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in recent years, gas has been observed in an increasing number of debris discs, though its nature remains to be determined. here, we analyse co molecular excitation in optically thin debris discs, and search atacama large millimeter/submillimeter array (alma) cycle-0 data for co j = 3-2 emission in the fomalhaut ring. no significant line emission is observed; we set a 3σ upper limit on the integrated line flux of 0.16 jy km s-1. we show a significant dependence of the co excitation on the density of collisional partners n, on the gas kinetic temperature tk and on the ambient radiation field j, suggesting that assumptions widely used for protoplanetary discs (e.g. local thermodynamic equilibrium, lte) do not necessarily apply to their low density debris counterparts. when applied to the fomalhaut ring, we consider a primordial origin scenario where h2 dominates collisional excitation of co, and a secondary origin scenario dominated by e- and h2o. in either scenario, we obtain a strict upper limit on the co mass of 4.9 × 10-4 m⊕. this arises in the non-lte regime, where the excitation of the molecule is determined solely by the well-known radiation field. in the secondary scenario, assuming any co present to be in steady state allows us to set an upper limit of ∼55 per cent on the co/h2o ice ratio in the parent planetesimals. this could drop to ∼3 per cent if lte applies, covering the range observed in solar system comets (0.4-30 per cent). finally, in light of our analysis, we present prospects for co detection and characterization in debris discs with alma. | co mass upper limits in the fomalhaut ring - the importance of nlte excitation in debris discs and future prospects with alma |
in the advent of the rosetta arrival at the comet 67p/churyumov-gerasimenko, we present a global 3d hybrid simulation model of the cometary plasma interaction which resolves the innermost coma sufficiently. as rosetta will only provide local information, global simulations are required to put these local observations into a wider global perspective. in the selected scenario close to the perihelion, the gas production of the comet is large enough to trigger a cometary bow shock and a small diamagnetic cavity around the nucleus. the simulation reveals the presence of a cometary ionopause and a recombination layer, which is in general agreement with single-fluid mhd simulations. however, we found an asymmetry in the interaction region caused by the pick-up of the cometary ions, which effects all known boundaries. in addition, we study the velocity distributions of the ions and find the presence of three distinct populations of cometary ions at the inner boundaries. the bifurcation created in the ion energy spectrum might be observable by the instruments onboard the rosetta spacecraft. | dynamical features and spatial structures of the plasma interaction region of 67p/churyumov-gerasimenko and the solar wind |
one of the primary objectives of the rosetta plasma consortium, a suite of five plasma instruments on-board the rosetta spacecraft, is to observe the formation and evolution of plasma interaction regions at the comet 67p/churyumov-gerasimenko (67p/cg). observations made between 2015 april and 2016 february show that solar wind-cometary plasma interaction boundaries and regions formed around 2015 mid-april and lasted through early 2016 january. at least two regions were observed, separated by an ion-neutral collisionopause boundary. the inner region was located on the nucleus side of the boundary and was characterized by low-energy water-group ions, reduced magnetic field pileup and enhanced electron densities. the outer region was located outside of the boundary and was characterized by reduced electron densities, water-group ions that are accelerated to energies above 100 ev and enhanced magnetic field pileup compared to the inner region. the boundary discussed here is outside of the diamagnetic cavity and shows characteristics similar to observations made on-board the giotto spacecraft in the ion pileup region at 1p/halley. we find that the boundary is likely to be related to ion-neutral collisions and that its location is influenced by variability in the neutral density and the solar wind dynamic pressure. | rpc observation of the development and evolution of plasma interaction boundaries at 67p/churyumov-gerasimenko |
context. studying the coma environment of comet 67p/churyumov-gerasimenko (67p) is one of the primary scientific goals of the virtis experiment on the esa rosetta mission.aims: the distribution and variability of water vapour and carbon dioxide in the comet's coma are needed to estimate their production rate, abundances in the nucleus, and the spatial distribution of the active regions.methods: infrared emission lines from vibrational bands of water and carbon dioxide at 2.67 and 4.27 μm, respectively, were observed by the virtis-m imaging channel and mapped from close to the nucleus up to ~10 km altitude with a resolution of ~40 m/px. a dataset consisting of 74 observations in the 1-5 μm spectral range acquired from 8 to 14 april 2015 when 67p was at a heliocentric distance of 1.9 au is analysed in this work. a statistical correlation between the gas distribution and the surface's active regions was performed.results: the maximum h2o emission is observed within 3 km from the nucleus and is mainly concentrated above two active regions, aten-babi and seth-hapi, while the co2 distribution appears more uniform with significant emissions coming from both the "head" and southern latitude regions. in the equatorial region, the column densities of both species decrease with altitude, although co2 decreases more rapidly than h2o. the calculated co2/h2o column density ratios above aten-babi and seth-hapi are 2.4 ± 0.6% and 3.0 ± 0.7%, respectively. a value equal to 3.9 ± 1.0% is observed at equatorial latitudes in the region encompassing imothep.conclusions: virtis-m has mapped the distribution of water vapour and carbon dioxide around the nucleus of 67p with unprecedented spatial resolution. the different water and carbon dioxide outgassing above the surface, seen in the virtis-m data, might be indicative of a different thermal history of the northern and southern hemispheres of 67p. | water and carbon dioxide distribution in the 67p/churyumov-gerasimenko coma from virtis-m infrared observations |
interstellar boundary explorer (ibex) measurements of energetic neutral atoms (enas) from the heliotail show a multi-lobe structure of ena fluxes as a function of energy between ∼0.71 and 4.29 kev. below ∼2 kev, there is a single structure of enhanced ena fluxes centered near the downwind direction. above ∼2 kev, this structure separates into two lobes, one north and one south of the solar equatorial plane. ena flux from these two lobes can be interpreted as originating from the fast solar wind (sw) propagating through the inner heliosheath (ihs). alternatively, a recently published model of the heliosphere suggests that the heliotail may split into a “croissant-like” shape, and that such a geometry could be responsible for the heliotail ena feature. here we present results from a time-dependent simulation of the heliosphere that produces a comet-like heliotail, and show that the 11-year solar cycle leads to the formation of ena lobes with properties remarkably similar to those observed by ibex. the ena energy at which the north and south lobes appear suggests that the pickup ion (pui) temperature in the slow sw of the ihs is ∼107 k. moreover, we demonstrate that the extinction of puis by charge-exchange is an essential process required to create the observed global ena structure. while the shape and locations of the ena lobes as a function of energy are well reproduced by puis that cross the termination shock, the results appear to be sensitive to the form of the distribution of puis injected in the ihs. | structure of the heliotail from interstellar boundary explorer observations: implications for the 11-year solar cycle and pickup ions in the heliosheath |
in this work, we present results that simultaneously constrain the dust size distribution, dust-to-gas ratio, fraction of dust re-deposition, and total mass production rates for comet 67p/churyumov-gerasimenko. we use a 3d direct simulation monte carlo (dsmc) gas dynamics code to simulate the inner gas coma of the comet for the duration of the rosetta mission. the gas model is constrained by rosina/cops data. further, we simulate for different epochs the inner dust coma using a 3d dust dynamics code including gas drag and the nucleus' gravity. using advanced dust scattering properties these results are used to produce synthetic images that can be compared to the osiris data set. these simulations allow us to constrain the properties of the dust coma and the total gas and dust production rates. we determined a total volatile mass loss of (6.1 ± 1.5) \cdot 10^9~kg during the 2015 apparition. further, we found that power laws with q=3.7^{+0.57}_{-0.078} are consistent with the data. this results in a total of 5.1^{+6.0}_{-4.9}\cdot10^9~kg of dust being ejected from the nucleus surface, of which 4.4^{+4.9}_{-4.2}\cdot10^9~kg escape to space and 6.8^{+11}_{-6.8}\cdot10^8~kg (or an equivalent of 14^{+22}_{-14}~cm over the smooth regions) is re-deposited on the surface. this leads to a dust-to-gas ratio of 0.73^{+1.3}_{-0.70} for the escaping material and 0.84^{+1.6}_{-0.81} for the ejected material. we have further found that the smallest dust size must be strictly smaller than $\sim30\mu$m and nominally even smaller than $\sim12\mu$m. | the dust-to-gas ratio, size distribution, and dust fall-back fraction of comet 67p/churyumov-gerasimenko: inferences from linking the optical and dynamical properties of the inner comae. |
in the last few years, multiwavelength observations have revealed the ubiquity of gaps/rings in circumstellar discs. here we report the first alma observations of hd 92945 at 0.86 mm, which reveal a gap at about 73 ± 3 au within a broad disc of planetesimals that extends from 50 to 140 au. we find that the gap is 20^{+10}_{-8} au wide. if cleared by a planet in situ, this planet must be less massive than 0.6 mjup, or even lower if the gap was cleared by a planet that formed early in the protoplanetary disc and prevented planetesimal formation at that radius. by comparing opposite sides of the disc, we also find that the disc could be asymmetric. motivated by the asymmetry and the fact that planets might be more frequent closer to the star in exoplanetary systems, we show that the gap and asymmetry could be produced by two planets interior to the disc through secular resonances. these planets excite the eccentricity of bodies at specific disc locations, opening radial gaps in the planetesimal distribution. new observations are necessary to confirm if the disc is truly asymmetric, thus favouring the secular resonance model, or if the apparent asymmetry is due to a background galaxy, favouring the in situ planet scenario. finally, we also report the non-detection of co and hcn gas, confirming that no primordial gas is present. the co and hcn non-detections are consistent with the destruction of volatile-rich solar system-like comets. | a gap in hd 92945's broad planetesimal disc revealed by alma |
we present an investigation of the emission intensity of co2 and h2o and their distribution in the coma of 67p/ churyumov-gerasimenko obtained by the virtis-m imaging spectrometer on the rosetta mission. we analyze 4 data cubes from feb. 28, and 7 data cubes from april 27, 2015. for both data sets the spacecraft was at a sufficiently large distance from the comet to allow images of the whole nucleus and the surrounding coma. we find that unlike water which has a reasonably predictable behavior and correlates well with the solar illumination, co2 outgasses mostly in local regions or spots. furthermore for the data on april 27, the co2 evolves almost exclusively from the southern hemisphere, a region of the comet that has not received solar illumination since the comet's last perihelion passage. because co2 and h2o have such disparate origins, deriving mixing ratios from local column density measurements cannot provide a meaningful measurement of the co2/h2o ratio in the coma of the comet. we obtain total production rates of h2o and co2 by integrating the band intensity in an annulus surrounding the nucleus and obtain pro-forma production rate co2/h2o mixing ratios of ∼5.0% and ∼2.5% for feb. 28 and april 27, respectively. because of the highly variable nature of the co2 evolution from the surface we do not believe that these numbers are diagnostic of the comet's bulk co2/h2o composition. we believe that our investigation provides an explanation for the large observed variations reported in the literature for the co2/h2o production rate ratios. our mixing ratio maps indicate that, besides the difference in vapor pressure of the two gases, this ratio depends on the comet's rotational orientation combined with its complex geometric shape which can result in quite variable rates of erosion for different surface areas such as the northern and southern hemisphere. our annulus measurement for the total water production for feb. 28 at 2.21au from the sun is 2.5 × 1026 molecules/s while for april 27 at 1.76 au it is 4.65 × 1026. we find that about 83% of the h2o resides in the illuminated portion of our annulus and about 17% on the night side. we also make an attempt to obtain the fraction of the h2o production coming from the highly active neck of the comet versus the rest of the illuminated surface from the pole-on view of feb. 28 and estimate that about 60% of the h2o derives from the neck area. a rough estimate of the water surface evaporation rate of the illuminated nucleus for april 27 yields about 5 × 1019 molecules/s/m2. spatial radial profiles of h2o on april 27 on the illuminated side of the comet, extending from 1.78 to 6.47 km from the nucleus center, show that water follows model predictions quite well, with the gas accelerating as it expands into the coma. our dayside radial profile allows us to make an empirical determination of the expansion velocity of water. on the night side the spatial profile of water follows 1/ρ. the co2 profiles do not exhibit any acceleration into the coma but are closely matched by a 1/ρ profile. | investigation into the disparate origin of co2 and h2o outgassing for comet 67/p |
the rosetta mission provided detailed observations of the growth of a cavity in the solar wind around comet 67p/churyumov-gerasimenko. as the comet approached the sun, the plasma of cometary origin grew enough in density and size to present an obstacle to the solar wind. our results demonstrate how the initial slight perturbations of the solar wind prefigure the formation of a solar wind cavity, with a particular interest placed on the discontinuity (solar wind cavity boundary) passing over the spacecraft. the slowing down and heating of the solar wind can be followed and understood in terms of single particle motion. we propose a simple geometric illustration that accounts for the observations, and shows how a cometary magnetosphere is seeded from the gradual steepening of an initially slight solar wind perturbation. a perspective is given concerning the difference between the diamagnetic cavity and the solar wind cavity. | the birth and growth of a solar wind cavity around a comet - rosetta observations |
the environment of a comet is a fascinating and unique laboratory to study plasma processes and the formation of structures such as shocks and discontinuities from electron scales to ion scales and above. the european space agency's rosetta mission collected data for more than two years, from the rendezvous with comet 67p/churyumov-gerasimenko in august 2014 until the final touch-down of the spacecraft end of september 2016. this escort phase spanned a large arc of the comet's orbit around the sun, including its perihelion and corresponding to heliocentric distances between 3.8 au and 1.24 au. the length of the active mission together with this span in heliocentric and cometocentric distances make the rosetta data set unique and much richer than sets obtained with previous cometary probes. here, we review the results from the rosetta mission that pertain to the plasma environment. we detail all known sources and losses of the plasma and typical processes within it. the findings from in-situ plasma measurements are complemented by remote observations of emissions from the plasma. overviews of the methods and instruments used in the study are given as well as a short review of the rosetta mission. the long duration of the rosetta mission provides the opportunity to better understand how the importance of these processes changes depending on parameters like the outgassing rate and the solar wind conditions. we discuss how the shape and existence of large scale structures depend on these parameters and how the plasma within different regions of the plasma environment can be characterised. we end with a non-exhaustive list of still open questions, as well as suggestions on how to answer them in the future. | the plasma environment of comet 67p/churyumov-gerasimenko |
the rosetta orbiter spectrometer for ion and neutral analysis (rosina) suite of instruments operated throughout the over two years of the rosetta mission operations in the vicinity of comet 67p/churyumov-gerasimenko. it measured gas densities and composition throughout the comet's atmosphere, or coma. here we present two-years' worth of measurements of the relative densities of the four major volatile species in the coma of the comet, h2o, co2, co and o2, by one of the rosina sub-systems called the double focusing mass spectrometer (dfms). the absolute total gas densities were provided by the comet pressure sensor (cops), another rosina sub-system. dfms is a very high mass resolution and high sensitivity mass spectrometer able to resolve at a tiny fraction of an atomic mass unit. we have analyzed the combined dfms and cops measurements using an inversion scheme based on spherical harmonics that solves for the distribution of potential surface activity of each species as the comet rotates, changing solar illumination, over short time intervals and as the comet changes distance from the sun and orientation of its spin axis over long time intervals. we also use the surface boundary conditions derived from the inversion scheme to simulate the whole coma with our fully kinetic direct simulation monte carlo model and calculate the production rates of the four major species throughout the mission. we compare the derived production rates with revised remote sensing observations by the visible and infrared thermal imaging spectrometer (virtis) as well as with published observations from the microwave instrument for the rosetta orbiter (miro). finally we use the variation of the surface production of the major species to calculate the total mass loss over the mission and, for different estimates of the dust/gas ratio, calculate the variation of surface loss all over the nucleus. | the surface distributions of the production of the major volatile species, h2o, co2, co and o2, from the nucleus of comet 67p/churyumov-gerasimenko throughout the rosetta mission as measured by the rosina double focusing mass spectrometer |
