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lunar regolith breccias are temporal archives of magmatic and impact bombardment processes on the moon. apollo 16 sample 60016 is an "ancient" feldspathic regolith breccia that was converted from a soil to a rock at ~3.8 ga. the breccia contains a small (70 × 50 μm) rock fragment composed dominantly of an fe-oxide phase with disseminated domains of troilite. fragments of plagioclase (an95-97), pyroxene (en74-75, fs21-22,wo3-4), and olivine (fo66-67) are distributed in and adjacent to the fe-oxide. the silicate minerals have lunar compositions that are similar to anorthosites. mineral chemistry, synchrotron x-ray absorption near edge spectroscopy (xanes) and x-ray diffraction (xrd) studies demonstrate that the oxide phase is magnetite with an estimated fe3+/σfe ratio of ~0.45. the presence of magnetite in 60016 indicates that oxygen fugacity during formation was equilibrated at, or above, the fe-magnetite or wüstite-magnetite oxygen buffer. this discovery provides direct evidence for oxidized conditions on the moon. thermodynamic modeling shows that magnetite could have been formed from oxidization-driven mineral replacement of fe-metal or desulphurisation from fe-sulfides (troilite) at low temperatures (<570 °c) in equilibrium with h2o steam/liquid or co2 gas. oxidizing conditions may have arisen from vapor transport during degassing of a magmatic source region, or from a hybrid endogenic-exogenic process when gases were released during an impacting asteroid or comet impact. | identification of magnetite in lunar regolith breccia 60016: evidence for oxidized conditions at the lunar surface |
context. centaurs are icy objects in transition between the trans-neptunian region and the inner solar system, orbiting the sun in the giant planet region. some centaurs display cometary activity, which cannot be sustained by the sublimation of water ice in this part of the solar system, and has been hypothesized to be due to the crystallization of amorphous water ice.aims: in this work, we investigate centaurs discovered by the outer solar system origins survey (ossos) and search for cometary activity. tentative detections would improve understanding of the origins of activity among these objects.methods: we search for comae and structures by fitting and subtracting both point spread functions and trailed point-spread functions from the ossos images of each centaur. when available, col-ossos images were used to search also for comae.results: no cometary activity is detected in the ossos sample. we track the recent orbital evolution of each new centaur to confirm that none would actually be predicted to be active, and we provide size estimates for the objects.conclusions: the addition of 20 ossos objects to the population of ~250 known centaurs is consistent with the currently understood scenario, in which drastic drops in perihelion distance induce changes in the thermal balance prone to trigger cometary activity in the giant planet region. | ossos. xi. no active centaurs in the outer solar system origins survey |
by conserving momentum during the mixing of fast solar wind flow and slow planetary ion flow in an inelastic way, mass loading converts kinetic energy to other forms - e.g. first to electrical energy through charge separation and then to thermal energy (randomness) through gyromotion of the newly born cold ions for the comet and mars cases. here, we consider the earth's exterior cusp and plasma mantle, where the ionospheric origin escaping ions with finite temperatures are loaded into the decelerated solar wind flow. due to direct connectivity to the ionosphere through the geomagnetic field, a large part of this electrical energy is consumed to maintain field-aligned currents (facs) toward the ionosphere, in a similar manner as the solar wind-driven ionospheric convection in the open geomagnetic field region. we show that the energy extraction rate by the mass loading of escaping ions (δk) is sufficient to explain the cusp facs, and that δk depends only on the solar wind velocity accessing the mass-loading region (usw) and the total mass flux of the escaping ions into this region (mloadfload), as δk ∼ -mloadfloadu2sw/4. the expected distribution of the separated charges by this process also predicts the observed flowing directions of the cusp facs for different interplanetary magnetic field (imf) orientations if we include the deflection of the solar wind flow directions in the exterior cusp. using empirical relations of u0 ∝ kp + 1.2 and fload ∝ exp(0.45kp) for kp = 1-7, where u0 is the solar wind velocity upstream of the bow shock, δk becomes a simple function of kp as log10(δk) = 0.2 ṡ kp + 2 ṡ log10(kp + 1.2) + constant. the major contribution of this nearly linear increase is the fload term, i.e. positive feedback between the increase of ion escaping rate fload through the increased energy consumption in the ionosphere for high kp, and subsequent extraction of more kinetic energy δk from the solar wind to the current system by the increased fload. since fload significantly increases for increased flux of extreme ultraviolet (euv) radiation, high euv flux may significantly enhance this positive feedback. therefore, the ion escape rate and the energy extraction by mass loading during ancient earth, when the sun is believed to have emitted much higher euv flux than at present, could have been even higher than the currently available highest values based on kp = 9. this raises a possibility that the ion escape has substantially contributed to the evolution of the earth's atmosphere. | energy conversion through mass loading of escaping ionospheric ions for different kp values |
