abstract stringlengths 3 192k | title stringlengths 4 857 |
|---|---|
advancing technology in near-infrared instrumentation and dedicated planetary telescope facilities have enabled nearly two decades of reconnoitering the spectral properties for near-earth objects (neos). we report measured spectral properties for more than 1000 neos, representing >5% of the currently discovered population. thermal flux detected below 2.5 μm allows us to make albedo estimates for nearly 50 objects, including two comets. additional spectral data are reported for more than 350 mars-crossing asteroids. most of these measurements were achieved through a collaboration between researchers at the massachusetts institute of technology and the university of hawaii, with full cooperation of the nasa infrared telescope facility (irtf) on mauna kea. we call this project the mit-hawaii near-earth object spectroscopic survey (mithneos; myth-neos). while mithneos has continuously released all spectral data for immediate use by the scientific community, our objectives for this paper are to: (1) detail the methods and limits of the survey data, (2) formally present a compilation of results including their taxonomic classification within a single internally consistent framework, (3) perform a preliminary analysis on the overall population characteristics with a concentration toward deducing key physical processes and identifying their source region for escaping the main belt. augmenting our newly published measurements are the previously published results from the broad neo community, including many results graciously shared by colleagues prior to formal publication. with this collective data set, we find the near-earth population matches the diversity of the main-belt, with all main-belt taxonomic classes represented in our sample. potentially hazardous asteroids (phas) as well as the subset of mission accessible asteroids (δv ≤ 7 km/s) both appear to be a representative mix of the overall neo population, consistent with strong dynamical mixing for the population that interacts most closely with earth. mars crossers, however, are less diverse and appear to more closely match the inner belt population from where they have more recently diffused. the fractional distributions of major taxonomic classes (60% s, 20% c, 20% other) appear remarkably constant over two orders of magnitude in size (10 km to 100 m), which is eight orders of magnitude in mass, though we note unaccounted bias effects enter into our statistics below about 500 m. given the range of surface ages, including possible refreshment by planetary encounters, we are able to identify a very specific space weathering vector tracing the transition from q- to sq- to s-types that follows the natural dispersion for asteroid spectra mapped into principal component space. we also are able to interpret a shock darkening vector that may account for some objects having featureless spectra. space weathering effects for c-types are complex; these results are described separately by lantz, binzel, demeo. (2018, icarus 302, 10-17). independent correlation of dynamical models with taxonomic classes map the escape zones for neos to main-belt regions consistent with well established heliocentric compositional gradients. we push beyond taxonomy to interpret our visible plus near-infrared spectra in terms of the olivine and pyroxene mineralogy consistent with the h, l, and ll classes of ordinary chondrites meteorites. correlating meteorite interpretations with dynamical escape region models shows a preference for ll chondrites to arrive from the ν6 resonance and h chondrites to have a preferential signature from the mid-belt region (3:1 resonance). l chondrites show some preference toward the outer belt, but not at a significant level. we define a space weathering parameter as a continuous variable and find evidence for step-wise changes in space weathering properties across different planet crossing zones in the inner solar system. overall we hypothesize the relative roles of planetary encounters, yorp spin-up, and thermal cycling across the inner solar system. | compositional distributions and evolutionary processes for the near-earth object population: results from the mit-hawaii near-earth object spectroscopic survey (mithneos) |
the mass-period or radius-period distribution of close-in exoplanets shows a paucity of intermediate mass/size (sub-jovian) planets with periods ≲3 d. we show that this sub-jovian desert can be explained by the photoevaporation of highly irradiated sub-neptunes and the tidal disruption barrier for gas giants undergoing high-eccentricity migration. the distinctive triangular shape of the sub-jovain desert results from the fact that photoevaporation is more effective closer to the host star, and that in order for a gas giant to tidally circularize closer to the star without tidal disruption it needs to be more massive. our work indicates that super-earths/mini-neptunes and hot-jupiters had distinctly separate formation channels and arrived at their present locations at different times. | photoevaporation and high-eccentricity migration created the sub-jovian desert |
land free of direct anthropogenic disturbance is considered essential for achieving biodiversity conservation outcomes but is rapidly eroding. in response, many nations are increasing their protected area (pa) estates, but little consideration is given to the context of the surrounding landscape. this is despite the fact that structural connectivity between pas is critical in a changing climate and mandated by international conservation targets. using a high-resolution assessment of human pressure, we show that while ~40% of the terrestrial planet is intact, only 9.7% of earth's terrestrial protected network can be considered structurally connected. on average, 11% of each country or territory's pa estate can be considered connected. as the global community commits to bolder action on abating biodiversity loss, placement of future pas will be critical, as will an increased focus on landscape-scale habitat retention and restoration efforts to ensure those important areas set aside for conservation outcomes will remain (or become) connected. | just ten percent of the global terrestrial protected area network is structurally connected via intact land |
present-day venus is an inhospitable place with surface temperatures approaching 750 k and an atmosphere 90 times as thick as earth's. billions of years ago the picture may have been very different. we have created a suite of 3-d climate simulations using topographic data from the magellan mission, solar spectral irradiance estimates for 2.9 and 0.715 gya, present-day venus orbital parameters, an ocean volume consistent with current theory, and an atmospheric composition estimated for early venus. using these parameters we find that such a world could have had moderate temperatures if venus had a prograde rotation period slower than ~16 earth days, despite an incident solar flux 46-70% higher than earth receives. at its current rotation period, venus's climate could have remained habitable until at least 0.715 gya. these results demonstrate the role rotation and topography play in understanding the climatic history of venus-like exoplanets discovered in the present epoch. | was venus the first habitable world of our solar system? |
we measure dynamical masses for five objects—three ultracool dwarfs, one low-mass star, and one white dwarf—by fitting orbits to a combination of the hipparcos-gaia catalog of accelerations, literature radial velocities, and relative astrometry. our approach provides precise masses without any assumptions about the primary star, even though the observations typically cover only a small fraction of an orbit. we also perform a uniform re-analysis of the host stars’ ages. two of our objects, hd 4747b and hr 7672b, already have precise dynamical masses near the stellar/substellar boundary and are used to validate our approach. for gl 758b, we obtain a mass of m={37.9}-1.5+1.4 {m}{{jup}}, the most precise mass measurement of this companion to date. gl 758b is the coldest brown dwarf with a dynamical mass, and the combination of our low mass and slightly older host-star age resolves its previously noted discrepancy with substellar evolutionary models. hd 68017b, a late m-dwarf, has a mass of m = 0.149 ± 0.002 m ⊙, consistent with stellar theory and previous empirical estimates based on its absolute magnitude. the progenitor of the white dwarf gl 86b has been debated in the literature, and our dynamical measurement of m = 0.597 ± 0.010 m ⊙ is consistent with a higher progenitor mass and younger age for this planet-hosting binary system. overall, these case studies represent only five of the thousands of accelerating systems identified by combining hipparcos and gaia. our analysis could be repeated for many of them to build a large sample of companions with dynamical masses. | precise dynamical masses of directly imaged companions from relative astrometry, radial velocities, and hipparcos-gaia dr2 accelerations |
we present results from high-resolution, optical to near-ir imaging of host stars of kepler objects of interest (kois), identified in the original kepler field. part of the data were obtained under the kepler imaging follow-up observation program over six years (2009-2015). almost 90% of stars that are hosts to planet candidates or confirmed planets were observed. we combine measurements of companions to koi host stars from different bands to create a comprehensive catalog of projected separations, position angles, and magnitude differences for all detected companion stars (some of which may not be bound). our compilation includes 2297 companions around 1903 primary stars. from high-resolution imaging, we find that ∼10% (∼30%) of the observed stars have at least one companion detected within 1″ (4″). the true fraction of systems with close (≲4″) companions is larger than the observed one due to the limited sensitivities of the imaging data. we derive correction factors for planet radii caused by the dilution of the transit depth: assuming that planets orbit the primary stars or the brightest companion stars, the average correction factors are 1.06 and 3.09, respectively. the true effect of transit dilution lies in between these two cases and varies with each system. applying these factors to planet radii decreases the number of koi planets with radii smaller than 2 {r}\oplusby ∼2%-23% and thus affects planet occurrence rates. this effect will also be important for the yield of small planets from future transit missions such as tess. | the kepler follow-up observation program. i. a catalog of companions to kepler stars from high-resolution imaging |
volcanic degassing of planetary interiors has important implications for their corresponding atmospheres. the oxidation state of rocky interiors affects the volatile partitioning during mantle melting and subsequent volatile speciation near the surface. here we show that the mantle redox state is central to the chemical composition of atmospheres while factors such as planetary mass, thermal state, and age mainly affect the degassing rate. we further demonstrate that mantle oxygen fugacity has an effect on atmospheric thickness and that volcanic degassing is most efficient for planets between 2 and 4 earth masses. we show that outgassing of reduced systems is dominated by strongly reduced gases such as h2?, with only smaller fractions of moderately reduced/oxidised gases (co?, h2o ?). overall, a reducing scenario leads to a lower atmospheric pressure at the surface and to a larger atmospheric thickness compared to an oxidised system. atmosphere predictions based on interior redox scenarios can be compared to observations of atmospheres of rocky exoplanets, potentially broadening our knowledge on the diversity of exoplanetary redox states. | mantle redox state drives outgassing chemistry and atmospheric composition of rocky planets |
the fault diagnosis of planetary gearboxes is crucial to reduce the maintenance costs and economic losses. this paper proposes a novel fault diagnosis method based on adaptive multi-scale morphological filter (ammf) and modified hierarchical permutation entropy (mhpe) to identify the different health conditions of planetary gearboxes. in this method, ammf is firstly adopted to remove the fault-unrelated components and enhance the fault characteristics. second, mhpe is utilized to extract the fault features from the denoised vibration signals. third, laplacian score (ls) approach is employed to refine the fault features. in the end, the obtained features are fed into the binary tree support vector machine (bt-svm) to accomplish the fault pattern identification. the proposed method is numerically and experimentally demonstrated to be able to recognize the different fault categories of planetary gearboxes. | a fault diagnosis scheme for planetary gearboxes using adaptive multi-scale morphology filter and modified hierarchical permutation entropy |
the matter in extreme conditions end station at the linac coherent light source (lcls) is a new tool enabling accurate pump-probe measurements for studying the physical properties of matter in the high-energy density (hed) physics regime. this instrument combines the world’s brightest x-ray source, the lcls x-ray beam, with high-power lasers consisting of two nanosecond nd:glass laser beams and one short-pulse ti:sapphire laser. these lasers produce short-lived states of matter with high pressures, high temperatures or high densities with properties that are important for applications in nuclear fusion research, laboratory astrophysics and the development of intense radiation sources. in the first experiments, we have performed highly accurate x-ray diffraction and x-ray thomson scattering measurements on shock-compressed matter resolving the transition from compressed solid matter to a co-existence regime and into the warm dense matter state. these complex charged-particle systems are dominated by strong correlations and quantum effects. they exist in planetary interiors and laboratory experiments, e.g., during high-power laser interactions with solids or the compression phase of inertial confinement fusion implosions. applying record peak brightness x-rays resolves the ionic interactions at atomic (ångstrom) scale lengths and measure the static structure factor, which is a key quantity for determining equation of state data and important transport coefficients. simultaneously, spectrally resolved measurements of plasmon features provide dynamic structure factor information that yield temperature and density with unprecedented precision at micron-scale resolution in dynamic compression experiments. these studies have demonstrated our ability to measure fundamental thermodynamic properties that determine the state of matter in the hed physics regime. | matter under extreme conditions experiments at the linac coherent light source |
protoplanetary disks (ppds) are believed to accrete onto their central t tauri star because of magnetic stresses. recently published shearing box simulations indicate that ohmic resistivity, ambipolar diffusion (ad) and the hall effect all play important roles in disk evolution. in the presence of a vertical magnetic field, the disk remains laminar between 1-5 au, and a magnetocentrifugal disk wind forms that provides an important mechanism for removing angular momentum. questions remain, however, about the establishment of a true physical wind solution in the shearing box simulations because of the symmetries inherent in the local approximation. we present global mhd simulations of ppds that include ohmic resistivity and ad, where the time-dependent gas-phase electron and ion fractions are computed under fuv and x-ray ionization with a simplified recombination chemistry. our results show that the disk remains laminar, and that a physical wind solution arises naturally in global disk models. the wind is sufficiently efficient to explain the observed accretion rates. furthermore, the ionization fraction at intermediate disk heights is large enough for magneto-rotational channel modes to grow and subsequently develop into belts of horizontal field. depending on the ionization fraction, these can remain quasi-global, or break-up into discrete islands of coherent field polarity. the disk models we present here show a dramatic departure from our earlier models including ohmic resistivity only. it will be important to examine how the hall effect modifies the evolution, and to explore the influence this has on the observational appearance of such systems, and on planet formation and migration. | global simulations of protoplanetary disks with ohmic resistivity and ambipolar diffusion |
the size distribution of asteroids and kuiper belt objects in the solar system is difficult to reconcile with a bottom-up formation scenario due to the observed scarcity of objects smaller than ~100 km in size. instead, planetesimals appear to form top-down, with large 100-1000 km bodies forming from the rapid gravitational collapse of dense clumps of small solid particles. in this paper we investigate the conditions under which solid particles can form dense clumps in a protoplanetary disk. we used a hydrodynamic code to model the interaction between solid particles and the gas inside a shearing box inside the disk, considering particle sizes from submillimeter-sized chondrules to meter-sized rocks. we found that particles down to millimeter sizes can form dense particle clouds through the run-away convergence of radial drift known as the streaming instability. we made a map of the range of conditions (strength of turbulence, particle mass-loading, disk mass, and distance to the star) that are prone to producing dense particle clumps. finally, we estimate the distribution of collision speeds between mm-sized particles. we calculated the rate of sticking collisions and obtain a robust upper limit on the particle growth timescale of ~105 years. this means that mm-sized chondrule aggregates can grow on a timescale much smaller than the disk accretion timescale (~106-107 years). our results suggest a pathway from the mm-sized grains found in primitive meteorites to fully formed asteroids. we speculate that asteroids may form from a positive feedback loop in which coagualation leads to particle clumping driven by the streaming instability. this clumping, in turn, reduces collision speeds and enhances coagulation. future simulations should model coagulation and the streaming instability together to explore this feedback loop further. appendices are available in electronic form at http://www.aanda.org | how to form planetesimals from mm-sized chondrules and chondrule aggregates |
we used infrared data from the lunar reconnaissance orbiter (lro) diviner lunar radiometer experiment to globally map thermophysical properties of the moon's regolith fines layer. thermal conductivity varies from 7.4 × 10-4 w m-1 k-1 at the surface to 3.4 × 10-3 w m-1 k-1 at depths of 1 m, given density values of 1,100 kg m-3 at the surface to 1,800 kg m-3 at 1 m depth. on average, the scale height of these profiles is 7 cm, corresponding to a thermal inertia of 55 ± 2 j m-2 k-1 s-1/2 at 273 k, relevant to the diurnally active near-surface layer, 4-7 cm. the temperature dependence of thermal conductivity and heat capacity leads to an 2 times diurnal variation in thermal inertia at the equator. on global scales, the regolith fines are remarkably uniform, implying rapid homogenization by impact gardening of this layer on timescales <1 gyr. regional- and local-scale variations show prominent impact features <1 gyr old, including higher thermal inertia (> 100 j m-2 k-1 s-1/2) in the interiors and ejecta of copernican-aged impact craters and lower thermal inertia (< 50 j m-2 k-1 s-1/2) within the lunar cold spots identified by bandfield et al. (2014). observed trends in ejecta thermal inertia provide a potential tool for age dating craters of previously unknown age, complementary to the approach suggested by ghent et al. (2014). several anomalous regions are identified in the global 128 pixels per degree maps presented here, including a high-thermal inertia deposit near the antipode of tycho crater. | global regolith thermophysical properties of the moon from the diviner lunar radiometer experiment |