solar wind turbulence within high-speed streams is reviewed from the point of view of embedded single nonlinear alfvén wave cycles, discontinuities, magnetic decreases (mds), and shocks. for comparison and guidance, cometary plasma turbulence is also briefly reviewed. it is demonstrated that cometary nonlinear magnetosonic waves phase-steepen, with a right-hand circular polarized foreshortened front and an elongated, compressive trailing edge. the former part is a form of "wave breaking" and the latter that of "period doubling." interplanetary nonlinear alfvén waves, which are arc polarized, have a 180° foreshortened front and with an elongated trailing edge. alfvén waves have polarizations different from those of cometary magnetosonic waves, indicating that helicity is a durable feature of plasma turbulence. interplanetary alfvén waves are noted to be spherical waves, suggesting the possibility of additional local generation. they kinetically dissipate, forming mds, indicating that the solar wind is partially "compressive" and static. the 2 mev protons can nonresonantly interact with mds leading to rapid cross-field ( 5.5% bohm) diffusion. the possibility of local ( 1 au) generation of alfvén waves may make it difficult to forecast high-intensity, long-duration ae activity and relativistic magnetospheric electrons with great accuracy. the future solar orbiter and solar probe plus missions should be able to not only test these ideas but to also extend our knowledge of plasma turbulence evolution. | a review of alfvénic turbulence in high-speed solar wind streams: hints from cometary plasma turbulence |
many existing optical meteor trajectory estimation methods use the approximation that the velocity of the meteor at the beginning of its luminous phase is equivalent to its velocity before atmospheric entry. meteoroid kinetic energy loss prior to the luminous phase cannot be measured, but for some masses and entry geometries neglecting this loss may lead to non-negligible deceleration prior to thermal ablation. using a numerical meteoroid ablation model, we simulate the kinematics of meteoroids beginning at 180 km with initial velocities ranging from 11 km s-1 to 71 km s-1, and compare model velocities at the moment of detection to measurements. we validate the simulations by comparing the simulated luminous beginning heights with observed beginning heights of different populations of meteors detected with different optical systems. we find that most low-velocity meteoroids have a significant velocity difference of 100 m s-1 to 750 m s-1 (depending on meteoroid type, mass, and observation system). this systematic underestimate of meteoroid speeds also results in systematically lower semimajor axes for meteoroid orbits. | modelling the measurement accuracy of pre-atmosphere velocities of meteoroids |
the role of radiation pressure in shaping exoplanet photoevaporation remains a topic of contention. radiation pressure from the exoplanet's host star has been proposed as a mechanism to drive the escaping atmosphere into a 'cometary' tail and explain the high velocities observed in systems where mass-loss is occurring. in this paper, we present results from high-resolution 3d hydrodynamic simulations of a planet similar to hd 209458b. we self-consistently launch a wind flowing outwards from the planet by calculating the ionization and heating resulting from incident high-energy radiation, and account for radiation pressure. we first present a simplified calculation, setting a limit on the lyman-α flux required to drive the photoevaporated planetary material to larger radii and line-of-sight velocities. we then present the results of our simulations, which confirm the limits determined by our analytic calculation. we thus demonstrate that, within the limits of our hydrodynamic simulation and for the lyman-α fluxes expected for hd 209458, radiation pressure is unlikely to significantly affect photoevaporative winds or to explain the high velocities at which wind material is observed, though further possibilities remain to be investigated. | effects of radiation pressure on the evaporative wind of hd 209458b |
when viewed from earth, most of what we observe of a comet is dust. the influence of solar radiation pressure on the trajectories of dust particles depends on their cross-section to mass ratio. hence solar radiation pressure acts like a mass spectrometer inside a cometary tail. the appearances of cometary dust tails have long been studied to obtain information on the dust properties, such as characteristic particle size and initial velocity when entering the tail. over the past two decades, several spacecraft missions to comets have enabled us to study the dust activity of their targets at much greater resolution than is possible with a telescope on earth or in near-earth space, and added detail to the results obtained by the spacecraft visiting comet 1p/halley in 1986. we now know that the dynamics of dust in the inner cometary coma is complex and includes a significant fraction of particles that will eventually fall back to the surface. the filamented structure of the near-surface coma is thought to result from a combination of topographic focussing of the gas flow, inhomogeneous distribution of activity across the surface, and projection effects. it is possible that some larger-than-centimetre debris contains ice when lifted from the surface, which can affect its motion. open questions remain regarding the microphysics of the process that leads to the detachment and lifting of dust from the surface, the evolution of the dust while travelling away from the nucleus, and the extent to which information on the nucleus activity can be retrieved from remote observations of the outer coma and tail. | dust emission and dynamics |
alignment of dust grains in astrophysical environments results in the polarization of starlight as well as the polarization of radiation emitted by dust. we demonstrate the advances in grain alignment theory that allow the use of linear and circular polarization to probe not only the magnetic field, but also dust composition, the dust environment, etc. we revisit the process of grain alignment by radiative torques (rats) and focus on constraining magnetic susceptibility of grains via observations. we discuss the possibility of observational testing of the magnetic properties of grains as the alignment changes from being in respect to the magnetic field to being in respect to the radiation direction. this both opens a possibility of constraining the uncertain parameters of the rats theory and provides a new way of measuring magnetic fields in the interstellar medium and circumstellar regions. we provide a detailed discussion of the precession induced both by the magnetic field and the anisotropic radiation and revisit a number of key processes related to magnetic response of the grains. we consider various effects that increase the rate of magnetic relaxation both in silicate and carbonaceous grains. in particular, we find a new relaxation process related to the change of the amplitude of internal magnetization within a wobbling triaxial grain and identify a range of grain sizes in which this effect can dominate the internal alignment of angular momentum within grain axes. we show that these relaxation processes significantly change the dynamics of grains in the presence of rats. we apply our analysis for observed grain alignment in special environments to put constraints on the enhanced magnetic properties of dust grains in the cloud near supernovae, in cometary coma, and protoplanetary disks. | magnetic properties of dust grains, effect of precession, and radiative torque alignment |
we present hubble space telescope observations of a photometric outburst and splitting event in interstellar comet 2i/borisov. the outburst, first reported with the comet outbound at ∼2.8 au, was caused by the expulsion of solid particles having a combined cross section ∼100 km2 and a mass in 0.1 mm sized particles ∼2 × 107 kg. the latter corresponds to ∼10-4 of the mass of the nucleus, taken as a sphere of radius 500 m. a transient "double nucleus" was observed on ut 2020 march 30 (about 3 weeks after the outburst), having a cross section ∼0.6 km2 and corresponding dust mass ∼105 kg. the secondary was absent in images taken on and before march 28 and in images taken on and after april 3. the unexpectedly delayed appearance and rapid disappearance of the secondary are consistent with an origin through rotational bursting of one or more large (meter-sized) boulders under the action of outgassing torques, following their ejection from the main nucleus. overall, our observations reveal that the outburst and splitting of the nucleus are minor events involving a negligible fraction of the total mass: 2i/borisov will survive its passage through the planetary region largely unscathed. | outburst and splitting of interstellar comet 2i/borisov |
optical observations of the oort cloud comet c/2017 k2 (panstarrs) show that its activity began at large heliocentric distances (up to 35 au), which cannot be explained by either the sublimation or the crystallization of water ice. supervolatile sublimation, most likely of carbon monoxide (co), has been proposed as a plausible driver of the observed mass loss. here, we present the detection of the j = 2-1 rotational transition in outgassed co from c/2017 k2 when at heliocentric distance rh = 6.72 au, using the james clerk maxwell telescope. the co line is blueshifted by 0.20 ± 0.03 km s-1 with an area and width of 8.3 ± 2.3 mk km s-1 and 0.28 ± 0.08 km s-1, respectively. the co production rate is qco = (1.6 ± 0.5) × 1027 s-1. these are the first observations of a gaseous species in c/2017 k2 and provide observational confirmation of the role of supervolatile sublimation in this comet. | discovery of carbon monoxide in distant comet c/2017 k2 (panstarrs) |
1i/'oumuamua (or 1i) and 2i/borisov (or 2i), the first interstellar objects (isos) discovered passing through the solar system, have opened up entirely new areas of exobody research. finding additional isos and planning missions to intercept or rendezvous with these bodies will greatly benefit from knowledge of their likely orbits and arrival rates. here, we use the local velocity distribution of stars from the gaia early data release 3 catalogue of nearby stars and a standard gravitational focusing model to predict the velocity dependent flux of isos entering the solar system. with an 1i-type iso number density of $\sim$0.1 au$^{-3}$, we predict that a total of $\sim$6.9 such objects per year should pass within 1 au of the sun. there will be a fairly large high-velocity tail to this flux, with half of the incoming isos predicted to have a velocity at infinity, v$_{\infty}$, $>$ 40 km s$^{-1}$. our model predicts that $\sim$92\% of incoming isos will be residents of the galactic thin disk, $\sim$6\% ($\sim$4 per decade) will be from the thick disk, $\sim$1 per decade will be from the halo and at most $\sim$3 per century will be unbound objects, ejected from our galaxy or entering the milky way from another galaxy. the rate of isos with very low v$_{\infty}$ $\lesssim$ 1.5 km s$^{-1}$ is so low in our model that any incoming very low velocity isos are likely to be previously lost solar system objects. finally, we estimate a cometary iso number density of $\sim$7 $\times$ 10$^{-5}$ au$^{-3}$ for 2i type isos, leading to discovery rates for these objects possibly approaching once per decade with future telescopic surveys. | interstellar objects in the solar system: 1. isotropic kinematics from the gaia early data release 3 |
a large quantity of ch4 is emitted to the atmosphere via ventilation shafts of underground coal mines. according to the european pollutant release and transfer register (e-prtr), hard coal mines in the upper silesia coal basin (uscb) are a strong contributor (447 kt ch4 in 2017) to the annual european ch4 emissions. however, atmospheric emissions of ch4 from coal mines are poorly characterized, as they are dispersed over large areas. as part of the carbon dioxide and ch4 mission (comet) pre-campaign, a study of the uscb's regional ch4 emissions took place in august 2017. we flew a recently developed active aircore system aboard an unmanned aerial vehicle (uav) to obtain ch4 mole fractions downwind of a single coal mining ventilation shaft. besides ch4, we also measured co2, co, atmospheric temperature, pressure, and relative humidity. wind-speed and wind-direction measurements were made using a lightweight balloon-borne radiosonde. fifteen uav flights were performed flying perpendicular to the wind direction at several altitude levels, to effectively build a 'curtain' of ch4 mole fractions in a two-dimensional plane at a distance between 150 and 350 m downwind of a single ventilation shaft. furthermore, we have developed an inverse gaussian approach for quantifying ch4 emissions from a point source using the uav-based observations, and have applied it as well as the mass balance approach to both simulated data and actual flight data to quantify ch4 emissions. the simulated data experiments revealed the importance of having multiple transects at different altitudes, appropriate vertical spacing between the individual transects, and proper distance between the center height of the plume and the center flight transect. they also showed that the inverse gaussian approach performed better than the mass balance approach. our estimate of the ch4 emission rates from the sampled shaft ranges from 0.5 to 14.5 kt/year using a mass balance approach, and between 1.1 and 9.0 kt/year using an inverse gaussian method. the average difference between the mass balance and the inverse gaussian approach was 2.3 kt/year. based on the observed correlation between co2 and ch4 (r-squared > 0.69), the co2 emissions from the shaft were estimated to be between 0.3 and 9.8 kt/year. this study demonstrates that the uav-based active aircore system provides an effective way of quantifying coal mining shaft emissions of ch4 and co2. | quantifying methane emissions from coal mining ventilation shafts using an unmanned aerial vehicle (uav)-based active aircore system |
the rosetta spacecraft has escorted comet 67p/churyumov-gerasimenko since 6 august 2014 and has offered an unprecedented opportunity to study plasma physics in the coma. we have used this opportunity to make the first characterization of cometary electrons with kappa distributions. two three-dimensional kappa functions were fit to the observations, which we interpret as two populations of dense and warm (density = 10 cm-3, temperature = 2 × 105 k, invariant kappa index = 10->1000), and rarefied and hot (density = 0.005 cm-3, temperature = 5 × 105 k, invariant kappa index = 1-10) electrons. we fit the observations on 30 october 2014 when rosetta was 20 km from 67p, and 3 au from the sun. we repeated the analysis on 15 august 2015 when rosetta was 300 km from the comet and 1.3 au from the sun. comparing the measurements on both days gives the first comparison of the cometary electron environment between a nearly inactive comet far from the sun and an active comet near perihelion. we find that the warm population density increased by a factor of 3, while the temperature cooled by a factor of 2, and the invariant kappa index was unaffected. we find that the hot population density increased by a factor of 10, while the temperature and invariant kappa index were unchanged. we conclude that the hot population is likely the solar wind halo electrons in the coma. the warm population is likely of cometary origin, but its mechanism for production is not known. | characterizing cometary electrons with kappa distributions |
using a 3d fully kinetic approach, we disentangle and explain the ion and electron dynamics of the solar wind interaction with a weakly outgassing comet. we show that, to first order, the dynamical interaction is representative of a four-fluid coupled system. we self-consistently simulate and identify the origin of the warm and suprathermal electron distributions observed by esa's rosetta mission to comet 67p/churyumov-gerasimenko and conclude that a detailed kinetic treatment of the electron dynamics is critical to fully capture the complex physics of mass-loading plasmas. | electron and ion dynamics of the solar wind interaction with a weakly outgassing comet |
context. unlike all previous cometary space missions, the rosetta spacecraft accompanied its target, comet 67p/churyumov-gerasimenko, for more than two years on its way around the sun. thereby, an unexpected diversity and complexity of the chemical composition was revealed.aims: our first step of decrypting the exact chemical composition of the gaseous phase is the identifying and quantifying the bulk composition of the pure aromatic and aliphatic hydrocarbons.methods: for this study, data from rosina-double focusing mass spectrometer (dfms) onboard the rosetta spacecraft and the laboratory twin model were used. a joint campaign of laboratory calibration measurements and space data analysis was performed to derive the hydrocarbon bulk composition for the post-inbound equinox period at 1.52 au in may 2015. furthermore, several other mission phases were investigated to determine the dependencies of season, location, and heliocentric distance on the relative abundances of hydrocarbons.results: it is shown that the bulk composition of the gaseous phase includes a high number of aliphatic compounds such as methane, ethane, and propane, as well as the aromatic compounds benzene and toluene. butane and pentane were successfully identified in measurements at closer distance to the comet in may 2016. furthermore, the presence of hexane and heptane in the coma is confirmed on rare occasions during the mission. their presence in dfms space data appears to be linked to days or periods of high dust activity. in addition to the saturated aliphatic and aromatic compounds, a high number of remaining unsaturated species is present, which cannot be explained by fragmentation of saturated species or contribution from other organic molecules in addition to pure hydrocarbons. this indicates the existence of unsaturated aliphatic and aromatic hydrocarbon molecules in the coma of comet 67p. | aliphatic and aromatic hydrocarbons in comet 67p/churyumov-gerasimenko seen by rosina |
the european space agency's spacecraft rosetta has reached its final destination, comet 67p/churyumov-gerasimenko. whilst orbiting in the close vicinity of the nucleus the rosetta magnetometers detected a new type of low-frequency wave possibly generated by a cross-field current instability due to freshly ionized cometary water group particles. during separation, descent and landing of the lander philae on comet 67p/churyumov-gerasimenko, we used the unique opportunity to perform combined measurements with the magnetometers onboard rosetta (rpcmag) and its lander philae (romap). new details about the spatial distribution of wave properties along the connection line of the rosetta orbiter and the lander philae are revealed. an estimation of the observed amplitude, phase and wavelength distribution will be presented as well as the measured dispersion relation, characterizing the new type of low-frequency waves. the propagation direction and polarization features will be discussed using the results of a minimum variance analysis. thoughts about the size of the wave source will complete our study. | two-point observations of low-frequency waves at 67p/churyumov-gerasimenko during the descent of philae: comparison of rpcmag and romap |