it is a well-known fact that the presence of a massive perturber interacting with a population of minor bodies following very eccentric orbits can strongly affect the distribution of their nodal distances. the details of this process have been explored numerically and its outcome confirmed observationally in the case of jupiter, where a bimodal distribution of nodal distances of comets has been found. here, we show evidence for a possible bimodal distribution of the nodal distances of the extreme trans-neptunian objects (etnos) in the form of a previously unnoticed correlation between nodal distance and orbital inclination. this proposed correlation is unlikely to be the result of observational bias as data for both large semimajor axis centaurs and comets fit well into the pattern found for the etnos, and all these populations are subjected to similar background perturbations when moving well away from the influence of the giant planets. the correlation found is better understood if these objects tend to avoid a putative planet with semimajor axis in the range of 300-400 au. | evidence for a possible bimodal distribution of the nodal distances of the extreme trans-neptunian objects: avoiding a trans-plutonian planet or just plain bias? |
among the near-earth object (neo) population, there are comets and active asteroids which are sources of fragments that initially move together; in addition, some neos follow orbits temporarily trapped in a web of secular resonances. these facts contribute to increasing the risk of meteoroid strikes on earth, making its proper quantification difficult. the identification and subsequent study of groups of small neos that appear to move in similar trajectories are necessary steps in improving our understanding of the impact risk associated with meteoroids. here, we present results of a search for statistically significant dynamical groupings among the neo population. our monte carlo-based methodology recovers well-documented groupings like the taurid complex or the one resulting from the split comet 73p/schwassmann-wachmann 3, and new ones that may have been the source of past impacts. among the most conspicuous are the mjolnir and ptah groups, perhaps the source of recent impact events like almahata sitta and chelyabinsk, respectively. meteoroid 2014 aa, that hit the earth on 2014 january 2, could have its origin in a marginally significant grouping associated with bennu. we find that most of the substructure present within the orbital domain of the neos is of resonant nature, probably induced by secular resonances and the kozai mechanism that confine these objects into specific paths with well-defined perihelia. | far from random: dynamical groupings among the neo population |
a sequence of events, dominated by two outbursts and ending with the preperihelion disintegration of comet c/2017 s3, is examined. the onset times of the outbursts are determined with high accuracy from the light curve of the nuclear condensation before it disappeared following the second outburst. while the brightness of the condensation was declining precipitously, the total brightness continued to grow in the stereo-a's hi1 images until two days before perihelion. the red magnitudes measured in these images refer to a uniform cloud of nuclear fragments, 2200 km^2 in projected area, that began to expand at a rate of 76 m s^(-1) at the time of the second outburst. a tail extension, detected in some stereo-a images, consisted of dust released far from the sun. orbital analysis of the ground-based observations shows that the comet had arrived from the oort cloud in a gravitational orbit. treating positional residuals as offsets of a companion of a split comet, we confirm the existence of the cloud of radiation-pressure driven millimeter-sized dust grains emanating from the nucleus during the second outburst. we detect a similar, but compact and much fainter cloud (or a sizable fluffy dust aggregate fragment) released at the time of the first outburst. --- the debris would make a sphere of 140 m across and its kinetic energy is equivalent to the heat of crystallization liberated by 100 tons of amorphous water ice. ramifications for short-lived companions of the split comets and for 1i `oumuamua are discussed. | preperihelion outbursts and disintegration of comet c/2017 s3 (pan-starrs) |
given rapid photodissociation and photodegradation, the recently discovered organics in the martian subsurface and atmosphere were probably delivered in geologically recent times. possible parent bodies are c-type asteroids, comets, and interplanetary dust particles (idps). the dust infall rate was estimated, using different methods, to be between 0.71 and 2.96 × 106 kg/yr (nesvorny et al., 2011; borin et al., 2017; crismani et al., 2017); assuming a carbon content of 10% (flynn, 1996), this implies an idp carbon flux of 0.07 - 0.3 ×106 kg/yr. we calculate for the first time the carbon flux from impacts of asteroids and comets. to this end, we perform dynamical simulations of impact rates on mars. we use the n-body integrator rmvs/swifter to propagate the sun and the eight planets from their current positions. we separately add comets and asteroids to the simulations as massless test particles, based on their current orbital elements, yielding mars impact rates of 4.34 ×10-3 comets/myr and 3.3 asteroids/myr. we estimate the delivered amount of carbon using published carbon content values. in asteroids, only c types contain appreciable amounts of carbon. given the absence