sustainable footprint against other common natural-based adsorbents, anticipating a bright future for this water purification approach. | protein nanofibrils for next generation sustainable water purification |
we are well and truly in the anthropocene. humans can no longer be considered as mere external drivers or boundary conditions in the hydrologic systems we study. the interactions and feedbacks between human actions and water cycle dynamics on the planet, combined with the evolution of human norms/values in relation to water, are throwing up a range of emergent "big problems." understanding and offering sustainable solutions to these "big problems" require a broadening of hydrologic science to embrace the perspectives of both social and natural scientists. the new science of socio-hydrology was introduced with this in mind, yet faces major challenges due to the wide gulf that separates the knowledge foundations and methodologies of natural and social sciences. yet, the benefits of working together are enormous, including through adoption of natural science methods for social science problems, and vice versa. bringing together the perspectives of both social and natural scientists dealing with water is good for hydrologic science, having the salutary effect of revitalizing it as use-inspired basic science. it is good for management too, in that the broader, holistic perspectives provided by socio-hydrology can help recognize potential "big" problems that may otherwise be unforeseen and, equally, identify potential "alternative" solutions to otherwise intractable problems. | debates—perspectives on socio-hydrology: changing water systems and the "tyranny of small problems"—socio-hydrology |
magnetized winds may be important in dispersing protoplanetary disks and influencing planet formation. we carry out global magnetohydrodynamic simulations in axisymmetry, coupled with ray-tracing radiative transfer, consistent thermochemistry, and non-ideal mhd diffusivities. magnetized models lacking euv photons (hν > 13.6 {ev}) feature warm molecular outflows that have typical poloidal speeds ≳ 4 {km} {{{s}}}-1. when the magnetization is sufficient to drive accretion rates ∼ {10}-8 {m}⊙{yr}}-1, the wind mass-loss rate is comparable. such outflows are driven not centrifugally but by the pressure of toroidal magnetic fields produced by bending the poloidal field. both the accretion and outflow rates increase with the poloidal field energy density, the former almost linearly. the mass-loss rate is also strongly affected by ionization due to uv and x-ray radiation near the wind base. adding euv irradiation to the system heats, ionizes, and accelerates the part of the outflow nearest the symmetry axis, but reduces the overall mass-loss rate by exerting pressure on the wind base. most of our models are non-turbulent, but some with reduced dust abundance and therefore higher ionization fractions exhibit magnetorotational instabilities near the base of the wind. | global simulations of protoplanetary disk outflows with coupled non-ideal magnetohydrodynamics and consistent thermochemistry |
a giant planet embedded in a protoplanetary disk forms a gap. an analytic relationship among the gap depth, planet mass mp, disk aspect ratio hp, and viscosity α has been found recently, and the gap depth can be written in terms of a single parameter k={{({{m}p}/{{m}*})}2}hp-5{{α }-1}. we discuss how observed gap features can be used to constrain the disk and/or planet parameters based on the analytic formula for the gap depth. the constraint on the disk aspect ratio is critical in determining the planet mass so the combination of the observations of the temperature and the image can provide a constraint on the planet mass. we apply the formula for the gap depth to observations of hl tau and hd 169142. in the case of hl tau, we propose that a planet with ≳ 0.3 mj is responsible for the observed gap at 30 au from the central star based on the estimate that the gap depth is ≲ 1/3. in the case of hd 169142, the planet mass that causes the gap structure recently found by vla is ≳ 0.4{{m}j}. we also argue that the spiral structure, if observed, can be used to estimate the lower limit of the disk aspect ratio and the planet mass. | mass estimates of a giant planet in a protoplanetary disk from the gap structures |
surveys of young star-forming regions have discovered a growing population of planetary-mass (<13 mjup) companions around young stars1. there is an ongoing debate as to whether these companions formed like planets (that is, from the circumstellar disk)2, or if they represent the low-mass tail of the star-formation process3. in this study, we utilize high-resolution spectroscopy to measure rotation rates of three young (2-300 myr) planetary-mass companions and combine these measurements with published rotation rates for two additional companions4,5 to provide a picture of the spin distribution of these objects. we compare this distribution to complementary rotation-rate measurements for six brown dwarfs with masses <20 mjup, and show that these distributions are indistinguishable. this suggests that either these two populations formed via the same mechanism, or that processes regulating rotation rates are independent of formation mechanism. we find that rotation rates for both populations are well below their break-up velocities and do not evolve significantly during the first few hundred million years after the end of accretion. this suggests that rotation rates are set during the late stages of accretion, possibly by interactions with a circumplanetary disk. this result has important implications for our understanding of the processes regulating the angular momentum evolution of young planetary-mass objects, and of the physics of gas accretion and disk coupling in the planetary-mass regime. | constraints on the spin evolution of young planetary-mass companions |
the moon-forming impact and the subsequent evolution of the proto-earth is strongly dependent on the properties of materials at the extreme conditions generated by this violent collision. we examine the high pressure behavior of mgo, one of the dominant constituents in earth's mantle, using high-precision, plate impact shock compression experiments performed on sandia national laboratories' z machine and extensive quantum calculations using density functional theory (dft) and quantum monte carlo (qmc) methods. the combined data span from ambient conditions to 1.2 tpa and 42 000 k, showing solid-solid and solid-liquid phase boundaries. furthermore our results indicate that under impact the solid and liquid phases coexist for more than 100 gpa, pushing complete melting to pressures in excess of 600 gpa. the high pressure required for complete shock melting has implications for a broad range of planetary collision events. | shock response and phase transitions of mgo at planetary impact conditions |
understanding the formation and evolution of giant planets (≥1 mjup) at wide orbital separation (≥5 au) is one of the goals of direct imaging. over the past 15 yr, many surveys have placed strong constraints on the occurrence rate of wide-orbit giants, mostly based on non-detections, but very few have tried to make a direct link with planet formation theories. in the present work, we combine the results of our previously published vlt/naco large program with the results of 12 past imaging surveys to constitute a statistical sample of 199 fgk stars within 100 pc, including three stars with sub-stellar companions. using monte carlo simulations and assuming linear flat distributions for the mass and semi-major axis of planets, we estimate the sub-stellar companion frequency to be within 0.75-5.70% at the 68% confidence level (cl) within 20-300 au and 0.5-75 mjup, which is compatible with previously published results. we also compare our results with the predictions of state-of-the-art population synthesis models based on the gravitational instability (gi) formation scenario with and without scattering. we estimate that in both the scattered and non-scattered populations, we would be able to detect more than 30% of companions in the 1-75 mjup range (95% cl). with the threesub-stellar detections in our sample, we estimate the fraction of stars that host a planetary system formed by gi to be within 1.0-8.6% (95% cl). we also conclude that even though gi is not common, it predicts a mass distribution of wide-orbit massive companions that is much closer to what is observed than what the core accretion scenario predicts. finally, we associate the present paper with the release of the direct imaging virtual archive (diva), a public database that aims at gathering the results of past, present, and future direct imaging surveys. based on observations collected at the european southern observatory, chile (eso large program 184.c-0157 and open time 089.c-0137a and 090.c-0252a). | the vlt/naco large program to probe the occurrence of exoplanets and brown dwarfs at wide orbits. iv. gravitational instability rarely forms wide, giant planets |
isotope abundance ratios have an important role in astronomy and planetary sciences, providing insights into the origin and evolution of the solar system, interstellar chemistry and stellar nucleosynthesis1,2. in contrast to deuterium/hydrogen ratios, carbon isotope ratios are found to be roughly constant (around 89) in the solar system1,3, but do vary on galactic scales with a 12c/13c isotopologue ratio of around 68 in the current local interstellar medium4-6. in molecular clouds and protoplanetary disks, 12co/13co ratios can be altered by ice and gas partitioning7, low-temperature isotopic ion-exchange reactions8 and isotope-selective photodissociation9. here we report observations of 13co in the atmosphere of the young, accreting super-jupiter tyc 8998-760-1 b, at a statistical significance of more than six sigma. marginalizing over the planet's atmospheric temperature structure, chemical composition and spectral calibration uncertainties suggests a 12co/13co ratio of 31−10+17?(90% confidence), a substantial enrichment in 13c with respect to the terrestrial standard and the local interstellar value. as the current location of tyc 8998-760-1 b at greater than or equal to 160 astronomical units is far beyond the co snowline, we postulate that it accreted a substantial fraction of its carbon from ices enriched in 13c through fractionation. | the 13co-rich atmosphere of a young accreting super-jupiter |
the composition of gas and solids in protoplanetary discs sets the composition of planets that form out of them. recent chemical models have shown that the composition of gas and dust in discs evolves on myr time-scales, with volatile species disappearing from the gas phase. however, discs evolve due to gas accretion and radial drift of dust on time-scales similar to these chemical time-scales. here, we present the first model coupling the chemical evolution in the disc mid-planes with the evolution of discs due to accretion and radial drift of dust. our models show that transport will always overcome the depletion of co2 from the gas phase, and can also overcome the depletion of co and ch4 unless both transport is slow (viscous α ≲ 10-3) and the ionization rate is high (ζ ≈ 10-17). including radial drift further enhances the abundances of volatile species because they are carried in on the surface of grains before evaporating left at their ice lines. due to large differences in the abundances within 10 au for models with and without efficient radial drift, we argue that composition can be used to constrain models of planet formation via pebble accretion. | planet-forming material in a protoplanetary disc: the interplay between chemical evolution and pebble drift |
interstellar comets offer direct samples of volatiles from distant protoplanetary disks. 2i/borisov is the first notably active interstellar comet discovered in our solar system1. comets are condensed samples of the gas, ice and dust that were in a star's protoplanetary disk during the formation of its planets, and inform our understanding on how chemical compositions and abundances vary with distance from the central star. their orbital migration distributes volatiles2, organic material and prebiotic chemicals around their host system3. in our solar system, hundreds of comets have been observed remotely, and a few have been studied up close by space missions4. however, knowledge of extrasolar comets has been limited to what could be gleaned from distant, unresolved observations of cometary regions around other stars, with only one detection of carbon monoxide5. here we report that the coma of 2i/borisov contains substantially more co than h2o gas, with abundances of at least 173%, more than three times higher than previously measured for any comet in the inner (<2.5 au) solar system4. our ultraviolet hubble space telescope observations of 2i/borisov provide the first glimpse into the ice content and chemical composition of the protoplanetary disk of another star that is substantially different from our own. | the carbon monoxide-rich interstellar comet 2i/borisov |
we collect observational evidence that supports the scheme of mass transfer on the nucleus of comet 67p/churyumov-gerasimenko. the obliquity of the rotation axis of 67p causes strong seasonal variations. during perihelion the southern hemisphere is four times more active than the north. northern territories are widely covered by granular material that indicates back fall originating from the active south. decimetre sized chunks contain water ice and their trajectories are influenced by an antisolar force instigated by sublimation. osiris observations suggest that up to 20 per cent of the particles directly return to the nucleus surface taking several hours of traveltime. the back fall covered northern areas are active if illuminated but produce mainly water vapour. the decimetre chunks from the nucleus surface are too small to contain more volatile compounds such as co2 or co. this causes a north-south dichotomy of the composition measurements in the coma. active particles are trapped in the gravitational minimum of hapi during northern winter. they are `shock frozen' and only re-activated when the comet approaches the sun after its aphelion passage. the insolation of the big cavity is enhanced by self-heating, i.e. reflection and ir radiation from the walls. this, together with the pristinity of the active back fall, explains the early observed activity of the hapi region. sobek may be a role model for the consolidated bottom of hapi. mass transfer in the case of 67p strongly influences the evolution of the nucleus and the interpretation of coma measurements. | seasonal mass transfer on the nucleus of comet 67p/chuyumov-gerasimenko |
the axion, motivated as a solution to the strong c p problem, is also a viable dark matter candidate. the axion field takes random values in causally disconnected regions if the symmetry breaking that establishes the particle occurs after inflation, leading to white-noise density fluctuations at low wave numbers and forming dense minihalos with sub-planetary masses subsequently. there have been two recent proposals that appear capable of testing this scenario, namely using pulsar timing arrays and studying cosmological microlensing caustics. motivated by these proposals, we use n-body simulations to study the formation of substructures from white-noise density fluctuations. the density profiles of our relaxed axion minihalos can be described by the navarro-frenk-white profile, and the minihalos' concentration number agrees well with a simple, physically-motivated model. we develop a semianalytic formula to fit the mass function from our simulation, which agrees broadly at different redshifts and only differs at factor of two level from classic halo mass functions. this analytic mass function allows us to consider uncertainties in the post-inflation axion scenario, as well as extrapolate our high-redshift simulations results to the present. our work estimates the present-day abundance of axion substructures, as is necessary for predicting their effect on cosmological microlensing caustics and pulsar timing. our calculations suggest that if pulsar timing and microlensing probes can reach recent sensitivity forecasts, they may be sensitive to the post-inflation axion dark matter scenario, even when accounting for uncertainties pertaining to axion strings. for pulsar timing, the most significant caveat is whether axion minihalos are disrupted by stars, which our estimates show is mildly important at the most relevant masses. finally, as our gravitational simulations are scale invariant, the results can be extended to models where the dark matter is comprised of other axion-like particles and even clusters of primordial black holes. | simulations of axion minihalos |