chondritic porous interplanetary dust particles (cp idps) collected in the stratosphere are regarded as possibly being cometary dust, and are therefore the most primitive solar system material that is currently available for analysis in laboratories. in this paper we report the discovery of more than 40 chondritic porous micrometeorites (cp mms) in the surface snow and blue ice of antarctica, which are indistinguishable from cp idps. the cp mms are botryoidal aggregates, composed mainly of sub-micrometer-sized constituents. they contain two components that characterize them as cp idps: enstatite whiskers and gems (glass with embedded metal and sulfides). enstatite whiskers appear as <2-μm-long acicular objects that are attached on, or protrude from the surface, and when included in the interior of the cp mms are composed of a unit-cell scale mixture of clino- and ortho-enstatite, and elongated along the [100] direction. gems appear as 100-500 nm spheroidal objects containing <50 nm fe-ni metal and fe sulfide. the cp mms also contain low-iron-manganese-enriched (lime) and low-iron-chromium-enriched (lice) ferromagnesian silicates, kosmochlor (nacrsi2o6)-rich high-ca pyroxene, roedderite (k, na)2mg5si12o30, and carbonaceous nanoglobules. these components have previously been discovered in primitive solar system materials such as the cp idps, matrices of primitive chondrites, phyllosilicate-rich mms, ultracarbonaceous mms, and cometary particles recovered from the 81p/wild 2 comet. the most outstanding feature of these cp mms is the presence of kosmochlor-rich high-ca pyroxene and roedderite, which suggest that they have building blocks in common with cp idps and cometary dust particles and therefore suggest a possible cometary origin of both cp mms and cp idps. it is therefore considered that cp mms are cp idps that have fallen to earth and have survived the terrestrial environment. | cometary dust in antarctic ice and snow: past and present chondritic porous micrometeorites preserved on the earth's surface |
the optical, spectroscopic, and infrared remote imaging system (osiris) experiment onboard the rosetta spacecraft currently orbiting comet 67p/churyumov-gerasimenko has yielded unprecedented views of a comet's nucleus. we present here the first ever observations of meter-scale fractures on the surface of a comet. some of these fractures form polygonal networks. we present an initial assessment of their morphology, topology, and regional distribution. fractures are ubiquitous on the surface of the comet's nucleus. furthermore, they occur in various settings and show different topologies suggesting numerous formation mechanisms, which include thermal insulation weathering, orbital-induced stresses, and possibly seasonal thermal contraction. however, we conclude that thermal insolation weathering is responsible for creating most of the observed fractures based on their morphology and setting in addition to thermal models that indicate diurnal temperature ranges exceeding 200 k and thermal gradients of ~15 k/min at perihelion are possible. finally, we suggest that fractures could be a facilitator in surface evolution and long-term erosion. | fractures on comet 67p/churyumov-gerasimenko observed by rosetta/osiris |
the apparition of bright comets c/2012 f6 (lemmon) and c/2014 q2 (lovejoy) in march-april 2013 and january 2015, combined with the improved observational capabilities of submillimeter facilities, offered an opportunity to carry out sensitive compositional and isotopic studies of the volatiles in their coma. we observed comet lovejoy with the iram 30 m telescope between 13 and 26 january 2015, and with the odin submillimeter space observatory on 29 january-3 february 2015. we detected 22 molecules and several isotopologues. the h216o and h218o production rates measured with odin follow a periodic pattern with a period of 0.94 days and an amplitude of ~25%. the inferred isotope ratios in comet lovejoy are 16o/18o = 499 ± 24 and d/h = 1.4 ± 0.4 × 10-4 in water, 32s/34s = 24.7 ± 3.5 in cs, all compatible with terrestrial values. the ratio 12c/13c = 109 ± 14 in hcn is marginally higher than terrestrial and 14n/15n = 145 ± 12 in hcn is half the earth ratio. several upper limits for d/h or 12c/13c in other molecules are reported. from our observation of hdo in comet c/2014 q2 (lovejoy), we report the first d/h ratio in an oort cloud comet that is not larger than the terrestrial value. on the other hand, the observation of the same hdo line in the other oort-cloud comet, c/2012 f6 (lemmon), suggests a d/h value four times higher. given the previous measurements of d/h in cometary water, this illustrates that a diversity in the d/h ratio and in the chemical composition, is present even within the same dynamical group of comets, suggesting that current dynamical groups contain comets formed at very different places or times in the early solar system. based on observations carried out with the iram 30 m telescope. iram is supported by insu/cnrs (france), mpg (germany) and ign (spain).odin is a swedish-led satellite project funded jointly by the swedish national space board (snsb), the canadian space agency (csa), the national technology agency of finland (tekes) and the centre national d'études spatiales (cnes, france). the swedish space corporation is the prime contractor, also responsible for odin operations.the spectra dataset is only available at the cds via anonymous ftp to http://cdsarc.u-strasbg.fr (ftp://130.79.128.5) or via http://cdsarc.u-strasbg.fr/viz-bin/qcat?j/a+a/589/a78 | isotopic ratios of h, c, n, o, and s in comets c/2012 f6 (lemmon) and c/2014 q2 (lovejoy) |
complex organic molecules (coms) can be produced by energetic processing of interstellar ice mantles accreted on top of dust grains. two coms with proposed energetic ice formation pathways are formamide and acetaldehyde. both have been detected in solar system comets and in different circumstellar and interstellar environments. in this work, we study the nh2cho and ch3cho formation upon uv photoprocessing of co:nh3 and co:ch4 ice samples. the conversion from ${\mathrm{nh}}_{\dot{2}}$ radicals to nh2cho is 2-16 times higher than the conversion from ${\mathrm{ch}}_{\dot{3}}$ radicals to ch3cho under the explored experimental conditions, likely because the formation of the latter competes with the formation of larger hydrocarbons. in addition, the conversion of ${\mathrm{nh}}_{\dot{2}}$ into nh2cho at 10 k increases with the nh3 abundance in the ice, and also with the temperature in co-dominated co:nh3 ices. this is consistent with the presence of a small ${\mathrm{nh}}_{\dot{2}}$ and hco. reorientation barrier for the formation of nh2cho, which is overcome with an increase in the ice temperature. the measured nh2cho and ch3cho formation efficiencies and rates are similar to those found during electron irradiation of the same ice samples under comparable conditions, suggesting that both uv photons and cosmic rays would have similar contributions to the solid-state formation of these species in space. finally, the measured conversion yields (up to one order of magnitude higher for nh2cho) suggest that in circumstellar environments, where the observed nh2cho/ch3cho abundance ratio is ∼0.1, there are likely additional ice and/or gas-phase formation pathways for ch3cho. | formation of nh2cho and ch3cho upon uv photoprocessing of interstellar ice analogs |
the composition of comets in the solar system comes in multiple groups thought to encode information about their formation in different regions of the outer protosolar disk. the recent discovery of the second interstellar object, 2i/borisov, allows for spectroscopic investigations into its gas content and a preliminary classification of it within the solar system comet taxonomies to test the applicability of planetesimal formation models to other stellar systems. we present spectroscopic and imaging observations from 2019 september 20 through october 26 from the bok, mmt telescope (formerly the multiple mirror telescope, mount hopkins, arizona), and large binocular telescopes. we identify cn in the comet's spectrum and set precise upper limits on the abundance of c2 on all dates in october. we use a haser model to convert our integrated fluxes to production rates and find q(cn) = (1.1-1.9) ∗ 1024 mols s-1 increasing over 2019 october 1 to 26, consistent with contemporaneous observations. we set our lowest upper limit on a c2 production rate, q(c2) < 1.6 ∗ 1023 mols s-1 on 2019 october 10. the measured upper limit ratio for that date q(c2)/q(cn) < 0.1 indicates that 2i/borisov is strongly in the (carbon-chain) "depleted" taxonomic group if there is any c2 production at all. most "depleted" comets are jupiter-family comets (jfcs), perhaps indicating a similarity in formation conditions between the most depleted of the jfcs and 2i/borisov. more work is needed to understand the applicability of our knowledge of solar system comet taxonomies onto interstellar objects and we discuss future work that could help to clarify the usefulness of the approach. | carbon chain depletion of 2i/borisov |
we review multiwavelength properties of pulsar wind nebulae created by supersonically moving pulsars and the effects of pulsar motion on the pulsar wind nebulae morphologies and the ambient medium. supersonic pulsar wind nebulae are characterized by bow-shaped shocks around the pulsar and/or cometary tails filled with the shocked pulsar wind. in the past several years significant advances in supersonic pulsar wind nebula studies have been made in deep observations with the chandra and xmm-newton x-ray observatories and the hubble space telescope. in particular, these observations have revealed very diverse supersonic pulsar wind nebula morphologies in the pulsar vicinity, different spectral behaviours of long pulsar tails, the presence of puzzling outflows misaligned with the pulsar velocity and far-uv bow shocks. here we review the current observational status focusing on recent developments and their implications. | pulsar wind nebulae created by fast-moving pulsars |
on 2016 feb 19, nine rosetta instruments serendipitously observed an outburst of gas and dust from the nucleus of comet 67p/churyumov-gerasimenko. among these instruments were cameras and spectrometers ranging from uv over visible to microwave wavelengths, in situ gas, dust and plasma instruments, and one dust collector. at 09:40 a dust cloud developed at the edge of an image in the shadowed region of the nucleus. over the next two hours the instruments recorded a signature of the outburst that significantly exceeded the background. the enhancement ranged from 50 per cent of the neutral gas density at rosetta to factors >100 of the brightness of the coma near the nucleus. dust related phenomena (dust counts or brightness due to illuminated dust) showed the strongest enhancements (factors >10). however, even the electron density at rosetta increased by a factor 3 and consequently the spacecraft potential changed from ∼-16 v to -20 v during the outburst. a clear sequence of events was observed at the distance of rosetta (34 km from the nucleus): within 15 min the star tracker camera detected fast particles (∼25 m s-1) while 100 μm radius particles were detected by the giada dust instrument ∼1 h later at a speed of 6 m s-1. the slowest were individual mm to cm sized grains observed by the osiris cameras. although the outburst originated just outside the fov of the instruments, the source region and the magnitude of the outburst could be determined. | the 2016 feb 19 outburst of comet 67p/cg: an esa rosetta multi-instrument study |
we present the discovery of seven new proplyds (i.e., sources surrounded by cometary hα emission characteristic of offset ionization fronts (ifs)) in ngc 1977, located about 30‧ north of the orion nebula cluster (onc) at a distance of ∼400 pc. each of these proplyds is situated at projected distances 0.04-0.27 pc from the b1v star 42 orionis (c ori), which is the main source of uv photons in the region. in all cases the ifs of the proplyds are clearly pointing toward the common ionizing source, 42 ori, and six of the seven proplyds clearly show tails pointing away from it. these are the first proplyds to be found around a b star, with previously known examples instead being located around o stars, including those in the onc around θ 1 ori c. the radii of the offset ifs in our proplyds are between ∼200 and 550 au two objects also contain clearly resolved central sources that we associate with disks of radii 50-70 au. the estimated strength of the fuv radiation field impinging on the proplyds is around 10-30 times less than that incident on the classic proplyds in the onc. we show that the observed proplyd sizes are however consistent with recent models for fuv photoevaporation in relatively weak fuv radiation fields. | proplyds around a b1 star: 42 orionis in ngc 1977 |
multi-unit spectroscopic explorer (muse) observations of the cluster of galaxies cgr32 (m200 ≃ 2 × 1014 m⊙) at z = 0.73 reveal the presence of two massive star-forming galaxies with extended tails of diffuse gas detected in the [o ii]λλ3727-3729 å emission-line doublet. the tails, which have a cometary shape with a typical surface brightness of a few 10-18 erg s-1 cm-2 arcsec-2, extend up to ≃100 kpc (projected distance) from the galaxy discs, and are not associated with any stellar component. all this observational evidence suggests that the gas was removed during a ram-pressure stripping event. this observation is thus the first evidence that dynamical interactions with the intracluster medium were active when the universe was only half its present age. the density of the gas derived using the observed [o ii]λ3729/[o ii]λ3726 line ratio implies a very short recombination time, suggesting that a source of ionisation is necessary to keep the gas ionised within the tail. the reduced datacube is 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/631/a114 based on observations made with eso telescopes at the paranal observatory under programmes 097.a-0254, 100.a-0607, 101.a-0282. | evidence for ram-pressure stripping in a cluster of galaxies at z = 0.7 |
an important tracer of the origin and evolution of cometary ices is the comparison with ices found in dense clouds and toward young stellar objects (ysos). we present a survey of ices in the 2-5 μm spectra of 23 massive ysos, taken with the nasa infrared telescope facility spex spectrometer. the 4.90 μm absorption band of ocs ice is detected in 20 sight lines, more than 5 times the previously known detections. the absorption profile shows little variation and is consistent with ocs embedded in ch3oh-rich ices, and proton-irradiated h2s or so2-containing ices. the ocs column densities correlate well with those of ch3oh and ocn-, but not with h2o and apolar co ice. this association of ocs with ch3oh and ocn- firmly establishes their formation location deep inside dense clouds or protostellar envelopes. the median composition of this ice phase toward massive ysos, as a percentage of h2o, is co:ch3oh:ocn-:ocs = 24:20:1.53:0.15. cs, due to its low abundance, is likely not the main precursor to ocs. sulfurization of co is likely needed, although the source of this sulfur is not well constrained. compared to massive ysos, low-mass ysos and dense clouds have similar or somewhat lower co and ch3oh ice abundances, but less ocn- and more apolar co, while ocs awaits detection. comets tend to be underabundant in carbon-bearing species, but this does not appear to be the case for ocs, perhaps signalling ocs production in protoplanetary disks. | survey of ices toward massive young stellar objects. i. ocs, co, ocn-, and ch3oh |
questions regarding how primordial or pristine the comets of the solar system are have been an ongoing controversy. in this review, we describe comets' physical evolution from dust and ice grains in the solar nebula to the contemporary small bodies in the outer solar system. this includes the phases of dust agglomeration, the formation of planetesimals, their thermal evolution and the outcomes of collisional processes. we use empirical evidence about comets, in particular from the rosetta mission to comet 67p/churyumov–gerasimenko, to draw conclusions about the possible thermal and collisional evolution of comets. | formation of comets |
close encounters of stars to the sun could affect life on earth through gravitational perturbations of comets in the oort cloud or exposure to ionizing radiation. by integrating orbits through the galactic potential, i identify which of 33 million stars in gaia dr3 with complete phase space information come close to the sun. 61 stars formally approach within 1 pc, although there is high confidence in only 42 (two thirds) of these, the rest being spurious measurements or (in) binary systems. most of the stars will encounter within the past or future 6 myr; earlier/later encounters are less common due to the magnitude limit of the gaia radial velocities (rvs). several close encountering stars are identified for the first time, and the encounter times, distances, and velocities of previously known close encounters are determined more precisely on account of the significantly improved precision of gaia dr3 over earlier releases. the k7 dwarf gl 710 remains the closest known encounter, with an estimated (median) encounter distance of 0.0636 pc (90% confidence interval 0.0595-0.0678 pc) to take place in 1.3 myr. the new second closest encounter took place 2.8 myr ago: this was the g3 dwarf hd 7977, now 76 pc away, which approached within less than 0.05 pc of the sun with a probability of one third. the apparent close encounter of the white dwarf upm j0812-3529 is probably spurious due to an incorrect rv in gaia dr3. | stars that approach within one parsec of the sun: new and more accurate encounters identified in gaia data release 3 |
context. the esa rosetta spacecraft has been orbiting the nucleus of comet 67p/churyumov-gerasimenko since august 2014. the rotation axis of the irregularly shaped nucleus has a large obliquity (52°) and is oriented such that the southern hemisphere is insolated during perihelion.aims: we calculate the change in the rotation period as a function of the cometary orbital position due to forces exerted by cometary activity.methods: we used a detailed shape model of 67p with >105 facets. we calculated the efficiency of the facets to exert a torque based on their radial distance from the center of mass and their orientation. we applied our thermal model to calculate the diurnal water-ice sublimation rate from each facet. the reaction force per facet combined with its torque efficiency creates a torque and changes the angular momentum. the component of the torque parallel to the spin axis changes the rotation period.results: our model shows that the rotation period increases slightly during the approach of the comet to the sun. it reaches a maximum shortly before equinox and drops rapidly during perihelion passage. the magnitude of the change depends on the actual sublimation rates. the change in sign mainly depends on the shape of the nucleus and not much on the sublimation variation. the roughness of the nucleus has little influence.conclusions: for the given geometry of the rotation axis, the change in the rotation period is mainly influenced by the sublimation activity of the irregular shape of the nucleus. the rotation period increases until shortly before equinox in early may 2015, in good agreement with observations, and will then become shorter rapidly. | the changing rotation period of comet 67p/churyumov-gerasimenko controlled by its activity |
