abstract stringlengths 3 192k | title stringlengths 4 857 |
|---|---|
consert, a bistatic radar onboard the rosetta spacecraft and its philae lander, was designed to probe the nucleus of comet 67p/churyumov-gerasimenko with radio waves at 90 mhz frequency. in 2016 september, the exact position of philae was retrieved, within the region previously identified by consert. this allowed us to revisit the measurements and improve our analysis of the properties of the interior, the results of which we present here. the relative permittivity of the materials is found to range from about 1.7 to 1.95 in the shallow subsurface (<25 m) and about 1.2 to 1.32 in the interior. these differences indicate different average densities between the shallow subsurface and the interior of comet. they can be explained by various physical phenomena such as different porosities, the possible compaction of surface materials, or even perhaps different proportions of the same materials. this strongly suggests that the less dense interior has kept its pristine nature. | the interior of comet 67p/c-g; revisiting consert results with the exact position of the philae lander |
on neptune, carbon monoxide and phosphine are disequilibrium species, and their abundance profiles can provide insights into interior processes and the external space environment. here we use herschel/spire (spectral and photometric imaging receiver) observations from 14.9-51.5 cm-1 to obtain abundances from multiple co and ph3 spectral features. for co, we find that nine co bands can be simultaneously fitted using a step profile with a 0.22 ppm tropospheric abundance, a 1.03 ppm stratospheric abundance, and a step transition pressure of 0.11 bar near the tropopause. this is in broad agreement with previous studies. however, we also find that the co spectral features could be fitted, to well within measurement errors, with a profile that contains no tropospheric co for pressure levels deeper than 0.5 bar, which is our preferred interpretation. this differs from previous studies that have assumed co is well mixed throughout the troposphere, which would require an internal co source to explain and a high o/h enrichment. our interpretation removes the requirement for extreme interior o/h enrichment in thermochemical models and can finally reconcile d/h and co measurements. if true, the lack of lower tropospheric co would imply a decrease in neptune's interior water content, favouring a silicate-rich instead of an ice-rich interior. this would be consistent with a protoplanetary ice source with a similar d/h ratio to the current solar system comet population. the upper tropospheric and stratospheric co at pressures less than 0.5 bar could then be entirely externally sourced from a giant impact as suggested by lellouch et al.(2005). we also derive a 3-σ upper limit for ph3 of 1.1 ppb at 0.4-0.8 bar. this is the most stringent upper limit to-date and is entirely consistent with predictions from a simple photochemical model. | neptune's carbon monoxide profile and phosphine upper limits from herschel/spire: implications for interior structure and formation |
context. the rosetta orbiter spectrometer for ion and neutral analysis (rosina) was designed to measure the composition of the gas in the coma of comet 67p/churyumov-gerasimenko, the target of the european space agency's rosetta mission. in addition to the volatiles, rosina measured refractories sputtered off the comet by the interaction of solar wind protons with the surface of the comet.aims: the origin of different solar system materials is still heavily debated. isotopic ratios can be used to distinguish between different reservoirs and investigate processes occurring during the formation of the solar system.methods: rosina consisted of two mass spectrometers and a pressure sensor. in the rosina double focusing mass spectrometer (dfms), the neutral gas of cometary origin was ionized and then deflected in an electric and a magnetic field that separated the ions based on their mass-to-charge ratio. the dfms had a high mass resolution, dynamic range, and sensitivity that allowed detection of rare species and the known major volatiles.results: we measured the relative abundance of all three stable silicon isotopes with the rosina instrument on board the rosetta spacecraft. furthermore, we measured 13c/12c in c2h4, c2h5, and co. the dfms in situ measurements indicate that the average silicon isotopic composition shows depletion in the heavy isotopes 29si and 30si with respect to 28si and solar abundances, while 13c to 12c is analytically indistinguishable from bulk planetary and meteorite compositions. although the origin of the deficiency of the heavy silicon isotopes cannot be explained unambiguously, we discuss mechanisms that could have contributed to the measured depletion of the isotopes 29si and 30si. | evidence for depletion of heavy silicon isotopes at comet 67p/churyumov-gerasimenko |
context. evaporating rocky exoplanets, such as kic 12557548b, eject large amounts of dust, which can trail the planet in a comet-like tail. when such objects occult their host star, the resulting transit signal contains information about the dust in the tail.aims: we aim to use the detailed shape of the kepler light curve of kic 12557548b to constrain the size and composition of the dust grains that make up the tail, as well as the mass loss rate of the planet.methods: using a self-consistent numerical model of the dust dynamics and sublimation, we calculated the shape of the tail by following dust grains from their ejection from the planet to their destruction due to sublimation. from this dust cloud shape, we generated synthetic light curves (incorporating the effects of extinction and angle-dependent scattering), which were then compared with the phase-folded kepler light curve. we explored the free-parameter space thoroughly using a markov chain monte carlo method.results: our physics-based model is capable of reproducing the observed light curve in detail. good fits are found for initial grain sizes between 0.2 and 5.6 μm and dust mass loss rates of 0.6 to 15.6 m⊕ gyr-1 (2σ ranges). we find that only certain combinations of material parameters yield the correct tail length. these constraints are consistent with dust made of corundum (al2o3), but do not agree with a range of carbonaceous, silicate, or iron compositions.conclusions: using a detailed, physically motivated model, it is possible to constrain the composition of the dust in the tails of evaporating rocky exoplanets. this provides a unique opportunity to probe to interior composition of the smallest known exoplanets. | dusty tails of evaporating exoplanets. ii. physical modelling of the kic 12557548b light curve |
water has two nuclear-spin isomers: ortho- and para-h2o. some observations of interstellar space and cometary comae have reported the existence of gaseous h2o molecules with anomalous ortho-to-para ratios (oprs) less than the statistical value of three. this has been often used to estimate the formation temperature of ice on dust, which is inferred to be below 50 k. the relation between the nuclear-spin dynamics of h2o in ice at low temperatures and the opr of gaseous h2o desorbed from the ice has yet to be explored in a laboratory. consequently, the true meaning of the observed oprs remains debated. we measure the opr of h2o photodesorbed from ice made from para-h2o monomers at 11 k, which was prepared by the sublimation of ne from a para-h2o/ne matrix. the photodesorbed h2o molecules from the ice have the statistical opr value of three, demonstrating the immediate nuclear-spin-state mixing of h2o toward the statistical value of ice even at 11 k. the opr of h2o thermally desorbed from the ice also shows the expected statistical value. our results indicate that the opr of h2o desorbed from interstellar ice should be the statistical value regardless of the formation process of the ice, which cannot be used to deduce the ice-formation temperature. this study highlights the importance of interstellar gas-phase processes in understanding anomalous abundance ratios of nuclear-spin isomers of molecules in space. | the ortho-to-para ratio of water molecules desorbed from ice made from para-water monomers at 11 k |
aims: we develop a physical model to explain the potent outbursts that occurred in the fractured terrain of comet 67p near perihelion, and predict its temporal characteristics.methods: the feasibility of the proposed mechanism is studied using a numerical model accounting for the relevant microscopic/macroscopic processes. we rely on the thermophysical, compositional, and geo-morphological data from the published measurements of respective instruments on board rosetta.results: the key idea of this novel mechanism is built around observations of fractures/cracks in the region of interest. it is argued that as the stresses on the nucleus increased during the perihelion approach, a crack deepening event occurred reaching the deeper material containing super-volatile ices in equilibrium with the surrounding. this sudden opening lead to a violent sublimation of the super-volatile ices. the time scales and mass release of this process are modeled and reported. in our modeling we pay attention to the question of the existence of super-volatile ices in the deeper interior for a long time, and the thermal equilibrium in the interior.conclusions: the deepening of pre-existing cracks (fracture) into the material containing highly volatile ices can explain the observed outburst features. the sudden disequilibration of the steady-state reservoir of highly volatile ices results in a violent release of gas and dust. the proposed mechanism also explains the rapid shut down of this activity in accordance with the observations. the proposed mechanism is independent of solar illumination history of a given region, or the pre-existance of large sealed nucleus cavities. | a model of short-lived outbursts on the 67p from fractured terrains |
as a new class of comet, main belt comets (mbcs) have attracted more and more attention in recent years. to study activity and physical properties of three mbcs 176p/linear, 238p/read and 288p/(300163) 2006 vw139, we carried out broadband ccd photometry of three mbcs on ut 2016 november 18-19 with the 1-m optical telescope at lulin observatory in taiwan. by comparing cometary surface brightness profiles to stellar surface brightness profiles, and by comparing cometary absolute magnitude to the expected magnitude of inactive nucleus, we found that 176p/linear was inactive, while 238p/read and 288p/(300163) 2006 vw139 were active. by photometric studies, we obtained the afρ values and the dust production rates. finally, the activity of three mbcs were discussed. our photometric results show that the total dust mass of 238p/read and 288p/(300163) 2006 vw139 obtained in this work are of the same magnitude as the majority of known mbcs. | research of activity of main belt comets 176p/linear, 238p/read and 288p/(300163) 2006 vw139 |
context. the solar radiation in the lyman-α spectral line of hydrogen plays a significant role in the illumination of chromospheric and coronal structures, such as prominences, spicules, chromospheric fibrils, cores of coronal mass ejections, and solar wind. moreover, it is important for the investigation of the heliosphere, earth's ionosphere, and the atmospheres of planets, moons, and comets.aims: we derive a reference quiet-sun lyman-α spectral profile that is representative of the lyman-α radiation from the solar disk during a minimum of solar activity. this profile can serve as an incident radiation boundary condition for the radiative transfer modelling of chromospheric and coronal structures. because the solar radiation in the lyman lines is not constant over time but varies significantly with the solar cycle, we provide a method for the adaptation of the incident radiation lyman line profiles (lyman-α and higher lines) to a specific date. moreover, we analyse how the change in the incident radiation influences the synthetic spectra produced by the radiative transfer modelling.methods: we used soho/sumer lyman-α raster scans obtained without the use of the attenuator in various quiet-sun regions on the solar disk. the observations were performed on three consecutive days (june 24, 25, and 26, 2008) during a period of minimum solar activity. the reference lyman-α profile was obtained as a spatial average over eight available raster scans. to take into account the lyman-α variation with the solar cycle, we used the lisird composite lyman-α index. to estimate the influence of the change in the incident radiation in the lyman lines on the results of radiative transfer models, we used a 2d prominence fine structure model.results: we present the reference quiet-sun lyman-α profile and a table of coefficients describing the variation of the lyman lines with the solar cycle throughout the lifetime of soho. the analysis of the influence of the change in the incident radiation shows that the synthetic spectra are strongly affected by the modification of the incident radiation boundary condition. the most pronounced impact is on the central and integrated intensities of the lyman lines. there, the change in the synthetic spectra can often have the same amplitude as the change in the incident radiation itself. the impact on the specific intensities in the peaks of reversed lyman-line profiles is smaller but still significant. the hydrogen hα line can also be considerably affected, despite the fact that the hα radiation from the solar disk does not vary with the solar cycle. data are only available at the cds via anonymous ftp to http://cdsarc.u-strasbg.fr (ftp://130.79.128.5) or via http://cdsarc.u-strasbg.fr/viz-bin/cat/j/a+a/644/a109 | quiet-sun hydrogen lyman-α line profile derived from soho/sumer solar-disk observations |
debris disks are extrasolar analogs to our own kuiper belt and they are detected around at least 17% of nearby sun-like stars. the morphology and dynamics of a disk encode information about its history, as well as that of any exoplanets within the system. we used the atacama large millimeter/submillimeter array (alma) to obtain 1.3 mm observations of the debris disk around the nearby f5v star hd 170773. we image the face-on ring and determine its fundamental parameters by forward-modeling the interferometric visibilities through a markov chain monte carlo approach. using a symmetric gaussian surface density profile, we find a 71 ± 4 au wide belt with a radius of {193}-3+2 au, a relatively large radius compared with most other millimeter-resolved belts around late a/early f type stars. this makes hd 170773 part of a group of four disks around a and f stars with radii larger than expected from the recently reported planetesimal belt radius—stellar luminosity relation. two of these systems are known to host directly imaged giant planets, which may point to a connection between large belts and the presence of long-period giant planets. we also set upper limits on the presence of co and cn gas in the system, which imply that the exocomets that constitute this belt have co and hcn ice mass fractions of <77% and <3%, respectively. this is consistent with solar system comets and other exocometary belts. | the reasons survey: resolved millimeter observations of a large debris disk around the nearby f star hd 170773 |
aims: we present the most extensive catalog of exposures of volatiles on the 67p/churyumov-gerasimenko nucleus generated from observations acquired with the optical, spectroscopic, and infrared remote imaging system (osiris) on board the rosetta mission. we investigate the volatile exposure distribution across the nucleus, their size distribution, and their spectral slope evolution.methods: we analyzed medium- and high-resolution images acquired with the narrow angle camera (nac) of osiris at several wavelengths in the 250-1000 nm range, investigating images from 109 different color sequences taken between august 2014 and september 2016, and covering spatial resolution from a few m px−1 to 0.1 m px−1. to identify the icy bright spots, we adopted the following criteria: (i) they should be at least 50% brighter than the comet dark terrain; (ii) they should have neutral to moderate spectral slope values in the visible range (535-882 nm); (iii) they should be larger than 3 pixels.results: we identified more than 600 volatile exposures on the comet, and we analyzed them in a homogeneous way. bright spots are found isolated on the nucleus or grouped in clusters, usually at the bottom of cliffs, and most of them are small, typically a few square meters or smaller. the isolated ones are observed in different types of morphological terrains, including smooth surfaces, on top of boulders, or close to irregular structures. several of them are clearly correlated with the cometary activity, being the sources of jets or appearing after an activity event. we note a number of peculiar exposures of volatiles with negative spectral slope values in the high-resolution post-perihelion images, which we interpret as the presence of large ice grains (> 1000 µm) or local frosts condensation. we observe a clear difference both in the spectral slope and in the area distributions of the bright spots pre- and post-perihelion, with these last having lower average spectral slope values and a smaller size, with a median surface of 0.7 m2, even if the size difference is mainly due to the higher resolution achieved post-perihelion. the minimum duration of the bright spots shows three clusters: an area-independent cluster dominated by short-lifetime frosts; an area-independent cluster with lifetime of 0.5-2 days, probably associated with the seasonal fallout of dehydrated chunks; and an area-dependent cluster with lifetime longer than 2 days consistent with water-driven erosion of the nucleus.conclusions: even if numerous bright spots are detected, the total surface of exposed water ice is less than 50 000 m2, which is 0.1% of the total 67p nucleus surface. this confirms that the surface of comet 67p is dominated by refractory dark terrains, while exposed ice occupies only a tiny fraction. high spatial resolution is mandatory to identify ice on cometary nuclei surfaces. moreover, the abundance of volatile exposures is six times less in the small lobe than in the big lobe, adding additional evidence to the hypothesis that comet 67p is composed of two distinct bodies. the fact that the majority of the bright spots identified have a surface lower than 1 m2 supports a model in which water ice enriched blocks (webs) of 0.5-1 m size should be homogeneously distributed in the cometary nucleus embedded in a refractory matrix. full table a.1 is only available at the cds via anonymous ftp to cdsarc.cds.unistra.fr (ftp://130.79.128.5) or via https://cdsarc.cds.unistra.fr/viz-bin/cat/j/a+a/672/a136 | volatile exposures on the 67p/churyumov-gerasimenko nucleus |
we report observations of nine main-belt comets (mbcs) or candidate mbcs, most of which were obtained when the targets were apparently inactive. we find effective nucleus radii (assuming albedos of pv= 0.05 ± 0.02) of rn= (0.24 ± 0.05) km for 238p/read, rn= (0.9 ± 0.2) km for 313p/gibbs, rn= (0.6 ± 0.1) km for 324p/la sagra, rn= (1.0 ± 0.2) km for 426p/panstarrs, rn= (0.5 ± 0.1) km for 427p/atlas, rn< (0.3 ± 0.1) km for p/2016 j1-a (panstarrs), rn< (0.17 ± 0.04) km for p/2016 j1-b (panstarrs), rn≤ (0.5 ± 0.2) km for p/2017 s9 (panstarrs), recently redesignated 455p/panstarrs, and rn= (0.4 ± 0.1) km for p/2019 a3 (panstarrs). we identify evidence of activity in observations of 238p in 2021, and find similar inferred activity onset times and net initial mass-loss rates for 238p during perihelion approaches in 2010, 2016, and 2021. p/2016 j1-a and p/2016 j1-b are also found to be active in 2021 and 2022, making them collectively the tenth mbc confirmed to be recurrently active near perihelion and therefore likely to be exhibiting sublimation-driven activity. the nucleus of 313p is found to have colors of $g^{\prime} -r^{\prime} =0.52\pm 0.05$ and $r^{\prime} -i^{\prime} =0.22\pm 0.07$ , consistent with 313p being a lixiaohua family member. we also report nondetections of p/2015 x6 (panstarrs), where we conclude that its current nucleus size is likely below our detection limits (rn≲ 0.3 km). lastly, we find that of 17 mbcs or candidate mbcs for which nucleus sizes (or inferred parent body sizes) have been estimated, >80% have rn≤ 1.0 km, pointing to an apparent physical preference toward small mbcs, where we suggest that yarkovsky-o'keefe-radzievskii-paddack spin-up may play a significant role in triggering and/or facilitating mbc activity. | observational characterization of main-belt comet and candidate main-belt comet nuclei |
