abstract stringlengths 3 192k | title stringlengths 4 857 |
|---|---|
laboratory experiments that simulate the photo- and thermo-chemistry of extraterrestrial ices always lead to the formation of semi-refractory organic residues. these residues can be considered as laboratory analogs for the primitive organic matter incorporated into comets and asteroids. many specific organic molecules have been detected in them. here we focus on amino acids because of their possible relevance to further prebiotic chemistry on earth as well as in other solar system bodies. we compare the amino acid content and distribution measured in organic residues produced in our photochemical experiments to those observed in various cm chondrites presenting an increasing degree of aqueous alteration, a process that is thought to impact amino acid chemistry. we find that the amino acid profile of our residues shows similarities with that of the least aqueously altered cm chondrites. in particular, the β-alanine to glycine ratio is comparable to the one measured in the paris meteorite, a minimally altered cm chondrite, and matches the trend followed by other cm chondrites with different degrees of aqueous alteration. additionally, the relative abundances of α-, β-, and γ-amino acids in one of our residues are similar to those of the least altered cm chondrites. these results support the idea of a general formation process for amino acids from photo- and thermo-processing of icy grains as an important source for the inventory of amino acids in the early solar system. | the amino acid distribution in laboratory analogs of extraterrestrial organic matter: a comparison to cm chondrites |
large quantities of impact-related microspherules have been found in fine-grained sediments retained within seven out of nine, radiocarbon-dated, late pleistocene mammoth (mammuthus primigenius) and bison (bison priscus) skull fragments. the well-preserved fossils were recovered from frozen "muck" deposits (organic-rich silt) exposed within the fairbanks and klondike mining districts of alaska, usa, and the yukon territory, canada. in addition, elevated platinum abundances were found in sediment analysed from three out of four fossil skulls. in view of this new evidence, the mucks and their well-preserved but highly disrupted and damaged vertebrate and botanical remains are reinterpreted in part as blast deposits that resulted from several episodes of airbursts and ground/ice impacts within the northern hemisphere during late pleistocene time ( 46-11 ka b.p.). such a scenario might be explained by encounters with cometary debris in earth-crossing orbits (taurid complex) that was generated by fragmentation of a large short-period comet within the inner solar system. | impact-related microspherules in late pleistocene alaskan and yukon "muck" deposits signify recurrent episodes of catastrophic emplacement |
ices are omnipresent in cold regions in space on, e.g., comets, dust grains, transneptunian objects, surfaces of planets and their satellites. the dominant molecule in such ices is water, but also other small molecules or even complex organic molecules (coms) may be present. ionizing radiation (uv photons, electrons, ions from cosmic rays or solar wind) induces several physico-chemical processes such as radiolysis. the fragmentation of initial molecules followed by chemical reactions between radicals may lead to formation of new molecules. furthermore, also implanted projectiles can contribute to chemistry by forming new molecular species. other observed effects include structural changes (compaction, amorphization) and desorption (sputtering) of particles from the surface. at cimap (caen, france), using the different beam lines of the ganil facility, and at gsi (darmstadt, germany), the interaction of swift highly charged heavy ions with astrophysical ices has been studied in a wide projectile energy range from kev to gev. here, two examples of our studies on astrophysical and astrochemical applications will be discussed in detail: 1) the synthesis of coms under irradiation of ices made of small molecules, and 2) radiosensitivity of coms such as pyridine, glycine and adenine, both for isolated molecules in the gas phase and in condensed phase. special emphasis is given on pyridine and pyridine in water matrix. | ion radiation in icy space environments: synthesis and radioresistance of complex organic molecules |
context. remote light scattering and thermal infrared observations provide clues about the physical properties of cometary and interplanetary dust particles. identifying these properties will lead to a better understanding of the formation and evolution of the solar system.aims: we present a numerical solution for the radiative and conductive heat transport in a random particulate medium enclosed by an arbitrarily shaped surface. the method will be applied to study thermal properties of cometary dust particles.methods: the recently introduced incoherent monte carlo radiative transfer method developed for scattering, absorption, and propagation of electromagnetic waves in dense discrete random media is extended for radiative heat transfer and thermal emission. the solution is coupled with the conductive fourier transport equation that is solved with the finite-element method.results: the proposed method allows the synoptic analysis of light scattering and thermal emission by large cometary dust particles consisting of submicrometer-sized grains. in particular, we show that these particles can sustain significant temperature gradients resulting in the superheating factor phase function observed for the coma of comet 67p/churyumov-gerasimenko. | scattering, absorption, and thermal emission by large cometary dust particles: synoptic numerical solution |
context. determining whether asteroids in cometary orbits (acos) are dormant or extinct comets is relevant for understanding the end-states of comets and the sizes of the comet population.aims: we intend to study the value distributions of effective diameter (d), beaming parameter (η), and visible geometric albedo (pv) of aco populations, which can be derived from nasa's wide-field infrared explorer (wise) observations, and we aim to compare these with the same, independently determined properties of the comets.methods: the near-earth asteroid thermal model (neatm) is used with wise data and the absolute magnitude (h) of the acos to compute the d, pv and η.results: we obtained d and pv for 49 acos in jupiter family cometary orbits (jf-acos) and 16 acos in halley-type cometary orbits (damocloids). we also obtained the infrared beaming parameter η for 45 of them. all but three jf-acos (95% of the sample) present a low albedo compatible with a cometary origin. the pv and η distributions of both aco populations are very similar. for the entire sample of acos, the mean geometric albedo is p̅v = 0.05±0.02, (p̅v = 0.05±0.01 and p̅v = 0.05±0.02 for jf-acos and for damocloids, respectively) compatible with a narrow albedo distribution similar to that of the jupiter family comets (jfcs), with a p̅v ~ 0.04. the mean beaming parameter is η̅ = 1.0±0.2. we find no correlations between d, pv, or η. we also compare the cumulative size distribution (csd) of acos, centaurs, and jfcs. although the centaur sample contains larger objects, the linear parts in their log-log plot of the csds presents a similar cumulative exponent (β = 1.85 ± 0.30 and 1.76 ± 0.35, respectively). the csd for damocloids presents a much shallower exponent β = 0.89 ± 0.17.conclusions: the pv- and η-value distributions of acos are very similar to those of jf comet (jfcs) nuclei. the acos in tancredi's list are the best possible candidates to be dormant/inactive comets. the csd for jf-acos is shallower and shifted towards larger diameters with respect to the csd of active jfcs, which suggests that the mantling process has a size dependency whereby large comets tend to reach an inactive stage faster than small comets. finally, the population of jf-acos is comparable in number with the population of jfcs, although there are more tens-km jf-acos than jfcs. | size and albedo distributions of asteroids in cometary orbits using wise data |
we present high-resolution multiwavelength radio continuum images of the region within 150″ of sgr a*, revealing a number of new extended features and stellar sources in this region. first, we detect a continuous 2″ east-west ridge of radio emission, linking sgr a* and a cluster of stars associated with irs 13 n and irs 13e. the ridge suggests that an outflow of east-west blob-like structures is emerging from sgr a*. in particular, we find arc-like radio structures within the ridge with morphologies suggestive of photoevaporative protoplanetary disks. we use infrared ks and l‧ fluxes to show that the emission has similar characteristics to those of a protoplanetary disk irradiated by the intense radiation field at the galactic center. this suggests that star formation has taken place within the s-cluster 2″ from sgr a*. we suggest that the diffuse x-ray emission associated with sgr a* is due to an expanding hot wind produced by the mass loss from b-type main sequence stars, and/or the disks of photoevaporation of low mass young stellar objects (ysos) at a rate of ∼10-6 {m}⊙yr-1. the proposed model naturally reduces the inferred accretion rate and is an alternative to the inflow-outflow style models to explain the underluminous nature of sgr a*. second, on a scale of 5″ from sgr a*, we detect new cometary radio and infrared sources at a position angle pa ∼ 50° which is similar to that of two other cometary sources x3 and x7, all of which face sgr a*. in addition, we detect a striking tower of radio emission at a pa ∼ 50°-60° along the major axis of the sgr a east supernova remnant shell on a scale of 150″ from sgr a*. we suggest that the cometary sources and the tower feature are tracing interaction sites of a mildly relativistic jet from sgr a* with the atmosphere of stars and the nonthermal sgr a east shell at a pa ∼ 50°-60° with \dot{m}∼ 1× {10}-7 {m}⊙{{yr}}-1, and opening angle 10°. lastly, we suggest that the east-west ridge of radio emission traces an outflow that is potentially associated with past flaring activity from sgr a*. the position angle of the outflow driven by flaring activity is close to -90°. | sgr a* and its environment: low-mass star formation, the origin of x-ray gas and collimated outflow |
we describe the preparation and characterization (by uv-vis-ir spectroscopy) of a set of organic samples, stable at room temperature and above, that are part of the experiment "photochemistry on the space station (pss)" planned to be enclosed in the expose-r2 mission, which will be conducted on the expose-r facility. the core facility is placed outside the international space station (iss) on the universal platform d (urm-d platform) of the russian module zvezda. the organic materials are prepared in the catania laboratory after 200 kev he+ irradiation of icy mixtures, namely n2:ch4:co deposited at 16 k on mgf2 windows furnished by the european space agency. it is widely accepted that such a kind of materials produced by energetic processing are representative of organic material in some astrophysical environments as comets. once expelled from comets these materials are exposed to solar radiation during their interplanetary journey before they eventually land on earth and other planetary objects where they might give a contribution to the chemical and pre-biotical evolution. in particular our residues contain different chemical groups, including triple cn bonds that are considered relevant to pre-biotic chemistry. therefore the samples will be exposed, for several months, to the solar ultraviolet photons that are a major source of energy to initiate chemical evolution in the solar system. this will allow analysis of their destruction or modification and evaluation of their lifetime in the interplanetary medium. the samples have three different thicknesses that will allow estimation of the depth profile of destruction. this experiment overcomes the limits of ground tests which do not reproduce exactly the space parameters. | organic samples produced by ion bombardment of ices for the expose-r2 mission on the international space station |
we calculate the momentum flux and pressure of ions measured by the ion composition analyzer (ica) on the rosetta mission at comet 67p/churyumov-gerasimenko. the total momentum flux stays roughly constant over the mission, but the contributions of different ion populations change depending on heliocentric distance. the magnetic pressure, calculated from rosetta magnetometer measurements, roughly corresponds with the cometary ion momentum flux. when the spacecraft enters the solar wind ion cavity, the solar wind fluxes drop drastically, while the cometary momentum flux becomes roughly 10 times the solar wind fluxes outside of the ion cavity, indicating that pickup ions behave similarly to the solar wind ions in this region. we use electron density from the langmuir probe to calculate the electron pressure, which is particularly important close to the comet nucleus where flow changes from antisunward to radially outward. | momentum and pressure balance of a comet ionosphere |
the near-earth objects with low-jovian tisserand invariant (tj) represent about 9 per cent of the known objects orbiting in the near-earth space, being subject of numerous planetary encounters and large temperature variations. we aim to make a spectral characterization for a large sample of neos with tj ≤ 3.1. consequently, we can estimate the fraction of bodies with a cometary origin. we report new spectral observations for 26 low-tj neos. the additional spectra, retrieved from different public data bases, allowed us to perform the analysis over a catalogue of 150 objects. we classified them with respect to bus-demeo taxonomic system. the results are discussed regarding their orbital parameters. the taxonomic distribution of low-tj neos differs from the entire neos population. consequently, tj ~ 3 can act as a composition border too. we found that 56.2 per cent of low-tj neos have comet-like spectra and they become abundant (79.7 per cent) for tj ≤ 2.8. 16 d-type objects have been identified in this population, distributed on orbits with an average tj = 2.65 ± 0.6. using two dynamical criteria, together with the comet-like spectral classification as an identification method and by applying an observational bias correction, we estimate that the fraction of neos with a cometary nature and h ∈ (14, 21) mag has the lower and upper bounds (1.5 ± 0.15) and (10.4 ± 2.2) per cent. additionally, our observations show that all extreme cases of low-perihelion asteroids (q ≤ 0.3 au) belong to s-complex. | spectral properties of near-earth objects with low-jovian tisserand invariant |
we evaluate numerically three different models for the parent comet of the kreutz family of sungrazers: (i) a centaur on a highly inclined or retrograde orbit that diffuse to the inner planetary region where it became a sungrazer (model 1). (ii) a parent comet injected from the oort cloud straight into a near-parabolic, sungrazing orbit. near perihelion the comet was disrupted by tidal forces from the sun giving rise to a myriad of fragments that created the kreutz family (model 2). (iii) a two-step process by which an oort cloud comet is first injected in a non-sungrazing, earth-crossing orbit where its semimajor axis decreases from typical oort cloud values (a ~ 104 au) to around 102 au, and then it evolves to a sungrazing orbit by the lidov-kozai mechanism (model 3). model 1 fails to produce sungrazers of the kreutz type. model 2 produces some kreutz sungrazers and has the appeal of being the most straightforward. yet the impulses received by the fragments originated in the catastrophic disruption of the parent comet will tend to acquire a wide range of orbital energies or periods (from short-period to long-period orbits) that is in contradiction with the observations. model 3 seems to be the most promising one since it leads to the generation of some sungrazers of the kreutz type and, particularly, it reproduces the clustering of the argument of perihelion ω of the observed kreutz family members around 60°-90°, as a natural consequence of the action of the lidov-kozai mechanism. | on the origin of the kreutz family of sungrazing comets |
aims: 2i/borisov (hereafter 2i) is the first visibly active interstellar comet observed in the solar system, allowing us for the first time to sample the composition of a building block from another system. we report on the monitoring of 2i with the ultraviolet-visual echelle spectrograph, the high-resolution optical spectrograph of the eso very large telescope at paranal, for four months from november 15, 2019 to march 16, 2020. our goal is to characterise the activity and composition of 2i with respect to solar system comets.methods: we collected high-resolution spectra at 12 different epochs from 2.1 au pre-perihelion to 2.6 au post-perihelion.results: on december 24 and 26, 2019, close to perihelion, we detected several oh lines of the 309 nm (0-0) band and derived a water production rate of 2.2 ± 0.2 × 1026 molecules s−1. the three [oi] forbidden oxygen lines were detected at different epochs and we derived a green-to-red doublet intensity ratio (g/r) of 0.31 ± 0.05 close to perihelion. the nh2 ortho and para lines from various bands were measured and allowed us to derive an ortho-to-para abundance ratio (opr) of 3.21 ± 0.15, corresponding to an opr and spin temperature of ammonia of 1.11 ± 0.08 and 31−5+10 k, respectively. these values are consistent with the values usually measured for solar system comets. emission lines of the radicals nh (336 nm), cn (388 nm), ch (431 nm), and c2 (517 nm) were also detected. several fei and nii lines were identified and their intensities were measured to provide a ratio of log (nii/fei) = 0.21 ± 0.18, which is in agreement with the value recently found in solar system comets.conclusions: our high spectral resolution observations of 2i/borisov and the associated measurements of the nh2 opr and the ni/fe abundance ratio are remarkably similar to solar system comets. only the g/r ratio is unusually high, but it is consistent with the high abundance ratio of co/h2o found by other investigators. | the similarity of the interstellar comet 2i/borisov to solar system comets from high-resolution optical spectroscopy |
far-ultraviolet observations of comets yield information about the energetic processes that dissociate the sublimated gases from their primitive surfaces. understanding which emission processes are dominant, their effects on the observed cometary spectrum, and how to properly invert the spectrum back to the composition of the presumably pristine surface ices of a comet nuclei are all critical components for proper interpretation and analysis of comets. the close approach of comet 46p/wirtanen in 2018-2019 provided a unique opportunity to study the innermost parts of a cometary coma with the hubble space telescope cosmic origins spectrograph, rarely accessible with remote observations, at length scales (hundreds of kilometers) and wavelengths (900-1430 å) previously probed only by the european space agency's rosetta spacecraft. our observations show a complex picture for the inner coma; atomic production rates for h and o that show water is the dominant source of both, an abundance of atomic sulfur that is difficult to explain with the lifetimes of common sulfur parent molecules, and a density distribution that is poorly fit with both haser and vectorial models. | fuv observations of the inner coma of 46p/wirtanen |