rosetta and philae have been in hibernation until january 20, 2014. after the successful wakeup they underwent a post-hibernation commissioning. the orbiter instruments (like e.g. the osiris cameras, virtis, miro, alice and rosina) characterized the target comet and its environment to allow landing site selection and the definition of a separation, descent and landing (sdl) strategy for the lander. by september 2014 our previously poor knowledge of the characteristics of the nucleus of the comet has increased drastically and the nominal and backup landing could be selected. the nominal site, as well as the corresponding descent strategy have been confirmed in mid-october, one month before the landing. the paper summarizes the selection process for a landing site and the planning for separation-descent-landing (sdl). | rosetta lander - philae: landing preparations |
the esa's comet chaser rosetta has monitored the evolution of the ionized atmosphere of comet 67p/churyumov-gerasimenko (67p/cg) and its interaction with the solar wind, during more than 2 yr. around perihelion, while the cometary outgassing rate was highest, rosetta crossed hundreds of unmagnetized regions, but did not seem to have crossed a large-scale diamagnetic cavity as anticipated. using in situ rosetta observations, we characterize the structure of the unmagnetized plasma found around comet 67p/cg. plasma density measurements from rpc-mip are analysed in the unmagnetized regions identified with rpc-mag. the plasma observations are discussed in the context of the cometary escaping neutral atmosphere, observed by rosina/cops. the plasma density in the different diamagnetic regions crossed by rosetta ranges from ∼100 to ∼1500 cm-3. they exhibit a remarkably systematic behaviour that essentially depends on the comet activity and the cometary ionosphere expansion. an effective total ionization frequency is obtained from in situ observations during the high outgassing activity phase of comet 67p/cg. although several diamagnetic regions have been crossed over a large range of distances to the comet nucleus (from 50 to 400 km) and to the sun (1.25-2.4 au), in situ observations give strong evidence for a single diamagnetic region, located close to the electron exobase. moreover, the observations are consistent with an unstable contact surface that can locally extend up to about 10 times the electron exobase. | diamagnetic region(s): structure of the unmagnetized plasma around comet 67p/cg |
dust-acoustic (da) solitary and periodic waves investigations were performed in a magnetized self-gravitating dusty plasma consisting of negatively and positively charged dust grains in the presence of inertialess ions and electrons. the korteweg-de vries-burger (kdvb) equation has been derived. the numerical investigations revealed the compressive or rarefactive da solitons depending on the plasma parameters. the nonlinear homoclinic and periodic trajectories from the kdvb equation were obtained for the phase portrait profiles when employing the phase plane theory of dynamical systems. the periodic wave solution depends also on the system parameters. the present results are considered to be beneficial in understanding the nonlinear structures in experimental devices and different astrophysical environments such as the earth's mesosphere, cometary tails, and jupiter's magnetosphere. | dust-acoustic solitary and periodic waves in magnetized self-gravito-electrostatic opposite polarity dusty plasmas |
knowledge of the surface temperature distribution on a comet's nucleus and its temporal evolution at different timescales is key to constraining its thermophysical properties and understanding the physical processes that take place at and below the surface. here we report on time-resolved maps of comet 67p/churyumov-gerasimenko retrieved on the basis of infrared data acquired by the visible infrared and thermal imaging spectrometer (virtis) onboard the rosetta orbiter in 2014, over a roughly two-month period in the pre-perihelion phase at heliocentric distances between 3.62 and 3.31 au from the sun. we find that at a spatial resolution ≤15 m per pixel, the measured temperatures point out the major effect that self-heating, due to the complex shape of the nucleus, has on the diurnal temperature variation. the bilobate nucleus of comet 67p also induces daytime shadowing effects, which result in large thermal gradients. over longer periods, virtis-derived temperature values reveal seasonal changes driven by decreasing heliocentric distance combined with an increasing abundance of ice within the uppermost centimetre-thick layer, which implies the possibility of having a largely pristine nucleus interior already in the shallow subsurface. | the changing temperature of the nucleus of comet 67p induced by morphological and seasonal effects |
in 2017, 2018, and 2019, comets 46p/wirtanen, 45p/honda-mrkos-pajdusakova, and 41p/tuttle-giacobini-kresak all had perihelion passages. their hydrogen comae were observed by the solar wind anisotropies (swan) all-sky hydrogen lyα camera on the solar and heliospheric observer (soho) satellite: comet 46p for the fourth time and comets 45p and 41p for the third time each since 1997. comet 46p/wirtanen is one of a small class of so-called hyperactive comets whose gas production rates belie their small size. this comet was the original target comet of the rosetta mission. the swan all-sky hydrogen lyα camera on the soho satellite observed the hydrogen coma of comet 46p/wirtanen during the apparitions of 1997, 2002, 2008, and 2018. over the 22 yr, the activity decreased and its variation with heliocentric distance has changed markedly in a way very similar to that of another hyperactive comet, 103p/hartley 2. comet 45p/honda-mrkos-pajdusakova was observed by swan during its perihelion apparitions of 2001, 2011, and 2017. over this time period, the activity level has remained remarkably similar, with no long-term fading or abrupt decreases. comet 41p/tuttle-giacobini-kresak was observed by swan in its perihelion apparitions of 2001, 2006, and 2017 and has decreased in activity markedly over the same time period. in 1973 it was known for large outbursts, which continued during the 2001 (two outbursts) and 2006 (one outburst) apparitions. however, over the 2001 to 2017 time period covered by the soho/swan observations the water production rates have greatly decreased by factors of 10-30 over corresponding times during its orbit. | comet 41p/tuttle-giacobini-kresak, 45p/honda-mrkos-pajdusakova, and 46p/wirtanen: water production activity over 21 yr with soho/swan |
context. early measurements of rosetta's target comet, 67p/churyumov-gerasimenko (67p), showed a strongly heterogeneous coma in h2o, co, and co2.aims: the purpose of this work is to further investigate the coma heterogeneity of 67p, and to provide predictions for the near-perihelion outgassing profile based on the proposed explanations.methods: measurements of various minor volatile species by rosina/dfms on board rosetta are examined. the analysis focuses on the currently poorly illuminated winter (southern) hemisphere of 67p.results: coma heterogeneity is not limited to the major outgassing species. minor species show better correlation with either h2o or co2. the molecule ch4 shows a different diurnal pattern from all other analyzed species. such features have implications for nucleus heterogeneity and thermal processing.conclusions: future analysis of additional volatiles and modeling the heterogeneity are required to better understand the observed coma profile. | composition-dependent outgassing of comet 67p/churyumov-gerasimenko from rosina/dfms. implications for nucleus heterogeneity? |
context. isotopic abundances in comets are key to understanding and reconstructing the history and origin of material in the solar system. data for deuterium-to-hydrogen (d/h) ratios in water are available for several comets. however, no long-term studies of the d/h ratio in water of a comet during its passage around the sun have been reported thus far. linear alkanes are important organic molecules that have been found on several solar system bodies, including comets. to date, the processes of their deuteration are still poorly understood, only the upper limits of isotopic ratios for d/h and 13c/12c in linear alkanes are currently available.aims: the aim of this work is to carry out a detailed analysis of the d/h ratio in water as a function of cometary activity and spacecraft location above the nucleus. in addition, a first determination of the d/h and 13c/12c ratios in the first four linear alkanes, namely, methane (ch4), ethane (c2h6), propane (c3h8), and butane (c4h10) in the coma of 67p/churyumov-gerasimenko is provided.methods: we analysed in situ measurements from the rosetta/rosina double focusing mass spectrometer (dfms).results: the d/h ratio from hdo/h2o and the 16o/17o ratio from h216o/h217o did not change during 67p's passage around the sun between 2014 and 2016. all d/h ratio measurements were compatible within 1σ, with the mean value of 5.01 × 10−4 and its relative variation of 2.0%. this suggests that the d/h ratio in 67p's coma is independent of heliocentric distance, level of cometary activity, or spacecraft location with respect to the nucleus. additionally, the 16o/17o ratio could be determined with a higher accuracy than previously possible, yielding a value of 2347 with a relative variation of 2.3%. for the alkanes, the d/h ratio is between 4.1 and 4.8 times higher than in h2o, while the 13c/12c ratio is compatible, within the uncertainties, with the available data for other solar system objects. the relatively high d/h ratio in alkanes is in line with results for other cometary organic molecules and it suggests that these organics may be inherited from the presolar molecular cloud from which the solar system formed. | high d/h ratios in water and alkanes in comet 67p/churyumov-gerasimenko measured with rosetta/rosina dfms |
in this study, afm1 toxicity and the protective role of trans-resveratrol (t-rsv) against this toxicity were investigated with the help of multiple parameters in albino mice. as a result, afm1 (16 mg/kg b.w) administration caused a decrease in body, kidney and liver weights. this reduction was associated with a decrease in feed consumption. afm1 induced an increase in ast and alt enzyme parameters and bun, creatinine and mda levels and a decrease in gsh levels. these increases have been associated with liver and kidney cell damage. afm1 decreased mi and encouraged increases in mn and cas numbers. the decrease in mi was correlated with afm1-tubulin and the increase in cas was associated with the afm1-dna interaction, which was demonstrated by molecular docking and spectral shifting. besides, the decrease in dna damage and amount was demonstrated by the comet assay technique. administration of t-rsv (10 and 20 mg/kg b.w) reduced the toxic effects of afm1 and caused a dose-dependent improvement in all physiological, biochemical and cytogenetic parameter values studied. for this reason, foods containing t-rsv or food supplements should be consumed in the daily diet to reduce the effect of toxic agents. | toxicity mechanisms of aflatoxin m1 assisted with molecular docking and the toxicity-limiting role of trans-resveratrol |
context. osiris, the scientific imaging system onboard the esa rosetta spacecraft, has been imaging the nucleus of comet 67p/churyumov-gerasimenko and its dust and gas environment since march 2014. the images serve different scientific goals, from morphology and composition studies of the nucleus surface, to the motion and trajectories of dust grains, the general structure of the dust coma, the morphology and intensity of jets, gas distribution, mass loss, and dust and gas production rates.aims: we present the calibration of the raw images taken by osiris and address the accuracy that we can expect in our scientific results based on the accuracy of the calibration steps that we have performed.methods: we describe the pipeline that has been developed to automatically calibrate the osiris images. through a series of steps, radiometrically calibrated and distortion corrected images are produced and can be used for scientific studies. calibration campaigns were run on the ground before launch and throughout the years in flight to determine the parameters that are used to calibrate the images and to verify their evolution with time. we describe how these parameters were determined and we address their accuracy.results: we provide a guideline to the level of trust that can be put into the various studies performed with osiris images, based on the accuracy of the image calibration. | scientific assessment of the quality of osiris images |
1i/’oumuamua is the first interstellar interloper to have been detected. because planetesimal formation and ejection of predominantly icy objects are common by-products of the star and planet formation processes, in this study we address whether 1i/’oumuamua could be representative of this background population of ejected objects. the purpose of the study of its origin is that it could provide information about the building blocks of planets in a size range that remains elusive to observations, helping to constrain planet formation models. we compare the mass density of interstellar objects inferred from its detection to that expected from planetesimal disks under two scenarios: circumstellar disks around single stars and wide binaries, and circumbinary disks around tight binaries. our study makes use of a detailed study of the panstarrs survey volume; takes into account that the contribution from each star to the population of interstellar planetesimals depends on stellar mass, binarity, and planet presence; and explores a wide range of possible size distributions for the ejected planetesimals, based on solar system models and observations of its small-body population. we find that 1i/’oumuamua is unlikely to be representative of a population of isotropically distributed objects, favoring the scenario that it originated from the planetesimal disk of a young nearby star whose remnants are highly anisotropic. finally, we compare the fluxes of meteorites and micrometeorites observed on earth to those inferred from this population of interstellar objects, concluding that it is unlikely that one of these objects is already part of the collected meteorite samples. | origin of 1i/’oumuamua. i. an ejected protoplanetary disk object? |
millimeter observations of co gas in planetesimal belts show a high detection rate around a stars, but few detections for later type stars. we present the first co detection in a planetesimal belt around an m star, twa 7. the optically thin co (j = 3-2) emission is colocated with previously identified dust emission from the belt, and the emission velocity structure is consistent with keplerian rotation around the central star. the detected co is not well shielded against photodissociation, and must thus be continuously replenished by gas release from exocomets within the belt. we analyze in detail the process of exocometary gas release and destruction around young m dwarfs and how this process compares to earlier type stars. taking these differences into account, we find that co generation through exocometary gas release naturally explains the increasing co detection rates with stellar luminosity, mostly because the co production rate from the collisional cascade is directly proportional to stellar luminosity. more luminous stars will therefore on average host more massive (and hence more easily detectable) exocometary co disks, leading to the higher detection rates observed. the current co detection rates are consistent with a ubiquitous release of exocometary gas in planetesimal belts, independent of spectral type. | on the ubiquity and stellar luminosity dependence of exocometary co gas: detection around m dwarf twa 7 |
we introduce a new technique to estimate the comet nuclear size frequency distribution (sfd) that combines a cometary activity model with a survey simulation and apply it to 150 long period comets (lpc) detected by the pan-starrs1 near-earth object survey. the debiased lpc size-frequency distribution is in agreement with previous estimates for large comets with nuclear diameter ≳1 km but we measure a significant drop in the sfd slope for small objects with diameters <1 km and approaching only 100 m diameter. large objects have a slope αbig = 0.72 ± 0.09(stat.) ± 0.15(sys.) while small objects behave as αsmall = 0.07 ± 0.03(stat.) ± 0.09(sys.) where the sfd is ∝ 10 αhn and hn represents the cometary nuclear absolute magnitude. the total number of lpcs that are >1 km diameter and have perihelia q < 10 au is 0.46 ± 0.15 × 109 while there are only 2.4 ± 0.5(stat.) ± 2(sys.) × 109 objects with diameters >100 m due to the shallow slope of the sfd for diameters <1 km. we estimate that the total number of 'potentially active' objects with diameters ≥1 km in the oort cloud, objects that would be defined as lpcs if their perihelia evolved to <10 au, is (1.5 ± 1) × 1012 with a combined mass of 1.3 ± 0.9 m⊕. the debiased lpc orbit distribution is broadly in agreement with expectations from contemporary dynamical models but there are discrepancies that could point towards a future ability to disentangle the relative importance of stellar perturbations and galactic tides in producing the lpc population. | the orbit and size-frequency distribution of long period comets observed by pan-starrs1 |
most models of volatile delivery to accreting terrestrial planets assume that the carriers for water are similar in water content to the carbonaceous chondrites in our solar system. here we consider how the water content of planetesimals may be higher in many planetary systems, as they could lack the short-lived radionuclides that drove water loss in carbonaceous chondrites in our solar system. using n-body simulations, we explore how planetary accretion would be different if bodies beyond the water line contained a water-mass fraction consistent with chemical equilibrium calculations, and more similar to comets, as opposed to the more traditional water-depleted values. we apply this model to consider planet formation around stars of different masses and identify trends in the properties of habitable zone planets and planetary system architecture that could be tested by ongoing exoplanet census data collection. comparison of such data with the model-predicted trends will serve to evaluate how well the n-body simulations and the initial conditions used in studies of planetary accretion can be used to understand this stage of planet formation. | volatile delivery to planets from water-rich planetesimals around low mass stars |