we present a new method to constrain the grain size in protoplanetary disks with polarization observations at millimeter wavelengths. if dust grains are grown to the size comparable to the wavelengths, the dust grains are expected to have a large scattering opacity, and thus the continuum emission is expected to be polarized due to self-scattering. we perform 3d radiative transfer calculations to estimate the polarization degree for the protoplanetary disks having radial gaussian-like dust surface density distributions, which have been recently discovered. the maximum grain size is set to be 100 μ {{m}} and the observing wavelength to be 870 μ {{m}}. we find that the polarization degree is as high as 2.5% with a subarcsec spatial resolution, which is likely to be detected with near-future alma observations. the emission is polarized due to scattering of anisotropic continuum emission. the map of the polarization degree shows a double-peaked distribution, and the polarization vectors are in the radial direction in the inner ring and in the azimuthal direction in the outer ring. we also find the wavelength dependence of the polarization degree: the polarization degree is the highest if dust grains have a maximum size of {a}{max}∼ λ /2π , where λ is the observing wavelength. hence, multi-wave and spatially resolved polarization observations toward protoplanetary disks enable us to put a constraint on the grain size. the constraint on the grain size from polarization observations is independent of or may be even stronger than that from the opacity index. | millimeter-wave polarization of protoplanetary disks due to dust scattering |
how much of earth's compositional variation dates to processes that occurred during planet formation remains an unanswered question. high-precision tungsten isotopic data from rocks from two large igneous provinces, the north atlantic igneous province and the ontong java plateau, reveal preservation to the phanerozoic of tungsten isotopic heterogeneities in the mantle. these heterogeneities, caused by the decay of hafnium-182 in mantle domains with high hafnium/tungsten ratios, were created during the first ~50 million years of solar system history, indicating that portions of the mantle that formed during earth’s primary accretionary period have survived to the present. | preservation of earth-forming events in the tungsten isotopic composition of modern flood basalts |
in this chapter, we review the breakthrough progress that has been made in the field of high-resolution, high-contrast optical and near-infrared imaging of planet-forming disks. these advancements include the direct detection of protoplanets embedded in disks, and derived limits on planetary masses in others. morphological substructures, including: rings, spirals, arcs, and shadows, are seen in all imaged infrared-bright disks to date, and are ubiquitous across spectral types. these substructures are believed to be the result of disk evolution processes, and in particular disk-planet interactions. since small dust grains that scatter light are tightly bound to the disk's gas, these observations closely trace disk structures predicted by hydrodynamical models and serve as observational tests of the predictions of planet formation theories. we argue that the results of current and next-generation high-contrast imaging surveys will, when combined with complementary data from alma, lead to a much deeper understanding of the co-evolution of disks and planets, and the mechanisms by which planets form. | optical and near-infrared view of planet-forming disks and protoplanets |
we present the sixth catalog of kepler candidate planets based on nearly four years of high precision photometry. this catalog builds on the legacy of previous catalogs released by the kepler project and includes 1493 new kepler objects of interest (kois) of which 554 are planet candidates, and 131 of these candidates have best-fit radii \lt 1.5 {{r}\oplus }. this brings the total number of kois and planet candidates to 7348 and 4175 respectively. we suspect that many of these new candidates at the low signal-to-noise ratio limit may be false alarms created by instrumental noise, and discuss our efforts to identify such objects. we re-evaluate all previously published kois with orbital periods of \gt 50 days to provide a consistently vetted sample that can be used to improve planet occurrence rate calculations. we discuss the performance of our planet detection algorithms, and the consistency of our vetting products. the full catalog is publicly available at the nasa exoplanet archive. | planetary candidates observed by kepler. vi. planet sample from q1--q16 (47 months) |
the elemental compositions of hot jupiters are informative relics of planet formation that can help us answer long-standing questions regarding the origin and formation of giant planets. here, i present the main conclusions from a comprehensive atmospheric retrieval survey of eight hot jupiters with detectable molecular absorption in their near-infrared transmission spectra. i analyze the eight transmission spectra using the newly-developed, self-consistent atmospheric retrieval framework, scarlet. unlike previous methods, scarlet combines the physical and chemical consistency of complex atmospheric models with the statistical treatment of observational uncertainties known from atmospheric retrieval techniques. i find that all eight hot jupiters consistently require carbon-to-oxygen ratios (c/o) below 0.9. the finding of c/o<0.9 is highly robust for hd209458b, wasp-12b, wasp-19b, hat-p-1b, and xo-1b. for hd189733b, wasp-17b, and wasp-43b, i find that the published wfc3 transmission spectra favor c/o<0.9 at greater than 95% confidence. i further show that the water abundances on all eight hot jupiters are consistent with solar composition. the relatively small depth of the detected water absorption features is due to the presence of clouds, not due to a low water abundance as previously suggested for hd209458b. the presence of a thick cloud deck is inferred for hd209458b and wasp-12b. hd189733b may host a similar cloud deck, rather than the previously suggested rayleigh hazes, if star spots affect the observed spectrum. the approach taken in scarlet can be regarded as a new pathway to interpreting spectral observations of planetary atmospheres. in this work, including our prior knowledge of h-c-n-o chemistry enables me to constrain the c/o ratio without detecting a single carbon-bearing molecule. | strict upper limits on the carbon-to-oxygen ratios of eight hot jupiters from self-consistent atmospheric retrieval |
we present electron densities n e in the interstellar medium (ism) of star-forming galaxies at z = 4-9 observed by the jwst/nirspec glass, early release observations, and ceers programs. we carefully evaluate the line-spread functions of the nirspec instrument as a function of wavelength with the calibration data of a planetary nebula taken on board, and obtain secure [o ii] λ λ3726, 3729 doublet fluxes for 14 galaxies at z = 4.02-8.68 falling on the star formation main sequence with the nirspec high- and medium-resolution spectra. we thus derive the electron densities of singly ionized oxygen nebulae with the standard n e indicator of the [o ii] doublet, and find that the electron densities of the z = 4-9 galaxies are n e ≳ 300 cm-3 significantly higher than those of low-z galaxies at a given stellar mass, star formation rate (sfr), and specific sfr. interestingly, the typical electron densities of the singly ionized nebulae increase from z = 0 to z = 1-3 and z = 4-9, which is approximated by the evolutionary relation of n e ∝ (1 + z) pwith p ~ 1-2. although it is not obvious that the ism property of n e is influenced by global galaxy properties, these results may suggest that the nebula densities of high-z galaxies are generally high due to the compact morphologies of high-z galaxies evolving by ${r}_{{\rm{e}}}\mathop{\propto }\limits_{\sim }{(1+z)}^{-1}$ (r vir ∝ (1 + z)-1) for a given stellar (halo) mass whose inverse square corresponds to the p ~ 2 evolutionary relation. the p ~ 1-2 evolutionary relation can be explained by a combination of the compact morphology and the reduction of n e due to the high electron temperature of high-z metal-poor nebulae. | redshift evolution of electron density in the interstellar medium at z 0-9 uncovered with jwst/nirspec spectra and line-spread function determinations |
this paper presents an overview of spirou, the new-generation near-infrared spectropolarimeter/precision velocimeter recently installed on the 3.6-m canada-france-hawaii telescope (cfht). starting from the two main science goals, i.e., the quest for planetary systems around nearby m dwarfs and the study of magnetized star/planet formation, we outline the instrument concept that was designed to efficiently address these forefront topics, and detail the in-lab and on-sky instrument performances measured throughout the intensive testing phase that spirou was submitted to before passing the final acceptance review in early 2019 and initiating science observations. with a central position among the newly started programmes, the spirou legacy survey (sls) large programme was allocated 300 cfht nights until at least mid 2022. we also briefly describe a few of the first results obtained in the various science topics that spirou started investigating, focusing in particular on planetary systems of nearby m dwarfs, transiting exoplanets and their atmospheres, magnetic fields of young stars, but also on alternate science goals like the atmospheres of m dwarfs and the earth's atmosphere. we finally conclude on the key role that spirou and the cfht can play in coordination with forthcoming major facilities like the jwst, the elts, plato, and ariel over the decade. | spirou: nir velocimetry and spectropolarimetry at the cfht |
giant exoplanets orbiting close to their host stars have high temperatures because of the immense amount of stellar irradiation that they receive. the extreme energy input leads to the expansion of the atmosphere and the escape of neutral hydrogen1-3. an intriguing case among the hot giant planets is kelt-9b, an exoplanet orbiting very close to an early a-type star, with the highest temperature (around 4,600 k on the day-side) of any exoplanet known so far4. the atmospheric composition and dynamics of this planet have previously been unknown. here we report the detection of an extended hot hydrogen atmosphere around kelt-9b. the detection was achieved by measuring the atomic hydrogen absorption during transit by observing the balmer hα line, which is unusually strong, mainly owing to the high level of extreme-ultraviolet radiation from the star. we detected a wavelength shift of the hα absorption that is mostly attributed to the planetary orbital motion5. the obtained transmission spectrum has a noticeable line contrast (1.15% extra absorption at the hα line centre). the observation implies that the effective radius at the hα line centre is about 1.64 times the size of the planetary radius, indicating that the planet has an extended hydrogen envelope close to the size of the roche lobe (1.9 1-0.26+0.22rplanet) and is probably undergoing substantial escape of its atmosphere. | an extended hydrogen envelope of the extremely hot giant exoplanet kelt-9b |
context. recent observational findings have suggested a positive correlation between the occurrence rates of inner super-earths and outer giant planets. these results raise the question of whether this trend can be reproduced and explained by planet formation theory.aims: here, we investigate the properties of inner super-earths and outer giant planets that form according to a core accretion scenario. we study the mutual relations between these planet species in synthetic planetary systems and compare them to the observed exoplanet population.methods: we invoked the generation 3 bern model of planet formation and evolution to simulate 1000 multi-planet systems. we then confronted these synthetic systems with the observed sample, taking into account the detection bias that distorts the observed demographics.results: the formation of warm super-earths and cold jupiters in the same system is enhanced compared to the individual appearances, although it is weaker than what has been proposed through observations. we attribute the discrepancy to warm and dynamically active giant planets that frequently disrupt the inner systems, particularly in high-metallicity environments. in general, a joint occurrence of the two planet types requires intermediate solid reservoirs in the originating protoplanetary disk. furthermore, we find differences in the volatile content of planets in different system architectures and predict that high-density super-earths are more likely to host an outer giant. this correlation can be tested observationally. | the new generation planetary population synthesis (ngpps). iii. warm super-earths and cold jupiters: a weak occurrence correlation, but with a strong architecture-composition link |
the mass of a star is the most fundamental parameter for its structure, evolution, and final fate. it is particularly important for any kind of stellar archaeology and characterization of exoplanets. there exist a variety of methods in astronomy to estimate or determine it. in this review we present a significant number of such methods, beginning with the most direct and model-independent approach using detached eclipsing binaries. we then move to more indirect and model-dependent methods, such as the quite commonly used isochrone or stellar track fitting. the arrival of quantitative asteroseismology has opened a completely new approach to determine stellar masses and to complement and improve the accuracy of other methods. we include methods for different evolutionary stages, from the pre-main sequence to evolved (super)giants and final remnants. for all methods uncertainties and restrictions will be discussed. we provide lists of altogether more than 200 benchmark stars with relative mass accuracies between [0.3 ,2 ]% for the covered mass range of m ∈[0.1 ,16 ] m⊙ , 75 % of which are stars burning hydrogen in their core and the other 25 % covering all other evolved stages. we close with a recommendation how to combine various methods to arrive at a "mass-ladder" for stars. | weighing stars from birth to death: mass determination methods across the hrd |
observational evidence for escaping exoplanet atmospheres has been obtained for a few exoplanets to date. it comes from strong transit signals detected in the ultraviolet, most notably in the wings of the hydrogen lyα (lyα) line. however, the core of the lyα line is often heavily affected by interstellar absorption and geocoronal emission, limiting the information about the atmosphere that can be extracted from that part of the spectrum. transit observations in atomic lines that are (a) sensitive enough to trace the rarefied gas in the planetary wind and (b) do not suffer from significant extinction by the interstellar medium could enable more detailed observations, and thus provide better constraints on theoretical models of escaping atmospheres. the absorption line of a metastable state of helium at 10830 å could satisfy both of these conditions for some exoplanets. we develop a simple 1d model of escaping planetary atmospheres containing hydrogen and helium. we use it to calculate the density profile of helium in the 23s metastable excited state and the expected in-transit absorption at 10830 å for two exoplanets known to have escaping atmospheres. our results indicate that exoplanets similar to gj 436b and hd 209458b should exhibit enhanced transit depths at 10830 å, with ∼8% and ∼2% excess absorption in the line core, respectively. | a new window into escaping exoplanet atmospheres: 10830 å line of helium |
we present k2sc (k2 systematics correction), a python pipeline to model instrumental systematics and astrophysical variability in light curves from the k2 mission. k2sc uses gaussian process regression to model position-dependent systematics and time-dependent variability simultaneously, enabling the user to remove both (e.g. for transit searches) or to remove systematics while preserving variability (for variability studies). for periodic variables, k2sc automatically computes estimates of the period, amplitude and evolution time-scale of the variability. we apply k2sc to publicly available k2 data from campaigns 3-5 showing that we obtain photometric precision approaching that of the original kepler mission. we compare our results to other publicly available k2 pipelines, showing that we obtain similar or better results, on average. we use transit injection and recovery tests to evaluate the impact of k2sc on planetary transit searches in k2 pre-search data conditioning data, for planet-to-star radius ratios down to rp/r* = 0.01 and periods up to p = 40 d, and show that k2sc significantly improves the ability to distinguish between true and false detections, particularly for small planets. k2sc can be run automatically on many light curves, or manually tailored for specific objects such as pulsating stars or large amplitude eclipsing binaries. it can be run on ascii and fits light-curve files, regardless of their origin. both the code and the processed light curves are publicly available, and we provide instructions for downloading and using them. the methodology used by k2sc will be applicable to future transit search missions such as tess and plato. | k2sc: flexible systematics correction and detrending of k2 light curves using gaussian process regression |
solar system planets move on almost circular orbits. in strong contrast, many massive gas giant exoplanets travel on highly elliptical orbits, whereas the shape of the orbits of smaller, more terrestrial, exoplanets remained largely elusive. knowing the eccentricity distribution in systems of small planets would be important as it holds information about the planet's formation and evolution, and influences its habitability. we make these measurements using photometry from the kepler satellite and utilizing a method relying on kepler's second law, which relates the duration of a planetary transit to its orbital eccentricity, if the stellar density is known. our sample consists of 28 bright stars with precise asteroseismic density measurements. these stars host 74 planets with an average radius of 2.6 r⊕. we find that the eccentricity of planets in kepler multi-planet systems is low and can be described by a rayleigh distribution with σ = 0.049 ± 0.013. this is in full agreement with solar system eccentricities, but in contrast to the eccentricity distributions previously derived for exoplanets from radial velocity studies. our findings are helpful in identifying which planets are habitable because the location of the habitable zone depends on eccentricity, and to determine occurrence rates inferred for these planets because planets on circular orbits are less likely to transit. for measuring eccentricity it is crucial to detect and remove transit timing variations (ttvs), and we present some previously unreported ttvs. finally transit durations help distinguish between false positives and true planets and we use our measurements to confirm six new exoplanets. | eccentricity from transit photometry: small planets in kepler multi-planet systems have low eccentricities |