exoplanets orbiting m-dwarfs present a valuable opportunity for their detection and atmospheric characterization. this is evident from recent inferences of h2o in such atmospheres, including that of the habitable-zone exoplanet k2-18b. with a bulk density between earth and neptune, k2-18b may be expected to possess a h/he envelope. however, the extent of such an envelope and the thermodynamic conditions of the interior remain unexplored. in the present work, we investigate the atmospheric and interior properties of k2-18b based on its bulk properties and its atmospheric transmission spectrum. we constrain the atmosphere to be h2-rich with a h2o volume mixing ratio of 0.02%-14.8%, consistent with previous studies, and find a depletion of ch4 and nh3, indicating chemical disequilibrium. we do not conclusively detect clouds/hazes in the observable atmosphere. we use the bulk parameters and retrieved atmospheric properties to constrain the internal structure and thermodynamic conditions in the planet. the constraints on the interior allow multiple scenarios between rocky worlds with massive h/he envelopes and water worlds with thin envelopes. we constrain the mass fraction of the h/he envelope to be ≲6%; spanning ≲10-5 for a predominantly water world to ∼6% for a pure iron interior. the thermodynamic conditions at the surface of the h2o layer range from the supercritical to liquid phases, with a range of solutions allowing for habitable conditions on k2-18b. our results demonstrate that the potential for habitable conditions is not necessarily restricted to earth-like rocky exoplanets. | the interior and atmosphere of the habitable-zone exoplanet k2-18b |
large-scale vertical magnetic fields are believed to play a key role in the evolution of protoplanetary discs. associated with non-ideal effects, such as ambipolar diffusion, they are known to launch a wind that could drive accretion in the outer part of the disc (r > 1 au). they also potentially lead to self-organisation of the disc into large-scale axisymmetric structures, similar to the rings recently imaged by sub-millimetre or near-infrared instruments (alma and sphere). the aim of this paper is to investigate the mechanism behind the formation of these gaseous rings, but also to understand the dust dynamics and its emission in discs threaded by a large-scale magnetic field. to this end, we performed global magneto-hydrodynamics (mhd) axisymmetric simulations with ambipolar diffusion using a modified version of the pluto code. we explored different magnetisations with the midplane β parameter ranging from 105 to 103 and included dust grains -treated in the fluid approximation- ranging from 100 μm to 1 cm in size. we first show that the gaseous rings (associated with zonal flows) are tightly linked to the existence of mhd winds. secondly, we find that millimetre-size dust is highly sedimented, with a typical scale height of 1 au at r = 100 au for β = 104, compatible with recent alma observations. we also show that these grains concentrate into pressure maxima associated with zonal flows, leading to the formation of dusty rings. using the radiative transfer code mcfost, we computed the dust emission and make predictions on the ring-gap contrast and the spectral index that one might observe with interferometers like alma. | ring formation and dust dynamics in wind-driven protoplanetary discs: global simulations |
in this review/tutorial we explore planetary nebulae as a stage in the evolution of low-to-intermediate-mass stars, as major contributors to the mass and chemical enrichment of the interstellar medium, and as astrophysical laboratories. we discuss many observed properties of planetary nebulae, placing particular emphasis on element abundance determinations and comparisons with theoretical predictions. dust and molecules associated with planetary nebulae are considered as well. we then examine distances, binarity, and planetary nebula morphology and evolution. we end with mention of some of the advances that will be enabled by future observing capabilities. | planetary nebulae: sources of enlightenment |
an increasing number of observations have shown that gaseous debris discs are not an exception. however, until now, we only knew of cases around a stars. here we present the first detection of 12co (2-1) disc emission around an f star, hd 181327, obtained with the atacama large millimeter/submillimeter array (alma) observations at 1.3 mm. the continuum and co emission are resolved into an axisymmetric disc with ring-like morphology. using a markov chain monte carlo method coupled with radiative transfer calculations, we study the dust and co mass distribution. we find the dust is distributed in a ring with a radius of 86.0 ± 0.4 au and a radial width of 23.2 ± 1.0 au. at this frequency, the ring radius is smaller than in the optical, revealing grain size segregation expected due to radiation pressure. we also report on the detection of low-level continuum emission beyond the main ring out to ∼200 au. we model the co emission in the non-local thermodynamic equilibrium regime and we find that the co is co-located with the dust, with a total co gas mass ranging between 1.2 × 10-6 m⊕ and 2.9 × 10-6 m⊕, depending on the gas kinetic temperature and collisional partners densities. the co densities and location suggest a secondary origin, i.e. released from icy planetesimals in the ring. we derive a co+co2 cometary composition that is consistent with solar system comets. due to the low gas densities, it is unlikely that the gas is shaping the dust distribution. | exocometary gas in the hd 181327 debris ring |
the filamentary nature of accretion streams found around embedded sources suggests that protostellar disks experience heterogenous infall from the star-forming environment, consistent with the accretion behavior onto star-forming cores in top-down star-cluster formation simulations. this may produce disk substructures in the form of rings, gaps, and spirals that continue to be identified by high-resolution imaging surveys in both embedded class 0/i and later class ii sources. we present a parameter study of anisotropic infall, informed by the properties of accretion flows onto protostellar cores in numerical simulations, and varying the relative specific angular momentum of incoming flows as well as their flow geometry. our results show that anisotropic infall perturbs the disk and readily launches the rossby wave instability. it forms vortices at the inner and outer edges of the infall zone where material is deposited. these vortices drive spiral waves and angular momentum transport, with some models able to drive stresses corresponding to a viscosity parameter on the order of α ~ 10-2. the resulting azimuthal shear forms robust pressure bumps that act as barriers to radial drift of dust grains, as demonstrated by postprocessing calculations of drift-dominated dust evolution. we discuss how a self-consistent model of anisotropic infall can account for the formation of millimeter rings in the outer disk as well as producing compact dust disks, consistent with observations of embedded sources. | anisotropic infall and substructure formation in embedded disks |
clouds play an important role in the atmospheres of planetary bodies. it is expected that, like all the planetary bodies in our solar system, exoplanet atmospheres will also have substantial cloud coverage, and evidence is mounting for clouds in a number of hot jupiters. to better characterise planetary atmospheres, we need to consider the effects these clouds will have on the observed broadband transmission spectra. here we examine the expected cloud condensate species for hot jupiter exoplanets and the effects of various grain sizes and distributions on the resulting transmission spectra from the optical to infrared, which can be used as a broad framework when interpreting exoplanet spectra. we note that significant infrared absorption features appear in the computed transmission spectrum, the result of vibrational modes between the key species in each condensate, which can potentially be very constraining. while it may be hard to differentiate between individual condensates in the broad transmission spectra, it may be possible to discern different vibrational bonds, which can distinguish between cloud formation scenarios, such as condensate clouds or photochemically generated species. vibrational mode features are shown to be prominent when the clouds are composed of small sub-micron sized particles and can be associated with an accompanying optical scattering slope. these infrared features have potential implications for future exoplanetary atmosphere studies conducted with jwst, where such vibrational modes distinguishing condensate species can be probed at longer wavelengths. | transmission spectral properties of clouds for hot jupiter exoplanets |
proxima b is a terrestrial-mass planet in the habitable zone of proxima centauri. proxima centauri’s high stellar activity, however, casts doubt on the habitability of proxima b: sufficiently bright and frequent flares and any associated proton events may destroy the planet’s ozone layer, allowing lethal levels of uv flux to reach its surface. in 2016 march, the evryscope observed the first naked-eye-brightness superflare detected from proxima centauri. proxima increased in optical flux by a factor of ∼68 during the superflare and released a bolometric energy of 1033.5 erg, ∼10× larger than any previously detected flare from proxima. over the last two years the evryscope has recorded 23 other large proxima flares ranging in bolometric energy from 1030.6 to 1032.4 erg; coupling those rates with the single superflare detection, we predict that at least five superflares occur each year. simultaneous high-resolution high accuracy radial velocity planet searcher (harps) spectroscopy during the evryscope superflare constrains the superflare’s uv spectrum and any associated coronal mass ejections. we use these results and the evryscope flare rates to model the photochemical effects of no xatmospheric species generated by particle events from this extreme stellar activity, and show that the repeated flaring may be sufficient to reduce the ozone of an earth-like atmosphere by 90% within five years; complete depletion may occur within several hundred kyr. the uv light produced by the evryscope superflare would therefore have reached the surface with ∼100× the intensity required to kill simple uv-hardy microorganisms, suggesting that life would have to undergo extreme adaptations to survive in the surface areas of proxima b exposed to these flares. | the first naked-eye superflare detected from proxima centauri |
silicon and mg in differentiated rocky bodies exhibit heavy isotope enrichments that have been attributed to evaporation of partially or entirely molten planetesimals. we evaluate the mechanisms of planetesimal evaporation in the early solar system and the conditions that controlled attendant isotope fractionations. energy balance at the surface of a body accreted within 1 myr of cai formation and heated from within by 26al decay results in internal temperatures exceeding the silicate solidus, producing a transient magma ocean with a thin surface boundary layer of order <1 m that would be subject to foundering. bodies that are massive enough to form magma oceans by radioisotope decay (≥0.1% m⊕) can retain hot rock vapor even in the absence of ambient nebular gas. we find that a steady-state rock vapor forms within minutes to hours and results from a balance between rates of magma evaporation and atmospheric escape. vapor pressure buildup adjacent to the surfaces of the evaporating magmas would have inevitably led to an approach to equilibrium isotope partitioning between the vapor phase and the silicate melt. numerical simulations of this near-equilibrium evaporation process for a body with a radius of 700 km yield a steady-state far-field vapor pressure of 10-8 bar and a vapor pressure at the surface of 10-4 bar, corresponding to 95% saturation. approaches to equilibrium isotope fractionation between vapor and melt should have been the norm during planet formation due to the formation of steady-state rock vapor atmospheres and/or the presence of protostellar gas. we model the si and mg isotopic composition of bulk earth as a consequence of accretion of planetesimals that evaporated subject to the conditions described above. the results show that the best fit to bulk earth is for a carbonaceous chondrite-like source material with about 12% loss of mg and 15% loss of si resulting from near-equilibrium evaporation into the solar protostellar disk of h2 on timescales of 104 to 105 years. | near-equilibrium isotope fractionation during planetesimal evaporation |
earth and the moon are shown here to have indistinguishable oxygen isotope ratios, with a difference in δ‧17o of -1 ± 5 parts per million (2 standard error). on the basis of these data and our new planet formation simulations that include a realistic model for primordial oxygen isotopic reservoirs, our results favor vigorous mixing during the giant impact and therefore a high-energy, high-angular-momentum impact. the results indicate that the late veneer impactors had an average δ‧17o within approximately 1 per mil of the terrestrial value, limiting possible sources for this late addition of mass to the earth-moon system. | oxygen isotopic evidence for vigorous mixing during the moon-forming giant impact |
the discovery of more than 4500 extrasolar planets has created a need for modeling their interior structure and dynamics. given the prominence of iron in planetary interiors, we require accurate and precise physical properties at extreme pressure and temperature. a first-order property of iron is its melting point, which is still debated for the conditions of earth’s interior. we used high-energy lasers at the national ignition facility and in situ x-ray diffraction to determine the melting point of iron up to 1000 gigapascals, three times the pressure of earth’s inner core. we used this melting curve to determine the length of dynamo action during core solidification to the hexagonal close-packed (hcp) structure. we find that terrestrial exoplanets with four to six times earth’s mass have the longest dynamos, which provide important shielding against cosmic radiation. | measuring the melting curve of iron at super-earth core conditions |