long and short-term exposure to atmospheric particulate matter (pm) has detrimental effects on human health. the effective mechanisms leading to pm toxicity are still not fully understood, even if it is known that physical-chemical properties, strongly influenced by sources and atmospheric processes, are known to play an important role. in this work, pm10 samples were collected, at an urban background site in southern italy, to determine cytotoxicity (using mtt test on a549 cells), genotoxicity (using the comet assay), and intracellular oxidative stress on a549 cells exposed for 24 h to aqueous extracts of pm10 samples. organic carbon (oc) and elemental carbon (ec) content of pm10 and acellular determination of oxidative potential with dtt assay were performed to compare results of acellular and cellular biological assays. cellular (osgcv and mttv) and acellular (opdttv) outcomes, normalized in volume, are well correlated (statistically significant results) with carbon content suggesting that combustion sources play an important role in determining cellular oxidative stress and cytotoxicity of pm10. even if the number of data is limited, genotoxicity results are well correlated (pearson r > 0.95) with osgcv and mttv, and a weaker, but statistically significant correlation was observed with opdttv. osgcv is well correlated with the cell mortality observed with the mttv test and a lower, but still statistically significant correlation is observed between mttv and opddtv. a statistically significant correlation was found between opdttv and osgcv results. when the outcomes of the cellular and acellular assay are compared normalized in mass (i.e., intrinsic values), the correlations become significantly weaker suggesting that the different sources acting on the site produces particulate matter with different toxicological potential influencing differently the biological tests studied. | oxidative potential, cytotoxicity, and intracellular oxidative stress generating capacity of pm10: a case study in south of italy |
cometary nuclei imaged from flyby and rendezvous spacecraft show common evidence of layered structures and bilobed shapes. but how and when these features formed is much debated, with distinct implications for solar system formation, dynamics, and geology. we show that these features could be a direct result of accretionary collisions, based on three-dimensional impact simulations using realistic constitutive properties. we identify two regimes of interest: layer-forming splats and mergers resulting in bilobed shapes. for bodies with low tensile strength, our results can explain key morphologies of cometary nuclei, as well as their low bulk densities. this advances the hypothesis that nuclei formed by collisional coagulation—either out of cometesimals accreting in the early solar system or, alternatively, out of comparable-sized debris clumps paired in the aftermath of major collisions. | the shape and structure of cometary nuclei as a result of low-velocity accretion |
we review our current knowledge of comet 67p/churyumov-gerasimenko nucleus composition as inferred from measurements made by remote sensing and in-situ instruments aboard rosetta orbiter and philae lander. spectrophotometric properties (albedos, color indexes and hapke parameters) of 67p/cg derived by rosetta are discussed in the context of other comets previously explored by space missions. composed of an assemblage made of ices, organic materials and minerals, cometary nuclei exhibit very dark and red surfaces which can be described by means of spectrophotometric quantities and reproduced with laboratory measurements. the presence of surface water and carbon dioxide ices was found by rosetta to occur at localized sites where the activity driven by solar input, gaseous condensation or exposure of pristine inner layers can maintain these species on the surface. apart from these specific areas, 67p/cg's surface appears remarkably uniform in composition with a predominance of organic materials and minerals. the organic compounds contain abundant hydroxyl group and a refractory macromolecular material bearing aliphatic and aromatic hydrocarbons. the mineral components are compatible with a mixture of silicates and fine-grained opaques, including fe-sulfides, like troilite and pyrrhotite, and ammoniated salts. in the vicinity of the perihelion several active phenomena, including the erosion of surface layers, the localized activity in cliffs, fractures and pits, the collapse of overhangs and walls, the transfer and redeposition of dust, cause the evolution of the different regions of the nucleus by inducing color, composition and texture changes. | comet 67p/cg nucleus composition and comparison to other comets |
1i/’oumuamua is the first detected interstellar interloper. we test the hypothesis that it is representative of a background population of exo-oort cloud objects ejected under the effect of post-main sequence mass loss and stellar encounters. we do this by comparing the cumulative number density of interstellar objects inferred from the detection of 1i/’oumuamua to that expected from these two clearing processes. we consider the 0.08-8 m ⊙ mass range, take into account the dependencies with stellar mass, galactocentric distance, and evolutionary state, and consider a wide range of size distributions for the ejected objects. our conclusion is that 1i/’oumuamua is likely not representative of this background population, even though there are large uncertainties in the masses and size distributions of the exo-oort clouds. we discuss whether the number density of free-floating, planetary-mass objects derived from gravitational microlensing surveys could be used as a discriminating measurement regarding 1i/’oumuamua’s origin (given their potential common origin). we conclude that this is challenged by the mass limitation of the surveys and the resulting uncertainty of the mass distribution of the free floaters. the detection of interlopers may be one of the few observational constraints of the small end of this population, with the caveat that, as we conclude here and in moro-martín (2018), in the case of 1i/’oumuamua, it might not be appropriate to assume this object is representative of an isotropic background population, which makes the derivation of a number density very challenging. | origin of 1i/’oumuamua. ii. an ejected exo-oort cloud object? |
we present multiwavelength, ground-based follow-up photometry of the white dwarf wd 1145+017, which has recently been suggested to be orbited by up to six or more short-period, low-mass, disintegrating planetesimals. we detect nine significant dips in flux of between 10% and 30% of the stellar flux in our ∼32 hr of photometry, suggesting that wd 1145+017 is indeed being orbited by multiple, short-period objects. through fits to the asymmetric transits that we observe, we confirm that the transit egress is usually longer than the ingress, and that the transit duration is longer than expected for a solid body at these short periods, all suggesting that these objects have cometary tails streaming behind them. the precise orbital periods of the planetesimals are unclear, but at least one object, and likely more, have orbital periods of ∼4.5 hr. we are otherwise unable to confirm the specific periods that have been reported, bringing into question the long-term stability of these periods. our high-precision photometry also displays low-amplitude variations, suggesting that dusty material is consistently passing in front of the white dwarf, either from discarded material from these disintegrating planetesimals or from the detected dusty debris disk. we compare the transit depths in the v- and r-bands of our multiwavelength photometry, and find no significant difference; therefore, for likely compositions, the radius of single-size particles in the cometary tails streaming behind the planetesimals must be ∼0.15 μm or larger, or ∼0.06 μm or smaller, with 2σ confidence. | multiwavelength transit observations of the candidate disintegrating planetesimals orbiting wd 1145+017 |
the solar wind anisotropies (swan) instrument on the solar and heliospheric observatory (soho) satellite has observed 44 long period and new oort cloud comets and 36 apparitions of 17 short period comets since its launch in december 1995. water production rates have been determined from the over 3700 images producing a consistent set of activity variations over large parts of each comet's orbit. this has enabled the calculation of exponential power-law variations with heliocentric distance of these comets both before and after perihelion, as well as the absolute values of the water production rates. these various measures of overall water activity including pre- and post-perihelion exponents, absolute water production rates at 1 au, active surface areas and their variations have been compared with a number of dynamical quantities for each comet including dynamical class, original semi-major axis, nucleus radius (when available), and compositional taxonomic class. evidence for evolution of cometary nuclei is seen in both long-period and short-period comets. | a survey of water production in 61 comets from soho/swan observations of hydrogen lyman-alpha: twenty-one years 1996-2016 |
knowledge of the mechanical properties of protoplanetary and cometary matter is of key importance to better understand the activity of comets and the early stages of planet formation. the tensile strength determines the required pressure to lift off grains, pebbles, and agglomerates from the cometary surface and also describes how much strain a macroscopic body can withstand before material failure occurs. as organic materials are ubiquitous in space, they could have played an important role during the planet-formation process. this work provides new data on the tensile strength of five different microgranular organic materials, namely, humic acid, paraffin, brown coal, charcoal, and graphite. these materials are investigated by the so-called brazilian disc test and the resulting tensile strength values are normalized to a standard grain size and volume filling factor. we find that the tensile strength of these materials ranges over four orders of magnitude. graphite and paraffin possess tensile strengths much higher than silica, whereas coals have very low tensile-strength values. this work demonstrates that organic materials are not generally stickier than silicates, or water ice, as often believed. | sticky or not sticky? measurements of the tensile strength of microgranular organic materials |
in a previous work [asymptotically quasiperiodic solutions for time-dependent hamiltonians, arxiv preprint arxiv:2211.06623 (2022)], we consider time-dependent perturbations of a hamiltonian vector field having an invariant torus supporting quasiperiodic solutions. assuming the perturbation decays polynomially fast as time tends to infinity, we prove the existence of a non-autonomous kam torus. a non-autonomous kam torus is a time-dependent family of embedded tori converging in time to the invariant torus associated with the unperturbed system. in the first part of the present work, we generalise this theorem to the case where the time decay is weaker but always polynomial, as it appears naturally in physical problems. this requires the introduction of a generalization of the definition of non-autonomous kam torus. the proof relies on a nash-moser theorem. in the second part, we apply this new theorem to the example of the planar three-body problem perturbed by a given comet coming from and going back to infinity asymptotically along a hyperbolic keplerian orbit. | weakly asymptotically quasiperiodic solutions for time-dependent hamiltonians with a view to celestial mechanics |
power plants and large industrial facilities contribute more than half of global anthropogenic co2 emissions. quantifying the emissions of these point sources is therefore one of the main goals of the planned constellation of anthropogenic co2 monitoring satellites (co2m) of the european copernicus program. atmospheric transport models may be used to study the capabilities of such satellites through observing system simulation experiments and to quantify emissions in an inverse modeling framework. how realistically the co2 plumes of power plants can be simulated and how strongly the results may depend on model type and resolution, however, is not well known due to a lack of observations available for benchmarking. here, we use the unique data set of aircraft in situ and remote sensing observations collected during the comet (carbon dioxide and methane mission) measurement campaign downwind of the coal-fired power plants at bełchatów in poland and jänschwalde in germany in 2018 to evaluate the simulations of six different atmospheric transport models. the models include three large-eddy simulation (les) models, two mesoscale numerical weather prediction (nwp) models extended for atmospheric tracer transport, and one lagrangian particle dispersion model (lpdm) and cover a wide range of model resolutions from 200 m to 2 km horizontal grid spacing. at the time of the aircraft measurements between late morning and early afternoon, the simulated plumes were slightly (at jänschwalde) to highly (at bełchatów) turbulent, consistent with the observations, and extended over the whole depth of the atmospheric boundary layer (abl; up to 1800 m a.s.l. (above sea level) in the case of bełchatów). the stochastic nature of turbulent plumes puts fundamental limitations on a point-by-point comparison between simulations and observations. therefore, the evaluation focused on statistical properties such as plume amplitude and width as a function of distance from the source. les and nwp models showed similar performance and sometimes remarkable agreement with the observations when operated at a comparable resolution. the lagrangian model, which was the only model driven by winds observed from the aircraft, quite accurately captured the location of the plumes but generally underestimated their width. a resolution of 1 km or better appears to be necessary to realistically capture turbulent plume structures. at a coarser resolution, the plumes disperse too quickly, especially in the near-field range (0-8 km from the source), and turbulent structures are increasingly smoothed out. total vertical columns are easier to simulate accurately than the vertical distribution of co2, since the latter is critically affected by profiles of vertical stability, especially near the top of the abl. cross-sectional flux and integrated mass enhancement methods applied to synthetic co2m data generated from the model simulations with a random noise of 0.5-1.0 ppm (parts per million) suggest that emissions from a power plant like bełchatów can be estimated with an accuracy of about 20 % from single overpasses. estimates of the effective wind speed are a critical input for these methods. wind speeds in the middle of the abl appear to be a good approximation for plumes in a well-mixed abl, as encountered during comet. | evaluation of simulated co2 power plant plumes from six high-resolution atmospheric transport models |
the dynamics and collisions of dust acoustic (da) shock excitations traveling in opposite directions are theoretically investigated in a three-dimensional self-gravitating magnetized electron-depleted dusty plasma whose ingredients are extremely warm positively and negatively charged massive dust grains as well as ions that follow the q-nonextensive distribution. a linear analysis and the extended poincare-lighthill-kuo method are used to derive the dispersion relation, the two-sided korteweg-de vries burgers equations, and the phase shift that occurs due to the wave interaction. it is found that gravitation introduces jeans-like instability, reduces the wave damping rate, decays the aperiodic oscillatory structure of da excitations, and strongly affects the amplitude, steepness, and occurrence of monotonic compressive and rarefactive shocks. numerical simulations also highlighted the stabilizing role of the magnetic field and the singularities of the collision process of monotonic shock fronts as well as the undeniable influence of viscosity, ion nonextensivity, and obliqueness between counter-traveling waves on the phase shift and collision profiles. the present results may be useful to better understand interactions of dust acoustic shock waves in the laboratory and astrophysical scenarios, such as dust clouds in the galactic disk, photo-association regions separating h ii regions from dense molecular clouds, saturn's planetary ring, and halley comet. | dynamics and head-on collisions of multidimensional dust acoustic shock waves in a self-gravitating magnetized electron-depleted dusty plasma |
analysis of the propagation of the comet nucleus sounding experiment by radiowave transmission (consert) signal throughout the small lobe of the 67p/cg nucleus has permitted us to deduce the real part of the permittivity, at a value of 1.27 ± 0.05. the first interpretation of this value, using the dielectric properties of mixtures of ices (h2o, co2), refractories (i.e. dust) and porosity, led to the conclusion that the comet porosity lies in the range 75-85 per cent. in addition, the dust-to-ice ratio was found to range between 0.4 and 2.6 and the permittivity of dust (including 30 per cent porosity) was determined to be lower than 2.9. this last value corresponds to a permittivity lower than 4 for a material without any porosity. this article is intended to refine the dust permittivity estimate by taking into account updated values of the nucleus densities and dust/ice ratio and to provide further insights into the nature of the constituents of comet 67p/cg. we adopted a systematic approach: determination of the dust permittivity as a function of the volume fraction of ice, dust and vacuum (i.e. porosity) and comparison with the permittivity of meteoritic, mineral and organic materials from literature and laboratory measurements. then different composition models of the nuclei corresponding to cosmochemical end members of 67p/cg dust are tested. for each of these models, the location in the ice/dust/vacuum ternary diagram is calculated based on available dielectric measurements and confronted to the locus of 67p/cg. the number of compliant models is small and the cosmochemical implications of each of them is discussed, to conclude regarding a preferred model. | cosmochemical implications of consert permittivity characterization of 67p/cg |
a rigorous theoretical investigation is made to study the characteristics of dust-acoustic (da) waves (daws) in an electron depleted unmagnetized opposite polarity dusty plasma system that contains super-thermal ( κ-distributed) ions, mobile positively and negatively charged dust grains for the first time. the reductive perturbation method is employed to obtain the nlse to explore the modulational instability (mi) conditions for daws as well as the formation and characteristics of gigantic rogue waves. the nonlinear and dispersion properties of the dusty plasma medium are the prime reasons behind the formation of rogue waves. the height and thickness of the darws associated with daws as well as the mi conditions of daws are numerically analyzed by changing different dusty plasma parameters, such as dust charges, dust and ion number densities, and ion-temperature, etc. the implications of the results for various space dusty plasma systems (viz., mesosphere, f-rings of saturn, and cometary atmosphere, etc.) as well as laboratory dusty plasma produced by laser-matter interaction are briefly mentioned. | dust-acoustic rogue waves in an electron depleted plasma |