the rosetta mission to comet 67p/churyumov-gerasimenko has provided new data to better understand what comets are made of. the weak tensile strength of the cometary surface materials suggests that the comet is a hierarchical dust aggregate formed through gravitational collapse of a bound clump of small dust aggregates so-called 'pebbles' in the gaseous solar nebula. since pebbles are the building blocks of comets, which are the survivors of planetesimals in the solar nebula, estimating the size of pebbles using a combination of thermal observations and numerical calculations is of great importance to understand the planet formation in the outer solar system. in this study, we calculated the thermal inertias and thermal skin depths of the hierarchical aggregates of pebbles, for both diurnal and orbital variations of the temperature. we found that the thermal inertias of the comet 67p/churyumov-gerasimenko are consistent with the hierarchical aggregate of cm- to dm-sized pebbles. our findings indicate that the icy planetesimals may have formed via accretion of cm- to dm-sized pebbles in the solar nebula. | thermal inertias of pebble-pile comet 67p/churyumov-gerasimenko |
ceres, the largest reservoir of water in the main belt, was recently visited by the dawn spacecraft, which revealed several areas bearing h2o-ice features. independent telescopic observations showed a water exosphere of currently unknown origin. we explore the effects of meteoroid impacts on ceres by considering the topography obtained from the dawn mission using a widely used micrometeoroid model and ray-tracing techniques. meteoroid populations with 0.01-2 mm diameters are considered. we analyze the short-term effects ceres experiences during its current orbit, as well as long-term effects over the entire precession cycle. we find that the entire surface is subject to meteoroid bombardment, leaving no areas in permanent shadow with respect to meteoroid influx. the equatorial parts of ceres produce 80% more ejecta than the polar regions due to the large impact velocity of long-period comets. mass flux, energy flux, and ejecta production vary seasonally by a factor of 3-7 due to the inclined eccentric orbit. compared to mercury and the moon, ceres experiences significantly smaller effects of micrometeoroid bombardment, with a total mass flux of 4.5 ± 1.2 × 10-17 kg m-2 s-1. on average, mercury is subjected to a 50× larger mass flux and generates 700× more ejecta than ceres, while the lunar mass flux is 10× larger and the ejecta generation is 30× larger than on ceres. for these reasons, we find that meteoroid impacts are an unlikely candidate for the production of a water exosphere or significant excavation of surface features. the surface turnover rate from the micrometeoroid populations considered is estimated to be 1.25 myr on ceres. | erosion of volatiles by micrometeoroid bombardment on ceres and comparison to the moon and mercury |
one of the most striking and curious features of the small kuiper belt object (kbo), arrokoth, explored by new horizons is the bright, annular neck it exhibits at the junction between its two lobes. here we summarize past reported findings regarding the properties of this feature and then report new results regarding its dimensions, reflectivity and color, shape profile, and lack of identifiable craters. we conclude by enumerating possible origin scenarios for this unusual feature. new results include a new estimated measurement of the observed neck area of 8 ± 1.5 km2, a total neck surface area of 32 km2, a 12.5:1 ratio of circumference to height, a normal reflectance histogram of the observed neck, and the fact that no significant (i.e., >2σ) neck color units were identified, meaning the neck's color is generally spatially uniform at the 1.5 km pixel-1 scale of the best color images. although several origin hypotheses for the bright material in the neck are briefly discussed, none can be conclusively demonstrated to be the actual origin mechanism at this time; some future tests are identified. | some new results and perspectives regarding the kuiper belt object arrokoth's remarkable, bright neck |
we observed near-sun comet 323p/soho for the first time using ground and space telescopes. in late 2020 december, the object was recovered at subaru showing no cometary features on its way to perihelion. however, in our postperihelion observations, it developed a long narrow tail mimicking a disintegrated comet. the ejecta, composed of at least millimeter-sized dust with power-law size distribution index 3.2 ± 0.2, was impulsively produced shortly after the perihelion passage, during which ≳0.1%-10% of the nucleus mass was shed due to excessive thermal stress and rotational disruption. two fragments of ~20 m in radius (assuming a geometric albedo of 0.15) were seen in hubble space telescope observations from early 2021 march. the nucleus, with an effective radius of 86 ± 3 m (the same albedo assumed) and an aspect ratio of ~0.7, has a rotation period of 0.522 hr, which is the shortest for known comets in the solar system and implies cohesive strength ≳10-100 pa in the interior. the color of the object was freakish and changed temporally in a never-before-seen manner. using our astrometry, we found a strong nongravitational effect following a heliocentric dependency of ${r}_{{\rm{h}}}^{-8.5}$ in the transverse motion of the object. our n-body integration reveals that 323p has a likelihood of 99.7% to collide with the sun in the next two millennia driven by the ν 6 secular resonance. | the lingering death of periodic near-sun comet 323p/soho |
large portions of comet 67p/churyumov-gerasimenko's northern hemisphere are blanketed by fallback material consisting of centimeter-sized particles termed the smooth terrains. observations from the rosetta mission show that the most drastic transient changes during 67p's 2015 perihelion passage occurred within a subset of these deposits. however, we still do not understand the processes driving these changes, limiting our overall understanding of how comets evolve over both seasonal and multiorbit timescales. herein we provide a complete documentation of scarp-driven activity on 67p's largest smooth terrain deposit, a highly active portion of the imhotep region that is the southernmost of all smooth terrain basins on 67p. we also present a thermal model that accurately predicts when and where scarps originate during the course of the observed activity. assuming a uniform surface composition, our model shows that activity is heavily controlled by local topography rather than the presence of ice-enhanced hot spots on the surface. scarps within the smooth terrain deposits in central imhotep also exhibit a peculiar behavior, where three scarps originate from the same location but at different times and migrate in opposite directions. this behavior indicates that the landscape retains a memory of previous cycles of erosion and deposition, reflected by the depth of the volatile-rich layer. future work will need to couple our thermal model with a landscape evolution model in order to explain the complete dynamic evolution of these terrains. | topographically influenced evolution of large-scale changes in comet 67p/churyumov-gerasimenko's imhotep region |
40 000 collected cometary particles have been identified on the 21 targets exposed by the cosima experiment on-board rosetta to the environment of comet 67p/churyumov-gerasimenko from 2014 august to 2016 september. the images of the targets where obtained by the cosima microscope (cosiscope, 13.95 μm pixel-1) with near grazing incidence, which is optimal for the primary objective (detection of collected particles) but very challenging for photometry. however, more than 300 of the collected particles are larger than 100 μm which makes it possible to derive constraints on the optical properties from the distribution of light levels within the particles. two types of particles collected by cosima (compact particles and cluster particles) have been identified in langevin et al. the best estimate reflectance factors of compact particles range from 10 per cent to 23 per cent. for cluster particles (>90 per cent of large collected particles), the comparison of the signal profiles with illumination from two opposite directions shows that there is scattering within the particles, with a mean free path in the 20-25 μm range, which requires high porosity. the best estimate reflectance factors of cluster particles range from 3 per cent to 22 per cent. this range of reflectance factors overlaps with that obtained from observations of the cometary nucleus at macroscopic scales by osiris and it is consistent with that measured for interplanetary dust particles collected in the stratosphere of the earth. | optical properties of cometary particles collected by the cosima mass spectrometer on-board rosetta during the rendezvous phase around comet 67p/churyumov-gerasimenko |
the exospheres of small solar system bodies are now observed with high spatial resolution from space missions. interpreting infrared spectra of cometary gases obtained with the virtis experiment onboard the rosetta cometary mission requires detailed modeling of infrared fluorescence emission in optically thick conditions. efficient computing methods are required since numerous ro-vibrational lines excited by the sun need to be considered. we propose a new model working in a 3-d environment to compute numerically the local incoming radiation. it uses a new algorithm using pre-defined directions of ray propagation and ray grids to reduce the cpu cost in time with respect to monte carlo methods and to treat correctly the sunlight direction. the model is applied to the ν3 bands of co2 and h2o at 4.3 μ m and 2.7 μ m respectively, and to the co ∨ (1 → 0) band at 4.7 μ m. the results are compared to the ones obtained by a 1-d algorithm which uses the escape probability (ep) method, and by a 3-d ;coupled escape probability; (cep) model, for different levels of optical thickness. our results suggest that the total band flux may vary strongly with azimuth for optically thick cases whereas the azimuth average total band flux computed is close to the one obtained with ep. our model globally predicts less intensity reduction from opacity than the cep model of gersch and a'hearn (gersch, a.m., a'hearn, m.f. [2014]. astrophys. j. 787, 36-56). an application of the model to the observation of co2, co and h2o bands in 67/p atmosphere with virtis is presented to predict the evolution of band optical thickness along the mission. | a radiative transfer model to treat infrared molecular excitation in cometary atmospheres |
our interpretation of the data returned by rosetta and other cometary missions is based on the predictions of theoretical models and the results of laboratory experiments. for example, kossacki et al. (2015) showed that 67p's surface hardness reported by spohn et al. (2015) can be explained by sintering. the present work supports rosetta's observations by investigating the hardening process of the near-surface layers and the change in surface morphology during insolation. in order to create as simple an analogue as possible our sample consists of pure, porous h2o ice and carbon black particles. the observations suggest that translucence of the near-surface ice is important for enabling subsurface hardening. as an end product of our experiments we also obtained carbon agglomerates with some residual strength. | constraining the parameter space of comet simulation experiments |
aims: on july 3, 2015, an unprecedented increase in the magnetic field magnitude was measured by the rosetta spacecraft orbiting comet 67p/churyumov-gerasimenko (67p). this increase was accompanied by large variations in magnetic field and ion and electron density and energy. to our knowledge, this unusual event marks the highest magnetic field ever measured in the plasma environment of a comet. our goal here is to examine possible physical causes for this event, and to explain this reaction of the cometary plasma and magnetic field and its trigger.methods: we used observations from the entire rosetta plasma consortium as well as energetic particle measurements from the standard radiation monitor on board rosetta to characterize the event. to provide context for the solar wind at the comet, observations at earth were compared with simulations of the solar wind.results: we find that the unusual behavior of the plasma around 67p is of solar wind origin and is caused by the impact of an interplanetary coronal mass ejection, combined with a corotating interaction region. this causes the magnetic field to pile up and increase by a factor of six to about 300 nt compared to normal values of the enhanced magnetic field at a comet. this increase is only partially accompanied by an increase in plasma density and energy, indicating that the magnetic field is connected to different regions of the coma. | unusually high magnetic fields in the coma of 67p/churyumov-gerasimenko during its high-activity phase |
in this study, the toxicity of vanadium (vci3) in allium cepa l. was studied. germination-related parameters, mitotic index (mi), catalase (cat) activity, chromosomal abnormalities (cas), malondialdehyde (mda) level, micronucleus (mn) frequency and superoxide dismutase (sod) activity were investigated. the effects of vci3 exposure on the dna of meristem cells were investigated with the help of comet assay, and the relationships between physiological, cytogenetic and biochemical parameters were revealed by correlation and pca analyses. a. cepa bulbs were germinated with different concentrations of vci3 for 72 h. as a result, the maximum germination (100%), root elongation (10.4 cm) and weight gain (6.85 g) were determined in the control. vci3 treatment caused significant decreases in all tested germination-related parameters compared to the control. the highest percentage of mi (8.62%) was also observed in the control. no cas were found in the control, except for a few sticky chromosomes and unequal distribution of chromatin (p > 0.05). vci3 treatment caused significant decreases in mi and increases in the frequencies of cas and mn, depending on the dose. similarly, the comet assay showed that dna damage scores increased with increasing vci3 doses. the lowest root mda (6.50 µm/g) level and sod (36.7 u/mg) and cat (0.82 od240nmmin/g) activities were also measured in the control. vci3 treatment caused significant increases in root mda levels and antioxidant enzyme activities. besides, vci3 treatment induced anatomical damages such as flattened cell nucleus, epidermis cell damage, binuclear cell, thickening in the cortex cell wall, giant cell nucleus, damages in cortex cell and unclear vascular tissue. all examined parameters showed significant negative or positive correlations with each other. pca analysis confirmed the relations of investigated parameters and vci3 exposure. | dna fragmentation and multifaceted toxicity induced by high-dose vanadium exposure determined by the bioindicator allium test |
one of the most used rotary files in endodontics is niti files due to their superelastic properties. this property means that this instrument has extraordinary flexion that can adapt to large angles inside the tooth canals. however, these files lose their superelasticity and fracture during use. the aim of this work is to determine the cause of fracture of the endodontic rotary files. for this purpose, 30 niti f6 skytaper® files (komet, germany) were used. their chemical composition was determined by x-ray microanalysis, and their microstructure was determined by optical microscopy. successive drillings were carried out with artificial tooth molds at 30, 45, and 70°. these tests were carried out at a temperature of 37 °c with a constant load controlled by a high sensitivity dynamometer of 5.5 n, and every five cycles were lubricated with an aqueous solution of sodium hypochlorite. the cycles to fracture were determined, and the surfaces were observed by scanning electron microscopy. transformation (austenite to martensite) and retransformation (martensite to austenite) temperatures and enthalpies were determined by differential scanning calorimeter at different endodontic cycles. the results showed an original austenitic phase with a ms temperature of 15 °c and af of 7 °c. both temperatures increase with endodontic cycling, indicating that martensite forms at higher temperatures, and the temperature must be increased with cycling to retransform it to austenite. this fact indicates the stabilization of martensite with cycling, which is confirmed by the decrease in both transformation and retransformation enthalpies. the martensite is stabilized in the structure due to defects and does not retransform. this stabilized martensite has no superelasticity and, therefore, fractures prematurely. it has been possible to observe the stabilized martensite by studying the fractography, observing that the mechanism is by fatigue. the results showed that the files fracture earlier the greater the angle applied (for the tests at 70° at 280 s, at 45° at 385 s, and at 30° at 1200 s). as the angle increases, there is an increase in mechanical stress, and, therefore, the martensite stabilizes at lower cycles. to destabilize the martensite, a heat treatment can be carried out at 500 °c for 20 min, and the files recovers all its superelasticity. | effect of stabilized martensite on the long-term performance of superelastic niti endodontic files |
h2o:co, at concentrations of (3:2) and (10:1), was condensed on csi substrate at 15 k and irradiated with 46-mev 58ni11 + ion beam. radiolysis induced by fast heavy ions was analyzed by infrared spectroscopy (ftir). the formation of nine molecular species: co2, h2o2, hcooh, hco, h2co, 13co2, ch3oh, o3, and c3o2 was observed. for both concentrations, carbon dioxide (co2), formaldehyde (h2co), formic acid (hcooh), and hydrogen peroxide (h2o2) are the most abundant products species, and tricarbon dioxide (c3o2) is much less abundant. precursor destruction cross-sections and formation cross-sections of products are determined. the co destruction cross-section for the (3:2) concentration is almost five times higher than that of water, while those for the (10:1) concentration are practically the same. atomic sputtering yields are estimated for the two ice films, the total mass sputtered is approximately 2.5 × 106 u per impact. these results contribute to figure out the chemical pathways of compounds synthesized from the two most abundant organic species (h2o and co) observed in the ices of grain mantles of the circumstellar envelopes and interstellar medium. in additional, the finding results reveal that molecular astronomical percentages are comparable to those obtained after 15 ev molec-1 of deposited dose in current experiments compared with the relative concentration of molecules in solid phase observed in myso, lyso, bg stars, and comets. | chemical reactions in h2o:co interstellar ice analogues promoted by energetic heavy-ion irradiation |