space-based high-contrast imaging mission concepts for studying rocky exoplanets in reflected light are currently under community study. we develop an inverse modeling framework to estimate the science return of such missions given different instrument design considerations. by combining an exoplanet albedo model, instrument noise model, and ensemble markov chain monte carlo sampler, we explore retrievals of atmospheric and planetary properties for earth twins as a function of signal-to-noise ratio (s/n) and resolution (r). our forward model includes rayleigh-scattering, single-layer water clouds with patchy coverage, and pressure-dependent absorption due to water vapor, oxygen, and ozone. we simulate data at r = 70 and 140 from 0.4 to 1.0 μm with s/n = 5, 10, 15, and 20 at 550 nm (i.e., for habex/luvoir-type instruments). at these same s/ns, we simulate data for wfirst paired with a starshade, which includes two photometric points between 0.48 and 0.6 μm and r = 50 spectroscopy from 0.6 to 0.97 μm. given our noise model for wfirst-type detectors, we find that weak detections of water vapor, ozone, and oxygen can be achieved with observations with at least r = 70/s/n = 15 or r = 140/s/n = 10 for improved detections. meaningful constraints are only achieved with r = 140/s/n = 20 data. the wfirst data offer limited diagnostic information, needing at least s/n = 20 to weakly detect gases. most scenarios place limits on planetary radius but cannot constrain surface gravity and, thus, planetary mass. | characterizing earth analogs in reflected light: atmospheric retrieval studies for future space telescopes |
forecasting the geomagnetic effects of solar storms, known as coronal mass ejections (cmes), is currently severely limited by our inability to predict the magnetic field configuration in the cme magnetic core and by observational effects of a single spacecraft trajectory through its 3-d structure. cme magnetic flux ropes can lead to continuous forcing of the energy input to the earth's magnetosphere by strong and steady southward-pointing magnetic fields. here we demonstrate in a proof-of-concept way a new approach to predict the southward field bz in a cme flux rope. it combines a novel semiempirical model of cme flux rope magnetic fields (three-dimensional coronal rope ejection) with solar observations and in situ magnetic field data from along the sun-earth line. these are provided here by the messenger spacecraft for a cme event on 9-13 july 2013. three-dimensional coronal rope ejection is the first such model that contains the interplanetary propagation and evolution of a 3-d flux rope magnetic field, the observation by a synthetic spacecraft, and the prediction of an index of geomagnetic activity. a counterclockwise rotation of the left-handed erupting cme flux rope in the corona of 30° and a deflection angle of 20° is evident from comparison of solar and coronal observations. the calculated dst matches reasonably the observed dst minimum and its time evolution, but the results are highly sensitive to the cme axis orientation. we discuss assumptions and limitations of the method prototype and its potential for real time space weather forecasting and heliospheric data interpretation. | forward modeling of coronal mass ejection flux ropes in the inner heliosphere with 3dcore |
the so-called ultra-diffuse galaxy ngc 1052-df2 was announced to be a galaxy lacking dark matter based on a spectroscopic study of its constituent globular clusters. here we present the first spectroscopic analysis of the stellar body of this galaxy using the muse integral-field spectrograph at the (eso) very large telescope. the muse datacube simultaneously provides df2's stellar velocity field and systemic velocities for seven globular clusters (gcs). we further discovered three planetary nebulae (pne) that are likely part of this galaxy. while five of the clusters had velocities measured in the literature, we were able to confirm the membership of two more candidates through precise radial velocity measurements, which increases the measured specific frequency of gcs in df2. the mean velocity of the diffuse stellar body, 1792.9+1.4-1.8 km s-1, is consistent with the mean globular cluster velocity. we detect a weak but significant velocity gradient within the stellar body, with a kinematic axis close to the photometric major axis, making it a prolate-like rotator. we estimate a velocity dispersion from the clusters and pne of σint = 10.6-2.3+3.9 km s-1. the velocity dispersion σdf2⋆(re) for the stellar body within one effective radius is 10.8+3.2-4.0 km s-1. considering various sources of systemic uncertainties, this central value varies between 5 and 13 km s-1, and we conservatively report a 95% confidence upper limit to the dispersion within one re of 21 km s-1. we provide updated mass estimates based on these dispersions corresponding to the different distances to ngc 1052-df2 that have been reported in the recent literature. the reduced datacube is only available at the cds via anonymous ftp to http://cdsarc.u-strasbg.fr (ftp://130.79.128.5) or via http://cdsarc.u-strasbg.fr/viz-bin/qcat?j/a+a/625/a76based on observations collected at the european southern observatory under eso programmes 2101.b-5008(a) and 2101.b-5053(a). | the ultra-diffuse galaxy ngc 1052-df2 with muse. i. kinematics of the stellar body |
volcanic edifices are abundant on rocky bodies of the inner solar system. in the cold outer solar system, volcanism can occur on solid bodies with a water-ice shell, but derived cryovolcanic constructs have proved elusive. we report the discovery, using dawn framing camera images, of a landform on dwarf planet ceres that we argue represents a viscous cryovolcanic dome. parent material of the cryomagma is a mixture of secondary minerals, including salts and water ice. absolute model ages from impact craters reveal that extrusion of the dome has occurred recently. ceres’ evolution must have been able to sustain recent interior activity and associated surface expressions. we propose salts with low eutectic temperatures and thermal conductivities as key drivers for ceres’ long-term internal evolution. | cryovolcanism on ceres |
we present a collection of 450 598 eclipsing and ellipsoidal binary systems detected in the ogle fields toward the galactic bulge. the collection consists of binary systems of all types: detached, semi-detached, and contact eclipsing binaries, rs cvn stars, cataclysmic variables, hw vir binaries, double periodic variables, and even planetary transits. for all stars we provide the i- and v-band time-series photometry obtained during the ogle-ii, ogle-iii, and ogle-iv surveys. we discuss methods used to identify binary systems in the ogle data and present several objects of particular interest. | the ogle collection of variable stars. over 450 000 eclipsing and ellipsoidal binary systems toward the galactic bulge |
we analyse the transmission spectra of kelt-20b/mascara-2b to search for possible thermal inversion agents. the data consist of three transits obtained using harpsn and one using carmenes. we removed stellar and telluric lines before cross-correlating the residuals with spectroscopic templates produced using a 1d plane-parallel model, assuming an isothermal atmosphere and chemical equilibrium at solar metallicity. using a likelihood-mapping method, we detect fe i at > 13σ, ca ii h $\&$ k at > 6σ and confirm the previous detections of fe ii, ca ii ir triplet, and na i d. the detected signal of fe i is shifted by -3.4 ± 0.4 km s-1 from the planetary rest frame, which indicates a strong day-night wind. our likelihood-mapping technique also reveals that the absorption features of the detected species extend to different altitudes in the planet's atmosphere. assuming that the line lists are accurate, we do not detect other potential thermal inversion agents (nah, mgh, alo, sh, cao, vo, feh, and tio) suggesting that non-chemical equilibrium mechanisms (e.g. a cold-trap) might have removed ti- and v-bearing species from the upper atmosphere. our results, therefore, show that kelt-20b/mascara-2b cannot possess an inversion layer caused by a tio/vo-related mechanism. the presence of an inversion layer would therefore likely be caused by metal atoms such as fe i and fe ii. finally, we report a double-peak structure in the fe i signal in all of our data sets that could be a signature of atmospheric dynamics. however, further investigation is needed to robustly determine the origin of the signal. | searching for thermal inversion agents in the transmission spectrum of kelt-20b/mascara-2b: detection of neutral iron and ionised calcium h&k lines |
we present a visible-light full orbital phase curve of the transiting planet wasp-18b measured by the tess mission. the phase curve includes the transit, secondary eclipse, and sinusoidal modulations across the orbital phase shaped by the planet’s atmospheric characteristics and the star-planet gravitational interaction. we measure the beaming (doppler boosting) and tidal ellipsoidal distortion phase modulations and show that the amplitudes of both agree with theoretical expectations. we find that the light from the planet’s dayside hemisphere occulted during secondary eclipse, with a relative brightness of {341}-18+17 ppm, is dominated by thermal emission, leading to an upper limit on the geometric albedo in the tess band of 0.048 (2σ ). we also detect the phase modulation due to the planet’s atmosphere longitudinal brightness distribution. we find that its maximum is well aligned with the substellar point to within 2.°9 (2σ ). we do not detect light from the planet’s nightside hemisphere, with an upper limit of 43 ppm (2σ ), which is 13% of the dayside brightness. the low albedo, lack of atmospheric phase shift, and inefficient heat distribution from the day to night hemispheres that we deduce from our analysis are consistent with theoretical expectations and similar findings for other strongly irradiated gas giant planets. this work demonstrates the potential of tess data for studying the full orbital phase curves of transiting systems. finally, we complement our study by looking for transit timing variations (ttvs) in the tess data combined with previously published transit times, although we do not find a statistically significant ttv signal. | tess full orbital phase curve of the wasp-18b system |
planets are born from disks of gas and dust, and observations of protoplanetary disks are used to constrain the initial conditions of planet formation. however, dust mass measurements of class ii disks with alma have called into question whether they contain enough solids to build the exoplanets that have been detected to date. in this paper, we calculate the mass and spatial scale of solid material around sun-like stars probed by transit and radial velocity exoplanet surveys and compare those to the observed dust masses and sizes of class ii disks in the same stellar-mass regime. we show that the apparent mass discrepancy disappears when accounting for observational selection and detection biases. we find a discrepancy only when the planet formation efficiency is below 100%, or if there is a population of undetected exoplanets that significantly contributes to the mass in solids. we identify a positive correlation between the masses of planetary systems and their respective orbital periods, which is consistent with the trend between the masses and the outer radii of class ii dust disks. this implies that, despite a factor 100 difference in spatial scale, the properties of protoplanetary disks seem to be imprinted on the exoplanet population. | the mass budgets and spatial scales of exoplanet systems and protoplanetary disks |
the streaming instability (si) is a mechanism to aerodynamically concentrate solids in protoplanetary disks and facilitate the formation of planetesimals. recent numerical modeling efforts have demonstrated the increasing complexity of the initial mass distribution of planetesimals. to better constrain this distribution, we conduct si simulations including self-gravity with the highest resolution hitherto. to subsequently identify all of the self-bound clumps, we develop a new clump-finding tool, planetesimal analyzer. we then apply a maximum likelihood estimator to fit a suite of parameterized models with different levels of complexity to the simulated mass distribution. to determine which models are best-fitting and statistically robust, we apply three model selection criteria with different complexity penalties. we find that the initial mass distribution of clumps is not universal regarding both the functional forms and parameter values. our model selection criteria prefer models different from those previously considered in the literature. fits to multi-segment power-law models break to a steeper distribution above masses close to those of 100 km collapsed planetesimals, similar to observed size distributions in the kuiper belt. we find evidence for a turnover at the low-mass end of the planetesimal mass distribution in our high-resolution run. such a turnover is expected for gravitational collapse, but had not previously been reported. | demographics of planetesimals formed by the streaming instability |
we analyze two high-resolution spectral transit time series of the hot jupiter hat-p-32 b obtained with the carmenes spectrograph. our new xmm-newton x-ray observations of the system show that the fast-rotating f-type host star exhibits a high x-ray luminosity of 2.3 × 1029 erg s−1 (5-100 å), corresponding to a flux of 6.9 × 104 erg cm−2 s−1 at the planetary orbit, which results in an energy-limited escape estimate of about 1013 g s−1 for the planetary mass-loss rate. the spectral time series show significant, time-dependent absorption in the hα and he iλ10833 triplet lines with maximum depths of about 3.3% and 5.3%. the mid-transit absorption signals in the hα and he iλ10833 lines are consistent with results from one-dimensional hydrodynamic modeling, which also yields mass-loss rates on the order of 1013 g s−1. we observe an early ingress of a redshifted component of the transmission signal, which extends into a redshifted absorption component, persisting until about the middle of the optical transit. while a super-rotating wind can explain redshifted ingress absorption, we find that an up-orbit stream, transporting planetary mass in the direction of the star, also provides a plausible explanation for the pre-transit signal. this makes hat-p-32 a benchmark system for exploring atmospheric dynamics via transmission spectroscopy. | hα and he i absorption in hat-p-32 b observed with carmenes. detection of roche lobe overflow and mass loss |
transit surveys indicate that there is a deficit of neptune-sized planets on close-in orbits. if this "neptune desert" is entirely cleared out by atmospheric mass loss, then planets at its upper edge should only be marginally stable against photoevaporation, exhibiting strong outflow signatures in tracers like the metastable helium triplet. we test this hypothesis by carrying out a 12-night photometric survey of the metastable helium feature with palomar/wirc, targeting seven gas-giant planets orbiting k-type host stars. eight nights of data are analyzed here for the first time along with reanalyses of four previously published data sets. we strongly detect helium absorption signals for wasp-69b, hat-p-18b, and hat-p-26b; tentatively detect signals for wasp-52b and ngts-5b; and do not detect signals for wasp-177b and wasp-80b. we interpret these measured excess absorption signals using grids of parker wind models to derive mass-loss rates, which are in good agreement with predictions from the hydrodynamical outflow code ates for all planets except wasp-52b and wasp-80b, where our data suggest that the outflows are much smaller than predicted. excluding these two planets, the outflows for the rest of the sample are consistent with a mean energy-limited outflow efficiency of $\varepsilon ={0.41}_{-0.13}^{+0.16}$ . even when we make the relatively conservative assumption that gas-giant planets experience energy-limited outflows at this efficiency for their entire lives, photoevaporation would still be too inefficient to carve the upper boundary of the neptune desert. we conclude that this feature of the exoplanet population is a pristine tracer of giant planet formation and migration mechanisms. | the upper edge of the neptune desert is stable against photoevaporation |
