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in this study, heavy metal pollution in batlama stream flowing into the black sea from giresun (turkiye) province and the toxicity induced by this pollution were investigated by allium test. heavy metal concentrations in stream water were analyzed by using icp-ms. germination percentage, weight gain, root length, micronucleus (mn), mitotic index (mi), chromosomal abnormalities (cas), proline, chlorophyll, malondialdehyde (mda), antioxidant enzyme activities were used as indicators of physiological, cytogenetic and biochemical toxicity. in addition, comet assay was performed for detecting dna fragmentation. anatomical changes caused by heavy metals in the root meristem cells were observed under the microscope. a. cepa bulbs are divided into two groups as control and treatment. the bulbs in the control group were germinated with tap water and the bulbs in the treatment group were germinated with stream water. as a result, heavy metals such as al, ti and co and radioactive heavy metals such as rb, sr, sb and ba were detected in the stream water above the acceptable parametric values. heavy metals in the water caused a decrease in germination, root elongation, weight gain, mi and chlorophyll values, and an increase in mda, proline, sod, cat, mn and cas values. comet assays indicated the presence of severe dna damage. in addition, heavy metals in stream water caused different types of cas and anatomical damage in root meristem cells. as a result, it was determined that there is intense heavy metal pollution in the stream water and this pollution promotes multi-dimensional toxicity in a. cepa, which is an indicator organism. for this reason, the first priority should be to prevent pollution of water resources in order to prevent heavy metal-induced toxicity in water. | detection of heavy metal contamination in batlama stream (turkiye) and the potential toxicity profile |
this paper will constrain the possible sources and processes for the formation of recently observed h2o vapor plumes above the surface of the dwarf planet ceres. two hypotheses have been proposed: (1) cryovolcanism where the water source is the mantle and the heating source is still unknown or (2) comet-like sublimation where near-surface water ice is vaporized by seasonally increasing solar insolation. we test hypothesis 2, comet-like near-surface sublimation, by using a thermal model to examine the stability of water ice in the near surface. for a reasonable range of physical parameters (thermal inertia, surface roughness, and slopes), we find that water ice is only stable at latitudes higher than ~40-60°. these results indicate that either (a) the physical properties of ceres are unlike our expectations or (b) an alternative to comet-like sublimation, such as the cryovolcanism hypothesis, must be invoked. | ceres: predictions for near-surface water ice stability and implications for plume generating processes |
this paper presents a new approach to analysing the brightness change of a jupiter family comet. we assume that the coma contains particles composed of water ice, carbonaceous, and silicate dust. different sizes of dust particles were taken into account following the adopted size distribution. from an analysis of modern space missions, it is clear that the sizes of the dominant coma particles at the time of the outburst are in the order of micrometres to centimetres. however, most of these particles have dimensions that are comparable to the wavelength of electromagnetic radiation coming from the sun. in the case of dust particles, four groups were distinguished depending on their dimensions. the performed calculations show that the particle size significantly influences the change of the cometary brightness, i.e. the scattering efficiency of the incident sunlight that occurs on the particle. the conducted numerical simulations show that the changes in the brightness of the comet oscillate approximately from -8 to -1 mag. this means that we can talk about outbursts, the amplitudes of which are most often observed. | the influence of the size of ice-dust particles on the amplitude of the change in the brightness of a comet caused by an outburst |
modelling the evolution of comets is a complex task aiming at providing constraints on physical processes and internal properties that are inaccessible to observations, although they could potentially bring key elements to our understanding of the origins of these primitive objects. this field has made a tremendous step forward in the post-giotto area, owing to detailed space- and ground-based observations, as well as detailed laboratory simulations of comet nuclei. in this paper, we review studies that we believe are significant for interpreting the observations of 67p/churyumov-gerasimenko by the esa/rosetta mission, and provide new calculations where needed. these studies hold a strong statistical significance, which is exactly what is needed for this comet with an orbital evolution that cannot be traced back accurately for more than hundreds of years. we show that radial and lateral differentiation may have occurred on 67p's chaotic path to the inner solar system, and that internal inhomogeneities may result in an erratic activity pattern. finally, we discuss the origins of circular depressions seen on several comets including 67p, and suggest that they could be considered as evidence of the past processing of subsurface layers. | modelling the evolution of a comet subsurface: implications for 67p/churyumov-gerasimenko |
our work focuses on the spectrophotometric analysis of selected terrain and bright patches in the khonsu region on the comet 67p/churyumov-gerasimenko. despite the variety of geological features, their spectrophotometric properties appear to indicate a similar composition. it is noticeable that the smooth areas in khonsu possess similar spectrophotometric behaviour to some other regions of the comet. we observed bright patches on khonsu with an estimation of >40 per cent of normal albedo and suggest that they are associated with h2o ice. one of the studied bright patches has been observed to exist on the surface for more than 5 months without a major decay of its size, implying the existence of potential sub-surface icy layers. its location may be correlated with a cometary outburst during the perihelion passage of the comet in 2015 august, and we interpret it to have triggered the surface modifications necessary to unearth the stratified icy layers beneath the surface. a boulder analysis on khonsu leads to a power-law index of -3.1 +0.2/-0.3 suggesting a boulder formation, shaped by varying geological processes for different morphological units. | spectrophotometry of the khonsu region on the comet 67p/churyumov-gerasimenko using osiris instrument images |
multi‑walled carbon nanotubes (mwcnts) have many applications in industry and used as additives in polymers, catalysts, anodes in lithium‑battery and drug delivery. there is little information about mwcnts' (210 nm) genotoxic potential on juvenile freshwater fish channa punctatus. therefore, in this study, we have determined the toxic effects of mwcnts on freshwater fish c. punctatus by assessing toxicological endpoints such as oxidative stress, mutagenicity, and genotoxicity after acute mwcnts exposure for 5 days. mwcnts lc50‑96 hours value for c. punctatus was 21.8 mg/l and on this basis three different mwcnts concentrations were selected, that is, sub‑lethal i, ii, and iii, for 5‑days exposure trials with c. punctatus. the level of lipid peroxidation increased in the gills and kidney of exposed fish at sub‑lethal concentrations ii and iii. contrastingly, glutathione decreased more in the gills than in the kidney. the activity of catalase enzymes decreased more in the gills than in the kidney at sublethal concentrations i and ii. glutathione s‑transferase decreased in gill tissue but increased in kidney tissue following sub‑lethal iii exposure. moreover, the level of glutathione reductase decreased in both tissues. in addition, mwcnts genotoxicity was confirmed by dna damage in lymphocytes, gills, kidney cells, and production of micronuclei (mni) in red blood cells of freshwater fish following sub‑lethal i, ii, and iii exposures. in conclusion, this study revealed that application of micronucleus and comet assays for in vivo laboratory studies using freshwater fish for screening the genotoxic potential of mwcnts. | assessment of dna damage and oxidative stress in juvenile channa punctatus (bloch) after exposure to multi‑walled carbon nanotubes |
we investigate the existence of ion-acoustic shock waves in a five component cometary plasma consisting of positively and negatively charged oxygen ions, kappa described hydrogen ions, hot solar electrons, and slightly colder cometary electrons. the kdvb equation has been derived for the system, and its solution plotted for different kappa values, oxygen ion densities, as well as the temperature ratios for the ions. it is found that the amplitude of the shock wave decreases with increasing kappa values. the strength of the shock profile decreases with increasing temperatures of the positively charged oxygen ions and densities of negatively charged oxygen ions. | korteweg-devries-burgers (kdvb) equation in a five component cometary plasma with kappa described electrons and ions |
the optical, spectroscopic, and infrared remote imaging system (osiris), the scientific imaging system onboard the rosetta mission, has been acquiring images of the nucleus of the comet 67p/churyumov-gerasimenko since 2014 august with a resolution which allows a detailed analysis of its surface. indeed, data reveal a complex surface morphology which is likely the expression of different processes which occurred at different times on the cometary nucleus. in order to characterize these different morphologies and better understand their distribution, we performed a geologic mapping of comet's 67p northern hemisphere in which features have been distinguished based on their morphological, textural and stratigraphic characteristics. for this purpose, we used narrow-angle camera images acquired in 2014 august and september with a spatial scale ranging from 1.2 to 2.4 m pixel-1. several different geologic units have been identified on the basis of their different surface textures, granulometry and morphology. some of these units are distinctive and localized, whereas others are more common and distributed all over the northern hemisphere. moreover, different types of linear features have been distinguished on the basis of their morphology. some of these lineaments have never been observed before on a comet and can offer important clues on the internal structures of the nucleus itself. the geologic mapping results presented here will allow us to better understand the processes which affected the nucleus' surface and thus the origin and evolutionary history of comet 67p/churyumov-gerasimenko. | geologic mapping of the comet 67p/churyumov-gerasimenko's northern hemisphere |
the comet physics laboratory (cophylab) is an international research program to study the physical properties of cometary analog materials under simulated space conditions. the project is dedicated to studying, with the help of multiple instruments and the different expertise and background from the different partners, the physics of comets, including the processes inside cometary nuclei, the activity leading to the ejection of dust and gas, and the sub-surface and surface evolution of cometary nuclei when exposed to solar illumination. cophylab will provide essential information on the formation and evolution of comets and insights into the origins of primitive solar system bodies. to this end, we constructed a new laboratory that hosts several small-scale experiments and a large-scale comet-simulation chamber (l-chamber). this chamber has been designed and constructed to host ice-dust samples with a diameter of up to 250 mm and a variable height between 100 and 300 mm. the cometary-analog samples will be kept at temperatures below 120 k and pressures around 10−6 mbar to ensure cometary-like conditions. in total, 14 different scientific instruments are attached to the l-chamber to study the temporal evolution of the physical properties of the sample under different insolation conditions. due to the implementation of a scale inside the l-chamber that can measure weight changes of the samples with high precision, the cooling system is mechanically decoupled from the sample holder and cooling of the samples occurs by radiation only. the constructed chamber allows us to conduct uninterrupted experiments at low temperatures and pressures up to several weeks. | the cophylab comet-simulation chamber |
carbon, hydrogen, nitrogen, oxygen, and sulfur are the main elements involved in the solid-phase chemistry of various astrophysical environments. among these elements, sulfur chemistry is probably the least well understood. we investigated whether sulfur ion bombardment within simple astrophysical ice analogs (originating from h2o:ch3oh:nh3, 2:1:1) could trigger the formation of complex organosulfur molecules. over 1100 organosulfur (chnos) molecular formulas (12% of all assigned signals) were detected in resulting refractory residues within a broad mass range (from 100 to 900 amu, atomic mass unit). this finding indicates a diverse, rich and active sulfur chemistry that could be relevant for kuiper belt objects (kbo) ices, triggered by high-energy ion implantation. the putative presence of organosulfur compounds within kbo ices or on other icy bodies might influence our view on the search of habitability and biosignatures. | organosulfur compounds formed by sulfur ion bombardment of astrophysical ice analogs: implications for moons, comets, and kuiper belt objects |
the young (50-400 myr) a3v star β leo is a primary target to study the formation history and evolution of extrasolar planetary systems as one of the few stars with known hot (∼1600 k), warm (∼600 k), and cold (∼120 k) dust belt components. in this paper, we present deep mid-infrared measurements of the warm dust brightness obtained with the large binocular telescope interferometer (lbti) as part of its exozodiacal dust survey (hosts). the measured excess is 0.47% ± 0.050% within the central 1.5 au, rising to 0.81% ± 0.026% within 4.5 au, outside the habitable zone of β leo. this dust level is 50 ± 10 times greater than in the solar system's zodiacal cloud. poynting-robertson drag on the cold dust detected by spitzer, and herschel underpredicts the dust present in the habitable zone of β leo, suggesting an additional delivery mechanism (e.g., comets) or an additional belt at ∼5.5 au. a model of these dust components is provided that implies the absence of planets more than a few saturn masses between ∼5 au and the outer belt at ∼40 au. we also observationally constrain giant planets with the lbti imaging channel at 3.8 μm wavelength. assuming an age of 50 myr, any planet in the system between approximately 5-50 au must be less than a few jupiter masses, consistent with our dust model. taken together, these observations showcase the deep contrasts and detection capabilities attainable by the lbti for both warm exozodiacal dust and giant exoplanets in or near the habitable zone of nearby stars. | the hosts survey: evidence for an extended dust disk and constraints on the presence of giant planets in the habitable zone of β leo |
a detailed study is made of celestial observations recorded in east asian and european history around a.d. 774-5 and 993-4. these include reports of supernovae, comets, sunspots and aurorae. the aim is to attempt to provide astronomical evidence in support of the measured 14c increases in tree rings at these dates. however, the results prove to be far from convincing, leaving the physical cause of the increases still in doubt. | astronomical evidence relating to the observed 14c increases in a.d. 774-5 and 993-4 as determined from tree rings |
one of the biggest surprises of the rosetta mission was the detection of o2 in the coma of 67p/churyumov-gerasimenko in remarkably high abundances. the measured levels of o2 in the coma are generally assumed to reflect the overall abundance and chemical origin of cometary o2 in the nucleus. along with its strong association with h2o and weak association with co and co2, these measurements led to the consensus that the source and release of cometary o2 are linked to h2o. we analysed rosina observations and found a previously unrecognized change in the correlations of o2 with h2o, co2 and co that contradicts the prevailing notion that the release of o2 is linked to h2o at all times. these findings can be explained by the presence of two distinct reservoirs of o2: a pristine source in the deeper nucleus layers dating back to before nucleus formation, and an h2o-trapped secondary reservoir formed during the thermal evolution of the nucleus. these results imply that o2 must have been incorporated into the nucleus in a solid and distinct phase during accretion in significantly lower abundances than previously assumed. | dual storage and release of molecular oxygen in comet 67p/churyumov-gerasimenko |
comet interceptor (comet-i) was selected in june 2019 as the first esa f-class mission. in 2029+, comet-i will hitch a ride to a sun-earth l2 quasi-halo orbit, as a co-passenger of esa's m4 ariel mission. it will then remain idle at the l2 point until the right departure conditions are met to intercept a yet-to-be-discovered long period comet (or interstellar body). the fact that comet-i target is thus unidentified becomes a key aspect of the trajectory and mission design. the paper first analyses the long period comet population and concludes that 2 to 3 feasible targets a year should be expected. yet, comet-i will only be able to access some of these, depending mostly on the angular distance between the earth and the closest nodal point to the earth's orbit radius. a preliminary analysis of the transfer trajectories has been performed to assess the trade-off between the accessible region and the transfer time for a given spacecraft design, including a fully chemical, a fully electric and a hybrid propulsion system. the different earth escape options also play a paramount role to enhance comet-i capability to reach possible long period comet targets. particularly, earth-leading intercept configurations have the potential to benefit the most from lunar swing-by departures. finally, a preliminary monte carlo analysis shows that comet-i has a 95 to 99% likelihood of successfully visit a pristine newly-discovered long period comet in less than 6 years of mission timespan. | esa f-class comet interceptor: trajectory design to intercept a yet-to-be-discovered comet |