we report the first survey of molecular emission from cometary volatiles using standalone atacama compact array (aca) observations from the atacama large millimeter/submillimeter array (alma) toward comet c/2015 er61 (panstarrs) carried out on ut 2017 april 11 and 15, shortly after its april 4 outburst. these measurements of hcn, cs, ch3oh, h2co, and hnc (along with continuum emission from dust) probed the inner coma of c/2015 er61, revealing asymmetric outgassing and discerning parent from daughter/distributed source species. this work presents spectrally integrated flux maps, autocorrelation spectra, production rates, and parent scale lengths for each molecule and a stringent upper limit for co. hcn is consistent with direct nucleus release in c/2015 er61, whereas cs, h2co, hnc, and potentially ch3oh are associated with distributed sources in the coma. adopting a haser model, parent scale lengths determined for h2co (lp ~ 2200 km) and hnc (lp ~ 3300 km) are consistent with previous work in comets, whereas significant extended source production (lp ~ 2000 km) is indicated for cs, suggesting production from an unknown parent in the coma. the continuum presents a point-source distribution with a flux density implying an excessively large nucleus, inconsistent with other estimates of the nucleus size. it is best explained by the thermal emission of slowly moving outburst ejectas, with total mass 5-8 × 1010 kg. these results demonstrate the power of the aca for revealing the abundances, spatial distributions, and locations of molecular production for volatiles in moderately bright comets such as c/2015 er61. | leveraging the alma atacama compact array for cometary science: an interferometric survey of comet c/2015 er61 (panstarrs) and evidence for a distributed source of carbon monosulfide |
we present x-ray and radio observations of the recently discovered bow-shock pulsar wind nebula (pwn) associated with psr j0002+6216, characterizing the pwn morphology, which was unresolved in previous studies. the multifrequency, multiepoch very large array (vla) radio observations reveal a cometary tail trailing the pulsar and extending up to 5.'3, with multiple kinks along the emission. the presented radio continuum images from multiconfiguration broadband vla observations are one of the first results from the application of multiterm multifrequency synthesis deconvolution in combination with the awproject gridder implemented in the common astronomy software applications (casa) package. the x-ray emission observed with chandra extends to only 21″, fades quickly, and has some hot spots present along the extended radio emission. these kinks could indicate the presence of density variations in the local interstellar medium or turbulence. the bow-shock standoff distance estimates a small bow-shock region with a size of 0.003-0.009 pc, consistent with the pulsar spin-down power of $\dot{e}$ = 1.51 × 1035 erg s-1 estimated from timing. the high-resolution radio image reveals the presence of an asymmetry in the bow-shock region, which is also present in the x-ray image. the broadband radio image shows an unusually steep spectrum along with a flat-spectrum sheath, which could indicate varying opacity or energy injection into the region. spatially resolved x-ray spectra provide marginal evidence of synchrotron cooling along the extended tail. our analysis of the x-ray data also shows that this pulsar has a low spin-down power and one of the lowest x-ray efficiencies observed in these objects. | resolving the bow shock and tail of the cannonball pulsar psr j0002+6216 |
the τ-herculids (iau shower number 61 tah) is a minor meteor shower associated with comet 73p/schwassmann-wachmann 3, a jupiter-family comet that disintegrated into several fragments in 1995. as a consequence of the nucleus breakup, possible increased meteor rates were predicted for 2022. on may 30-31, observation networks around the world reported two distinct peaks of tah activity, around solar longitudes 69.°02 and 69.°42. this work examines the encounter conditions of the earth with meteoroids ejected from 73p during the splitting event and on previous perihelion passages. numerical simulations suggest that the main peak observed in 2022 was caused by meteoroids ejected from the splitting nucleus with four times the typical cometary gas expansion speed. high-resolution measurements performed with the canadian automated meteor observatory indicate that these meteoroids are fragile, with estimated bulk densities of 250 kg m-3. in contrast with the main peak, the first tah activity peak in 2022 is best modeled with trails ejected prior to 1960. we find that ordinary cometary activity could have produced other tah apparitions observed in the past, including in 1930 and 2017. the extension of our model to future years predicts significant returns of the shower in 2033 and 2049. | modeling the 2022 τ-herculid outburst |
numerous studies of cometary dust have shown that it has a fairly complex hierarchical structure. at the same time, space missions have provided evidence of solid particles. computer modeling of light scattering, for which agglomerate debris particles were used, showed that the characteristics of the scattered light strongly depend on the presence of solid particles. we propose a model that makes it possible to fractalize the agglomerate debris particles. a particle constructed in accordance with the proposed model combines large and small fragments. depending on the model parameters, you can make the particle fluffier or more compact. a comparison of the degree of linear polarization between quasi-fractal porous particles and solid particles, as well as between quasi-fractal porous particles and maxwell garnett particles is carried out. it has been established that there is the difference between really porous particles and particles, for which the porosity is taken into account by the maxwell garrett theory. we recommend using the maxwell garnett theory only for studying uniformly distributed inclusions, and for quasi-fractal structures it is better to use the exact calculations. | polarization properties of quasi-fractal porous particles |
surface processes and radical chemistry within interstellar ices are increasingly suspected to play an important role in the formation of complex organic molecules (coms) observed in several astrophysical regions and cometary environments. we present new laboratory experiments on the low-temperature solid state formation of complex organic molecules - glycolaldehyde, ethylene glycol, and polyoxymethylene - through radical-induced reactivity from vuv photolysis of formaldehyde in water-free and water-dominated ices. radical reactivity and endogenous formation of coms were monitored in situ via infrared spectroscopy in the solid state and post photolysis with temperature programmed desorption (tpd) using a quadripole mass spectrometer. we show the ability of free radicals to be stored when formed at low temperature in water-dominated ices, and to react with other radicals or on double bonds of unsaturated molecules when the temperature increases. it experimentally confirms the role of thermal diffusion in radical reactivity. we propose a new pathway for formaldehyde polymerisation induced by hco radicals that might explain some observations made by the ptolemy instrument on board the rosetta lander philae. in addition, our results seem to indicate that h-atom additions on h2co proceed preferentially through ch2oh intermediate radicals rather than the ch3o radical. | radical-induced chemistry from vuv photolysis of interstellar ice analogues containing formaldehyde |
high-resolution osiris/rosetta images of 67p/churyumov-gerasimenko acquired on the night run of 2016 april 9-10 show, at large scale, an opposition effect (oe) spot sweeping across imhotep as the phase angle ranges from 0° to 17°. in this work, we fitted the phase curve of the whole surface imaged as well as three particular features using both the linear-exponential and hapke models. these features encompass different types of spectral behaviour: a circular mesa, one venous structure and an assemblage of bright spots, going from red to blue colours. both the hapke and linear-exponential parameters indicate a stepwise sharpening of the oe from bright spots to circular mesa. yet a very broad nonlinear phase curve is verified and no sign of sharp oe associated with a coherent-backscattering mechanism is observed. we estimate that the 67p surface is dominated by opaque, desiccated and larger-than-wavelength irregular grains. veins and bright spots display photometric properties consistent with surfaces becoming slightly brighter as they are enriched by high-albedo ice grains. we also report the estimation of normal albedo for all cometary regions observed throughout the image sequence. comparison to pre-perihelion results indicates that far better insolation of northern brighter regions, i.e. hapi, hathor and seth, is sufficient to explain mismatches on the photometric parameters. however, metre-scale photometric analysis of the imhotep-ash boundary area advocates for mild darkening (<7 per cent) of the surface at local scale. | the opposition effect of 67p/churyumov-gerasimenko on post-perihelion rosetta images |
the geminid meteor shower was observed in 2015 using the western meteor physics group's canadian meteor orbit radar (cmor), marshall space flight center's (msfc) eight wide-field optical cameras, and telescopes of msfc's lunar impact monitoring program. these observations allowed geminid fluxes to be calculated in three unique mass-ranges, from 1.8×10-4 g to 30 g. from these fluxes, a mass index of 1.68±0.04 was measured. the quantities derived here, along with a profile of the geminid meteor shower activity in 2015 from cmor, were used to find a total geminid mass of 3.5×107 g the earth encountered in 2015, along with a minimum total mass for the geminid meteoroid stream of 1.6×1016 g. attempts have been made in the past to measure the mass of meteoroid streams using zhr profiles, but this new and improved treatment uses empirically derived fluxes and measured mass indices for the 2015 encounter with the meteoroid stream. these results are compared to meteoroid stream mass estimate measured for the perseids of 3.3×1017 g. instead of three flux values, a single flux value and an assumed mass index of 1.78 was used in perseid analysis. | the mass index and mass of the geminid meteoroid stream as determined with radar, optical and lunar impact data |
context. ic 63 and ic 59 are a pair of cometary-shaped nebulae in the vicinity of the star γcas (also known as tsih, "the whip"). both nebulae have very different optical appearances, despite the fact that both objects lie at similar projected distances from the star: ic 63 shows bright rims and filaments, while ic 59 looks more homogeneous and faint.aims: we aim to perform a general description of the two nebulae from an observational standpoint in order to study the physical conditions at the uv-illuminated surfaces of these objects.methods: we used the available data on both nebulae taken with spitzer and herschel to study the infrared emission at the tip of both clouds, and derive the intensity of the uv radiation field. using the photodetector array camera and spectrometer (pacs) in line spectroscopy mode, we obtained the intensity of the cooling lines [c ii] 157 μm and [o i] 63 μm, and we used these to estimate the density in these regions. excitation diagrams of molecular hydrogen were obtained to derive the gas temperature. we also used [c ii] 157 μm velocity maps of ic 59 taken with german receiver for astronomy at terahertz frequencies (great) on board sofia to explore the gas dynamics in this nebula.results: we find that the ir emission from polycyclic aromatic hydrocarbons (pahs) is very similar at the tip of both nebulae. even though it varies in intensity between the two, the derived pah band ratios are remarkably similar. these ratios are similar to those found in the more shielded regions of other nebulae such as ngc 7023 and ngc 2023. regarding the physical conditions, we get that while in ic 63 the intensity of the uv field, g0, is a factor of approximately ten higher than in ic 59, the density n at the tip of ic 59 is lower than in ic 63 by a similar factor. for both objects we derive g0 values significantly lower than what previous works have so far assumed. comparison with other reflection nebulae photo-dissociation regions (pdrs) and known correlations support our claim that both ic 63 and ic 59 are low-uv irradiated environments.conclusions: we conclude that the tips of ic 63 and ic 59 are about three and five times farther away from the star than their respective projected distances. the similarity of the mid-infrared emission between the two nebulae is consistent not only with both objects being overdensities within the same region around γcas, but it is also consistent with the similar g0/n and ionization parameters, which altogether rule the evolution of the hydrogenation and ionization level of the emitting population of pahs. finally, regarding the kinematics of the material in ic 59, we find evidence of photo-evaporation due to the incident radiation from γcas. | whipping ic 63/ic 59 |
amorphous silicates containing abundant nano-inclusions have been reported in the paris cm chondrite (leroux et al., 2015). they have chemical and morphological similarities to glass with embedded metal and sulfides (gems) found in interplanetary dust particles (idps) and micrometeorites believed to originate from comets. we used scanning transmission electron microscopy (stem) with energy-dispersive x-ray spectroscopy (eds) and nanodiffraction to study the chemistry and mineralogy of these inclusions in order to understand the origin of the gems-like material in paris and its possible relationships to other materials found in primitive chondritic materials including idp gems. eds and diffraction analyses indicate compositional and mineralogical differences between the nanophase inclusions in cometary gems and paris gems-like material. metal inclusions are notably absent within paris amorphous silicate. ni-rich sulfides, including pentlandite, are common in even the least altered matrix material of paris, while they are absent in gems-bearing idps and ultracarbonaceous antarctic micrometeorites (ucamms). from examination of the inclusions, we cannot yet confirm or refute the possibility that gems-like material in paris is related to cometary gems. the distinct compositions and mineralogy of the paris material may be due to aqueous alteration of cometary gems precursors, but they may also denote an independent origin for meteoritic gems-like assemblages. | search for meteoritic gems ii: comparison of inclusions in amorphous silicates from the paris chondrite and from anhydrous chondritic interplanetary dust particles |
during 2015 january 9-11, at a heliocentric distance of ∼2.58-2.57 au, the esa rosetta spacecraft resided at a cometocentric distance of ∼28 km from the nucleus of comet 67p/churyumov-gerasimenko, sweeping the terminator at northern latitudes of 43°n-58°n. measurements by the rosetta orbiter spectrometer for ion and neutral analysis/comet pressure sensor (rosina/cops) provided neutral number densities. we have computed modeled electron number densities using the neutral number densities as input into a field free chemistry free model, assuming h2o dominance and ion-electron pair formation by photoionization only. a good agreement (typically within 25%) is found between the modeled electron number densities and those observed from measurements by the mutual impedance probe (rpc/mip) and the langmuir probe (rpc/lap), both being subsystems of the rosetta plasma consortium. this indicates that ions along the nucleus-spacecraft line were strongly coupled to the neutrals, moving radially outward with about the same speed. such a statement, we propose, can be further tested by observations of h3o+/h2o+ number density ratios and associated comparisons with model results. | model-observation comparisons of electron number densities in the coma of 67p/churyumov-gerasimenko during january 2015 |
context. on 20 january 2015 the rosetta spacecraft was at a heliocentric distance of 2.5 au, accompanying comet 67p/churyumov-gerasimenko on its journey toward the sun. the ion composition analyser (rpc-ica), other instruments of the rosetta plasma consortium, and the rosina instrument made observations relevant to the generation of plasma waves in the cometary environment.aims: observations of plasma waves by the rosetta plasma consortium langmuir probe (rpc-lap) can be explained by dispersion relations calculated based on measurements of ions by the rosetta plasma consortium ion composition analyser (rpc-ica), and this gives insight into the relationship between plasma phenomena and the neutral coma, which is observed by the comet pressure sensor of the rosetta orbiter spectrometer for ion and neutral analysis instrument (rosina-cops).methods: we use the simple pole expansion technique to compute dispersion relations for waves on ion timescales based on the observed ion distribution functions. these dispersion relations are then compared to the waves that are observed. data from the instruments rpc-lap, rpc-ica and the mutual impedance probe (rpc-mip) are compared to find the best estimate of the plasma density.results: we find that ion acoustic waves are present in the plasma at comet 67p/churyumov-gerasimenko, where the major ion species is h2o+. the bulk of the ion distribution is cold, kbti = 0.01 ev when the ion acoustic waves are observed. at times when the neutral density is high, ions are heated through acceleration by the solar wind electric field and scattered in collisions with the neutrals. this process heats the ions to about 1 ev, which leads to significant damping of the ion acoustic waves.conclusions: in conclusion, we show that ion acoustic waves appear in the h2o+ plasmas at comet 67p/churyumov-gerasimenko and how the interaction between the neutral and ion populations affects the wave properties. computer code for the dispersion analysis is only available at the cds via anonymous ftp to http://cdsarc.u-strasbg.fr (http://130.79.128.5) or via http://cdsarc.u-strasbg.fr/viz-bin/qcat?j/a+a/600/a3 | ion acoustic waves at comet 67p/churyumov-gerasimenko. observations and computations |