the first discovered extrasolar worlds-giant, "hot jupiter" planets on short-period orbits-came as a surprise to solar system-centric models of planet formation, prompting the development of new theories for planetary system evolution. the near absence of observed nearby planetary companions to hot jupiters has been widely quoted as evidence in support of high-eccentricity tidal migration, a framework in which hot jupiters form further out in their natal protoplanetary disks before being thrown inward with extremely high eccentricities, stripping systems of any close-in planetary companions. in this work, we present new results from a search for transit timing variations across the full 4 yr kepler data set, demonstrating that at least 12% ± 6% of hot jupiters have a nearby planetary companion. this subset of hot jupiters is expected to have a quiescent dynamical history such that the systems could retain their nearby companions. we also demonstrate a ubiquity of nearby planetary companions to warm jupiters (≥70% ± 16%), indicating that warm jupiters typically form quiescently. we conclude by combining our results with existing observational constraints to propose an "eccentric migration" framework for the formation of short-period giant planets through postdisk dynamical sculpting in compact multiplanet systems. our framework suggests that hot jupiters constitute the natural end stage for giant planets spanning a wide range of eccentricities, with orbits that reach small enough periapses-either from their final orbital configurations in the disk phase or from eccentricity excitation in the postdisk phase-to trigger efficient tidal circularization. | evidence for hidden nearby companions to hot jupiters |
since early 2019, the insight mission has proven that mars is seismically active, with more than 900 seismic events recorded. among them, several events have characteristics close to terrestrial tectonic earthquakes. most of these events are located on the major graben system of cerberus fossae and, a little further north, on the secondary system of grjotá valles. in this study, we invert the seismic moment tensors for nine of these tectonic marsquakes characterized by high quality data. seven of them are located on cerberus fossae/grjotá valles and two of them are located near the martian dichotomy. the moment tensors allow us to interpret the nature and depth of the seismic sources at the origin of these events. in our approach, we invert the p and s body waveforms, the pp, ss, ppp and sss secondary phase maximum amplitudes and we look for solutions with surface waves weaker than the martian noise. from our results on moment tensors, we determine that all our events have been triggered at moderate depths of 15-36 km. we deduce that the seven events located on cerberus fossae have geometries similar to the fractures and are generated by tectonics. this activity is supposed to result from the reactivation of previous faults and fractures, which would have been initially induced by the propagation of volcanic dikes at depth. the two dichotomy events are due to deep compressive fracturing of the martian lowlands. they are therefore triggered by the planetary thermal contraction. our results are in strong agreement with recent studies on the event depths and on the previous moment tensors calculated for two events. | seismic sources of insight marsquakes and seismotectonic context of elysium planitia, mars |
the earth is a unique planet, which has been highly evolved, diversified and complicated through geologic time, and underwent many key events, including giant impact, magma ocean, core formation, large-scale mantle differentiation and late heavy bombardment, especially in its dawn. but, our knowledge of early earth is limited due to the lack of the hadean supracrustal rocks. the supracrustal rocks with the eoarchean ages provide key evidence for the earth's early evolution, but few supracrustal rocks have been comprehensively investigated. therefore, we mapped in seven areas of the saglek block, northern labrador, where ancient supracrustal sequences are interleaved with a diverse assemblage of orthogneisses. early studies suggested that some of them have the mesoarchean ages because of the lack of the mesoarchean saglek dyke, but we found the saglek dykes in the areas to recognize the eoarchean nulliak supracrustal rocks and uivak gneiss in all the areas. recent reassessment of u-pb dating and cathodoluminescence observation of zircons from the oldest suites of the uivak gneiss showed that the uivak gneiss has the eoarchean age, > 3.95 ga, and forms the iqaluk-uivak gneiss series. because our geological survey clearly showed that the iqaluk-uivak gneisses were intruded into the nulliak supracrustal belts, the nulliak supracrustal rocks are the oldest supracrustal rock in the world. the supracrustal belts consist of piles of fault-bounded blocks, which are composed of the ultramafic rocks, mafic rocks and sedimentary rocks in ascending order, similar to modern ocean plate stratigraphy (ops). in addition, small-scale duplex structures are found over the areas. the presence of duplex structure and ops indicates that the > 3.95 ga nulliak supracrustal belts originate from an accretionary complex. the presence of the accretionary complex, ophiolite and granitic continental crust provides the oldest evidence for the plate tectonics on the early earth. | geology of the eoarchean, > 3.95 ga, nulliak supracrustal rocks in the saglek block, northern labrador, canada: the oldest geological evidence for plate tectonics |
markku kulmala calls for continuous, comprehensive monitoring of interactions between the planet's surface and atmosphere. | build a global earth observatory |
terrestrial planets are thought to experience episode(s) of large-scale melting early in their history. fractionation during magma-ocean freezing leads to unstable stratification within the related cumulate layers due to progressive iron enrichment upward, but the effects of incremental cumulate overturns during mo crystallization remain to be explored. here, we use geodynamic models with a moving-boundary approach to study convection and mixing within the growing cumulate layer, and thereafter within the fully crystallized mantle. for fractional crystallization, cumulates are efficiently stirred due to subsequent incremental overturns, except for strongly iron-enriched late-stage cumulates, which persist as a stably stratified layer at the base of the mantle for billions of years. less extreme crystallization scenarios can lead to somewhat more subtle stratification. in any case, the long-term preservation of at least a thin layer of extremely enriched cumulates with fe# > 0.4, as predicted by all our models, is inconsistent with seismic constraints. based on scaling relationships, however, we infer that final-stage fe-rich magma-ocean cumulates originally formed near the surface should have overturned as small diapirs, and hence undergone melting and reaction with the host rock during sinking. the resulting moderately iron-enriched metasomatized/hybrid rock assemblages should have accumulated at the base of the mantle, potentially fed an intermittent basal magma ocean, and be preserved through the present-day. such moderately iron-enriched rock assemblages can reconcile the physical properties of the large low shear-wave velocity provinces in the present-day lower mantle. thus, we reveal hadean melting and rock-reaction processes by integrating magma-ocean crystallization models with the seismic-tomography snapshot. | reconciling magma-ocean crystallization models with the present-day structure of the earth's mantle |
we study the red-optical photometry of the ultrahot jupiter wasp-121 b as observed by the transiting exoplanet survey satellite (tess) and model its atmosphere through a radiative transfer simulation. given its short orbital period of ∼1.275 days, inflated state, and bright host star, wasp-121 b is exceptionally favorable for detailed atmospheric characterization. toward this purpose, we use allesfitter to characterize its full red-optical phase curve, including the planetary phase modulation and secondary eclipse. we measure the day- and nightside brightness temperatures in the tess passband as ${3012}_{-42}^{+40}$ and ${2022}_{-602}^{+254}$ k, respectively, and do not find a statistically significant phase shift between the brightest and substellar points. this is consistent with inefficient heat recirculation on the planet. we then perform an atmospheric retrieval analysis to infer the dayside atmospheric properties of wasp-121 b, such as its bulk composition, albedo, and heat recirculation. we confirm the temperature inversion in the atmosphere and suggest h-, tio, and vo as potential causes of the inversion, absorbing heat at optical wavelengths at low pressures. future hubble space telescope and james webb space telescope observations of wasp-121 b will benefit from its first full phase curve measured by tess. | tess observations of the wasp-121 b phase curve |
we present results from a high-contrast adaptive optics imaging search for giant planets and brown dwarfs (gsim1 m jup) around 122 newly identified nearby (lsim40 pc) young m dwarfs. half of our targets are younger than 135 myr and 90% are younger than the hyades (620 myr). after removing 44 close stellar binaries (implying a stellar companion fraction of >35.4% ± 4.3% within 100 au), 27 of which are new or spatially resolved for the first time, our remaining sample of 78 single m dwarfs makes this the largest imaging search for planets around young low-mass stars (0.1-0.6 m ⊙) to date. our h- and k-band coronagraphic observations with keck/nirc2 and subaru/hiciao achieve typical contrasts of 12-14 mag and 9-13 mag at 1'', respectively, which correspond to limiting planet masses of 0.5-10 m jup at 5-33 au for 85% of our sample. we discovered four young brown dwarf companions: 1rxs j235133.3+312720 b (32 ± 6 m jup; l0+2-1; 120 ± 20 au), gj 3629 b (64+30-23 m jup; m7.5 ± 0.5; 6.5 ± 0.5 au), 1rxs j034231.8+121622 b (35 ± 8 m jup; l0 ± 1; 19.8 ± 0.9 au), and 2mass j15594729+4403595 b (43 ± 9 m jup; m8.0 ± 0.5; 190 ± 20 au). over 150 candidate planets were identified; we obtained follow-up imaging for 56% of these but all are consistent with background stars. our null detection of planets enables strong statistical constraints on the occurrence rate of long-period giant planets around single m dwarfs. we infer an upper limit (at the 95% confidence level) of 10.3% and 16.0% for 1-13 m jup planets between 10-100 au for hot-start and cold-start (fortney) evolutionary models, respectively. fewer than 6.0% (9.9%) of m dwarfs harbor massive gas giants in the 5-13 m jup range like those orbiting hr 8799 and β pictoris between 10-100 au for a hot-start (cold-start) formation scenario. the frequency of brown dwarf (13-75 m jup) companions to single m dwarfs between 10-100 au is 2.8+2.4-1.5%. altogether we find that giant planets, especially massive ones, are rare in the outskirts of m dwarf planetary systems. although the first directly imaged planets were found around massive stars, there is currently no statistical evidence for a trend of giant planet frequency with stellar host mass at large separations as predicted by the disk instability model of giant planet formation. some of the data presented herein were obtained at the w.m. keck observatory, which is operated as a scientific partnership among the california institute of technology, the university of california and the national aeronautics and space administration. the observatory was made possible by the generous financial support of the w.m. keck foundation. this work was also based on data collected at subaru telescope, which is operated by the national astronomical observatory of japan. | planets around low-mass stars (palms). iv. the outer architecture of m dwarf planetary systems |
context. while planet formation is thought to occur early in the history of a protoplanetary disk, the presence of planets embedded in disks, or of other processes driving disk evolution, might be traced from their imprints on the disk structure.aims: we study the morphology of the disk around the t tauri star hd 143006, located in the ~5-11 myr-old upper sco region, and we look for signatures of the mechanisms driving its evolution.methods: we observed hd 143006 in polarized scattered light with vlt/sphere at near-infrared (j-band, 1.2 μm) wavelengths, reaching an angular resolution of ~0.037'' (~6 au). we obtained two datasets, one with a 145 mas diameter coronagraph, and the other without, enabling us to probe the disk structure down to an angular separation of ~0.06'' (~10 au).results: in our observations, the disk of hd 143006 is clearly resolved up to ~0.5'' and shows a clear large-scale asymmetry with the eastern side brighter than the western side. we detect a number of additional features, including two gaps and a ring. the ring shows an overbrightness at a position angle (pa) of ~140°, extending over a range in position angle of ~60°, and two narrow dark regions. the two narrow dark lanes and the overall large-scale asymmetry are indicative of shadowing effects, likely due to a misaligned inner disk. we demonstrate the remarkable resemblance between the scattered light image of hd 143006 and a model prediction of a warped disk due to an inclined binary companion. the warped disk model, based on the hydrodynamic simulations combined with three-dimensional radiative transfer calculations, reproduces all major morphological features. however, it does not account for the observed overbrightness at pa ~ 140°.conclusions: shadows have been detected in several protoplanetary disks, suggesting that misalignment in disks is not uncommon. however, the origin of the misalignment is not clear. as-yet-undetected stellar or massive planetary companions could be responsible for them, and naturally account for the presence of depleted inner cavities. based on observations performed with sphere/vlt under program id 097.c-0902(a) and 095.c-0693(a). | shadows and asymmetries in the t tauri disk hd 143006: evidence for a misaligned inner disk |
the lucy mission is a nasa discovery-class mission to send a highly capable and robust spacecraft to investigate seven primitive bodies near both the l4 and l5 lagrange points with jupiter: the jupiter trojan asteroids. these planetesimals from the outer planetary system have been preserved since early in solar system history. the lucy mission will fly by and extensively study a diverse selection of trojan asteroids, including all the recognized taxonomic classes, a collisional family member, and a near equal-mass binary. it will visit objects with diameters ranging from roughly 1 km to 100 km. the payload suite consists of a color camera and infrared imaging spectrometer, a high-resolution panchromatic imager, and a thermal infrared spectrometer. additionally, two spacecraft subsystems will also contribute to the science investigations: the terminal tracking cameras will supplement imaging during closest approach and the telecommunication subsystem will be used to measure the mass of the trojans. the science goals are derived from the 2013 planetary decadal survey and include determining the surface composition, assessing the geology, determining the bulk properties, and searching for satellites and rings. | lucy mission to the trojan asteroids: science goals |