the compositions of stars are a critical diagnostic tool for many topics in astronomy such as the evolution of our galaxy, the formation of planets, and the uniqueness of the sun. previous spectroscopic measurements indicate a large intrinsic variation in the elemental abundance patterns of stars with similar overall metal content. however, systematic errors arising from inaccuracies in stellar models are known to be a limiting factor in such studies, and thus it is uncertain to what extent the observed diversity of stellar abundance patterns is real. here we report the abundances of 30 elements with precisions of 2% for 79 sun-like stars within 100 pc. systematic errors are minimized in this study by focusing on solar twin stars and performing a line-by-line differential analysis using high-resolution, high-signal-to-noise spectra. we resolve [x/fe] abundance trends in galactic chemical evolution at precisions of 10-3 dex gyr-1 and reveal that stars with similar ages and metallicities have nearly identical abundance patterns. contrary to previous results, we find that the ratios of carbon-to-oxygen and magnesium-to-silicon in solar-metallicity stars are homogeneous to within 10% throughout the solar neighborhood, implying that exoplanets may exhibit much less compositional diversity than previously thought. finally, we demonstrate that the sun has a subtle deficiency in refractory material relative to >80% of solar twins (at 2σ confidence), suggesting a possible signpost for planetary systems like our own. | the chemical homogeneity of sun-like stars in the solar neighborhood |
a large planet orbiting a star in a protoplanetary disk opens a density gap along its orbit due to the strong disk-planet interaction and migrates with the gap in the disk. it is expected that in the ideal case, a gap-opening planet migrates at the viscous drift speed, which is referred to as type ii migration. however, recent hydrodynamic simulations have shown that, in general, the gap-opening planet is not locked to the viscous disk evolution. a new physical model is required to explain the migration speed of such a planet. for this reason, we re-examined the migration of a planet in the disk, by carrying out the two-dimensional hydrodynamic simulations in a wide parameter range. we have found that the torque exerted on the gap-opening planet depends on the surface density at the bottom of the gap. the planet migration slows down as the surface density of the bottom of the gap decreases. using the gap model developed in our previous studies, we have constructed an empirical formula of the migration speed of the gap-opening planets, which is consistent with the results given by the hydrodynamic simulations performed by us and other researchers. our model easily explains why the migration speed of the gap-opening planets can be faster than the viscous gas drift speed. it can also predict the planet mass at which the type i migration is no longer adequate due to the gap development in the disk, providing a gap formation criterion based on planetary migration. | radial migration of gap-opening planets in protoplanetary disks. i. the case of a single planet |
there is a growing appreciation that the environmental conditions that we call space weather impact the technological infrastructure that powers the coupled economies around the world. with that comes the need to better shield society against space weather by improving forecasts, environmental specifications, and infrastructure design. we recognize that much progress has been made and continues to be made with a powerful suite of research observatories on the ground and in space, forming the basis of a sun-earth system observatory. but the domain of space weather is vast - extending from deep within the sun to far outside the planetary orbits - and the physics complex - including couplings between various types of physical processes that link scales and domains from the microscopic to large parts of the solar system. consequently, advanced understanding of space weather requires a coordinated international approach to effectively provide awareness of the processes within the sun-earth system through observation-driven models. this roadmap prioritizes the scientific focus areas and research infrastructure that are needed to significantly advance our understanding of space weather of all intensities and of its implications for society. advancement of the existing system observatory through the addition of small to moderate state-of-the-art capabilities designed to fill observational gaps will enable significant advances. such a strategy requires urgent action: key instrumentation needs to be sustained, and action needs to be taken before core capabilities are lost in the aging ensemble. we recommend advances through priority focus (1) on observation-based modeling throughout the sun-earth system, (2) on forecasts more than 12 h ahead of the magnetic structure of incoming coronal mass ejections, (3) on understanding the geospace response to variable solar-wind stresses that lead to intense geomagnetically-induced currents and ionospheric and radiation storms, and (4) on developing a comprehensive specification of space climate, including the characterization of extreme space storms to guide resilient and robust engineering of technological infrastructures. the roadmap clusters its implementation recommendations by formulating three action pathways, and outlines needed instrumentation and research programs and infrastructure for each of these. an executive summary provides an overview of all recommendations. | understanding space weather to shield society: a global road map for 2015-2025 commissioned by cospar and ilws |
we present scattered light images of the tw hya disk performed with the spectro-polarimetric high-contrast exoplanet research instrument in polarimetric differential imaging mode at 0.63, 0.79, 1.24, and 1.62 μm. we also present h2/h3-band angular differential imaging (adi) observations. three distinct radial depressions in the polarized intensity distribution are seen, around ≈85, ≈21, and ≲6 au.21 the overall intensity distribution has a high degree of azimuthal symmetry; the disk is somewhat brighter than average toward the south and darker toward the north-west. the adi observations yielded no signifiant detection of point sources in the disk. our observations have a linear spatial resolution of 1-2 au, similar to that of recent alma dust continuum observations. the sub-micron-sized dust grains that dominate the light scattering in the disk surface are strongly coupled to the gas. we created a radiative transfer disk model with self-consistent temperature and vertical structure iteration and including grain size-dependent dust settling. this method may provide independent constraints on the gas distribution at higher spatial resolution than is feasible with alma gas line observations. we find that the gas surface density in the “gaps” is reduced by ≈50% to ≈80% relative to an unperturbed model. should embedded planets be responsible for carving the gaps then their masses are at most a few 10 {{{m}}}\oplus . the observed gaps are wider, with shallower flanks, than expected for planet-disk interaction with such low-mass planets. if forming planetary bodies have undergone collapse and are in the “detached phase,” then they may be directly observable with future facilities such as the mid-infrared e-elt imager and spectrograph at the e-elt. | three radial gaps in the disk of tw hydrae imaged with sphere |
the dynamic activity of the sun—sustained by a magnetohydrodynamic dynamo mechanism working in its interior—modulates the electromagnetic, particulate, and radiative environment in space. while solar activity variations on short timescale create space weather, slow long-term modulation forms the basis of space climate. space weather impacts diverse space-reliant technologies while space climate influences planetary atmospheres and climate. having prior knowledge of the sun's activity is important in these contexts. however, forecasting solar-stellar magnetic activity has remained an outstanding challenge. in this review, predictions for sunspot cycle 24 and the upcoming solar cycle 25 are summarized, and critically assessed. the analysis demonstrates that while predictions based on diverse techniques disagree across solar cycles 24-25, physics-based predictions for solar cycle 25 have converged and indicates a weak to moderate-weak sunspot cycle. i argue that this convergence in physics-based predictions is indicative of progress in the fundamental understanding of solar cycle predictability. based on this understanding, resolutions to several outstanding questions related to solar cycle predictions are discussed; these questions include: is it possible to predict the solar cycle, what is the best proxy for predictions, how early can we predict the solar cycle and how many cycles into the future can we predict relying on our current understanding? based on our analysis, we also suggest a rigorous pathway towards generating and disseminating a "consensus forecast" by any solar cycle prediction panels tasked with such a challenge. | progress in solar cycle predictions: sunspot cycles 24-25 in perspective |
we present allesfitter, a public and open-source python software for flexible and robust inference of stars and exoplanets given photometric and radial velocity data. allesfitter offers a rich selection of orbital and transit/eclipse models, accommodating multiple exoplanets, multistar systems, transit-timing variations, phase curves, stellar variability, starspots, stellar flares, and various systematic noise models, including gaussian processes. it features both parameter estimation and bayesian model selection, allowing either a markov chain monte carlo or nested sampling fit to be easily run. for novice users, a graphical user interface allows all input and perform analyses to be specified; for python users, all modules can be readily imported into any existing script. allesfitter also produces publication-ready tables, latex commands, and figures. the software is publicly available (https://github.com/mnguenther/allesfitter), pip-installable (pip install allesfitter), and well documented (www.allesfitter.com). finally, we demonstrate the software's capabilities in several examples and provide updates to the literature where possible for pi mensae, toi-216, wasp-18, koi-1003, and gj 1243. | allesfitter: flexible star and exoplanet inference from photometry and radial velocity |
constellations of cubesats are emerging as a novel observational resource with the potential to overcome the spatiotemporal constraints of conventional single-sensor satellite missions. with a constellation of more than 170 active cubesats, planet has realized daily global imaging in the rgb and near-infrared (nir) at ~3 m resolution. while superior in terms of spatiotemporal resolution, the radiometric quality is not equivalent to that of larger conventional satellites. variations in orbital configuration and sensor-specific spectral response functions represent an additional limitation. here, we exploit a cubesat enabled spatio-temporal enhancement method (cestem) to optimize the utility and quality of very high-resolution cubesat imaging. cestem represents a multipurpose data-driven scheme for radiometric normalization, phenology reconstruction, and spatiotemporal enhancement of biophysical properties via synergistic use of cubesat, landsat 8, and modis observations. phenological reconstruction, based on original cubesat normalized difference vegetation index (ndvi) data derived from top of atmosphere or surface reflectances, is shown to be susceptible to large uncertainties. in comparison, a cestem-corrected ndvi time series is able to clearly resolve several consecutive multicut alfalfa growing seasons over a six-month period, in addition to providing precise timing of key phenological transitions. cestem adopts a random forest machine-learning approach for producing landsat-consistent leaf area index (lai) at the cubesat scale with a relative mean absolute difference on the order of 4–6%. the cubesat-based lai estimates highlight the spatial resolution advantage and capability to provide temporally consistent and time-critical insights into within-field vegetation dynamics, the rate of vegetation green-up, and the timing of harvesting events that are otherwise missed by 8- to 16-day landsat imagery. | daily retrieval of ndvi and lai at 3 m resolution via the fusion of cubesat, landsat, and modis data |
the conduction of heat through minerals and melts at extreme pressures and temperatures is of central importance to the evolution and dynamics of planets. in the cooling earth’s core, the thermal conductivity of iron alloys defines the adiabatic heat flux and therefore the thermal and compositional energy available to support the production of earth’s magnetic field via dynamo action. attempts to describe thermal transport in earth’s core have been problematic, with predictions of high thermal conductivity at odds with traditional geophysical models and direct evidence for a primordial magnetic field in the rock record. measurements of core heat transport are needed to resolve this difference. here we present direct measurements of the thermal conductivity of solid iron at pressure and temperature conditions relevant to the cores of mercury-sized to earth-sized planets, using a dynamically laser-heated diamond-anvil cell. our measurements place the thermal conductivity of earth’s core near the low end of previous estimates, at 18-44 watts per metre per kelvin. the result is in agreement with palaeomagnetic measurements indicating that earth’s geodynamo has persisted since the beginning of earth’s history, and allows for a solid inner core as old as the dynamo. | direct measurement of thermal conductivity in solid iron at planetary core conditions |
satellite-based rainfall estimates over land have great potential for a wide range of applications, but their validation is challenging due to the scarcity of ground-based observations of rainfall in many areas of the planet. recent studies have suggested the use of triple collocation (tc) to characterize uncertainties associated with rainfall estimates by using three collocated rainfall products. however, tc requires the simultaneous availability of three products with mutually uncorrelated errors, a requirement which is difficult to satisfy with current global precipitation data sets.in this study, a recently developed method for rainfall estimation from soil moisture observations, sm2rain, is demonstrated to facilitate the accurate application of tc within triplets containing two state-of-the-art satellite rainfall estimates and a reanalysis product. the validity of different tc assumptions are indirectly tested via a high-quality ground rainfall product over the contiguous united states (conus), showing that sm2rain can provide a truly independent source of rainfall accumulation information which uniquely satisfies the assumptions underlying tc. on this basis, tc is applied with sm2rain on a global scale in an optimal configuration to calculate, for the first time, reliable global correlations (vs. an unknown truth) of the aforementioned products without using a ground benchmark data set.the analysis is carried out during the period 2007-2012 using daily rainfall accumulation products obtained at 1° × 1° spatial resolution. results convey the relatively high performance of the satellite rainfall estimates in eastern north and south america, southern africa, southern and eastern asia, eastern australia, and southern europe, as well as complementary performances between the reanalysis product and sm2rain, with the first performing reasonably well in the northern hemisphere and the second providing very good performance in the southern hemisphere.the methodology presented in this study can be used to identify the best rainfall product for hydrologic models with sparsely gauged areas and provide the basis for an optimal integration among different rainfall products. | an assessment of the performance of global rainfall estimates without ground-based observations |
we present a survey at subarcsecond resolution of the 340 ghz dust continuum emission from 50 nearby protoplanetary disks, based on new and archival observations with the submillimeter array. the observed visibility data were modeled with a simple prescription for the radial surface brightness profile. the results were used to extract intuitive, empirical estimates of the emission “size” for each disk, {r}{eff}, defined as the radius that encircles a fixed fraction of the total continuum luminosity, {l}{mm}. we find a significant correlation between the sizes and luminosities, such that {r}{eff}\propto {l}{mm}0.5, providing a confirmation and quantitative characterization of a putative trend that was noted previously. this correlation suggests that these disks have roughly the same average surface brightness interior to their given effective radius, ∼0.2 jy arcsec-2 (or 8 k in brightness temperature). the same trend remains, but the 0.2 dex of dispersion perpendicular to this relation essentially disappears, when we account for the irradiation environment of each disk with a crude approximation of the dust temperatures based on the stellar host luminosities. we consider two (not mutually exclusive) explanations for the origin of this size-luminosity relationship. simple models of the growth and migration of disk solids can account for the observed trend for a reasonable range of initial conditions, but only on timescales that are much shorter than the nominal ages present in the sample. an alternative scenario invokes optically thick emission concentrated on unresolved scales, with filling factors of a few tens of percent, which is perhaps a manifestation of localized particle traps. | a millimeter continuum size-luminosity relationship for protoplanetary disks |
comparing compositional models of the terrestrial planets provides insights into physicochemical processes that produced planet-scale similarities and differences. the widely accepted compositional model for mars assumes mn and more refractory elements are in ci chondrite proportions in the planet, including fe, mg, and si, which along with o make up >90% of the mass of mars. however, recent improvements in our understandings on the composition of the solar photosphere and meteorites challenge the use of ci chondrite as an analog of mars. here we present an alternative model composition for mars that avoids such an assumption and is based on data from martian meteorites and spacecraft observations. our modeling method was previously applied to predict the earth's composition. the model establishes the absolute abundances of refractory lithophile elements in the bulk silicate mars (bsm) at 2.26 times higher than that in ci carbonaceous chondrites. relative to this chondritic composition, mars has a systematic depletion in moderately volatile lithophile elements as a function of their condensation temperatures. given this finding, we constrain the abundances of siderophile and chalcophile elements in the bulk mars and its core. the martian volatility trend is consistent with ⩽ 7 wt% s in its core, which is significantly lower than that assumed in most core models (i.e., >10 wt% s). furthermore, the occurrence of ringwoodite at the martian core-mantle boundary might have contributed to the partitioning of o and h into the martian core. | the composition of mars |
the early earth’s environment is controversial. climatic estimates range from hot to glacial, and inferred marine ph spans strongly alkaline to acidic. better understanding of early climate and ocean chemistry would improve our knowledge of the origin of life and its coevolution with the environment. here, we use a geological carbon cycle model with ocean chemistry to calculate self-consistent histories of climate and ocean ph. our carbon cycle model includes an empirically justified temperature and ph dependence of seafloor weathering, allowing the relative importance of continental and seafloor weathering to be evaluated. we find that the archean climate was likely temperate (0-50 °c) due to the combined negative feedbacks of continental and seafloor weathering. ocean ph evolves monotonically from 6.6-0.4+0.6 (2σ) at 4.0 ga to 7.0-0.5+0.7 (2σ) at the archean-proterozoic boundary, and to 7.9-0.2+0.1 (2σ) at the proterozoic-phanerozoic boundary. this evolution is driven by the secular decline of pco2, which in turn is a consequence of increasing solar luminosity, but is moderated by carbonate alkalinity delivered from continental and seafloor weathering. archean seafloor weathering may have been a comparable carbon sink to continental weathering, but is less dominant than previously assumed, and would not have induced global glaciation. we show how these conclusions are robust to a wide range of scenarios for continental growth, internal heat flow evolution and outgassing history, greenhouse gas abundances, and changes in the biotic enhancement of weathering. | constraining the climate and ocean ph of the early earth with a geological carbon cycle model |