neonicotinoids are a relatively new type of insecticide to control a variety of pests. although they are generally considered to be safe, they can lead to harmful effects on human and environmental health. we aimed to investigate possible effects of common neonicotinoid insecticides (acetamiprid, clothianidin, imidacloprid, thiacloprid, and thiamethoxam) on cytotoxicity and dna damage in human neuroblastoma (sh-sy5y) and human hepatocellular carcinoma (hepg2) cells. our results indicated that 50% of inhibitory concentration values of neonicotinoids are in the range of 0.96 to >4 mm in sh-sy5y cells and 0.53 to >4 mm in hepg2 cells by the methyl tetrazolium and neutral red uptake tests after 24 and 48 h exposure. we observed significant dna damage at 500 µm of five neonicotinoids in shsy-5y cells, while only imidacloprid, thiametoxam, and thiacloprid showed some alterations in hepg2 cells after 24 h exposure using the alkaline comet assay. in conclusion, neonicotinoid insecticides may induce cytotoxicity and dna damage in cell cultures; therefore, further studies are needed to better understand the toxicity of neonicotinoids. | investigation of the genotoxic and cytotoxic effects of widely used neonicotinoid insecticides in hepg2 and sh-sy5y cells |
we present a photometric analysis of individual dust grains in the coma of comet 67p/churyumov-gerasimenko using osiris images taken from 2015 july to 2016 january. we analysed a sample of 555 taken during 18 d at heliocentric distances ranging between 1.25 and 2.04 au and at nucleocentric distances between 80 and 437 km. an automated method to detect the tracks was specifically developed. the images were taken by osiris nac in four different filters: near-ir (882 nm), orange (649 nm), farorange (649 nm) and blue (480 nm). it was not always possible to recognize all the grains in the four filters, hence we measured the spectral slope in two wavelengths ranges: in the interval [480-649] nm, for 1179 grains, and in the interval [649-882] nm, for 746 grains. we studied the evolution of the two populations' average spectral slopes. the data result scattered around the average value in the range [480-649] nm, while in the [649-882] nm we observe a slight decreasing moving away from the sun as well as a slight increasing with the nucleocentric distance. a spectrophotometric analysis was performed on a subsample of 339 grains. three major groups were defined, based on the spectral slope between [535-882] nm: (i) the steep spectra that may be related with organic material, (ii) the spectra with an intermediate slope, likely a mixture of silicates and organics and (iii) flat spectra that may be associated with a high abundance of water ice. | post-perihelion photometry of dust grains in the coma of 67p churyumov-gerasimenko |
geoconservation is an increasingly widely adopted theoretical, practical and administrative approach to the protection of geological and geomorphological features of special scientific, functional, historic, cultural, aesthetic, or ecological value. protected sites on earth include natural rocky outcrops, shorelines, river banks, and landscapes, as well as human-made structures such as road cuts and quarries exposing geological phenomena. however, geoconservation has rarely been discussed in the context of other rocky and icy planets, rings, moons, dwarf planets, asteroids, or comets, which present extraordinarily diverse, beautiful, and culturally, historically and scientifically important geological phenomena. here we propose to adapt geoconservation strategies for protecting the geological heritage of these celestial bodies, and introduce the term 'exogeoconservation' and other associated terms for this purpose. we argue that exogeoconservation is acutely necessary for the scientific exploration and responsible stewardship of celestial bodies, and suggest how this might be achieved and managed by means of international protocols. we stress that such protocols must be sensitive to the needs of scientific, industrial, and other human activities, and not unduly prohibitive. however, with space exploration and exploitation likely to accelerate in coming decades, it is increasingly important that an internationally agreed, holistic framework be developed for the protection of our common 'exogeoheritage'. | exogeoconservation: protecting geological heritage on celestial bodies |
coal mining accounts for ∼12 % of the total anthropogenic methane (ch4) emissions worldwide. the upper silesian coal basin (uscb), poland, where large quantities of ch4 are emitted to the atmosphere via ventilation shafts of underground hard coal (anthracite) mines, is one of the hot spots of methane emissions in europe. however, coal bed ch4 emissions into the atmosphere are poorly characterized. as part of the carbon dioxide and ch4 mission 1.0 (comet 1.0) that took place in may-june 2018, we flew a recently developed active aircore system aboard an unmanned aerial vehicle (uav) to obtain ch4 and co2 mole fractions 150-300 m downwind of five individual ventilation shafts in the uscb. in addition, we also measured δ13c-ch4, δ2h-ch4, ambient temperature, pressure, relative humidity, surface wind speed, and surface wind direction. we used 34 uav flights and two different approaches (inverse gaussian approach and mass balance approach) to quantify the emissions from individual shafts. the quantified emissions were compared to both annual and hourly inventory data and were used to derive the estimates of ch4 emissions in the uscb. we found a high correlation (r2=0.7-0.9) between the quantified and hourly inventory data-based shaft-averaged ch4 emissions, which in principle would allow regional estimates of ch4 emissions to be derived by upscaling individual hourly inventory data of all shafts. currently, such inventory data is available only for the five shafts we quantified. as an alternative, we have developed three upscaling approaches, i.e., by scaling the european pollutant release and transfer register (e-prtr) annual inventory, the quantified shaft-averaged emission rate, and the shaft-averaged emission rate, which are derived from the hourly emission inventory. these estimates are in the range of 256-383 kt ch4 yr-1 for the inverse gaussian (ig) approach and 228-339 kt ch4 yr-1 for the mass balance (mb) approach. we have also estimated the total co2 emissions from coal mining ventilation shafts based on the observed ratio of ch4/co2 and found that the estimated regional co2 emissions are not a major source of co2 in the uscb. this study shows that the uav-based active aircore system can be a useful tool to quantify local to regional point source methane emissions. | local-to-regional methane emissions from the upper silesian coal basin (uscb) quantified using uav-based atmospheric measurements |
prebiotic sugars are thought to be formed on primitive earth by the formose reaction. however, their formation is not fully understood and it is plausible that key intermediates could have formed in extraterrestrial environments and subsequently delivered on early earth by cometary bodies. 1,2-ethenediol, the enol form of glycolaldehyde, represents a highly reactive intermediate of the formose reaction and is likely detectable in the interstellar medium. here, we report the identification and first characterization of (z)-1,2-ethenediol by means of rotational spectroscopy. the title compound has been produced in the gas phase by flash vacuum pyrolysis of bis-exo-5-norbornene-2,3-diol at 750 °c, through a retro-diels-alder reaction. the spectral analysis was guided by high-level quantum-chemical calculations, which predicted spectroscopic parameters in very good agreement with the experiment. our study provides accurate spectral data to be used for searches of (z)-1,2-ethenediol in the interstellar space. | gas-phase identification of ( z )-1,2-ethenediol, a key prebiotic intermediate in the formose reaction |
when cosmic bodies of asteroidal and cometary origin, with a size from 20 to approximately 100 m, enter dense atmospheric layers, they are destroyed with a large probability under the action of aerodynamic forces and decelerated with the transfer of their energy to the air at heights from 20-30 to several kilometers. the forming shock wave reaches the earth's surface and can cause considerable damage at great distances from the entry path similar to the action of a high-altitude explosion. we have performed a numerical simulation of the disruption (with allowance for evaporation of fragments) and deceleration of meteoroids having the aforesaid dimensions and entering the earth's atmosphere at different angles and determined the height of the equivalent explosion point generating the same shock wave as the fall of a cosmic body with the given parameters. it turns out that this height does not depend on the velocity of the body and is approximately equal to the height at which this velocity is reduced by half. the obtained results were successfully approximated by a simple analytical formula allowing one to easily determine the height of an equivalent explosion depending on the dimensions of the body, its density, and angle of entry into the atmosphere. a comparison of the obtained results with well-known approximate analytical (pancake) models is presented and an application of the obtained formula to specific events, in particular, to the fall of the chelyabinsk meteorite on february 15, 2013, and tunguska event of 1908, is discussed. | determination of the height of the "meteoric explosion" |
the formation and main features of the fully nonlinear structure in a six-component dusty plasma system have been investigated using sagdeev potential approach. by means of pseudo-potential technique, the fluid equations describing the plasma system were diminished into a single nonlinear differential equation, called energy equation modified by presenting the parameters of addition plasma components. for certain values of the configurationally plasma parameters, our findings show that in addition to the solitary waves, double-layers and super-solitons exist and propagate in this plasma system. the main features of these waves have been studied by investigating the associated phase-portrait trajectories and potential curves as well and are found to be very sensitive to the variation of these parameters. the obtained results are mainly relevant to the cometary plasma and it may also provide better and helpful understanding of the nonlinear nature of space, astrophysical and cometary plasmas. | formation of double-layers and super-solitons in a six-component cometary dusty plasma |
paraquat (pq) is a herbicide belonging to the group of bipyridylium salts. the objective of this study was to evaluate oxidative stress, dna damage, and cytotoxicity induced by paraquat in peripheral lymphocyte cells in vivo as well as pathological changes in various tissues. for this purpose, 28 male wistar rats in 6 different groups were poisoned by paraquat gavage and blood samples were taken from the hearts of rats after during the poisoning period. oxidative stress, dna damage, cell membrane integrity, serum lactate dehydrogenase, and cytotoxicity, were investigated by ferric reducing antioxidant potential (frap) test, alkaline comet assay, measuring serum lactate dehydrogenase (ldh), hoechst staining and flow cytometry with propidium iodide (pi) respectively. the lung, kidney, and liver tissues were also examined pathologically. paraquat caused dose-dependent dna damage in peripheral lymphocyte cells and significant oxidative cell membrane damage. the most damage was caused by a single dose of 200 mg/kg b.w of paraquat by gavage. the gradual exposure to a dose of 300 mg/kg b.w of paraquat showed less damage, which could be due to the activation of the antioxidant defense mechanism. | paraquat induced oxidative stress, dna damage, and cytotoxicity in lymphocytes |
es wird davon ausgegangen, dass das älteste weitgehend unveränderte material aus der frühphase des sonnensystems in form von eis und staub in kometen vorliegt. die esa‑mission rosetta trug daher mit philae eine landeeinheit, die die zusammensetzung des nukleus von komet 67p/churyumov‑gerassimenko in situ untersuchen sollte. fünfundzwanzig minuten nach dem ersten bodenkontakt philaes im november 2014 nahm das cosac flugzeit‑massenspektrometer ein spektrum der gasphase des kometen auf. eine erneute analyse dieses spektrums mittels non‑negative least‑squares fitting und einer monte‑carlo simulation ergibt neue erkenntnisse über die chemische zusammensetzung des kometen 67p. insgesamt 12 organische moleküle, von denen 9 bereits in der ersten analyse der daten identifiziert wurden, zeigen eine hohe statistische wahrscheinlichkeit für eine präsenz im eis des kometen. diese flüchtigen organischen verbindungen mit zum teil hoher konzentration stellen die ersten molekularen ingredienzien des frühen sonnensystems dar. | esas kometen‑mission rosetta – neu‑analyse der daten des cosac massenspektrometers |
an apparently asteroidal object found on images taken by h. b. zhao, b. li, g. zhaori, r. q. hong, and l. f. hu (and measured by zhao, li, h. lu, and g. zhaori) with the purple mountain observatory's 1.04-m f/1.8 schmidt telescope at its xuyi station (discovery observations tabulated below) has been found to show cometary activity elsewhere. 2017 ut r.a. (2000) decl. mag. observer mar. 1.82132 13 32 26.43 + 7 10 06.8 19.7 zhao 1.84135 13 32 25.01 + 7 10 04.9 19.5 " 1.86138 13 32 23.57 + 7 10 02.2 19.5 " the object was also found as apparently asteroidal on ccd images obtained on mar. 3.3 ut with the 3.5-m f/1 space surveillance telescope on atom peak in the white sands missile range, nm, usa, in the course of the linear survey, and again posted on the minor planet center's neocp, from which follow-up g-band images were taken by w. h. ryan and e. v. ryan on mar. 5.3 with the magdalena ridge observatory 2.4-m f/8.9 reflector, which show the object to be a comet of magnitude 19.4-19.6 with a tail in p.a. approximately 300 degrees. | comet c/2017 e2 (xuyi) |
on 19 october 2014, comet c/2013 a1 (siding spring) had a close encounter with mars and deposited cometary dust particles into the martian atmosphere. we report a comprehensive analysis of the resulting meteor shower and its perturbation on mars' atmosphere and ionosphere. using mars atmosphere and volatile evolution/imaging ultraviolet spectrograph observations of ablated meteoric metallic species, we show this shower lasted less than 3 hr and was therefore limited to one hemisphere. meteoric ablation occurred in a narrow altitude layer, with mg+, mg, fe+, and fe deposited between about 105 and 120 km, consistent with comet siding spring's relative velocity of 56 km/s. we find that 82 ± 25 t of dust was deposited, improving previous measurements and a thousand times larger than model expectations. with regular observations over two mars days, we show that horizontal winds globally redistribute this material and also suggest new vertical transport mechanisms for metallic ions. such transport is inconsistent with diffusion and may be related to electrodynamic processes. the rapid loss of neutral species and presence of ions at high altitudes indicate that our understanding of existing martian meteoric chemistry modeling and ionospheric dynamics is incomplete. | the impact of comet siding spring's meteors on the martian atmosphere and ionosphere |
we present a historical account of advances in the study of the trans-neptunian (tn) population since pluto's discovery until present. early cosmogonic ideas about a tn belt or ring assumed that it was the leftover at the edge of a protoplanetary disk where densities were too low for the planetesimals to accumulate into a single planet. early attempts to constrain its mass were based on the perturbations that such a belt could cause on the motions of uranus, neptune, or comets that penetrate it like 1p/halley. it was shown later that jupiter family comets (jfcs) are likely to come from a flat source at the edge of the planetary region. jfcs then became the "smoking gun" that uncovered the existence of a large population of tn bodies arranged in a flat near-ecliptic distribution. we will next describe the discovery of tn objects, some rivaling pluto in size, and how they started to challenge pluto's status as the "ninth" planet of the solar system, that finally led to the revision of the definition of planet. finally, we will briefly describe our current understanding of the population and nature of tn objects and some of the hot issues under discussion. | introduction: the trans-neptunian zone: past, present and future |
the rosetta probe around comet 67p/churyumov-gerasimenko (67p) reveals an anisotropic dust distribution of the inner coma with jet-like structures. the physical processes leading to jet formation are under debate, with most models for cometary activity focusing on localized emission sources, such as cliffs or terraced regions. here we suggest, by correlating high-resolution simulations of the dust environment around 67p with observations, that the anisotropy and the background dust density of 67p originate from dust released across the entire sunlit surface of the nucleus rather than from few isolated sources. we trace back trajectories from coma regions with high local dust density in space to the non-spherical nucleus and identify two mechanisms of jet formation: areas with local concavity in either two dimensions or only one. pits and craters are examples of the first case; the neck region of the bi-lobed nucleus of 67p is an example of the latter case. the conjunction of multiple sources, in addition to dust released from all other sunlit areas, results in a high correlation coefficient (∼0.8) of the predictions with observations during a complete diurnal rotation period of 67p. | on the origin of inner coma structures observed by rosetta during a diurnal rotation of comet 67p/churyumov--gerasimenko. |
on 2019 august 30, a second interstellar object 2i/borisov was discovered 2 years after the discovery of the first known interstellar object, 1i/'oumuamua. can we send a spacecraft to this object, using existing and near-term technologies? in this paper we assess the technical feasibility of a near-term mission to 2i/borisov. we apply the optimum interplanetary trajectory software (oits) tool to generate trajectories to 2i/borisov. as results, we get the minimal δv trajectory with a launch date in 2018 july. for this trajectory, a falcon heavy launcher could have hauled an 8 ton spacecraft to 2i/borisov. for a later launch date, results for a combined powered jupiter flyby with a solar oberth maneuver are presented. for a launch in 2027, we could reach 2i/borisov in 2052, using the space launch system (sls), up-scaled parker probe heat shield technology, and solid propulsion engines. using a sls a spacecraft with a mass of 765 kg could be sent to 2i/borisov. a falcon heavy could deliver 202 kg to 2i/borisov. arrival times sooner than 2052 can potentially be achieved but with higher δv requirements and lower spacecraft payload masses. 2i/borisov's discovery shortly after the discovery of 1i/'oumuamua implies that the next interstellar object might be discovered in the near future. the feasibility of a mission to both, 1i/'oumuamua and 2i/borisov using scaled versions of existing technologies indicates that missions to at least some future interstellar objects are feasible as well. | sending a spacecraft to interstellar comet 2i/borisov |
we report the detection of a dense ionized layer in the upper atmosphere of mars caused by the impact of dust from comet siding spring. the observations were made by the ionospheric radar sounder on the mars express spacecraft during two low-altitude passes approximately 7 h and 14 h after closest approach of the comet to mars. during these passes an unusual transient layer of ionization was detected at altitudes of about 80 to 100 km with peak electron densities of (1.5 to 2.5) × 105 cm-3, much higher than normally observed in the martian ionosphere. from comparisons to previously observed ionization produced by meteors at earth and mars, we conclude that the layer was produced by dust from the comet impacting and ionizing the upper atmosphere of mars. | an ionized layer in the upper atmosphere of mars caused by dust impacts from comet siding spring |