planetary debris disks around other stars are analogous to the asteroid and kuiper belts in the solar system. their structure reveals the configuration of small bodies and provides hints for the presence of planets. the nearby star fomalhaut hosts one of the most prominent debris disks, resolved by the hubble space telescope, spitzer, herschel and the atacama large millimeter array. images of this system at mid-infrared wavelengths using jwst/miri not only show the narrow kuiper belt-analogue outer ring, but also that (1) what was thought from indirect evidence to be an asteroid-analogue structure is instead broad, extending outward into the outer system, and (2) there is an intermediate belt, probably shepherded by an unseen planet. the newly discovered belt is demarcated by an inner gap, located at ~78 au, and it is misaligned relative to the outer belt. the previously known collisionally generated dust cloud, fomalhaut b, could have originated from this belt, suggesting increased dynamical stirring and collision rates there. we also discovered a large dust cloud within the outer ring, possible evidence of another dust-creating collision. taken together with previous observations, fomalhaut appears to be the site of a complex and possibly dynamically active planetary system. | spatially resolved imaging of the inner fomalhaut disk using jwst/miri |
while cooler giant planets are often observed with nonzero eccentricities, the short-period circular orbits of hot jupiters suggest that they lose orbital energy and angular momentum due to tidal interactions with their host stars. however, orbital decay has never been unambiguously observed. we use data from gaia data release 2 to show that hot jupiter host stars have a smaller galactic velocity dispersion than a similar population of stars without hot jupiters. since galactic velocity dispersion is correlated with age, this observation implies that the population of hot jupiter host stars is on average younger than the field population. the best explanation for this inference is that tidal interactions cause hot jupiters to inspiral while their host stars are on the main sequence. this observation requires that the typical modified stellar tidal quality factor {q}* {\prime } for solar-type stars is in the range {log}}10{q}* {\prime }≲ 7. | hot jupiters are destroyed by tides while their host stars are on the main sequence |
the earth has warmed in the last century and a large component of that warming has been attributed to increased anthropogenic greenhouse gases. there are also numerous processes that introduce strong, regionalized variations to the overall warming trend. however, the ability of a forcing to change the surface air temperature depends on its spatial and temporal distribution. here we show that the efficacy of a forcing is determined by the effective heat capacity of the atmosphere, which in cold and dry climates is defined by the depth of the planetary boundary layer. this can vary by an order of magnitude on different temporal and spatial scales, and so we get a strongly amplified temperature response in shallow boundary layers. this must be accounted for to assess the efficacy of a climate forcing, and also implies that multiple climate forcings cannot be linearly combined to determine the temperature response. | differences in the efficacy of climate forcings explained by variations in atmospheric boundary layer depth |
while it is widely accepted that planets are formed in protoplanetary disks, there is still much debate on when this process happens. in a few cases protoplanets have been directly imaged, but for the vast majority of systems, disk gaps and cavities—seen especially in dust continuum observations—have been the strongest evidence of recent or ongoing planet formation. we present atacama large millimeter/submillimeter array observations of a nearly edge-on (i = 75°) disk containing a giant gap seen in dust but not in 12co gas. inside the gap, the molecular gas has a warm (100 k) component coinciding in position with a tentative free-free emission excess observed with the karl g. jansky very large array. using 1d hydrodynamic models, we find the structure of the gap is consistent with being carved by a planet with 4-70 mjup. the coincidence of free-free emission inside the planet-carved gap points to the planet being very young and/or still accreting. in addition, the 12co observations reveal low-velocity large-scale filaments aligned with the disk major axis and velocity coherent with the disk gas that we interpret as ongoing gas infall from the local interstellar medium. this system appears to be an interesting case where both a star (from the environment and the disk) and a planet (from the disk) are growing in tandem. | a case of simultaneous star and planet formation |
context. the detection of a super-earth and three mini-neptunes transiting the bright (v = 9.2 mag) star hd 108236 (also known as toi-1233) was recently reported on the basis of tess and ground-based light curves.aims: we perform a first characterisation of the hd 108236 planetary system through high-precision cheops photometry and improve the transit ephemerides and system parameters.methods: we characterise the host star through spectroscopic analysis and derive the radius with the infrared flux method. we constrain the stellar mass and age by combining the results obtained from two sets of stellar evolutionary tracks. we analyse the available tess light curves and one cheops transit light curve for each known planet in the system.results: we find that hd 108236 is a sun-like star with r⋆ = 0.877 ± 0.008 r⊙, m⋆ = 0.869-0.048+0.050 m⊙, and an age of 6.7-5.1+4.0 gyr. we report the serendipitous detection of an additional planet, hd 108236 f, in one of the cheops light curves. for this planet, the combined analysis of the tess and cheops light curves leads to a tentative orbital period of about 29.5 days. from the light curve analysis, we obtain radii of 1.615 ± 0.051, 2.071 ± 0.052, 2.539-0.065+0.062, 3.083 ± 0.052, and 2.017-0.057+0.052 r⊕ for planets hd 108236 b to hd 108236 f, respectively. these values are in agreement with previous tess-based estimates, but with an improved precision of about a factor of two. we perform a stability analysis of the system, concluding that the planetary orbits most likely have eccentricities smaller than 0.1. we also employ a planetary atmospheric evolution framework to constrain the masses of the five planets, concluding that hd 108236 b and hd 108236 c should have an earth-like density, while the outer planets should host a low mean molecular weight envelope.conclusions: the detection of the fifth planet makes hd 108236 the third system brighter than v = 10 mag to host more than four transiting planets. the longer time span enables us to significantly improve the orbital ephemerides such that the uncertainty on the transit times will be of the order of minutes for the years to come. a comparison of the results obtained from the tess and cheops light curves indicates that for a v ~ 9 mag solar-like star and a transit signal of ~500 ppm, one cheops transit light curve ensures the same level of photometric precision as eight tess transits combined, although this conclusion depends on the length and position of the gaps in the light curve. light curves are only available at the cds via anonymous ftp to http://cdsarc.u-strasbg.fr (ftp://130.79.128.5) or via http://cdsarc.u-strasbg.fr/viz-bin/cat/j/a+a/646/a157 | cheops observations of the hd 108236 planetary system: a fifth planet, improved ephemerides, and planetary radii |
this study provides the first comprehensive assessment of regional climate model version 4.6.1 (regcm4) for the tibetan plateau (tp) region. a wide range of model configurations were analyzed with different parameterizations employed to represent cumulus convection (kuo, grell, emanuel, kain, and tiedtke), land surface processes (bats and clm), planetary boundary layer turbulence (holtslag and uw pbl), and radiation (ccm3 and rrtm). in addition to the above experiments at a 30-km horizontal resolution, another experiment was conducted based upon the use of a double-nested dynamic downscaling method to construct a simulation at a 10-km resolution to study the sensitivity to the model resolution. we evaluated a 20-year simulation for precipitation, cloud cover, surface radiation budget, 2-m air temperature, and the surface atmospheric circulation against ground and satellite-based observations during the period 1989-2008. among the factors analyzed regarding sensitivity, precipitation was unsurprisingly found to be sensitive to the cumulus parameterization scheme, and the clm is found to reduce rainfall compared with bats, which is satisfactory for both the emanuel and tiedtke schemes. compared with the cumulus convection schemes, the cloud cover and surface radiation budget are sensitive to the land surface, pbl, and radiation schemes. generally, the clm is characterized by reduced mean cloud cover and enhanced surface longwave and shortwave radiation compared with bats. conversely, the uw pbl and rrtm radiation schemes result in increased cloud cover and less surface radiation compared with the default options in regcm4. all experiments, except those employing the kuo scheme, represent the mean 2-m air temperature and regional circulation patterns reasonably well. at the basin scale, the seasonal cycle and interannual variations of precipitation are found to be not well depicted by most model configurations, although the temperature field was well reproduced. considering all the analyzed variables collectively, the tiedtke scheme combined with the clm land surface model is demonstrated to provide the best performance over the tp. however, the higher-resolution version of the model improves the precipitation simulation significantly, particularly in the brahmaputra river basin, which is located in the north of the himalayas. | sensitivity studies and comprehensive evaluation of regcm4.6.1 high-resolution climate simulations over the tibetan plateau |
the urban heat island intensity (uhii) is the temperature difference between urban areas and their rural surroundings. it is commonly attributed to changes in the underlying surface structure caused by urbanization. air pollution caused by aerosol particles can affect the uhii through changing (1) the surface energy balance by the aerosol radiative effect (are) and (2) planetary-boundary-layer (pbl) stability and airflow intensity by modifying thermodynamic structure, which is referred to as the aerosol dynamic effect (ade). by analyzing satellite data and ground-based observations collected from 2001 to 2010 at 35 cities in china and using the wrf-chem model, we find that the impact of aerosols on uhii differs considerably: reducing the uhii in summer but increasing the uhii in winter. this seasonal contrast is proposed to be caused by the different strengths of the are and ade between summer and winter. in summer, the are on uhii is dominant over the ade, cooling down surface temperature more strongly in urban areas than in rural areas because of much higher aerosol loading, and offsets the urban heating, therefore weakening uhii. in winter, however, the ade is more dominant, because aerosols stabilize the pbl more in the polluted condition, weakening the near-surface heat transport over urban areas in both vertical and horizontal directions. this means that the heat accumulated in urban areas is dispersed less effectively, and thus the uhii is enhanced. these findings shed new light on the impact of the interaction between urbanization-induced surface changes and air pollution on urban climate. | the mechanisms and seasonal differences of the impact of aerosols on daytime surface urban heat island effect |
the silk road pattern (srp), which is the leading mode of upper-tropospheric meridional wind anomalies over midlatitude eurasia, has been widely used to explain the impacts of the summer north atlantic oscillation (snao) on east asian climate. however, the relationship between the snao and srp has not been fully elaborated yet. this study classifies the snao into two categories according to whether it is closely associated with the srp or not: the strongly linked category and weakly linked category, on the interannual time scale. the snao of the strongly linked category features a concentrated and significant southern pole over the northwestern europe, and corresponding significant negative (positive) precipitation and upper-tropospheric wind convergence (divergence) anomalies over the northwestern europe. the wind convergence (divergence) anomalies directly induce the positive (negative) planetary vortex stretching anomalies, which contribute overwhelmingly to positive (negative) rossby wave source anomalies of the northwestern europe. these rossby wave source anomalies, acting as disturbances, further inspire circulation anomalies of surrounding regions, including meridional wind anomalies over the caspian sea, which are crucial for the srp formation. as a result, the downstream srp is triggered. all these essential features responsible for a strong snao-srp linkage are weak for the weakly linked category. the snao-srp correspondence on the interdecadal time scale is also discussed, and generally similar results are found. results suggest the importance of shapes for the snao southern pole (including the location, the space extent, and the intensity) in determining whether the snao can closely link the srp. therefore, the shape of the snao southern pole should be involved in the discussion of the snao's remote impacts. | the relationship between the north atlantic oscillation and the silk road pattern in summer |
transmission spectroscopy provides a powerful probe of the atmospheric properties of transiting exoplanets. to date, studies of exoplanets in transit have focused on inferring their atmospheric properties such as chemical compositions, cloud/haze properties, and temperature structures. however, surface inhomogeneities in the host stars of exoplanets in the form of cool spots and hot faculae can in principle imprint signatures on the observed planetary transit spectrum. here we present aura, a new retrieval paradigm for inferring both planetary and stellar properties from a transmission spectrum. we apply our retrieval framework to a sample of hot giant exoplanets to determine the significance of stellar heterogeneity and clouds/hazes in their spectra. the retrieval analyses distinguish four groups of planets. first, the spectra of wasp-6b and wasp-39b are best characterized by imprints of stellar heterogeneity and hazes and/or clouds. hd 209458b and hat-p-12b comprise the second group for which there is weak evidence for stellar heterogeneity and a high significance of hazes and/or clouds. the third group constitutes hat-p-1b and wasp-31b and shows weak evidence against stellar heterogeneity but weak to substantial indications of clouds/hazes. the fourth group - wasp-19b, wasp-17b, and wasp-12b - is fit best by molecular and alkali absorbers with h2 scattering without evidence for stellar heterogeneity and weak to no evidence for clouds/hazes. our retrieval methodology paves the way to simultaneous information on the star and planet from higher resolution spectra using future facilities such as the james webb space telescope and large ground-based facilities. | retrieval of planetary and stellar properties in transmission spectroscopy with aura |
researchers apply an economic model to trade-offs facing the un's ambitious sustainable development goals agenda.the 17 sustainable development goals (sdgs) call for a comprehensive new approach to development rooted in planetary boundaries, equity, and inclusivity. the wide scope of the sdgs will necessitate unprecedented integration of siloed policy portfolios to work at international, regional, and national levels toward multiple goals and mitigate the conflicts that arise from competing resource demands. in this analysis, we adopt a comprehensive modeling approach to understand how coherent policy combinations can manage trade-offs among environmental conservation initiatives and food prices. our scenario results indicate that sdg strategies constructed around sustainable consumption and production policies can minimize problem-shifting, which has long placed global development and conservation agendas at odds. we conclude that sustainable consumption and production policies (goal 12) are most effective at minimizing trade-offs and argue for their centrality to the formulation of coherent sdg strategies. we also find that alternative socioeconomic futures—mainly, population and economic growth pathways—generate smaller impacts on the eventual achievement of land resource–related sdgs than do resource-use and management policies. we expect that this and future systems analyses will allow policy-makers to negotiate trade-offs and exploit synergies as they assemble sustainable development strategies equal in scope to the ambition of the sdgs. | assessing the land resource–food price nexus of the sustainable development goals |