in this work we model the dynamical evolution of meteoroid streams of comet 96p/machholz, and the largest member of the marsden sunskirters, comet p/1999 j6. we simultaneously fit the characteristics of eight meteor showers which have been proposed to be linked to the complex, using observations from a range of techniques - visual, video, tv and radar. the aim is to obtain a self-consistent scenario of past capture of a large comet into a short-period orbit, and its subsequent fragmentation history. moreover, we also aim to constrain the dominant parent of these showers. the fit of our simulated shower characteristics to observations is consistent with the scenario of a capture of a proto-comet 96p/machholz by jupiter circa 20000 bce, and a subsequent major breakup around 100-950 ce which resulted in the formation of the marsden group of comets. we find that the marsden group of comets are not the immediate parents of the daytime arietids and northern and southern δ-aquariids, as previously suggested. in fact, the hypothesis that the northern δ-aquariids are related to the marsden group of comets is not supported by this study. the bulk of the observational characteristics of all eight showers can be explained by meteoroid ejection primarily from comet 96p/machholz between 10000 bce and 20000 bce. assuming the marsden group of comets originated between 100 ce-950 ce, we conclude that sunskirting comets contribute mainly to the meteoroid stream near the time of the peak of the daytime arietids, southern δ-aquariids, κ-velids. finally, we find that the meteor showers identified by babadzhanov and obrubov (1992) as the α-cetids, the ursids and carinids correspond to the daytime λ-taurids, the november ι-draconids or december α-draconids and the θ-carinids. | formation and past evolution of the showers of 96p/machholz complex |
polybrominated diphenyl ethers (pbdes) are ubiquitous and prolific contaminant in both the abiotic and biotic environment because of the wide industrial applications of these chemicals. in the present study, the effects of 2,2′,4,4′‑tetrabrominateddiphenyl ether (bde‑47) and 2,2′,4,4′,5,5′‑hexabromodiphenyl ether (bde‑153) exposure on the induction of hepatic oxidative stress, dna damage, and the expression of apoptosis‑related genes in adult zebrafish were investigated. the activities of antioxidant enzymes, such as catalase and superoxide dimutase, significantly increased when adult zebrafish was exposed to various concentrations of bde‑47 and bde‑153 for 7 and 15 days. bde‑47 and bde‑153 elicited significant alterations in zebrafish 7‑ethoxyresorufin‑o‑deethylase activity at 3, 7, or 15 days of exposure. in addition, the significant increase in comet assay parameters of zebrafish hepatocytes in a concentration‑dependent manner indicated bde‑47 and bde‑153 induced dna damage, probably due to observed oxidative stress. furthermore, a monotonically upregulation of p53 and caspase3, which are apoptotic‑regulated genes, and decreased expression ratio of the anti‑apoptotic b‑cell lymphoma/leukaemia‑2 and bcl2‑associated x protein genes for all bde‑47 and bde‑153 treatments at 7 and 15 days indicated apoptosis induction in zebrafish liver. our findings help elucidate the mechanisms of bde‑47‑ and bde‑153‑induced toxicity in zebrafish hepatocytes. | hepatic oxidative stress, dna damage and apoptosis in adult zebrafish following sub‑chronic exposure to bde‑47 and bde‑153 |
low-energy ions are difficult to measure, mainly due to spacecraft charging. the ions are attracted to or repelled from the charged surface prior to detection, which changes both the energy and travel direction of the ions. this results in distortions of the data, and the changed travel directions distort the effective field of view (fov) of the instrument performing the measurements. the ion composition analyzer (rpc-ica) was measuring positive ions down to an energy of a few ev around comet 67p/churyumov-gerasimenko. low-energy ions play important parts in processes in the cometary environment, but the fov of rpc-ica has been shown to get severely distorted at low ion energies. several factors are believed to affect the distortion level. in this study we use the spacecraft plasma interaction software (spis) to investigate the influence of varying spacecraft potentials and debye lengths on the fov distortion of rpc-ica. we show that the distortion level is dependent on the debye length of the surrounding plasma, but the sensitivity varies substantially between different viewing directions of the instrument. we also show that a small nonlinearity exists in the relation between fov distortion, ion energy, and spacecraft potential, mainly caused by the photoemission and bulk flow of the cometary plasma. | the influence of varying spacecraft potentials and debye lengths on in situ low-energy ion measurements |
we observe comet c/2019 y4 (atlas) before and after its disintegration while making polarimetric measurements over a wide range of phase angles. the disintegration event was marked with a dramatic growth of the positive polarization branch that is consistent with a large relative abundance of absorbing material of up to (96.5 ± 3.4) per cent. this polarization spike relaxed as the carbonaceous particles are preferentially swept from the coma due to solar-radiation pressure. the observations suggest that the primordial material stored within comets is extremely rich in carbonaceous material. the pristine cometary material is processed by subsequent solar interactions, forming a refractory crust on the nucleus surface. polarimetry provides a means of measuring the volume ratio of carbonaceous material, and hence the weathering that has occurred on the comet due to these interactions. the polarimetric response of comet c/2019 y4 (atlas) appears similar to that of comet c/1995 o1 (hale-bopp), except on few epochs that are similar to that of comet c/1996 b2 (hyakutake). | polarization of disintegrating comet c/2019 y4 (atlas) |
rosetta has detected the presence of the hydrogen halides hf, hcl, and hbr in the coma of comet 67p/churyumov-gerasimenko. these species are known to freeze out on icy grains in molecular clouds. analysis of the abundances of hf and hcl as a function of cometocentric distance suggests that these hydrogen halides are released both from the nucleus surface and off dust particles in the inner coma. we present three lines of evidence. first, the abundances of hf and hcl relative to the overall neutral gas in the coma appear to increase with distance, indicating that a net source must be present; since there is no hint at any possible parent species with sufficient abundances that could explain the observed levels of hf or hcl, dust particles are the likely origin. second, the amplitude of the daily modulation of the halide-to-water density due to the rotation and geometry of 67p's nucleus and the corresponding surface illumination is observed to progressively diminish with distance and comet dust activity; this can be understood from the range of dust particle speeds well below the neutral gas expansion speed, which tends to smooth the coma density profiles. third, strong halogen abundance changes detected locally in the coma cannot be easily explained from composition changes at the surface, while they can be understood from differences in local gas production from the dust particles. | evidence for distributed gas sources of hydrogen halides in the coma of comet 67p/churyumov-gerasimenko |
numerous water-ice-rich deposits surviving more than several months on comet 67p/churyumov-gerasimenko were observed during the rosetta mission. we announce the first-time detection of water-ice features surviving up to 2 yr since their first observation via osiris (optical, spectroscopic, and infrared remote imaging system) nac (narrow angle camera). their existence on the nucleus of comet 67p at the arrival of the rosetta spacecraft suggests that they were exposed to the surface during the comet's previous orbit. we investigated the temporal variation of large water-ice patches to understand the long-term sustainability of water ice on cometary nuclei on time-scales of months and years. large clusters are stable over typical periods of 0.5 yr and reduce their size significantly around the comet's perihelion passage, while small exposures disappear. we characterized the temporal variation of their multispectral signatures. in large clusters, dust jets were detected, whereas in large isolated ones no associated activity was detected. our thermal analysis shows that the long-term sustainability of water-ice-rich features can be explained by the scarce energy input available at their locations over the first half year. however, the situation reverses for the period lasting several months around perihelion passage. our two end-member mixing analysis estimates a pure water-ice equivalent thickness up to 15 cm within one isolated patch, and up to 2 m for the one still observable through the end of the mission. our spectral modelling estimates up to 48 per cent water-ice content for one of the large isolated feature, and up to 25 per cent water ice on the large boulders located within clusters. | long-term survival of surface water ice on comet 67p |
with the discovery of 1i 'oumuamua and 2i borisov, interstellar objects (isos) have been thrust into the forefront of planetary science, and the robotic exploration of isos is now of significant interest. with current propulsion technology, rendezvous with these objects is likely infeasible, and thus the maximum science return results from a combination of flyby spacecraft and impactor spacecraft, as demonstrated by the deep impact encounter with comet tempel 1. interstellar objects by nature have hyperbolic orbits and pass through the inner solar system at extreme velocities, which presents several unique challenges to navigation. this paper first establishes the possible encounter space intercepts with isos may present. we then evaluate the ability for intercepting spacecraft to navigate to isos and autonomously track/impact targets across the possible encounter space, depending on key navigation hardware such as camera and attitude determination system. | navigation evaluation for fast interstellar object flybys |
on the 12th of november 2014, the rosetta philae lander descended to make the first soft touchdown on the surface of a comet - comet 67p/churyumov-gerasimenko. that soft touchdown did occur but due to the failure in the firing of its two harpoons, philae bounced and travelled across the comet making contact with the surface twice more before finally landing in a shaded rocky location somewhere on the southern hemisphere of the comet. the search campaign, led by esa, involved multiple teams across europe with a wide range of techniques used in support of it. this search campaign would continue through 2015 where a prime candidate on the surface was identified and on into 2016 to end on the 2nd of september 2016 when a definitive and conclusive image was taken of the lander on the surface of the comet, confirming the prime candidate to indeed be philae. | the search campaign to identify and image the philae lander on the surface of comet 67p/churyumov-gerasimenko |
we consider the discrete directed polymer model with i.i.d. environment and we study the fluctuations of the tail $n^{(d-2)/4}(w_\infty - w_n)$ of the normalized partition function. it was proven by comets and liu, that for sufficiently high temperature, the fluctuations converge in distribution towards the product of the limiting partition function and an independent gaussian random variable. we extend the result to the whole $l^2$-region, which is predicted to be the maximal high-temperature region where the gaussian fluctuations should occur under the considered scaling. to do so, we manage to avoid the heavy 4th-moment computation and instead rely on the local limit theorem for polymers and homogenization. | gaussian fluctuations for the directed polymer partition function for $d\\geq 3$ and in the whole $l^2$-region |
aims: we analyze the physical properties and dynamical origin of a curved jet of comet 67p/churyumov-gerasimenko that was observed repeatedly in several nucleus rotations starting on may 30 and persisting until early august, 2015.methods: we simulated the motion of dust grains ejected from the nucleus surface under the influence of the gravity and viscous drag effect of the expanding gas flow from the rotating nucleus.results: the formation of the curved jet is a combination of the size of the dust particles (~0.1-1 mm) and the location of the source region near the nucleus equator. this enhances the spiral feature of the collimated dust stream after the dust is accelerated to a terminal speed on the order of m s-1. | observations and analysis of a curved jet in the coma of comet 67p/churyumov-gerasimenko |
we present millimetre (submillimeter array) and submillimetre (scuba-2) continuum observations of the peculiar star kic 8462852 which displayed several deep and aperiodic dips in brightness during the kepler mission. our observations are approximately confusion-limited at 850 μm and are the deepest millimetre and submillimetre photometry of the star that has yet been carried out. no significant emission is detected towards kic 8462852. we determine upper limits for dust between a few 10-6 m⊕ and 10-3 m⊕ for regions identified as the most likely to host occluding dust clumps and a total overall dust budget of <7.7 m⊕ within a radius of 200 au. such low limits for the inner system make the catastrophic planetary disruption hypothesis unlikely. integrating over the kepler light curve we determine that at least 10-9 m⊕ of dust is required to cause the observed q16 dip. this is consistent with the currently most favoured cometary breakup hypothesis, but nevertheless implies the complete breakup of ∼30 comet 1/p halley type objects. finally, in the wide scuba-2 field of view we identify another candidate debris disc system that is potentially the largest yet discovered. | constraints on the circumstellar dust around kic 8462852 |
context. cometary activity affects the orbital motion and rotation state through sublimation-induced forces. the availability of precise rotation-axis orientation and position data from the rosetta mission allows us to accurately determine the outgassing of comet churyumov-gerasimenko/67p (67p).aims: we derived the observed non-gravitational acceleration of 67p directly from the trajectory of the rosetta spacecraft. from the non-gravitational acceleration, we recovered the diurnal outgassing variations and study a possible delay of the sublimation response with respect to the peak of the solar illumination. this allowed us to compare the non-gravitational acceleration of 67p with expectations based on empirical models and common assumptions about the sublimation process.methods: we used an iterative orbit refinement and fourier decomposition of the diurnal activity to derive the outgassing-induced non-gravitational acceleration. the uncertainties of the data reduction were established by a sensitivity analysis of an ensemble of best-fit orbits for comet 67p.results: we find that the marsden non-gravitational acceleration parameters reproduce part of the non-gravitational acceleration, but need to be augmented by an analysis of the nucleus geometry and surface illumination to draw conclusions about the sublimation process on the surface. the non-gravitational acceleration closely follows the subsolar latitude (seasonal illumination), with a small lag angle with respect to local noon around perihelion. the observed minor changes of the rotation axis do not favor forced precession models for the non-gravitational acceleration.conclusions: in contrast to the sublimation-induced torques, the non-gravitational acceleration does not place strong constraints on localized active areas on the nucleus. we find a close agreement of the orbit-deduced non-gravitational acceleration and the water production that is independently derived from rosetta in situ measurements. | outgassing-induced acceleration of comet 67p/churyumov-gerasimenko |
the oort cloud (oc) probably formed more than 4 gyr ago and has been moving with the sun in the galaxy since, exposed to external influences, most prominently to the galactic tide and passing field stars. theories suggest that other stars might possess exocomets distributed similarly to our oc. we study the erosion of the oc and the possibility for capturing exocomets during the encounters with such field stars. we carry out simulations of flybys, where both stars are surrounded by a cloud of comets. we measure how many exocomets are transferred to the oc, how many oc's comets are lost, and how this depends on the other star's mass, velocity and impact parameter. exocomets are transferred to the oc only during relatively slow (≲0.5 km s-1) and close (≲105 au) flybys and these are expected to be extremely rare. assuming that all passing stars are surrounded by a cloud of exocomets, we derive that the fraction of exocomets in the oc has been about 10-5-10-4. finally, we simulate the oc for the whole lifetime of the sun, taking into account the encounters and the tidal effects. the oc has lost 25-65 per cent of its mass, mainly due to stellar encounters, and at most 10 per cent (and usually much less) of its mass can be captured. however, exocomets are often lost shortly after the encounter that delivers them, due to the galactic tide and consecutive encounters. | capture of exocomets and the erosion of the oort cloud due to stellar encounters in the galaxy |
the propagation of three-dimensional nonlinear dust acoustic waves in a dusty plasma consisting of positive and negative dust grains as well as boltzmann distributed electrons and ions is investigated. using a reductive perturbation method, cylindrical kadomtsev-petviashvili and spherical kadomtsev-petviashvili equations, appropriate for describing the evolution of the system, are derived. the generalized expansion method is used to find the various solutions of the obtained nonlinear kadomtsev-petviashvili equations. new classes of triangular, hyperbolic solitary, rational, and jacobi elliptical type solutions are obtained and graphically presented. it is found that the proposed dusty plasma model can support solitary waves with compressive and rarefactive potential pulses. moreover, the effects of plasma parameters on this solitary wave structure are investigated. the current findings are applied to a cosmic-type plasma in different regions of space, viz. cometary tails, mesosphere, and jupiter's magnetosphere as well as laboratory-type plasma such as low temperature experiments, where a dusty plasma with opposite polarity is dominant. | solutions of nonplanar kp-equations for dusty plasma system with ge-method |
six essential oils (from oregano, thyme, clove, lavender, clary sage, and arborvitae) exhibited different antibacterial and antifungal properties. antimicrobial activity was shown against pathogenic (escherichia coli, salmonella typhimurium, yersinia enterocolitica, staphylococcus aureus, listeria monocytogenes, and enterococcus faecalis) and environmental bacteria (bacillus cereus, arthrobacter protophormiae, pseudomonas fragi) and fungi (chaetomium globosum, penicillium chrysogenum, cladosporium cladosporoides, alternaria alternata, and aspergillus fumigatus). oregano, thyme, clove and arborvitae showed very strong antibacterial activity against all tested strains at both full strength and reduced concentrations. these essential oils showed different fungistatic and fungicidal activities when tested by direct application and in the vapor phase. the genotoxic effects of these oils on hel 12469 human embryo lung cells were evaluated using an alkaline comet assay for the first time, revealing that none of the oils induced significant dna damage in vitro after 24 h. this study provides novel approaches for assessing the antimicrobial potential of essential oils in both direct contact and the vapor phase and also demonstrates the valuable properties of the phenol-free arborvitae oil. these results suggest that all the tested essential oils might be used as broad-spectrum anti-microbial agents for decontaminating an indoor environment. | the antibacterial and antifungal activity of six essential oils and their cyto/genotoxicity to human hel 12469 cells |