aims: we study the meteoroid stream of the long-period comet c/1975 t2 (suzuki-saigusa-mori). this comet was suggested as the parent body of the established λ-ursae majorid meteor shower, no. 524.methods: we modeled 32 parts of a theoretical meteoroid stream of the parent comet considered. each of our models is characterized with a single value of the evolutionary time and a single value of the strength of poynting-robertson effect. the evolutionary time ranges from 10 000 to 80 000 yr. it is the period during which the evolution of the stream part is followed. in each model, the dynamical evolution of 10 000 test particles was then followed, via a numerical integration, from the time of the modeling up to the present. at the end of the integration, we analyzed the mean orbital characteristics of particles in the orbits that approach the earth's orbit, which thus enabled us to predict a shower related to the parent comet. the predicted shower was subsequently compared with its observed counterparts. we separated the latter from the databases of real meteors. as well, we attempted to identify the predicted shower to a shower recorded in the international astronomical union meteor data center (iau mdc) list of all showers.results: almost all modeled parts of the stream of comet c/1975 t2 are identified with the corresponding real shower in three video-meteor databases. no real counterpart is found in the iau mdc photographic or radio-meteor data. in the iau mdc list of showers and in our current study, this shower is identified with the established λ-ursae majorid shower, no. 524. hence, our modeling confirms the results of previous authors. at the same time we exclude an existence of other meteor shower associated with c/1975 t2. | modeling of the meteoroid stream of comet c/1975 t2 and λ-ursae majorids |
ginkgo biloba leaf extract has been shown to increase the incidence in liver tumors in mice in a 2-year bioassay conducted by the national toxicology program. in this study, the dna damaging effects of ginkgo biloba leaf extract and many of its constituents were evaluated in human hepatic hepg2 cells and the underlying mechanism was determined. a molecular docking study revealed that quercetin, a flavonoid constituent of ginkgo biloba, showed a higher potential to interact with topoisomerase ii (topo ii) than did the other ginkgo biloba constituents; this in silico prediction was confirmed by using a biochemical assay to study topo ii enzyme inhibition. moreover, as measured by the comet assay and the induction of γ-h2a.x, quercetin, followed by keampferol and isorhamnetin, appeared to be the most potent dna damage inducer in hepg2 cells. in topo ii knockdown cells, dna damage triggered by ginkgo biloba leaf extract or quercetin was dramatically decreased, indicating that dna damage is directly associated with topo ii. dna damage was also observed when cells were treated with commercially available ginkgo biloba extract product. our findings suggest that ginkgo biloba leaf extract- and quercetin-induced in vitro genotoxicity may be the result of topo ii inhibition. | ginkgo biloba leaf extract induces dna damage by inhibiting topoisomerase ii activity in human hepatic cells |
in this paper, we present the results of a morphological study performed on a sample of 28 ultracompact h ii (uc h ii) regions located near extended free-free emission, using radio continuum (rc) observations at 3.6 cm with the c and d very large array (vla) configurations, with the aim of determining a direct connection between them. by using previously published observations in b and d vla configurations, we compiled a final catalogue of 21 uc h ii regions directly connected with the surrounding extended emission (ee). the observed morphology of most of the uc h ii regions in rc emission is irregular (single- or multipeaked sources) and resembles a classical bubble structure in the galactic plane with well-defined cometary arcs. rc images superimposed on colour composite spitzer images reinforce the assignations of direct connection by the spatial coincidence between the uc components and regions of saturated 24 μm emission. we also find that the presence of ee may be crucial to understand the observed infrared excess because an underestimation of ionizing lyman photons was considered in previous works (e.g. wood & churchwell; kurtz, churchwell & wood). | ultracompact h ii regions with extended emission: the complete view |
we have studied the combined effect of the pressure anisotropies of lighter and heavier ions of opposite polarities on solitary waves in a plasma composed of these ions as well as kappa described electrons of solar and cometary origin. using the theory of chew, goldberger, and low (the cgl theory), the anisotropies of all three ions have been included in the derivation of the zakharov-kuznetsov equation. the effects of various combinations of pressure anisotropies of both lighter as well as heavier ions of opposite polarities have been considered. from the figures, plotted for parameters observed at comet halley, it is seen that different properties of the solitary wave such as width and amplitude, as well as dispersion and nonlinear coefficients, are profoundly affected by the anisotropies of the ions. also, the pressure anisotropy of the lighter ions determines the polarity of the solitary waves: the plasma supports compressive (rarefactive) solitary waves when the lighter ions are pressure isotropic (anisotropic). | effect of anisotropy of lighter and heavier ions on solitary waves in a multi-ion plasma |
in this work we provide measurements of the bidirectional reflectance in the vis-nir spectral range for a selection of laboratory samples to deduce parameters such as their visible spectrum, phase curve, hemispheric albedo and phase reddening. the aim is to simulate the reflectance of the comet nucleus in order to aid the interpretation of data from the surface of comet 67p/churyumov-gerasimenko (67p) acquired by the rosetta osiris imaging system. we produced a broad variety of well characterised and reproducible samples containing water ice, carbonaceous compounds and complex organic molecules. we were able to reproduce the individual global spectrophotometric parameters (albedo, spectrum, phase reddening, phase curve) of 67p by using mixtures of activated charcoal, tholins and water ice. however, no mixture was able to fit all parameters simultaneously. the samples with highest porosities best match the phase curve of 67p. spectral considerations from our experiments show that the particle size of the darkening agent on the cometary surface should have a lower limit of a few hundred nanometres to several micrometres and cannot be dominated by particles in the range of some tens of nanometres. furthermore, our findings indicate that the bright ice patches observed by osiris and virtis should be relatively dust free at small scale. | bidirectional reflectance of laboratory cometary analogues to interpret the spectrophotometric properties of the nucleus of comet 67p/churyumov-gerasimenko |
nongravitational forces induced by sublimation of volatiles affect the rotational and orbital dynamics of comets. in addition to contributing to the improvement of ephemerides and of rotational models, nongravitational effects can help constrain the regional distribution and temporal evolution of cometary activity, which in turn provides input for the development of thermophysical and dust transport models. we review the progress that has been made in this field thanks to the rosetta mission and we highlight the open questions. | nongravitational effects of cometary activity |
we report an apparent outburst of comet c/2014 un271 (bernardinelli-bernstein), as seen in las cumbres observatory 1-m telescope data. following our initial observations (kokotanekova et al. 2021, atel #14733), the comet had faded in brightness to r=19.57+/-0.04 mag, measured within a 4" radius aperture on 2021 sep 09.103 utc and calibrated to the ps1 magnitude system. | apparent outburst of comet c/2014 un271 (bernardinelli-bernstein) |
high-energy observations of the sun provide an opportunity to test the limits of our ability to accurately measure the properties of transiting exoplanets in the presence of stellar activity. here we insert the transit of a hot jupiter into continuous disk integrated data of the sun in lyα from nasa’s solar dynamics observatory/eve instrument to assess the impact of stellar activity on the measured planet-to-star radius ratio (rp/r⋆). in 75% of our simulated light curves, we measure the correct radius ratio; however, incorrect values can be measured if there is significant short-term variability in the light curve. the maximum measured value of rp/r⋆ is 50% larger than the input value, which is much smaller than the large lyα transit depths that have been reported in the literature, suggesting that for stars with activity levels comparable to the sun, stellar activity alone cannot account for these deep transits. we ran simulations without a transit and found that stellar activity cannot mimic the lyα transit of 55 cancari b, strengthening the conclusion that this planet has a partially transiting exopshere. we were able to compare our simulations to more active stars by artificially increasing the variability in the solar lyα light curve. in the higher variability data, the largest value of rp/r⋆ we measured is <3× the input value, which again is not large enough to reproduce the lyα transit depth reported for the more active stars hd 189733 and gj 436, supporting the interpretation that these planets have extended atmospheres and possible cometary tails. | transiting the sun. ii. the impact of stellar activity on lyα transits |
radial transport of particles, elements and fluid driven by internal stresses in three-dimensional (3d) astrophysical accretion disks is an important phenomenon, potentially relevant for the outward dust transport in protoplanetary disks, origin of the refractory particles in comets, isotopic equilibration in the earth-moon system, etc. to gain better insight into these processes, we explore the dependence of meridional circulation in 3d disks with shear viscosity on their thermal stratification, and demonstrate a strong effect of the latter on the radial flow. previous locally isothermal studies have normally found a pattern of the radial outflow near the midplane, switching to inflow higher up. here we show, both analytically and numerically, that a flow that is inward at all altitudes is possible in disks with entropy and temperature steeply increasing with height. such thermodynamic conditions may be typical in the optically thin, viscously heated accretion disks. disks in which these conditions do not hold should feature radial outflow near the midplane, as long as their internal stress is provided by the shear viscosity. our results can also be used for designing hydrodynamical disk simulations with a prescribed pattern of the meridional circulation. | radial transport and meridional circulation in accretion disks |
comets are generally considered to contain the best-preserved material from the beginning of our planetary system, although the mechanism of their formation and subsequent evolution are still poorly understood. here we report the direct in situ measurement of h2o, co, and co2 by the ptolemy mass spectrometer onboard the philae lander, part of the european space agency's rosetta mission, at the abydos site of the jupiter-family comet 67p/churyumov-gerasimenko. a co/co2 ratio of around 0.07 ± 0.04 is found at the surface of the comet, a value substantially lower than the one measured by rosina in the coma. such a major difference is a potential indication of heterogeneity of the nucleus and not of changes in the co/co2 ratio of the coma with radial distance. | low co/co2 ratios of comet 67p measured at the abydos landing site by the ptolemy mass spectrometer |
context. the esa rosetta mission investigated the environment of comet 67p/churyumov-gerasimenko (hereafter 67p) from august 2014 to september 2016. one of the experiments on board the spacecraft, the rosetta orbiter spectrometer for ion and neutral analysis (rosina) included a comet pressure sensor (cops) and two mass spectrometers to analyze the composition of neutrals and ions, the reflectron-type time-of-flight mass spectrometer (rtof), and the double focusing mass spectrometer (dfms).aims: rtof species detections cover the whole mission. this allows us to study the seasonal evolution of the main volatiles (h2o, co2, and co) and their spatial distributions.methods: we studied the rtof dataset during the two-year long comet escort phase focusing on the study of h2o, co2, and co. we also present the detection by rtof of o2, the fourth main volatile recorded in the coma of 67p. this work includes the calibration of spectra and the analysis of the signature of the four volatiles. we present the analysis of the dynamics of the main volatiles and visualize the distribution by projecting our results onto the surface of the nucleus. the temporal and spatial heterogeneities of h2o, co2, and co are studied over the two years of mission, but the o2 is only studied over a two-month period.results: the global outgassing evolution follows the expected asymmetry with respect to perihelion. the co/co2 ratio is not constant through the mission, even though both species appear to originate from the same regions of the nucleus. the outgassing of co2 and co was more pronounced in the southern than in the northern hemisphere, except for the time from august to october 2014. we provide a new and independent estimate of the relative abundance of o2.conclusions: we show evidence of a change in molecular ratios throughout the mission. we observe a clear north-south dichotomy in the coma composition, suggesting a composition dichotomy between the outgassing layers of the two hemispheres. our work indicates that co2 and co are located on the surface of the southern hemisphere as a result of the strong erosion during the previous perihelion. we also report a cyclic occurrence of co and co2 detections in the northern hemisphere. we discuss two scenarios: devolatilization of transported wet dust grains from south to north, and different stratigraphy for the upper layers of the cometary nucleus between the two hemispheres. | two years with comet 67p/churyumov-gerasimenko: h2o, co2, and co as seen by the rosina/rtof instrument of rosetta |
biosynthesis of gold nanoparticles of distinct geometric shapes with highly functional protein coats without additional capping steps is rarely reported. this study describes green synthesis of protein-coated gold nanoparticles for the first time from the edible, mycorrhizal fungus tricholoma crassum (berk.) sacc . the nanoparticles were of the size range 5-25 nm and of different shapes. spectroscopic analysis showed red shift of the absorption maxima with longer reaction period during production and blue shift with increase in ph. these were characterized with spectroscopy, sem, tem, afm, xrd, and dls. the particle size could be altered by changing synthesis parameters. these had potent antimicrobial activity against bacteria, fungi, and multi-drug-resistant pathogenic bacteria. these also had inhibitory effect on the growth kinetics of bacteria and germination of fungal spores. these showed apoptotic properties on eukaryotic cells when tested with comet assays. moreover, the particles are capped with a natural 40 kda protein which was utilized as attachment sites for genes to be delivered into sarcoma cancer cells. the present work also attempted at optimizing safe dosage of these nanoparticles using hemolysis assays, for application in therapy. large-scale production of the nanoparticles in fermentors and other possible applications of the particles have been discussed. | evaluating the antimicrobial, apoptotic, and cancer cell gene delivery properties of protein-capped gold nanoparticles synthesized from the edible mycorrhizal fungus tricholoma crassum |
ice in main belt asteroids and near-earth objects is of scientific and resource exploration interest, but small airless bodies gradually lose their ice to space by outward diffusion. here we quantitatively estimate the time it takes a porous airless body to lose all of its interior ice, based on an analytic solution for the interior temperature field of bodies in stable orbits. without latent heat, the average surface temperature, which is lower than the classic effective temperature, is representative of the body interior and hence an appropriate temperature to evaluate desiccation timescales. in a spherically averaged model, an explicit analytic solution is obtained for the depth to ice as a function of time and the time to complete desiccation. half of the ice volume is lost after 11% of this time. a bilobate structure emerges from the strong latitude dependence of desiccation rates. cold polar regions can harbor subsurface ice, even when the body center does not. latent heat retards ice loss, and we obtain a succinct expression for the temperature difference between the surface and the ice. in the outer main belt, nearly all bodies 10 km in size or larger should have been able to retain ice in their interiors over the age of the solar system. each of the following factors favors the presence of ice inside near-earth objects: a semimajor axis in the outer belt or beyond, a mantle of very low thermal inertia, a young age, or a small and stable axis tilt. | ice loss from the interior of small airless bodies according to an idealized model |
near-earth objects (neos) owe their origins to both the main-belt asteroids and comets. they include (by definition) precursors for all meteorite samples. thus understanding neo connections is central to the modern study of small bodies in our solar system and serves as the principal focus of this chapter. herein we also briefly highlight how the proximity of near-earth objects enables detailed study of the smallest known and most accessible natural objects in space, and we provide links to other chapters addressing these aspects more fully. the success of japan's hayabusa mission sample return yields a definitive link between the most common class of near-earth asteroids and one of the most common meteorites, a watershed whose ground truth enables a deeper level of understanding and new questions. we can now investigate the near-earth population to pinpoint specific main-belt source regions for broad taxonomic classes and specific meteorite types in addition to estimating the extinct comet contribution. spectral properties combined with long-term orbital modeling reveal a strong role played by planetary encounters to resurface (and likely reshape) many objects. outstanding puzzles remain for many of the newly revealed details; their resolution will generate new insights to the basic physical processes governing small bodies. | the near-earth object population: connections to comets, main-belt asteroids, and meteorites |