of direct taxonomic information on the mars impactors, we base ourselves on the measured distribution of taxonomic types in combination with dynamic models of the origin of mars-crossing asteroids. we estimate the global carbon flux on mars from cometary impacts to be ∼ 0.013 × 106 kg/yr within an order of magnitude, while asteroids deliver ∼ 0.05 × 106 kg/yr. these values correspond to ∼ 4 - 19 % and ∼ 17 - 71 % , respectively, of the idp-borne carbon flux estimated by nesvorny et al., borin et al. and crismani et al. unlike the spatially homogeneous idp infall, impact ejecta are distributed locally, concentrated around the impact site. we find organics from asteroids and comets to dominate over idp-borne organics at distances up to 150 km from the crater center. our results may be important for the interpretation of in situ detections of organics on mars. | delivery of organics to mars through asteroid and comet impacts |
the corsair (comet rendezvous, sample acquisition, investigation, and return) mission was a proposal for the nasa new frontiers program. it belongs to the comet surface sample return mission theme which focuses on acquiring and returning to earth a macroscopic sample from the surface of a comet nucleus. corsair uses a harpoon-based sample acquisition system (sas) with the spacecraft hovering several meters above the comet surface. this stand-off strategy overcomes disadvantages of other systems such as drills. since comets are low gravity objects, those techniques would require anchoring before sampling, which is not necessary here. moreover, the harpoon-based system allows for acquiring several samples from different locations on the comet maximizing the scientific output of the mission. each sas assembly consists of a pyro-driven launcher, a sample acquisition and retrieval projectile (sarp) and a retraction system using a deployable composite boom structure. in order to collect enough cometary material, the launcher has to provide the required kinetic energy to the sarp. due to high energy densities, pyrotechnically actuated devices ultimately reduce the overall system mass and dimensions. first, the scientific and technological background of the corsair mission is explained. then, an overview of the development, design and testing of the launcher is given. finally, the launcher theory is introduced explaining the entire reaction chain: initiation → gas dynamics → sarp motion. | development and testing of a pyro-driven launcher for harpoon-based comet sample acquisition |
deep impact, epoxi and rosetta missions visited comets 9p/tempel 1, 103p/hartley 2 and 67p/churyumov-gerasimenko, respectively. each of these three missions was equipped with both multispectral imagers and infrared spectrometers. bright blue features containing water ice were detected in each of these comet nuclei. we analysed multispectral properties of enriched water ice features observed via optical, spectroscopic, and infrared remote imaging system narrow angle camera on comet 67p in the wavelength range of 260-1000 nm and then compared with multispectral data of water ice deposits observed on comets 9p and 103p. we characterize the uv/vis properties of water-ice-rich features observed on the nuclei of these three comets. when compared to the average surface of each comet, our analysis shows that the water ice deposits seen on comet 9p are similar to the clustered water-ice-rich features seen on comet 67p, while the water ice deposit seen on comet 103p is more akin to two large isolated water-ice-rich features seen on comet 67p. our results indicate that the water ice deposit observed on comet 103p contains more water ice than the water-ice-rich features observed on comets 9p and 67p, proportionally to the average surface of each nucleus. | comparative study of water ice exposures on cometary nuclei using multispectral imaging data |
breast cancer is a major complication in women and numerous approaches are being developed to overcome this problem. in conventional treatments such as chemotherapy and radiotherapy the post side effects cause an unsuitable effect in treatment of cancer. hence, it is essential to develop a novel strategy for the treatment of this disease. in the present investigation, a possible route for green synthesis of gold nanoparticles (aunps) using leaf extract of mimosa pudica and its anticancer efficacy in the treatment of breast cancer cell lines is studied. the synthesized nanoparticles were found to be effective in killing cancer cells (mda-mb-231 & mcf-7) which were studied using various anticancer assays (mtt assay, cell morphology determination, cell cycle analysis, comet assay, annexin v-fitc/pi staining and dapi staining). cell morphological analysis showed the changes occurred in cancer cells during the treatment with aunps. cell cycle analysis revealed apoptosis in g0/g1 to s phase. similarly in comet assay, there was an increase in tail length in treated cells in comparison with the control. annexin v-fitc/pi staining assay showed prompt fluorescence in treated cells indicating the translocation of phosphatidylserine from the inner membrane. pi and dapi staining showed the dna damage in treated cells. | anti-proliferative effect of biogenic gold nanoparticles against breast cancer cell lines (mda-mb-231 & mcf-7) |