context. near- and mid-infrared interferometric observations have revealed populations of hot and warm dust grains populating the inner regions of extrasolar planetary systems. these are known as exozodiacal dust clouds, or exozodis, reflecting the similarity with the solar system's zodiacal cloud. radiative transfer models have constrained the dust to be dominated by tiny submicron-sized, carbon-rich grains that are accumulated very close to the sublimation radius. the origin of this dust is an unsolved issue.aims: we explore two exozodiacal dust production mechanisms, first re-investigating the poynting-robertson drag pile-up scenario, and then elaborating on the less explored but promising exocometary dust delivery scenario.methods: we developed a new, versatile numerical model that calculates the dust dynamics, with non-orbit-averaged equations for the grains close to the star. the model includes dust sublimation and incorporates a radiative transfer code for direct comparison to the observations. we consider in this study four stellar types, three dust compositions, and we assume a parent belt at 50 au.results: in the case of the poynting-robertson drag pile-up scenario, we find that it is impossible to produce long-lived submicron-sized grains close to the star. the inward drifting grains fill in the region between the parent belt and the sublimation distance, producing an unrealistically strong mid-infrared excess compared to the near-infrared excess. the dust pile-up at the sublimation radius is by far insufficient to boost the near-ir flux of the exozodi to the point where it dominates over the mid-infrared excess. in the case of the exocometary dust delivery scenario, we find that a narrow ring can form close to the sublimation zone, populated with large grains from several tens to several hundreds of micrometers in radius. although not perfect, this scenario provides a better match to the observations, especially if the grains are carbon-rich. we also find that the number of active exocomets required to sustain the observed dust level is reasonable.conclusions: we conclude that the hot exozodiacal dust detected by near-infrared interferometry is unlikely to result from inward grain migration by poynting-robertson drag from a distant parent belt, but could instead have an exocometary origin. | hot exozodiacal dust: an exocometary origin? |
the langmuir probe instrument on rosetta monitored the photoelectron emission current of the probes during the rosetta mission at comet 67p/churyumov-gerasimenko, in essence acting as a photodiode monitoring the solar ultraviolet radiation at wavelengths below 250 nm. we have used three methods of extracting the photoelectron saturation current from the langmuir probe measurements. the resulting data set can be used as an index of the solar far and extreme ultraviolet at the rosetta spacecraft position, including flares, in wavelengths which are important for photoionization of the cometary neutral gas. comparing the photoemission current to data measurements by maven/euvm and timed/see, we find good correlation when 67p was at large heliocentric distances early and late in the mission, but up to 50 per cent decrease of the expected photoelectron current at perihelion. we discuss possible reasons for the photoemission decrease, including scattering and absorption by nanograins created by disintegration of cometary dust far away from the nucleus. | rosetta photoelectron emission and solar ultraviolet flux at comet 67p |
for the second discovered interstellar comet 2i/borisov we searched for a candidate for its home system. we will never be sure which star or stellar system does this comet come from but obtaining a very small relative velocity and a promisingly small miss-distance, when tracing the motion of 2i/borisov back in time in its movement through the space, makes an encountered body a good candidate for a source of this comet. in our long-standing project on studying oort spike comets dynamics, we recently updated a list of potential stellar perturbers of cometary motion. this list was checked against a past, close and slow encounter with 2i/borisov. only one object from among 647 stars or stellar systems in our list, a double star kruger 60, appeared as a potential candidate for the origin of this comet. however, a detailed analysis of this system's radial velocity uncertainty influence on our result showed, that the probability that kruger 60 is a home system of 2i/borisov is small. finally, the usage of a new, unpublished systemic radial velocity of kruger 60 system practically ruled out this possibility. | kruger 60 as a home system for 2i/borisov -- a case study |
we present a study of c/2019 y4 (atlas) using sloan gri observations from 2020 mid-january to early april. during this time span, the comet brightened with a growth in the effective cross-section of $\left(2.0\pm 0.1\right)\times {10}^{2}$ m2 s-1 from the beginning to ∼70 days preperihelion in late 2020 march, followed by a brightness fade and the comet gradually losing the central condensation. meanwhile, the comet became progressively bluer, and was even bluer than the sun (g - r ≈ 0.2) when the brightness peaked, likely due to activation of subterranean fresh volatiles exposed to sunlight. with the tailward bias-corrected astrometry we found an enormous radial nongravitational parameter, ${a}_{1}=\left(+2.25\pm 0.13\right)\times {10}^{-7}$ au day-2 in the heliocentric motion of the comet. taking all of these findings into consideration, we conclude that the comet has disintegrated since 2020 mid-march. by no means was the split new to the comet, as we quantified that the comet had undergone another split event around last perihelion ∼5 kyr ago, during which its sibling c/1844 y1 (great comet) was produced, with the in-plane component of the separation velocity ≳1 m s-1. we constrained that the nucleus of c/2019 y4 before disintegration was ≳60 m in radius, and has been protractedly ejecting dust grains of ∼10-40 μm (assuming a dust bulk density of 0.5 g cm-3) with an ejection speed of ∼30 m s-1 in early 2020 march and increased to ∼80 m s-1 toward the end of the month for grains of ∼10 μm. | observations of disintegrating long-period comet c/2019 y4 (atlas): a sibling of c/1844 y1 (great comet) |
context. in this letter we aim to explore whether gas is also expected in the kuiper belt (kb) in our solar system.aims: to quantify the gas release in our solar system, we use models for gas release that have been applied to extrasolar planetary systems as well as a physical model that accounts for gas released due to the progressive internal warming of large planetesimals.methods: we find that only bodies larger than about 4 km can still contain co ice after 4.6 gyr of evolution. this finding may provide a clue as to why jupiter-family comets, thought to originate in the kb, are deficient in co compared to oort cloud comets. we predict that gas is still currently being produced in the kb at a rate of 2 × 10−8 m⊕ myr−1 for co and that this rate was orders of magnitude higher when the sun was younger. once released, the gas is quickly pushed out by the solar wind. therefore, we predict a gas wind in our solar system starting at the kb location and extending far beyond with regards to the heliosphere, with a current total co mass of ∼2 × 10−12 m⊕ (i.e., 20 times the co quantity that was lost by the hale-bopp comet during its 1997 passage) and co density in the belt of 3 × 10−7 cm−3. we also predict the existence of a slightly more massive atomic gas wind made of carbon and oxygen (neutral and ionized), with a mass of ∼10−11 m⊕.results: we predict that gas is currently present in our solar system beyond the kb and that, although it cannot be detected with current instrumentation, it could be observed in the future with an in situ mission using an instrument similar to alice on new horizons but with larger detectors. our model of gas release due to slow heating may also work for exoplanetary systems and provide the first real physical mechanism for the gas observations. lastly, our model shows that the amount of gas in the young solar system should have been orders of magnitude greater and that it may have played an important role in, for example, planetary atmosphere formation. | a molecular wind blows out of the kuiper belt |
we present analysis of ir and optical spectroscopy of jupiter-family comet (jfc) 46p/wirtanen obtained in 2019 january, when the comet had sufficient geocentric velocity to enable studies of the hypervolatiles co and ch4, as well as [o ] emission. these species could not be studied near closest approach in mid-december because there was insufficient doppler shift to separate the cometary emission from their corresponding telluric absorption lines. we employed the [o ] observations as a proxy for the co2/h2o ratio, as co2 cannot be observed directly from the ground, and space-based assets sensitive to co2 were not able to observe 46p during this apparition. we focused our analysis on h2o, co, ch4, c2h6, ch3oh, and co2 (via [o ] emission). we detected strong emissions from h2o, c2h6, and ch3oh. over the 3 nights, we found evidence for changing mixing ratios, mostly due to a variable h2o production rate. in 46p, c2h6 and ch3oh are enriched compared to cometary averages, with mixing ratios relative to h2o of ∼1% and ∼3%, respectively. measurements of ch4 and co have been especially rare in jfcs. we report significant 3σ upper limits on ch4/h2o < 0.97% and co/h2o < 0.54%. they place ch4 being near-average or depleted, and co being strongly depleted in 46p compared with oort cloud comets. 46p has comparable co/h2o to the few other measurements in jfcs, but enriched in c2h6 and ch3oh. our inferred co2/h2o mixing ratio is ∼15%, though accounting for systematic uncertainties from the lack of knowledge of [o ] photochemistry means a value between 10% and 20% is likely. the compositional profile of 46p is similar to another small, hyperactive comet: 103p/hartley 2. the mechanism of co2-driven water-rich ice grain production proposed for 103p/hartley 2 may be operating on 46p as well. | quantifying the hypervolatile abundances in jupiter-family comet 46p/wirtanen |
formation of the first planetesimals remains an unsolved problem. growth by sticking must initiate the process, but multiple studies have revealed a series of barriers that can slow or stall growth, most of them due to nebula turbulence. in a companion paper, we study the influence of these barriers on models of fractal aggregate and solid, compact particle growth in a viscously evolving solar-like nebula for a range of turbulent intensities α t = 10-5-10-2. here, we examine how the disk composition in these same models changes with time. we find that advection and diffusion of small grains and vapor, and radial inward drift for larger compact particles and fractal aggregates, naturally lead to diverse outcomes for planetesimal composition. larger particles can undergo substantial inward radial migration due to gas drag before being collisionally fragmented or partially evaporating at various temperatures. this leads to enhancement of the associated volatile in both vapor inside, and solids outside, their respective evaporation fronts, or snowlines. in cases of lower α t, we see narrow belts of volatile or supervolatile material develop in the outer nebula, which could be connected to the bands of pebbles seen by the atacama large millimeter/submillimeter array. volatile bands, which migrate inwards as the disk cools, can persist over long timescales as their gas phase continues to advect or diffuse outward across its evaporation front. these belts could be sites where supervolatile-rich planetesimals form, such as the rare co-rich and water-poor comets; giant planets formed just outside the h2o snowline may be enhanced in water. | global modeling of nebulae with particle growth, drift, and evaporation fronts. iii. redistribution of refractories and volatiles |
we present a comprehensive analysis of the chemical composition of the jupiter-family comet and potential spacecraft target 46p/wirtanen, in the near-ir wavelength range. we used ishell at the nasa infrared telescope facility to observe the comet on 11 pre-, near-, and postperihelion dates in 2018 december and 2019 january and february during its historic apparition. we report rotational temperatures, production rates, and mixing ratios with respect to h2o and c2h6 or 3σ upper limits of the primary volatiles h2o, hcn, ch4, c2h6, ch3oh, h2co, nh3, co, c2h2, and hc3n. we also discuss the spatial outgassing of the primary volatiles, to understand their sources and the spatial associations between them. the spatial profiles of h2o in 46p/wirtanen suggest the presence of extended h2o outgassing sources in the coma, similar to the epoxi target comet 103p/hartley 2. 46p/wirtanen is among the few known hyperactive comets, and we note that its composition and outgassing behavior are similar to those of other hyperactive comets in many ways. we note that the analyzed parent volatiles showed different variations (relative mixing ratios) during the apparition. we compared the chemical composition of 46p/wirtanen with the mean abundances in jupiter-family comets and the comet population as measured with ground-based near-ir facilities to date. the molecular abundances in 46p/wirtanen suggest that although they were changing, the variations were small compared to the range in the comet population, with ch3oh showing notably more variation as compared to the other molecules. | comprehensive study of the chemical composition and spatial outgassing behavior of hyperactive comet 46p/wirtanen using near-ir spectroscopy during its historic 2018 apparition |
models of the zodiacal cloud's thermal emission and sporadic meteoroids suggest jupiter-family comets (jfcs) as the dominant source of interplanetary dust. however, comet sublimation is insufficient to sustain the quantity of dust presently in the inner solar system, suggesting that spontaneous disruptions of jfcs may supply the zodiacal cloud. we present a model for the dust produced in comet fragmentations and its evolution. using results from dynamical simulations, the model follows individual comets drawn from a size distribution as they evolve and undergo recurrent splitting events. the resulting dust is followed with a kinetic model which accounts for the effects of collisional evolution, poynting-robertson drag, and radiation pressure. this allows to model the evolution of both the size distribution and radial profile of dust, and we demonstrate the importance of including collisions (both as a source and sink of dust) in zodiacal cloud models. with physically motivated free parameters this model provides a good fit to zodiacal cloud observables, supporting comet fragmentation as the plausibly dominant dust source. the model implies that dust in the present zodiacal cloud likely originated primarily from disruptions of ~50-km comets, since larger comets are ejected before losing all their mass. thus much of the dust seen today was likely deposited as larger grains ~0.1 myr in the past. the model also finds the dust level to vary stochastically; e.g. every ~50 myr large (>100 km) comets with long dynamical lifetimes inside jupiter cause dust spikes with order of magnitude increases in zodiacal light brightness lasting ~1 myr. if exozodiacal dust is cometary in origin, our model suggests it should be similarly variable. | comet fragmentation as a source of the zodiacal cloud |
the standard approach to obtaining knowledge about the properties of the surface layer of a comet from observations of gas production consists of two stages. first, various thermophysical models are used to calculate gas production for a few sets of parameters. second, a comparison of observations and theoretical predictions is performed. this approach is complicated because the values of many model characteristics are known only approximately. therefore, it is necessary to investigate the sensitivity of the simulated outgassing to variations in the properties of the surface layer. this problem was recently considered by us for aggregates up to tens of microns in size. for millimetre-size aggregates, a qualitative extension of the method used to model the structural characteristics of the layer is required. it is also necessary to study the role of radiative thermal conductivity, which may play an important role for such large particles. we investigated layers constructed from large aggregates and having various thicknesses and porosity and evaluated the effective sublimation of water ice at different heliocentric distances. for radiative conductivity, approximate commonly used models and the complicated model based on the dense-medium radiative transfer theory were compared. it was shown that for millimetre-size aggregates careful consideration of the radiative thermal conductivity is required since this mechanism of energy transfer may change the resulting gas productivity by several times. we demonstrate that our model is more realistic for an evolved comet than simple models parameterizing the properties of the cometary surface layer, yet maintains comparable computational complexity. | cometary surface dust layers built out of millimetre-scale aggregates: dependence of modelled cometary gas production on the layer transport properties |
we quantitatively investigated the hydrogen addition reactions of acetylene (c2h2) and ethylene (c2h4) on amorphous solid water (asw) at 10 and 20 k relevant to the formation of ethane (c2h6) on interstellar icy grains. we found that the asw surface enhances the reaction rates for c2h2 and c2h4 by approximately a factor of 2 compared to those on the pure-solid c2h2 and c2h4 at 10 k, probably due to an increase in the sticking coefficient and adsorption energy of the h atoms on asw. in contrast to the previous proposal that the hydrogenation rate of c2h4 is orders of magnitude larger than that of c2h2, the present results show that the difference in hydrogenation rates of c2h2 and c2h4 is only within a factor of 3 on both the surfaces of pure solids and asw. in addition, we found the small kinetic isotope effect for hydrogenation/deuteration of c2h2 and c2h4 at 10 k, despite the requirement of quantum tunneling. at 20 k, the reaction rate of deuteration becomes even larger than that of hydrogenation. these unusual isotope effects might originate from a slightly larger number density of d atoms than h atoms on asw at 20 k. the hydrogenation of c2h2 is four times faster than co hydrogenation and can produce c2h6 efficiently through c2h4 even in the environment of a dark molecular cloud. | hydrogenation and deuteration of c2h2 and c2h4 on cold grains: a clue to the formation mechanism of c2h6 with astronomical interest |