we present the results of a long-term telescopic observation campaign of comet 21p/giacobini-zinner, parent body of the draconid meteor shower, spanning ∼240 days during its 2018 apparition. determinations of comet 21p’s dust production rate through the afρ parameter derived from these images show that the comet had a highly asymmetric dust production rate that peaked ∼10-30 days before perihelion, when the comet was at a heliocentric distance of ∼1.02-1.08 au. the single highest afρ measurement occurred on 2018 august 14 (27 days before perihelion), and had a measured value of afρ = 1594 cm. the comet’s afρ profile is well described by a double-exponential model that rises rapidly during ingress and declines even more rapidly during its egress. these results are fully consistent with observations of comet 21p’s dust and gas production rates during past apparitions, and suggest that the double-exponential model we have derived provides a reasonable and stable approximation for the comet’s activity over the past 30 to 40 years. | dust production of comet 21p/giacobini-zinner throughout its 2018 apparition |
aims: we study the formation of the [oi] lines - that is, 5577.339 å (the green line), 6300.304 å and 6363.776 å (the two red lines) - in the coma of comets and determine the parent species of the oxygen atoms using the ratio of the green-to-red-doublet emission intensity, i5577/(i6300 + i6364), (hereafter the g/r ratio) and the line velocity widths.methods: we acquired high-resolution spectroscopic observations at the eso very large telescope of comets c/2002 t7 (linear), 73p-c/schwassmann-wachmann 3, 8p/tuttle, and 103p/hartley 2 when they were close to earth (<0.6 au). using the observed spectra, which have a high spatial resolution (<60 km/pixel), we determined the intensities and widths of the three [oi] lines. we spatially extracted the spectra to achieve the best possible resolution of about 1-2'', that is, nucleocentric projected distances of 100 to 400 km depending on the geocentric distance of the comet. we decontaminated the [oi] green line from c2 lines blends that we identified.results: the observed g/r ratio in all four comets varies as a function of nucleocentric projected distance (between ~0.25 to ~0.05 within 1000 km). this is mainly due to the collisional quenching of o(1s) and o(1d) by water molecules in the inner coma. the observed green emission line width is about 2.5 km s-1 and decreases as the distance from the nucleus increases, which can be explained by the varying contribution of co2 to the o(1s) production in the innermost coma. the photodissociation of co2 molecules seem to produce o(1s) closer to the nucleus, while the water molecule forms all the o(1s) and o(1d) atoms beyond 103 km. thus we conclude that the main parent species producing o(1s) and o(1d) in the inner coma is not always the same. the observations have been interpreted in the framework of the previously described coupled-chemistry-emission model, and the upper limits of the relative abundances of co2 were derived from the observed g/r ratios. measuring the [oi] lines might provide a new way to determine the co2 relative abundance in comets. based on observations made with eso telescope at the la silla paranal observatory under programs id 073.c-0525, 277.c-5016, 080.c-0615 and 086.c-0958.tables 3 and 4 are available in electronic form at http://www.aanda.org | forbidden oxygen lines at various nucleocentric distances in comets |
the paris carbonaceous chondrite represents the most pristine carbonaceous chondrite, providing a unique opportunity to investigate the composition of early solar system materials prior to the onset of significant aqueous alteration. a dual origin (namely from the inner and outer solar system) has been demonstrated for water in the paris meteorite parent body (piani et al. <link href="#maps13213-bib-0064"/>). here, we aim to evaluate the contribution of outer solar system (cometary-like) water ice to the inner solar system water ice using xe isotopes. we report ar, kr, and high-precision xe isotopic measurements within bulk cm 2.9 and cm 2.7 fragments, as well as ne, ar, kr, and xe isotope compositions of the insoluble organic matter (iom). noble gas signatures are similar to chondritic phase q with no evidence for a cometary-like xe component. small excesses in the heavy xe isotopes relative to phase q within bulk samples are attributed to contributions from presolar materials. cm 2.7 fragments have lower ar/xe relative to more pristine cm 2.9 fragments, with no systematic difference in xe contents. we conclude that kr and xe were little affected by aqueous alteration, in agreement with (1) minor degrees of alteration and (2) no significant differences in the chemical signature of organic matter in cm 2.7 and cm 2.9 areas (vinogradoff et al. <link href="#maps13213-bib-0085"/>). xenon contents in the iom are larger than previously published data of xe in chondritic iom, in line with the xe component in paris being pristine and preserved from xe loss during aqueous alteration/thermal metamorphism. | primordial heavy noble gases in the pristine paris carbonaceous chondrite |
modern techniques for planetary defense from comets and asteroids involve the deflection of the bolide via kinetic, gravitational, ablative, or radiative means. while potentially effective, none of these methods are capable of operating in a terminal interdiction mode wherethe threat is discovered with little time prior to impact. we present a practical and effective method for planetary defense which enables extremely short interdiction time scales, but can also operate within longer time scales and can be effective for extremely large threats. called pi ("pulverize it"), the method makes use of an array of hypervelocity penetrators which uses the kinetic energy of the asteroid or comet to disrupt it. in the terminal interdiction mode, the fragments of maximum ∼ 10 m diameter disperse laterally as they continue towards the earth, and then enter the earth's atmosphere where they burn up as a series of airburst events which spatially and temporally de-correlate the energy of the original parent bolide for any arbitrary observer on the ground in the form of acoustical shockwaves and optical pulses. we show that terminal interdiction modes ranging from 2 minutes prior to impact for 20-meter class bolides (such as the chelyabinsk asteroid), 1 day prior to impact for 100 m-class asteroids, 10 days prior to impact for apophis-class asteroids (∼ 370 m), and even 60 days prior to impact for 1 km-class threats are all possible, though longer warning times are always preferred. using only technologies readily available today, the pi method allows for a cost-effective and practical roadmap towards robust planetary defense capability. | asteroid interception and disruption for terminal planetary defense |
carbon dioxide is one of the most abundant ices present in comets and is therefore important for understanding cometary composition and activity. we present analysis of observations of co2 and [o i] emission in three comets to measure the co2 abundance and evaluate the possibility of employing observations of [o i] emission in comets as a proxy for co2. we obtained nir imaging sensitive to co2 of comets c/2012 k1 (panstarrs), c/2012 k5 (linear), and 290p/jäger with the irac instrument on spitzer. we acquired observations of [o i] emission in these comets with the arces echelle spectrometer mounted on the 3.5-m telescope at apache point observatory and observations of oh with the swift observatory (panstarrs) and with keck hires (jäger). the co2/h2o ratios derived from the spitzer images are 12.6 ± 1.3% (panstarrs), 28.9 ± 3.6% (linear), and 31.3 ± 4.2% (jäger). these abundances are derived under the assumption that contamination from co emission is negligible. the co2 abundance for panstarrs is close to the average abundance measured in comets at similar heliocentric distance to date, while the abundances measured for linear and jäger are significantly larger than the average abundance. from the coma morphology observed in panstarrs and the assumed gas expansion velocity, we derive a rotation period for the nucleus of about 9.2 h. comparison of h2o production rates derived from arces and swift data, as well as other observations, suggest the possibility of sublimation from icy grains in the inner coma. we evaluate the possibility that the [o i] emission can be employed as a proxy for co2 by comparing co2/h2o ratios inferred from the [o i] lines to those measured directly by spitzer. we find that for panstarrs we can reproduce the observed co2 abundance to an accuracy of ∼20%. for linear and jäger, we were only able to obtain upper limits on the co2 abundance inferred from the [o i] lines. these upper limits are consistent with the co2 abundances measured by spitzer. | the co2 abundance in comets c/2012 k1 (panstarrs), c/2012 k5 (linear), and 290p/jäger as measured with spitzer |
context. the binary asteroid 288p/(300163) is unusual both for its combination of wide-separation and high mass ratio and for its comet-like activity. it is not currently known whether there is a causal connection between the activity and the unusual orbit or if instead the activity helped to overcome a strong detection bias against such sub-arcsecond systems.aims: we aim to find observational constraints discriminating between possible formation scenarios and to characterise the physical properties of the system components.methods: we measured the component separation and brightness using point spread function fitting to high-resolution hubble space telescope/wide field camera 3 images from 25 epochs between 2011 and 2020. we constrained component sizes and shapes from the photometry, and we fitted a keplerian orbit to the separation as a function of time.results: approximating the components a and b as prolate spheroids with semi-axis lengths a < b and assuming a geometric albedo of 0.07, we find aa ≤ 0.6 km, ba ≥ 1.4 km, ab ≤ 0.5 km, and bb ≥ 0.8 km. we find indications that the dust production may have concentrated around b and that the mutual orbital period may have changed by 1-2 days during the 2016 perihelion passage. orbit solutions have semi-major axes in the range of (105-109) km, eccentricities between 0.41 and 0.51, and periods of (117.3-117.5) days pre-perihelion and (118.5-119.5) days post-perihelion, corresponding to system masses in the range of (6.67-7.23) × 1012 kg. the mutual and heliocentric orbit planes are roughly aligned.conclusions: based on the orbit alignment, we infer that spin-up of the precursor by the yarkovsky-o'keefe-radzievskii-paddack (yorp) effect led to the formation of the binary system. we disfavour (but cannot exclude) a scenario of very recent formation where activity was directly triggered by the break-up, because our data support a scenario with a single active component. | component properties and mutual orbit of binary main-belt comet 288p/(300163) 2006 vw139 |
the detection of interstellar bodies passing near the sun offers the opportunity to observe not just objects similar to those in the solar system, but also unfamiliar objects without solar system analogues. here i show that asymptotic giant branch (agb) stellar evolution may lead to the creation, out of stardust, of substantial numbers of nomadic post-main-sequence objects (pmsos). abg nucleosynthesis will produce three broad classes of pmso chemistry, oxygen, carbon and nitrogen rich (o-rich, c-rich, n-rich, respectively), depending largely on the original stellar mass. i further show that the interstellar comet 2i/borisov (2i) belongs to a kinematic dynamical stream, the wolf 630 stream, with an age and galactic orbit consistent with its origination as a stardust comet; the apparent lack of water in the 2i coma is consistent with it being a c-rich pmso. i also provide predictions for distinguishing stardust comets from more conventional interstellar comets and asteroids ejected during planetary formation; these can be applied to 2i in its upcoming observational phase in early 2020 as it moves away from the sun. in particular, isotope ratios of the cno elements could be dispositive, ir detection of the 11.3 {\mu}m sic line, the 30 {\mu}m line, or the ir pah lines would provide strong evidence for a c-rich pmso and detection of na or li enhancement would indicate an n-rich pmso. | is interstellar object 2i/borisov a stardust comet? predictions for the post perihelion period |
we present the results of photometry, linear spectropolarimetry, and imaging circular polarimetry of comet c/2009 p1 (garradd) performed at the 6-m telescope bta of the special astrophysical observatory (russia) equipped by the multi-mode focal reducer scorpio-2. the comet was observed at two epochs post-perihelion: on february 2-14, 2012 at rh∼1.6 au and α∼36*deg; and on april 14-21, 2012 at rh∼2.2 au and α∼27°. the spatial maps of the relative intensity and circular polarization as well as the spectral distribution of linear polarization are presented. there were two features (dust and gas tails) oriented in the solar and antisolar directions on february 2 and 14 that allowed us to determine rotation period of the nucleus as 11.1±0.8 hours. we detected emissions of c2, c3, cn, ch, nh2 molecules as well as co+ and h2o+ ions, along with a high level of the dust continuum. on february 2, the degree of linear polarization in the continuum, within the wavelength range of 0.67-0.68 μm, was about 5±0.2% in the near-nucleus region up to ∼6000 km and decreased to about 3±0.2% at ∼40,000 km. after correction for the continuum contamination, the inherent degree of polarization in the emission band c2 (δν=0) is about 3.3%. we detected a small increase of linear polarization with the wavelength with the spectral gradient δp/δλ=+4±0.8%/μm and δp/δ&lambda=+6.2±1.3%/μm, respectively, on february 2 and april 14. linear polarization indicates that this dust-rich comet can be attributed to the high-pmax comets. the left-handed (negative) circular polarization at the level approximately from -0.06±0.02% to -0.4±0.02% was observed at the distances up to 3×104 km from the nucleus on february 14 and april 21, respectively. | polarimetry, photometry, and spectroscopy of comet c/2009 p1 (garradd) |
this paper presents a new method of determining the brightness and size of cometary nuclei that has been applied to the following 32 observed comets: 2p/encke, 29p/schwassmann-wachmann 1, 102p/shoemaker 1, 103p/hartley 2, 168p/hergenrother, 189p/neat, 260p/mcnaught, 315p/loneos, p/2012 nj (la sagra), p/2013 j2 (mcnaught), c/2006 s3 (loneos), c/2009 p1 (garradd), c/2010 s1 (linear), c/2010 x1 (elenin), c/2011 j2 (linear), c/2011 l4 (panstarrs), c/2011 w3 (lovejoy), c/2012 f6 (lemmon), c/2012 j1 (catalina), c/2012 k1 (panstarrs), c/2012 s1 (ison), c/2013 r1 (lovejoy), c/2013 us10 (catalina), c/2014 b1 (schwartz), c/2014 e2 (jacques), c/2014 q2 (lovejoy), c/2015 f4 (jacques), c/2015 v2 (johnson), c/2015 er61 (panstarrs), c/2015 vl62 (lemmon-yeung-panstarrs), c/2016 a8 (linear), and c/2017 o1 (asassn). the method consists in fitting the exponential decay function to the measured coma brightness in the aperture radius range from 0.5 to 2 pixels, and extrapolating this function to 0 pixels to obtain nuclear brightness. the r-band absolute nuclear magnitude rn(1, 1, 0), and the logarithm of the nucleus diameter dn expressed in kilometres, follow a linear dependence with the absolute total visual magnitude h. this dependence is of the form rn(1, 1, 0) = 12.5943 + 0.648h, and log dn[km] = 1.2415 - 0.13h. comet 2p/encke does not fit this dependence due to its high nuclear density of 800 kg m-3 (sosa & fernández 2009). the mean bulk density of the observed comets (except 2p/encke) is 453 ± 29 kg m-3. the accuracy of the method in determining the brightness of comet nuclei at a level of 1σ is 8 per cent. | a new method of determining brightness and size of cometary nuclei |
comet c/2015 er61 (panstarrs) is a long-period oort cloud comet whose favorable approach to the inner parts of the solar system in 2017 april-may enabled us to characterize its primary volatile composition using the ishell spectrograph mounted on the 3 m nasa infrared telescope facility (irtf) on maunakea, hawaii. we used three ishell settings (covering ~2.8-5.2 μm) to sample fluorescent emissions from ${{\rm{h}}}_{2}$ o, oh, ${\mathrm{ch}}_{3}$ oh, hcn, ${{\rm{c}}}_{2}$ ${{\rm{h}}}_{2}$, ${\mathrm{nh}}_{3}$, co, ${\mathrm{ch}}_{4}$, ${{\rm{c}}}_{2}$ ${{\rm{h}}}_{6}$, ${{\rm{h}}}_{2}$ co, and ocs on multiple dates ranging from ut 2017 april 15 (shortly after its april 4 outburst) to may 13, nearly 30 days before the detection of its double nucleus. our observations also offered the opportunity to obtain sensitive $3\sigma $ upper limits for cyanoacetylene (${\mathrm{hc}}_{3}$ n). we report rotational temperatures (${t}_{\mathrm{rot}}$ ), production rates (qs), abundance (mixing) ratios (relative to ${{\rm{h}}}_{2}{\rm{o}}$ and ${{\rm{c}}}_{2}$ ${{\rm{h}}}_{6}$ ), and spatial distributions in the coma. er61 exhibits variability in production rates of many species on short (day-to-day) and long (pre- versus post-perihelion) timescales. the relative abundances of these volatile species remained consistent within uncertainties during our pre-perihelion observations but tended to decrease during our post-perihelion observations (with the exception of ${\mathrm{ch}}_{3}$ oh and hcn). the short-timescale variability in the production rates of these volatiles could be due to diurnal effects (over the course of the rotation of the nucleus) and/or the effect of its outburst. the decrease in the production rates and hence the mixing ratios in some volatiles in post-perihelion dates could be due to the presence of seasonal effects in er61. | chemical composition of outbursting comet c/2015 er61 (panstarrs) |
gas-phase molecules in cometary atmospheres (comae) originate primarily from (1) outgassing by the nucleus, (2) sublimation of icy grains in the near-nucleus coma, and (3) coma (photo)chemical processes. however, the majority of cometary gases observed at radio wavelengths have yet to be mapped, so their production/release mechanisms remain uncertain. here we present observations of six molecular species toward comet 46p/wirtanen, obtained using the atacama large millimeter/submillimeter array during the comet's unusually close (~0.1 au) approach to earth in 2018 december. interferometric maps of hcn, ch3oh, ch3cn, h2co, cs, and hnc were obtained at an unprecedented sky-projected spatial resolution of up to 25 km, enabling the nucleus and coma sources of these molecules to be accurately quantified. the hcn, ch3oh, and ch3cn spatial distributions are consistent with production by direct outgassing from (or very close to) the nucleus, with a significant proportion of the observed ch3oh originating from sublimation of icy grains in the near-nucleus coma (at a scale length lp= 36 ± 7 km). on the other hand, h2co, cs, and hnc originate primarily from distributed coma sources (with lpvalues in the range 550-16,000 km), the identities of which remain to be established. the hcn, ch3oh, and hnc abundances in 46p are consistent with the average values previously observed in comets, whereas the h2co, ch3cn, and cs abundances are relatively low. | gas sources from the coma and nucleus of comet 46p/wirtanen observed using alma |