jiram is an imager/spectrometer on board the juno spacecraft bound for a polar orbit around jupiter. jiram is composed of ir imager and spectrometer channels. its scientific goals are to explore the jovian aurorae and the planet's atmospheric structure, dynamics and composition. this paper explains the characteristics and functionalities of the instrument and reports on the results of ground calibrations. it discusses the main subsystems to the extent needed to understand how the instrument is sequenced and used, the purpose of the calibrations necessary to determine instrument performance, the process for generating the commanding sequences, the main elements of the observational strategy, and the format of the scientific data that jiram will produce. | jiram, the jovian infrared auroral mapper |
amidst declarations of planetary emergency and reports that the window for limiting climate change to 1.5 °c is rapidly closing, global average temperatures and fossil fuel emissions continue to rise. global fossil co2 emissions have grown three years consecutively: +1.5% in 2017, +2.1% in 2018, and our slower central projection of +0.6% in 2019 (range of -0.32% to 1.5%) to 37 ± 2 gt co2 (friedlingstein et al 2019 earth syst. sci. data accepted), after a temporary growth hiatus from 2014 to 2016. economic indicators and trends in global natural gas and oil use suggest a further rise in emissions in 2020 is likely. co2 emissions are decreasing slowly in many industrialized regions, including the european union (preliminary estimate of -1.7% [-3.4% to +0.1%] for 2019, -0.8%/yr for 2003-2018) and united states (-1.7% [-3.7% to +0.3%] in 2019, -0.8%/yr for 2003-2018), while emissions continue growing in india (+1.8% [+0.7% to 3.7%] in 2019, +5.1%/yr for 2003-2018), china (+2.6% [+0.7% to 4.4%] in 2019, +0.4%/yr for 2003-2018), and rest of the world ((+0.5% [-0.8% to 1.8%] in 2019, +1.4%/yr for 2003-2018). two under-appreciated trends suggest continued long-term growth in both oil and natural gas use is likely. because per capita oil consumption in the us and europe remains 5- to 20-fold higher than in china and india, increasing vehicle ownership and air travel in asia are poised to increase global co2 emissions from oil over the next decade or more. liquified natural gas exports from australia and the united states are surging, lowering natural gas prices in asia and increasing global access to this fossil resource. to counterbalance increasing emissions, we need accelerated energy efficiency improvements and reduced consumption, rapid deployment of electric vehicles, carbon capture and storage technologies, and a decarbonized electricity grid, with new renewable capacities replacing fossil fuels, not supplementing them. stronger global commitments and carbon pricing would help implement such policies at scale and in time. | persistent fossil fuel growth threatens the paris agreement and planetary health |
observations of multiple rotational transitions from a single molecule allow for unparalleled constraints on the physical conditions of the emitting region. we present an analysis of cs in tw hya using the j = 7-6, 5-4 and 3-2 transitions imaged at ∼0.″5 spatial resolution, resulting in a temperature and column density profile of the cs emission region extending out to 230 au, far beyond previous measurements. in addition, the 15 khz resolution of the observations and the ability to directly estimate the temperature of the cs emitting gas, allow for one of the most sensitive searches for turbulent broadening in a disk to date. limits of v turb ≲ 0.1cscan be placed across the entire radius of the disk. we are able to place strict limits of the local h2 density due to the collisional excitations of the observed transitions. from these we find that a minimum disk mass of 3 × 10-4 m sun is required to be consistent with the cs excitation conditions and can uniquely constrain the gas surface density profile in the outer disk. | temperature, mass, and turbulence: a spatially resolved multiband non-lte analysis of cs in tw hya |
context. the consortium of the spectro-polarimetric high-contrast exoplanet research installed at the very large telescope (sphere/vlt) has been operating its guaranteed observation time (260 nights over five years) since february 2015. the main part of this time (200 nights) is dedicated to the detection and characterization of young and giant exoplanets on wide orbits.aims: the large amount of data must be uniformly processed so that accurate and homogeneous measurements of photometry and astrometry can be obtained for any source in the field.methods: to complement the european southern observatory pipeline, the sphere consortium developed a dedicated piece of software to process the data. first, the software corrects for instrumental artifacts. then, it uses the speckle calibration tool (specal) to minimize the stellar light halo that prevents us from detecting faint sources like exoplanets or circumstellar disks. specal is meant to extract the astrometry and photometry of detected point-like sources (exoplanets, brown dwarfs, or background sources). specal was intensively tested to ensure the consistency of all reduced images (cadi, loci, tloci, pca, and others) for any sphere observing strategy (adi, sdi, asdi as well as the accuracy of the astrometry and photometry of detected point-like sources.results: specal is robust, user friendly, and efficient at detecting and characterizing point-like sources in high contrast images. it is used to process all sphere data systematically, and its outputs have been used for most of the sphere consortium papers to date. specal is also a useful framework to compare different algorithms using various sets of data (different observing modes and conditions). finally, our tests show that the extracted astrometry and photometry are accurate and not biased. based on observations collected at the european organisation for astronomical research in the southern hemisphere under eso programme 097.c-0865. | astrometric and photometric accuracies in high contrast imaging: the sphere speckle calibration tool (specal) |
the organic content of protoplanetary disks sets the initial compositions of planets and comets, thereby influencing subsequent chemistry that is possible in nascent planetary systems. we present observations of the complex nitrile-bearing species ch3cn and hc3n toward the disks around the t tauri stars as 209, im lup, lkca 15, and v4046 sgr as well as the herbig ae stars mwc 480 and hd 163296. hc3n is detected toward all disks except im lup, and ch3cn is detected toward v4046 sgr, mwc 480, and hd 163296. rotational temperatures derived for disks with multiple detected lines range from 29 to 73 k, indicating emission from the temperate molecular layer of the disk. v4046 sgr and mwc 480 radial abundance profiles are constrained using a parametric model; the gas-phase ch3cn and hc3n abundances with respect to hcn are a few to tens of percent in the inner 100 au of the disk, signifying a rich nitrile chemistry at planet- and comet-forming disk radii. we find consistent relative abundances of ch3cn, hc3n, and hcn between our disk sample, protostellar envelopes, and solar system comets; this is suggestive of a robust nitrile chemistry with similar outcomes under a wide range of physical conditions. | a survey of ch3cn and hc3n in protoplanetary disks |
context. when a planet becomes massive enough, it gradually carves a partial gap around its orbit in the protoplanetary disk. a pressure maximum can be formed outside the gap where solids that are loosely coupled to the gas, typically in the pebble size range, can be trapped. the minimum planet mass for building such a trap, which is called the pebble isolation mass (pim), is important for two reasons: it marks the end of planetary growth by pebble accretion, and the trapped dust forms a ring that may be observed with millimetre observations.aims: we study the effect of disk turbulence on the pim and find its dependence on the gas turbulent viscosity, aspect ratio, and particles stokes number.methods: by means of 2d gas hydrodynamical simulations, we found the minimum planet mass to form a radial pressure maximum beyond the orbit of the planet, which is the necessary condition to trap pebbles. we then carried out 2d gas plus dust hydrodynamical simulations to examine how dust turbulent diffusion impacts particles trapping at the pressure maximum. we finally provide a semi-analytical calculation of the pim based on comparing the radial drift velocity of solids and the root mean square turbulent velocity fluctuations around the pressure maximum.results: from our results of gas simulations, we provide an expression for the pim vs. disk aspect ratio and turbulent viscosity. our gas plus dust simulations show that the effective pim can be nearly an order of magnitude larger in high-viscosity disks because turbulence diffuse particles out of the pressure maximum. this is quantified by our semi-analytical calculation, which gives an explicit dependence of the pim with stokes number of particles.conclusions: disk turbulence can significantly alter the pim, depending on the level of turbulence in regions of planet formation. | how much does turbulence change the pebble isolation mass for planet formation? |
sphere (beuzit et al,. 2019) has now been in operation at the vlt for more than 5 years, demonstrating a high level of performance. sphere has produced outstanding results using a variety of operating modes, primarily in the field of direct imaging of exoplanetary systems, focusing on exoplanets as point sources and circumstellar disks as extended objects. the achievements obtained thus far with sphere (~200 refereed publications) in different areas (exoplanets, disks, solar system, stellar physics...) have motivated a large consortium to propose an even more ambitious set of science cases, and its corresponding technical implementation in the form of an upgrade. the sphere+ project capitalizes on the expertise and lessons learned from sphere to push high contrast imaging performance to its limits on the vlt 8m-telescope. the scientific program of sphere+ described in this document will open a new and compelling scientific window for the upcoming decade in strong synergy with ground-based facilities (vlt/i, elt, alma, and ska) and space missions (gaia, jwst, plato and wfirst). while sphere has sampled the outer parts of planetary systems beyond a few tens of au, sphere+ will dig into the inner regions around stars to reveal and characterize by mean of spectroscopy the giant planet population down to the snow line. building on sphere's scientific heritage and resounding success, sphere+ will be a dedicated survey instrument which will strengthen the leadership of eso and the european community in the very competitive field of direct imaging of exoplanetary systems. with enhanced capabilities, it will enable an even broader diversity of science cases including the study of the solar system, the birth and death of stars and the exploration of the inner regions of active galactic nuclei. | sphere+: imaging young jupiters down to the snowline |
context. lhs 1140 is an m dwarf known to host two transiting planets at orbital periods of 3.77 and 24.7 days. they were detected with harps and spitzer. the external planet (lhs 1140 b) is a rocky super-earth that is located in the middle of the habitable zone of this low-mass star. all these properties place this system at the forefront of the habitable exoplanet exploration, and it therefore constitutes a relevant case for further astrobiological studies, including atmospheric observations.aims: we further characterize this system by improving the physical and orbital properties of the known planets, search for additional planetary-mass components in the system, and explore the possibility of co-orbitals.methods: we collected 113 new high-precision radial velocity observations with espresso over a 1.5-yr time span with an average photon-noise precision of 1.07 m s-1. we performed an extensive analysis of the harps and espresso datasets and also analyzed them together with the new tess photometry. we analyzed the bayesian evidence of several models with different numbers of planets and orbital configurations.results: we significantly improve our knowledge of the properties of the known planets lhs 1140 b (pb ~ 24.7 days) and lhs 1140 c (pc ~ 3.77 days). we determine new masses with a precision of 6% for lhs 1140 b (6.48 ± 0.46 m⊕) and 9% for lhs 1140 c (mc = 1.78 ± 0.17 m⊕). this reduces the uncertainties relative to previously published values by half. although both planets have earth-like bulk compositions, the internal structure analysis suggests that lhs 1140 b might be iron-enriched and lhs 1140 c might be a true earth twin. in both cases, the water content is compatible to a maximum fraction of 10-12% in mass, which is equivalent to a deep ocean layer of 779 ± 650 km for the habitable-zone planet lhs 1140 b. our results also provide evidence for a new planet candidate in the system (md = 4.8 ± 1.1m⊕) on a 78.9-day orbital period, which is detected through three independent methods. the analysis also allows us to discard other planets above 0.5 m⊕ for periods shorter than 10 days and above 2 m⊕ for periods up to one year. finally, our co-orbital analysis discards co-orbital planets in the tadpole and horseshoe configurations of lhs 1140 b down to 1 m⊕ with a 95% confidence level (twice better than with the previous harps dataset). indications for a possible co-orbital signal in lhs 1140 c are detected in both radial velocity (alternatively explained by a high eccentricity) and photometric data (alternatively explained by systematics), however.conclusions: the new precise measurements of the planet properties of the two transiting planets in lhs 1140 as well as the detection of the planet candidate lhs 1140 d make this system a key target for atmospheric studies of rocky worlds at different stellar irradiations. full table b.1 is only available at the cds via anonymous ftp to http://cdsarc.u-strasbg.fr (ftp://130.79.128.5) or via http://cdsarc.u-strasbg.fr/viz-bin/cat/j/a+a/642/a121 | planetary system lhs 1140 revisited with espresso and tess |