context. the second gaia data release (gaia dr2) provided us with the precise five-parameter astrometry for 1.3 billion of sources. as stars passing close to the solar system are thought to influence the dynamical history of long-period comets, we update and extend the list of stars that could potentially perturb the motion of these comets.aims: we announce a publicly available database containing an up-to-date list of stars and stellar systems potentially perturbing the motion of long-period comets. we add new objects and revise previously published lists. special emphasis is placed on stellar systems. a discussion of mass estimation is included.methods: using the astrometry, preferably from gaia dr2, augmented with data from other sources, we calculate nominal spatial positions and velocities for each star. to filter studied objects on the basis of their nominal minimum heliocentric distances we numerically integrate the motion of stars under the galactic potential and their mutual interactions.results: we announce the updated list of stellar perturbers of cometary motion, including the masses of perturbers along with the publicly available database interface. these data are ready to be used with the observed long-period comets orbits to study an individual influence of a whole sample of perturbers, or specific stars, on a dynamical past or future of a specific comet. new potential perturbers were added; there are 138 more than in the previously published sources.conclusions: we demonstrate that a new set of prospective perturbers is an important tool in studies of cometary dynamics. the use of our data changes the results of the past and future cometary motion analysis. we point out a puzzling object in our list, star als 9243. the gaia dr2 astrometry suggests a very close encounter of this star with the sun; however, its astrophysical parameters result in a completely different current distance of als 9243 and its high mass. the database described in this paper is available at: https://pad2.astro.amu.edu.pl/stars | a surprise in the updated list of stellar perturbers of long-period comet motion |
we present infrared telescope facility/spex and neowise observations of the dynamically new comet c/2013 us10 (catalina), hereafter us10, from 5.8 au inbound, to near perihelion at 1.3 au, and back to 5.0 au outbound. we detect water ice in the coma of us10, assess and monitor the physical properties of the ice as insolation varies with heliocentric distance, and investigate the relationship between water ice and co2. this set of measurements is unique in orbital coverage and can be used to infer both the physical evolution of the ice, and, potentially, the nucleus composition. we report (1) nearly identical near-infrared spectroscopic measurements of the coma at -5.8 au, -5.0 au, +3.9 au (where <0 au indicates pre-perihelion epochs), all presenting evidence of water-ice grains, (2) a dust-dominated coma at 1.3 and 2.3 au and, (3) an increasing co2/afρ ratio from -4.9 to 1.8 au. we propose that sublimation of the hyper-volatile co2 is responsible for dragging water-ice grains into the coma throughout the orbit. once in the coma, the observability of the water-ice grains is controlled by the ice grain sublimation lifetime, which seems to require some small dust contaminant (i.e., non-pure ice grains). at | {r}{{h}}| ≥slant 3.9 {au}, the ice grains are long-lived and may be unchanged since leaving the comet nucleus. we find that the nucleus of comet us10 is made of, among other components, ∼1 μm water-ice grains containing up to 1% refractory materials. | icy grains from the nucleus of comet c/2013 us10 (catalina) |
agglomerated debris particles are realistic model cosmic dust particles that reproduce their highly irregular and fluffy morphology. we compute the absolute magnitude of these model particles in the broad-band filters b, v, r, and i from the widely used johnson-cousins photometric system. these data are aimed at providing simple quantitative interpretation of brightness of a cloud of cosmic dust, such as cometary coma, zodiacal light, lunar horizon glow, etc. using this information, number of dust particles can be estimated from the apparent magnitude of the cloud and therefore the total volume of dust. it is significant that the smallest volume of dust is achieved using submicron particles. | absolute magnitude of small cosmic dust particles |
we investigate the thermal evolution of comet 67p/churyumov-gerasimenko’s subsurface in the seth_01 region, where active pits have been observed by the esa/rosetta mission. our simulations show that clathrate destabilization and amorphous ice crystallization can occur at depths corresponding to those of the observed pits in a timescale shorter than 67p/churyumov-gerasimenko’s lifetime in the comet’s activity zone in the inner solar system. sublimation of crystalline ice down to such depths is possible only in the absence of a dust mantle, which requires the presence of dust grains in the matrix small enough to be dragged out by gas from the pores. our results are consistent with both pits formation via sinkholes or subsequent to outbursts, the dominant process depending on the status of the subsurface porosity. a sealed dust mantle would favor episodic and disruptive outgassing as a result of increasing gas pressure in the pores, while high porosity should allow the formation of large voids in the subsurface due to the continuous escape of volatiles. we finally conclude that the subsurface of 67p/churyumov-gerasimenko is not uniform at a spatial scale of ∼100-200 m. | pits formation from volatile outgassing on 67p/churyumov-gerasimenko |
an interdisciplinary review of the chemical literature that points to a unifying scenario for the origin of life, referred to as the primordial multifunctional organic entity (prime) scenario, is provided herein. in the prime scenario it is suggested that the insoluble organic matter (iom) in carbonaceous chondrites, as well as interplanetary dust particles from meteorites and comets may have played an important role in the three most critical processes involved in the origin of life, namely 1) metabolism, via a) the provision and accumulation of molecules that are the building blocks of life, b) catalysis (e.g., by templation), and c) protection of developing life molecules against radiation by excited state deactivation; 2) compartmentalization, via adsorption of compounds on the exposed organic surfaces in fractured meteorites, and 3) replication, via deaggregation, desorption and related physical phenomena. this scenario is based on the hitherto overlooked structural and physicochemical similarities between the iom and the dark, insoluble, multifunctional melanin polymers found in bacteria and fungi and associated with the ability of these microorganisms to survive extreme conditions, including ionizing radiation. the underlying conceptual link between these two materials is strengthened by the fact that primary precursors of bacterial and fungal melanins (collectively referred to herein as allomelanins) are hydroxylated aromatic compounds like homogentisic acid and 1,8-dihydroxynaphthalene, and that similar hydroxylated aromatic compounds, including hydroxynaphthalenes, figure prominently among possible components of the organic materials on dust grains and ices in the interstellar matter, and may be involved in the formation of iom in meteorites. inspired by this rationale, a vis-à-vis review of the properties of iom from various chondrites and non-nitrogenous allomelanin pigments from bacteria and fungi is provided herein. the unrecognized similarities between these materials may pave the way for a novel scenario at the origin of life, in which iom-related complex organic polymers delivered to the early earth are proposed to serve as prime and were preserved and transformed in those primitive forms of life that shared the ability to synthesize melanin polymers playing an important role in the critical processes underlying the establishment of terrestrial eukaryotes. | insoluble organic matter in chondrites: archetypal melanin-like pah-based multifunctionality at the origin of life? |
we investigate the generation of waves in the lower hybrid frequency range by density gradients in the near plasma environment of comet 67p/churyumov-gerasimenko. when the plasma is dominated by water ions from the comet, a situation with magnetized electrons and unmagnetized ions is favourable for the generation of lower hybrid waves. these waves can transfer energy between ions and electrons and reshape the plasma environment of the comet. we consider cometocentric distances out to a few hundred km. we find that when the electron motion is not significantly interrupted by collisions with neutrals, large average gradients within tens of km of the comet, as well as often observed local large density gradients at larger distances, are often likely to be favourable for the generation of lower hybrid waves. overall, we find that waves in the lower hybrid frequency range are likely to be common in the near plasma environment. | lower hybrid waves at comet 67p/churyumov-gerasimenko |
we related morphological (size/shape) and dynamical properties of the dust ejected from the 67p/churyumov-gerasimenko comet by combining data from two instruments onboard the esa's rosetta mission, i.e. the midas atomic force microscope and the giada dust detector. the two instruments detected dust of different size (10-6-10-5 and 10-4-10-3 m, respectively). midas detected dust in four periods, three during the inbound orbit arc (2014 september-november; 2014 december- 2015 february; 2015 february-march) and one corresponding to a post-perihelion outburst (2016 february 19). for these periods, we analysed the dust particles' spatial distribution on the midas targets to obtain the number of parent particles hitting the instrument by means of an empirical procedure and to measure the corresponding dust flux. for the same periods, we retrieved the dust flux measured by giada. the ratio between the two dust fluxes is constant. by coupling this result with activity models, we inferred that the particles detected by midas are fragments of hundreds-micron- to mm-sized particles detected by giada. in addition, the similar dust flux ratios between nominal activity and outburst indicates that the outburst did not include micro- and nano-sized dust, differently from other outbursts previously observed. dust and surface properties were related by applying a traceback algorithm to giada data to retrieve the source regions of dust ejected in different periods. we did not detect variations of morphological properties between dust ejected from more and less processed terrains, concluding that compact dust particles (detected by midas) have the same properties across the comet surface. | combining rosetta's giada and midas data: morphological versus dynamical properties of dust at 67p/churyumov-gerasimenko |
we examined the al-mg isotope systematics of plagioclase in a feo-poor ferromagnesian wild 2 particle (c2092,7,81,1,0; named pyxie) using a ∼2 μm spot. three analyses show average 27al/24mg ratio of ∼65 and excess δ26mg* value of + 0.1 ± 4.5 ‰ (2σ), indicating no resolvable 26mg excess in the particle. the inferred initial (26al/27al)0 ratio of plagioclase in pyxie is estimated as (- 0.6 ± 4.5) ×10-6 with an upper limit of 4 ×10-6. the result is very similar to that of the feo-rich ferromagnesian particle “iris” (ogliore et al., 2012). assuming homogeneous distribution of 26al in the early solar system, pyxie formed at least 2.6 ma after the oldest ca-al-rich inclusions. this minimum formation age is marginally younger than formation ages of most chondrules in type ∼3.0 chondrites but comparable with those of mg# < 98 chondrules in cr3 chondrites. considered in conjunction with similar oxygen isotope ratios between pyxie (and iris) and mg# < 98 chondrules in cr3 chondrites, it is inferred that the ferromagnesian wild 2 particles and mg# < 98 chondrules in cr3 chondrites formed late in local disk environments that had similar oxygen isotope ratios and redox states. | late formation of a comet wild 2 crystalline silicate particle, pyxie, inferred from al-mg chronology of plagioclase |
we study the dynamical properties of objects in hyperbolic orbits passing through the inner solar system in the context of two different potential sources: interstellar space and the oort cloud. we analytically derive the probability distributions of eccentricity, e, and perihelion distance, q, for each source and estimate the numbers of objects produced per unit of time as a function of these quantities. by comparing the numbers from the two sources, we assess which origin is more likely for a hyperbolic object having a given eccentricity and perihelion distance. we find that the likelihood that a given hyperbolic object is of interstellar origin increases with decreasing eccentricity and perihelion. conversely, the likelihood that a hyperbolic object has been scattered from the oort cloud by a passing star increases with decreasing eccentricity and increasing perihelion. by carefully considering their orbital elements, we conclude that both 1i/2017 u1 'oumuamua (e ≃ 1.2 and q ≃ 0.26 au) and 2i/2019 q4 borisov (e ≃ 3.3 and q ≃ 2 au) are most likely of interstellar origin, not scattered from the oort cloud. however, we also find that oort cloud objects can be scattered into hyperbolic orbits like those of the two known examples, by sub-stellar and even sub-jovian mass perturbers. this highlights the need for better characterization of the low mass end of the free-floating brown dwarf and planet population. | hyperbolic orbits in the solar system: interstellar origin or perturbed oort cloud comets? |
the bulk density of a meteoroid affects its dynamics in space, its ablation in the atmosphere, and the damage it does to spacecraft and lunar or planetary surfaces. meteoroid bulk densities are also notoriously difficult to measure, and we are typically forced to assume a density or attempt to measure it via a proxy. in this paper, we construct a density distribution for sporadic meteoroids based on existing density measurements. we considered two possible proxies for density: the kb parameter introduced by ceplecha and tisserand parameter, tj. although kb is frequently cited as a proxy for meteoroid material properties, we find that it is poorly correlated with ablation-model-derived densities. we therefore follow the example of kikwaya et al. in associating density with the tisserand parameter. we fit two density distributions to meteoroids originating from halley-type comets (tj < 2) and those originating from all other parent bodies (tj > 2); the resulting two-population density distribution is the most detailed sporadic meteoroid density distribution justified by the available data. finally, we discuss the implications for meteoroid environment models and spacecraft risk assessments. we find that correcting for density increases the fraction of meteoroid-induced spacecraft damage produced by the helion/antihelion source. | a two-population sporadic meteoroid bulk density distribution and its implications for environment models |
a number of planetary spacecraft missions have carried instruments with sensors covering the ultraviolet (uv) wavelength range. however, there exists a general lack of relevant uv reflectance laboratory data to compare against these planetary surface remote sensing observations in order to make confident material identifications. to address this need, we have systematically analyzed reflectance spectra of carbonaceous materials in the 200-500 nm spectral range, and found spectral-compositional-structural relationships that suggest this wavelength region could distinguish between otherwise difficult-to-identify carbon phases. in particular (and by analogy with the infrared spectral region), large changes over short wavelength intervals in the refractive indices associated with the trigonal sp2π-π* transition of carbon can lead to fresnel peaks and christiansen-like features in reflectance. previous studies extending to shorter wavelengths also show that anomalous dispersion caused by the σ-σ* transition associated with both the trigonal sp2 and tetrahedral sp3 sites causes these features below λ = 200 nm. the peak wavelength positions and shapes of π-π* and σ-σ* features contain information on sp3/sp2, structure, crystallinity, and powder grain size. a brief comparison with existing observational data indicates that the carbon fraction of the surface of mercury is likely amorphous and submicroscopic, as is that on the surface of the martian satellites phobos and deimos, and possibly comet 67p/churyumov-gerasimenko, while further coordinated observations and laboratory experiments should refine these feature assignments and compositional hypotheses. the new laboratory diffuse reflectance data reported here provide an important new resource for interpreting uv reflectance measurements from planetary surfaces throughout the solar system, and confirm that the uv can be rich in important spectral information. | ultraviolet spectral reflectance of carbonaceous materials |
the centaurs are the small solar system bodies intermediate between the active inner solar system jupiter family comets and their inactive progenitors in the trans-neptunian region. among the fraction of centaurs which show comet-like activity, 174p/echeclus is best known for its massive 2005 outburst in which a large apparently active fragment was ejected above the escape velocity from the primary nucleus. we present visible imaging and near-infrared spectroscopy of echeclus during the first week after its 2017 december outburst taken at the faulkes north and south telescopes and the nasa irtf, the largest outburst since 2005. the coma was seen to be highly asymmetric. a secondary peak was seen in the near-infrared 2d spectra, which is strongly hinted at in the visible images, moving hyperbolically with respect to the nucleus. the retrieved reflectance spectrum of echelcus is consistent with the unobscured nucleus but becomes bluer when a wider extraction aperture is used. we find that echeclus’s coma is best explained as dominated by large blue dust grains, which agrees with previous work. we also conducted a high-resolution orbital integration of echeclus’s recent evolution and found no large orbital changes that could drive its modern evolution. we interpret the second peak in the visible and near-infrared data sets as a large cloud of larger-than-dust debris ejected at the time of outburst. if echeclus is typical of the centaurs, there may be several debris ejection or fragmentation events per year on other centaurs that are going unnoticed. | physical characterization of the 2017 december outburst of the centaur 174p/echeclus |
the presence of n2 in the surface environment of pluto is critical in creating pluto's richness of features and processes. here, we propose that the nitrogen atoms in the n2 observed on pluto were accreted in that chemical form during the formation of pluto. we use new horizons data and models to estimate the amounts of n2 in the following exterior reservoirs: atmosphere, escape, photochemistry, and surface. the total exterior inventory is deduced to be dominated by a glacial sheet of n2-rich ices at sputnik planitia, or by atmospheric escape if past rates of escape were much faster than at present. pluto's atmosphere is a negligible reservoir of n2, and photochemical destruction of n2 may also be of little consequence. estimates are made of the amount of n2 accreted by pluto based on cometary and solar compositions. it is found that the cometary model can account for the amount of n2 in sputnik planitia, while the solar model can provide a large initial inventory of n2 that would make prodigious atmospheric escape possible. these consistencies can be considered preliminary evidence in support of a primordial origin of pluto's n2. however, both models predict accreted ratios of co/n2 that are much higher than that in pluto's atmosphere. possible processes to explain "missing co" that are given quantitative support here are fractional crystallization from the atmosphere resulting in co burial at the surface, and aqueous destruction reactions of co subject to metastable thermodynamic equilibrium in the subsurface. the plausibility of primordial n2 as the primary source of pluto's nitrogen (vs. nh3 or organic n) can be tested more rigorously using future constraints on the 14 n/15 n ratio in n2 and the 36ar/n2 ratio. | primordial n2 provides a cosmochemical explanation for the existence of sputnik planitia, pluto |