glycine (gly), the simplest amino-acid building-block of proteins, has been identified on icy dust grains in the interstellar medium, icy comets, and ice covered meteorites. these astrophysical ices contain simple molecules (e.g., co2, h2o, ch4, hcn, and nh3) and are exposed to complex radiation fields, e.g., uv, γ, or x-rays, stellar/solar wind particles, or cosmic rays. while much current effort is focused on understanding the radiochemistry induced in these ices by high energy radiation, the effects of the abundant secondary low energy electrons (lees) it produces have been mostly assumed rather than studied. here we present the results for the exposure of multilayer co2:ch4:nh3 ice mixtures to 0-70 ev electrons under simulated astrophysical conditions. mass selected temperature programmed desorption (tpd) of our electron irradiated films reveals multiple products, most notably intact glycine, which is supported by control measurements of both irradiated or un-irradiated binary mixture films, and un-irradiated co2:ch4:nh3 ices spiked with gly. the threshold of gly formation by lees is near 9 ev, while the tpd analysis of gly film growth allows us to determine the "quantum" yield for 70 ev electrons to be about 0.004 gly per incident electron. our results show that simple amino acids can be formed directly from simple molecular ingredients, none of which possess preformed c—c or c—n bonds, by the copious secondary lees that are generated by ionizing radiation in astrophysical ices. | glycine formation in co2:ch4:nh3 ices induced by 0-70 ev electrons |
context. the rosetta spacecraft provided us with a unique opportunity to study comet 67p/churyumov-gerasimenko (67p) from a close perspective and over a 2-yr time period. comet 67p is a weakly active comet. it was therefore unexpected to find an active and dynamic ionosphere where the cometary ions were largely dominant over the solar wind ions, even at large heliocentric distances.aims: our goal is to understand the different drivers of the cometary ionosphere and assess their variability over time and over the different conditions encountered by the comet during the rosetta mission.methods: we used a multi-instrument data-based ionospheric model to compute the total ion number density at the position of rosetta. in-situ measurements from the rosetta orbiter spectrometer for ion and neutral analysis (rosina) and the rosetta plasma consortium (rpc)-ion and electron sensor (ies), together with the rpc-langmuir probe instrument (lap) were used to compute the local ion total number density. the results are compared to the electron densities measured by rpc-mutual impedance probe (mip) and rpc-lap.results: we were able to disentangle the physical processes responsible for the formation of the cometary ions throughout the 2-yr escort phase and we evaluated their respective magnitudes. the main processes are photo-ionization and electron-impact ionization. the latter is a significant source of ionization at large heliocentric distance (>2 au) and was predominant during the last 4 months of the mission. the ionosphere was occasionally subject to singular solar events, temporarily increasing the ambient energetic electron population. solar photons were the main ionizer near perihelion at 1.3 au from the sun, during summer 2015. | plasma source and loss at comet 67p during the rosetta mission |
the first known interstellar object, 1i/2017 u1 'oumuamua, displayed such unusual properties that its origin remains a subject of much debate. we propose that 'oumuamua's properties could be explained as those of a fractal dust aggregate (a "dust bunny") formed in the inner coma of a fragmenting exo-oort cloud comet. such fragments could serve as accretion sites by accumulating dust particles, resulting in the formation of a fractal aggregate. the fractal aggregate eventually breaks off from the fragment due to hydrodynamic stress. with their low density and tenuously bound orbits, most of these cometary fractal aggregates are then ejected into interstellar space by radiation pressure. | \'oumuamua as a cometary fractal aggregate: the "dust bunny" model |
complex organic molecules (coms) have been observed toward several low-mass young stellar objects (lysos). small and heterogeneous samples have so far precluded conclusions on typical com abundances, as well as the origin(s) of abundance variations between sources. we present observations toward 16 deeply embedded (class 0/i) low-mass protostars using the iram 30 m telescope. we detect ch2co, ch3cho, ch3och3, ch3ocho, ch3cn, hnco, and hc3n toward 67%, 37%, 13%, 13%, 44%, 81%, and 75% of sources, respectively. median column densities derived using survival analysis range between 6.0 × 1010 cm-2 (ch3cn) and 2.4 × 1012 cm-2 (ch3och3), and median abundances range between 0.48% (ch3cn) and 16% (hnco) with respect to ch3oh. column densities for each molecule vary by about one order of magnitude across the sample. abundances with respect to ch3oh are more narrowly distributed, especially for oxygen-bearing species. we compare observed median abundances with a chemical model for low-mass protostars and find fair agreement, although some modeling work remains to bring abundances higher with respect to ch3oh. median abundances with respect to ch3oh in lysos are also found to be generally comparable to observed abundances in hot cores, hot corinos, and massive ysos. compared with comets, our sample is comparable for all molecules except hc3n and ch2co, which likely become depleted at later evolutionary stages. based on observations carried out under project nos. 003-14 and 006-13 with the iram 30 m telescope. iram is supported by insu/cnrs (france), mpg (germany), and ign (spain). | complex organic molecules toward embedded low-mass protostars |
the question of what triggered the nongravitational acceleration of 1i/`oumuamua continues to attract researchers' attention. the absence of any signs of activity notwithstanding, the prevailing notion is that the acceleration of the stellar, cigar-like object was prompted by outgassing. however, the spitzer space telescope's failure to detect `oumuamua not only ruled out the co_2 and/or co driven activity (trilling et al. 2018), but made the cigar shape incompatible with the optical observations. choice of water ice as the source of outgassing is shown to be flawed as well: (i) the water sublimation law is demonstrably inconsistent with the observed variations in the nongravitational acceleration derived by micheli et al. (2018), the point that should have been assertively highlighted; and (ii) an upper limit of the production rate of water is estimated at as low as 4 x 10^(23) molecules s^(-1), requiring that, at most, only a small area of the surface be active. in this case the conservation of momentum law is satisfied only when `oumuamua's bulk density is extremely low, <0.001 g cm^(-3), reminiscent of the formerly proposed scenario with `oumuamua as a fragment of a dwarf interstellar comet, possibly an embryo planetesimal, disintegrating near perihelion, with the acceleration driven by solar radiation pressure (sekanina 2019a) and no need for activity at all. high quality of astrometry and micheli et al.'s orbital analysis, whose results were confirmed by the computations of other authors, is acknowledged. | outgassing as trigger of 1i/`oumuamua's nongravitational acceleration: could this hypothesis work at all? |
intrinsically faint comets in nearly-parabolic orbits with perihelion distances much smaller than 1 au exhibit strong propensity for suddenly disintegrating at a time not long before perihelion, as shown by bortle (1991). evidence from available observations of such comets suggests that the disintegration event usually begins with an outburst and that the debris is typically a massive cloud of dust grains that survives over a limited period of time. recent ccd observations revealed, however, that also surviving could be a sizable fragment, resembling a devolatilized aggregate of loosely-bound dust grains that may have exotic shape, peculiar rotational properties, and extremely high porosity, all acquired in the course of the disintegration event. given that the brightness of 1i/`oumuamua's parent could not possibly equal or exceed the bortle survival limit, there are reasons to believe that it suffered the same fate as do the frail comets. the post-perihelion observations then do not refer to the object that was entering the inner solar system in early 2017, as is tacitly assumed, but to its debris. comparison with c/2017 s3 and c/2010 x1 suggests that, as a monstrous fluffy dust aggregate released in the recent explosive event, `oumuamua should be of strongly irregular shape, tumbling, not outgassing, and subjected to effects of solar radiation pressure, consistent with observation. the unknown timing of the disintegration event may compromise studies of the parent's home stellar system. limited search for possible images of the object to constrain the time of the (probably minor) outburst is recommended. | 1i/`oumuamua as debris of dwarf interstellar comet that disintegrated before perihelion |
aims: we present the spatial and diurnal variation of water outgassing on comet 67p/churyumov-gerasimenko using the ho rotational transition line at 556.936 ghz observed from rosetta/miro in august 2014.methods: the water line was analyzed with a non-lte radiative transfer model and an optimal estimation method to retrieve the ho outgassing intensity, expansion velocity, and gas kinetic temperature. on august 7-9, 2014 and august 18-19, 2014, miro performed long steady nadir-pointing observations of the nucleus while it was rotating around its spin axis. the ground track of the miro beam during the observation was mostly on the northern hemisphere of comet 67p, covering its three distinct parts: the so-called head, body, and neck areas.results: the miro spectral observation data show that the water-outgassing intensity varies by a factor of 30, from 0.1 × 1025 molecules s-1 sr-1 to 3.0 × 1025 molecules s-1 sr-1, the terminal gas expansion velocity varies by 0.17 km s-1 from 0.61 km s-1 to 0.78 km s-1, and the terminal gas temperature varies by 27 k from 47 k to 74 k. the retrieved coma parameters are co-registered with local environment variables such as the subsurface temperatures, measured in the miro continuum bands, the local solar time, illumination condition, and beam location on nucleus. the spatial variation of the outgassing activity is very noticeable, and the largest outgassing activity in august 2014 occurs near the neck region of the nucleus. the outgassing activity in the neck region is also found to be correlated with the local solar hour, which is related to the local illumination condition. | spatial and diurnal variation of water outgassing on comet 67p/churyumov-gerasimenko observed from rosetta/miro in august 2014 |
most of the gaseous molecules that are detected in cometary atmospheres are produced through sublimation of nucleus ices. distributed sources may also occur, that is, production within the coma, from the solid component of dust particles that are ejected from the nucleus. glycine, the simplest amino acid, was observed episodically in the atmosphere of comet 67p/churyumov-gerasimenko (67p) by the rosina mass spectrometer on board the rosetta probe. a series of measurements on 28 march 2015 revealed a distributed density profile at between 14 and 26 km away from the nucleus. we here present and discuss three study cases: (i) glycine emitted directly and only from the nucleus, (ii) glycine emitted from the sublimation of solid-state glycine on the dust particles that are ejected from the nucleus, and (iii) glycine molecules embedded in water ice that are emitted from the sublimation of this ice from the dust particles that are ejected from the nucleus. a numerical model was developed to calculate the abundance of glycine in the atmosphere of comet 67p as a function of the distance from the nucleus, and to derive its initial abundance in the lifted dust particles. we show that a good fit to the observations corresponds to a distributed source of glycine that is embedded in sublimating water ice from dust particles that are ejected from the nucleus (iii). the few hundred ppb of glycine embedded in water ice on dust particles (nominally 170 ppb by mass) agree well with the observed distribution. | distributed glycine in comet 67p/churyumov-gerasimenko |
according to modern concepts bodies of the solar system formed from a single cloud of gas and dust. calculations show that in the protoplanetary nebula where the temperature is lowered to 1600 k - appeared the first type of metal (aluminum and titanium) and metal oxides in the form of dust particles. with further decreasing temperature of the nebula to 1400 k - appeared also dust of iron and iron-nikel alloy; at 1300 k - appear solid silicates; magnesium minerals formed at t 1200 k. these components are material for the formation of basaltic rocks. at temperatures t 300 k begins to form water molecules. at 100-200 k in a remote part of the nebula - ammonia, methane and their ice are formed. in the outer part of solar system this ices are now preserved in comet nuclei and in the icy satellites of giant planets. during t 400 million years after the formation of the sun, at first - from dust component of the protoplanetary cloud was formed many intermediate bodies with the size of hundreds kilometers. their gravitational interaction was reinforced in process of their grow. the bodies, which were growing fastest, they became the embryos of the future planets. all bodies of the solar system in different degrees show manifestations of different types of activity processes on the surface or at the level of the visible clouds. this activity depends on the distance of a particular body from the sun, surface chemical composition, physical conditions at the surface and so on. the farther away from the sun is the object, the temperature of its visible surface is lower, and by that more interesting is the set of processes, of chemical and physical transformations that there is possible to register. the surface of each planets of solar system is very active in a variety of set temperature and chemical composition | activity of processes on the visible surface of planets of solar system |
both heliophysics and planetary physics seek to understand the complex nature of the solar wind's interaction with solar system obstacles like earth's magnetosphere, the ionospheres of venus and mars, and comets. studies with this objective are frequently conducted with the help of single or multipoint in situ electromagnetic field and particle observations, guided by the predictions of both local and global numerical simulations, and placed in context by observations from far and extreme ultraviolet (fuv, euv), hard x-ray, and energetic neutral atom imagers (ena). each proposed interaction mechanism (e.g., steady or transient magnetic reconnection, local or global magnetic reconnection, ion pick-up, or the kelvin-helmholtz instability) generates diagnostic plasma density structures. the significance of each mechanism to the overall interaction (as measured in terms of atmospheric/ionospheric loss at comets, venus, and mars or global magnetospheric/ionospheric convection at earth) remains to be determined but can be evaluated on the basis of how often the density signatures that it generates are observed as a function of solar wind conditions. this paper reviews efforts to image the diagnostic plasma density structures in the soft (low energy, 0.1-2.0 kev) x-rays produced when high charge state solar wind ions exchange electrons with the exospheric neutrals surrounding solar system obstacles. the introduction notes that theory, local, and global simulations predict the characteristics of plasma boundaries such the bow shock and magnetopause (including location, density gradient, and motion) and regions such as the magnetosheath (including density and width) as a function of location, solar wind conditions, and the particular mechanism operating. in situ measurements confirm the existence of time- and spatial-dependent plasma density structures like the bow shock, magnetosheath, and magnetopause/ionopause at venus, mars, comets, and the earth. however, in situ measurements rarely suffice to determine the global extent of these density structures or their global variation as a function of solar wind conditions, except in the form of empirical studies based on observations from many different times and solar wind conditions. remote sensing observations provide global information about auroral ovals (fuv and hard x-ray), the terrestrial plasmasphere (euv), and the terrestrial ring current (ena). ena instruments with low energy thresholds (∼1 kev) have recently been used to obtain important information concerning the magnetosheaths of venus, mars, and the earth. recent technological developments make these magnetosheaths valuable potential targets for high-cadence wide-field-of-view soft x-ray imagers. section 2 describes proposed dayside interaction mechanisms, including reconnection, the kelvin-helmholtz instability, and other processes in greater detail with an emphasis on the plasma density structures that they generate. it focuses upon the questions that remain as yet unanswered, such as the significance of each proposed interaction mode, which can be determined from its occurrence pattern as a function of location and solar wind conditions. section 3 outlines the physics underlying the charge exchange generation of soft x-rays. section 4 lists the background sources (helium focusing cone, planetary, and cosmic) of soft x-rays from which the charge exchange emissions generated by solar wind exchange must be distinguished. with the help of simulations employing state-of-the-art magnetohydrodynamic models for the solar wind-magnetosphere interaction, models for earth's exosphere, and knowledge concerning these background emissions, sect. 5 demonstrates that boundaries and regions such as the bow shock, magnetosheath, magnetopause, and cusps can readily be identified in images of charge exchange emissions. section 6 reviews observations by (generally narrow) field of view (fov) astrophysical telescopes that confirm the presence of these emissions at the intensities predicted by the simulations. section 7 describes the design of a notional wide fov "lobster-eye" telescope capable of imaging the global interactions and shows how it might be used to extract information concerning the global interaction of the solar wind with solar system obstacles. the conclusion outlines prospects for missions employing such wide fov imagers. | imaging plasma density structures in the soft x-rays generated by solar wind charge exchange with neutrals |
symmetric cell division requires the even partitioning of genetic information and cytoplasmic contents between daughter cells. whereas the mechanisms coordinating the segregation of the genome are well known, the processes that ensure organelle segregation between daughter cells remain less well understood1. here we identify multiple actin assemblies with distinct but complementary roles in mitochondrial organization and inheritance in mitosis. first, we find a dense meshwork of subcortical actin cables assembled throughout the mitotic cytoplasm. this network scaffolds the endoplasmic reticulum and organizes three-dimensional mitochondrial positioning to ensure the equal segregation of mitochondrial mass at cytokinesis. second, we identify a dynamic wave of actin filaments reversibly assembling on the surface of mitochondria during mitosis. mitochondria sampled by this wave are enveloped within actin clouds that can spontaneously break symmetry to form elongated comet tails. mitochondrial comet tails promote randomly directed bursts of movement that shuffle mitochondrial position within the mother cell to randomize inheritance of healthy and damaged mitochondria between daughter cells. thus, parallel mechanisms mediated by the actin cytoskeleton ensure both equal and random inheritance of mitochondria in symmetrically dividing cells. | actin cables and comet tails organize mitochondrial networks in mitosis |