we report observations of the reactivations of the main-belt comets (mbcs) 238p/read and 288p/(300163) 2006 vw139 that also track the evolution of each object’s activity over several months in 2016 and 2017. we additionally identify and analyze archival sdss data showing 288p to have been active in 2000, meaning that both 238p and 288p have now each been confirmed to be active near perihelion on three separate occasions. from data obtained of 288p from 2012-2015 when it appeared inactive, we find best-fit r-band h, g phase function parameters of hr= 16.80 ± 0.12 mag and gr= 0.18 ± 0.11, corresponding to effective component radii of rc= 0.80 ± 0.04 km, assuming a binary system with equally sized components. fitting linear functions to ejected dust masses inferred for 238p and 288p soon after their observed reactivations in 2016, we find an initial average net dust production rate of {\dot{m}}d=0.7+/- 0.3 kg s-1 and a best-fit start date of 2016 march 11 (when the object was at a true anomaly of ν = -63°) for 238p, and an initial average net dust production rate of {\dot{m}}d=5.6+/- 0.7 kg s-1 and a best-fit start date of 2016 august 5 (when the object was at ν = -27°) for 288p. applying similar analyses to archival data, we find similar start points for previous active episodes for both objects, suggesting that minimal mantle growth or ice recession occurred between the active episodes in question. some changes in dust production rates between active episodes are detected, however. more detailed dust modeling is suggested to further clarify the process of activity evolution in mbcs. based on observations obtained with megaprime/megacam, a joint project of cfht and cea/dapnia, at the canada-france-hawaii telescope (cfht) (programs 12bh43, 15at05, and 16bt05), which is operated by the national research council (nrc) of canada, the institut national des science de l’univers of the centre national de la recherche scientifique (cnrs) of france, and the university of hawaii, and at the gemini observatory (programs gn-2011b-q-17, gn-2012a-q-68, gn-2012b-q-106, gn-2016b-lp-11, and gs-2016b-lp-11), which is operated by the association of universities for research in astronomy, inc., under a cooperative agreement with the national science foundation (nsf) on behalf of the gemini partnership: the nsf (united states), the national research council (canada), conicyt (chile), ministerio de ciencia, tecnología e innovación productiva (argentina), and ministério da ciência, tecnologia e inovaçāo (brazil). | the 2016 reactivations of the main-belt comets 238p/read and 288p/(300163) 2006 vw139 |
the paper presents a new approach to determining the change in the brightness of a comet during an outburst. it was investigated how the porosity of the dust particle translates into an increase in comet brightness during an outburst. it has been shown that the greater the porosity of a given particle, the greater the scattering efficiency, which directly translates into a greater amplitude of the change in the cometary brightness. in the case of dense aggregates with porosity ψ = 0.05, the brightness rate varies from -0.74 to -4.24 mag. in the case of porous agglomerates, the porosity of which is in the range from 0.30 to 0.90, the brightness change ranges from -0.91 to -6.66 mag. | the influence of the porosity of dust particles on the amplitude of the change in the brightness of a comet |
bisphenol a (bpa), an infamous xenoestrogen, can cause the inimical environmental and health implications via generation of extremely reactive oxygen species (ros) and/or by mimicking the endocrine activity. the intention of this study was to understand the concentration range of bpa between 0.02-200 μg ml-1 that may induce dna damage and cytotoxicity, individually and/or through amelioration by gallic acid (ga) (10-50 μg ml-1) in hepg2 cell line by comet, lactate dehydrogenase (ldh) leakage and mtt assay. the results revealed that bpa was not found genotoxic (0.02-0.2 μg ml-1) and cytotoxic at low dose exposure (0.02 μg ml-1). however, bpa at a concentration of 2-200 μg ml-1, induced significant dna damage and cytotoxicity (p<0.05) in a dose-relying manner in hepg2 cell line. however, dna damage and cytotoxicity were inhibited when ga (10-50 g ml-1) and bpa (200 g ml-1) were added together. to investigate the mechanism of toxicity and the binding potential of bpa/bpa-q to dna and ga, an in silico molecular docking approach and molecular dynamics simulation were performed. the obtained results revealed strong binding affinity between bpa/bpa-q with dna which induces dna damage. | exploration of the ameliorative effect of dietary polyphenol on bisphenol-a prompted dna damage by in vitro and in silico approaches |
there are many discrepancies among the results of studies on the genotoxicity of lead. the aim of the study was to explore lead-induced dna damage, including oxidative damage, in relation to oxidative stress intensity parameters and the antioxidant defense system in human leukocytes. the study population consisted of 100 male workers exposed to lead. according to the blood lead (pbb) levels, they were divided into the following three subgroups: a group with pbb of 20–35 μg/dl (low exposure to lead (le) group), a group with a pbb of 35–50 µg/dl (medium exposure to lead (me) group), and a group with a pbb of >50 μg/dl (high exposure to lead (he) group). the control group consisted of 42 healthy males environmentally exposed to lead (pbb < 10 μg/dl). a comet assay was used to measure the dna damage in leukocytes. we measured the activity of superoxide dismutase (sod), catalase, glutathione reductase (gr), glucose-6-phosphate dehydrogenase (g6pd), and glutathione-s-transferase (gst) as well as the concentration of malondialdehyde (mda), and the value of the total antioxidant capacity. the level of pbb was significantly higher in the examined subgroups than in the control group. the percentage of dna in the tail was significantly higher in the le, me, and he subgroups than in the control group by 10% ( p = 0.001), 15% ( p < 0.001), and 20% ( p < 0.001), respectively. the activity of gr was significantly lower in the le and me subgroups than in the control group by 25% ( p = 0.007) and 17% ( p = 0.028), respectively. the activity of g6pd was significantly lower in the me subgroup by 25% ( p = 0.022), whereas the activity of gst was significantly higher in the he subgroup by 101% ( p = 0.001) than in the control group. similarly, the activity of sod was significantly higher in the le and me subgroups by 48% ( p = 0.026) and 34% ( p = 0.002), respectively. the concentration of mda was significantly higher in the le, me, and he subgroups than in the control group by 43% ( p = 0.016), 57% ( p < 0.001), and 108% ( p < 0.001), respectively. occupational lead exposure induces dna damage, including oxidative damage, in human leukocytes. the increase in dna damage was accompanied by an elevated intensity of oxidative stress. | oxidative dna damage and oxidative stress in lead-exposed workers |
context. we investigate the dust coma within the hill sphere of comet 67p/churyumov-gerasimenko.aims: we aim to determine osculating orbital elements for individual distinguishable but unresolved slow-moving grains in the vicinity of the nucleus. in addition, we perform photometry and constrain grain sizes.methods: we performed astrometry and photometry using images acquired by the osiris wide angle camera on the european space agency spacecraft rosetta. based on these measurements, we employed standard orbit determination and orbit improvement techniques.results: orbital elements and effective diameters of four grains were constrained, but we were unable to uniquely determine them. two of the grains have light curves that indicate grain rotation.conclusions: the four grains have diameters nominally in the range 0.14-0.50 m. for three of the grains, we found elliptic orbits, which is consistent with a cloud of bound particles around the nucleus. however, hyperbolic escape trajectories cannot be excluded for any of the grains, and for one grain this is the only known option. one grain may have originated from the surface shortly before observation. these results have possible implications for the understanding of the dispersal of the cloud of bound debris around comet nuclei, as well as for understanding the ejection of large grains far from the sun. | orbital elements of the material surrounding comet 67p/churyumov-gerasimenko |
non-thermal radiation has been predicted within bow shocks around runaway stars by recent theoretical works. we present x-ray observations toward the runaway stars ζ oph by chandra and suzaku and of bd+43°3654 by xmm-newton to search for the presence of non-thermal x-ray emission. we found no evidence of non-thermal emission spatially coincident with the bow shocks; nonetheless, diffuse emission was detected in the vicinity of ζ oph. after a careful analysis of its spectral characteristics, we conclude that this emission has a thermal nature with a plasma temperature of t ≈ 2 × 106 k. the cometary shape of this emission seems to be in line with recent predictions of radiation-hydrodynamic models of runaway stars. the case of bd+43°3654 is puzzling, as non-thermal emission has been reported in a previous work for this source. | x-ray observations of bow shocks around runaway o stars. the case of ζ oph and bd+43°3654 |
multiple outbursts of a jupiter-family comet (jfc), 15p/finlay, occurred from late 2014 to early 2015. we conducted an observation of the comet after the first outburst and subsequently witnessed another outburst on 2015 january 15.6-15.7. the gas, consisting mostly of c2 and cn, and dust particles expanded at speeds of 1110 ± 180 m s-1 and 570 ± 40 m s-1 at a heliocentric distance of 1.0 au. we estimated the maximum ratio of solar radiation pressure with respect to the solar gravity β max = 1.6 ± 0.2, which is consistent with porous dust particles composed of silicates and organics. we found that 108-109 kg of dust particles (assumed to be 0.3 μm-1 mm) were ejected through each outburst. although the total mass is three orders of magnitude smaller than that of the 17p/holmes event observed in 2007, the kinetic energy per unit mass (104 j kg-1) is equivalent to the estimated values of 17p/holmes and 332p/2010 v1 (ikeya-murakami), suggesting that the outbursts were caused by a similar physical mechanism. from a survey of cometary outbursts on the basis of voluntary reports, we conjecture that 15p/finlay-class outbursts occur >1.5 times annually and inject dust particles from jfcs and encke-type comets into interplanetary space at a rate of ∼10 kg s-1 or more. | 2014-2015 multiple outbursts of 15p/finlay |
in the era of "big data" and with the advent of web 2.0 technologies, esasky (http://sky.esa.int) aims at providing a modern and visual way to access astronomical science-ready data products and metadata. the main goal of the application is to simplify the interaction between the scientific community and the ever-growing amount of data collected over the past decades from the most important astronomy missions. the esasky concept is to offer a complementary scientific application to the more-traditional table-oriented exploitation of astronomical data, by allowing a more natural and visual approach and enabling the exploration of astronomical objects across the entire electromagnetic spectrum. to fulfil this goal, esasky provides a multiwavelength interface to a set of astronomy data from an increasing number of missions and surveys, with the intention of becoming the single-point of entry to perform visual analysis and cross-matching among different energy ranges. a lot of effort has been invested on the design of a user-friendly, responsive graphical user interface (gui) by the definition and optimisation of algorithms running behind each visual feature offered. in this contribution, we describe in detail the design and solutions adopted for the technical challenges arising during the development. we present the data services and features implemented in the latest version of esasky (v2.1), including a mission planning tool to support current james webb space telescope (jwst) planning, the possibility to search for observations of solar system objects (planets, comets and moons) taken by astronomy missions, the integration of the sao/nasa astrophysics data system (ads) publication system in the esasky gui, and the retrieval of metadata and data products available within a specific region of the sky. | esasky: a science-driven discovery portal for space-based astronomy missions |
the properties of dust inertial alfvén waves (diaws) in a dusty plasma with the effects of polarization force are investigated. first, the dispersion equation is obtained from the fluid equations by considering the polarization force. then, the energy balance equation is deduced by applying the sagdeev pseudopotential method. it is shown that the polarization force affects the characteristics of diaws as well as the pseudopotential significantly. in addition, the existence of the polarization force changes the width of diaws. the present results may be helpful in further understanding the effect of polarization forces on the formation of linear and nonlinear structures of alfvén waves in the laboratory plasma, astrophysical dusty plasma systems, planetary ring systems, cometary tails, etc. | inertial alfvén waves with polarization force in a dusty plasma |
outbursts and variations of brightness are well known manifestations of the physical activity of the comets. most cometary outbursts are recorded not very far from the sun, where sublimation of water ice plays a major role in the activity of this celestial bodies. however, comets sometimes show physical activity far from the sun, where the rate of water ice sublimation is small. also a special kind of small bodies, i.e. centaurs sometimes show strong physical activity far from the sun. the paper is based on the idea that the nuclei of centaurs may contain numerous cavities that are filled with gas under pressure and debris of cometary material. numerical simulations were carried out for realistically assumed values of a wide range of physical parameters of centaurs. the obtained results are consistent with the observations of the physical activity of these celestial bodies. | a new simple model of comets-like activity of centaurs |
in the present article, we propose a new method of mass estimation which is ejected from a nucleus of a comet during its outburst of brightness. the phenomena of cometary outburst are often reported for both periodic and parabolic comets. the outburst of a comet brightness is a sudden increase in its brightness greater than one magnitude, average by 2-5 mag. this should not be confused with explosions such as outbreak of a bomb. the essence of the phenomenon is only a sudden brightening of the comet. long-term observations and studies of this phenomenon lead to the conclusion that the very probable direct cause of the many outbursts is the ejection of the some part of surface layer of a comet's nucleus and an increase in the rate of a sublimation (hughes (1990), gronkowski (2007), gronkowski and wesołowski (2015)). the purpose of this article is presentation of a new simple method of the estimation of the mass which is ejected from the comet's nucleus during considered phenomenon. to estimate the mass released during an outburst, different probable coefficients of extinction for cometary matter was assumed. the scattering cross-sections of cometary grains were precisely calculated on the basis of mie's theory. this method was applied to the outburst of a hypothetical comet x/pc belonging to the jupiter-family comets and to the case of the comet 17p/holmes outburst in 2007. | a new method for determining the mass ejected during the cometary outburst - application to the jupiter-family comets |
context. the issue of the long term dynamics of jupiter family comets (jfcs) involves uncertain assumptions about the physical evolution and lifetimes of these comets. contrary to what is often assumed, real effects of secular dynamics cannot be excluded and therefore merit investigation.aims: we use a random sample of late heavy bombardment cometary projectiles to study the long-term dynamics of jfcs by a monte carlo approach. in a steady-state picture of the jupiter family, we investigate the orbital distribution of jfcs, including rarely visited domains like retrograde orbits or orbits within the outer parts of the asteroid main belt.methods: we integrate 100 000 objects over a maximum of 100 000 orbital revolutions including the sun, a comet, and four giant planets. considering the steady-state number of jfcs to be proportional to the total time spent in the respective orbital domain, we derive the capture rate based on observed jfcs with small perihelia and large nuclei. we consider a purely dynamical model and one where the nuclei are eroded by ice sublimation.results: the jfc inclination distribution is incompatible with our erosional model. this may imply that a new type of comet evolution model is necessary. considering that comets may live for a long time, we show that jfcs can evolve into retrograde orbits as well as asteroidal orbits in the outer main belt or cybele regions. the steady-state capture rate into the jupiter family is consistent with 1 × 109 scattered disk objects with diameters d > 2 km.conclusions: our excited scattered disk makes it difficult to explain the jfc inclination distribution, unless the physical evolution of jfcs is more intricate than assumed in standard, erosional models. independent of this, the population size of the jupiter family is consistent with a relatively low-mass scattered disk. | secular orbital evolution of jupiter family comets |