context. accurate hydrogen spectra emitted by the entire solar disc in the ly-α and ly-βlines are valuable for deriving the distribution and the behaviour of atomic hydrogen in the heliosphere, for understanding the uv emissions of solar type stars better, and finally for estimating the solar energy input that mainly initiates the chemical processes occurring in the planetary and cometary outer atmospheres.aims: in this paper we want to accurately determine the irradiance solar spectral profiles of ly-α and ly-β and their evolution through the solar activity cycle 23.methods: the sumer/soho spectrometer is a slit spectrometer that is only able to analyse a small part of the solar image. consequently, we used the scattered light properties of the telescope to obtain average spectra over the solar disc. then the profile is calibrated using the solstice/uars and timed/see irradiance spectra.results: we obtained a set of irradiance ly-α and ly-β solar spectra with a 0.002 nm resolution through the solar activity cycle 23. in each line a relation between the integrated profile and the line centre intensity was obtained.knowing the line irradiance, it is possible to deduce the central line profile intensity, a critical input into the interplanetary and planetary oxygen and hydrogen fluorescent processes.conclusions: the observation of h i ly-α and ly-β line profiles by sumer/soho during the cycle 23 allows analysis of the evolution of their characteristics and accurate determination of uv radiation input into the solar system. profiles 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/581/a26 | hydrogen ly-α and ly-β full sun line profiles observed with sumer/soho (1996-2009) |
amorphous solid water (asw) is found on icy dust grains in the interstellar medium (ism), as well as on comets and other icy objects in the outer solar system. the optical properties of asw are thus relevant for many astrophysical environments, but in the ultraviolet-visible (uv-vis), its refractive index is not well constrained. here, we introduce a new method based on uv-vis broadband interferometry to measure the wavelength-dependent refractive index n(λ) of amorphous water ice from 10 to 130 k, i.e., for different porosities, in the wavelength range of 210-757 nm. we also present n(λ) for crystalline water ice at 150 k, which allows us to compare our new method with literature data. based on this, a method to calculate n(λ, ρ) as a function of wavelength and porosity is reported. this new approach carries much potential and is generally applicable to pure and mixed ice, both amorphous and crystalline. the astronomical and physical-chemical relevance and future potential of this work are discussed. | the refractive index of amorphous and crystalline water ice in the uv-vis |
context. the rosetta spacecraft escorted comet 67p/churyumov-gerasimenko for 2 yr along its journey through the solar system between 3.8 and 1.24 au. thanks to the high resolution mass spectrometer on board rosetta, the detailed ion composition within a coma has been accurately assessed in situ for the very first time.aims: previous cometary missions, such as giotto, did not have the instrumental capabilities to identify the exact nature of the plasma in a coma because the mass resolution of the spectrometers onboard was too low to separate ion species with similar masses. in contrast, the double focusing mass spectrometer (dfms), part of the rosetta orbiter spectrometer for ion and neutral analysis on board rosetta (rosina), with its high mass resolution mode, outperformed all of them, revealing the diversity of cometary ions.methods: we calibrated and analysed the set of spectra acquired by dfms in ion mode from october 2014 to april 2016. in particular, we focused on the range from 13-39 u q-1. the high mass resolution of dfms allows for accurate identifications of ions with quasi-similar masses, separating 13c+ from ch+, for instance.results: we confirm the presence in situ of predicted cations at comets, such as chm+ (m = 1-4), hno+ (n = 1-3), o+, na+, and several ionised and protonated molecules. prior to rosetta, only a fraction of them had been confirmed from earth-based observations. in addition, we report for the first time the unambiguous presence of a molecular dication in the gas envelope of a solar system body, namely co2++. | rosina ion zoo at comet 67p |
we present high resolution, deep imaging of interstellar comet 2i/borisov taken with the hubble space telescope/wide field camera 3 (hst/wfc3) on 2019 december 8 utc and 2020 january 27 utc (hst go 16040, pi: bolin) before and after its perihelion passage in combination with hst/wfc3 images taken on 2019 october 12 utc and 2019 november 16 utc (hst go/dd 16009, pi: jewitt) before its outburst and fragmentation of 2020 march, thus observing the comet in a relatively undisrupted state. we locate 1-2 arcsec long (2000-3000 km projected length) jet-like structures near the optocentre of 2i that appear to change position angles from epoch to epoch. with the assumption that the jet is located near the rotational pole supported by its stationary appearance on ~10-100 h time frames in hst images, we determine that 2i's pole points near α = 322 ± 10° and δ = 37 ± 10° (λ = 341° and β = 48°) and may be in a simple rotation state. additionally, we find evidence for possible periodicity in the hst time-series light curve on the time-scale of ~5.3 h with a small amplitude of ~0.05 mag implying a lower limit on its b/a ratio of ~1.5 unlike the large ~2 mag light curve observed for 1i/'oumuamua. however, these small light-curve variations may not be the result of the rotation of 2i's nucleus due to its dust-dominated light-scattering cross-section. therefore, uniquely constraining the pre-solar system encounter, pre-outburst rotation state of 2i may not be possible even with the resolution and sensitivity provided by hst observations. | constraints on the spin-pole orientation, jet morphology, and rotation of interstellar comet 2i/borisov with deep hst imaging |
we present the results of the photometric and spectrophotometric properties of the 67p/churyumov-gerasimenko nucleus derived with the optical, spectroscopic and infrared remote imaging system instrument during the closest fly-by over the comet, which took place on 2015 february 14 at a distance of ∼6 km from the surface. several images covering the 0°-33° phase angle range were acquired, and the spatial resolution achieved was 11 cm pixel-1. the flown-by region is located on the big lobe of the comet, near the borders of the ash, apis and imhotep regions. our analysis shows that this region features local heterogeneities at the decimetre scale. we observed difference of reflectance up to 40 per cent between bright spots and sombre regions, and spectral slope variations up to 50 per cent. the spectral reddening effect observed globally on the comet surface by fornasier et al. (2015) is also observed locally on this region, but with a less steep behaviour. we note that numerous metre-sized boulders, which exhibit a smaller opposition effect, also appear spectrally redder than their surroundings. in this region, we found no evidence linking observed bright spots to exposed water-ice-rich material. we fitted our data set using the hapke 2008 photometric model. the region overflown is globally as dark as the whole nucleus (geometric albedo of 6.8 per cent) and it has a high porosity value in the uppermost layers (86 per cent). these results of the photometric analysis at a decimetre scale indicate that the photometric properties of the flown-by region are similar to those previously found for the whole nucleus. | decimetre-scaled spectrophotometric properties of the nucleus of comet 67p/churyumov-gerasimenko from osiris observations |
we report on our extensive photometry and imaging of comet 46p/wirtanen during its 2018/19 apparition and use these data to constrain the modeling of wirtanen's activity. narrowband photometry was obtained in 9 epochs from 2018 october through 2019 march as well as 10 epochs during the 1991, 1997, and 2008 apparitions. the ensemble photometry reveals a typical composition and a secular decrease in activity since 1991. production rates were roughly symmetric around perihelion for the carbon-bearing species (cn, c3, and c2), but steeper for oh and nh outbound. our imaging program emphasized cn, whose coma morphology and lightcurve yielded rotation periods reported in a companion paper (farnham et al. 2021). here, we compare the gas and dust morphology on the 18 nights for which observations of additional species were obtained. the carbon-bearing species exhibited similar morphology that varied with rotation. oh and nh had broad, hemispheric brightness enhancements in the tailward direction that did not change significantly with rotation, which we attribute to their originating from a substantial icy grain component. we constructed a monte carlo model that replicates the shape, motion, and brightness distribution of the cn coma throughout the apparition with a single, self-consistent solution in principal axis rotation. our model yields a pole having (r.a., decl.) = 319°, -5° (pole obliquity of 70°) and two large sources (radii of 50° and 40°) centered at near-equatorial latitudes and separated in longitude by ∼160°. applications of the model to explain observed behaviors are discussed. | narrowband observations of comet 46p/wirtanen during its exceptional apparition of 2018/19. ii. photometry, jet morphology, and modeling results |
context. as the esa rosetta mission approached, orbited, and sent a lander to comet 67p/churyumov-gerasimenko in 2014, a large campaign of ground-based observations also followed the comet.aims: we constrain the total activity level of the comet by photometry and spectroscopy to place rosetta results in context and to understand the large-scale structure of the comet's coma pre-perihelion.methods: we performed observations using a number of telescopes, but concentrate on results from the 8 m vlt and gemini south telescopes in chile. we use r-band imaging to measure the dust coma contribution to the comet's brightness and uv-visible spectroscopy to search for gas emissions, primarily using vlt/fors. in addition we imaged the comet in near-infrared wavelengths (jhk) in late 2014 with gemini-s/flamingos-2.results: we find that the comet was already active in early 2014 at heliocentric distances beyond 4 au. the evolution of the total activity (measured by dust) followed previous predictions. no gas emissions were detected despite sensitive searches.conclusions: the comet maintains a similar level of activity from orbit to orbit, and is in that sense predictable, meaning that rosetta results correspond to typical behaviour for this comet. the gas production (for cn at least) is highly asymmetric with respect to perihelion, as our upper limits are below the measured production rates for similar distances post-perihelion in previous orbits. based on observations made with eso telescopes at the la silla paranal observatory under programme ids 592.c-0924, 093.c-0593, 094.c-0054, and at gemini south under gs-2014b-q-15 and gs-2014b-q-76. | distant activity of 67p/churyumov-gerasimenko in 2014: ground-based results during the rosetta pre-landing phase |
there has been growing observational evidence for the presence of condensates in the atmospheres and/or comet-like tails of extrasolar planets. as a result, systematic and homogeneous tables of dust properties are useful in order to facilitate further observational and theoretical studies. in this paper we present calculations and analysis of non-isotropic phase functions, asymmetry parameter (mean cosine of the scattering angle), absorption and scattering opacities, single scattering albedos, equilibrium temperatures, and radiative accelerations of dust grains relevant for extrasolar planets. our assumptions include spherical grain shape, deirmendjian particle size distribution, and mie theory. we consider several species: corundum/alumina, perovskite, olivines with 0 and 50 per cent iron content, pyroxenes with 0, 20, and 60 per cent iron content, pure iron, carbon at two different temperatures, water ice, liquid water, and ammonia. the presented tables cover the wavelength range of 0.2-500 μm and modal particle radii from 0.01 to 100 μm. equilibrium temperatures and radiative accelerations assume irradiation by a non-blackbody source of light with temperatures from 7000 to 700 k seen at solid angles from 2π to 10-6 sr. the tables are provided to the community together with a simple code which allows for an optional, finite, angular dimension of the source of light (star) in the phase function. | tables of phase functions, opacities, albedos, equilibrium temperatures, and radiative accelerations of dust grains in exoplanets |
we present an intensive monitoring of high-resolution spectra of the ca ii k line in the a7iv shell star φ leo at very short (minutes, hours), short (night to night), and medium (weeks, months) timescales. the spectra show remarkable variable absorptions on timescales of hours, days, and months. the characteristics of these sporadic events are very similar to most that are observed toward the debris disk host star β pic, which are commonly interpreted as signs of the evaporation of solid, comet-like bodies grazing or falling onto the star. therefore, our results suggest the presence of solid bodies around φ leo. to our knowledge, with the exception of β pic, our monitoring has the best time resolution at the mentioned timescales for a star with events attributed to exocomets. assuming the cometary scenario and considering the timescales of our monitoring, our results indicate that φ leo presents the richest environment with comet-like events known to date, second only to β pic. | exocomet signatures around the a-shell star φ leonis? |
comets are usually considered to be the most primitive bodies in the solar system. the level of truth of this paradigm, however, is a matter of debate, especially if by primitive we mean that they represent a sample of intact, unprocessed material. we now have the possibility of analysing the comet 67p/churyumov-gerasimenko with an unprecedented level of detail, but its interior remains largely unprobed and unknown. the questions we address in this paper concern the depth of the processed layers, and whether the comet nucleus, under these processed layers, is really representative of the original material. we applied the rome model for the thermal evolution and differentiation of nuclei to give an estimation of the evolution and depth of the active layers and of the interplay between the erosion process and the penetration of the heat wave. in order to characterize the illumination regime and the activity on the nucleus, two locations with very different illumination histories were chosen for the simulation. for both locations, the bulk of the activity tends to be concentrated around the perihelion time, giving rise to a high erosion rate. as a consequence, the active layers tend to remain close to the surface, and the interior of the comet, below a layer of few tens of centimetres, can be considered as pristine. | how pristine is the interior of the comet 67p/churyumov-gerasimenko? |
we study how uncertainties in knowledge of the microstructure of the porous dust surface layer affect our estimates of effective gas production of comet 67p/churyumov-gerasimenko. we analyse the transport properties (distribution of free paths, mean pore size, permeability) for random densely packed porous layers. bimodal layers, as well as various cases of inhomogeneous layers having cavities and cracks, are considered. modelling is performed for various values of effective porosity and various particle sizes and thicknesses of the dust layer. the results of computer simulations are embedded in thermal models of the surface region of the cometary nucleus, including explicitly a radiation thermal conductivity and a resistance of the dust layer for the gas flow is used. the simulations show that the porosity variations within the range of values expected for the 67p can change the effective gas production by tens of percent for thin layers, and can vary by several times with increasing layer thickness. these effects are manifested at all heliocentric distances where sublimation of water ice makes a significant contribution to the energy budget of the nucleus. modelling also shows that in all considered cases the microscopic cavities and cracks have a minor effect on the effective gas production: changes in the presence and number of inhomogeneities in comparison with a uniform layer of the same effective porosity are negligible. | the effect of varying porosity and inhomogeneities of the surface dust layer on the modelling of comet gas production |
comets are considered the most primitive planetary bodies in our solar system, i.e., they should have best preserved the solid components of the matter from which our solar system formed. esa's recent rosetta mission to jupiter family comet 67p/churyumov-gerasimenko (67p/cg) has provided a wealth of isotope data which expanded the existing data sets on isotopic compositions of comets considerably. in this paper we review our current knowledge on the isotopic compositions of h, c, n, o, si, s, ar, and xe in primitive solar system materials studied in terrestrial laboratories and how the rosetta data acquired with the rosina (rosetta orbiter sensor for ion and neutral analysis) and cosima (cometary secondary ion mass analyzer) mass spectrometer fit into this picture. the h, si, s, and xe isotope data of comet 67p/cg suggest that this comet might be particularly primitive and might have preserved large amounts of unprocessed presolar matter. we address the question whether the refractory si component of 67p/cg contains a presolar isotopic fingerprint from a nearby type ii supernova (sn) and discuss to which extent c and o isotope anomalies originating from presolar grains should be observable in dust from 67p/cg. finally, we explore whether the isotopic fingerprint of a potential late sn contribution to the formation site of 67p/cg in the solar nebula can be seen in the volatile component of 67p/cg. | presolar isotopic signatures in meteorites and comets: new insights from the rosetta mission to comet 67p/churyumov-gerasimenko |
we present 2d hydrodynamical simulations of the transition of a protoplanetary nebula (ppn) to a planetary nebula for central stars in binary systems that have undergone a common-envelope event. after 1000 yr of magnetically driven dynamics (ppn phase), a line-driven stellar wind is introduced into the computational domain and the expansion of the nebula is simulated for another 10 000 yr, including the effects of stellar photoionization. in this study we consider central stars with main sequence (final) masses of 1 (0.569) and 2.5 (0.677) m⊙, together with a 0.6-m⊙ main-sequence companion. extremely bipolar, narrow-waisted ppne result in bipolar planetary nebulae, while the rest of the shapes mainly evolve into elliptical planetary nebulae. the initial magnetic field's effects on the collimated structures, such as jets, tend to disappear in most of the cases, leaving behind the remnants of those features in only a few cases. equatorial zones fragmented mainly by photoionization (1-m⊙progenitors), result in 'necklace' structures made of cometary clumps aligned with the radiation field. on the other hand, fragmentation by photoionization and shocked wind (2.5-m⊙progenitors) give rise to the formation of multiple clumps in the latitudinal direction, which remain within the lobes, close to the center, which are immersed and surrounded by hot shocked gas, not necessarily aligned with the radiation field. these results reveal that the fragmentation process has a dependence on the stellar-mass progenitor. this fragmentation is made possible by the distribution of gas in the previous post-common-envelope ppn as sculpted by the action of the jets. | common-envelope shaping of planetary nebulae - iv. from protoplanetary to planetary nebula |