modern ideas about objects approaching the earth are discussed. this population includes near-earth asteroids (neas), including potentially hazardous asteroids, short-period comets, meteoroid streams, and large sporadic meteoroids. an overview is given of the currently available information on the dynamic and physical properties of neas and comets. almost 5% of the currently known neas are extinct cometary nuclei or their fragments. being outwardly similar with true asteroids, they differ markedly in their dynamic and physical properties. in order to distinguish between these groups of objects, it is necessary to study both their dynamic and physical parameters. some of the known meteoroid streams are shown to contain, along with the countless small meteoroids, also large extinct fragments of cometary nuclei, which are classified as neas. a meteoroid stream and such bodies belonging to it form together an asteroid-meteoroid complex. observational and theoretical data are presented to confirm the modern understanding of near-earth objects. | current knowledge of objects approaching the earth |
the problem of sky pollution with artificial light currently affects practically all branches that are related to the broadly understood environment. this is especially true for astronomical observations. this paper presents the results of measurements of the surface brightness of the night sky for the city of rzeszów and the surrounding area, which were made in 2015, 2018 and 2021 using the photometer sky quality meter (sqm-l). the measurements show that the surface brightness of the night sky in rzeszów in 2015 was in the range from 19.20 to 18.67 mag/arcsec2, in 2018 the value of brightness oscillated in the range from 18.53 to 16.47 mag/arcsec2, and in 2021 this value was in the range from 17.13 by 15.11 mag/arcsec2. translating the obtained values on the bortle scale, we can see an increase in the brightness of the night sky from class vi in 2015 to class ix in 2021. a similar trend applies to neighboring towns, for which an increase in brightness from class iv in 2015 to class viii in 2021 was also observed. an increase in the surface brightness of the night sky causes a deterioration or even loss of visibility of astronomical objects in the night sky. this is especially true for comets and low-brightness stars. based on the measurement results, a forecast of the development of light pollution was prepared for the study areas until 2025. this forecast shows that we will still have to deal with an increase in the surface brightness of the night sky. due to the further projected increase in the brightness of the night sky, it should be expected that observers in small towns will experience changes in the quality of the sky over the coming years, which will undoubtedly make astronomical observations difficult, in particular for faint celestial bodies such as comets. | the increase in the surface brightness of the night sky and its importance in visual astronomical observations |
aims: to understand how the multitude of planetary systems that have been discovered come to be, we need to study systems at different evolutionary stages, with different central stars but also in different environments. the most challenging environment for planet formation may be the harsh uv radiation field of nearby massive stars which quickly erodes disks by external photo-evaporation. we observed the at pyx system, located in the head of a cometary globule in the gum nebula, to search for signs of ongoing planet formation.methods: we used the extreme adaptive optics imager vlt/sphere in dual beam polarization imaging mode in h-band as well as in irdifs extended mode (k12-band imaging and y-h integral field spectroscopy) to observe at pyx in polarized light and total intensity. additionally, we employed vlt/naco to observe the system in the l-band.results: we resolve the disk around at pyx for the first time in scattered light across multiple wavelengths in polarized light and total intensity. we find an extended (≥126 au) disk, with an intermediate inclination of between 35° and 42°. the disk shows a complex substructure and we identify two or possibly three spiral-like features. depending on the precise geometry of the disk (which we cannot unambiguously infer from our data), the disk may be eccentric with an eccentricity of ~0.16 or partially self-shadowed. the spiral features and possible eccentricity are both consistent with signatures of an embedded gas giant planet with a mass of ~1 mjup. our own observations can rule out brown dwarf companions embedded in the resolved disk, but are nevertheless not sensitive enough to confirm or rule out the presence of a gas giant.conclusions: at pyx is the first disk to be spatially resolved in a cometary globule in the gum nebula. by comparison with disks in the orion nebula cluster we note that the extension of the disk may be exceptional for this environment if the external uv radiation field is indeed comparable to other cometary globules in the region. the signposts of ongoing planet formation are intriguing and need to be followed up with either higher sensitivity or at different wavelengths. based on observations performed with vlt/sphere under program id 099.c-0147(b) and 1100.c-0481(f), as well as vlt/naco under program id 1101.c-0092(d). | an extended scattered light disk around at pyx. possible planet formation in a cometary globule |
any early or late dynamical instability in the outer solar system should have left their footprint on the trans-neptunian object (tno) populations. here, we study the collisional and dynamical evolution of such populations numerically by an updated version of alicandep, which suitably takes into account the onset of an early dynamical instability. key parameters for collisional and dynamical evolution are chosen to match results with current observables. the new model (alicandep-22) considers an original region located between 22 and 30 au, containing 20-30 m⊕ from which bodies are either dynamically ejected from the region or implanted into the current plutinos and hot classical trans-neptunian belt. an in situ population of objects is also present since the beginning, corresponding to the current cold-classical population. collisional and dynamical evolution is allowed starting from initial conditions accounting for streaming instability models and observational constraints. alicandep-22 successfully reproduces observational constraints as well as the shape of the size-frequency distribution expected for the trojan population. the model concludes that arrokoth is likely a primordial body but cannot be conclusive on the origin of comet 67p/churyumov-gerasimenko. the current presence of bodies larger than pluto in the outer tno population - waiting to be discovered - is compatible with the initial distributions that allow the model to match current constraints. | collisional evolution of the trans-neptunian region in an early dynamical instability scenario |
meteor astronomy employs the atmosphere of the earth as a large area detector for 0.01-1000 mm meteoroids [1]. monitoring the atmospheres of other planets for meteor activity offers the opportunity to study the parent bodies of as-yet-undetected meteor showers, test ablation models under non-terrestrial conditions and allow spacecraft operators to mitigate the risk of meteoroid impact damage [2]. by adjusting existing techniques to simulate meteoroid ablation in a venus-like atmosphere [3-8], we show that venusian meteors are generally brighter but shorter-lived than terrestrial meteors and ablate at a higher altitude, in a predominantly clear region of the atmosphere. these simulations are complemented with a list of cometary bodies and known meteoroid streams that we consider to be prime candidates for producing significant meteor activity at venus [9,10]. such predictions may be used in developing future observational campaigns to be carried out from earth or from venus orbit.references: [1] jenniskens, p. (2006) meteor showers and their parent comets, cambridge university press, cambridge. [2] christou a. a. et al (2019) in: meteoroids: sources of meteors on earth and beyond, cambridge university press, p.119-135. [3] christou a. a. (2004) icarus 168, 23-33 [4] mcauliffe, j. p., christou, a. a. (2006) icarus 180, 8-22 [5] gritsevich m., koschny d. (2011) icarus 212, 877-884 [6] bouquet a. et al (2012) planet. space sci. 103, 238-249 [7] gritsevich, m. i. (2009) adv. space res. 44, 323-334 [8] lyytinen, e., gritsevich, m. (2016) planet. space sci. 120, 35-42 [9] christou a. a. (2010) mnras 402, 2759-2770 [10] christou, a. a., vaubaillon, j. (2011) in: proc. meteoroids conf, nasa/cp-2011-216469, p.26 | meteor phenomena in the atmosphere of venus |
the oort cloud is thought to be a reservoir of icy planetesimals and the source of long-period comets (lpcs) implanted from the outer solar system during the time of giant-planet formation. the abundance of rocky ice-free bodies is a key diagnostic of solar system formation models as it can distinguish between `massive' and `depleted' proto-asteroid-belt scenarios and thus disentangle competing planet formation models. here we report a direct observation of a decimetre-sized (~2 kg) rocky meteoroid on a retrograde lpc orbit (eccentricity ~1.0, inclination 121°). during its flight, it fragmented at dynamic pressures similar to fireballs dropping ordinary chondrite meteorites. a numerical ablation model fit produces bulk density and ablation properties also consistent with asteroidal meteoroids. we estimate the flux of rocky objects impacting earth from the oort cloud to be 1.0 8−0.95+2.81 meteoroids per 106 km2 yr−1 to a mass limit of 10 g. this corresponds to an abundance of rocky meteoroids of ~6−5+13 % of all objects originating in the oort cloud and impacting earth to these masses. our result gives support to migration-based dynamical models of the formation of the solar system, which predict that significant rocky material is implanted in the oort cloud, a result not explained by traditional solar system formation models. | direct measurement of decimetre-sized rocky material in the oort cloud |
the origin and evolution of gas in debris disks are still not well understood. secondary gas production from cometary material or a primordial origin have been proposed. so far, observations have mostly concentrated on co, with only a few c observations available. we overview the c and co content of debris disk gas and test state-of-the-art models. we use new and archival atacama large millimeter/submillimeter array (alma) observations of co and c i emission, complemented by c ii data from herschel, for a sample of 14 debris disks. this expands the number of disks with alma measurements of both co and c i by 10 disks. we present new detections of c i emission toward three disks: hd 21997, hd 121191, and hd 121617. we use a simple disk model to derive gas masses and column densities. we find that current state-of-the-art models of secondary gas production overpredict the c0 content of debris disk gas. this does not rule out a secondary origin, but might indicate that the models require an additional c removal process. alternatively, the gas might be produced in transient events rather than a steady-state collisional cascade. we also test a primordial gas origin by comparing our results to a simplified thermochemical model. this yields promising results, but more detailed work is required before a conclusion can be reached. our work demonstrates that the combination of c and co data is a powerful tool to advance our understanding of debris disk gas. * herschel is an esa space observatory with science instruments provided by european-led principal investigator consortia and with important participation from nasa. | primordial or secondary? testing models of debris disk gas with alma |
it was recently proposed that there exists a "gateway" in the orbital parameter space through which centaurs transition to jupiter-family comets (jfcs). further studies have implied that the majority of objects that eventually evolve into jfcs should leave the centaur population through this gateway. this may be naively interpreted as gateway centaurs being pristine progenitors of jfcs. this is the point we want to address in this work. we show that the opposite is true: gateway centaurs are, on average, more thermally processed than the rest of the population of centaurs crossing jupiter's orbit. using a dynamically validated jfc population, we find that only ~20% of centaurs pass through the gateway prior to becoming jfcs, in accordance with previous studies. we show that more than half of jfc dynamical clones entering the gateway for the first time have already been jfcs-they simply avoided the gateway on their first pass into the inner solar system. by coupling a thermal evolution model to the orbital evolution of jfc dynamical clones, we find a higher than 50% chance that the layer currently contributing to the observed activity of gateway objects has been physically and chemically altered, due to previously sustained thermal processing. we further illustrate this effect by examining dynamical clones that match the present-day orbits of 29p/schwassmann-wachmann 1, p/2019 ld2 (atlas), and p/2008 cl94 (lemmon). | the gateway from centaurs to jupiter-family comets: thermal and dynamical evolution |
european space agency's rosetta spacecraft at comet 67p/churyumov-gerasimenko (67p) was the first mission that accompanied a comet over a substantial fraction of its orbit. on board was the rosetta orbiter spectrometer for ion and neutral analysis mass spectrometer suite to measure the local densities of the volatile species sublimating from the ices inside the comet's nucleus. understanding the nature of these ices was a key goal of rosetta. we analysed the primary cometary molecules at 67p, namely h2o and co2, together with a suite of minor species for almost the entire mission. our investigation reveals that the local abundances of highly volatile species, such as ch4 and co, are reproduced by a linear combination of both h2o and co2 densities. these findings bear similarities to laboratory-based temperature-programmed desorption experiments of amorphous ices and imply that highly volatile species are trapped in h2o and co2 ices. our results do not show the presence of ices dominated by these highly volatile molecules. most likely, they were lost due to thermal processing of 67p's interior prior to its deflection to the inner solar system. deviations in the proportions co-released with h2o and co2 can only be observed before the inbound equinox, when the comet was still far from the sun and the abundance of highly volatile molecules associated with co2 outgassing were lower. the corresponding co2 is likely seasonal frost, which sublimated and lost its trapped highly volatile species before re-freezing during the previous apparition. co, on the other hand, was elevated during the same time and requires further investigation. | volatiles in the h2o and co2 ices of comet 67p/churyumov-gerasimenko |
asteroid pairs are genetically related asteroids that recently separated (<few million years), but still reside on similar heliocentric orbits. a few hundred of these systems have been identified, primarily in the asteroid main belt. here, we studied a newly discovered pair of near-earth objects (neos): 2019 pr2 and 2019 qr6. based on broad-band photometry, we found these asteroids to be spectrally similar to d-types, a type rare amongst neos. we recovered astrometric observations for both asteroids from the catalina sky survey from 2005, which significantly improved their fitted orbits. with these refinements we ran backwards orbital integrations to study formation and evolutionary history. we found that neither a pure gravitational model nor a model with the yarkovsky effect could explain their current orbits. we thus implemented two models of comet-like non-gravitational forces based on water or co sublimation. the first model assumed quasi-continuous, comet-like activity after separation, which suggested a formation time of the asteroid pair $300^{+120}_{-70}$ yr ago. the second model assumed short-term activity for up to one heliocentric orbit (~13.9 yr) after separation, which suggested that the pair formed 272 ± 7 yr ago. image stacks showed no activity for 2019 pr2 during its last perihelion passage. these results strongly argue for a common origin that makes these objects the youngest asteroid pair known to date. questions remain regarding whether these objects derived from a parent comet or asteroid, and how activity may have evolved since their separation. | recent formation and likely cometary activity of near-earth asteroid pair 2019 pr2-2019 qr6 |
over 200 molecules have been detected in multiple extraterrestrial environments, including glycolaldehyde (c2(h2o)2, gla), a two-carbon sugar precursor that has been detected in regions of the interstellar medium. its recent in situ detection on the nucleus of comet 67p/churyumov-gerasimenko and through remote observations in the comae of others provides tantalizing evidence that it is common on most (if not all) comets. impact experiments conducted at the experimental impact laboratory at nasa's johnson space center have shown that samples of gla and gla mixed with montmorillonite clays can survive impact delivery in the pressure range of 4.5 to 25 gpa. extrapolated to amounts of gla observed on individual comets and assuming a monotonic impact rate in the first billion years of solar system history, these experimental results show that up to 1023 kg of cometary gla could have survived impact delivery, with substantial amounts of threose, erythrose, glycolic acid, and ethylene glycol also produced or delivered. importantly, independent of the profile of the impact flux in the early solar system, comet delivery of gla would have provided (and may continue to provide) a reservoir of starting material for the formose reaction (to form ribose) and the strecker reaction (to form amino acids). thus, comets may have been important delivery vehicles for starting molecules necessary for life as we know it. | cometary glycolaldehyde as a source of pre-rna molecules |
our aim was to analyze the variation of johnson-kron-cousins bvri color indexes of a sample with 22 active comets of various dynamic groups with the time, geometrical, observational and dynamical parameters. we performed photometric observations of 16 comets between 2010 and 2014, using robotic telescopes in three continents. in addition to the sample, we used data of six comets available in the literature. a statistical comparison between the distributions of color indexes was performed using the kruskal-wallis h-test. the color indexes of active comets can vary a few tenths up to a magnitude on time scales that range from hours to weeks. using the b-v colors of the observed comets, we generated a relationship that correlates the cometary visual and ccd magnitudes. we did not identify any relationship between b-v and v-r colors with heliocentric distance and phase angle. the color b-v is correlated with the photometric aperture that can be described by a logarithmic function. we did not identify any differences in the distribution of b-v color among the comets analyzed at a confidence level equal to or greater than 95%. the mean color of active comets are b-r = 1.20 ± 0.24 , b-v = 0.76 ± 0.16 and v-r = 0.42 ± 0.16 . active comets with v-r colors outside the three standard deviation interval can be considered objects with unusual physical characteristics. | an analysis of the bvri colors of 22 active comets |