using 3d radiative mhd simulations and lyman-α transit calculations, we investigate the effect of magnetic fields on the observational signatures of atmospheric escape in exoplanets. using the same stellar wind, we vary the planet's dipole field strength (bp) from 0 to 10g. for bp < 3g, the structure of the escaping atmosphere begins to break away from a comet-like tail following the planet (bp = 0), as we see more absorbing material above and below the orbital plane. for bp ≥ 3g, we find a 'dead-zone' around the equator, where low velocity material is trapped in the closed magnetic field lines. the dead-zone separates two polar outflows where absorbing material escapes along open field lines, leading to a double tail structure, above and below the orbital plane. we demonstrate that atmospheric escape in magnetized planets occurs through polar outflows, as opposed to the predominantly night-side escape in non-magnetized models. we find a small increase in escape rate with bp, though this should not affect the time-scale of atmospheric loss. as the size of the dead-zone increases with bp, so does the line centre absorption in lyman-α, as more low-velocity neutral hydrogen covers the stellar disc during transit. for bp < 3g the absorption in the blue wing decreases, as the escaping atmosphere is less funnelled along the line of sight by the stellar wind. in the red wing (and for bp > 3g in the blue wing) the absorption increases caused by the growing volume of the magnetosphere. finally we show that transits below and above the mid-disc differ caused by the asymmetry of the double tail structure. | the effects of magnetic fields on observational signatures of atmospheric escape in exoplanets: double tail structures |
extreme debris disks (edds) are rare systems with peculiarly large amounts of warm dust that may stem from recent giant impacts between planetary embryos during the final phases of terrestrial planet growth. here we report on the identification and characterization of six new edds. these disks surround f5-g9 type main-sequence stars with ages >100 myr, have dust temperatures higher than 300 k, and fractional luminosities between 0.01 and 0.07. using time-domain photometric data at 3.4 and 4.6 μm from the wise all-sky surveys, we conclude that four of these disks exhibited variable mid-infrared (ir) emission between 2010 and 2019. analyzing the sample of all known edds, now expanded to 17 objects, we find that 14 of them showed changes at 3-5 μm over the past decade, suggesting that mid-ir variability is an inherent characteristic of edds. we also report that wide-orbit pairs are significantly more common in edd systems than in the normal stellar population. while current models of rocky planet formation predict that the majority of giant collisions occur in the first 100 myr, we find that the sample of edds is dominated by systems older than this age. this raises the possibility that the era of giant impacts may be longer than we think, or that some other mechanism(s) can also produce edds. we examine a scenario where the observed warm dust stems from the disruption and/or collisions of comets delivered from an outer reservoir into the inner regions, and explore what role the wide companions could play in this process. | a new sample of warm extreme debris disks from the allwise catalog |
we study the dynamics of the interaction between the solar wind ions and a partially ionized atmosphere around a comet, at a distance of 2.88 au from the sun during a period of low nucleus activity. comparing particle data and magnetic field data for a case study, we highlight the prime role of the solar wind electric field in the cometary ion dynamics. cometary ion and solar wind proton flow directions evolve in a correlated manner, as expected from the theory of mass loading. we find that the main component of the accelerated cometary ion flow direction is along the antisunward direction and not along the convective electric field direction. this is interpreted as the effect of an antisunward polarization electric field adding up to the solar wind convective electric field. | mass loading at 67p/churyumov-gerasimenko: a case study |
the star β pictoris harbors a young planetary system of about 20 million years old, which is characterized by the presence of a gaseous and dusty debris disk, at least two massive planets and many minor bodies. for more than thirty years, exocomets transiting the star have been detected using spectroscopy, probing the gaseous part of the cometary comas and tails. the detection of the dusty component of the tails can be performed through photometric observations of the transits. since 2018, the transiting exoplanet survey satellite has observed β pic for a total of 156 days. here we report an analysis of the tess photometric data set with the identification of a total of 30 transits of exocomets. our statistical analysis shows that the number of transiting exocomet events (n) as a function of the absorption depth (ad) in the light curve follows a power law in the form d n (a d ) ∝a d-α, where α =2.3 ±0.4. this distribution of absorption depth leads to a differential comet size distribution proportional to r-γ, where γ =3.6 ±0.8, showing a striking similarity to the size distribution of comets in the solar system and the distribution of a collisionally relaxed population (γd=3.5). | exocomets size distribution in the β pictoris planetary system |
esa's rosetta mission has followed comet 67p/churyumov-gerasimenko from 3.6 au inbound to 3.6 au outbound. many results are largely unexpected, as compared to previous models based on in situ and ground-based observations of jupiter-family comets. the main topics discussed in this review are (1) the importance of the large concavities characterizing the 67p nucleus, that, (2) coupled to the nucleus obliquity, make seasons an unexpectedly important source of many phenomena observed in this and probably in most comets; (3) the mostly uniform distribution of ices over the nucleus surface; (4) the high dust-to-water mass ratio, which implies that much of the nucleus mass is in the form of minerals partly coming from the inner proto-solar nebula, thus making 67p very porous and less hydrated than primitive ci chondrites. 67p nucleus may have never experienced any collision at speeds larger than 1 m s-1. | unexpected and significant findings in comet 67p/churyumov-gerasimenko: an interdisciplinary view |
in this study, cypermethrin toxicity was investigated using physiological, biochemical and cytogenetic parameters, and more than one organ and cell type was preferred to determine these effects. in this multifaceted study, the genotoxicity mechanism of cypermethrin was elucidated by molecular docking. in addition, comet assay technique was applied to detect and quantify dna damage at the cell level. for this aim, body and organ weights, aspartate aminotransferase (ast), alanine aminotransferase (alt), malondialdehyde (mda), glutathione (gsh), blood urea nitrogen (bun) and creatinine levels, mitotic index (mi), dna fragmentation, frequency of micronucleus (mn) and chromosomal aberrations (cas) were used as indicators of toxicity. mice were divided into 4 groups. the control group was fed with tap water and the administration groups were orally exposed to 62.5, 125 and 250 mg/kg b.w cypermethrin for 28 days. then, the mice were sacrificed and tissue samples were collected. cypermethrin caused a decrease in body and organ weights, gsh levels and mi and an increase in ast, alt, mda, bun, creatinine levels and the frequency of mn and cas (break, ring, gap, acentric, etc.). cypermethrin promoted mn formation in leukocyte, erythrocyte, buccal mucosa epithelial cells. cas and mn formation promoted by cypermethrin have been associated with dna-cypermethrin interactions. this interaction has been demonstrated by simulation with molecular docking method and experimentally by spectral measurements of dna. as a result, all three doses of cypermethrin caused toxicity in different cell types. in other words, the effect of cypermethrin taken into the body was not limited to only one cell type or region. therefore, cypermethrin is a pyrethroid insecticide that promotes multifaceted toxicity in non-target organisms. | investigation of cypermethrin toxicity in swiss albino mice with physiological, genetic and biochemical approaches |
context. since august 2014, the osiris narrow angle camera (nac) onboard the rosetta spacecraft has acquired high spatial resolution images of the nucleus of comet 67p/churyumov-gerasimenko, down to the decimeter scale. this paper focuses on the imhotep region, located on the largest lobe of the nucleus, near the equator.aims: we map, inventory, and describe the geomorphology of the imhotep region. we propose and discuss some processes to explain the formation and ongoing evolution of this region.methods: we used osiris nac images, gravitational heights and slopes, and digital terrain models to map and measure the morphologies of imhotep.results: the imhotep region presents a wide variety of terrains and morphologies: smooth and rocky terrains, bright areas, linear features, roundish features, and boulders. gravity processes such as mass wasting and collapse play a significant role in the geomorphological evolution of this region. cometary processes initiate erosion and are responsible for the formation of degassing conduits that are revealed by elevated roundish features on the surface. we also propose a scenario for the formation and evolution of the imhotep region; this implies the presence of large primordial voids inside the nucleus, resulting from its formation process. | geomorphology of the imhotep region on comet 67p/churyumov-gerasimenko from osiris observations |
context. comet formation by gravitational instability requires aggregates that trigger the streaming instability and cluster in pebble-clouds. these aggregates form as mixtures of dust and ice from (sub-)micrometre-sized dust and ice grains via coagulation in the solar nebula. aim. we investigate the growth of aggregates from (sub-)micrometre-sized dust and ice monomer grains. we are interested in the properties of these aggregates: whether they might trigger the streaming instability, how they compare to pebbles found on comets, and what the implications are for comet formation in collapsing pebble-clouds.methods: we used monte carlo simulations to study the growth of aggregates through coagulation locally in the comet-forming region at 30 au. we used a collision model that can accommodate sticking, bouncing, fragmentation, and porosity of dust- and ice-mixed aggregates. we compared our results to measurements of pebbles on comet 67p/churyumov-gerasimenko.results: we find that aggregate growth becomes limited by radial drift towards the sun for 1 μm sized monomers and by bouncing collisions for 0.1 μm sized monomers before the aggregates reach a stokes number that would trigger the streaming instability (stmin). we argue that in a bouncing-dominated system, aggregates can reach stmin through compression in bouncing collisions if compression is faster than radial drift. in the comet-forming region ( 30 au), aggregates with stmin have volume-filling factors of 10-2 and radii of a few millimetres. these sizes are comparable to the sizes of pebbles found on comet 67p/churyumov-gerasimenko. the porosity of the aggregates formed in the solar nebula would imply that comets formed in pebble-clouds with masses equivalent to planetesimals of the order of 100 km in diameter. | local growth of dust- and ice-mixed aggregates as cometary building blocks in the solar nebula |
we present atacama large millimetre/sub-millimetre array (alma) 1.3 and 0.86 mm observations of the nearby (17.34 pc) f9v star q1 eri (hd 10647, hr 506). this system, with age ~1.4 gyr, hosts a ~2 au radial velocity planet and a debris disc with the highest fractional luminosity of the closest 300 fgk type stars. the alma images, with resolution ~0${_{.}^{\prime\prime}}$5, reveal a broad (34-134 au) belt of millimetre emission inclined by 76.7 ± 1.0 degrees with maximum brightness at 81.6 ± 0.5 au. the images reveal an asymmetry, with higher flux near the south-west ansa, which is also closer to the star. scattered light observed with the hubble space telescope is also asymmetric, being more radially extended to the north-east. we fit the millimetre emission with parametric models and place constraints on the disc morphology, radius, width, dust mass, and scale height. we find that the south-west ansa asymmetry is best fitted by an extended clump on the inner edge of the disc, consistent with perturbations from a planet with mass $8\, m_{\oplus } {-} 11\, m_{\rm jup}$ at ~60 au that may have migrated outwards, similar to neptune in our solar system. if the measured vertical aspect ratio of h = 0.04 ± 0.01 is due to dynamical interactions in the disc, then this requires perturbers with sizes >1200 km. we find tentative evidence for a 0.86 mm excess within 10 au, $70{\pm }22\, \mu$jy, that may be due to an inner planetesimal belt. we find no evidence for co gas, but set an upper bound on the co gas mass of 4 × 10-6 m⊕ ($3\sigma$), consistent with cometary abundances in the solar system. | high-resolution alma and hst images of q1 eri: an asymmetric debris disc with an eccentric jupiter |
cometary dust particles are best preserved remnants of the matter present at the onset of the formation of the solar system. space missions, telescopic observations and laboratory analyses advanced the knowledge on the properties of cometary dust. cometary samples were returned from comet 81p/wild2 by the stardust mission. the chondritic (porous) anhydrous interplanetary dust particles and chondritic porous micrometeorites, and the ultracarbonaceous antarctic micrometeorites (ucamms) also show strong evidence for a cometary origin. the composition of cometary dust is generally chondritic, but with high c and n compared with ci. the cometary organic matter is mixed with minor amounts of crystalline and amorphous minerals. the most abundant crystalline minerals are ferromagnesian silicates, refractory minerals and low ni fe sulfides are also present. the presence of carbonates in cometary dust is still debated, but a phyllosilicate-like phase was observed in a ucamm. gems phases are usually abundant. some of the organic matter present in cometary dust particle resembles the insoluble organic matter present in primitive meteorites, but amorphous carbon and exotic (e.g. n-rich) organic phases are also present. the h isotopic composition of the organic matter traces a formation at very low temperatures, in the protosolar cloud or in the outer regions of the protoplanetary disk. the presolar dust concentration in cometary dust can reach about 1%, which is the most elevated value observed in extraterrestrial samples. the differential size distribution of cometary dust in comet trails is well represented by a power-law distribution with a mean power index n typically ranging from -3 to -4. polarimetric and light scattering studies suggest mixtures of porous agglomerates of sub-micrometer minerals with organic matter. cometary dust particles have low tensile strength, and low density. | chemical and physical properties of cometary dust |
we present observations of sunset jets on comet 67p/churyumov-gerasimenko by rosetta/osiris camera. in late april 2015, when the comet was at a heliocentric distance of ~1.8 au, clusters of dust jets that originated in the ma'at region on the comet's small lobe were identified from multipleimages and were apparently sustained for about an hour beyond local sunset. emanating from the shadowed nucleus, these jets became visible by solar illumination at their apparent sources up to only a few tens of meters above the nucleus surface. we investigate the plausibility of these jets as having been triggered by water ice sublimation and sustained by thermal lag in the subsurface beyond sunset. a general thermo-physical model was parameterized such that the thermal lag in the subsurface is consistent with the elapsed time of observation after sunset. it is found that the sublimation of water ice from a depth of 6 mm and with a low thermal inertia of 50 w m-2 k-1 s1/2 could explain the spatial pattern and evolution of the apparent sources, particularly their disappearance due to the eventual cooling of the subsurface. our analysis suggests that these sunset jets were essentially day-side dust activities that continued after sunset. specific observational conditions for the sunset jets constrain their possible sources to mostly within the less abrupt, dusty terrains. the uneven distribution of these jets is possibly related to subsurface inhomogeneities in the dusty area. | sunset jets observed on comet 67p/churyumov-gerasimenko sustained by subsurface thermal lag |
it has long been observed that the coma of a comet is often green while its tail is not. while the explanation for this must be that the molecules responsible for the green emission, c2, are photodissociated, the mechanism was, until now, unknown. we have observed the photodissociation of c2 in the laboratory for the first time and, in doing so, have determined its bond dissociation energy with unprecedented precision. invoking the observed mechanism, the calculated lifetime of cometary c2 is found to be consistent with astronomical observations. | photodissociation of dicarbon: how nature breaks an unusual multiple bond |
the fixation probability is the probability that a new mutant introduced in a homogeneous population eventually takes over the entire population. the fixation probability is a fundamental quantity of natural selection, and known to depend on the population structure. amplifiers of natural selection are population structures which increase the fixation probability of advantageous mutants, as compared to the baseline case of well-mixed populations. in this work we focus on symmetric population structures represented as undirected graphs. in the regime of undirected graphs, the strongest amplifier known has been the star graph, and the existence of undirected graphs with stronger amplification properties has remained open for over a decade. in this work we present the comet and comet-swarm families of undirected graphs. we show that for a range of fitness values of the mutants, the comet and comet-swarm graphs have fixation probability strictly larger than the fixation probability of the star graph, for fixed population size and at the limit of large populations, respectively. | amplification on undirected population structures: comets beat stars |