we have carried out very large array imaging and a fermi timing analysis of the 115 ms γ-ray and radio pulsar psr j0002+6216. we found that the pulsar lies at the apex of a narrowly collimated cometary-like 7‧ tail of nonthermal radio emission, which we identify as a bow-shock pulsar wind nebula. the tail of the nebula points back toward the geometric center of the supernova remnant ctb 1 (g116.9+0.2) 28‧ away, at a position angle θμ= 113°. we measure a proper motion with 2.9σ significance from a fermi timing analysis giving μ = 115 ± 33 mas yr-1 and θμ= 121° ± 13°, corresponding to a large transverse pulsar velocity of 1100 km s-1 at a distance of 2 kpc. this proper motion is of the right magnitude and direction to support the claim that psr j0002+6216 was born from the same supernova that produced ctb 1. we explore the implications for pulsar birth periods, asymmetric supernova explosions, and mechanisms for pulsar natal kick velocities. | the tail of psr j0002+6216 and the supernova remnant ctb 1 |
the plasma around comet 67p/churyumov-gerasimenko showed remarkable variability throughout the entire rosetta mission. plasma boundaries such as the diamagnetic cavity, solar wind ion cavity and infant bow shock separate regions with distinct plasma parameters from each other. here, we focus on a particular feature in the plasma: warm, slow solar wind protons. we investigate this particular proton population further by focusing on the proton behaviour and surveying all of the rosetta comet phase data. we find over 300 events where rosetta transited from a region with fast, cold protons into a region with warm, slow protons. we investigate the properties of the plasma and magnetic field at this boundary and the location where it can be found. we find that the protons are preferentially detected at intermediate gas production rates with a slight trend towards larger cometocentric distances for higher gas production rates. the events can mostly be found in the positive convective electric field hemisphere. these results agree well with simulations of the infant bow shock (ibs), an asymmetric structure in the plasma environment previously detected on only 2 d during the comet phase. the properties of the plasma on both sides of this structure are harder to constrain, but there is a trend towards higher electron flux, lower magnetic field, higher magnetic field power spectral density and higher density in the region that contains the warm protons. this is in partial agreement with the previous ibs definitions; however, it also indicates that the plasma and this structure are highly non-stationary. for future research, comet interceptor, with its multi-point measurements, can help to disentangle the spatial and temporal effects and give more clarity on the influence of changing upstream conditions on the movement of boundaries in this unusual environment. | warm protons at comet 67p/churyumov-gerasimenko - implications for the infant bow shock |
context. we present a new numerical model of the η-aquariid and orionid meteor showers.aims: the model investigates the origin, variability, and age of the η-aquariid and orionid apparitions from 1985 to the present day in order to forecast their activity over the next several decades.methods: through the numerical integration of millions of simulated meteoroids and a custom-made particle weighting scheme, we model the characteristics of every η-aquariid and orionid apparition between 1985 and 2050. the modeled showers are calibrated using 35 yr of meteor observations, including the shower activity profiles and interannual variability.results: our model reproduces the general characteristics of the present-day η-aquariids and part of the orionid activity. simulations suggest that the age of the η-aquariids somewhat exceeds 5000 yr, while a greater fraction of the orionids is composed of older material. the 1:6 mean motion resonance with jupiter plays a major role in generating some (but not all) halleyid stream outbursts. we find consistent evidence for a periodicity of 11.8 yr in both the observations and modeled maximum meteor rates for the orionids. weaker evidence of a 10.7 yr period in the peak activity for the η-aquariids needs to be investigated with future meteor observations. the extension of our model to future years predicts no significant orionid outbursts through 2050 and four significant η-aquariid outbursts, in 2023, 2024, 2045, and 2046. the movie associated to fig. 11 is available at https://www.aanda.org | modeling the past and future activity of the halleyid meteor showers |
high-resolution bathymetry collected with an autonomous underwater vehicle (auv) along the flanks of three ridges of the accretionary prism offshore southwestern (sw) taiwan revealed more than 650 elongated depressions in water depths ranging from 1155 to 1420 m. the depressions are between 12 and 129 m long, 5 to 70 m wide, and up 9 m deep at their center and shallowing downslope to about 1-m depth. due to their shape in downslope cross section, they are termed comet-shaped depressions (csd). the csd occur in patches of more than 100 with densities of 53 to 98 csd/km2. in addition, seven topographic mounds were mapped and interpreted as pingos, which remotely operate vehicle (rov) observations and sampling show to be covered with authigenic carbonate. these features overlie areas where multichannel seismic reflection (mcs) profiles show bottom simulating reflectors (bsr) and dipping strata extending from below the bsr to near the seafloor. we consider comet-shaped depression, a new type of pockmark, forms on a sloping seafloor where fluids expulsion occurred. we also suggest that the two types of distinctive geomorphic features are attributed to fluid venting which occurs at different rates, with the mounds developing slowly over time, but the csd forming in discrete events perhaps associated with large earthquakes. | discovery of numerous pingos and comet-shaped depressions offshore southwestern taiwan |
iron oxide-fe2o3 nanoparticles-nps and microparticles-mps widely used in medical applications were comparatively investigated for in vitro mutagenicity and in vivo cytotoxicity/genotoxicity using the ames test in salmonella typhimurium strains (125, 250, 500, 750, 1,000 µg/ml) and chromosome aberration/comet assays in allium cepa (all concentrations but 1,000 µg/ml), for the first time. neither of the particles was mutagenic in all the bacterial strains in the media without (-s9) mix. however, with the s9 mix, a significant increase was determined in the reverting colonies in some concentrations in ta 97a. in ta 102, all the concentrations but 125 µg/ml also revealed a significant increase. these effects were regarded as weak mutagens since they were < twofold of the negative value. in the allium test, almost all concentrations of nps and mps significantly decreased mitotic index (mi) compared to the negative control at all treatment times (down to 6.06% at 250 µg/ml and 6.40% at 750 µg/ml at 48 h, respectively). the frequency of aberrations significantly increased following all concentrations of nps in all treatment periods (the highest was 62.03%). however, only a few concentrations of mps induced significant aberrations (the highest was 32.18%). in the comet assay, while the two lowest concentrations of nps were more effective in dna damage, fe2o3 mps significantly increased dna damage at more treatment points at both treatment periods. both particles were also characterized morphologically and physicochemically. the results revealed that further investigations using different organisms and test systems are necessary for the safer usage of these particles. | comparative investigation of iron oxide nanoparticles and microparticles using the in vitro bacterial reverse mutation and in vivo allium chromosome aberration and comet assays |
the rosetta spacecraft made a rendezvous with comet 67p/churyumov-gerasimenko (67p) in 2014 august, soon after the philae module landed on the small lobe of the nucleus on 2014 november 12. the consert instrument, onboard rosetta and philae, sounded the upper part of the interior of 67p with radiowaves at 90 mhz and determined an average of the real part of the permittivity (hereafter ɛ΄) equal to about 1.27. the sesame-pp instrument, onboard philae, sounded the near-surface of the small lobe in the 400-800 hz range and determined a lower limit of ɛ΄ equal to 2.45. we use a semi-empirical formula obtained from measurements of ɛ΄ performed in the laboratory at 243 k on water ice and ice-basaltic dust mixtures, with a controlled porosity in the 31-91 per cent range and a dust-to-ice volumetric ratio in the 0.1-2.8 range, to interpret the results of the two instruments, taking into account the temperature and frequency dependences. a graphical method is proposed to derive ranges of porosity and dust-mass fraction from a value of ɛ΄ derived from observations. the non-dispersive behaviour of ɛ΄ below 175 k, allows us to compare the values of ɛ΄ obtained by consert and sesame-pp. we show that the porosity of the small lobe of 67p increases with depth. based on new measurements of analogues of complex extraterrestrial organic matter, the so-called tholins, we also suggest that, for the dust component in the cometary material, the presence of silicates has more effect on ɛ΄ than organic materials. | a porosity gradient in 67p/c-g nucleus suggested from consert and sesame-pp results: an interpretation based on new laboratory permittivity measurements of porous icy analogues |
we report the first infrared study of the low-energy (<20 ev) electron-induced reactions of condensed methanol. our goal is to simulate processes which occur when high-energy cosmic rays interact with interstellar and cometary ices, where methanol, a precursor of several prebiotic species, is relatively abundant. the interactions of high-energy radiation, such as cosmic rays (emax ∼ 1020 ev), with matter produce large numbers of low-energy secondary electrons, which are known to initiate radiolysis reactions in the condensed phase. using temperature programmed desorption (tpd) and infrared reflection absorption spectroscopy (iras), we have investigated low-energy (5-20 ev) and high-energy (∼1000 ev) electron-induced reactions in condensed methanol (ch3oh). iras has the benefit that it does not require thermal processing prior to product detection. using iras, we have found evidence for the formation of ethylene glycol (hoch2ch2oh), formaldehyde (ch2o), dimethyl ether (ch3och3), methane (ch4), carbon dioxide (co2), carbon monoxide (co), and the hydroxyl methyl radical (·ch2oh) upon both low-energy and high-energy electron irradiation of condensed methanol at ∼85 k. additionally, tpd results, presented herein, are similar for methanol films irradiated with both 1000 ev and 20 ev electrons. these iras and tpd findings are qualitatively consistent with the hypothesis that high-energy condensed phase radiolysis is mediated by low-energy electron-induced reactions. moreover, methoxymethanol (ch3och2oh) could serve as a tracer molecule for electron-induced reactions in the interstellar medium. the results of experiments such as ours may provide a fundamental understanding of how complex organic molecules are synthesized in cosmic ices. | low-energy (<20 ev) and high-energy (1000 ev) electron-induced methanol radiolysis of astrochemical interest |
the paper presents a new method for determining the change in the brightness of a comet during an outburst in which particles are ejected into the coma at a uniform rate, i.e. via a long-lived jet. in the proposed approach, the mass flow rate by a jet and the time it takes to increase the brightness of the comet play key roles. absolute values adopted for h2o ice and co2 ice were taken from measurements by rosetta of the jets observed on 67p/churyumov-gerasimenko. these two parameters significantly affect the amplitude of the change in the brightness of a comet during its outburst. the performed numerical calculations concern a hypothetical comet from the jupiter family for which it was assumed that its sublimation activity was controlled by the sublimation of water ice and carbon dioxide. based on numerical simulations, it was shown that the difference between the change in brightness for h2o ice and co2 ice is about -3.4 magnitude for the same fraction of the area that is active and the same mass flow rate. this value corresponds to the rise time of the amplitude of the brightness change t = 3 h. in addition, it should be emphasized that this difference is a consequence of thermodynamic parameters, such as the speed of sublimating gas molecules, the sublimation rate of given ice, which determine the numerical values of the individual scattering cross-sections c(t1) and c(t2). | the rise time of the change of cometary brightness during its outburst |
the cophylab (cometary physics laboratory) project is designed to study the physics of comets through a series of earth-based experiments. for these experiments, a dust analogue was created with physical properties comparable to those of the non-volatile dust found on comets. this 'cophylab dust' is planned to be mixed with water and co2 ice and placed under cometary conditions in vacuum chambers to study the physical processes taking place on the nuclei of comets. in order to develop this dust analogue, we mixed two components representative for the non-volatile materials present in cometary nuclei. we chose silica dust as a representative for the mineral phase and charcoal for the organic phase, which also acts as a darkening agent. in this paper, we provide an overview of known cometary analogues before presenting measurements of eight physical properties of different mixtures of the two materials and a comparison of these measurements with known cometary values. the physical properties of interest are particle size, density, gas permeability, spectrophotometry, and mechanical, thermal, and electrical properties. we found that the analogue dust that matches the highest number of physical properties of cometary materials consists of a mixture of either 60 per cent/40 per cent or 70 per cent/30 per cent of silica dust/charcoal by mass. these best-fit dust analogue will be used in future cophylab experiments. | cometary dust analogues for physics experiments |
the coma and the comet-solar wind interaction of comet 67p/churyumov-gerasimenko changed dramatically from the initial rosetta spacecraft encounter in 2014 august through perihelion in 2015 august. just before equinox (at 1.6 au from the sun), the solar wind signal disappeared and two regions of different cometary ion characteristics were observed. these 'outer' and 'inner' regions have cometary ion characteristics similar to outside and inside the ion pileup region observed during the giotto approach to comet 1p/halley. rosetta/double-focusing mass spectrometer ion mass spectrometer observations are used here to investigate the h3o+/h2o+ ratio in the outer and inner regions at 67p/ churyumov-gerasimenko. the h3o+/h2o+ ratio and the h3o+ signal are observed to increase in the transition from the outer to the inner region and the h3o+ signal appears to be weakly correlated with cometary ion energy. these ion composition changes are similar to the ones observed during the 1p/halley flyby. modelling is used to determine the importance of neutral composition and transport of neutrals and ions away from the nucleus. this modelling demonstrates that changes in the h3o+/h2o+ ratio appear to be driven largely by transport properties and only weakly by neutral composition in the coma. | ion chemistry in the coma of comet 67p near perihelion |
the inner structure of icy moons comprises ices, liquid water, a silicate rocky core and sometimes an inner metallic core depending on thermal evolution and differentiation. mineralogy and density models for the silicate part of the icy satellites cores were assessed assuming a carbonaceous chondritic (ci) bulk composition and using a free-energy minimization code and experiments. densities of other components, solid and liquid sulfides, carbonaceous matter, were evaluated from available equations of state. model densities for silicates are larger than assessed from magnesian terrestrial minerals, by 200 to 600 kg.m-3 for the hydrated silicates, and 300 to 500 kg.m-3 for the dry silicates, due to the high iron bulk concentration in ci. the stability of na-phlogopite in the silicate fraction up to 1300 k favors the trapping of most 40k in the rocky/carbonaceous cores with important consequences for modeling of the thermal evolution of icy satellites. we find that ci density models of icy satellite cores taking into account only the silicate and metal/sulfide fraction cannot account for the observed densities and reduced moment of inertia of titan and ganymede without adding a lower density component. we propose that this low-density component is carbonaceous matter derived from insoluble organic matter, in proportion of ∼30-40% in volume and 15-20% in mass. this proportion is compatible with contributions from ci and comets, making these primitive bodies including their carbonaceous matter component likely precursors of icy moons, and potentially of most of the objects formed behind the snow line of the solar system. | a carbonaceous chondrite and cometary origin for icy moons of jupiter and saturn |
residues of anti-neoplastic drugs represent new and emerging pollutants in aquatic environments. many of these drugs are genotoxic, and it has been postulated that they can cause adverse effects in aquatic ecosystems. 5-fluorouracil (5-fu) is one of the most extensively used anti-neoplastic drugs in cancer therapy, and this article describes the results of the first investigation using a two-generation toxicity study design with zebrafish (danio rerio). exposure of zebrafish to 5-fu (0.01, 1.0 and 100 μg/l) was initiated with adult zebrafish (f0 generation) and continued through the hatchings and adults of the f1 generation, and the hatchings of the f2 generation, to day 33 post-fertilisation. the exposure did not affect survival, growth and reproduction of the zebrafish; however, histopathological changes were observed in the liver and kidney, along with genotoxic effects, at all 5-fu concentrations. increases in dna damage determined using the comet assay were significant in the liver and blood cells, but not in the gills and gonads. in erythrocytes, a significant, dose-dependent increase in frequency of micronuclei was observed at all 5-fu concentrations. whole genome transcriptomic analysis of liver samples of f1 generation zebrafish exposed to 0.01 μg/l and 1 μg/l 5-fu revealed dose-dependent increases in the number of differentially expressed genes, including up-regulation of several dna-damage-responsive genes and oncogenes (i.e., jun, myca). although this chronic exposure to environmentally relevant concentrations of 5-fu did not affect the reproduction of the exposed zebrafish, it cannot be excluded that 5-fu can lead to degenerative changes, including cancers, which over long-term exposure of several generations might affect fish populations. the data from this study contribute to a better understanding of the potential consequences of chronic exposure of fish to low concentrations of anti-neoplastic drugs, and they demonstrate that further studies into multi-generation toxicity are needed. | assessment of toxicity and genotoxicity of low doses of 5-fluorouracil in zebrafish (danio rerio) two-generation study |