this paper describes in detail hydroplastic structures, which are 'odd' kinematic indicators in the basal part of the eocene middle rus formation. such structures were previously ignored or falsely interpreted. these hydroplastic structures are found in the massive limestone exposures on the king fahd university of petroleum and minerals (kfupm) campus. they occur in relation to a principal displacement zone along the boundary/interface between the lower/middle rus, which is referred to as the rus soft-sediment detachment. the structures are fist-sized vugs associated with carrot- or comet-trail imprints (vct structures) which were previously translated calcite geodes that have been weathered out. vct structures show transport/slip towards the nnw (345°) and are found on flat to low-dipping surfaces classified as y, r and p shears with respect to the orientation of the rus detachment. palaeostress analysis indicates an andersonian transtension stress regime, though it does not facilitate the activation of the rus soft-sediment detachment. detachment activity occurred due to the negative effective principal stress σ3′ and the abnormally low frictional coefficient caused by fluid pressure. the soft-sediment rus detachment can be considered a 'sensitive stress sensor' for the zagros collision since it indicates the arabian platform's instability in the wider area of the dammam dome during the late eocene. this instability is attributed to the inception of the zagros collision, which was previously considered to occur during the oligocene based on the well-established pre-neogene unconformity. | rus detachment in dammam dome, eastern saudi arabia: a new soft-sediment structure as a 'sensitive stress sensor' for the zagros collision |
it has been suggested that the comet-like activity of main-belt comets (mbcs) is due to the sublimation of sub-surface water-ice that is exposed when these objects are impacted by meter-sized bodies. we recently examined this scenario and showed that such impacts can, in fact, excavate ice and present a plausible mechanism for triggering the activation of mbcs. however, because the purpose of that study was to prove the concept and identify the most viable ice-longevity model, the porosity of the object and the loss of ice due to the heat of impact were ignored. in this paper, we extend our impact simulations to porous materials and account for the loss of ice due to an impact. we show that for a porous mbc, impact craters are deeper, reaching to ∼15 m, implying that if the activation of mbcs is due to the sublimation of sub-surface ice, this ice has to be within the top 15 m of the object. results also indicate that the loss of ice due to the heat of impact is negligible, and the re-accretion of ejected ice is small. the latter suggests that the activities of current mbcs are most probably from multiple impact sites. our study also indicates that for sublimation from multiple sites to account for the observed activity of the currently known mbcs, the water content of mbcs (and their parent asteroids) needs to be larger than the values traditionally considered in models of terrestrial planet formation. | triggering the activation of main-belt comets: the effect of porosity |
we use n-body/hydrodynamical simulations to interpret the newly discovered bullet-cluster-like merging cluster zwcl 0008.8+5215 (zwcl008 hereafter), where a dramatic collision is apparent from multiwavelength observations. we have been able to find a self-consistent solution for the radio, x-ray, and lensing phenomena by projecting an off-axis, binary cluster encounter viewed just after first core passage. a pair of radio relics traces the leading (bow) and trailing (back) shock fronts that our simulation predicts, providing constraints on the collision parameters. we can also account for the observed distinctive comet-like x-ray morphology and the positions of the x-ray peaks relative to the two lensing mass centroids and the location of the well-defined bow shock. relative to the bullet cluster, the total mass is about 70% lower, ∼1.2 × 1015 m ⊙, with a correspondingly lower infall velocity, ∼1800 km s-1, and an impact parameter of p ∼ 400 kpc. as a result, the gas component of the infalling cluster is not trailing significantly behind the associated dark matter as in the case of the bullet cluster. | multi-phenomena modeling of the new bullet-like cluster zwcl 008.8+52 using n-body/hydrodynamical simulations |
the water production rate of a comet is one of the fundamental parameters necessary to understand cometary activity when a comet approaches the sun within 2.5 au, because water is the most abundant icy material in the cometary nucleus. wide-field imaging observations of the hydrogen lyα emission in comet 67p/churyumov-gerasimenko were performed by the lyman alpha imaging camera (laica) on board the 50 kg class micro spacecraft, the proximate object close flyby with optical navigation (procyon), on ut 2015 september 7.40, 12.37, and 13.17 (corresponding to 25.31, 30.28, and 31.08 days after the perihelion passage of the comet, respectively). we derive the water production rates, {q}{{{h}}2{{o}}}, of the comet from lyα images of the comet by using a 2d axi-symmetric direct simulation monte-carlo model of the atomic hydrogen coma; (1.46 ± 0.47) × 1028, (1.24 ± 0.40) × 1028, and (1.30 ± 0.42) × 1028 molecules s-1 on 7.40, 12.37, and 13.17 september, respectively. these values are comparable to the values from in situ measurements by the rosetta instruments in the 2015 apparition and the ground-based and space observations during the past apparitions. the comet did not show significant secular change in average water production rates just after the perihelion passage for the apparitions from 1982 to 2015. we emphasize that the measurements of absolute {q}{{{h}}2{{o}}} based on the wide field of view (e.g., by the laica/procyon) are so important to judge the soundness of the coma models used to infer {q}{{{h}}2{{o}}} based on in situ measurements by spacecraft, like the rosetta. | imaging observations of the hydrogen coma of comet 67p/churyumov-gerasimenko in 2015 september by the procyon/laica |
as the solar system moves through the interstellar medium, the solar wind is deflected forming the heliosphere. the standard picture of the heliosphere is a comet-shape like structure with the tail extending for 1000s of astronomical units. this standard picture stems from a view where magnetic forces are negligible and the solar magnetic field is convected passively down the tail. recently, we showed that the magnetic tension of the solar magnetic field plays a crucial role on organizing the solar wind in the heliosheath into two jet-like structures. the two jets are separated by the interstellar medium that flows between them. the heliosphere then has a "croissant"-like shape where the distance to the heliopause downtail is almost the same as towards the nose. this new view of the heliosphere is in agreement with the energetic neutral atoms maps taken by the interstellar boundary explorer and inca/cassini. we developed as well an analytic model of the heliosheath in the axisymmetric limit that shows how the magnetic tension force is the driver for the north and south jets. we confirmed that the formation of these jets with magnetohydrodynamic (mhd) simulations. the main reason why previous global mhd simulations did not see these jets is due to spurious magnetic dissipation that was present at the heliospheric current sheet. we instead kept the same polarity for the interplanetary (solar) magnetic field in both the northern and southern hemispheres, eliminating spurious magnetic dissipation effects at the heliospheric current sheet. in this paper, we extend these previous results to include additional cases where we used: (a) weaker solar magnetic field; (b) solar magnetic field that reverses polarity at the solar equator in the axisymmetric limit; and (c) slower motion through the interstellar system. we discuss as well future challenges regarding the structure of the heliosphere. | magnetized jets driven by the sun: the structure of the heliosphere revisited—updates |
the disruption of an icy moon in a collision with an interloping comet a few hundred million years ago is a simple way to create saturn's rings. a ring parent moon with a mass comparable to mimas could be trapped in mean motion resonance with enceladus and dione in an orbit near the current outer edge of the rings just beyond the roche zone. i present collisional n-body simulations of cometary impacts that lead to the partial disruption of a differentiated moon with a rocky core and icy mantle. the core can survive largely intact while the debris from the mantle settles into a ring of predominantly ice particles straddling the orbital radius of the parent moon. the nascent ring spreads radially due to collisional viscosity while mass re-accretes onto the remnant rocky core to form a new moon that can be identified as mimas. the icy debris that migrates into the roche zone evolves into saturn's ring system. torques from tidal interaction with saturn and resonant interactions with the rings push the recently formed mimas outward to its current position on the same timescale of a few hundred million years. this scenario accounts for the high ice fraction observed in saturn's rings and explains why the ring mass is comparable to the mass of mimas. the prior existence of a ring parent moon in mean motion resonance results in a tidal heating rate for enceladus in the recent past that is significantly larger than the current rate. | a recent origin for saturn's rings from the collisional disruption of an icy moon |
based on the high abundance of fine-grained material and its dark appearance, nwa 11024 was recognized as a cm chondrite, which is also confirmed by oxygen isotope measurements. but contrary to known cm chondrites, the typical phases indicating aqueous alteration (e.g., phyllosilicates, carbonates) are missing. using multiple analytical techniques, this study reveals the differences and similarities to known cm chondrites and will discuss the possibility that nwa 11024 is the first type 3 cm chondrite. during the investigation, two texturally apparent tochilinite-cronstedtite intergrowths were identified within two thin sections. however, the former phyllosilicates were recrystallized to fe-rich olivine during a heating event without changing the textural appearance. a peak temperature of 400-600 °c is estimated, which is not high enough to destroy or recrystallize calcite grains. thus, calcites were never constituents of the mineral paragenesis. another remarkable feature of nwa 11024 is the occurrence of unknown clot-like inclusions (uclis) within fine-grained rims, which are unique in this clarity. their density and s concentration are significantly higher than of the surrounding fine-grained rim and uclis can be seen as primary objects that were not formed by secondary alteration processes inside the rims. similarities to chondritic and cometary interplanetary dust particles suggest an ice-rich first-generation planetesimal for their origin. in the earliest evolution, nwa 11024 experienced the lowest degree of aqueous alteration of all known cm chondrites and subsequently, a heating event dehydrated the sample. we suggest to classify the meteorite nwa 11024 as the first type 3 cm chondrite similar to the classification of cv3 chondrites (like allende) that could also have lost their matrix phyllosilicates by thermal dehydration. | northwest africa 11024—a heated and dehydrated unique carbonaceous (cm) chondrite |
we imaged comet 252p/2000 g1 (linear; hereafter 252p) with the hubble space telescope and both 252p and p/2016 ba14 (panstarrs; hereafter ba14) with the discovery channel telescope in 2016 march and april, surrounding its close encounter to earth. the r‧-band afρ of 252p in a 0.″2-radius aperture were 16.8 ± 0.3 and 57 ± 1 cm on march 14 and april 4, respectively, and its gas production rates were q(oh) = (5.8 ± 0.1) × 1027 s-1, and q(cn) = (1.25 ± 0.01) × 1025 s-1 on april 17. the r‧-band upper limit afρ of ba14 was 0.19 ± 0.01 cm in a 19.″2-radius aperture, and q(cn) = (1.4 ± 0.1) × 1022 s-1 on 2017 april 17. 252p shows a bright and narrow jet of a few hundred kilometers long in the sunward direction, changing its projected position angle in the sky with a periodicity consistent with 7.24 hr. however, its photometric light curve is consistent with a periodicity of 5.41 hr. we suggest that the nucleus of 252p is likely in a non-principal axis rotation. the nucleus radius of 252p is estimated to be about 0.3 ± 0.03 km, indicating an active fraction of 40% to >100% in its 2016 apparition. evidence implies a possible cloud of slow-moving grains surrounding the nucleus. the activity level of 252p in the 2016 apparition increased by two orders of magnitude from its previous apparitions, making this apparition unusual. on the other hand, the activity level of ba14 appears to be at least three orders of magnitude lower than that of 252p, despite its 10 times or larger surface area. | the unusual apparition of comet 252p/2000 g1 (linear) and comparison with comet p/2016 ba14 (panstarrs) |
small bodies in the solar system are conventionally classified into asteroids and comets. however, it is recently found that a small number of objects can exhibit properties of both asteroids and comets. some are more consistent with asteroids despite episodic ejections and are labeled as "active asteroids", while some might be aging comets with depleting volatiles. ejecta produced by active asteroids and/or dormant comets are potentially detectable as meteor showers at the earth if they are in earth-crossing orbits, allowing us to retrieve information about the historic activities of these objects. meteor showers from small bodies with low and/or intermittent activities are usually weak, making shower confirmation and parent association challenging. we show that statistical tests are useful for identifying likely parent-shower pairs. comprehensive analyses of physical and dynamical properties of meteor showers can lead to deepen understanding on the history of their parents. meteor outbursts can trace to recent episodic ejections from the parents, and "orphan" showers may point to historic disintegration events. the flourish of neo and meteor surveys during the past decade has produced a number of high-confidence parent-shower associations, most have not been studied in detail. more work is needed to understand the formation and evolution of these parent-shower pairs. | meteor showers from active asteroids and dormant comets in near-earth space: a review |
we apply a principal component analysis (pca)-based pre-whitening method to the entire collection of main kepler mission long-cadence data for kic 8462852 spanning four years. this technique removes the correlated variations of instrumental origin in both the detected light curves and astrometry, resolving intrinsic changes in flux and image position of less than 100 ppm and 1 mas, respectively. beside the major dips in the light curve during mission quarters 8 and 16, when the flux dropped by up to 20%, we confirm multiple smaller dips across the time span of observation with amplitudes ranging from 0.1% to 7%. a variation of flux with a period of 0.88 day and a half-amplitude of approximately 90 ppm is confirmed in the pca-cleaned data. we find that the phase of the wave is steady over a 15 month interval. we confidently detect a weak variability-induced motion (vim) effect in the cleaned astrometric trajectories, when the moment-based centroids shift synchronously with the flux dips by up to 0.0008 pixels on the detector. the inconsistent magnitude and direction of vim effects within the same quarter point at more than one source of photometric variability in the blended image. the 0.88 day periodicity comes from a different source, not from the target star kic 8462852. we discuss a possible interpretation of the bizarre properties of the source as a swarm of interstellar junk (comets and planetoids) crossing the line of sight to the star and its optical companions at approximately 7 mas yr-1. | photometric and astrometric vagaries of the enigma star kic 8462852 |
aims: 2p/encke is a short period comet that was discovered in 1786 and has been extensively observed and studied for more than 200 years. the taurid meteoroid stream has long been linked with 2p/encke owing to a good match of their orbital elements, even though the comet's activity is not strong enough to explain the number of observed meteors. various small near-earth objects (neos) have been discovered with orbits that can be linked to 2p/encke and the taurid meteoroid stream. maribo and sutter's mill are cm type carbonaceous chondrite that fell in denmark on january 17, 2009 and april 22, 2012, respectively. their pre-atmospheric orbits place them in the middle of the taurid meteoroid stream, which raises the intriguing possibility that comet 2p/encke could be the parent body of cm chondrites.methods: to investigate whether a relationship between comet 2p/encke, the taurid complex associated neos, and cm chondrites exists, we performed photometric and spectroscopic studies of these objects in the visible wavelength range. we observed 2p/encke and 10 neos on august 2, 2011 with the fors instrument at the 8.2 m very large telescope on cerro paranal (chile).results: images in the r filter, used to investigate the possible presence of cometary activity around the nucleus of 2p/encke and the neos, show that no resolved coma is present. none of the fors spectra show the 700 nm absorption feature due to hydrated minerals that is seen in the cm chondrite meteorites. all objects show featureless spectra with moderate reddening slopes at λ< 800 nm. apart for 2003 qc10 and 1999 vt25, which show a flatter spectrum, the spectral slope of the observed neos is compatible with that of 2p/encke. however, most of the neos show evidence of a silicate absorption in lower s/n data at λ> 800 nm, which is not seen in 2p/encke, which suggests that they are not related.conclusions: despite similar orbits, we find no spectroscopic evidence for a link between 2p/encke, the taurid complex neos and the maribo and sutter's mill meteorites. however, we cannot rule out a connection to the meteorites either, as the spectral differences may be caused by secondary alteration of the surfaces of the neos. based on observations performed at the european southern observatory, paranal, chile: program 087.c-0788(a). | 2p/encke, the taurid complex neos and the maribo and sutter's mill meteorites |