the atacama large aperture submillimeter telescope (atlast) is a concept for a 50m class single-dish telescope that will provide high sensitivity, fast mapping of the (sub-)millimeter sky. expected to be powered by renewable energy sources, and to be constructed in the atacama desert in the 2030s, atlast's suite of up to six stateof-the-art instruments will take advantage of its large field of view and high throughput to deliver efficient continuum and spectroscopic observations of the faint, large-scale emission that eludes current facilities. the atlast design study project is currently supported by a horizon 2020 grant aimed at studying the governance, telescope design, site selection, telescope operations, sustainable energy supply, and science drivers of the future atlast observatory. with quantified and specific science goals, we can begin to place technical specifications on the telescope and its instrumentation. as a first step in this process, we conducted a consultation on potential atlast science with the global (sub-)millimeter astrophysics community. the consultation involved nearly 100 scientists based in 22 countries, and the resulting 28 use cases indicate the breadth of transformational science that such a high-throughput facility could make possible: from exploring the prebiotic molecular chemistry of comets in our own solar system, detecting the extended, diffuse cold gas in the circumgalactic medium of both our own and distant galaxies, to detailed measurements of the thermal, kinetic, and relativistic sunyaev-zeldovich effect and mapping of large-scale structure. already these science cases define some core requirements for atlast's instrumentation: wide bandwidths, multichroic observations, high spectral resolution, fast mapping and a large field of view. further refinement of these is planned over the course of the current eu-funded project, resulting in detailed case studies of the telescope and instrumentation requirements needed by the community to deliver a next-generation submillimeter observing facility. | the atacama large aperture submillimetre telescope: key science drivers |
comets hold the key to the understanding of our solar system, its formation and its evolution, and to the fundamental plasma processes at work both in it and beyond it. a comet nucleus emits gas as it is heated by the sunlight. the gas forms the coma, where it is ionised, becomes a plasma, and eventually interacts with the solar wind. besides these neutral and ionised gases, the coma also contains dust grains, released from the comet nucleus. as a cometary atmosphere develops when the comet travels through the solar system, large-scale structures, such as the plasma boundaries, develop and disappear, while at planets such large-scale structures are only accessible in their fully grown, quasi-steady state. in situ measurements at comets enable us to learn both how such large-scale structures are formed or reformed and how small-scale processes in the plasma affect the formation and properties of these large scale structures. furthermore, a comet goes through a wide range of parameter regimes during its life cycle, where either collisional processes, involving neutrals and charged particles, or collisionless processes are at play, and might even compete in complicated transitional regimes. thus a comet presents a unique opportunity to study this parameter space, from an asteroid-like to a mars- and venus-like interaction. the rosetta mission and previous fast flybys of comets have together made many new discoveries, but the most important breakthroughs in the understanding of cometary plasmas are yet to come. the comet interceptor mission will provide a sample of multi-point measurements at a comet, setting the stage for a multi-spacecraft mission to accompany a comet on its journey through the solar system. this white paper, submitted in response to the european space agency's voyage 2050 call, reviews the present-day knowledge of cometary plasmas, discusses the many questions that remain unanswered, and outlines a multi-spacecraft european space agency mission to accompany a comet that will answer these questions by combining both multi-spacecraft observations and a rendezvous mission, and at the same time advance our understanding of fundamental plasma physics and its role in planetary systems. | cometary plasma science |
context. a τ herculid meteor outburst or even storm was predicted to occur by several models around 5 ut on 31 may 2022 as a consequence of the break-up of comet 73p/schwassmann-wachmann 3 in 1995. the multi-instrument and multi-station experiment was carried out within the czech republic to cover possible earlier activity of the shower between 21 and 1 ut on 30/31 may.aims: we report meteor shower activity that occurred before the main peak and provide a comparison with the dynamical simulations of the stream evolution. the physical properties of the meteoroids are also studied.methods: multi-station observations using video and photographic cameras were used to calculate the atmospheric trajectories and heliocentric orbits of the meteors. their arrival times were used to determine the shower activity profile. the physical properties of the meteoroids were evaluated using various criteria based on meteor heights. the evolution of the spectra of three meteors were studied as well.results: this annual but poor meteor shower was active for the whole night many hours before the predicted peak. a comparison with dynamical models shows that a mix of older material ejected after 1900 and fresh particles originating from the 1995 comet fragmentation event was observed. the radiant positions of both groups of meteors were identified and were found to agree well with the simulated radiants. meteoroids with masses between 10 mg and 10 kg were recorded. the mass distribution index was slightly higher than 2. the study of the physical properties shows that the τ herculid meteoroids belong to the most fragile particles observed ever, especially among higher masses of meteoroids. the exceptionally bright bolide observed during the dawn represents a challenge for the dynamical simulations as it is necessary to explain how a half-metre body was transferred to the vicinity of the earth at the same time as millimetre-sized particles. | τ herculid meteor shower in the night of 30/31 may 2022 and the meteoroid properties |
approximation of the gravitational field of an irregular celestial body by the gravitational attraction field of four massive points is studied here in the framework of k-means method, known from the theory of pattern recognition. using this approach, the simplified models for gravitational fields of asteroid (1620) geographos and comet (67p) churyumov-gerasimenko are constructed. for asteroid (1620) geographos, the proposed model is compared with the previously used one when this asteroid is represented by four cotangent spheres with co-planar centers. | approximation for attraction field of irregular celestial bodies using four massive points |
recent detections of potentially habitable exoplanets around sunlike stars demand increased exploration of the physical conditions that can sustain life, by whatever methods available. insight into these conditions can be gained by considering the multiverse hypothesis; in a multiverse setting, the probability of living in our universe depends on assumptions made about the factors affecting habitability. various proposed habitability criteria can be systematically considered to rate each on the basis of their compatibility with the multiverse, generating predictions which can both guide expectations for life's occurrence and test the multiverse hypothesis. here, we evaluate several aspects of planetary habitability, and show that the multiverse does indeed induce strong preferences among them. we find that the notion that a large moon is necessary for habitability is untenable in the multiverse scenario, as in the majority of parameter space, moons are not necessary to maintain stable obliquity. further, we consider various proposed mechanisms for water delivery to the early earth, including delivery from asteroids, both during giant planet formation and a grand tack, delivery from comets, and oxidation of a primary atmosphere by a magma ocean. we find that, depending on assumptions for how habitability depends on water content, some of these proposed mechanisms are disfavored in the multiverse scenario by bayes factors of up to several hundred. | multiverse predictions for habitability: planetary characteristics |
if a dust trail of bolide illuminated by the rays of the sun, which had just hid behind the horizon, it is visible as bright lanes in the night sky or in twilight. that's why we call its the twilight bolides. we have obtained several thousands of different tracks in the sky over kiev. therefore, we have identified a special class of twilight observations of fireballs | observations of twilight fireballs over kiev in 2013-2015 |
allyl isothiocyanate (aitc), a glucosinolates' hydrolytic product, was studied for its anti-insect potential against an economically important, destructive tephritid pest, zeugodacus cucurbitae (coquillett). the first, second and third instar maggots of the pest were fed on artificial diets amended with varied concentrations of aitc viz. 5 ppm, 25 ppm, 50 ppm, 100 ppm, 150 ppm and 200 ppm with dmso (0.5%) as control. results revealed high larval mortality, alteration of larval period, prolongation of pupal and total developmental periods in all instars of the maggots treated with aitc as compared to controls. percent pupation and percent adult emergence decreased in all larval instars. growth indices viz. larval growth index (lgi) and total growth index (tgi) were negatively affected. anti-nutritional/post ingestive toxicity of aitc was also revealed by the decrease in food assimilation (fa) and mean relative growth rate (mrgr) values with respect to control. profiles of po (phenol oxidase) and other detoxifying enzymes including sod (superoxide dismutases), cat (catalases), gst (glutathione-s-transferases), est (esterases), akp (alkaline phosphatases) and acp (acid phosphatases) were also significantly influenced. the genotoxic effect of aitc was also evaluated by conducting comet assays at lc30 and lc50. significant dna damage in hemocytes was reflected by increase in tail length (μm), percent tail dna, tail moment (tm) and olive tail moment (otm) as compared to controls. the results indicated high potential of aitc as biopesticide for pest management. | appraisal of growth inhibitory, biochemical and genotoxic effects of allyl isothiocyanate on different developmental stages of zeugodacus cucurbitae (coquillett) (diptera: tephritidae) |
this work is intended to be the second publication in a series of papers reporting on the spectro-photometric properties of cometary analogues measured in the laboratory. herein, we provide in-situ hyperspectral imaging data in the 0.40-2.35 μm range from three sublimation experiments under simulated space conditions in thermal vacuum from samples made of water ice, carbonaceous compounds and complex organic molecules. the dataset is complemented by measurements of the bidirectional reflectance in the visible (750 nm) spectral range before and after sublimation. a qualitative characterization of surface evolution processes is provided as well as a description of morphological changes during the simulation experiment. the aim of these experiments is to mimic the spectrum of comet 67p/churyumov-gerasimenko (67p) as acquired by the rosetta mission by applying sublimation experiments on the mixtures of water ice with a complex organic material (tholins) and carbonaceous compounds (carbon black; activated charcoal) studied in our companion publication (jost et al., submitted). sublimation experiments are needed to develop the particular texture (high porosity), expected on the nucleus' surface, which might have a strong influence on spectro-photometric properties. the spectrally best matching mixtures of non volatile organic molecules from jost et al. (submitted) are mixed with fine grained water ice particles and evolved in a thermal vacuum chamber, in order to monitor the influence of the sublimation process on their spectro-photometric properties. we demonstrate that the way the water ice and the non-volatile constituents are mixed, plays a major role in the formation and evolution of a surface residue mantle as well as having influence on the consolidation processes of the underlying ice. additionally it results in different activity patterns under simulated insolation cycles. further we show that the phase curves of samples having a porous surface mantle layer display higher coincidence with data of 67p than the phase curves of the samples having a more compact surface layer with smooth texture. the analysis of spectral absorption bands of water ice in the near-infrared (nir) range, similar to those acquired by the virtis instrument onboard rosetta, allows to link compositional considerations with surface activity and texture. | bidirectional reflectance and vis-nir spectroscopy of cometary analogues under simulated space conditions |
one of the major discoveries of nasa's 1979-1991 pioneer venus orbiter is that the nightside ionosphere becomes filamentary at high altitude, forming comet-like tail rays. pioneer venus orbiter could not establish how much farther into the wake of venus tail rays extend, nor understand how they form. here we present plasma and fields data from the fourth flyby of venus by nasa's parker solar probe consistent with an intercept with an ionospheric tail ray. the observations unambiguously demonstrate that venusian ionotail rays can extend to at least 7,800 km in altitude. using the new parker observations we are able to identify a tail ray encounter within the venus express dataset. we thus present a unified picture of the structure of the magnetotail of venus based on combined venus express, pioneer venus orbiter, and parker observations, and recent hybrid modeling. | a revised understanding of the structure of the venusian magnetotail from a high-altitude intercept with a tail ray by parker solar probe |
the paper presents two models that allow us to determine the change in the brightness of a comet during its outburst. the first of them (model a) is associated with the impact of individual scattering cross-sections on the brightness jump of the comet. the second (model b) is associated with the increase of sublimation active surface during an outburst. based on these two models, we determine the change in the brightness of comets during the outburst. we assume that cometary particles consist of ice, dust, or their interconnections. for water-ice particles, the key factor is determining the lifetime in a coma. we find that the cometary outburst phase lasts until a significant amount of water-ice in the coma runs out. the loss of water-ice due to sublimation reduces the surface on which the incident sunlight is scattered. consequently, this causes a slow decrease in brightness to the level before the outburst. | two methods for determining the brightness change of a comet during its outburst |
the recent discovery of a hundred-kilometer-scale comet, c/2014 un271 (bernardinelli-bernstein), has provoked interest in the activity displayed by such a large body inbound from the oort cloud. we examine the serendipitous observation of un271 in long-cadence imaging by the tess satellite in 2018 and 2020, while bernardinelli-bernstein was at 23.8 and 21.3 au, for any notable periodicity. bernardinelli-bernstein does not display detectable rotational variability above the noise level in these data. | no rotational variability in c/2014 un271 (bernardinelli-bernstein) at 23.8 au and 21.1 au as seen by tess |
we conducted a deep search for deuterated water (hdo) in the oort cloud comet c/2014 q2 (lovejoy), through infrared (ir) spectroscopy with nirspec at the keck observatory. in this letter, we present our detections of hdo and water (h2o) in comet lovejoy on 2015 february 4 (post-perihelion) after 1 hr integration on source. the ir observations allowed simultaneous detection of h2o and hdo, yielding production rates of 5.9 ± 0.13 × 1029 and 3.6 ± 1.0 × 1026 molecules s-1, respectively. the simultaneous detection permitted accurate determination of the isotopic ratio (d/h) in water of 3.02 ± 0.87 × 10-4, i.e., larger than the value for water in terrestrial oceans (or vienna standard mean ocean water, vsmow) by a factor of 1.94 ± 0.56. this d/h ratio in water exceeds the value obtained independently at millimeter wavelengths (0.89 ± 0.25 vsmow; pre-perihelion). we discuss these parameters in the context of origins and emphasize the need for contemporaneous measurements of hdo and h2o. | ground-based detection of deuterated water in comet c/2014 q2 (lovejoy) at ir wavelengths |
context. the luminous efficiency, τ, can be used to compute the pre-atmospheric masses of meteoroids from corresponding recorded meteor brightnesses. the derivation of the luminous efficiency is non-trivial and is subject to biases and model assumptions. this has led to greatly varying results in the last decades of studies.aims: the present paper aims to investigate how a reduction in various observational biases can be achieved to derive (more) reliable values for the luminous efficiency.methods: a total of 281 meteors observed by the fireball recovery and interplanetary observation network (fripon) are studied. the luminous efficiencies of the events are computed using an ablation-based model. the relations of τ as a function of the pre-atmospheric meteoroid velocity, ve, and mass, me, are studied. various aspects that could render the method less valid, cause inaccuracies, or bias the results are investigated. on this basis, the best suitable meteors were selected for luminous efficiency computations.results: the presented analysis shows the limits of the used method. the most influential characteristics that are necessary for reliable results for the τ computation were identified. we study the dependence of τ on the assumed meteoroid's density, ρ, and include improved ρ-values for objects with identified meteoroid stream association. based on the discovered individual biases and constraints we create a pre-debiased subset of 54 well-recorded events with a relative velocity change >80%, a final height <70 km, and a knudsen number kn < 0.01; this last value indicates that the events were observed in the continuum-flow regime. we find τ-values in the range between 0.012% and 1.1% for this pre-debiased subset and relations of τ to ve and me of: τ=7.33⋅ve−1.10 and τ=0.28⋅me−0.33.conclusions: the derived luminous efficiency of meteoroids depends on the assumed material density. our results indicate that the applied debiasing method improves the analysis of τ from decelerated meteoroids. the underlying method is only valid for meteors in the continuum-flow regime. these events tend to have low end heights, large masses, and high deceleration. | luminous efficiency of meteors derived from ablation model after assessment of its range of validity |