we report the discovery of a white dwarf exhibiting deep, irregularly shaped transits, indicative of circumstellar planetary debris. using zwicky transient facility dr2 photometry of ztf j013906.17+524536.89 and follow-up observations from the las cumbres observatory, we identify multiple transit events that recur every ≈107.2 days, much longer than the 4.5-4.9 hr orbital periods observed in wd 1145+017, the only other white dwarf known with transiting planetary debris. the transits vary in both depth and duration, lasting 15-25 days and reaching 20%-45% dips in flux. optical spectra reveal strong balmer lines, identifying the white dwarf as a da with ${t}_{\mathrm{eff}}=10,530\pm 140\,{\rm{k}}$ and $\mathrm{log}(g)=7.86\pm 0.06$ . a ca ii k absorption feature is present in all spectra both in and out of transit. spectra obtained during one night at roughly 15% transit depth show increased ca ii k absorption with a model atmospheric fit suggesting [ca/h] = -4.6 ± 0.3, whereas spectra taken on three nights out of transit have [ca/h] of -5.5, -5.3, and -4.9 with similar uncertainties. while the ca ii k line strength varies by only 2σ, we consider a predominantly interstellar origin for ca absorption unlikely. we suggest a larger column density of circumstellar metallic gas along the line of site or increased accretion of material onto the white dwarf's surface are responsible for the ca absorption, but further spectroscopic studies are required. in addition, high-speed time series photometry out of transit reveals variability with periods of 900 and 1030 s, consistent with zz ceti pulsations. | a white dwarf with transiting circumstellar material far outside the roche limit |
planet-disk interactions, where an embedded massive body interacts gravitationally with the protoplanetary disk it was formed in, can play an important role in reshaping both the disk and the orbit of the planet. spiral density waves are launched into the disk by the planet, which, if they are strong enough, can lead to the formation of a gap. both effects are observable with current instruments. the back-reaction of perturbations induced in the disk, both wave-like and non-wavelike, is a change in orbital elements of the planet. the efficiency of orbital migration is a long-standing problem in planet formation theory. we discuss recent progress in planet-disk interactions for different planet masses and disk parameters, in particular the level of turbulence, and progress in modeling observational signatures of embedded planets | planet-disk interactions and orbital evolution |
the past 5 years have dramatically changed our view of the disks of gas and dust around young stars. observations with the atacama large millimeter/submillimeter array (alma) and extreme adaptive optics systems have revealed that disks are dynamical systems. most disks contain resolved structures, both in gas and dust, including rings, gaps, spirals, azimuthal dust concentrations, shadows cast by misaligned inner disks, as well as deviations from keplerian rotation. the origin of these structures and how they relate to the planet formation process remain poorly understood. spatially resolved kinematic studies offer a new and necessary window to understand and quantify the physical processes (turbulence, winds, radial and meridional flows, stellar multiplicity, instabilities) at play during planet formation and disk evolution. recent progress, driven mainly by resolved alma observations, includes the detection and mass determination of embedded planets, the mapping of the gas flow around the accreting planets, the confirmation of tidal interactions and warped disk geometries, and stringent limits on the turbulent velocities. in this chapter, we will review our current understanding of these dynamical processes and highlight how kinematic mapping provides new ways to observe planet formation in action. | kinematic structures in planet-forming disks |
the central molecular zone (cmz) is a ring-like accumulation of molecular gas in the innermost few hundred parsecs of the milky way, generated by the inward transport of matter driven by the galactic bar. the cmz is the most extreme star-forming environment in the galaxy. the unique combination of large-scale dynamics and extreme interstellar medium conditions, characterized by high densities, temperatures, pressures, turbulent motions, and strong magnetic fields, make the cmz an ideal region for testing current star and planet formation theories. we review the recent observational and theoretical advances in the field, and combine these to draw a comprehensive, multi-scale and multi-physics picture of the cycle of matter and energy in the context of star formation in the closest galactic nucleus. | star formation in the central molecular zone of the milky way |
the deep atmosphere venus investigation of noble gases, chemistry, and imaging (davinci) mission described herein has been selected for flight to venus as part of the nasa discovery program. davinci will be the first mission to venus to incorporate science-driven flybys and an instrumented descent sphere into a unified architecture. the anticipated scientific outcome will be a new understanding of the atmosphere, surface, and evolutionary path of venus as a possibly once-habitable planet and analog to hot terrestrial exoplanets. the primary mission design for davinci as selected features a preferred launch in summer/fall 2029, two flybys in 2030, and descent-sphere atmospheric entry by the end of 2031. the in situ atmospheric descent phase subsequently delivers definitive chemical and isotopic composition of the venus atmosphere during an atmospheric transect above alpha regio. these in situ investigations of the atmosphere and near-infrared (nir) descent imaging of the surface will complement remote flyby observations of the dynamic atmosphere, cloud deck, and surface nir emissivity. the overall mission yield will be at least 60 gbits (compressed) new data about the atmosphere and near surface, as well as the first unique characterization of the deep atmosphere environment and chemistry, including trace gases, key stable isotopes, oxygen fugacity, constraints on local rock compositions, and topography of a tessera. | revealing the mysteries of venus: the davinci mission |
this report continues the practice where the iau working group on cartographic coordinates and rotational elements revises recommendations regarding those topics for the planets, satellites, minor planets, and comets approximately every 3 years. the working group has now become a "functional working group" of the iau, and its membership is open to anyone interested in participating. we describe the procedure for submitting questions about the recommendations given here or the application of these recommendations for creating a new or updated coordinate system for a given body. regarding body orientation, the following bodies have been updated: mercury, based on messenger results; mars, along with a refined longitude definition; phobos; deimos; (1) ceres; (52) europa; (243) ida; (2867) šteins; neptune; (134340) pluto and its satellite charon; comets 9p/tempel 1, 19p/borrelly, 67p/churyumov-gerasimenko, and 103p/hartley 2, noting that such information is valid only between specific epochs. the special challenges related to mapping 67p/churyumov-gerasimenko are also discussed. approximate expressions for the earth have been removed in order to avoid confusion, and the low precision series expression for the moon's orientation has been removed. the previously online only recommended orientation model for (4) vesta is repeated with an explanation of how it was updated. regarding body shape, text has been included to explain the expected uses of such information, and the relevance of the cited uncertainty information. the size of the sun has been updated, and notation added that the size and the ellipsoidal axes for the earth and jupiter have been recommended by an iau resolution. the distinction of a reference radius for a body (here, the moon and titan) is made between cartographic uses, and for orthoprojection and geophysical uses. the recommended radius for mercury has been updated based on messenger results. the recommended radius for titan is returned to its previous value. size information has been updated for 13 other saturnian satellites and added for aegaeon. the sizes of pluto and charon have been updated. size information has been updated for (1) ceres and given for (16) psyche and (52) europa. the size of (25143) itokawa has been corrected. in addition, the discussion of terminology for the poles (hemispheres) of small bodies has been modified and a discussion on cardinal directions added. although they continue to be used for planets and their satellites, it is assumed that the planetographic and planetocentric coordinate system definitions do not apply to small bodies. however, planetocentric and planetodetic latitudes and longitudes may be used on such bodies, following the right-hand rule. we repeat our previous recommendations that planning and efforts be made to make controlled cartographic products; newly recommend that common formulations should be used for orientation and size; continue to recommend that a community consensus be developed for the orientation models of jupiter and saturn; newly recommend that historical summaries of the coordinate systems for given bodies should be developed, and point out that for planets and satellites planetographic systems have generally been historically preferred over planetocentric systems, and that in cases when planetographic coordinates have been widely used in the past, there is no obvious advantage to switching to the use of planetocentric coordinates. the working group also requests community input on the question submitting process, posting of updates to the working group website, and on whether recommendations should be made regarding exoplanet coordinate systems. | report of the iau working group on cartographic coordinates and rotational elements: 2015 |
water ice is one of the most abundant materials in dense molecular clouds and in the outer reaches of protoplanetary disks. in contrast to other materials (e.g., silicates), water ice is assumed to be stickier due to its higher specific surface energy, leading to faster or more efficient growth in mutual collisions. however, experiments investigating the stickiness of water ice have been scarce, particularly in the astrophysically relevant micrometer-sized region and at low temperatures. in this work, we present an experimental setup to grow aggregates composed of μm-sized water-ice particles, which we used to measure the sticking and erosion thresholds of the ice particles at different temperatures between 114 k and 260 k. we show with our experiments that for low temperatures (below ~210 k), μm-sized water-ice particles stick below a threshold velocity of 9.6 m s-1, which is approximately 10 times higher than the sticking threshold of μm-sized silica particles. furthermore, erosion of the grown ice aggregates is observed for velocities above 15.3 m s-1. a comparison of the experimentally derived sticking threshold with model predictions is performed to determine important material properties of water ice, i.e., the specific surface energy and the viscous relaxation time. our experimental results indicate that the presence of water ice in the outer reaches of protoplanetary disks can enhance the growth of planetesimals by direct sticking of particles. | the stickiness of micrometer-sized water-ice particles |
context. atmospheric properties of exoplanets can be constrained with transit spectroscopy. at low spectral resolution, this technique is limited by the presence of clouds. the signature of atomic sodium (na i), known to be present above the clouds, is a powerful probe of the upper atmosphere, where it can be best detected and characterized at high spectral resolution.aims: our goal is to obtain a high-resolution transit spectrum of hd 189733b in the region around the resonance doublet of na i at 589 nm, to characterize the absorption signature that was previously detected from space at low resolution.methods: we analyzed archival transit data of hd 189733b obtained with the harps spectrograph (ℛ = 115 000) at the eso 3.6-m telescope. we performed differential spectroscopy to retrieve the transit spectrum and light curve of the planet, implementing corrections for telluric contamination and planetary orbital motion. we compared our results to synthetic transit spectra calculated from isothermal models of the planetary atmosphere.results: we spectrally resolve the na i d doublet and measure line contrasts of 0.64 ± 0.07% (d2) and 0.40 ± 0.07% (d1) and fwhms of 0.52 ± 0.08 å. this corresponds to a detection at the 10σ level of excess of absorption of 0.32 ± 0.03% in a passband of 2 × 0.75 å centered on each line. we derive temperatures of 2600 ± 600 k and 3270 ± 330 k at altitudes of 9800 ± 2800 and 12 700 ± 2600 km in the na i d1 and d2 line cores, respectively. we measure a temperature gradient of ~0.2 k km-1 in the region where the sodium absorption dominates the haze absorption from a comparison with theoretical models. we also detect a blueshift of 0.16 ± 0.04 å (4σ) in the line positions. this blueshift may be the result of winds blowing at 8 ± 2 km s-1 in the upper layers of the atmosphere.conclusions: we demonstrate the relevance of studying exoplanet atmospheres with high-resolution spectrographs mounted on 4-m-class telescopes. our results pave the way for an in-depth characterization of physical conditions in the atmospheres of many exoplanetary systems with future spectrographs such as espresso on the vlt or hires and metis on the e-elt. using observations with the harps spectrograph from the eso 3.6 m installed at la silla, in chile, under the allocated programmes 072.c-0488(e), 079.c-0828(a) and 079.c-0127(a). | spectrally resolved detection of sodium in the atmosphere of hd 189733b with the harps spectrograph |
young exoplanets are snapshots of the planetary evolution process. planets that orbit stars in young associations are particularly important because the age of the planetary system is well constrained. we present the discovery of a transiting planet larger than neptune but smaller than saturn in the 45 myr tucana-horologium young moving group. the host star is a visual binary, and our follow-up observations demonstrate that the planet orbits the g6v primary component, ds tuc a (hd 222259a, tic 410214986). we first identified transits using photometry from the transiting exoplanet survey satellite (tess; alerted as toi 200.01). we validated the planet and improved the stellar parameters using a suite of new and archival data, including spectra from southern astrophysical research/goodman, south african extremely large telescope/high resolution spectrograph and las cumbres observatories/network of robotic echelle spectrographs; transit photometry from spitzer; and deep adaptive optics imaging from gemini/gemini planet imager. no additional stellar or planetary signals are seen in the data. we measured the planetary parameters by simultaneously modeling the photometry with a transit model and a gaussian process to account for stellar variability. we determined that the planetary radius is 5.70 ± 0.17 r ⊕ and that the orbital period is 8.1 days. the inclination angles of the host star’s spin axis, the planet’s orbital axis, and the visual binary’s orbital axis are aligned within 15° to within the uncertainties of the relevant data. ds tuc ab is bright enough (v = 8.5) for detailed characterization using radial velocities and transmission spectroscopy. | tess hunt for young and maturing exoplanets (thyme): a planet in the 45 myr tucana-horologium association |
using new data from the k2 mission, we show that wasp-47, a previously known hot jupiter host, also hosts two additional transiting planets: a neptune-sized outer planet and a super-earth inner companion. we measure planetary properties from the k2 light curve and detect transit timing variations (ttvs), confirming the planetary nature of the outer planet. we performed a large number of numerical simulations to study the dynamical stability of the system and to find the theoretically expected ttvs. the theoretically predicted ttvs are in good agreement with those observed, and we use the ttvs to determine the masses of two planets, and place a limit on the third. the wasp-47 planetary system is important because companion planets can both be inferred by ttvs and are also detected directly through transit observations. the depth of the hot jupiter's transits make ground-based ttv measurements possible, and the brightness of the host star makes it amenable for precise radial velocity measurements. the system serves as a rosetta stone for understanding ttvs as a planet detection technique. | wasp-47: a hot jupiter system with two additional planets discovered by k2 |
earth has had oceans for nearly four billion years1 and mars had lakes and rivers 3.5-3.8 billion years ago2. however, it is still unknown whether water has ever condensed on the surface of venus3,4 because the planet—now completely dry5—has undergone global resurfacing events that obscure most of its history6,7. the conditions required for water to have initially condensed on the surface of solar system terrestrial planets are highly uncertain, as they have so far only been studied with one-dimensional numerical climate models3 that cannot account for the effects of atmospheric circulation and clouds, which are key climate stabilizers. here we show using three-dimensional global climate model simulations of early venus and earth that water clouds—which preferentially form on the nightside, owing to the strong subsolar water vapour absorption—have a strong net warming effect that inhibits surface water condensation even at modest insolations (down to 325 watts per square metre, that is, 0.95 times the earth solar constant). this shows that water never condensed and that, consequently, oceans never formed on the surface of venus. furthermore, this shows that the formation of earth's oceans required much lower insolation than today, which was made possible by the faint young sun. this also implies the existence of another stability state for present-day earth: the `steam earth', with all the water from the oceans evaporated into the atmosphere. | day-night cloud asymmetry prevents early oceans on venus but not on earth |
recent observations of extrasolar gas giants suggest super-stellar c/o ratios in planetary atmospheres, while interior models of observed extrasolar giant planets additionally suggest high heavy element contents. furthermore, recent observations of protoplanetary disks revealed super-solar c/h ratios, which are explained by inward drifting and evaporating pebbles enhancing the volatile content of the disk. we investigate in this work how the inward drift and evaporation of volatile-rich pebbles influences the atmospheric c/o ratio and heavy element content of giant planets growing by pebble and gas accretion. to achieve this goal, we perform semi-analytical 1d models of protoplanetary disks, including the treatment of viscous evolution and heating, pebble drift, and simple chemistry to simulate the growth of planets from planetary embryos to jupiter-mass objects by the accretion of pebbles and gas while they migrate through the disk. our simulations show that the composition of the planetary gas atmosphere is dominated by the accretion of vapor that originates from inward drifting evaporating pebbles at evaporation fronts. this process allows the giant planets to harbor large heavy element contents, in contrast to models that do not take pebble evaporation into account. in addition, our model reveals that giant planets originating farther away from the central star have a higher c/o ratio on average due to the evaporation of methane-rich pebbles in the outer disk. these planets can then also harbor super-solar c/o ratios, in line with exoplanet observations. however, planets formed in the outer disk harbor a smaller heavy element content due to a smaller vapor enrichment of the outer disk compared to the inner disk, where the very abundant water ice also evaporates. our model predicts that giant planets with low or large atmospheric c/o should harbor a large or low total heavy element content. we further conclude that the inclusion of pebble evaporation at evaporation lines is a key ingredient for determining the heavy element content and composition of giant planets. | how drifting and evaporating pebbles shape giant planets. i. heavy element content and atmospheric c/o |