the astropause (heliopause for the sun) is the tangential discontinuity separating the stellar wind from the interstellar plasma. the global shape of the heliopause is a matter of debates. two types of the shape are under discussion: comet-like and tube-like. in the second type, the two-jets oriented towards the stellar rotation axis are formed by the action of azimuthal component of the stellar magnetic field. we explore a simplified global astrosphere in which (1) the surrounding and moving with respect to the star circumstellar medium is fully ionized, (2) the interstellar magnetic field is neglected, (3) the radial component of the stellar magnetic field is neglected as compared with the azimuthal component, and (4) the stellar wind outflow is spherically symmetric and supersonic. we present the results of numerical 3d mhd modelling and explore how the global structure depends on the gas-dynamic mach number of the interstellar flow, m∞, and the alfvenic mach number in the stellar wind. it is shown that the astropause has a tube-like shape for small values of m∞. the wings of the tube are distorted towards the tail as larger as larger the mach number is. the new (to our knowledge) result is the reverse interstellar flow in the vicinity of the astropause in the tail. the larger the interstellar mach number is the narrower the reverse flow is. at some values of the mach number, the stellar wind overcomes the reverse interstellar flow and moves out in downwind. in this regime, the astropause changes its topology from tube-like to sheet-like. | new unexpected flow patterns in the problem of the stellar wind interaction with the interstellar medium: stationary ideal-mhd solutions |
the astronomical detection of formamide (nh2cho) toward various star-forming regions and in cometary material implies that the simplest amide might have an early origin in dark molecular clouds at low temperatures. laboratory studies have proven the efficient nh2cho formation in interstellar co:nh3 ice analogs upon energetic processing. however, it is still under debate, whether the proposed radical-radical recombination reactions forming complex organic molecules remain valid in an abundant h2o environment. the aim of this work was to investigate the formation of nh2cho in h2o- and co-rich ices under conditions prevailing in molecular clouds. therefore, different ice mixtures composed of h2o:co:nh3 (10:5:1), co:nh3 (4:1), and co:nh3 (0.6:1) were exposed to vacuum ultraviolet photons in an ultra-high vacuum chamber at 10 k. fourier-transform infrared spectroscopy was utilized to monitor in situ the initial and newly formed species as a function of photon fluence. the infrared spectral identifications are complementarily secured by a temperature-programmed desorption experiment combined with a quadrupole mass spectrometer. the energetic processing of co:nh3 ice mixtures mainly leads to the formation of nh2cho, along with its chemical derivatives such as isocyanic acid (hnco) and cyanate ion (ocn-). the formation kinetics of nh2cho shows an explicit dependency on ice ratios and compositions; the highest yield is found in h2o-rich ice. the astronomical relevance of the resulting reaction network is discussed. | formation of the simplest amide in molecular clouds: formamide (nh2cho) and its derivatives in h2o-rich and co-rich interstellar ice analogs upon vuv irradiation |
gliese 710 is a k7v star located 19 pc from the sun in the constellation of serpens cauda, which is headed straight for the solar system. berski & dybczynski (2016) used data from gaia dr1 to show that this star will be 13366 au from the sun in 1.35 myr from now. here, we present an independent confirmation of this remarkable result using gaia dr2. our approach is first validated using as test case that of the closest known stellar flyby, by the binary wise j072003.20-084651.2 or scholz's star. our results confirm, within errors, those in berski & dybczynski (2016), but suggest a somewhat closer, both in terms of distance and time, flyby of gliese 710 to the solar system. such an interaction might not significantly affect the region inside 40 au as the gravitational coupling among the known planets against external perturbation can absorb efficiently such a perturbation, but it may trigger a major comet shower that will affect the inner solar system. | an independent confirmation of the future flyby of gliese 710 to the solar system using gaia dr2 |
evidence in radar, reflectance, and visible imagery indicates that surface and subsurface water ice is present inside permanently shadowed regions in the north polar region of mercury. the origin of this ice and the time at which it was delivered to the planet are both unknown. finding the smallest, most easily eroded ice deposits on mercury can help answer these questions. here we present evidence for volatiles trapped in cold traps of scales ∼ 1-10 m. we consider two possible delivery methods for these deposits: a gradual, slow accumulation by micrometeorites or solar wind implantation and an episodic deposition, either primordial or by a recent comet impact. we conclude that the mechanism that best explains the presence of volatiles in these micro cold traps is a comet impact that most likely occurred in the last ∼ 100 ma. | ice in micro cold traps on mercury: implications for age and origin |
methyl isocyanate (ch3nco) is one of the important complex organic molecules detected on the comet 67p/churyumov-gerasimenko by rosetta's philae lander. it was also detected in hot cores around high-mass protostars along with a recent detection in the solar-type protostar iras 16293-2422. we propose here a gas-grain chemical model to form ch3nco after reviewing various formation pathways with quantum chemical computations. we have used nautilus three-phase gas-grain chemical model to compare observed abundances in the iras 16293-2422. our chemical model clearly indicates the ice phase origin of ch3nco. | methyl isocyanate (ch3nco): an important missing organic in current astrochemical networks |
climate change due to global warming can alter the salinity and ph in aquatic ecosystems. low salinity (ls) and ocean acidification (oa) are stressors involved in osmotic regulation and can alter the antioxidant capacity of the body. in this study, we observed na+/k+-atpase (nka) expression and activity in disk abalone gill tissue and changes in hemolymph osmolarity in relation to osmotic regulation over a short period (5 days). to confirm the degree of oxidative stress caused by changes in salinity and ph, changes in h2o2 levels, reactive oxygen species (ros) levels, antioxidant enzyme (superoxide dismutase [sod] and catalase [cat]) expression, and caspase-7 expression were investigated at the molecular level. the degree of dna damage was evaluated using the comet assay. mrna expression, activity of gill nka, and osmolarity of the hemolymph were significantly decreased in the ls group. nonetheless, no noteworthy distinction was observed in mrna expression or nka activity between the control group and oa group. hemolymph h2o2 levels and mrna expression of sod, cat, and caspase-7 were significantly higher under the ls + oa condition than under single conditions of ls and oa. further, caspase-7 mrna expression and dna damage increased with increasing exposure time. the group exposed to ls + oa showed the highest levels of caspase-7 expression and dna damage. these results indicate that a combination of low salinity and ph induces more stress than a single condition does. unmanageable ros-mediated stress caused by environmental changes can lead to cell death and dna damage. | short-term exposure to combined condition of low salinity and ph affects ros-mediated stress in disk abalone (haliotis discus hannai) |
the nuclear-spin chemistry of interstellar water is investigated using the university of grenoble alpes astrochemical network (ugan). this network includes reactions involving the different nuclear-spin states of the hydrides of carbon, nitrogen, oxygen, and sulphur, as well as their deuterated forms. nuclear-spin selection rules are implemented within the scrambling hypothesis for reactions involving up to seven protons. the abundances and ortho-to-para ratios (oprs) of gas-phase water and water ions (h2o+ and h3o+) are computed under the steady-state conditions representative of a dark molecular cloud and during the early phase of gravitational collapse of a pre-stellar core. the model incorporates the freezing of the molecules on to grains, simple grain surface chemistry, and cosmic ray induced and direct desorption of ices. the predicted oprs are found to deviate significantly from both thermal and statistical values and to be independent of temperature below ∼30 k. the opr of h2o is shown to lie between 1.5 and 2.6, depending on the spin state of h2, in good agreement with values derived in translucent clouds with relatively high extinction. in the pre-stellar core-collapse calculations, the opr of h2o is shown to reach the statistical value of 3 in regions with severe depletion (nh > 107 cm-3). we conclude that a low water opr (≲ 2.5) is consistent with gas-phase ion-neutral chemistry and reflects a gas with opr(h2) ≲ 1. available opr measurements in protoplanetary discs and comets are finally discussed. | the ortho-to-para ratio of water in interstellar clouds |
the hdo/h2o ratio measured in interstellar gas is often used to draw conclusions on the formation and evolution of water in star-forming regions and, by comparison with cometary data, on the origin of water on earth. in cold cores and in the outer regions of protoplanetary disks, an important source of gas-phase water comes from photodesorption of water ice. this research note presents fitting formulae for implementation in astrochemical models using previously computed photodesorption efficiencies for all water ice isotopologues obtained with classical molecular dynamics simulations. the results are used to investigate to what extent the gas-phase hdo/h2o ratio reflects that present in the ice or whether fractionation can occur during the photodesorption process. probabilities for the top four monolayers are presented for photodesorption of x (x = h, d) atoms, ox radicals, and x2o and hdo molecules following photodissociation of h2o, d2o, and hdo in h2o amorphous ice at ice temperatures from 10-100 k. significant isotope effects are found for all possible products: (1) h atom photodesorption probabilities from h2o ice are larger than those for d atom photodesorption from d2o ice by a factor of 1.1; the ratio of h and d photodesorbed upon hdo photodissociation is a factor of 2. this process will enrich the ice in deuterium atoms over time; (2) the od/oh photodesorption ratio upon d2o and h2o photodissociation is on average a factor of 2, but the od/oh photodesorption ratio upon hdo photodissociation is almost constant at unity for all ice temperatures; (3) d atoms are more effective in kicking out neighbouring water molecules than h atoms. however, the ratio of the photodesorbed hdo and h2o molecules is equal to the hdo/h2o ratio in the ice, therefore, there is no isotope fractionation when hdo and h2o photodesorb from the ice. nevertheless, the enrichment of the ice in d atoms due to photodesorption can over time lead to an enhanced hdo/h2o ratio in the ice, and, when photodesorbed, also in the gas. the extent to which the ortho/para ratio of h2o can be modified by the photodesorption process is discussed briefly as well. appendices are available in electronic form at http://www.aanda.orgcompiled simulation data and raw data 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/575/a121 | photodesorption of h2o, hdo, and d2o ice and its impact on fractionation |
around the time of its perihelion passage, the observability of 67p/churyumov-gerasimenko from earth was limited to very short windows each morning from any given site, due to the low solar elongation of the comet. the peak in the comet's activity was therefore difficult to observe with conventionally scheduled telescopes, but was possible where service/queue-scheduled mode was possible, and with robotic telescopes. we describe the robotic observations that allowed us to measure the total activity of the comet around perihelion, via photometry (dust) and spectroscopy (gas), and compare these results with the measurements at this time by rosetta's instruments. the peak of activity occurred approximately two weeks after perihelion. the total brightness (dust) largely followed the predictions from snodgrass et al., with no significant change in total activity levels from previous apparitions. the cn gas production rate matched previous orbits near perihelion, but appeared to be relatively low later in the year. | the perihelion activity of comet 67p/churyumov-gerasimenko as seen by robotic telescopes |
context. during september and october 2014, the osiris cameras onboard the esa rosetta mission detected millions of single particles. many of these dust particlesappear as long tracks (due to both the dust proper motion and the spacecraft motion during the exposure time) with a clear brightness periodicity.aims: we interpret the observed periodic features as a rotational and translational motion of aspherical dust grains.methods: by counting the peaks of each track, we obtained statistics of a rotation frequency. we compared these results with the rotational frequency predicted by a model of aspherical dust grain dynamics in a model gas flow. by testing many possible sets of physical conditions and grain characteristics, we constrained the rotational properties of dust grains.results: we analyzed on the motion of rotating aspherical dust grains with different cross sections in flow conditions corresponding to the coma of 67p/churyumov-gerasimenko qualitatively and quantitatively. based on the osiris observations, we constrain the possible physical parameters of the grains. | rotating dust particles in the coma of comet 67p/churyumov-gerasimenko |
although a merging galaxy cluster is a useful laboratory to study many important astrophysical processes and fundamental physics, only limited interpretations are possible without careful analysis of the merger scenario. however, the study is demanding because a thorough comparison of multiwavelength observations with detailed numerical simulations is required. in this paper, we present such a study for the off-axis binary merger a115. the system possesses a number of remarkable observational features, but no convincing merger scenario explaining the shape and location of the radio relic in harmony with the orientation of the cometary x-ray tails has been presented. our hydrodynamical simulation with adaptive mesh refinement suggests that the cometary x-ray tail of a115 might be a slingshot tail that can arise ∼0.3 gyr after the impact, before the two subclusters reach their apocenters. this scenario can predict the location and orientation of the giant radio relic, which is parallel to the northern x-ray tail. in addition, our study indicates that diffusive shock acceleration alone cannot generate the observed radio power unless aided by stronger magnetic fields and/or more significant presence of fossil electrons. | reconstruction of radio relics and x-ray tails in an off-axis cluster merger: hydrodynamical simulations of a115 |
aims: interstellar objects passing through our solar system offer a rare opportunity to probe the physical and chemical processes involved in solid body and planet formation in extrasolar systems. the main objective of our study is to search for diagnostic absorption features of water ice in the near-infrared (nir) spectrum of the second interstellar object 2i/2019 q4 (borisov) and compare its ice features to those of the solar system icy objects.methods: we observed 2i in the nir on three separate occasions. the first observation was made on 2019 september 19 ut using the spex spectrograph at the 3m irtf and again on september 24 ut with the gnirs spectrograph at the 8m gemini telescope; the last observation was made on october 09 ut with irtf.results: the spectra obtained from all three nights appear featureless. no absorption features associated with water ice are detected. spectral modeling suggests that water grains, if present, comprise no more than 10% of the coma cross section. the comet consistently exhibits a red d-type like spectrum with a spectral slope of about 6% per 1000 å, which is similar to that of 1i/'oumuamua and is comparable to solar system comets. the spectra are also available at the cds via anonymous ftp to http://cdsarc.u-strasbg.fr (ftp://130.79.128.5) or via http://cdsarc.u-strasbg.fr/viz-bin/cat/j/a+a/634/l6 | searching for water ice in the coma of interstellar object 2i/borisov |
context. the optical properties of the second generation dust that we observe in debris disks remain quite elusive, whether it is the absorption efficiencies at millimeter wavelengths or the (un)polarized phase function at near-infrared wavelengths. thankfully, the same particles are experiencing forces that are size dependent (e.g., radiation pressure) and, with high angular resolution observations, we can take advantage of this natural spatial segregation.aims: observations at different wavelengths probe different ranges of sizes; millimeter observations trace the larger grains, while near-infrared observations are sensitive to the other extreme of the size distribution. consequently, there is a great synergy in combining both observational techniques to better constrain the optical properties of the particles.methods: we present a new approach to simultaneously model observations from"spectro-polarimetric high contrast exoplanet research" (sphere) and the"atacama large millimeter array" (alma) and apply it to the debris disk around hd 32297, putting the emphasis on the spatial distribution of the grains with different β values. this modeling approach requires few assumptions on the actual sizes of the particles and the interpretation can therefore be done a posteriori.results: we find that the alma observations are best reproduced with a combination of small and large β values (0.03 and 0.42) while the sphere observations require several intervals of β values. we discuss the nature of the halo previously reported in alma observations, and hypothesize it could be caused by over-abundant μm-sized particles (the over-abundance being the consequence of their extended lifetime). we modeled the polarized phase function at near-infrared wavelengths, and fluffy aggregates larger than a few μm provide the best solution.conclusions: comparing our results with comets of the solar system, we postulate that the particles released in the disk originate from rather pristine cometary bodies (to avoid compaction of the fluffy aggregates) and they are then set on highly eccentric orbits, which could explain the halo detected at long wavelengths. | the halo around hd 32297: μm-sized cometary dust |
in this chapter, we explore the origins of cometary material and discuss the clues cometary composition provides in the context of the origin of our solar system. the review focuses on both cometary refractory and volatile materials, which jointly provide crucial information about the processes that shaped the solar system into what it is today. both areas have significantly advanced over the past decade. we also view comets more broadly and discuss compositions considering laboratory studies of cometary materials, including interplanetary dust particles and meteoritic material that are potential cometary samples, along with meteorites, and in situ/remote studies of cometary comae. in our review, we focus on key areas from elemental/molecular compositions, isotopic ratios, carbonaceous and silicate refractories, short-lived radionuclides, and solar system dynamics that can be used as probes of the solar birth environment. we synthesize this data that points towards the birth of our solar system in a clustered star-forming environment. | interstellar heritage and the birth environment of the solar system |
Subsets and Splits
No community queries yet
The top public SQL queries from the community will appear here once available.