this paper develops a unified linear theory of local cross-field plasma instabilities, such as the farley-buneman, electron thermal, and ion thermal instabilities, in collisional plasmas with fully or partially unmagnetized multi-species ions. collisional lasma instabilities in low-ionized, highly dissipative, weakly magnetized plasmas play an important role in the lower earth's ionosphere and may be of importance in other planet ionospheres, star atmospheres, cometary tails, molecular clouds, accretion disks, etc. in the solar chromosphere, macroscopic effects of collisional plasma instabilities may contribute into significant heating -- an effect originally suggested from spectroscopic observations and relevant modeling. based on a simplified 5-moment multi-fluid model, the theoretical analysis produces the general linear dispersion relation for the combined thermal-farley-buneman instability (tfbi). important limiting cases are analyzed in detail. the analysis demonstrates acceptable applicability of this model for the rocesses under study. fluid-model simulations usually require much less computer resources than do more accurate kinetic simulations, so that the apparent success of this approach to the linear theory of collisional plasma instabilities makes it possible to investigate the tfbi (along with its possible macroscopic effects) using global fluid codes originally developed for large-scale modeling of the solar and planetary atmospheres. | unified fluid-model theory of $\\mathbf{e}\\times\\mathbf{b}$ instabilities in low-ionized collisional plasmas with arbitrarily magnetized multi-species ions |
the diffusion of gas through porous material is important to understand the physical processes underlying cometary activity. we study the diffusion of a rarefied gas (knudsen regime) through a packed bed of monodisperse spheres via experiments and numerical modelling, providing an absolute value of the diffusion coefficient and compare it to published analytical models. the experiments are designed to be directly comparable to numerical simulations, by using precision steel beads, simple geometries, and a trade-off of the sample size between small boundary effects and efficient computation. for direct comparison, the diffusion coefficient is determined in direct simulation monte carlo (dsmc) simulations, yielding a good match with experiments. this model is further-on used on a microscopic scale, which cannot be studied in experiments, to determine the mean path of gas molecules and its distribution, and compare it against an analytical model. scaling with sample properties (particle size and porosity) and gas properties (molecular mass and temperature) is consistent with analytical models. as predicted by these, results are very sensitive on sample porosity and we find that a tortuosity q(ɛ) depending linearly on the porosity ɛ can well reconcile the analytical model with experiments and simulations. mean paths of molecules are close to those described in the literature, but their distribution deviates from the expectation for small path lengths. the provided diffusion coefficients and scaling laws are directly applicable to thermophysical models of idealized cometary material. | simulation and experiment of gas diffusion in a granular bed |
the rosetta mission escorted comet 67p/churyumov-gerasimenko for approximately two years including the perihelion passage (1.24 au, 2015 august), allowing us to monitor the seasonal evolution of the water and carbon dioxide loss rates. here, we model 67p/churyumov-gerasimenko water and carbon dioxide production as measured by the rosina experiment during the entire escort phase by applying the water-ice-enriched block (web) model, namely a structural and activity model for a nucleus made of pebbles. furthermore, we compare the surface temperature distribution inferred by virtis-m observations in 2014 august (≈3.5 au inbound, northern summer) with the expected temperatures from our simulations in the nucleus' northern hemisphere, investigating the relevance of self-illumination effects in the comet 'neck' and assessing the active area extent during the northern summer. our simulations imply that: (1) water production at perihelion is mostly from the dehydration of water-poor pebbles, continuously exposed by co2-driven erosion; (2) at large heliocentric distances outbound the water loss rate is dominated by the self-cleaning of fallout deposits; (3) the outbound steep decrease of the water production curve with heliocentric distance results from the progressive reduction of the nucleus water-active area, as predicted by the proposed model; (4) in 2014 august the water production is dominated by distributed sources, originating in the active 'neck'; (5) distributed sources originating in water-ice-rich exposures dominate the water production approximately up to the inbound equinox; (6) the time evolution of the co2 loss rate during the rosetta escort phase is consistent with the web model. | comparison of a pebbles-based model with the observed evolution of the water and carbon dioxide outgassing of comet 67p/churyumov-gerasimenko |
context. high-mass stars form in much richer environments than those associated with isolated low-mass stars, and once they reach a certain mass, produce ionised (hii) regions. the formation of these pockets of ionised gas are unique to the formation of high-mass stars (m > 8 m⊙), and present an excellent opportunity to study the final stages of accretion, which could include accretion through the hii region itself. aim. this study of the dynamics of the gas on both sides of these ionisation boundaries in very young hii regions aims to quantify the relationship between the hii regions and their immediate environments.methods: we present high-resolution ( 0.5″) alma observations of nine hii regions selected from the red msx source survey with compact radio emission and bolometric luminosities greater than 104 l⊙. we focus on the initial presentation of the data, including initial results from the radio recombination line h29α, some complementary molecules, and the 256 ghz continuum emission.results: of the six (out of nine) regions with h29α detections, two appear to have cometary morphologies with velocity gradients across them, and two appear more spherical with velocity gradients suggestive of infalling ionised gas. the remaining two were either observed at low resolution or had signals that were too weak to draw robust conclusions. we also present a description of the interactions between the ionised and molecular gas (as traced by cs (j = 5 - 4)), often (but not always) finding the hii region had cleared its immediate vicinity of molecules.conclusions: of our sample of nine, the observations of the two clusters expected to have the youngest hii regions (from previous radio observations) are suggestive of having infalling motions in the h29α emission, which could be indicative of late stage accretion onto the stars despite the presence of an hii region. table a.2 is also 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/611/a99 | the evolution of young hii regions. i. continuum emission and internal dynamics |
'oumuamua and borisov were the first two interstellar objects confirmed in the solar system. the upcoming commencement of the vera c. rubin observatory&'s legacy survey of space of time (lsst) will enhance greatly the discovery rate of interstellar objects. this raises the question, what can be learned from large-number statistics of interstellar objects? here, we show that discovery statistics provided by lsst will allow low- and high-ejection-speed populations to be distinguished using the velocity dispersion and angular anisotropy of interstellar objects. these findings can be combined with physical characterizations to yield a better understanding of planetary system origin and nature. | observable signatures of the ejection speed of interstellar objects from their birth systems |
we investigate the chemical composition of the solar system's giant planets atmospheres using a physical formation model with chemistry. the model incorporate disc evolution, pebbles and gas accretion, type i and ii migration, simplified disc photoevaporation and solar system chemical measurements. we track the chemical compositions of the formed giant planets and compare them to the observed values. two categories of models are studied: with and without disc chemical enrichment via photoevaporation (pe). predictions for the oxygen and nitrogen abundances, core masses and total amount of heavy elements for the planets are made for each case. we find that in the case without disc pe, both jupiter and saturn will have a small residual core and comparable total amounts of heavy elements in the envelopes. we predict oxygen abundances enrichments in the same order as carbon, phosphorus and sulfur for both planets. cometary nitrogen abundances does not allow us to easily reproduce jupiter's nitrogen observations. in the case with disc pe, less core erosion is needed to reproduce the chemical composition of the atmospheres, so both planets will end up with possibly more massive residual cores and higher total mass of heavy elements. it is also significantly easier to reproduce jupiter's nitrogen abundance. no single disc was found to form both jupiter and saturn with all their constraints in the case without photoevaporation. no model was able to fit the constraints on uranus and neptune, hinting towards a more complicated formation mechanism for these planets. the predictions of these models should be compared to the upcoming juno measurements to better understand the origins of the solar system giant planets. | a pebbles accretion model with chemistry and implications for the solar system |
we re-introduce a semiclassical methodology based on theories developed for the determination of broadening coefficients. we show that this simple and extremely fast methodology provides results that are in good agreement with results obtained using the more sophisticate mqct approach. this semiclassical methodology could be an alternative approach which allows to provide large sets of collisional data for very complex molecular systems. it saves time both on the determination of potential energy surfaces and on the collisional dynamical calculations. in addition, this paper provides more complete sets of rotational de-excitation cross-sections and rate coefficients of h2o perturbed by a thermal average of water molecules. those data can be used in the radiative transfer modelling of cometary atmospheres. | new h2o-h2o collisional rate coefficients for cometary applications |
the discovery of the first interstellar comet 2i/borisov confirmed the astronomers' speculation that the passage through the solar system of relatively large objects (asteroids and comets) formed outside of it is a common occurrence. there may be many such objects, but their discovery is still a rare case. large professional telescopes and existing observation programs with these telescopes have limitations that can be overcome with more modest instruments. the paper describes for the first time how comet 2i/borisov was discovered with the 65-cm telescope designed by g.v. borisov and those features of the observation program that made it possible to make this discovery. recommendations are given for constructing future programs for detecting such bodies. the spatial density of interstellar objects (such as asteroid 1i/'oumuamua or comet 2i/borisov) in the solar neighborhood has been estimated. according to our estimate, there may be about 50 interstellar bodies >50 m in size in the solar system in a sphere with a radius of 50 au at any given time. since the speeds of possible approach to the earth of such objects can be very high, such probable approaches require special attention. the use of special space projects for their study is discussed. | discovery of the first interstellar comet and the spatial density of interstellar objects in the solar neighborhood |
we present a study of interstellar comet 2i/2019 q4 (borisov) using both preperihelion and postperihelion observations spanning late september 2019 through late january 2020. the intrinsic brightness of the comet was observed to continuously decline throughout the timespan, likely due to the decreasing effective scattering cross-section as a result of volatile sublimation with a slope of $-0.43 \pm 0.02$ km$^{2}$ d$^{-1}$. we witnessed no significant change in the slightly reddish colour of the comet, with mean values of $\left \langle g - r \right \rangle = 0.68 \pm 0.04$, $\left \langle r - i \right \rangle = 0.23 \pm 0.03$, and the normalised reflectivity gradient across the $g$ and $i$ bands $\overline{s'} \left(g,i\right) = \left(10.6 \pm 1.4\right)$ % per $10^3$ å, all unremarkable in the context of solar system comets. using the available astrometric observations, we confidently detect the nongravitational acceleration of the comet following a shallow heliocentric distance dependency of $r_{\rm h}^{-1 \pm 1}$. accordingly, we estimate that the nucleus is most likely $\lesssim$0.4 km in radius, and that a fraction of $\gtrsim$0.2% of the total nucleus in mass has been eroded due to the sublimation activity since the earliest observation of the comet in 2018 december by the time of perihelion. our morphology simulation suggests that the dust ejection speed increased from $\sim$4 m s$^{-1}$ in september 2019 to $\sim$7 m s$^{-1}$ around perihelion for the optically dominant dust grains of $\beta \sim 0.01$, and that the observable dust grains are no smaller than micron size. | physical characterisation of interstellar comet 2i/2019 q4 (borisov) |
the near-sun comet c/2019 y4 (atlas) is the first member of a long-period comet group observed to disintegrate well before perihelion. here we present our investigation into this disintegration event using images obtained in a three-day hubble space telescope campaign. we identify two fragment clusters produced by the initial disintegration event, corresponding to fragments c/2019 y4-a and c/2019 y4-b identified in ground-based data. these two clusters started with similar integrated brightness but exhibit different evolutionary behavior. c/2019 y4-a was much shorter-lived compared to c/2019 y4-b and showed signs of significant mass loss and changes in size distribution throughout the three-day campaign. the cause of the initial fragmentation is undetermined by the limited evidence but crudely compatible with either the spin-up disruption of the nucleus or runaway sublimation of subsurface supervolatile ices, either of which would lead to the release of a large amount of gas as inferred from the significant bluing of the comet observed shortly before its disintegration. gas can only be produced by the sublimation of volatile ices, which must have survived at least one perihelion passage at a perihelion distance of q = 0.25 au. we speculate that comet atlas is derived from the ice-rich interior of a nonuniform, kilometer-wide progenitor that split during its previous perihelion. this suggests that comets down to a few kilometers in diameter can still possess complex, nonuniform interiors that can protect ices against intense solar heating. | disintegration of long-period comet c/2019 y4 (atlas). i. hubble space telescope observations |
planetary embryos are built through the collisional growth of 10-100 km-sized objects called planetesimals, a formerly large population of objects, of which asteroids, comets, and kuiper belt objects represent the leftovers from planet formation in our solar system. here, we follow the paradigm that turbulence created overdense pebble clouds, which then collapse under their own self-gravity. we use the multiphysics code gizmo to model the pebble cloud density as a continuum, with a polytropic equation of state to account for collisional interactions and capturing the phase transition to a quasi-incompressible "solid" object, i.e., a planetesimal in hydrostatic equilibrium. thus, we study cloud collapse effectively at the resolution of the forming planetesimals, allowing us to derive an initial mass function for planetesimals in relation to the total pebble mass of the collapsing cloud. the redistribution of angular momentum in the collapsing pebble cloud is the main mechanism leading to multiple fragmentation. the angular momentum of the pebble cloud and thus the centrifugal radius increases with distance to the sun, but the solid size of the forming planetesimals is constant. therefore we find that with increasing distance to the sun, the number of forming planetesimals per pebble cloud increases. for all distances, the formation of binaries occurs within higher hierarchical systems. the size distribution is top-heavy and can be described with a gaussian distribution of planetesimal mass. for the asteroid belt, we can infer a most likely size of 125 km, all stemming from pebble clouds of equivalent size 152 km. | high-resolution study of planetesimal formation by gravitational collapse of pebble clouds |
we review the properties of dust formed during classical nova eruptions and the very late thermal pulses (vltps) that occur during the later stages of post-asymptotic giant branch evolution of low-mass stars. in both cases, carbon and hydrocarbon dust is produced. novae may also produce silicate dust, contrary to the usual paradigm about the c:o ratio and dust composition. despite the expectation that these dust sources are not expected to make significant contributions to the galactic dust population, there is a significant body of evidence that grains from both stellar sources have been identified in recovered meteoritic and cometary material, and that certain infrared spectral signatures seen in comets are common to novae, vltps and pre-solar grains. | pre-solar grains from novae and "born-again giants" |