since the discovery of the multiring structure of the hl tau disk, alma data suggest that the dust continuum emission of many, if not all, protoplanetary disks consists of rings and gaps, no matter their spectral type or age. the origin of these gaps so far remains unclear. we present a sample study of 16 disks with multiple ring-like structures in the continuum, using published alma archival data, to compare their morphologies and gap locations in a systematic way. the 16 targets range from early- to late-type stars, from <0.5 myr to >10 myr and from ∼0.2 to 40 l ⊙, and include both full and transitional disks with cleared inner dust cavities. stellar ages are revised using new gaia distances. gap locations are derived using a simple radial fit to the intensity profiles. using a radiative transfer model, the temperature profiles are computed. the gap radii generally do not correspond to the orbital radii of snow lines of the most common molecules. a snow line model can likely be discarded as a common origin of multiring systems. in addition, there are no systematic trends in the gap locations that could be related to resonances of planets. finally, the outer radius of the disks decreases for the oldest disks in the sample, indicating that if multiring disks evolve in a similar way, outer dust rings either dissipate with the gas or grow into planetesimal belts. | protoplanetary disk rings and gaps across ages and luminosities |
we present an overview of the sample of northern hemisphere white dwarfs within 40 pc of the sun detected from gaia data release 2 (dr2). we find that 521 sources are spectroscopically confirmed degenerate stars, 111 of which were first identified as white dwarf candidates from gaia dr2 and followed up recently with the william herschel telescope and gran telescopio canarias. three additional white dwarf candidates remain spectroscopically unobserved and six unresolved binaries are known to include a white dwarf but were not in our initial selection in the gaia dr2 hertzsprung-russell diagram. atmospheric parameters are calculated from gaia and pan-starrs photometry for all objects in the sample, confirming most of the trends previously observed in the much smaller 20 pc sample. local white dwarfs are overwhelmingly consistent with galactic disc kinematics, with only four halo candidates. we find that daz white dwarfs are significantly less massive than the overall da population ( $\overline{m}_\mathrm{daz}$ = 0.59 m⊙, $\overline{m}_\mathrm{da}$ = 0.66 m⊙). it may suggest that planet formation is less efficient at higher mass stars, producing more massive white dwarfs. we detect a sequence of crystallized white dwarfs in the mass range from 0.6 $\lesssim m/\mbox{$\mathrm{m}_\odot $}\ \lesssim$ 1.0 and find that the vast majority of objects on the sequence have standard kinematic properties that correspond to the average of the sample, suggesting that their nature can be explained by crystallization alone. we also detect 26 double degenerates and white dwarf components in 56 wide binary systems. | gaia white dwarfs within 40 pc ii: the volume-limited northern hemisphere sample |
the atmospheric northward energy transport plays a crucial role for the arctic climate; this transport brings to the arctic an amount of energy comparable to that provided directly by the sun. the transport is accomplished by atmospheric waves-for instance large-scale planetary waves and meso-scale cyclones-and the zonal-mean circulation. these different components of the energy transport impact the arctic climate differently.a split of the transport into stationary and transient waves constitutes a traditional way of decomposing the transport. however this procedure does not take into account the transport accomplished separately by the planetary and synoptic-scale waves. here a fourier decomposition is applied, which decomposes the transport with respect to zonal wave numbers. reanalysis and model data reveal that the planetary waves impact arctic temperatures much more than do synoptic-scale waves. in addition the latent transport by these waves affects the arctic climate more than does the dry-static part. finally, the ec-earth model suggests that changes of the energy transport over the twentyfirst century will contribute to arctic warming, despite the fact that in this model the total energy transport to the arctic will decrease. this apparent contradictory result is due to the cooling induced by a decrease of the dry-static transport by planetary waves being more than compensated for by a warming caused by the latent counterpart. | arctic amplification enhanced by latent energy transport of atmospheric planetary waves |
we present a study on the effect of undetected stellar companions on the derived planetary radii for kepler objects of interest (kois). the current production of the koi list assumes that each koi is a single star. not accounting for stellar multiplicity statistically biases the planets toward smaller radii. the bias toward smaller radii depends on the properties of the companion stars and whether the planets orbit the primary or the companion stars. defining a planetary radius correction factor, xr, we find that if the kois are assumed to be single, then, on average, the planetary radii may be underestimated by a factor of < {{x}r}> ≈ 1.5. if typical radial velocity and high-resolution imaging observations are performed and no companions are detected, then this factor reduces to < {{x}r}> ≈ 1.2. the correction factor < {{x}r}> is dependent on the primary star properties and ranges from < {{x}r}> ≈ 1.6 for a and f stars to < {{x}r}> ≈ 1.2 for k and m stars. for missions like k2 and tess where the stars may be closer than the stars in the kepler target sample, observational vetting (primary imaging) reduces the radius correction factor to < {{x}r}> ≈ 1.1. finally, we show that if the stellar multiplicity rates are not accounted for correctly, then occurrence rate calculations for earth-sized planets may overestimate the frequency of small planets by as much as 15%-20%. | understanding the effects of stellar multiplicity on the derived planet radii from transit surveys: implications for kepler, k2, and tess |
binary interactions dominate the evolution of massive stars, but their role is less clear for low- and intermediate-mass stars. the evolution of a spherical wind from an asymptotic giant branch (agb) star into a nonspherical planetary nebula (pn) could be due to binary interactions. we observed a sample of agb stars with the atacama large millimeter/submillimeter array (alma) and found that their winds exhibit distinct nonspherical geometries with morphological similarities to planetary nebulae (pne). we infer that the same physics shapes both agb winds and pne; additionally, the morphology and agb mass-loss rate are correlated. these characteristics can be explained by binary interaction. we propose an evolutionary scenario for agb morphologies that is consistent with observed phenomena in agb stars and pne. | (sub)stellar companions shape the winds of evolved stars |
pressure-driven shock waves in solid materials can cause extreme damage and deformation. understanding this deformation and the associated defects that are created in the material is crucial in the study of a wide range of phenomena, including planetary formation and asteroid impact sites, the formation of interstellar dust clouds, ballistic penetrators, spacecraft shielding and ductility in high-performance ceramics. at the lattice level, the basic mechanisms of plastic deformation are twinning (whereby crystallites with a mirror-image lattice form) and slip (whereby lattice dislocations are generated and move), but determining which of these mechanisms is active during deformation is challenging. experiments that characterized lattice defects have typically examined the microstructure of samples after deformation, and so are complicated by post-shock annealing and reverberations. in addition, measurements have been limited to relatively modest pressures (less than 100 gigapascals). in situ x-ray diffraction experiments can provide insights into the dynamic behaviour of materials, but have only recently been applied to plasticity during shock compression and have yet to provide detailed insight into competing deformation mechanisms. here we present x-ray diffraction experiments with femtosecond resolution that capture in situ, lattice-level information on the microstructural processes that drive shock-wave-driven deformation. to demonstrate this method we shock-compress the body-centred-cubic material tantalum—an important material for high-energy-density physics owing to its high shock impedance and high x-ray opacity. tantalum is also a material for which previous shock compression simulations and experiments have provided conflicting information about the dominant deformation mechanism. our experiments reveal twinning and related lattice rotation occurring on the timescale of tens of picoseconds. in addition, despite the common association between twinning and strong shocks, we find a transition from twinning to dislocation-slip-dominated plasticity at high pressure (more than 150 gigapascals), a regime that recovery experiments cannot accurately access. the techniques demonstrated here will be useful for studying shock waves and other high-strain-rate phenomena, as well as a broad range of processes induced by plasticity. | in situ x-ray diffraction measurement of shock-wave-driven twinning and lattice dynamics |
recognizing whether a planet can support life is a primary goal of future exoplanet spectral characterization missions, but past research on habitability assessment has largely ignored the vastly different conditions that have existed in our planet's long habitable history. this study presents simulations of a habitable yet dramatically different phase of earth's history, when the atmosphere contained a titan-like, organic-rich haze. prior work has claimed a haze-rich archean earth (3.8-2.5 billion years ago) would be frozen due to the haze's cooling effects. however, no previous studies have self-consistently taken into account climate, photochemistry, and fractal hazes. here, we demonstrate using coupled climate-photochemical-microphysical simulations that hazes can cool the planet's surface by about 20 k, but habitable conditions with liquid surface water could be maintained with a relatively thick haze layer (τ ∼ 5 at 200 nm) even with the fainter young sun. we find that optically thicker hazes are self-limiting due to their self-shielding properties, preventing catastrophic cooling of the planet. hazes may even enhance planetary habitability through uv shielding, reducing surface uv flux by about 97% compared to a haze-free planet and potentially allowing survival of land-based organisms 2.7-2.6 billion years ago. the broad uv absorption signature produced by this haze may be visible across interstellar distances, allowing characterization of similar hazy exoplanets. the haze in archean earth's atmosphere was strongly dependent on biologically produced methane, and we propose that hydrocarbon haze may be a novel type of spectral biosignature on planets with substantial levels of co2. hazy archean earth is the most alien world for which we have geochemical constraints on environmental conditions, providing a useful analogue for similar habitable, anoxic exoplanets. | the pale orange dot: the spectrum and habitability of hazy archean earth |
we present an update to the everest k2 pipeline that addresses various limitations in the previous version and improves the photometric precision of the light curves. we develop a fast regularization scheme for pixel-level decorrelation (pld) and adapt the algorithm to include the pld vectors of other stars to enhance the predictive power of the model and minimize overfitting, particularly for faint stars. we also modify pld to work for saturated stars and improve its performance on variable stars, although some high-frequency variables may still suffer from overfitting. on average, everest 2.0 light curves have 10-20% higher photometric precision than those in version 1, yielding the highest-precision light curves at all {kp} magnitudes of any publicly available k2 catalog. for most k2 campaigns, we recover the original kepler precision to at least {kp} = 14, and to at least {kp} = 15 for campaigns 1, 5, 6, and 13. we also detrend most short-cadence targets observed by k2, obtaining even higher photometric precision for these stars. like all aggressive, flexible models, everest is prone to overfitting, and may cause a decrease in transit depths by ∼10% we urge users to mask signals of interest using our open-source software, which we show removes this bias. light curves for campaigns 0-8 and 10-13 are available online in the everest catalog, which will be updated with future campaigns. everest 2.0 is open source and is coded in a framework that can be adapted to other photometric surveys, including kepler and the upcoming tess mission. | an update to the everest k2 pipeline: short cadence, saturated stars, and kepler-like photometry down to kp = 15 |
the isotopic composition of meteorites and terrestrial planets holds important clues about the earliest history of the solar system and the processes of planet formation. recent work has shown that meteorites exhibit a fundamental isotopic dichotomy between non-carbonaceous (nc) and carbonaceous (cc) groups, which most likely represent material from the inner and outer solar system, respectively. here we review the isotopic evidence for this nc-cc dichotomy, discuss its origin and highlight the far-reaching implications for the dynamics of the solar protoplanetary disk. the nc-cc dichotomy combined with the chronology of meteorite parent-body accretion mandate an early and prolonged spatial separation of inner (nc) and outer (cc) disk reservoirs, lasting between ~1 and ~4 myr after solar system formation. this is most easily reconciled with the early and rapid growth of jupiter's core, inhibiting substantial exchange of material from inside and outside its orbit. the growth and migration of jupiter also led to the later implantation of cc bodies into the inner solar system and, therefore, can explain the co-occurrence of nc and cc bodies in the asteroid belt, and the delivery of volatile and water-rich cc bodies to the terrestrial planets. | the great isotopic dichotomy of the early solar system |
ultracool dwarfs (ucd; teff < ∼3000 k) cool to settle on the main sequence after ∼1 gyr. for brown dwarfs, this cooling never stops. their habitable zones (hz) thus sweeps inward at least during the first gyr of their lives. assuming they possess water, planets found in the hz of ucds have experienced a runaway greenhouse phase too hot for liquid water prior to enter the hz. it has been proposed that such planets are desiccated by this hot early phase and enter the hz as dry worlds. here, we model the water loss during this pre-hz hot phase taking into account recent upper limits on the xuv emission of ucds and using 1d radiation-hydrodynamic simulations. we address the whole range of ucds but also focus on the planets recently found around the 0.08 m⊙ dwarf trappist-1. despite assumptions maximizing the fuv photolysis of water and the xuv-driven escape of hydrogen, we find that planets can retain significant amount of water in the hz of ucds, with a sweet spot in the 0.04-0.06 m⊙ range. we also studied the trappist-1 system using observed constraints on the xuv flux. we find that trappist-1b and c may have lost as much as 15 earth oceans and planet d - which might be inside the hz - may have lost less than 1 earth ocean. depending on their initial water contents, they could have enough water to remain habitable. trappist-1 planets are key targets for atmospheric characterization and could provide strong constraints on the water erosion around ucds. | water loss from terrestrial planets orbiting ultracool dwarfs: implications for the planets of trappist-1 |
giant exoplanets orbiting very close to their parent star (hot jupiters) are subject to tidal forces expected to synchronize their rotational and orbital periods on short timescales (tidal locking). however, spin rotation has never been measured directly for hot jupiters. furthermore, their atmospheres can show equatorial super-rotation via strong eastward jet streams, and/or high-altitude winds flowing from the day- to the night-side hemisphere. planet rotation and atmospheric circulation broaden and distort the planet spectral lines to an extent that is detectable with measurements at high spectral resolution. we observed a transit of the hot jupiter hd 189733 b around 2.3 μm and at a spectral resolution of r∼105 with crires at the eso very large telescope. after correcting for the stellar absorption lines and their distortion during transit (the rossiter-mclaughlin effect), we detect the absorption of carbon monoxide and water vapor in the planet transmission spectrum by cross-correlating with model spectra. the signal is maximized (7.6σ) for a planet rotational velocity of ({3.4}-2.1+1.3) km s-1, corresponding to a rotational period of ({1.7}-0.4+2.9) days. this is consistent with the planet orbital period of 2.2 days, and therefore with tidal locking. we find that the rotation of hd 189733 b is longer than 1 day (3σ). the data only marginally (1.5σ) prefer models with rotation versus models without rotation. we measure a small day- to night-side wind speed of (-{1.7}-1.2+1.1) km s-1. compared to the recent detection of sodium blueshifted by (8+/- 2) km s-1, this likely implies a strong vertical wind shear between the pressures probed by near-infrared and optical transmission spectroscopy. | rotation and winds of exoplanet hd 189733 b measured with high-dispersion transmission spectroscopy |
we present a consistent optimal estimation retrieval analysis of 10 hot jupiter exoplanets, each with transmission spectral data spanning the visible to near-infrared wavelength range. using the nemesis radiative transfer and retrieval tool, we calculate a range of possible atmospheric states for wasp-6b, wasp-12b, wasp-17b, wasp-19b, wasp-31b, wasp-39b, hd 189733b, hd 209458b, hat-p-1b, and hat-p-12b. we find that the spectra of all 10 planets are consistent with the presence of some atmospheric aerosol; wasp-6b, wasp-12b, wasp-17b, wasp-19b, hd 189733b, and hat-p-12b are all fit best by rayleigh scattering aerosols, whereas wasp-31b, wasp-39b and hd 209458b are better represented by a gray cloud model. hat-p-1b has solutions that fall into both categories. wasp-6b, hat-p-12b, hd 189733b, and wasp-12b must have aerosol extending to low atmospheric pressures (below 0.1 mbar). in general, planets with equilibrium temperatures between 1300 and 1700 k are best represented by deeper, gray cloud layers, whereas cooler or hotter planets are better fit using high rayleigh scattering aerosol. we find little evidence for the presence of molecular absorbers other than h2o. retrieval methods can provide a consistent picture across a range of hot jupiter atmospheres with existing data, and will be a powerful tool for the interpretation of james webb space telescope observations. | a consistent retrieval analysis of 10 hot jupiters observed in transmission |