nitrogen-rich refractory organics are scarce phases recovered as a fraction of stratospheric idps and constitute the bulk of the organic matter of some ultracarbonaceous antarctic micrometeorites. they are likely formed under very specific conditions within a nitrogen-rich environment and may provide valuable clues on the origin of the population of interplanetary dusts accreted by earth. in this study, we produced relevant analogs of such refractory organics characterized in three ultracarbonaceous antarctic micrometeorites, starting from the carbonization of an hcn polymer and a tholin. indeed, carbonization is a process that can increase the polyaromatic character toward a structure similar to that observed in these cosmomaterials. both these precursors were degraded in an ar atmosphere at 300, 500, 700 and 1000 °c over ∼1 h and characterized by elemental analysis, micro-ftir and raman micro-spectroscopy (at 244 and 514 nm excitation wavelengths). our results show that the precursors evolve along distinct chemical and structural pathways during carbonization and that the influence of the precursor structure is still very strong at 1000 °c. interestingly, these different carbonization routes appear in the spectral characteristics of the g and d bands of their raman spectra. several of the residues present chemical and structural similarities with three recently studied ultracarbonaceous micrometeorites (dobrica et al. [2011]. meteorit. planet. sci. 46, 1363; dartois et al. [2013]. icarus 224, 243) and with n-rich inclusions in stratospheric idps. however, the residues do not simultaneously account for the carbon structure (raman) and the chemical composition (ir, n/c ratio). this indicates that the precursors and/or heating conditions in our experiments are not fully relevant. despite this lack of full relevancy, the formation of a polyaromatic structure fairly similar to that of ucamms and idps suggests that the origin of n-rich refractory organics lies in a thermal process in the proto-solar disk, however radiolysis cannot be excluded. | formation of analogs of cometary nitrogen-rich refractory organics from thermal degradation of tholin and hcn polymer |
context. with only a few low- and high-mass star-formation regions studied in detail so far, it is unclear what role the enviroment plays in complex molecule formation. in this light, a comparison of relative abundances of related species between sources might be useful for explaining any observed differences.aims: we seek to measure the relative abundance between three important complex organic molecules, ethylene glycol ((ch2oh)2), glycolaldehyde (ch2ohcho) and methyl formate (hcooch3), toward high-mass protostars and thereby provide additional constraints on their formation pathways.methods: we use iram 30 m single-dish observations of the three species toward two high-mass star-forming regions - w51/e2 and g34.3+0.2 - and report a tentative detection of (ch2oh)2 toward both sources.results: assuming that (ch2oh)2, ch2ohcho, and hcooch3 spatially coexist, relative abundance ratios, hcooch3/(ch2oh)2, of 31 and 35 are derived for g34.3+0.2 and w51/e2, respectively. ch2ohcho is not detected, but the data provide lower limits to the hcooch3/ch2ohcho abundance ratios of ≥193 for g34.3+0.2 and ≥550 for w51/e2. a comparison of these results to measurements from various sources in the literature indicates that the source luminosities may be correlated with the hcooch3/(ch2oh)2 and hcooch3/ch2ohcho ratios. this apparent correlation may be a consequence of the relative time scales each source spend at different temperature ranges in their evolution. furthermore, we obtain lower limits to the ratio of (ch2oh)2/ch2ohcho for g34.3+0.2 (≥6) and w51/e2 (≥16). this result confirms that a high (ch2oh)2/ch2ohcho abundance ratio is not a specific property of comets, as previously speculated. based on observations carried out with the iram 30 m telescope.the reduced spectra (fits files) are only available at the cds via anonymous ftp to http://cdsarc.u-strasbg.fr (ftp://130.79.128.5) or via http://cdsarc.u-strasbg.fr/viz-bin/qcat?j/a+a/582/a64appendices are available in electronic form at http://www.aanda.org | tentative detection of ethylene glycol toward w51/e2 and g34.3+0.2 ⋆⋆⋆ |
the present study emphasizes the possible impact of coastal water quality on marine zooplankton community from six different sampling sites of south india (kalpakkam, nemmeli, muttukadu, kasimedu, ennore and kattupalli). water samples were collected in the sampling sites and physicochemical parameters were studied. the results showed significant variations in the concentration and distribution pattern of selected physicochemical parameters (temperatures, ph, salinity, do, no-3, no-2, nh3, po43- and sio2) and heavy metals (ni, cu, zn, pb, fe, mg, co, and cr). the concentration of nutrients and trace elements were reported high at site iv (kasimedu) and low at site ii (nemmeli). further, diversity indices showed maximum shannon_h and simpson_1-d indexes (h = 3.492; d = 0.966) at site iv (kasimedu). similarly, low diversity indices (h = 3.128; d = 0.9508) was registered at site ii (nemmeli) and site iii (muttukadu), indicating plankton population was attracted by high concentration of nutrients loads in the study areas. finally, genotoxicity (genomic integrity) was assessed by dna fragmentation and alkaline comet assay, which resulted in maximum genomic integrity loss for the sample collected from kalpakkam (42.84 ± 08.38), ennore (41.44 ± 06.59), and kasimedu (39.5 ± 09.68) sites. the results revealed that the maximum heavy metal concentration has impact on the zooplankton population as evidence from dna fragmentation compared with that of freshly hatched out artemia nauplii as control. hence, the present investigation documents the alarming threat in coastal water quality which will have an impact on the zooplankton community in selected coastal zones. | coastal water quality impact on community structure and genotoxicity of marine zooplankton |
ion acoustic waves were observed in the diamagnetic cavity of comet 67p/churyumov-gerasimenko by the rosetta spacecraft on 2015 august 3, when the comet was 1.25 au from the sun. wave spectra recorded by the langmuir probe (rpc-lap), peak near 200 hz, decrease for higher frequencies and reach the noise floor at approximately 1.5 khz. these waves were observed only when the spacecraft was in the diamagnetic cavity or at its boundary, which is identified as a sharp drop in magnetic field magnitude, measured by rpc-mag. the plasma, on both sides of the boundary, is dominated by a cold (a few hundred k) water group ion population, one cold (kbte ∼ 0.1 ev) and one warm (kbte ∼ 10 ev) electron population. the observations are interpreted in terms of current-driven ion acoustic waves, generated by currents that flow through bulges on the boundary of the diamagnetic cavity. | plasma waves confined to the diamagnetic cavity of comet 67p/churyumov-gerasimenko |
the knowledge about sulphur isotopic fractionation in volatile cometary species is limited as only measurements in five comets have been done and only for 34s/32s. the lack of information about the fractionation of 33s/32s makes it impossible to compare them with what is known from refractories. we present results of 34s/32s and for the first time 33s/32s isotopic ratio in h2s, ocs, and cs2 in the coma of comet 67p/churyumov-gerasimenko. observations used for this study were performed with rosetta orbiter spectrometer for ion and neutral analysis/double focusing mass spectrometer during 2014 october and 2016 may. bulk isotopic 33s/32s and 34s/32s ratios derived from these three species yield δ33s = (-302 ± 29)‰ and δ34s = (-41 ± 17)‰, respectively. the observed isotopic fractionation is significantly different from the assumed solar system standard [vienna-canyon diablo troilite (v-cdt)] and all other reported values for solar system objects, except other comets. furthermore, we show that neither mass-dependent nor mass-independent fractionation due to photodissociation as it has been observed in recent laboratory studies can be the cause of the significant depletion compared to solar system standard. in addition, we conclude that there seems to be an intrinsic difference in sulphur isotopic fractionation in cometary volatiles and refractories while the difference between molecules is most likely due to different chemical pathways. the significant fractionation of sulphur isotopes together with a high d2o/hdo versus hdo/h2o and non-solar isotopic ratio for xenon as well as for si point towards a non-homogeneously mixed protosolar nebula. | sulphur isotope mass-independent fractionation observed in comet 67p/churyumov-gerasimenko by rosetta/rosina |
context. here we describe a new model of the dust streams of comet 67p/churyumov-gerasimenko that has been developed using the interplanetary meteoroid environment for exploration (imex). this is a new universal model for recently created cometary meteoroid streams in the inner solar system.aims: the model can be used to investigate characteristics of cometary trails: here we describe the model and apply it to the trail of comet 67p/churyumov-gerasimenko to develop our understanding of the trail and assess the reliability of the model.methods: our imex model provides trajectories for a large number of dust particles released from ~400 short-period comets. we use this to generate optical depth profiles of the dust trail of comet 67p/churyumov-gerasimenko and compare these to spitzer observations of the trail of this comet from 2004 and 2006.results: we find that our model can match the observed trails if we use very low ejection velocities, a differential size distribution index of α ≈ -3.7, and a dust production rate of 300-500 kg s-1 at perihelion. the trail is dominated by mm-sized particles and can contain a large proportion of dust produced before the most recent apparition. we demonstrate the strength of imex in providing time-resolved histories of meteoroid streams. we find that the passage of mars through the stream in 2062 creates visible gaps. this indicates the utility of this model in providing insight into the dynamical evolution of streams and trails, as well as impact hazard assessment for spacecraft on interplanetary missions. a movie is available in electronic form at http://www.aanda.org | characteristics of the dust trail of 67p/churyumov-gerasimenko: an application of the imex model |
the internal properties of porous and icy bodies in the solar system can be investigated by ground-penetrating radars (gprs), like the comet nucleus sounding experiment by radiowave transmission instrument on board the rosetta spacecraft which has sounded the interior of the nucleus of comet 67p/churyumov-gerasimenko. accurate constraints on the permittivity of icy media are needed for the interpretation of the data. we report novel permittivity measurements performed on water ice samples and icy mixtures with porosities in the 31-91% range. the measurements have been performed between 50 mhz and 2 ghz with a coaxial cell on a total of 38 samples with a good reproducibility. we used controlled procedures to produce fine-grained and coarse-grained ice samples with a mean diameter of 4.5 μm and 67 μm, respectively, and to prepare icy mixtures. the jsc-1a lunar regolith simulant was used as the dust component in the mixtures. the results are focused on the real-part ɛ' of the permittivity, which constrains the phase velocity of the radio waves in low-loss media. the values of ɛ' show a nondispersive behavior and are within the range of 1.1 to 2.7. they decrease with the increasing porosity φ according to e(1 - φ), with e equal to about 3.13 for pure water ice, and in the 3.8-7.5 range for ice-dust mixtures with a dust-to-ice volumetric ratio in the 0.1-2.8 range, respectively. these measurements are also relevant for radiometers operating in the millimeter-submillimeter domains, as suggested by the nondispersive behavior of the mixtures and of the pure components. | characterization of the permittivity of controlled porous water ice-dust mixtures to support the radar exploration of icy bodies |
my journey in science began with the study of volcanic gases, sparking an interest in the origin, and ultimate fate, of the volatile elements in the interior of our planet. how did these elements, so crucial to life and our surface environment, come to be sequestered within the deepest regions of the earth, and what can they tell us about the processes occurring there? my approach has been to establish geochemical links between the noble gases, physical tracers par excellence, with major volatile elements of environmental importance, such as water, carbon and nitrogen, in mantle-derived rocks and gases. from these analyses we have learned that the earth is relatively depleted in volatile elements when compared to its potential cosmochemical ancestors (e.g., ~2 ppm nitrogen compared to several hundreds of ppm in primitive meteorites) and that natural fluxes of carbon are two orders of magnitude lower than those emitted by current anthropogenic activity. further insights into the origin of terrestrial volatiles have come from space missions that documented the composition of the proto-solar nebula and the outer solar system. the consensus behind the origin of the atmosphere and the oceans is evolving constantly, although recently a general picture has started to emerge. at the dawn of the solar system, the volatile-forming elements (h, c, n, noble gases) that form the majority of our atmosphere and oceans were trapped in solid dusty phases (mostly in ice beyond the snowline and organics everywhere). these phases condensed from the proto-solar nebula gas, and/or were inherited from the interstellar medium. these accreted together within the next few million years to form the first planetesimals, some of which underwent differentiation very early on. the isotopic signatures of volatiles were also fixed very early and may even have preceded the first episodes of condensation and accretion. throughout the accretion of the earth, volatile elements were delivered by material from both the inner (dry, volatile-poor) and outer (volatile-rich) solar system. this delivery was concomitant with the metals and silicates that form the bulk of the planet. the contribution of bodies that formed in the far outer solar system, a region now populated by comets, is likely to have been very limited. in that sense, volatile elements were contributed continuously throughout earth's accretion from inner solar system reservoirs, which also provided the silicates and metal building blocks of the inner planets. following accretion, it likely took a few hundred million years for the earth's atmosphere and oceans to stabilise. luckily, we have been able to access a compositional record of the early atmosphere and oceans through the analysis of palaeo-atmospheric fluids trapped in archean hydrothermal quartz. from these analyses, it appears that the surface reservoirs of the earth evolved due to interactions between the early sun and the top of the atmosphere, as well as the development of an early biosphere that progressively altered its chemistry. | origins and early evolution of the atmosphere and the oceans |
the 1.5-km-wide, 40-m-deep, crater-like structure in the 10 ma old barda negra basaltic plateau in central argentina was discovered in the early 2000s. based on remote sensing surveys and on its morphological characteristics, similar to those of the barringer crater in arizona, the structure is described to be originated by an impact. in this study we ran several field work campaigns and collected and analysed samples, in order to find more evidences to endorse or reject this hypothesis. we observe a circular depression not generally surrounded by raised rims, in contrast to craters produced either by a meteorite impact or phreatomagmatic eruption (maars). mineralogical investigations of rocks and sediments do not show high pressure and temperature minerals, such as coesite or stishovite, or any remnants of an impactite or impact melt/glass. likewise, no textural evidences for impact-related fracturing or stress are observed. a detailed geomorphological mapping indicates a successive crater development which invokes local stepwise subsidence. magnetic mapping performed with the eu-funded newton multisensor novel instrument shows a ~2000 nt field anomaly associated to the edges of the crater, and susceptibility measurements cast an important contrast between the basaltic rims and plateau, and the crater interior. therefore, we propose a sinkhole origin for the crater, with a former collapse of the plateau basalts and a latter infill with sedimentary material. this hypothesis is supported by the fact that the 40 to 85 m thick and 14 to 15 ma old carbonate-bearing collón curá formation, underneath the 100 to 150 m thick basaltic plateau lava sheet, represents ideal rocks for dissolution and karst formation; remote sensing data show other nearby sinkholes (20 km westward), with extensions of 3 × 6 km and 100 m depth, which are emplaced within a cogenetic neighboring basaltic plateau with a similar underlying lithology; and the consistence of the magnetic model computed with this scheme and on measured rock remanence and susceptibilities of the structure and surroundings. these giant collapse sinkholes, up to 6 km in diameter, within caprocks of very thick plateau basalts, represent unique examples for planetary surface shaping processes which also occur on mars and comets in areas with basalts or rigid caprocks. | the formation of a giant collapse caprock sinkhole on the barda negra plateau basalts (argentina): magnetic, mineralogical and morphostructural evidences |
evolution of the surfaces of cometary nuclei is determined by the sublimation of ice. the rate of sublimation is commonly calculated using the simple hertz-knudsen formula, which should be corrected by a temperature dependent sublimation coefficient αs (kossacki et al., 1999; gundlach et al., 2011; kossacki and leliwa-kopystynski, 2014). in this work influence of c3h6o (acetone), and ch3oh (methanol) present in cometary ice on the sublimation coefficient is investigated. we have found, that the mass fraction of admixtures ≤ 2% in water ice is sufficient for an increase of αs by a factor about 5, depending on the temperature. the sublimation coefficient is sensitive to very small concentrations of admixtures. when the admixture is acetone and the mass fraction f = 0.005 is αs(215 k) ∼ 0.46 instead of ∼ 0.18 for pure water ice. when f = 0.01 is αs(215 k) ∼ 0.74, and when f = 0.02 is αs(215 k) ∼ 0.78. the presence of 0.01 mass fraction of methanol has similar influence on the sublimation coefficient as the presence of 0.01 mass fraction of acetone. at temperatures t > 235 k for all investigated compositions of ice αs ∼ 0.15. | sublimation of cometary ices in the presence of organic volatiles |
we report the beginning of activity for comet c/2015 er61 (panstarrs), the first instance of watching a long-period comet turn on. pre-discovery observations and observations from the neowise space telescope suggest that the nucleus is large, with a radius of rn∼ 9 km, assuming an albedo of 0.025. our photometric data follows the comet from r = 8.9 to 4.8 au as it moved into solar conjunction in 2016 july. our sublimation model shows that activity began near r = 8.8 au (true anomaly, ta = -139°) in early 2015, driven by co2 sublimation, which peaked in 2016 april at r = 5.1 au (ta = -127°). appreciable water sublimation began around r = 5.0 au. our sublimation model is consistent with an active water sublimation area of 1% of the surface (equivalent to 10.2 km2), and an active surface area for co2 sublimation of 0.029% (0.3 km2). the co2 production rate at r = 4.66 au as measured by neowise is (8.4 ± 2) × 1025 s-1. if co2-ice had been present on the surface, dust dragged from the surface by sublimation would have been observed much farther out—as far as 20 au. our thermal models suggest that the co2 ice was present at a depth of 0.4 m. the comet came out of solar conjunction in 2016 december and, unless it brightens significantly, is unlikely to have water production rates much higher than a few ×1028 s-1. | beginning of activity in long-period comet c/2015 er61 (panstarrs) |
Subsets and Splits
No community queries yet
The top public SQL queries from the community will appear here once available.