we study the size frequency distribution of the blocks located in the deeply fractured, geologically active enceladus south polar terrain with the aim to suggest their formative mechanisms. through the cassini iss images, we identify ~17,000 blocks with sizes ranging from ~25 m to 366 m, and located at different distances from the damascus, baghdad and cairo sulci. on all counts and for both damascus and baghdad cases, the power-law fitting curve has an index that is similar to the one obtained on the deeply fractured, actively sublimating hathor cliff on comet 67p/churyumov-gerasimenko, where several non-dislodged blocks are observed. this suggests that as for 67p, sublimation and surface stresses favor similar fractures development in the enceladus icy matrix, hence resulting in comparable block disaggregation. a steeper power-law index for cairo counts may suggest a higher degree of fragmentation, which could be the result of localized, stronger tectonic disruption of lithospheric ice. eventually, we show that the smallest blocks identified are located from tens of m to 20–25 km from the sulci fissures, while the largest blocks are found closer to the tiger stripes. this result supports the ejection hypothesis mechanism as the possible source of blocks. | blocks size frequency distribution in the enceladus tiger stripes area: implications on their formative processes |
cometary ice analogs: amorphous h2o ice can trap other molecules up to ∼30% by number, which are outgassed during ice crystallization (130 k to 150 k). beyond 160 k, crystalline ice sublimes with only a minor fraction (<1%) of other molecules with it. ice is a major component of astrophysical environments – from interstellar molecular clouds through protoplanetary disks to evolved solar systems. ice and complex organic matter coexist in these environments as well, and it is thought primordial ice brought the molecules of life to earth four billion years ago, which could have kickstarted the origin of life on earth. to understand the journey of ice and organics from their origins to becoming a part of evolved planetary systems, it is important to complement high spatial and spectral resolution telescopes such as jwst with laboratory experimental studies that provide deeper insight into the processes that occur in these astrophysical environments. our laboratory studies are aimed at providing this knowledge. in this article we present simultaneous mass spectrometric and infrared spectroscopic investigation on how molecular ice mixtures behave at different temperatures and how this information is critical to interpret observational data from protoplanetary disks as well as comets. we find that amorphous to crystalline water ice transformation is the most critical phenomenon that differentiates between outgassing of trapped volatiles such as co2vs. outgassing of pure molecular ice domains of the same in a mixed molecular ice. crystalline water ice is found to trap only a small fraction of other volatiles (<5%), indicating ice grain composition in astrophysical and planetary environments must be different depending on whether the ice is in amorphous phase or transformed into crystalline phase, even if the crystalline ice undergoes radiation-induced amorphization subsequently. crystallization of water ice is a key differentiator for many ices in astronomical environments as well as in our solar system. | thermal behavior of astrophysical amorphous molecular ices |
optical properties are required for the correct understanding and modelling of protoplanetary and debris discs. by assuming that comets are the most pristine bodies in the solar system, our goal is to derive optical constants of real protoplanetary material. we determine the complex index of refraction of the near-surface material of comet 67p/churyumov-gerasimenko by fitting the sub-millimetre/millimetre observations of the thermal emission of the comet's sub-surface made by the microwave instrument for the rosetta orbiter with synthetic temperatures derived from a thermophysical model and radiative-transfer models. according to the two major formation scenarios of comets, we model the sub-surface layers to consist of pebbles as well as of homogeneously packed dust grains. in the case of a homogeneous dusty surface material, we find a solution for the length-absorption coefficient of α ≈ 0.22 cm-1 for a wavelength of 1.594 mm and α ≥ 3.84 cm-1 for a wavelength of 0.533 mm and a constant thermal conductivity of 0.006 w m-1 k-1. for the pebble scenario, we find for the pebbles and a wavelength of 1.594 mm a complex refractive index of $n = (1.074 \!-\! 1.256) + \mathit{i} \, (2.580 \!-\! 7.431)\times 10^{-3}$ for pebble radii between 1 and 6 mm. taking into account other constraints, our results point towards a pebble make-up of the cometary sub-surface with pebble radii between 3 and 6 mm. the derived real part of the refractive index is used to constrain the composition of the pebbles and their volume filling factor. the optical and physical properties are discussed in the context of protoplanetary and debris disc observations. | sub-mm/mm optical properties of real protoplanetary matter derived from rosetta/miro observations of comet 67p |
in this paper we presented the results of laboratory experiments dealing with the sliding of desiccated sand on the inclined surfaces of cometary analogs. the experiments were performed in a vacuum, using porous mixtures of water ice and quartz sand. the inclination angle of the surfaces of the samples was about 10 degrees lower than the repose angle. the sliding was possible when the mobility coefficient defined as the ratio of forces was lower than unity i.e. when the layer of sand as the whole was not fluidized. the observed effect of sliding was due to the rolling, or sliding of grains present on the surface. it is important, that the process of sliding of desiccated sand can be caused by the sublimation of underlying water ice despite its relatively low volatility. | comets, sliding of surface dust ii |
planetesimals - asteroids and comets - are the building blocks of planets in protoplanetary discs and the source of dust, ice, and gas in debris discs. along with planets they comprise the left-over material after star formation that constitutes a planetary system. planets influence the dynamics of planetesimals, sculpting the orbits of debris belts to produce asymmetries or gaps. we can constrain the architecture of planetary systems, and infer the presence of unseen planetary companions, by high spatial resolution imaging of debris discs. hd 16743 is a relatively young f-type star that hosts a bright edge-on debris disc. based on far-infrared herschel observations its disc was thought to be stirred by a planetary companion. here, we present the first spatially resolved observations at near-infrared and millimetre wavelengths with hst and alma, revealing the disc to be highly inclined at $87{_{.}^{\circ}} 3~^{+1{_{.}^{\circ}} 9}_{-2{_{.}^{\circ}} 5}$ with a radial extent of 157.7$^{+2.6}_{-1.5}$ au and an full width at half maximum of 79.4$^{+8.1}_{-7.8}$ au (δr/r = 0.5). the vertical scale height of the disc is 0.13 ± 0.02, significantly greater than typically assumed unstirred value of 0.05, and could be indicative of stirring of the dust-producing planetesimals within the disc by bodies at least a few times the mass of pluto up to 18.3 m⊕ in the single object limit. | stirred but not shaken: a multiwavelength view of hd 16743's debris disc |
i call attention to extraordinary features displayed by the genetically related long-period comet pair of c/1844 y1 (great comet) and c/2019 y4 (atlas). the issue addressed most extensively is the fragmentation and disintegration of the latter object, itself a thousands-of-years-old fragment. of the four fragments of c/2019 y4 recognized by the minor planet center -- a, b, c, and d -- i confirm that b was the principal mass, which stayed undetected until early april. the comet's 2020 fragmentation is proposed to have begun with a separation of b and a near 22 january, when the nuclear condensation suddenly started to brighten rapidly. from late january to early april, only fragment a was observed. the remaining fragments c and d split off most probably from a in mid-march, but they too were detected only in april. a new fragment, e, is proposed to have been observed on three days. further addressed are the issues of the orbital period and antitail of c/1844 y1 and the extreme position of this pair among the genetically related groups/pairs of long-period comets. | fragmentation and history of comet pair c/1844 y1 and c/2019 y4 |
i summarize and streamline the results of recent modeling of the orbital evolution and cascading fragmentation of the kreutz sungrazers. the model starts with aristotle's comet -- the progenitor whose nucleus is assumed to be a contact binary -- splitting near aphelion into the two lobes and concludes with the soho dwarf objects as the end products of the fragmentation process. the great march comet of 1843, a member of population i, and the great september comet of 1882, a member of population ii, are deemed the largest surviving masses of the lobes. i establish that the kreutz system consists currently of nine populations, one of which -- associated with comet pereyra -- is a side branch of population i. the additions to the kreutz system proposed as part of the new model are the daylight comets of ad 363, recorded by the roman historian ammianus marcellinus, and the chinese comets of september 1041 and september 1138, both listed in ho's catalogue. the comets of 363 are the first-generation fragments, the latter -- together with the great comet of 1106 -- the second-generation fragments. attention is directed toward the populations' histograms of perihelion distance of the soho sungrazers and the plots of this distance as a function of the longitude of the ascending node. arrival of bright, naked-eye kreutz sungrazers in the coming decades is predicted. | kreutz sungrazers: summary of recent modeling and orbits of the soho objects |
volatiles, notably water, are key to the habitability of rocky planets. the presence of water in planetary material can be inferred from the atmospheric oxygen abundances of polluted white dwarfs, but this interpretation is often complex. we study the accretion process, and find that ices may sublimate and accrete before more refractory minerals reach the star. as a result, a white dwarf's relative photospheric abundances may vary with time during a single accretion event, and do not necessarily reflect the bulk composition of a pollutant. we offer two testable predictions for this hypothesis: (1) cooler stars will more often be inferred to have accreted wet pollutants, and (2) there will be rare occurrences of accretion events with inferred volatile levels far exceeding those of pristine comets. to observationally test these predictions, we statistically constrain the water content of white dwarf pollutants. we find that in the current sample, only three stars show statistically significant evidence of water at the 2σ level, due to large typical uncertainties in atmospheric abundances and accretion states. in the future, an expanded sample of polluted white dwarfs with hydrogen-dominated atmospheres will allow for the corroboration of our theoretical predictions. our work also shows the importance of interpreting pollutant compositions statistically, and emphasizes the requirement to reduce uncertainties on measured abundances to allow for statistically significant constraints on their water content. | asynchronous accretion can mimic diverse white dwarf pollutants ii: water content |
main belt comets (mbcs) exhibit sublimation-driven activity while occupying asteroid-like orbits in the main asteroid belt. mbcs and candidates show stronger clustering of their longitudes of perihelion around 15° than other objects from the outer main belt (omb). this potential property of mbcs could facilitate the discovery of new candidates by observing objects in similar orbits. we acquired deep r-band images of 534 targeted asteroids using the isaac newton telescope/wide field camera between 2018 and 2020. our sample is comprised of omb objects observed near perihelion, with longitudes of perihelion between 0 and 30° and orbital parameters similar to known mbcs. our pipeline applied activity detection methods to 319 of these objects to look for tails or comae, and we visually inspected the remaining asteroids. our activity detection pipeline highlighted a faint antisolar tail-like feature around 2001 nl19 (279870) observed on 2018 november 07, 6 months after perihelion. this is consistent with cometary activity; however, additional observations of this object will be needed during its next perihelion to investigate its potential mbc status. if it is active our survey yields a detection rate of ~1:300, which is higher than previous similar surveys, supporting the idea of dynamical clustering of mbcs. if not, it is consistent with previously estimated abundance rates of mbcs in the omb (<1:500). | a targeted search for main belt comets |
planetesimals in the primordial disc may have experienced a collisional cascade. if so, the comet nuclei later placed in the kuiper belt, scattered disc, and oort cloud would primarily be fragments and collisional rubble piles from that cascade. however, the heating associated with the collisions cannot have been strong enough to remove the hypervolatiles that are trapped within more durable ices, because comet nuclei are rich in hypervolatiles. this places constraints on the diameter of the largest bodies allowed to participate in collisional cascades, and limits the primordial disc lifetime or population size. in this paper, the thermophysical code nimbus is used to study the thermal evolution of planetesimals before, during, and after catastrophic collisions. the loss of co during segregation of co2:co mixtures and during crystallization of amorphous h2o is calculated, as well as mobilization and internal relocation of co2. if an amorphous h2o host existed, and was protected by a co2:co heat sink, only diameter $d\lt 20\, \mathrm{km}$ (inner disc) and $d\lt 64\, \mathrm{km}$ (outer disc) bodies could have been involved in a collisional cascade. if co2 was the only co host, the critical diameters drop to d < 20-$32\, \mathrm{km}$. avoiding disruption of larger bodies requires a primordial disc lifetime of <9 myr at 15 au and <50-70 myr at 30 au. alternatively, if a 450 myr disc lifetime is required to associate the primordial disc disruption with the late heavy bombardment, the disc population size must have been 6-60 times below current estimates. | collisional heating of icy planetesimals - i. catastrophic collisions |
the omnipresence of dust particulates in space and astrophysical plasmas has been attracting numerous researchers to study the collective excitation and propagation dynamics of different eigen-mode structures in diversified astrocosmic circumstances for years. it includes planetary rings, interplanetary space, cometary tails, asteroid zones, planetary atmospheres, etc. the ubiquitous charged dust particulates possess collective degrees of dynamic freedom resulting in the excitation of relatively low-frequency modes, such as dust-ion-acoustic waves (diaws), dust-acoustic waves (daws), dust-coulomb waves (dcws), and so forth. an interesting prevalency of dusty plasma stability research lies in the jupiter's magnetosphere (i.e., jovian plasmas), embedded inside the supersonic solar wind. a brief review of the updated research works on dust-acoustic waves and related collective instability dynamics in the presence of trapped plasma particles is presented herein. the key aim of the proposed explorative meta-analysis is rooted in outlining concisely the main up-to-date investigations on such collective instability processes chronologically. an especial attention is given primarily to the thermostatistical distribution laws of the constitutive lighter electrons and ions against the heavier positively charged dust grains (microspheres). the trapping mechanism of both the lighter species (electrons + ions) is another additive feature revisited here properly. finally, we clearly extrapolate a number of futuristic directions in light of sensible novelties with a wider scope, both horizontally as well as vertically. | acoustic waves in the jovian dusty magnetosphere: a brief review and meta-analysis |
kuiper-like belts of planetesimals orbiting stars other than the sun are most commonly detected from the thermal emission of small dust produced in collisions. emission from gas, most notably co, highlights the cometary nature of these planetesimals. here, we present models for the release of gas from comet-like bodies in these belts, both due to their thermophysical evolution, most notably the decay of long-lived radioactive nuclides, and collisional evolution, including catastrophic and gentler resurfacing collisions. we show that the rate of gas release is not proportional to the rate of dust release, if non-catastrophic collisions or thermal evolution dominate the release of co gas. in this case, care must be taken when inferring the composition of comets. non-catastrophic collisions dominate the gas production at earlier times than catastrophic collisions, depending on the properties of the planetesimal belt. we highlight the importance of the thermal evolution of comets, including crucially the decay of long-lived radioactive nuclides, as a source of co gas around young (<50 myr) planetary systems, if large (10-100 km) planetesimals are present. | secondary gas in debris discs released following the decay of long-lived radioactive nuclides, catastrophic, or resurfacing collisions |
the claims of periodicity in impact cratering and biological extinction events are controversial. a newly revised record of dated impact craters has been analyzed for periodicity, and compared with the record of extinctions over the past 260 myr. a digital circular spectral analysis of 37 crater ages (ranging in age from 15 to 254 myr ago) yielded evidence for a significant 25.8 ± 0.6 myr cycle. using the same method, we found a significant 27.0 ± 0.7 myr cycle in the dates of the eight recognized marine extinction events over the same period. the cycles detected in impacts and extinctions have a similar phase. the impact crater dataset shows 11 apparent peaks in the last 260 myr, at least 5 of which correlate closely with significant extinction peaks. these results suggest that the hypothesis of periodic impacts and extinction events is still viable. | periodic impact cratering and extinction events over the last 260 million years |