context. complex organic molecules (coms) are thought to form on icy dust grains in the earliest phase of star formation. the evolution of these coms from the youngest class 0/i protostellar phases toward the more evolved class ii phase is still not fully understood. since planet formation seems to start early, and mature disks are too cold for characteristic com emission lines, studying the inventory of coms on solar- system scales in the class 0/i stage is relevant.aims: our aim is to determine the abundance ratios of oxygen-bearing coms in class 0 protostellar systems on scales of ~100 au radius. we aim to compare these abundances with one another, and to the abundances of other low-mass protostars such as iras 16293-2422b and hh 212. additionally, using both cold and hot com lines, the gas-phase abundances can be tracked from a cold to a hot component, and ultimately be compared with those in ices to be measured with the james webb space telescope (jwst). the abundance of deuterated methanol allows us to probe the ambient temperature during the formation of this species.methods: alma band 3 (3 mm) and band 6 (1 mm) observations are obtained for seven class 0 protostars in the perseus and serpens star-forming regions. by modeling the inner protostellar region using local thermodynamic equilibrium models, the excitation temperature and column densities are determined for several o-bearing coms including methanol (ch3oh), acetaldehyde (ch3cho), methyl formate (ch3ocho), and dimethyl ether (ch3och3). abundance ratios are taken with respect to ch3oh.results: three out of the seven of the observed sources, b1-c, b1-bs (both perseus), and serpens s68n (serpens), show com emission. no clear correlation seems to exist between the occurrence of coms and source luminosity. the abundances of several coms such as ch3ocho, ch3och3, acetone (ch3coch3), and ethylene glycol ((ch2oh)2) are remarkably similar for the three com-rich sources; this similarity also extends to iras 16293-2422b and hh 212, even though collectively these sources originate from four different star-forming regions (i.e., perseus, serpens, ophiuchus, and orion). for other coms like ch3cho, ethanol (ch3ch2oh), and glycolaldehyde (ch2ohcho), the abundances differ by up to an order of magnitude, indicating that local source conditions become important. b1-c hosts a cold (tex ≈ 60 k), more extended component of com emission with a column density of typically a few percent of the warm/hot (tex ~ 200 k) central component. a d/h ratio of 1-3% is derived for b1-c, s68n, and b1-bs based on the ch2doh/ch3oh ratio (taking into account statistical weighting) suggesting a temperature of ~15 k during the formation of methanol. this ratio is consistent with other low-mass protostars, but is lower than for high-mass star-forming regions.conclusions: the abundance ratios of most o-bearing coms are roughly fixed between different star-forming regions, and are presumably set at an earlier cold prestellar phase. for several coms, local source properties become important. future mid-infrared facilities such as jwst/miri will be essential for the direct observation of com ices. combining this with a larger sample of com-rich sources with alma will allow ice and gas-phase abundances to be directly linked in order to constrain the routes that produce and maintain chemical complexity during the star formation process. tables e.1-e.3 are only available at the cds via anonymous ftp to http://cdsarc.u-strasbg.fr (ftp://130.79.128.5) or via http://cdsarc.u-strasbg.fr/viz-bin/cat/j/a+a/639/a87 | complex organic molecules in low-mass protostars on solar system scales. i. oxygen-bearing species |
we have conducted a survey of young single and multiple systems in the taurus-auriga star-forming region with the atacama large millimeter array (alma), substantially improving both the spatial resolution and sensitivity with which individual protoplanetary disks in these systems have been observed. these alma observations can resolve binary separations as small as 25-30 au and have an average 3σ detection level of 0.35 mjy, equivalent to a disk mass of 4 × 10-5 m ⊙ for an m3 star. our sample was constructed from stars that have an infrared excess and/or signs of accretion and have been classified as class ii. for the binary and higher-order multiple systems observed, we detect λ = 1.3 mm continuum emission from one or more stars in all of our target systems. combined with previous surveys of taurus, our 21 new detections increase the fraction of millimeter-detected disks to over 75% in all categories of stars (singles, primaries, and companions) earlier than spectral type m6 in the class ii sample. given the wealth of other information available for these stars, this has allowed us to study the impact of multiplicity with a much larger sample. while millimeter flux and disk mass are related to stellar mass as seen in previous studies, we find that both primary and secondary stars in binary systems with separations of 30-4200 au have lower values of millimeter flux as a function of stellar mass than single stars. we also find that for these systems, the circumstellar disk around the primary star does not dominate the total disk mass in the system and contains on average 62% of the total mass. | resolved young binary systems and their disks |
strong absorption signatures in the helium line at 1083 nm have recently been detected in transmission spectra of several close-in exoplanets. this absorption line originates from neutral helium atoms in an excited, metastable 23s state. the population of helium atoms in this excited state is governed by the spectral shape and intensity of the incident stellar radiation field. we investigate what kind of stellar environments are most favorable for populating the metastable helium state in extended planetary atmospheres. our results suggest that planets orbiting at close separations from late-type stars—particularly k-stars—are the most promising candidates for transit absorption signals at 1083 nm. this result is supported by observations, as all four exoplanets with currently reported helium detections orbit k-type stars. in general, conditions for exciting helium atoms become more favorable at closer orbital separations, and around stars with higher levels of extreme-ultraviolet (euv) flux, which ionizes the helium ground state, and lower levels of mid-ultraviolet (mid-uv) flux, which ionizes the helium metastable state. | helium absorption at 1083 nm from extended exoplanet atmospheres: dependence on stellar radiation |
the process by which the sun affects the terrestrial environment on short timescales is predominately driven by the amount of magnetic reconnection between the solar wind and earth's magnetosphere. reconnection occurs most efficiently when the solar wind magnetic field has a southward component. the most severe impacts are during the arrival of a coronal mass ejection (cme) when the magnetosphere is both compressed and magnetically connected to the heliospheric environment. unfortunately, forecasting magnetic vectors within coronal mass ejections remain elusive. here we report how, by combining a statistically robust helicity rule for a cme's solar origin with a simplified flux rope topology, the magnetic vectors within the earth-directed segment of a cme can be predicted. in order to test the validity of this proof-of-concept architecture for estimating the magnetic vectors within cmes, a total of eight cme events (between 2010 and 2014) have been investigated. with a focus on the large false alarm of january 2014, this work highlights the importance of including the early evolutionary effects of a cme for forecasting purposes. the angular rotation in the predicted magnetic field closely follows the broad rotational structure seen within the in situ data. this time-varying field estimate is implemented into a process to quantitatively predict a time-varying kp index that is described in detail in paper ii. future statistical work, quantifying the uncertainties in this process, may improve the more heuristic approach used by early forecasting systems. | predicting the magnetic vectors within coronal mass ejections arriving at earth: 1. initial architecture |
hybrid symplectic integrators such as mercury are widely used to simulate complex dynamical phenomena in planetary dynamics that could otherwise not be investigated. a hybrid integrator achieves high accuracy during close encounters by using a high-order integration scheme for the duration of the encounter while otherwise using a standard second-order wisdom-holman scheme, thereby optimizing both speed and accuracy. in this paper we reassess the criteria for choosing the switching function that determines which parts of the hamiltonian are integrated with the high-order integrator. we show that the original motivation for choosing a polynomial switching function in mercury is not correct. we explain the nevertheless excellent performance of the mercury integrator and then explore a wide range of different switching functions including an infinitely differentiable function and a heaviside function. we find that using a heaviside function leads to a significantly simpler scheme compared to mercury , while maintaining the same accuracy in short-term simulations. | hybrid symplectic integrators for planetary dynamics |
atmospheric characterization of temperate, rocky planets is the holy grail of exoplanet studies. these worlds are at the limits of our capabilities with current instrumentation in transmission spectroscopy and challenge our state-of-the-art statistical techniques. here we present the transmission spectrum of the temperate super-earth lhs 1140b using the hubble space telescope (hst). the wide field camera 3 (wfc3) g141 grism data of this habitable-zone (teq = 235 k) super-earth (r = 1.7 r⊕) shows tentative evidence of water. however, the signal-to-noise ratio, and thus the significance of the detection, is low and stellar contamination models can cause modulation over the spectral band probed. we attempt to correct for contamination using these models and find that, while many still lead to evidence for water, some could provide reasonable fits to the data without the need for molecular absorption although most of these cause features in the visible ground-based data which are nonphysical. future observations with the james webb space telescope would be capable of confirming, or refuting, this atmospheric detection. | hubble wfc3 spectroscopy of the habitable-zone super-earth lhs 1140 b |
small, cool planets represent the typical end-products of planetary formation. studying the architectures of these systems, measuring planet masses and radii, and observing these planets’ atmospheres during transit directly informs theories of planet assembly, migration, and evolution. here we report the discovery of three small planets orbiting a bright (ks = 8.6 mag) m0 dwarf using data collected as part of k2, the new ecliptic survey using the re-purposed kepler spacecraft. stellar spectroscopy and k2 photometry indicate that the system hosts three transiting planets with radii 1.5-2.1 {{r}\oplus }, straddling the transition region between rocky and increasingly volatile-dominated compositions. with orbital periods of 10-45 days the planets receive just 1.5-10× the flux incident on earth, making these some of the coolest small planets known orbiting a nearby star; planet d is located near the inner edge of the system’s habitable zone. the bright, low-mass star makes this system an excellent laboratory to determine the planets’ masses via doppler spectroscopy and to constrain their atmospheric compositions via transit spectroscopy. this discovery demonstrates the ability of k2 and future space-based transit searches to find many fascinating objects of interest. | a nearby m star with three transiting super-earths discovered by k2 |
we have mapped the major-element composition of mercury's surface from orbital messenger x-ray spectrometer measurements. these maps constitute the first global-scale survey of the surface composition of a solar system body conducted with the technique of planetary x-ray fluorescence. full maps of mg and al, together with partial maps of s, ca, and fe, each relative to si, reveal highly variable compositions (e.g., mg/si and al/si range over 0.1-0.8 and 0.1-0.4, respectively). the geochemical variations that we observe are consistent with those inferred from other messenger geochemical remote sensing datasets, but they do not correlate well with units mapped previously from spectral reflectance or morphology. location-dependent, rather than temporally evolving, partial melt sources were likely the major influence on the compositions of the magmas that produced different geochemical terranes. a large (> 5 ×106km2) region with the highest mg/si, ca/si, and s/si ratios, as well as relatively thin crust, may be the site of an ancient and heavily degraded impact basin. the distinctive geochemical signature of this region could be the consequence of high-degree partial melting of a reservoir in a vertically heterogeneous mantle that was sampled primarily as a result of the impact event. | evidence for geochemical terranes on mercury: global mapping of major elements with messenger's x-ray spectrometer |
building the terrestrial planets has been a challenge for planet formation models. in particular, classical theories have been unable to reproduce the small mass of mars and instead predict that a planet near 1.5 astronomical units (au) should roughly be the same mass as earth. recently, a new model called viscously stirred pebble accretion (vspa) has been developed that can explain the formation of the gas giants. this model envisions that the cores of the giant planets formed from 100- to 1,000-km bodies that directly accreted a population of pebblesâsubmeter-sized objects that slowly grew in the protoplanetary disk. here we apply this model to the terrestrial planet region and find that it can reproduce the basic structure of the inner solar system, including a small mars and a low-mass asteroid belt. our models show that for an initial population of planetesimals with sizes similar to those of the main belt asteroids, vspa becomes inefficient beyond ~1.5 au. as a result, marsâs growth is stunted, and nothing large in the asteroid belt can accumulate. | growing the terrestrial planets from the gradual accumulation of sub-meter sized objects |
the mass of a protoplanetary disk limits the formation and future growth of any planet. masses of protoplanetary disks are usually calculated from measurements of the dust continuum emission by assuming an interstellar gas-to-dust ratio. to investigate the utility of co as an alternate probe of disk mass, we use alma to survey 13co and c18o j = 3-2 line emission from a sample of 93 protoplanetary disks around stars and brown dwarfs with masses from in the nearby chamaeleon i star-forming region. we detect 13co emission from 17 sources and c18o from only one source. gas masses for disks are then estimated by comparing the co line luminosities to results from published disk models that include co freeze-out and isotope-selective photodissociation. under the assumption of a typical interstellar medium co-to-h2 ratio of 10-4, the resulting gas masses are implausibly low, with an average gas mass of ∼0.05 m jup as inferred from the average flux of stacked 13co lines. the low gas masses and gas-to-dust ratios for cha i disks are both consistent with similar results from disks in the lupus star-forming region. the faint co line emission may instead be explained if disks have much higher gas masses, but freeze-out of co or complex c-bearing molecules is underestimated in disk models. the conversion of co flux to co gas mass also suffers from uncertainties in disk structures, which could affect gas temperatures. co emission lines will only be a good tracer of the disk mass when models for c and co depletion are confirmed to be accurate. | an alma survey of co isotopologue emission from protoplanetary disks in chamaeleon i |
as protostars evolve from optically faint/infrared-bright (class i) sources to optically bright/infrared-faint (class ii) the solid material in their surrounding disks accumulates into planetesimals and protoplanets. the nearby, young ophiuchus star-forming region contains hundreds of protostars in a range of evolutionary states. using the atacama large millimeter array to observe their millimeter continuum emission, we have measured masses of, or placed strong upper limits on, the dust content of 279 disks. the masses follow a log-normal distribution with a clear trend of decreasing mass from less to more evolved protostellar infrared class. the (logarithmic) mean class i disk mass, m = 3.8 m ⊕, is about 5 times greater than the mean class ii disk mass, but the dispersion in each class is so high, σ logm≃ 0.8-1, that there is a large overlap between the two distributions. the disk mass distribution of flat-spectrum protostars lies in between classes i and ii. in addition, three class iii sources with little to no infrared excess are detected with low disk masses, m ≃ 0.3 m ⊕. despite the clear trend of decreasing disk mass with protostellar evolutionary state in this region, a comparison with surveys of class ii disks in other regions shows that masses do not decrease monotonically with age. this suggests that the cloud-scale environment may determine the initial disk mass scale or that there is substantial dust regeneration after 1 myr. | the ophiuchus disk survey employing alma (odisea): disk dust mass distributions across protostellar evolutionary classes |