the cometary secondary ion mass analyzer (cosima) on board the rosetta mission has analysed numerous cometary dust particles collected at very low velocities (a few m s-1) in the environment of comet 67p/churyumov-gerasimenko (hereafter 67p). in these particles, carbon and nitrogen are expected mainly to be part of the organic matter. we have measured the nitrogen-to-carbon (n/c) atomic ratio of 27 cometary particles. it ranges from 0.018 to 0.06 with an averaged value of 0.035 ± 0.011. this is compatible with the measurements of the particles of comet 1p/halley and is in the lower range of the values measured in comet 81p/wild 2 particles brought back to earth by the stardust mission. moreover, the averaged value found in 67p particles is also similar to the one found in the insoluble organic matter extracted from cm, ci and cr carbonaceous chondrites and to the bulk values measured in most interplanetary dust particles and micrometeorites. the close agreement of the n/c atomic ratio in all these objects indicates that their organic matters share some similarities and could have a similar chemical origin. furthermore, compared to the abundances of all the detected elements in the particles of 67p and to the elemental solar abundances, the nitrogen is depleted in the particles and the nucleus of 67p as was previously inferred also for comet 1p/halley. this nitrogen depletion could constrain the formation scenarios of cometary nuclei. | nitrogen-to-carbon atomic ratio measured by cosima in the particles of comet 67p/churyumov-gerasimenko |
we investigate the plausibility of a cometary source of the unusual transits observed in the kic 8462852 light curve. a single comet of similar size to those in our solar system produces a transit depth of the order of 10-3 lasting less than a day which is much smaller and shorter than the largest dip observed (∼ 20% for ∼3 days), but a large, closely traveling cluster of comets can fit the observed depths and durations. we find that a series of large comet swarms, with all except one on the same orbit, provides a good fit for the kic 8462852 data during quarters 16 and 17, but does not explain the large dip observed during quarter 8. however, the transit dips only loosely constrain the orbits and can be fit by swarms with periastrons differing by a factor of 10. to reach a transit depth of ∼0.2, the comets need to be in a close group of ∼30, if they are ∼100 km in radius or in a group of ∼300 if they are ∼10 km in radius. the total number of comets required to fit all of the dips is ∼70 ∼ 100 km or ∼700 ∼ 10 km comets. a single comet family from a tidally disrupted ceres-sized progenitor or the start of a late heavy bombardment period explains the last ∼60 days of the unusual kic 8462852 light curve. | kic 8462852: transit of a large comet family |
we observed the interstellar comet 2i/borisov using the neil gehrels swift observatory's ultraviolet/optical telescope. we obtained images of the oh gas and dust surrounding the nucleus at six epochs spaced before and after perihelion (-2.56 to 2.54 au). water production rates increased steadily before perihelion from (7.0 ± 1.5) × 1026 molecules s-1 on 2019 november 1, to (10.7 ± 1.2) × 1026 molecules s-1 on december 1. this rate of increase in water production rate is quicker than that of most dynamically new comets and at the slower end of the wide range of jupiter-family comets. after perihelion, the water production rate decreased to (4.9 ± 0.9) × 1026 molecules s-1 on december 21, which is much more rapidly than that of all previously observed comets. our sublimation model constrains the minimum radius of the nucleus to 0.37 km, and indicates an active fraction of at least 55% of the surface. a(0)fρ calculations show a variation between 57.5 and 105.6 cm with a slight trend peaking before the perihelion, lower than previous and concurrent published values. the observations confirm that 2i/borisov is carbon-chain depleted and enriched in nh2 relative to water. | water production rates and activity of interstellar comet 2i/borisov |
the immersion grating infrared spectrometer (igrins) is a revolutionary instrument that exploits broad spectral coverage at high-resolution in the near-infrared. igrins employs a silicon immersion grating as the primary disperser, and volume-phase holographic gratings cross-disperse the h and k bands onto teledyne hawaii-2rg arrays. the use of an immersion grating facilitates a compact cryostat while providing simultaneous wavelength coverage from 1.45 - 2.5 μm. there are no cryogenic mechanisms in igrins and its high-throughput design maximizes sensitivity. igrins on the 2.7 meter harlan j. smith telescope at mcdonald observatory is nearly as sensitive as crires at the 8 meter very large telescope. however, igrins at r≍45,000 has more than 30 times the spectral grasp of crires* in a single exposure. here we summarize the performance of igrins from the first 300 nights of science since commissioning in summer 2014. igrins observers have targeted solar system objects like pluto and ceres, comets, nearby young stars, star forming regions like taurus and ophiuchus, the interstellar medium, photo dissociation regions, the galactic center, planetary nebulae, galaxy cores and super novae. the rich near-infrared spectra of these objects motivate unique science cases, and provide information on instrument performance. there are more than ten submitted igrins papers and dozens more in preparation. with igrins on a 2.7m telescope we realize signal-to-noise ratios greater than 100 for k=10.3 magnitude sources in one hour of exposure time. although igrins is cassegrain mounted, instrument flexure is sub-pixel thanks to the compact design. detector characteristics and stability have been tested regularly, allowing us to adjust the instrument operation and improve science quality. a wide variety of science programs motivate new tools for analyzing high-resolution spectra including multiplexed spectral extraction, atmospheric model fitting, rotation and radial velocity, unique line identification, and circumstellar disk modeling. here we discuss details of instrument performance, summarize early science results, and show the characteristics of igrins as a versatile near-infrared spectrograph and forerunner of future silicon immersion grating spectrographs like ishell2 and gmtnirs.3 | 300 nights of science with igrins at mcdonald observatory |
extremely metal-poor (xmp) galaxies are defined to have a gas-phase metallicity smaller than a tenth of the solar value (12+{log}[{{o/h}}]< 7.69). they are uncommon, chemically and possibly dynamically primitive, with physical conditions characteristic of earlier phases of the universe. we search for new xmps in the sloan digital sky survey (sdss) in a work that complements paper i. this time, high electron temperature objects are selected; metals are a main coolant of the gas, so metal-poor objects contain high-temperature gas. using the algorithm k-means, we classify 788,677 spectra to select 1281 galaxies that have particularly intense [o iii]λ4363 with respect to [o iii]λ5007, which is a proxy for high electron temperature. the metallicity of these candidates was computed using a hybrid technique consistent with the direct method, rendering 196 xmps. a less restrictive noise constraint provides a larger set with 332 candidates. both lists are provided in electronic format. the selected xmp sample has a mean stellar mass around {10}8 {m}⊙ , with the dust mass ∼ {10}3{m}⊙for typical star-forming regions. in agreement with previous findings, xmps show a tendency to be tadpole-like or cometary. their underlying stellar continuum corresponds to a fairly young stellar population (< 1 {{gyr}}), although young and aged stellar populations coexist at the low-metallicity starbursts. about 10% of the xmps show large n/o. based on their location in constrained cosmological numerical simulations, xmps have a strong tendency to appear in voids and to avoid galaxy clusters. the puzzling 2%-solar low-metallicity threshold exhibited by xmps remains. | search for extremely metal-poor galaxies in the sloan digital sky survey. (ii). high electron temperature objects |
we present new, ice species-specific new horizons/alice upper gas coma production limits from the 2019 january 1 mu69/arrokoth flyby of gladstone et al. and use them to make predictions about the rarity of majority hypervolatile (co, n2, ch4) ices in kuiper belt objects and oort cloud comets. these predictions have a number of important implications for the study of the oort cloud, including the determination of hypervolatile-rich comets as the first objects emplaced into the oort cloud, the measurement of co/n2/ch4 abundance ratios in the protoplanetary disk from hypervolatile-rich comets, and population statistical constraints on early (<20 myr) planetary aggregation driven versus later (>50 myr) planetary migration driven emplacement of objects into the oort cloud. they imply that the phenomenon of ultradistant active comets like c/2017k2 should be rare, and thus not a general characteristic of all comets. they also suggest that interstellar object 2i/borisov may not have originated in a planetary system that was inordinately co rich, but rather could have been ejected onto an interstellar trajectory very early in its natal system's history. | a predicted dearth of majority hypervolatile ices in oort cloud comets |
our universe is most radiant at terahertz frequencies (0.1-10.0 thz) (ref. 1), providing critical information on the formation of the planets, stars and galaxies, as well as the atmospheric constituents of the planets, their moons, comets and asteroids2-9. the detection of faint fluxes of photons at terahertz frequencies is crucial for many planetary, cosmological and astrophysical studies10-14. for example, understanding the physics and molecular chemistry of the life cycle of stars and their relationship with the interstellar medium in galaxies requires heterodyne detectors with noise temperatures close to the quantum limit15. near-quantum-limited heterodyne terahertz detection has so far been possible only through the use of cryogenically cooled superconducting mixers as frequency downconverters15-18. here we introduce a heterodyne terahertz detection scheme that uses plasmonic photomixing for frequency downconversion to offer quantum-level sensitivities at room temperature. frequency downconversion is achieved by mixing terahertz radiation and a heterodyning optical beam with a terahertz beat frequency in a plasmonics-enhanced semiconductor active region. we demonstrate terahertz detection sensitivities down to three times the quantum limit at room temperature. with a versatile design capable of broadband operation over a 0.1-5.0 thz bandwidth, this plasmonic photomixer has broad applicability to astronomy, cosmology, atmospheric studies, gas sensing and quantum optics. | room-temperature heterodyne terahertz detection with quantum-level sensitivity |
collisions of ice particles play an important role in the formation of planetesimals and comets. in recent work, we showed that co2 ice behaves like silicates in collisions. the resulting assumption was that it should therefore stick less efficiently than h2o ice. within this paper, a quantification of the latter is presented. we used the same experimental setup to study collisions of pure co2 ice, pure water ice, and 50% mixtures by mass between co2 and water at 80 k, 1 mbar, and an average particle size of ∼90 μm. the results show a strong increase of the threshold velocity between sticking and bouncing with increasing water content. this supports the idea that water ice is favorable for early growth phases of planets in a zone within the h2o and the co2 iceline. | ice grain collisions in comparison: co2, h2o, and their mixtures |
we study kardar-parisi-zhang equation in spatial dimension 3 or larger driven by a gaussian space-time white noise with a small convolution in space. when the noise intensity is small, it is known that the solutions converge to a random limit as the smoothing parameter is turned off. we identify this limit, in the case of general initial conditions ranging from flat to droplet. we provide strong approximations of the solution which obey exactly the limit law. we prove that this limit has sub-gaussian lower tails, implying existence of all negative (and positive) moments. | renormalizing the kardar-parisi-zhang equation in d ≥3 in weak disorder |
recently, the rosina mass spectrometer suite on board the european space agency's rosetta spacecraft discovered an abundant amount of molecular oxygen, o2, in the coma of jupiter family comet 67p/churyumov-gerasimenko of o2/h2o = 3.80 ± 0.85%. it could be shown that o2 is indeed a parent species and that the derived abundances point to a primordial origin. crucial questions are whether the o2 abundance is peculiar to comet 67p/churyumov-gerasimenko or jupiter family comets in general, and also whether oort cloud comets such as comet 1p/halley contain similar amounts of molecular oxygen. we investigated mass spectra obtained by the neutral mass spectrometer instrument during the flyby by the european space agency's giotto probe of comet 1p/halley. our investigation indicates that a production rate of o2 of 3.7 ± 1.7% with respect to water is indeed compatible with the obtained halley data and therefore that o2 might be a rather common and abundant parent species. | molecular oxygen in oort cloud comet 1p/halley |
we numerically study the dynamical evolution of observed samples of active and inactive centaurs and clones that reach the jupiter-saturn region. our aim is to compare the evolution between active and inactive centaurs, their end states and their transfer to jupiter family comets and halley-type comets. we find that the median lifetime of inactive centaurs is about twice longer than that for active centaurs, suggesting that activity is related to the residence time in the region. this view is strengthened by the observation that high-inclination and retrograde centaurs (tisserand parameters with respect to jupiter tj < 2) which have the longest median dynamical lifetime (= 1.37 ×106 yr) are all inactive. we also find that the perihelion distances of some active, comet-like centaurs have experienced drastic drops of a few au in the recent past (∼102 -103 yr), while such drops are not found among inactive centaurs. inactive centaurs with tj ≲ 2.5 usually evolve to halley-type comets, whereas inactive centaurs with tj ≳ 2.5 and active centaurs (that also have tj ≳ 2.5) evolve almost always to jupiter family comets and very seldom to halley type comets. inactive centaurs are also more prone to end up as sungrazers, and both inactive and active centaurs transit through different mean motion resonances (generally with jupiter) during their evolution. | dynamical evolution and end states of active and inactive centaurs |
the occurrence of emerging organic micropollutants (omps) in sewage sludge has been widely reported; nevertheless, their fate during sludge treatment remains unclear. the objective of this work was to study the fate of omps during mesophilic and thermophilic anaerobic digestion (ad), the most common processes used for sludge stabilization, by using raw sewage sludge without spiking omps. moreover, the results of analytical chemistry were complemented with biological assays in order to verify the possible adverse effects (estrogenic and genotoxic) on the environment and human health in view of an agricultural (re)use of digested sludge. musk fragrances (ahtn, hhcb), ibuprofen (ibp) and triclosan (tcs) were the most abundant compounds detected in sewage sludge. in general, the efficiency of the ad process was not dependent on operational parameters but compound-specific: some omps were highly biotransformed (e.g. sulfamethoxazole and naproxen), while others were only slightly affected (e.g. ibp and tcs) or even unaltered (e.g. ahtn and hhcb). the mcf-7 assay evidenced that estrogenicity removal was driven by temperature. the ames test did not show point mutation in salmonella typhimurium while the comet test exhibited a genotoxic effect on human leukocytes attenuated by ad. this study highlights the importance of combining chemical analysis and biological activities in order to establish appropriate operational strategies for a safer disposal of sewage sludge. actually, it was demonstrated that temperature has an insignificant effect on the disappearance of the parent compounds while it is crucial to decrease estrogenicity. | is anaerobic digestion effective for the removal of organic micropollutants and biological activities from sewage sludge? |
since its discovery in the first half of the 20th century, scientists have puzzled over the origins of titan’s atmosphere. current models suggest that atmospheric n2 on titan may have originated from nh3-bearing ice with n-isotopic ratios similar to those observed in nh2 in cometary comae (14n/15n ∼ 136). in contrast, n2 ice appears to be too 15n poor to explain titan’s atmosphere (14n/15n ∼ 168). additionally, data from the rosetta mission to comet 67p/churyumov-gerasimenko suggest that the ar/n2 ratio of outer solar system planetesimals may be too high for a comet-like n2 source on titan. the rosetta mission also revealed an astonishing abundance of n-bearing complex organic material. while thermal fractionation of cometary sources during titan accretion may explain the loss of n2- and ar-rich ices, more refractory materials such as complex organics would be retained. later heating in the interior may lead to volatilization of accreted organics, consistent with cassini-huygens measurements of 40ar that suggest outgassing from the interior may have played a role in atmosphere formation. here, we develop a three endmember mixing model for n isotopes and the 36ar/14n ratio of titan’s atmosphere, and consider the implications for the source of atmospheric methane. our model suggests that titan’s interior is likely warm, and that n from accreted organics may contribute on the order of 50% of titan’s present-day nitrogen atmosphere. | contributions from accreted organics to titan’s atmosphere: new insights from cometary and chondritic data |
a new interstellar molecule, ch3nco (methyl isocyanate), has been detected using the 12 m telescope of the arizona radio observatory (aro). ch3nco was identified in spectra covering 48 ghz (68-116 ghz) in the 3 mm segment of a broadband survey of sgr b2(n). thirty very favorable rotational lines (ka = 0 and ka = 1 only; eu < 60 k) originating in five consecutive transitions (j = 8 \to 7, 9 \to 8, 10 \to 9, 11 \to 10, and 12 \to 11) in both the a and e internal rotation species are present in this frequency range. emission was observed at all of the predicted frequencies, with 17 lines appearing as distinct, uncontaminated spectral features, clearly showing the classic a-type, asymmetric top pattern, with {{t}r}* ≈ 20-70 mk. the ch3nco spectra also appear to exhibit two velocity components near vlsr ≈ 62 and 73 km s-1, both with δv1/2 ≈ 10 km s-1—typical of molecules such as ch2chcn, hnco, and hcooch3 in sgr b2(n). the column density of ch3nco in sgr b2(n) was determined to be ntot ≈ 2.3 × 1013 and 1.5 × 1013 cm-2 for the 62 and 73 km s-1 components, corresponding to fractional abundances, relative to h2, of f ≈ 7.6 × 10-12 and 5.0 × 10-12, respectively. ch3nco was recently detected in volatized material from comet 67p/churyumov-gerasimenko by rosetta's philae lander, with an abundance ∼1.3% of water; in sgr b2(n), ch3nco is roughly ∼0.04% of the h2o abundance. | interstellar detection of methyl isocyanate ch3nco in sgr b2(n): a link from molecular clouds to comets |
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