nasa's plans for space exploration include a return to the moon to stay—boots back on the lunar surface with an orbital outpost. this station will be a launch point for voyages to destinations further away in our solar system, including journeys to the red planet mars. to ensure success of these missions, health and performance risks associated with the unique hazards of spaceflight must be adequately controlled. these hazards—space radiation, altered gravity fields, isolation and confinement, closed environments, and distance from earth—are linked with over 30 human health risks as documented by nasa's human research program. the programmatic goal is to develop the tools and technologies to adequately mitigate, control, or accept these risks. the risks ranked as "red" have the highest priority based on both the likelihood of occurrence and the severity of their impact on human health, performance in mission, and long-term quality of life. these include: (1) space radiation health effects of cancer, cardiovascular disease, and cognitive decrements (2) spaceflight-associated neuro-ocular syndrome (3) behavioral health and performance decrements, and (4) inadequate food and nutrition. evaluation of the hazards and risks in terms of the space exposome—the total sum of spaceflight and lifetime exposures and how they relate to genetics and determine the whole-body outcome—will provide a comprehensive picture of risk profiles for individual astronauts. in this review, we provide a primer on these "red" risks for the research community. the aim is to inform the development of studies and projects with high potential for generating both new knowledge and technologies to assist with mitigating multisystem risks to crew health during exploratory missions. | red risks for a journey to the red planet: the highest priority human health risks for a mission to mars |
flow in a stably stratified environment is characterized by anisotropic and intermittent turbulence and wavelike motions of varying amplitudes and periods. understanding turbulence intermittency and wave-turbulence interactions in a stably stratified flow remains a challenging issue in geosciences including planetary atmospheres and oceans. the stable atmospheric boundary layer (sabl) commonly occurs when the ground surface is cooled by longwave radiation emission such as at night over land surfaces, or even daytime over snow and ice surfaces, and when warm air is advected over cold surfaces. intermittent turbulence intensification in the sabl impacts human activities and weather variability, yet it cannot be generated in state-of-the-art numerical forecast models. this failure is mainly due to a lack of understanding of the physical mechanisms for seemingly random turbulence generation in a stably stratified flow, in which wave-turbulence interaction is a potential mechanism for turbulence intermittency. a workshop on wave-turbulence interactions in the sabl addressed the current understanding and challenges of wave-turbulence interactions and the role of wavelike motions in contributing to anisotropic and intermittent turbulence from the perspectives of theory, observations, and numerical parameterization. there have been a number of reviews on waves, and a few on turbulence in stably stratified flows, but not much on wave-turbulence interactions. this review focuses on the nocturnal sabl; however, the discussions here on intermittent turbulence and wave-turbulence interactions in stably stratified flows underscore important issues in stably stratified geophysical dynamics in general. | review of wave-turbulence interactions in the stable atmospheric boundary layer |
during the period from approximately 150 to 35 million years ago, the cretaceous-paleocene-eocene (cpe), the earth was in a "greenhouse" state with little or no ice at either pole. it was also a period of considerable global change, from the warmest periods of the mid-cretaceous, to the threshold of icehouse conditions at the end of the eocene. however, the relative contribution of palaeogeographic change, solar change, and carbon cycle change to these climatic variations is unknown. here, making use of recent advances in computing power, and a set of unique palaeogeographic maps, we carry out an ensemble of 19 general circulation model simulations covering this period, one simulation per stratigraphic stage. by maintaining atmospheric co2 concentration constant across the simulations, we are able to identify the contribution from palaeogeographic and solar forcing to global change across the cpe, and explore the underlying mechanisms. we find that global mean surface temperature is remarkably constant across the simulations, resulting from a cancellation of opposing trends from solar and palaeogeographic change. however, there are significant modelled variations on a regional scale. the stratigraphic stage-stage transitions which exhibit greatest climatic change are associated with transitions in the mode of ocean circulation, themselves often associated with changes in ocean gateways, and amplified by feedbacks related to emissivity and planetary albedo. we also find some control on global mean temperature from continental area and global mean orography. our results have important implications for the interpretation of single-site palaeo proxy records. in particular, our results allow the non-co2 (i.e. palaeogeographic and solar constant) components of proxy records to be removed, leaving a more global component associated with carbon cycle change. this "adjustment factor" is used to adjust sea surface temperatures, as the deep ocean is not fully equilibrated in the model. the adjustment factor is illustrated for seven key sites in the cpe, and applied to proxy data from falkland plateau, and we provide data so that similar adjustments can be made to any site and for any time period within the cpe. ultimately, this will enable isolation of the co2-forced climate signal to be extracted from multiple proxy records from around the globe, allowing an evaluation of the regional signals and extent of polar amplification in response to co2 changes during the cpe. finally, regions where the adjustment factor is constant throughout the cpe could indicate places where future proxies could be targeted in order to reconstruct the purest co2-induced temperature change, where the complicating contributions of other processes are minimised. therefore, combined with other considerations, this work could provide useful information for supporting targets for drilling localities and outcrop studies. | palaeogeographic controls on climate and proxy interpretation |
bed load sediment transport, in which wind or water flowing over a bed of sediment causes grains to roll or hop along the bed, is a critically important mechanism in contexts ranging from river restoration1 to planetary exploration2. despite its widespread occurrence, predictions of bed load sediment flux are notoriously imprecise3,4. many studies have focused on grain size variability5 as a source of uncertainty, but few have investigated the role of grain shape, even though shape has long been suspected to influence transport rates6. here we show that grain shape can modify bed load transport rates by an amount comparable to the scatter in many sediment transport datasets4,7,8. we develop a theory that accounts for grain shape effects on fluid drag and granular friction and predicts that the onset and efficiency of transport depend on the coefficients of drag and bulk friction of the transported grains. laboratory experiments confirm these predictions and reveal that the effect of grain shape on sediment transport can be difficult to intuit from the appearance of grains. we propose a shape-corrected sediment transport law that collapses our experimental measurements. our results enable greater accuracy in predictions of sediment transport and help reconcile theories developed for spherical particles with the behaviour of natural sediment grains. | grain shape effects in bed load sediment transport |
two >130-meter-diameter impact craters formed on mars during the later half of 2021. these are the two largest fresh impact craters discovered by the mars reconnaissance orbiter since operations started 16 years ago. the impacts created two of the largest seismic events (magnitudes greater than 4) recorded by insight during its 3-year mission. the combination of orbital imagery and seismic ground motion enables the investigation of subsurface and atmospheric energy partitioning of the impact process on a planet with a thin atmosphere and the first direct test of martian deep-interior seismic models with known event distances. the impact at 35°n excavated blocks of water ice, which is the lowest latitude at which ice has been directly observed on mars. | largest recent impact craters on mars: orbital imaging and surface seismic co-investigation |
observations of planet earth from space are a critical resource for science and society. satellite measurements represent very large investments and united states (us) agencies organize their effort to maximize the return on that investment. the us national research council conducts a survey of earth science and applications to prioritize observations for the coming decade. the most recent survey prioritized a visible to shortwave infrared imaging spectrometer and a multispectral thermal infrared imager to meet a range of needs for studying surface biology and geology (sbg). sbg will be the premier integrated observatory for observing the emerging impacts of climate change by characterizing the diversity of plant life and resolving chemical and physiological signatures. it will address wildfire risk, behavior, and recovery as well as responses to hazards such as oil spills, toxic minerals in minelands, harmful algal blooms, landslides, and other geological hazards. the sbg team analyzed needed instrument characteristics (spatial, temporal, and spectral resolutions, measurement uncertainty) and assessed the cost, mass, power, volume, and risk of different architectures. we present an overview of the research and applications trade-study analysis of algorithms, calibration and validation needs, and societal applications with specifics of substudies detailed in other articles in this special collection. we provide a value framework to converge from hundreds down to three candidate architectures recommended for development. the analysis identified valuable opportunities for international collaboration to increase the revisit frequency, adding value for all partners, leading to a clear measurement strategy for an observing system architecture. | designing an observing system to study the surface biology and geology (sbg) of the earth in the 2020s |
deep inside planets, extreme density, pressure, and temperature strongly modify the properties of the constituent materials. in particular, how much heat solids can sustain before melting under pressure is key to determining a planet’s internal structure and evolution. we report laser-driven shock experiments on fused silica, α-quartz, and stishovite yielding equation-of-state and electronic conductivity data at unprecedented conditions and showing that the melting temperature of sio2 rises to 8300 k at a pressure of 500 gigapascals, comparable to the core-mantle boundary conditions for a 5-earth mass super-earth. we show that mantle silicates and core metal have comparable melting temperatures above 500 to 700 gigapascals, which could favor long-lived magma oceans for large terrestrial planets with implications for planetary magnetic-field generation in silicate magma layers deep inside such planets. | shock compression of stishovite and melting of silica at planetary interior conditions |
symmetry-breaking transitions associated with the buckling and folding of curved multilayered surfaces—which are common to a wide range of systems and processes such as embryogenesis, tissue differentiation and structure formation in heterogeneous thin films or on planetary surfaces—have been characterized experimentally. yet owing to the nonlinearity of the underlying stretching and bending forces, the transitions cannot be reliably predicted by current theoretical models. here, we report a generalized swift-hohenberg theory that describes wrinkling morphology and pattern selection in curved elastic bilayer materials. by testing the theory against experiments on spherically shaped surfaces, we find quantitative agreement with analytical predictions for the critical curves separating labyrinth, hybrid and hexagonal phases. furthermore, a comparison to earlier experiments suggests that the theory is universally applicable to macroscopic and microscopic systems. our approach builds on general differential-geometry principles and can thus be extended to arbitrarily shaped surfaces. | curvature-induced symmetry breaking determines elastic surface patterns |
the tibetan plateau and its surrounding mountains have an average elevation of 4,400 m and a glaciated area of ∼100,000 km2 giving it the name "third pole (tp) region". the tp is the headwater of many major rivers in asia that provide fresh water to hundreds of millions of people. climate change is altering the energy and water cycle of the tp at a record pace but the future of this region is highly uncertain due to major challenges in simulating weather and climate processes in this complex area. the convection-permitting third pole (cptp) project is a coordinated regional downscaling experiment (cordex) flagship pilot study (fps) that aims to revolutionize our understanding of climate change impacts on the tp through ensemble-based, kilometer-scale climate modeling. here we present the experimental design and first results from multi-model, multi-physics ensemble simulations of three case studies. the five participating modeling systems show high performance across a range of meteorological situations and are close to having "observational quality" in simulating precipitation and near-surface temperature. this is partly due to the large differences between observational datasets in this region, which are the leading source of uncertainty in model evaluations. however, a systematic cold bias above 2000 m exists in most modeling systems. model physics sensitivity tests performed with the weather research and forecasting (wrf) model show that planetary boundary layer (pbl) physics and microphysics contribute equally to model uncertainties. additionally, larger domains result in better model performance. we conclude by describing high-priority research needs and the next steps in the cptp project. | towards ensemble-based kilometer-scale climate simulations over the third pole region |
intense lasers interacting with dense targets accelerate relativistic electron beams, which transport part of the laser energy into the target depth. however, the overall laser-to-target energy coupling efficiency is impaired by the large divergence of the electron beam, intrinsic to the laser-plasma interaction. here we demonstrate that an efficient guiding of mev electrons with about 30 ma current in solid matter is obtained by imposing a laser-driven longitudinal magnetostatic field of 600 t. in the magnetized conditions the transported energy density and the peak background electron temperature at the 60-μm-thick target's rear surface rise by about a factor of five, as unfolded from benchmarked simulations. such an improvement of energy-density flux through dense matter paves the ground for advances in laser-driven intense sources of energetic particles and radiation, driving matter to extreme temperatures, reaching states relevant for planetary or stellar science as yet inaccessible at the laboratory scale and achieving high-gain laser-driven thermonuclear fusion. | guiding of relativistic electron beams in dense matter by laser-driven magnetostatic fields |
an accurate description of the center-to-limb variation (clv) of stellar spectra is becoming an increasingly critical factor in both stellar and exoplanet characterization. in particular, the clv of spectral lines is extremely challenging as its characterization requires highly detailed knowledge of the stellar physical conditions. to this end, we present the numerical empirical sun-as-a-star integrator (nessi) as a tool for translating high-resolution solar observations of a partial field of view into disk-integrated spectra that can be used to test common assumptions in stellar physics. | center-to-limb variation of spectral lines and their effect on full-disk observations |
the jwst disk infrared spectral chemistry survey (jdiscs) aims to understand the evolution of the chemistry of inner protoplanetary disks using the mid-infrared instrument (miri) on the james webb space telescope (jwst). with a growing sample of >30 disks, the survey implements a custom method to calibrate the miri medium resolution spectrometer (mrs) to contrasts of better than 1:300 across its 4.9-28 micron spectral range. this is achieved using observations of themis-family asteroids as precise empirical reference sources. high spectral contrast enables precise retrievals of physical parameters, searches for rare molecular species and isotopologues, and constraints on the inventories of carbon- and nitrogen-bearing species. jdiscs also offers significant improvements to the mrs wavelength and resolving power calibration. we describe the jdiscs calibrated data and demonstrate its quality using observations of the disk around the solar-mass young star fz tau. the fz tau miri spectrum is dominated by strong emission from warm water vapor. we show that the water and co line emission originates from the disk surface and traces a range of gas temperatures of ~500-1500 k. we retrieve parameters for the observed co and h2o lines, and show that they are consistent with a radial distribution represented by two temperature components. a high water abundance of n(h2o)~10^-4 fills the disk surface at least out to the 350 k isotherm at 1.5 au. we search the fz tau environs for extended emission detecting a large (radius of ~300 au) ring of emission from h2 gas surrounding fz tau, and discuss its origin. | high-contrast jwst-miri spectroscopy of planet-forming disks for the jdisc survey |
wasp-12b is a transiting hot jupiter on a 1.09 day orbit around a late-f star. since the planet’s discovery in 2008, the time interval between transits has been decreasing by 29 ± 2 ms yr-1. this is a possible sign of orbital decay, although the previously available data left open the possibility that the planet’s orbit is slightly eccentric and is undergoing apsidal precession. here, we present new transit and occultation observations that provide more decisive evidence for orbital decay, which is favored over apsidal precession by a {{δ }}{bic} of 22.3 or bayes factor of 70,000. we also present new radial-velocity data that rule out the rømer effect as the cause of the period change. this makes wasp-12 the first planetary system for which we can be confident that the orbit is decaying. the decay timescale for the orbit is p/\dot{p}=3.25+/- 0.23 {myr}. interpreting the decay as the result of tidal dissipation, the modified stellar tidal quality factor is {q}\star {\prime }=1.8× {10}5. | the orbit of wasp-12b is decaying |