we present a three-dimensional model of the evolution of the asteroid-cometary-planetary (acp) component of the solar system under the gravitational influence of jupiter. we demonstrate the origin of the kuiper belt of the sun, the oort cloud of the sun and jupiter, as well as the acp "spear," which becomes elongated with time and transforms into a "ring" of acp objects along the trajectory of the sun orbiting the galaxy center. when generalizing to the case of the galaxy, we conclude that a noticeable portion of acp objects turn out to be unbound with the host stars and form a field of free asteroids, comets, and planets of the galaxy. galaxies with small masses (m < 108m⊙) lose a part of their unbound acp material to the intergalactic space of their clusters and possess galactic acp spears. | generation of unbound comets and planets by planetary systems |
context. several authors predicted an outburst of the draconid meteor shower in 2018, but with an uncertain level of activity.aims: optical meteor observations were used to derive the population and mass indices, flux, and radiant positions of draconid meteors.methods: we performed 90 min of multi-station observations after the predicted peak of activity using highly sensitive electron multiplying charge coupled device cameras. the data calibration is discussed in detail. a novel maximum likelihood estimation method was developed to compute the population and mass index with robust error estimation. we applied the method to observed draconids and used the values to derive the flux. meteor trajectories were computed and compared to predicted radiant positions from meteoroid ejection models.results: we find a mass index of 1.74 ± 0.18 in the 30 min bin after the predicted peak, and 2.32 ± 0.27 in the subsequent 60 min. the location and the dispersion of the radiant are a good match to modeled values, but there is an offset of 0.4° in solar longitude. the input data and the trajectory solutions 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/635/a153 | a new method for measuring the meteor mass index: application to the 2018 draconid meteor shower outburst |
while water and sulfuric acid droplets are the main component of stratospheric aerosols, measurements performed for about 30 years have shown that non-sulfate particles (nsps) are also present. such particles, released from the earth mainly through volcanic eruptions, pollution or biomass burning, or coming from space, present a wide variety of compositions, sizes, and shapes. to better understand the origin of nsps, we have performed measurements with the light optical aerosol counter (loac) during 151 flights under weather balloons in the 2013–2019 period reaching altitudes up to 35 km. coupled with previous counting measurements conducted over the 2004–2011 period, the loac measurements indicate the presence of stratospheric layers of enhanced concentrations associated with nsps, with a bimodal vertical repartition ranging between 17 and 30 km altitude. such enhancements are not correlated with permanent meteor shower events. they may be linked to dynamical and photophoretic effects lifting and sustaining particles coming from the earth. besides, large particles, up to several tens of μm, were detected and present decreasing concentrations with increasing altitudes. all these particles can originate from earth but also from meteoroid disintegrations and from the interplanetary dust cloud and comets. | origins and spatial distribution of non-pure sulfate particles (nsps) in the stratosphere detected by the balloon-borne light optical aerosols counter (loac) |
the chapter provides a comprehensive and up to date review of physical properties (structure, strength, porosity etc.) and chemical composition of small solar system bodies with sizes ranging from several micrometers to several meters. experts from different fields of research, using different methods, joined their efforts to present and compare results of laboratory investigation of meteorites, interplanetary dust particles (idps), and micrometeorites, studies of cometary and asteroidal dust by remote sensing, in-situ investigation or sample-return missions, and properties of meteoroids derived from observations of meteors. meteors sample the whole population of meteoroids in the vicinity of the earth and provide data of their orbits. the best currently available methods and models of inferring physical properties of meteoroids from their behavior during the atmospheric entry, in particular fragmentation, are discussed. chemical compositions are extracted from meteor spectra. perfectly designed figures and tables convey the information clearly and concisely to the reader. the data are relevant for understanding other solar system objects, especially comets and asteroids. | physical and chemical properties of meteoroids |
ancient chinese, korean, and vietnamese observers left us records of celestial sightings, the so‑called "guest stars" dated up to ∼2500 years ago. their identification with modern observable targets could open interesting insights into the long‑term behavior of astronomical objects, as shown by the successful identification of eight galactic supernovae. here, we evaluate the possibility to identify ancient classical novae with presently known cataclysmic variables (cvs). for this purpose, we have developed a method which reconsiders in detail positions and sizes of ancient asterisms, in order to define areas on the sky that should be used for a search of modern counterparts. these areas range from a few to several 100 square degrees, depending on the details given in ancient texts; they should replace the single coordinate values given by previous authors. any appropriate target (cvs, x‑ray binaries etc.) within these areas can be considered as a valid candidate for identification with the corresponding ancient event. based on the original descriptions of several 100 old events, we selected those without movement and without a tail (to exclude comets) and which was not only visible within a certain hour (to exclude meteors). this way, we present a shortlist of 24 most promising events which could refer to classical nova eruptions. our method is checked by applying it to the known sn identifications, leading to a margin of error between 0 and 4.5 degrees, meaning that some sn remnants lay exactly inside the areas given by the historical reports while in some other cases they are laying at considerable distances. | a new approach to generate a catalogue of potential historical novae |
we present measurements of comet 46p/wirtanen obtained by the neowise spacecraft in 2017 through 2019. we detected signal in excess of the dust in the 4.6 μm channel attributable to the presence of co, or more likely, co2 emission. the excess, when the comet was outbound at a heliocentric distance of 1.9 au, was consistent with a co2 production rate of 1.3(±0.07) × 1026 molecules per second, which is equivalent to an active area on the order of a percent of the comet nucleus' total surface. * released on 2020 september 30th. | neowise observed co and co2 production rates of 46p/wirtanen during the 2018-2019 apparition |
the lander philae of the rosetta mission landed on the surface of the comet 67 p/churyumov-gerasimenko on november 12, 2014. among the specific subsystems and instruments carried on philae, the sampling, drilling and distribution (sd2) subsystem had the role of providing in-situ operations devoted to soil drilling, sample collection, and their distribution to three scientific instruments. after landing, a first sequence of scientific activities was carried out, relying mainly on the energy stored in the lander primary battery. due to the limited duration and the communication delay, these activities had to be carried out automatically, with a limited possibility of developing and uploading commands from the ground. philae's landing was not nominal and sd2 was operated in unexpected conditions: the lander was not anchored to the soil and leant on the comet surface shakily. nevertheless, one sampling procedure was attempted. this paper provides an overview of sd2 operation planning and on-comet operations, and analyses sd2 achievements during the first science sequence of philae's on-comet operations. | planning and implementation of the on-comet operations of the instrument sd2 onboard the lander philae of rosetta mission |
this paper reviews the current knowledge on the composition of cometary dust (ice, minerals and organics) in order to constrain their origin and formation mechanisms. comets have been investigated by astronomical observations, space missions (giotto to rosetta), and by the analysis of cometary dust particles collected on earth, chondritic porous interplanetary dust particles (cp-idps) and ultracarbonaceous antarctic micrometeorites (ucamms). most ices detected in the dense phases of the interstellar medium (ism) have been identified in cometary volatiles. however, differences also suggest that cometary ices cannot be completely inherited from the ism. cometary minerals are dominated by crystalline mg-rich silicates, fe sulphides and glassy phases including gems (glass with embedded metals and sulphides). the crystalline nature and refractory composition of a significant fraction of the minerals in comets imply a high temperature formation/processing close to the proto-sun, resetting a possible presolar signature of these phases. these minerals were further transported up to the external regions of the disc and incorporated in comet nuclei. cometary matter contains a low abundance of isotopically anomalous minerals directly inherited from the presolar cloud. at least two different kinds of organic matter are found in dust of cometary origin, with low or high nitrogen content. n-poor organic matter is also observed in primitive interplanetary materials (like carbonaceous chondrites) and its origin is debated. the n-rich organic matter is only observed in cp-idps and ucamms and can be formed by galactic cosmic ray irradiation of n2- and ch4-rich icy surface at large heliocentric distance beyond a 'nitrogen snow line'. | variations in cometary dust composition from giotto to rosetta, clues to their formation mechanisms |
context. sulfur is an abundant element in the cosmos and it is thus an important contributor to astrochemistry in the interstellar medium and in the solar system. astronomical observations of the gas and of the solid phases in the dense interstellar/circumstellar regions have evidenced that sulfur is underabundant. the hypothesis to explain such a circumstance is that it is incorporated in some species in the solid phase (i.e. as frozen gases and/or refractory solids) and/or in the gas phase, which for different reasons have not been observed so far.aims: here we wish to give a contribution to the field by studying the chemistry induced by thermal and energetic processing of frozen mixtures of sulfur dioxide (one of the most abundant sulfur-bearing molecules observed so far) and water.methods: we present the results of a series of laboratory experiments concerning thermal processing of different h2o:so2 mixtures and ion bombardment (30 kev he+) of the same mixtures. we used in situ fourier transform infrared (ftir) spectroscopy to investigate the induced effects.results: the results indicate that ionic species such as hso, hso, and s2o are easily produced. energetic processing also produces so3 polymers and a sulfurous refractory residue.conclusions: the produced ionic species exhibit spectral features in a region that, in astronomical spectra of dense molecular clouds, is dominated by strong silicate absorption. however, such a dominant feature is associated with some spectral features, some of which have not yet been identified. we suggest adding the sulfur-bearing ionic species to the list of candidates to help explain some of those features. in addition, we suggest that once expelled in the gas phase by sublimation, due to the temperature increase, and/or by non-thermal erosion those species would constitute a class of molecular ions not detected so far. we also suggest that molecular sulfur-bearing ions could be present on the surfaces and/or in the atmospheres of several objects in the solar system, for example icy satellites of the giant planets and comets. | thermal and energetic processing of astrophysical ice analogues rich in so2 |
we searched for rotational lines of h12c14n in comet 46p/wirtanen, using the purple mountain observatory 13.7 m radio telescope. the j = 1-0 lines of hcn (3.4 mm wavelength) were unambiguously detected in 46p during the 2018 december 14-15 period, with a beam resolution of 62"2 and a velocity resolution of ∼0.21 km s-1 per channel. the molecular production rates were computed. the mean hcn(1-0) production rate of 46p was (6.45 ± 1.31) × 1024 molec s-1 in the above two days. we found possible indications of time variation in the outgassing activity. the average hcn abundance relative to water q[hcn]/ ${q}_{[{{\rm{h}}}_{2}{\rm{o}}]} of 46p was (0.09 ± 0.01)%. the hcn line shapes gave primary information on the kinematics of the cometary atmosphere. the hcn linewidths provided a direct determination of the coma expansion velocity, which was about 0.5 ± 0.05 km s-1 at post-perihelion (1.056 au). | observations of the hydrogen cyanide in comet 46p/wirtanen at a 3.4 mm wavelength |
the nucleus of the jupiter-family comet 67p/churyumov-gerasimenko was discovered to be bi-lobate in shape when the european space agency spacecraft rosetta first approached it in 2014 july. the bi-lobate structure of the cometary nucleus has led to much discussion regarding the possible manner of its formation and on how the composition of each lobe might compare with that of the other. during its two-year-long mission from 2014 to 2016, rosetta remained in close proximity to 67p/churyumov-gerasimenko, studying its coma and nucleus in situ. based on lobe-specific measurements of hdo and h2o performed with the rosina double focusing mass spectrometer (dfms) on board rosetta, the deuterium-to-hydrogen (d/h) ratios in water from the two lobes can be compared. no appreciable difference was observed, suggesting that both lobes formed in the same region and are homogeneous in their d/h ratios. | a comparison between the two lobes of comet 67p/churyumov-gerasimenko based on d/h ratios in h2o measured with the rosetta/rosina dfms |
uncontrolled urbanization growth contributes to the pollution of aquatic environments. heavy metals released by domestic and industrial effluents can negatively affect aquatic organisms. this study aimed to evaluate the effect of environmental pollutants, such as metals, on fish dna damage, in stretches of an urban stream. specimens of the neotropical fish, astyanax lacustris, were exposed in situ for 96 h along the antas stream, a brazilian aquatic system deteriorated by anthropogenic factors. water and sediment samples were collected simultaneously for physicochemical and heavy metal analyses. the comet assay was performed as a biomarker of genotoxicity. fish located downstream had a higher frequency of dna damage than in the reference site. we found concentrations of cr and ni above acceptable levels in sediment samples. generally, ba, mn, mg, zn, cr, and ni were the elements most associated with genotoxic damage. water and sediment of the antas stream showed genotoxic potential in a. lacustris according to the urbanization gradient, demonstrating the importance to prevent the release of environmental pollutants, especially heavy metals in urban areas. | genotoxic effect of heavy metals on astyanax lacustris in an urban stream |
without a significant atmosphere or global magnetic field, the lunar surface is exposed to micrometeoroid bombardment, ultraviolet (uv) radiation, and the solar wind. micrometeoroid bombardment grinds the surface into a regolith comprised of dust grains ranging in size from 10 nm to 1 mm (grün et al., 2011). incident uv radiation and solar wind electrons and ions electrically charge the surface forming a plasma sheath whose structure is dependent on both the plasma and surface properties (campanell, 2013; guernsey and fu, 1970; poppe and horányi, 2010; nitter et al., 1998). dust grains that are liberated from the surface can collect additional charge and interact with the plasma sheath. these interactions have been suggested to explain a variety of phenomena observed on airless bodies including horizon glow and dust ponding (colwell et al., 2005; hughes et al., 2008; poppe et al., 2012; wang et al., 2009). the effect of surface topography on the plasma environment and ensuing dust dynamics is poorly understood and serves as the focus of this paper. we present the results of a three-dimensional particle-in-cell (pic) code used to model the dayside near-surface lunar plasma environment at a variety of solar zenith angles (sza) for two different topographies. using the results of the pic code, we model the effects on dust dynamics and bulk transport. the simulations also address dust transport on smaller bodies such as asteroid 433 eros and comet 67p/churyumov-gerasimenko to identify effects of reduced gravity. | the effect of asymmetric surface topography on dust dynamics on airless bodies |
the esa mission comet interceptor will target an oort or interstellar comet during its first approach to the sun. meanwhile, the vera rubin lsst survey will observe hundreds of active comets per month beyond 4 au from the sun, where water vapour pressure is expected to be too low to eject dust. we discuss observations of dust tails at heliocentric distances larger than 4 au in order to retrieve the physical parameters driving cometary activity beyond jupiter by means of a probabilistic tail model, which is consistent with the activity model defining the gas coma parameters due to the sublimation of carbon monoxide, molecular oxygen, methane, ethane, and carbon dioxide since the activity onset at 85 au from the sun. we find that: (i) all the observed dust tails are consistent with the adopted activity model; (ii) the tail fits depend on three free parameters only, all correlated to the nucleus size; (iii) tail fits are always improved by anisotropic dust ejection, suggesting activity of oort nuclei dominated by seasons; (iv) inbound seasons suggest cometary activity before the ejection of protocomets into the oort cloud, as predicted by the activity model; (v) oort nuclei larger than 1 km may be characterized by a fallout up to ≈100 m thick deposited during ≈60 yr inbound; (vi) on the other side, oort nuclei smaller than 1 km may appear more pristine than jupiter family comets when observed at 1 au from the sun. | comets beyond 4 au: how pristine are oort nuclei? |