two studies utilizing sparse aperture-masking (sam) interferometry and h αdifferential imaging have reported multiple jovian companions around the young solar-mass star, lkca 15 (lkca 15 bcd): the first claimed direct detection of infant, newly formed planets (“protoplanets”). we present new near-infrared direct imaging/spectroscopy from the subaru coronagraphic extreme adaptive optics (scexao) system coupled with coronagraphic high angular resolution imaging spectrograph (charis) integral field spectrograph and multi-epoch thermal infrared imaging from keck/nirc2 of lkca 15 at high strehl ratios. these data provide the first direct imaging look at the same wavelengths and in the same locations where previous studies identified the lkca 15 protoplanets, and thus offer the first decisive test of their existence. the data do not reveal these planets. instead, we resolve extended emission tracing a dust disk with a brightness and location comparable to that claimed for lkca 15 bcd. forward-models attributing this signal to orbiting planets are inconsistent with the combined scexao/charis and keck/nirc2 data. an inner disk provides a more compelling explanation for the sam detections and perhaps also the claimed h αdetection of lkca 15 b. we conclude that there is currently no clear, direct evidence for multiple protoplanets orbiting lkca 15, although the system likely contains at least one unseen jovian companion. to identify jovian companions around lkca 15 from future observations, the inner disk should be detected and its effect modeled, removed, and shown to be distinguishable from planets. protoplanet candidates identified from similar systems should likewise be clearly distinguished from disk emission through modeling. | no clear, direct evidence for multiple protoplanets orbiting lkca 15: lkca 15 bcd are likely inner disk signals |
context. the detection of radio emissions from exoplanets will open up a vibrant new research field. observing planetary auroral radio emission is the most promising method to detect exoplanetary magnetic fields, the knowledge of which will provide valuable insights into the planet's interior structure, atmospheric escape, and habitability.aims: we present lofar (low-frequency array) low band antenna (lba: 10-90 mhz) circularly polarized beamformed observations of the exoplanetary systems 55 cancri, υ andromedae, and τ boötis. all three systems are predicted to be good candidates to search for exoplanetary radio emission.methods: we applied the borealis pipeline that we have developed to mitigate radio frequency interference and searched for both slowly varying and bursty radio emission. our pipeline has previously been quantitatively benchmarked on attenuated jupiter radio emission.results: we tentatively detect circularly polarized bursty emission from the τ boötis system in the range 14-21 mhz with a flux density of ~890 mjy and with a statistical significance of ~3σ. for this detection, we do not see any signal in the off-beams, and we do not find any potential causes which might cause false positives. we also tentatively detect slowly variable circularly polarized emission from τ boötis in the range 21-30 mhz with a flux density of ~400 mjy and with a statistical significance of >8σ. the slow emission is structured in the time-frequency plane and shows an excess in the on-beam with respect to the two simultaneous off-beams. while the bursty emission seems rather robust, close examination casts some doubts on the reality of the slowly varying signal. we discuss in detail all the arguments for and against an actual detection, and derive methodological tests that will also apply to future searches. furthermore, a ~2σ marginal signal is found from the υ andromedae system in one observation of bursty emission in the range 14-38 mhz and no signal is detected from the 55 cancri system, on which we placed a 3σ upper limit of 73 mjy for the flux density at the time of the observation.conclusions: assuming the detected signals are real, we discuss their potential origin. their source probably is the τ boötis planetary system, and a possible explanation is radio emission from the exoplanet τ boötis b via the cyclotron maser mechanism. assuming a planetary origin, we derived limits for the planetary polar surface magnetic field strength, finding values compatible with theoretical predictions. further observations with lofar-lba and other low-frequency telescopes, such as nenufar or utr-2, are required to confirm this possible first detection of an exoplanetary radio signal. | the search for radio emission from the exoplanetary systems 55 cancri, υ andromedae, and τ boötis using lofar beam-formed observations |
we aim at estimating the dust scale height of protoplanetary disks from millimeter continuum observations. first, we present a general expression of intensity of a ring in a protoplanetary disk and show that we can constrain the dust scale height by the azimuthal intensity variation. then, we apply the presented methodology to the two distinct rings at 68 au and at 100 au of the protoplanetary disk around hd 163296. we constrain the dust scale height by comparing the high-resolution millimeter dust continuum image obtained in the disk substructures at high angular resolution project (dsharp) with radiative transfer simulations using radmc-3d. we find that hd/hg > 0.84 at the inner ring and hd/hg < 0.11 at the outer ring with 3σ uncertainties, where hd is the dust scale height and hg is the gas scale height. this indicates that the dust is flared at the inner ring and settled at the outer ring. we further constrain the ratio of the turbulence parameter α to the gas-to-dust-coupling parameter st from the derived dust scale height; α/st > 2.4 at the inner ring, and α/st < $1.1\times {10}^{-2}$ at the outer ring. this result shows that the turbulence is stronger or the dust is smaller at the inner ring than at the outer ring. | estimate on dust scale height from the alma dust continuum image of the hd 163296 protoplanetary disk |
wasp-52b is a low-density hot jupiter orbiting a moderately active k2v star. previous low-resolution studies have revealed a cloudy atmosphere and found atomic na above the cloud deck. here we report on the detection of excess absorption at the na doublet, the hα line, and the k d1 line. we derived a high-resolution transmission spectrum based on three transits of wasp-52b, observed with the ultra-stable, high-resolution spectrograph espresso at the very large telescope array. we measured a line contrast of 1.09 ± 0.16% for na d1, 1.31 ± 0.13% for na d2, 0.86 ± 0.13% for hα, and 0.46 ± 0.13% for k d1, with a line fwhm range of 11-22 km s-1. we also found that the velocity shift of these detected lines during the transit is consistent with the planet's orbital motion, thus confirming their planetary origin. we did not observe any significant net blueshift or redshift that could be attributed to planetary winds. we used activity indicator lines as control but found no excess absorption. however, we did notice signatures arising from the center-to-limb variation (clv) and the rossiter-mclaughlin (rm) effect at these control lines. this highlights the importance of the clv + rm correction in correctly deriving the transmission spectrum, which, if not corrected, could resemble or cancel out planetary absorption in certain cases. wasp-52b is the second non-ultra-hot jupiter to show excess hα absorption after hd 189733b. future observations targeting non-ultra-hot jupiters that show hα could help reveal the relation between stellar activity and the heating processes in the planetary upper atmosphere. based on observations collected at the european southern observatory under eso programmes 0102.c-0493 and 0102.d-0789. | detection of na, k, and hα absorption in the atmosphere of wasp-52b using espresso |
ultra-hot jupiters are gas giants planets whose dayside temperature is greater than 2200 k as a consequence of the strong irradiation received from the host star. these kinds of objects are perfect laboratories to study the chemistry of exoplanetary upper atmospheres via transmission spectroscopy. exo-atmospheric absorption features are buried in the noise of the in-transit residual spectra. however we can retrieve information of hundreds of atmospheric absorption lines by performing a cross-correlation with an atmospheric transmission model, which allows us to greatly increase the exo-atmospheric signal. the rossiter-mclaughlin effect and centre-to-limb variation contribute strongly at the high spectral resolution of our data. we present the first detection of fe i and confirmation of absorption features of fe ii in the atmosphere of the ultra-hot jupiter mascara-2b/kelt-20b, by using three transit observations with harps-n. after combining all transit observations we find a high cross-correlation signal of fe i and fe ii with signal-to-noise ratios of 10.5 ± 0.4 and 8.6 ± 0.5, respectively. the peak absorption for both species appear to be blue-shifted with velocities of - 6.3 ± 0.8 km s-1 for fe i and - 2.8 ± 0.8 km s-1 for fe ii, suggesting the presence of winds from the day- to night-side of the atmosphere of the planet. these results confirm previous studies of this planet and add a new atomic species (fe i) to the long list of detected species in the atmosphere of mascara-2b, making it, together with kelt-9b, the most feature-rich ultra-hot jupiter to date. | detection of fe i and fe ii in the atmosphere of mascara-2b using a cross-correlation method |
aerospace technologies are crucial for modern civilization; space-based infrastructure underpins weather forecasting, communications, terrestrial navigation and logistics, planetary observations, solar monitoring, and other indispensable capabilities. extraplanetary exploration -- including orbital surveys and (more recently) roving, flying, or submersible unmanned vehicles -- is also a key scientific and technological frontier, believed by many to be paramount to the long-term survival and prosperity of humanity. all of these aerospace applications require reliable control of the craft and the ability to record high-precision measurements of physical quantities. magnetometers deliver on both of these aspects, and have been vital to the success of numerous missions. in this review paper, we provide an introduction to the relevant instruments and their applications. we consider past and present magnetometers, their proven aerospace applications, and emerging uses. we then look to the future, reviewing recent progress in magnetometer technology. we particularly focus on magnetometers that use optical readout, including atomic magnetometers, magnetometers based on quantum defects in diamond, and optomechanical magnetometers. these optical magnetometers offer a combination of field sensitivity, size, weight, and power consumption that allows them to reach performance regimes that are inaccessible with existing techniques. this promises to enable new applications in areas ranging from unmanned vehicles to navigation and exploration. | precision magnetometers for aerospace applications: a review |
the system of two transiting neptune-sized planets around the bright, young m-dwarf au mic provides a unique opportunity to test models of planet formation, early evolution, and star-planet interaction. however, the intense magnetic activity of the host star makes measuring the masses of the planets via the radial velocity (rv) method very challenging. we report on a 1-yr, intensive monitoring campaign of the system using 91 observations with the harps spectrograph, allowing for detailed modelling of the ~600 ${\rm m\, s^{-1}}$ peak-to-peak activity-induced rv variations. we used a multidimensional gaussian process framework to model these and the planetary signals simultaneously. we detect the latter with semi-amplitudes of kb = 5.8 ± 2.5 ${\rm m\, s^{-1}}$ and kc = 8.5 ± 2.5 ${\rm m\, s^{-1}}$, respectively. the resulting mass estimates, mb = 11.7 ± 5.0 m⊕ and mc = 22.2 ± 6.7 m⊕, suggest that planet b might be less dense, and planet c considerably denser than previously thought. these results are in tension with the current standard models of core-accretion. they suggest that both planets accreted a h/he envelope that is smaller than expected, and the trend between the two planets' envelope fractions is the opposite of what is predicted by theory. | one year of au mic with harps - i. measuring the masses of the two transiting planets |
although the main goal of the transiting exoplanet survey satellite (tess) is to search for new transiting exoplanets, its data can also be used to study already-known systems in further detail. the tess bandpass is particularly interesting to study the limb-darkening effect of the stellar host that is imprinted in transit light curves, as the widely used phoenix and atlas stellar models predict different limb-darkening profiles. here we study this effect by fitting the transit light curves of 176 known exoplanetary systems observed by tess, which allows us to extract empirical limb-darkening coefficients (ldcs) for the widely used quadratic law but also updated transit parameters (including ephemeride refinements) as a by-product. comparing our empirically obtained ldcs with theoretical predictions, we find significant offsets when using tabulated tess ldcs. specifically, the u 2 coefficients obtained using phoenix models show the largest discrepancies depending on the method used to derive them, with offsets that can reach up to δu 2 ≈ 0.2, on average. most of those average offsets disappear, however, if one uses the spam algorithm introduced by howarth to calculate the ldcs instead. our results suggest, however, that for stars cooler than about 5000 k, no methodology is good enough to explain the limb-darkening effect; we observe a sharp deviation between measured and predicted ldcs on both quadratic ldcs of order δu 1, δu 2 ≈ 0.2 for those cool stars. we recommend caution when assuming ldcs as perfectly known, in particular for these cooler stars when analyzing tess transit light curves. | empirical limb-darkening coefficients and transit parameters of known exoplanets from tess |
we apply the theory of radiative torque (rat) alignment for studying protoplanetary disks around a t-tauri star and perform 3d radiative transfer calculations to provide the expected maps of polarized radiation to be compared with observations, such as with alma. we revisit the issue of grain alignment for large grains expected in the protoplanetary disks and find that mm-sized grains at the midplane do not align with the magnetic field since the larmor precession timescale for such large grains becomes longer than the gaseous damping timescale. hence, for these grains the rat theory predicts that the alignment axis is determined by the grain precession with respect to the radiative flux. as a result, we expect that the polarization will be in the azimuthal direction for a face-on disk. it is also shown that if dust grains have superparamagnetic inclusions, magnetic field alignment is possible for (sub-)micron grains at the surface layer of disks, and this can be tested by mid-infrared polarimetric observations. | radiative grain alignment in protoplanetary disks: implications for polarimetric observations |
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