axisymmetric dust rings are a ubiquitous feature of young protoplanetary disks. these rings are likely caused by pressure bumps in the gas profile; a small bump can induce a traffic-jam-like pattern in the dust density, while a large bump may halt radial dust drift entirely. the resulting increase in dust concentration may trigger planetesimal formation by the streaming instability (si), as the si itself requires some initial concentration of dust. here we present the first 3d simulations of planetesimal formation in the presence of a pressure bump modeled specifically after those seen by atacama large millimeter/submillimeter array. we place a pressure bump at the center of a large 3d shearing box, along with an initial solid-to-gas ratio of z = 0.01, and we include both particle back-reaction and particle self-gravity. we consider millimeter-sized and centimeter-sized particles separately. for simulations with centimeter-sized particles, we find that even a small pressure bump leads to the formation of planetesimals via the si; a pressure bump does not need to fully halt radial particle drift for the si to become efficient. furthermore, pure gravitational collapse via concentration in pressure bumps (such as would occur at sufficiently high concentrations and without the si) is not responsible for planetesimal formation. for millimeter-sized particles, we find tentative evidence that planetesimal formation does not occur. if this result is confirmed at higher resolution, it could put strong constraints on where planetesimals can form. ultimately, our results show that for centimeter-sized particles planetesimal formation in pressure bumps is extremely robust. | protoplanetary disk rings as sites for planetesimal formation |
circumbinary accretion occurs throughout the universe, from the formation of stars and planets to the aftermath of major galactic mergers. we present an extensive investigation of circumbinary accretion disks, studying circular binaries with mass ratios ($q\equiv m_2/m_1$) from 0.01 to 1 and at each mass ratio probing the effects of disk thickness and viscosity. we study disks with aspect ratios $h/r\in\{0.1, 0.05, 0.033\}$, and vary both the magnitude and spatial dependance of viscosity. although thin accretion disks have previously been found to promote rapid inspirals of equal-mass binaries, we find that gravitational torques become weaker at lower mass ratios and most binaries with $0.01\leq q\leq0.04$ outspiral, which may delay the coalescence of black hole binaries formed from minor mergers and cause high-mass exoplanets to migrate outwards. however, in a number of cases, the disks accreting onto binaries with mass ratios $\sim 0.07$ fail to develop eccentric modes, leading to extremely rapid inspirals. variability in black hole accretion correlates with disk eccentricity, and we observe variability above the $\sim10\%$ level even for mass ratios of $0.01$. we demonstrate that the spatial dependence of the viscosity (e.g. $\alpha$ vs constant-$\nu$) significantly affects the degree of preferential accretion onto the secondary, resolving discrepancies between previous studies. colder circumbinary disks remain eccentric even at $q\sim0.01$ and sustain deep, asymmetric cavities. | the evolution of accreting binaries: from brown dwarfs to supermassive black holes |
the presence of an atmosphere over sufficiently long timescales is widely perceived as one of the most prominent criteria associated with planetary surface habitability. we address the crucial question of whether the seven earth-sized planets transiting the recently discovered ultracool dwarf star trappist-1 are capable of retaining their atmospheres. to this effect, we carry out numerical simulations to characterize the stellar wind of trappist-1 and the atmospheric ion escape rates for all of the seven planets. we also estimate the escape rates analytically and demonstrate that they are in good agreement with the numerical results. we conclude that the outer planets of the trappist-1 system are capable of retaining their atmospheres over billion-year timescales. the consequences arising from our results are also explored in the context of abiogenesis, biodiversity, and searches for future exoplanets. in light of the many unknowns and assumptions involved, we recommend that these conclusions must be interpreted with due caution. | atmospheric escape from the trappist-1 planets and implications for habitability |
the origins space telescope (origins) traces our cosmic history, from the formation of the first galaxies and the rise of metals to the development of habitable worlds and present-day life. origins does this through exquisite sensitivity to infrared radiation from ions, atoms, molecules, dust, water vapor and ice, and observations of extra-solar planetary atmospheres, protoplanetary disks, and large-area extragalactic fields. origins operates in the wavelength range 2.8 to 588 microns and is 1000 times more sensitive than its predecessors due to its large, cold (4.5 k) telescope and advanced instruments. origins was one of four large missions studied by the community with support from nasa and industry in preparation for the 2020 decadal survey in astrophysics. this is the final study report. | origins space telescope mission concept study report |
context. the discovery of proxima b marked one of the most important milestones in exoplanetary science in recent years. yet the limited precision of the available radial velocity data and the difficulty in modelling the stellar activity calls for a confirmation of the earth-mass planet.aims: we aim to confirm the presence of proxima b using independent measurements obtained with the new espresso spectrograph, and refine the planetary parameters taking advantage of its improved precision.methods: we analysed 63 spectroscopic espresso observations of proxima (gl 551) taken during 2019. we obtained radial velocity measurements with a typical radial velocity photon noise of 26 cm s-1. we combined these data with archival spectroscopic observations and newly obtained photometric measurements to model the stellar activity signals and disentangle them from planetary signals in the radial velocity (rv) data. we ran a joint markov chain monte carlo analysis on the time series of the rv and full width half maximum of the cross-correlation function to model the planetary and stellar signals present in the data, applying gaussian process regression to deal with the stellar activity signals.results: we confirm the presence of proxima b independently in the espresso data and in the combined espresso+ harps+uves dataset. the espresso data on its own shows proxima b at a period of 11.218 ± 0.029 days, with a minimum mass of 1.29 ± 0.13 m⊕. in the combined dataset we measure a period of 11.18427 ± 0.00070 days with a minimum mass of 1.173 ± 0.086 m⊕. we get a clear measurement of the stellar rotation period (87 ± 12 d) and its induced rv signal, but no evidence of stellar activity as a potential cause for the 11.2 days signal. we find some evidence for the presence of a second short-period signal, at 5.15 days with a semi-amplitude of only 40 cm s-1. if caused by a planetary companion, it would correspond to a minimum mass of 0.29 ± 0.08 m⊕. we find that forthe case of proxima, the full width half maximum of the cross-correlation function can be used as a proxy for the brightness changes and that its gradient with time can be used to successfully detrend the rv data from part of the influence of stellar activity. the activity-induced rv signal in the espresso data shows a trend in amplitude towards redder wavelengths. velocities measured using the red end of the spectrograph are less affected by activity, suggesting that the stellar activity is spot dominated. this could be used to create differential rvs that are activity dominated and can be used to disentangle activity-induced and planetary-induced signals. the data collected excludes the presence of extra companions with masses above 0.6 m⊕ at periods shorter than 50 days. the data used in this paper 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/a77 based [in part] on guaranteed time observations collected at the european southern observatory under eso programme 1102.c-0744. by the espresso consortium. this work makes use of observations from the lcogt network. | revisiting proxima with espresso |
we present the discovery and validation of a three-planet system orbiting the nearby (31.1 pc) m2 dwarf star toi-700 (tic 150428135). toi-700 lies in the tess continuous viewing zone in the southern ecliptic hemisphere; observations spanning 11 sectors reveal three planets with radii ranging from 1 r⊕ to 2.6 r⊕ and orbital periods ranging from 9.98 to 37.43 days. ground-based follow-up combined with diagnostic vetting and validation tests enables us to rule out common astrophysical false-positive scenarios and validate the system of planets. the outermost planet, toi-700 d, has a radius of 1.19 ± 0.11 r⊕ and resides within a conservative estimate of the host star's habitable zone, where it receives a flux from its star that is approximately 86% of earth's insolation. in contrast to some other low-mass stars that host earth-sized planets in their habitable zones, toi-700 exhibits low levels of stellar activity, presenting a valuable opportunity to study potentially rocky planets over a wide range of conditions affecting atmospheric escape. while atmospheric characterization of toi-700 d with the james webb space telescope (jwst) will be challenging, the larger sub-neptune, toi-700 c (r = 2.63 r⊕), will be an excellent target for jwst and future space-based observatories. tess is scheduled to once again observe the southern hemisphere, and it will monitor toi-700 for an additional 11 sectors in its extended mission. these observations should allow further constraints on the known planet parameters and searches for additional planets and transit timing variations in the system. | the first habitable-zone earth-sized planet from tess. i. validation of the toi-700 system |
the characterization of objects that have best preserved the mineralogical and molecular phases formed in the earliest stages of the solar system evolution is key to understanding the processes that led to the formation of the planets in their diversity. the hayabusa2 mission of the japan aerospace exploration agency has returned for the first time samples collected at the surface of a c-type asteroid, ryugu1,2. they are now preserved at the extraterrestrial samples curation center of the japan aerospace exploration agency at the institute of space and astronautical science in sagamihara, japan, where they are submitted to a first round of purely non-destructive analyses. the micromega hyperspectral microscope developed at the institut d'astrophysique spatiale (orsay, france), which operates in the near-infrared range (0.99-3.65 µm), is performing their mineralogical and molecular characterization down to the scale of a few tens of micrometres. strong features at 2.7 µm (indicating their oh-rich content) and at 3.4 µm (diagnostic of the presence of organics) dominate at a global scale, but key distinctive signatures have been identified at a submillimetre scale. in particular, carbonates (a fraction of them enriched in iron) as well as nh-rich compounds have been detected. the occurrence of volatile-rich species, likely originating from the outer solar system, would support ryugu having preserved both pristine material and altered phases, which are now available for refined laboratory analyses with the potential to draw new insights into the formation and evolution paths of planetary bodies in our solar system. | first compositional analysis of ryugu samples by the micromega hyperspectral microscope |
the james webb space telescope (jwst) is a large, infrared space telescope that has recently started its science program which will enable breakthroughs in astrophysics and planetary science. notably, jwst will provide the very first observations of the earliest luminous objects in the universe and start a new era of exoplanet atmospheric characterization. this transformative science is enabled by a 6.6 m telescope that is passively cooled with a 5 layer sunshield. the primary mirror is comprised of 18 controllable, low areal density hexagonal segments, that were aligned and phased relative to each other in orbit using innovative image-based wave front sensing and control algorithms. this revolutionary telescope took more than two decades to develop with a widely distributed team across engineering disciplines. we present an overview of the telescope requirements, architecture, development, superb on-orbit performance, and lessons learned. jwst successfully demonstrates a segmented aperture space telescope and establishes a path to building even larger space telescopes. | the james webb space telescope mission: optical telescope element design, development, and performance |
(abridged) we investigate the impact of radiative feedback from massive stars on their natal cloud and focus on the transition from the hii region to the atomic pdr (crossing the ionisation front (if)), and the subsequent transition to the molecular pdr (crossing the dissociation front (df)). we use high-resolution near-ir integral field spectroscopic data from nirspec on jwst to observe the orion bar pdr as part of the pdrs4all jwst early release science program. the nirspec data reveal a forest of lines including, but not limited to, hei, hi, and ci recombination lines, ionic lines, oi and ni fluorescence lines, aromatic infrared bands (aibs including aromatic ch, aliphatic ch, and their cd counterparts), co2 ice, pure rotational and ro-vibrational lines from h2, and ro-vibrational lines hd, co, and ch+, most of them detected for the first time towards a pdr. their spatial distribution resolves the h and he ionisation structure in the huygens region, gives insight into the geometry of the bar, and confirms the large-scale stratification of pdrs. we observe numerous smaller scale structures whose typical size decreases with distance from ori c and ir lines from ci, if solely arising from radiative recombination and cascade, reveal very high gas temperatures consistent with the hot irradiated surface of small-scale dense clumps deep inside the pdr. the h2 lines reveal multiple, prominent filaments which exhibit different characteristics. this leaves the impression of a "terraced" transition from the predominantly atomic surface region to the co-rich molecular zone deeper in. this study showcases the discovery space created by jwst to further our understanding of the impact radiation from young stars has on their natal molecular cloud and proto-planetary disk, which touches on star- and planet formation as well as galaxy evolution. | pdrs4all iii: jwst's nir spectroscopic view of the orion bar |
we present an analysis of atacama large millimeter/submillimeter array 1.25 mm continuum observations of spiral structures in three protoplanetary disks from the disk substructures at high angular resolution project. the disks around elias 27, im lup, and waoph 6 were observed at a resolution of ∼40-60 mas (∼6-7 au). all three disks feature m = 2 spiral patterns in conjunction with annular substructures. gas kinematics established by 12co j = 2-1 observations indicate that the continuum spiral arms are trailing. the arm-interarm intensity contrasts are modest, typically less than 3. the elias 27 spiral pattern extends throughout much of the disk, and the arms intersect the gap at r ∼ 69 au. the spiral pattern in the im lup disk is particularly complex—it extends about halfway radially through the disk, exhibiting pitch angle variations with radius and interarm features that may be part of ring substructures or spiral arm branches. spiral arms also extend most of the way through the waoph 6 disk, but the source overall is much more compact than the other two disks. we discuss possible origins for the spiral structures, including gravitational instability and density waves induced by a stellar or planetary companion. unlike the millimeter continuum counterparts of many of the disks with spiral arms detected in scattered light, these three sources do not feature high-contrast crescent-like asymmetries or large (r > 20 au) emission cavities. this difference may point to multiple spiral formation mechanisms operating in disks. | the disk substructures at high angular resolution project (dsharp). iii. spiral structures in the millimeter continuum of the elias 27, im lup, and waoph 6 disks |
aerocapture is the technique of using planetary atmospheres to decelerate a spacecraft in a single pass to achieve nearly fuel-free orbit insertion. aerocapture has been extensively studied since the 1980s but has never been flown yet. the entry conditions encountered during aerocapture are strongly destination dependent, and performance benefit offered by aerocapture is also destination dependent. aerocapture is applicable to all atmosphere-bearing destinations with the exception of jupiter and saturn, whose extreme entry conditions make aerocapture infeasible. a recent study by the nasa science mission directorate highlighted the need for baseline design reference missions, as a starting point for system level architecture studies. the present study uses the aerocapture mission analysis tool (amat) to compile a list of design reference missions at venus, earth, mars, titan, uranus, and neptune. these reference missions can provide an initial assessment of the feasibility of aerocapture for a proposed mission, and provide intial baseline values for more detailed system studies. the reference mission set provides a quick estimate of the entry conditions, control requirements, and aero-thermal loads for architectural level studies. | aerocapture design reference missions for solar system exploration: from venus to neptune |
the composition of giant planets is imprinted by their migration history and the compositional structure of their hosting disks. studies in recent literature have investigated how the abundances of c and o can constrain the formation pathways of giant planets forming within few tens of au from a star. new alma observations, however, suggest planet-forming regions possibly extending to hundreds of au. we explore the implications of these wider formation environments through n-body simulations of growing and migrating giant planets embedded in planetesimal disks, coupled with a compositional model of the protoplanetary disk where volatiles are inherited from the molecular cloud and refractories are calibrated against extrasolar and solar system data. we find that the c/o ratio provides limited insight on the formation pathways of giant planets that undergo large-scale migration. this limitation can be overcome, however, thanks to nitrogen and sulfur. jointly using the c/n, n/o, and c/o ratios breaks any degeneracy in the formation and migration tracks of giant planets. the use of elemental ratios normalized to the respective stellar ratios supplies additional information on the nature of giant planets, thanks to the relative volatility of o, c, and n in disks. when the planetary metallicity is dominated by the accretion of solids c/n* > c/o* > n/o* (* denoting this normalized scale), otherwise n/o* > c/o* > c/n*. the s/n ratio provides an additional independent probe into the metallicity of giant planets and their accretion of solids. | tracing the formation history of giant planets in protoplanetary disks with carbon, oxygen, nitrogen, and sulfur |
understanding how marine low clouds and their radiative effects respond to changing meteorological conditions is crucial to constrain low-cloud feedbacks to greenhouse warming and internal climate variability. in this study, we use observations to quantify the low-cloud radiative response to meteorological perturbations over the global oceans to shed light on physical processes governing low-cloud and planetary radiation budget variability in different climate regimes. we assess the independent effect of perturbations in sea surface temperature, estimated inversion strength, horizontal surface temperature advection, 700-hpa relative humidity, 700-hpa vertical velocity, and near-surface wind speed. stronger inversions and stronger cold advection greatly enhance low-level cloudiness and planetary albedo in eastern ocean stratocumulus and midlatitude regimes. warming of the sea surface drives pronounced reductions of eastern ocean stratocumulus cloud amount and optical depth, and hence reflectivity, but has a weaker and more variable impact on low clouds in the tropics and middle latitudes. by reducing entrainment drying, higher free-tropospheric relative humidity enhances low-level cloudiness. at low latitudes, where cold advection destabilizes the boundary layer, stronger winds enhance low-level cloudiness; by contrast, wind speed variations have weak influence at midlatitudes where warm advection frequently stabilizes the marine boundary layer, thus inhibiting vertical mixing. these observational constraints provide a framework for understanding and evaluating marine low-cloud feedbacks and their simulation by models. | observed sensitivity of low-cloud radiative effects to meteorological perturbations over the global oceans |