here, two of a range of possible models are explored that assume that: (i) two of the main chondritic components (chondrules and refractory inclusions) dominated the earth's building blocks, (ii) that their relative abundances differed from those of known chondrites, and (iii) that the elemental compositions of all components, as well as the isotopic compositions of refractory inclusions, resembled those of the components in carbonaceous chondrites. in terms of the elemental abundances, the chondrules can explain the moderately volatile element fractionations in the bulk silicate earth (bse), except for a few elements like f and in, while the refractory inclusions explain the bse's refractory lithophile element enrichment. accretion of a cm- or el-like late veneer reproduces the s, se, te and highly siderophile element abundances in the bse. the accretion of ci- or cm-like material prior to the late veneer, along with small amounts of cometary and implanted solar wind material, can explain the bse elemental and isotopic abundances of the noble gases as well as the elemental abundances of most other highly volatile elements (e.g., h, c and n) provided that variable fractions of them can be sequestered into the core or into hidden mantle reservoirs. this ci- or cm-like material provides an upper limit for the contribution to the bse from matrix that is much less than in any chondrites. in the models, si, o and s are the dominant light elements in the core, in that order, and their abundances are constrained to be consistent with the first principles calculations of umemoto and hirose (2020). the core compositions of the models are also consistent with most geochemical constraints. satisfying all isotopic constraints is a challenge. the bse os isotopes are consistent with an el dominated late veneer, but ru isotopic evidence is best explained by the addition of cm-like material in the late veneer. either ci- or cm-like material, in combination with small amounts of cometary and implanted solar wind material, can reproduce the bse ne, ar and kr isotopic compositions. cm-like, but not ci-like, material can roughly reproduce the bse's h and c isotopic compositions, but neither material can explain the bse n isotopic composition. the bse composition requires that the o isotopic compositions of the refractory inclusions (initially δ17o ≤ -20‰) in earth's building blocks were reset in the nebula by interaction with high δ17o h2o, perhaps during chondrule formation. to plot on the inner solar system ε54cr vs. ε50ti (or ε48ca) trend, either the average cr content of the chondrules was roughly half of that assumed here or most of the ci/cm-like and refractory-inclusion-rich materials were accreted late. | an exploration of whether earth can be built from chondritic components, not bulk chondrites |
asteroids show a variety of shapes, ranging from roundish to elongated to binary systems and 'contact binaries' like (25143) itokawa, the target of the hayabusa mission (jaxa). these bodies spend most of their time within a collisional system, the asteroid belt, where impact processes are relatively frequent. speculations on the origin of asteroid shapes invoke mechanisms such as collisions and spin-up effects. n-body numerical simulations of fragment evolution following catastrophic collisions have been recently carried out (campo bagatin et al., 2018). in this study the idea that the stochastic process of gravitational re-accumulation may be responsible for many observed asteroid shapes is introduced. asteroid 'contact binaries' are shown to be regularly produced by the gravitational re-accumulation process following catastrophic impact. similar processes may have occurred in the case of some comets and trans-neptunian objects. | gravitational re-accumulation as the origin of most contact binaries and other small body shapes |
cometary dust provides a unique window on dust growth mechanisms during the onset of planet formation. measurements by the rosetta spacecraft show that the dust in the coma of comet 67p/churyumov-gerasimenko has a granular structure at size scales from sub-μmup to several hundreds of μm, indicating hierarchical growth took place across these size scales. however, these dust particles may have been modified during their collection by the spacecraft instruments. here, we present the results of laboratory experiments that simulate the impact of dust on the collection surfaces of the cosima (cometary secondary ion mass anaylzer) and midas (micro-imaging dust analysis system) instruments onboard the rosetta spacecraft. we map the size and structure of the footprints left by the dust particles as a function of their initial size (up to several hundred μm) and velocity (up to 6 m s-1). we find that in most collisions, only part of the dust particle is left on the target; velocity is the main driver of the appearance of these deposits. a boundary between sticking/bouncing and fragmentation as an outcome of the particle-target collision is found at v ∼ 2 m s-1. for velocities below this value, particles either stick or leave a single deposit on the target plate, or bounce, leaving a shallow footprint of monomers. at velocities >2 m s-1and sizes >80 μm, particles fragment upon collision, transferring up to 50 per cent of their mass in a rubble-pile-like deposit on the target plate. the amount of mass transferred increases with the impact velocity. the morphologies of the deposits are qualitatively similar to those found by the cosima instrument. | the footprint of cometary dust analogues - i. laboratory experiments of low-velocity impacts and comparison with rosetta data |
using chemical and petrologic evidence and modeling, we deduce that two chondrule-like particles named iris and callie, from stardust cometary track c2052,12,74, formed in an environment very similar to that seen for type ii chondrules in meteorites. iris was heated near liquidus, equilibrated, and cooled at ≤100 °c h-1 and within ≈2 log units of the iw buffer with a high partial pressure of na such as would be present with dust enrichments of ≈103. there was no detectable metamorphic, nebular, or aqueous alteration. in previous work, ogliore et al. (2012) reported that iris formed late, >3 myr after cais, assuming 26al was homogenously distributed, and was rich in heavy oxygen. iris may be similar to assemblages found only in interplanetary dust particles and stardust cometary samples called kool particles. callie is chemically and isotopically very similar, but not identical to iris. | constraints on the formation environment of two chondrule-like igneous particles from comet 81p/wild 2 |
this study explores the long-duration (0.8-2.3 ma), time-averaged micrometeorite flux (mass and size distribution) reaching earth, as recorded by the transantarctic mountains (tam) micrometeorite collection. we investigate a single sediment trap (tam65), performing an exhaustive recovery and characterization effort and identifying 1,643 micrometeorites (between 100 and 2,000 μm). approximately 7% of particles are unmelted or scoriaceous, of which 75% are fine-grained. among cosmic spherules, 95.6% are silicate-dominated s-types, and further subdivided into porphyritic (16.9%), barred olivine (19.9%), cryptocrystalline (51.6%), and vitreous (7.5%). our (rank)-size distribution is fit against a power law with a slope of -3.9 (r2 = 0.98) over the size range 200-700 μm. however, the distribution is also bimodal, with peaks centered at ~145 and ~250 μm. remarkably similar peak positions are observed in the larkman nunatak data. these observations suggest that the micrometeorite flux is composed of multiple dust sources with distinct size distributions. in terms of mass, the tam65 trap contains 1.77 g of extraterrestrial dust in 15 kg of sediment (<5 mm). upscaling to a global annual estimate gives 1,555 (±753) t/year—consistent with previous micrometeorite abundance estimates and almost identical to the south pole water well estimate (~1,600 t/year), potentially indicating minimal variation in the background cosmic dust flux over the quaternary. the greatest uncertainty in our mass flux calculation is the accumulation window. a minimum age (0.8 ma) is robustly inferred from the presence of australasian microtektites, while the upper age (~2.3 ma) is loosely constrained based on 10be exposure dating of glacial surfaces at roberts butte (6 km from our sample site). | the extraterrestrial dust flux: size distribution and mass contribution estimates inferred from the transantarctic mountains (tam) micrometeorite collection |
we examine the development of the active asteroid 311p/panstarrs (formerly, 2013 p5) in the period from 2013 september to 2014 february using high resolution images from the hubble space telescope. this multi-tailed object is characterized by a single, reddish nucleus of absolute magnitude h >= 18.98 ± 0.10, corresponding to an equal-area sphere of radius <=200 ± 20 m (for assumed geometric albedo 0.29 ± 0.09). we set an upper limit to the radii of possible companion nuclei at ~10 m. the nucleus ejected debris in nine discrete episodes, spread irregularly over a nine month interval, each time forming a distinct tail. particles in the tails range from about 10 μm to at least 80 mm in radius, and were ejected at speeds <1 m s-1. the ratio of the total ejected dust mass to the nucleus mass is ~3×10-5, corresponding to a global surface layer ~2 mm thick, or to a deeper layer covering a smaller fraction of the surface. the observations are incompatible with an origin of the activity by impact or by the sublimation of entrapped ice. this object appears to be shedding its regolith by rotational (presumably yorp-driven) instability. long-term fading of the photometry (months) is attributed to gradual dissipation of near-nucleus dust. photometric variations on short timescales (<0.7 hr) are probably caused by fast rotation of the nucleus. however, because of limited time coverage and dilution of the nucleus signal by near-nucleus dust, we have not been able to determine the rotation period. | episodic ejection from active asteroid 311p/panstarrs |
within the framework of the heterogeneous dust evolution model for interstellar solids (themis), this work explores the surface processes and chemistry relating to core/mantle interstellar and cometary grain structures and their influence on the nature of these fascinating particles. it appears that a realistic consideration of the nature and chemical reactivity of interstellar grain surfaces could self-consistently and within a coherent framework explain: the anomalous oxygen depletion, the nature of the co dark gas, the formation of `polar ice' mantles, the red wing on the 3 μm water ice band, the basis for the o-rich chemistry observed in hot cores, the origin of organic nano-globules and the 3.2 μm `carbonyl' absorption band observed in comet reflectance spectra. it is proposed that the reaction of gas phase species with carbonaceous a-c(:h) grain surfaces in the interstellar medium, in particular the incorporation of atomic oxygen into grain surfaces in epoxide functional groups, is the key to explaining these observations. thus, the chemistry of cosmic dust is much more intimately related with that of the interstellar gas than has previously been considered. the current models for interstellar gas and dust chemistry will therefore most likely need to be fundamentally modified to include these new grain surface processes. | dust evolution, a global view: iii. core/mantle grains, organic nano-globules, comets and surface chemistry |
the branching ratios for the n(4s) + n(2d), n(4s) + n(2p), and n(2d) + n(2d) channels are measured for the photodissociation of {{{n}}}2({x}1{{{{σ }}}g}+;v\prime\prime =0,j\prime\prime ) in the vacuum ultraviolet (vuv) region of 100,808-122,159 cm-1 using the vuv-vuv pump-probe approach combined with velocity-map-imaging-photoion detection. no evidence of forming the ground-state n(4s) + n(4s) products is found. no potential barrier is observed for the n(2d) + n(2d) channel, but the n(4s) + n(2p) channel has a small potential barrier of ≈740 cm-1. the branching ratios are found to depend on the symmetry of predissociative n2 states instead of the total vuv excitation energy, indicating that n2 photodissociation is nonstatistical. when the branching ratios for n(4s) + n(2d) and n(4s) + n(2p) products are plotted as a function of the vuv excitation energy for the valence n2 1πu and {}1{{{{σ }}}{{u}}}+ states, oscillations in these ratios are observed demonstrating how these channels are competing with each other. these data can be used to select both the velocity and internal states of the atomic products by picking the quantum state that is excited. high-level ab initio potential energy curves of the excited n2 states are calculated to provide insight into the mechanisms for the observed branching ratios. the calculations predict that the formation of both n(4s) + n(2d) and n(4s) + n(2p) channels involves potential energy barriers, in agreement with experimental observations. a discussion of the application of the present results to astronomy, planetary sciences, and comets is given. | quantum-state dependence of product branching ratios in vacuum ultraviolet photodissociation of n2 |
the observed rate of water production of comet 67p/churyumov-gerasimenko near its perihelion can be approximated by a very steep power function of the heliocentric distance. widely used thermophysical models based on a static dust layer on top of the icy/refractory matrix are poorly consistent with these observations. we analyse published model results and demonstrate that thermophysical models with a uniform and static ice free layer do not reproduce the observed steep water production rates of 67p near perihelion. based on transient thermal modeling we conclude that the accelerated gas activity can be explained assuming that the active area fraction near the south pole is increased. the deeper penetration of the heat wave during polar day (no sunset) can activate sublimation through thicker inert dust layers. this can also lead to removal of thicker dust layers and consequently to an expansion of the active area. | near-perihelion activity of comet 67p/churyumov-gerasimenko. a first attempt of non-static analysis |
the james webb space telescope (jwst), as the largest space-based astronomical observatory with near- and mid-infrared instrumentation, will elucidate many mysterious aspects of comets. we summarize four cometary science themes especially suited for this telescope and its instrumentation: the drivers of cometary activity, comet nucleus heterogeneity, water ice in comae and on surfaces, and activity in faint comets and main belt asteroids. with jwst, we can expect the most distant detections of gas, especially co2, in what we now consider to be only moderately bright comets. for nearby comets, coma dust properties can be simultaneously studied with their driving gases, measured simultaneously with the same instrument or contemporaneously with another. studies of water ice and gas in the distant solar system will help us test our understanding of cometary interiors, and coma evolution. the question of cometary activity in main belt comets will be further explored with the possibility of a direct detection of coma gas. we explore the technical approaches to these science cases and provide simple tools for estimating comet dust and gas brightness. finally, we consider the effects of the observatory's non-sidereal tracking limits and provide a list of potential comet targets during the first five years of the mission. | cometary science with the james webb space telescope |
we provide a three-dimensional model of the inner layered structure of comet 67p based on the hypothesis of an extended layering independently wrapping each lobe. a large set of terrace orientations was collected on the latest shape model and then used as a proxy for the local orientation of the surfaces of discontinuity which defines the layers. we modelled the terraces as a family of concentric ellipsoidal shells with fixed axis ratios, producing a model that is completely defined by just eight free parameters. each lobe of 67p has been modelled independently, and the two sets of parameters have been estimated by means of non-linear optimization of the measured terrace orientations. the proposed model is able to predict the orientation of terraces, the elongation of cliffs, the linear traces observed in the wosret and hathor regions and the peculiar alignment of boulder-like features which has been observed in the hapi region, which appears to be related to the inner layering of the big lobe. our analysis allowed us to identify a plane of junction between the two lobes, further confirming the independent nature of the lobes. our layering models differ from the best-fitting topographic ellipsoids of the surface, demonstrating that the terraces are aligned to an internal structure of discontinuities, which is unevenly exposed on the surface, suggesting a complex history of localized material removal from the nucleus. | a three-dimensional modelling of the layered structure of comet 67p/churyumov-gerasimenko |
staphylococcus aureus is historically regarded as a non-motile organism. more recently it has been shown that s. aureus can passively move across agar surfaces in a process called spreading. we re-analysed spreading motility using a modified assay and focused on observing the formation of dendrites: branching structures that emerge from the central colony. we discovered that s. aureus can spread across the surface of media in structures that we term ‘comets’, which advance outwards and precede the formation of dendrites. we observed comets in a diverse selection of s. aureus isolates and they exhibit the following behaviours: (1) they consist of phenotypically distinct cores of cells that move forward and seed other s. aureus cells behind them forming a comet ‘tail’ (2) they move when other cells in the comet tail have stopped moving; (3) the comet core is held together by a matrix of slime; and (4) the comets etch trails in the agar as they move forwards. comets are not consistent with spreading motility or other forms of passive motility. comet behaviour does share many similarities with a form of active motility known as gliding. our observations therefore suggest that s. aureus is actively motile under certain conditions. | staphylococcus aureus forms spreading dendrites that have characteristics of active motility |