bepicolombo is a joint mission between the european space agency, esa, and the japanese aerospace exploration agency, jaxa, to perform a comprehensive exploration of mercury. launched on 20th october 2018 from the european spaceport in kourou, french guiana, the spacecraft is now en route to mercury. | bepicolombo - mission overview and science goals |
human-induced climate change impacts the hydrological cycle and thus the availability of water resources. however, previous assessments of observed warming-induced changes in dryness have not excluded natural climate variability and show conflicting results due to uncertainties in our understanding of the response of evapotranspiration. here we employ data-driven and land-surface models to produce observation-based global reconstructions of water availability from 1902 to 2014, a period during which our planet experienced a global warming of approximately 1 °c. our analysis reveals a spatial pattern of changes in average water availability during the driest month of the year over the past three decades compared with the first half of the twentieth century, with some regions experiencing increased and some decreased water availability. the global pattern is consistent with climate model estimates that account for anthropogenic effects, and it is not expected from natural climate variability, supporting human-induced climate change as the cause. there is regional evidence of drier dry seasons predominantly in extratropical latitudes and including europe, western north america, northern asia, southern south america, australia and eastern africa. we also find that the intensification of the dry season is generally a consequence of increasing evapotranspiration rather than decreasing precipitation. | observed changes in dry-season water availability attributed to human-induced climate change |
giant planets migrate though the protoplanetary disc as they grow their solid core and attract their gaseous envelope. previously, we have studied the growth and migration of an isolated planet in an evolving disc. here, we generalise such models to include the mutual gravitational interaction between a high number of growing planetary bodies. we have investigated how the formation of planetary systems depends on the radial flux of pebbles through the protoplanetary disc and on the planet migration rate. our n-body simulations confirm previous findings that jupiter-like planets in orbits outside the water ice line originate from embryos starting out at 20-40 au when using nominal type-i and type-ii migration rates and a pebble flux of approximately 100-200 earth masses per million years, enough to grow jupiter within the lifetime of the solar nebula. the planetary embryos placed up to 30 au migrate into the inner system (rp < 1au). there they form super-earths or hot and warm gas giants, producing systems that are inconsistent with the configuration of the solar system, but consistent with some exoplanetary systems. we also explored slower migration rates which allow the formation of gas giants from embryos originating from the 5-10 au region, which are stranded exterior to 1 au at the end of the gas-disc phase. these giant planets can also form in discs with lower pebbles fluxes (50-100 earth masses per myr). we identify a pebble flux threshold below which migration dominates and moves the planetary core to the inner disc, where the pebble isolation mass is too low for the planet to accrete gas efficiently. in our model, giant planet growth requires a sufficiently high pebble flux to enable growth to out-compete migration. an even higher pebble flux produces systems with multiple gas giants. we show that planetary embryos starting interior to 5 au do not grow into gas giants, even if migration is slow and the pebble flux is large. these embryos instead grow to just a few earth masses, the mass regime of super-earths. this stunted growth is caused by the low pebble isolation mass in the inner disc and is therefore independent of the pebble flux. additionally, we show that the long-term evolution of our formed planetary systems can naturally produce systems with inner super-earths and outer gas giants as well as systems of giant planets on very eccentric orbits. | formation of planetary systems by pebble accretion and migration: growth of gas giants |
the advent of global precipitation data sets with increasing temporal span has made it possible to use them for validating climate models. in order to fulfill the requirement of global coverage, existing products integrate satellite-derived retrievals from many sensors with direct ground observations (gauges, disdrometers, radars), which are used as reference for the satellites. while the resulting product can be deemed as the best-available source of quality validation data, awareness of the limitations of such data sets is important to avoid extracting wrong or unsubstantiated conclusions when assessing climate model abilities. this paper provides guidance on the use of precipitation data sets for climate research, including model validation and verification for improving physical parameterizations. the strengths and limitations of the data sets for climate modeling applications are presented, and a protocol for quality assurance of both observational databases and models is discussed. the paper helps elaborating the recent ipcc ar5 acknowledgment of large observational uncertainties in precipitation observations for climate model validation. | global precipitation measurements for validating climate models |
the third data release of gaia was the first to include orbital solutions assuming non-single stars. here, we apply the astrometric triage technique of shahaf et al. 2019 to identify binary star systems with companions that are not single main-sequence stars. gaia's synthetic photometry of these binaries is used to distinguish between systems likely to have white-dwarf companions and those that may be hierarchical triples. the study uncovered a population of nearly 3200 binaries, characterised by orbital separations on the order of an astronomical unit, in which the faint astrometric companion is probably a white dwarf. remarkably, over 110 of these systems exhibit significant ultraviolet excess flux, confirming this classification and, in some cases, indicating their relatively young cooling ages. we show that the sample is not easily reproduced by binary population synthesis codes. therefore, it challenges current binary evolution models, offering a unique opportunity to gain insights into the processes governing white-dwarf formation, binary evolution, and mass transfer. | triage of the gaia dr3 astrometric orbits. ii. a census of white dwarfs |
the large sky area multi-object fiber spectroscopic telescope (lamost), also known as the guoshoujing telescope, is a major national scientific facility for astronomical research located in xinglong, china. beginning with a pilot survey in 2011, lamost has been surveying the night sky for more than 10 years. the lamost survey covers various objects in the universe, from normal stars to peculiar ones, from the milky way to other galaxies, and from stellar black holes and their companions to quasars that ignite ancient galaxies. until the latest data release 8, the lamost survey has released spectra for more than 10 million stars, ∼220,000 galaxies, and ∼71,000 quasars. with this largest celestial spectra database ever constructed, lamost has helped astronomers to deepen their understanding of the universe, especially for our milky way galaxy and the millions of stars within it. in this article, we briefly review the characteristics, observations, and scientific achievements of lamost. in particular, we show how astrophysical knowledge about the milky way has been improved by lamost data. | overview of the lamost survey in the first decade |
over the past decade, observations of giant exoplanets (jupiter-size) have provided key insights into their atmospheres, but the properties of lower-mass exoplanets (sub-neptune) remain largely unconstrained because of the challenges of observing small planets. numerous efforts to observe the spectra of super-earths—exoplanets with masses of one to ten times that of earth—have so far revealed only featureless spectra. here we report a longitudinal thermal brightness map of the nearby transiting super-earth 55 cancri e (refs 4, 5) revealing highly asymmetric dayside thermal emission and a strong day-night temperature contrast. dedicated space-based monitoring of the planet in the infrared revealed a modulation of the thermal flux as 55 cancri e revolves around its star in a tidally locked configuration. these observations reveal a hot spot that is located 41 ± 12 degrees east of the substellar point (the point at which incident light from the star is perpendicular to the surface of the planet). from the orbital phase curve, we also constrain the nightside brightness temperature of the planet to 1,380 ± 400 kelvin and the temperature of the warmest hemisphere (centred on the hot spot) to be about 1,300 kelvin hotter (2,700 ± 270 kelvin) at a wavelength of 4.5 micrometres, which indicates inefficient heat redistribution from the dayside to the nightside. our observations are consistent with either an optically thick atmosphere with heat recirculation confined to the planetary dayside, or a planet devoid of atmosphere with low-viscosity magma flows at the surface. | a map of the large day-night temperature gradient of a super-earth exoplanet |
we use more than 2 years of magnetic data from the swarm mission, and monthly means from 160 ground observatories as available in march 2016, to update the chaos time-dependent geomagnetic field model. the new model, chaos-6, provides information on time variations of the core-generated part of the earth's magnetic field between 1999.0 and 2016.5. we present details of the secular variation (sv) and secular acceleration (sa) from chaos-6 at earth's surface and downward continued to the core surface. at earth's surface, we find evidence for positive acceleration of the field intensity in 2015 over a broad area around longitude 90°e that is also seen at ground observatories such as novosibirsk. at the core surface, we are able to map the sv up to at least degree 16. the radial field sa at the core surface in 2015 is found to be largest at low latitudes under the india-south-east asia region, under the region of northern south america, and at high northern latitudes under alaska and siberia. surprisingly, there is also evidence for significant sa in the central pacific region, for example near hawaii where radial field sa is observed on either side of a jerk in 2014. on the other hand, little sv or sa has occurred over the past 17 years in the southern polar region. inverting for a quasi-geostrophic core flow that accounts for this sv, we obtain a prominent planetary-scale, anti-cyclonic, gyre centred on the atlantic hemisphere. we also find oscillations of non-axisymmetric, azimuthal, jets at low latitudes, for example close to 40°w, that may be responsible for localized sa oscillations. in addition to scalar data from ørsted, champ, sac-c and swarm, and vector data from ørsted, champ and swarm, chaos-6 benefits from the inclusion of along-track differences of scalar and vector field data from both champ and the three swarm satellites, as well as east-west differences between the lower pair of swarm satellites, alpha and charlie. moreover, ground observatory sv estimates are fit to a huber-weighted rms level of 3.1 nt/year for the eastward components and 3.8 and 3.7 nt/year for the vertical and southward components. we also present an update of the chaos high-degree lithospheric field, making use of along-track differences of champ scalar and vector field data to produce a new static field model that agrees well with the mf7 field model out to degree 110. | recent geomagnetic secular variation from swarm and ground observatories as estimated in the chaos-6 geomagnetic field model |
throughout earth's history, redox transformations in sedimentary environments have occurred through chemical processes (abiotic pathways) or via the activity of living microorganisms (biotic pathway). tools able to discriminate between these two mechanisms are of major interest, as they would contribute significantly to the understanding of biogeochemical events that shaped the evolution of life on our planet. here, we show that there is a clear difference between the isotopic signature associated with abiotic and biotic transformations of uranium (u). thus, u isotopic composition can serve as a marker for biological processes in many sedimentary rocks. based on this result, we conclude that microbial activity has contributed to reductive sedimentary processes in many low-temperature redox-active terrestrial and marine environments. | uranium isotopes fingerprint biotic reduction |
atmospheric aerosols have been found to influence the development of planetary boundary layer (pbl) and hence to enhance haze pollution in megacities. previous works on aerosol-pbl interaction were mainly based on model simulation for short-term cases; so far, there is a lack of long-term observational evidences. in this study, based on multiyear measurements and reanalysis meteorological data, we give observational evidences on aerosol-pbl interaction and its impact on pollution aggravation. we found a significant heating in upper pbl with maximum temperature change about 0.7 °c on average and a substantial dimming near surface with a mean temperature drop of -2.2 °c under polluted condition. by integrating eulerian forward simulation and lagrangian backward trajectory calculation, we demonstrated that the atmospheric heating was mainly induced by light-absorbing aerosols like black carbon. then an index representing such effect was proposed, which could well characterize aerosol-pbl interaction and its impact on air pollution. | impact of aerosol-pbl interaction on haze pollution: multiyear observational evidences in north china |
this paper presents new high angular resolution alma 1.3 mm dust continuum observations of the protoplanetary system as 209 in the ophiuchus star forming region. the dust continuum emission is characterized by a main central core and two prominent rings at r = 75 au and r = 130 au intervaled by two gaps at r = 62 au and r = 103 au. the two gaps have different widths and depths, with the inner one being narrower and shallower. we determined the surface density of the millimeter dust grains using the 3d radiative transfer disk code dali. according to our fiducial model the inner gap is partially filled with millimeter grains while the outer gap is largely devoid of dust. the inferred surface density is compared to 3d hydrodynamical simulations (fargo-3d) of planet-disk interaction. the outer dust gap is consistent with the presence of a giant planet (mplanet 0.7 msaturn); the planet is responsible for the gap opening and for the pile-up of dust at the outer edge of the planet orbit. the simulations also show that the same planet could be the origin of the inner gap at r = 62 au. the relative position of the two dust gaps is close to the 2:1 resonance and we have investigated the possibility of a second planet inside the inner gap. the resulting surface density (including location, width and depth of the two dust gaps) are in agreement with the observations. the properties of the inner gap pose a strong constraint to the mass of the inner planet (mplanet < 0.1 mj). in both scenarios (single or pair of planets), the hydrodynamical simulations suggest a very low disk viscosity (α < 10-4). given the young age of the system (0.5-1 myr), this result implies that the formation of giant planets occurs on a timescale of ≲1 myr. the reduced image (fits file) is only available at the cds via anonymous ftp to http://cdsarc.u-strasbg.fr (http://130.79.128.5) or via http://cdsarc.u-strasbg.fr/viz-bin/qcat?j/a+a/610/a24 | alma continuum observations of the protoplanetary disk as 209. evidence of multiple gaps opened by a single planet |
we present three transit observations of hd 189733 b obtained with the high-resolution spectrograph carmenes at calar alto. a strong absorption signal is detected in the near-infrared he i triplet at 10830 å in all three transits. during mid-transit, the mean absorption level is 0.88 ± 0.04% measured in a ±10 km s-1 range at a net blueshift of - 3.5 ± 0.4 km s-1 (10829.84-10830.57 å). the absorption signal exhibits radial velocities of + 6.5 ± 3.1 km s-1 and - 12.6 ± 1.0 km s-1 during ingress and egress, respectively; all radial velocities are measured in the planetary rest frame. we show that stellar activity related pseudo-signals interfere with the planetary atmospheric absorption signal. they could contribute as much as 80% of the observed signal and might also affect the observed radial velocity signature, but pseudo-signals are very unlikely to explain the entire signal. the observed line ratio between the two unresolved and the third line of the he i triplet is 2.8 ± 0.2, which strongly deviates from the value expected for an optically thin atmospheres. when interpreted in terms of absorption in the planetary atmosphere, this favors a compact helium atmosphere with an extent of only 0.2 planetary radii and a substantial column density on the order of 4 × 1012 cm-2. the observed radial velocities can be understood either in terms of atmospheric circulation with equatorial superrotation or as a sign of an asymmetric atmospheric component of evaporating material. we detect no clear signature of ongoing evaporation, like pre- or post-transit absorption, which could indicate material beyond the planetary roche lobe, or radial velocities in excess of the escape velocity. these findings do not contradict planetary evaporation, but only show that the detected helium absorption in hd 189733 b does not trace the atmospheric layers that show pronounced escape signatures. | detection of he i λ10830 å absorption on hd 189733 b with carmenes high-resolution transmission spectroscopy |
in situ research of cometary chemistry began when measurements from the giotto mission at comet 1p/halley revealed the presence of complex organics in the coma. new telescopes and space missions have provided detailed remote and in situ measurements of the composition of cometary volatiles. recently, the rosetta mission to comet 67p/churyumov-gerasimenko (67p) more than doubled the number of parent species and the number of isotopic ratios known for comets. forty of the 71 parent species have also been detected in pre- and protostellar clouds. most isotopic ratios are nonsolar. this diverse origin is in contrast to that of the sun, which received its material from the bulk of the collapsing cloud. the xenon isotopic ratios measured in 67p can explain the long-standing question about the origin of terrestrial atmospheric xenon. these findings strengthen the notion that comets are indeed an important link between the ism and today's solar system including life on earth. nonsolar isotopic ratios for species such as xe, n, s, and si point to a nonhomogenized protoplanetary disk from which comets received their material. the similarity of the organic inventories of comets and presolar and protostellar material makes it plausible that this material was accreted almost unaltered by comets from the presolar stage. large variations in the deuterium-to-hydrogen ratio in water for comets indicate a large range in the protoplanetary disk from which comets formed. the amount of organics delivered by comets to earth may be highly significant. | cometary chemistry and the origin of icy solar system bodies: the view after rosetta |
Subsets and Splits
No community queries yet
The top public SQL queries from the community will appear here once available.