a catalogue of equatorial coordinates and magnitudes for 2162 asteroids and 11 comets was compiled based on the results of processing of digitized photographic observations of the northern sky performed in 1981-1985. the positions were compared with the jpl de431 ephemeris. the mean (o - c)αδ values for all positions obtained in this comparison are -0.08″ and 0.04″, and their root-mean-square errors are 0.70″ and 0.64″ in α and δ, respectively. it was found that the observations of 54 asteroids predate their discoveries, and the observations of four of them are the earliest known for these asteroids. | catalogue of asteroids from digitized photographic plates of the fon program |
debris discs are second-generation dusty discs thought to be devoid of gas. however, this idea has been challenged in the last years by gas detections in some systems. we compiled a database of 301 debris discs and collected high-resolution optical spectra for ∼77 per cent of them. from the analysis of these data we identified a group of 23 debris discs presenting several absorption features superimposed to the photospheric ca ii and na i doublets. these absorptions could be due to circumstellar material or interstellar clouds. in order to discriminate between the two scenarios, we characterized each feature in terms of its radial velocity, equivalent width, and column density. additionally, we searched in the literature for local clouds in the line of sight of the stars, and looked for the presence of similar absorption features in nearby stars. our study concludes that while all the objects present interstellar absorptions in their spectra, three objects show features more compatible with circumstellar origin: hd 110058 presents a stable circumstellar absorption, while hr 4796 and c aql present variable absorption features likely due to exocometary activity. the minute-scale variability we detect towards c aql is the shortest of this kind detected so far. the detection of circumstellar features in these objects is consistent with their near edge-on inclinations. we also provide evidence challenging previous claims of circumstellar gas detections for hr 6507. given the properties of the sample, we speculate that transient gaseous events must be a common phenomenon among debris discs. | debris discs with multiple absorption features in metallic lines: circumstellar or interstellar origin? |
on the nucleus of comet 67p/churyumov-gerasimenko numerous pits and depressions of different sizes are identified. in the present work the origin of depression hatmehit is investigated. we propose a mechanism that includes recession of the surface due to sub-dust sublimation together with formation of cavities. recession of the surface is calculated taking into account the sub-dust sublimation of water ice with volatile organic components, formation of a strengthened ice-dust crust due to sintering of ice grains and the increase of the gas pressure in pores due to release of gaseous co. our simulations indicate, that the formation of a 300 m deep depression due to the sub-dust sublimation of ice can take as little as 50 orbital periods assuming that the heliocentric distance at perihelion is close to its present value (ip. et al., 2016). when amorphous water ice is present at small depth the release of gaseous co may cause either compression of low-strength material beneath the strengthened crust, or ejection of the crust. in both cases a cavity is formed and grows due to the sublimation of ice from the wall and the floor. | comet 67p/churyumov-gerasimenko, possible origin of the depression hatmehit |
suprathermal electrons with energies of ∼70 ev and above are observed at 1 au as dispersionless halo electrons and magnetic field-aligned beams of strahls. for a long time, it has been thought that both populations originate only from the solar corona, and that the only active process impacting their properties in the solar wind is scattering. this view has consequently impacted the interpretation of typical patterns of pitch-angle distributions (pads) of suprathermal electrons. meanwhile, recent observational studies supported by numerical simulations have shown that there is an unaccounted population of electrons accelerated to suprathermal energies at reconnecting current sheets (rcss) and 3d dynamical plasmoids (or 2d magnetic islands (mis)) directly in the heliosphere. we present multispacecraft observations of counterstreaming strahls and heat flux dropouts in pads within a region filled with plasmoids and rcss unaffected by interplanetary shocks, comparing observed pad features with those predicted by particle-in-cell simulations. we show typical pad patterns determined by local acceleration of thermal-core electrons up to hundreds of electron volts. resulting pad views depend on properties and topology of particular rcss, mis, and plasma/magnetic field parameters. our study suggests that solar wind-borne suprathermal electrons coexist with those of solar origin. therefore, some of heat flux dropout and bidirectional strahl events can be explained by local dynamical processes involving magnetic reconnection. possible implications of the results for the interpretation of the actively debated decrease in the strahl/halo relative density with heliocentric distance and puzzling features of suprathermal electrons observed at crossings of the heliospheric current sheet and cometary comas are also discussed. | counterstreaming strahls and heat flux dropouts as possible signatures of local particle acceleration in the solar wind |
air pollution is one the main causes of dna damage in living organisms. continuous exposure to the complex mixture of gases of polluted atmospheres affects health in many ways. sentinel organisms are good biological models to assess the genotoxic damage caused by various chemicals such as atmospheric pollutants. in this study the plant species taraxacum officinale and robinsonecio gerberifolius were exposed during 2015, in the dry and rainy seasons, for 0, 2, 4 and 6 weeks to two different atmospheres of mexico valley, one rural in altzomoni atmospheric observatory (altz) and other urban in the atmospheric observatory of centro de ciencias de la atmósfera (cca), located in universidad nacional autónoma de méxico (unam). leaves of exposed plants were processed to analyze genotoxic damage by single-cell gel electrophoresis. to found any relation, the presence of pollutants in the atmosphere of both sites was analyzed with a cavity ring-down spectrometer (crds) and in the leaves the presence of heavy metals with an inductively coupled plasma mass spectrometer. single-cell gel electrophoresis results showed higher damage in the leaves exposed to higher pollution in the unam atmospheric station in comparison to the altz and controls, which was maintained in growth chambers under controlled conditions. significant differences between rainy and dry seasons were found. chemical analysis showed a significant increase in various heavy metals, especially in rainy season in both exposure sites. increased dna damage observed in both plant species at cca station could be caused by accumulation trough six weeks. | in situ biomonitoring of air quality in rural and urban environments of mexico valley through genotoxicity evaluated in wild plants |
the international rosetta mission was launched on 2nd march 2004 and after its ten year journey, arrived at its target destination of comet 67p/churyumov-gerasimenko, during 2014. following the january 2014 exit from a two and half year hibernation period, rosetta approached and arrived at the comet in august 2014. in november 2014, the philae lander was deployed from rosetta onto the comet's surface after which the orbiter continued its approximately one and a half year comet escort phase. the rosetta science ground segment's primary roles within the project are to support the project scientist and the science working team, in order to ensure the coordination, development, validation and delivery of the desired science operations plans and their associated operational products throughout the mission., whilst also providing support to the principle investigator teams (including the philae lander team) in order to ensure the provision of adequate data to the planetary science archive. the lead up to, and execution of, the november 2014 philae landing, and the subsequent philae activities through 2015, have presented numerous unique challenges to the project teams. this paper discusses these challenges, and more specifically, their impact on the overall mission science planning activities. it details how the rosetta science ground segment has addressed these issues in collaboration with the other project teams in order to accommodate philae operations within the continually evolving rosetta science planning process. | rosetta science operations in support of the philae mission |
we use a thermodynamic statistical model to evaluate how the composition of europa’s internal ocean may have been affected by clathrate hydrate formation. assuming an input of the observed o2 and co2 from the surface into a mildly acidic ocean (ph < 6), and considering the possibility of contributions by reduced (with ch4 and h2s) or oxidized (co2-bearing) hydrothermal fluids, we calculate the fractional occupancies in clathrate and deduce the effect on the ocean’s composition. the structure of the clathrate formed, and therefore its density and composition is influenced by the relative amount of o2 compared to the other compounds present. we also include a mixture of noble gases—argon, krypton, and xenon—based on cometary abundances measured at comet 67p and find that the ar/kr ratio can be affected by almost two orders of magnitude. in most cases, the formed clathrate is likely to become part of the icy crust, with guest molecules possibly accessible to future in situ measurements by the europa clipper and juice missions. | the role of clathrate formation in europa’s ocean composition |
over the past thirty years, spacecraft missions, earth-based radar experiments, and telescopic observations have revolutionized our knowledge of main belt asteroids, near-earth asteroids, and comet nuclei. as a result of this effort, we now possess high resolution shape models and well-constrained spin rates, pole orientations, and basic surface properties for a few dozen such small bodies. here we present the results of a geomorphological examination of 32 such small body shape models along with their associated spin properties, and show that small body shape, gravity, and spin combine to gradually drive the surface towards a condition of maximum topographic stability; that is, a state of low topographic variation, low slopes, and low surface erosion (mass-wasting) rates. of the 32 bodies investigated, 15 (47%) reside within this 'zone of maximum topographic stability', and when asteroid lightcurve-derived rotation rate and body elongation estimates are included, 1941 (70%) of 2791 well-observed asteroids reside within this zone. this finding indicates that given a mobile surface layer and sufficient time, small body surfaces naturally tend to erode, and their spin states gradually evolve, towards a state of maximum topographic stability, which also corresponds to a state of lowest internal stress. this erosional effect is most prominent on bodies several kilometers and larger in diameter, where yorp induced spin-state changes are small. | small body shapes and spins reveal a prevailing state of maximum topographic stability |
the lunar dust experiment (ldex), aboard nasa's lunar atmosphere and dust environment explorer (ladee) successfully mapped the dust density distribution over the lunar surface up to an altitude of ∼ 250 km. ldex detected dust grains launched off the surface in ejecta plumes generated by impacts of cometary and asteroidal micrometeoroids striking the moon. while on average ldex detected particles at a rate of 1 min-1 , periodically it measured bursts of particles at a rate exceeding the average value by up to two orders of magnitude. the timing and location of the most intense period of bursts is used here to independently determine the radiant for the geminids meteoroid stream. the method is proposed to be of general interest to characterize meteoroid streams bombarding any of the airless bodies in the solar system using in-situ dust detectors. | detecting meteoroid streams with an in-situ dust detector above an airless body |
the internal properties of cometary nuclei are the best clues to the size distribution and properties of the early planetesimals that formed the planets during the early solar system nebula processes. the consert radar was designed to probe the interior of comet 67p/churyumov-gerasimenko with a wavelength of about 3 m. it was successfully operated during the first science sequence of the rosetta mission when the consert's wave propagated through part of the nucleus' small lobe. the shape of the received signals provides some hints about the internal structure of the comet's small lobe. the limited broadening observed on the received pulses is compared to simulations performed on a series of non-homogeneous nucleus models to put constrains on the potential structures at the wavelength's scale. the study allows to exclude structures showing a permittivity contrast larger than 0.25 inside the sounded part of the nucleus at a few metres size scale. | consert constrains the internal structure of 67p at a few metres size scale |
context. molecular oxygen, nitrogen, and ozone have been detected on some satellites of saturn and jupiter, as well as on comets. they are also expected to be present in ice-grain mantles within star-forming regions. the continuous energetic processing of icy objects in the solar system induces physical and chemical changes within the ice. laboratory experiments that simulate energetic processing (ions, photons, and electrons) of ices are therefore essential for interpreting and directing future astronomical observations.aims: we provide vacuum ultraviolet (vuv) photoabsorption spectroscopic data of energetically processed nitrogen- and oxygen-rich ices that will help to identify absorption bands and/or spectral slopes observed on icy objects in the solar system and on ice-grain mantles of the interstellar medium.methods: we present vuv photoabsorption spectra of frozen o2 and n2, a 1:1 mixture of both, and a new systematic set of pure and mixed nitrogen oxide ices. spectra were obtained at 22 k before and after 1 kev electron bombardment of the ice sample. ices were then annealed to higher temperatures to study their thermal evolution. in addition, fourier-transform infrared spectroscopy was used as a secondary probe of molecular synthesis to better identify the physical and chemical processes at play.results: our vuv data show that ozone and the azide radical (n3) are observed in our experiments after electron irradiation of pure o2 and n2 ices, respectively. energetic processing of an o2:n2 = 1:1 ice mixture leads to the formation of ozone along with a series of nitrogen oxides. the electron irradiation of solid nitrogen oxides, pure and in mixtures, induces the formation of new species such as o2, n2, and other nitrogen oxides not present in the initial ice. results are discussed here in light of their relevance to various astrophysical environments. finally, we show that vuv spectra of solid no2 and water can reproduce the observational vuv profile of the cold surface of enceladus, dione, and rhea, strongly suggesting the presence of nitrogen oxides on the surface of the icy saturn moons. | vacuum ultraviolet photoabsorption spectroscopy of space-related ices: 1 kev electron irradiation of nitrogen- and oxygen-rich ices |
context. the southern hemisphere of comet 67p/churyumov-gerasimenko (67p) became observable by the rosetta mission in march 2015, a few months before cometary southern vernal equinox. the anhur region in the southern part of the comet's larger lobe was found to be highly eroded, enriched in volatiles, and highly active.aims: we analyze high-resolution images of the anhur region pre- and post-perihelion acquired by the osiris imaging system on board the rosetta mission. the narrow angle camera is particularly useful for studying the evolution in anhur in terms of morphological changes and color variations.methods: radiance factor images processed by the osiris pipeline were coregistered, reprojected onto the 3d shape model of the comet, and corrected for the illumination conditions.results: we find a number of morphological changes in the anhur region that are related to formation of new scarps; removal of dust coatings; localized resurfacing in some areas, including boulders displacements; and vanishing structures, which implies localized mass loss that we estimate to be higher than 50 million kg. the strongest changes took place in and nearby the anhur canyon-like structure, where significant dust cover was removed, an entire structure vanished, and many boulders were rearranged. all such changes are potentially associated with one of the most intense outbursts registered by rosetta during its observations, which occurred one day before perihelion passage. moreover, in the niche at the foot of a new observed scarp, we also see evidence of water ice exposure that persisted for at least six months. the abundance of water ice, evaluated from a linear mixing model, is relatively high (>20%). our results confirm that the anhur region is volatile-rich and probably is the area on 67p with the most pristine exposures near perihelion. the movies associated to figs. 2, 7, 8, and 10 are available at https://www.aanda.org | surface evolution of the anhur region on comet 67p/churyumov-gerasimenko from high-resolution osiris images |
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