iras 17256-3631 is a southern galactic massive star-forming region located at a distance of 2 kpc. in this paper, we present a multiwavelength investigation of the embedded cluster, the h ii region, as well as the parent cloud. radio images at 325, 610 and 1372 mhz were obtained using giant metrewave radio telescope, india while the near-infrared imaging and spectroscopy were carried out using united kingdom infrared telescope and mt. abu infrared telescope, india. the near-infrared k-band image reveals the presence of a partially embedded infrared cluster. the spectral features of the brightest star in the cluster, irs-1, spectroscopically agree with a late o or early b star and could be the driving source of this region. filamentary h2 emission detected towards the outer envelope indicates the presence of highly excited gas. the parent cloud is investigated at far-infrared to millimetre wavelengths and 18 dust clumps have been identified. the spectral energy distributions of these clumps have been fitted as modified blackbodies and the best-fitting peak temperatures are found to range from 14 to 33 k, while the column densities vary from 0.7 to 8.5 × 1022 cm-2. the radio maps show a cometary morphology for the distribution of ionized gas that is density bounded towards the north-west and ionization bounded towards the south-east. this morphology is better explained with the champagne flow model as compared to the bow-shock model. using observations at near-, mid- and far-infrared, submillimetre and radio wavelengths, we examine the evolutionary stages of various clumps. | star formation towards the southern cometary h ii region iras 17256-3631 |
the eruption of mount tambora in indonesia in 1815 was one of the most powerful of its kind in recorded history. this contribution addresses climatic responses to it, the post-eruption weather, and its impacts on human life in the czech lands. the climatic effects are evaluated in terms of air temperature and precipitation on the basis of long-term homogenised series from the prague-klementinum and brno meteorological stations, and mean czech series in the short term (1810-1820) and long term (1800-2010). this analysis is complemented by other climatic and environmental data derived from rich documentary evidence. czech documentary sources make no direct mention of the tambora eruption, neither do they relate any particular weather phenomena to it, but they record an extremely wet summer for 1815 and an extremely cold summer for 1816 (the "year without a summer") that contributed to bad grain harvests and widespread grain price increases in 1817. possible reasons for the cold summers in the first decade of the 19th century reflected in the contemporary press included comets, sunspot activity, long-term cooling and finally - as late as 1817 - earthquakes with volcanic eruptions. | climatic effects and impacts of the 1815 eruption of mount tambora in the czech lands |
the rolis, civa-p and osiris instruments on-board the philae lander and the rosetta orbiter acquired high-resolution images during the lander's descent towards the targeted landing site agilkia, during its unexpected rebounds and at the final landing site abydos on comet 67p/churyumov-gerasimenko. we, exploited these images, using robotic vision techniques, to locate the first touchdown on the surface of the comet nucleus, to reconstruct the lander's 3d trajectory during the descent and at the beginning of the first rebound, and to create local digital terrain models and depth maps of agilkia and abydos sites. using the rolis close-up images we could also determine the actual movements of the lander between the beginning and the end of the first science sequence and we propose a new lander's bubble movement command meant to increase the probability for a successful drilling during a hypothetical future long term science phase. | philae locating and science support by robotic vision techniques |
the rosetta observations have greatly advanced our knowledge of the cometary nucleus and its immediate environment. however, constraints on the mission (both planned and unplanned), the only partially successful philae lander, and other instrumental issues have inevitably resulted in open questions. surprising results from the many successful rosetta observations have also opened new questions, unimagined when rosetta was first planned. we discuss these and introduce several mission concepts that might address these issues. it is apparent that a sample return mission as originally conceived in the 1980s during the genesis of rosetta would provide many answers but it is arguable whether it is technically feasible even with today's technology and knowledge. less ambitious mission concepts are described to address the suggested main outstanding scientific goals. | towards new comet missions |
we report here time-domain infrared spectroscopy and optical photometry of the hd 145263 silica-rich circumstellar-disk system taken from 2003 through 2014. we find an f4v host star surrounded by a stable, massive 1022-1023 kg (mmoon to mmars) dust disk. no disk gas was detected, and the primary star was seen rotating with a rapid ∼1.75 day period. after resolving a problem with previously reported observations, we find the silica, mg-olivine, and fe-pyroxene mineralogy of the dust disk to be stable throughout and very unusual compared to the ferromagnesian silicates typically found in primordial and debris disks. by comparison with mid-infrared spectral features of primitive solar system dust, we explore the possibility that hd 145263's circumstellar dust mineralogy occurred with preferential destruction of fe-bearing olivines, metal sulfides, and water ice in an initially comet-like mineral mix and their replacement by fe-bearing pyroxenes, amorphous pyroxene, and silica. we reject models based on vaporizing optical stellar megaflares, aqueous alteration, or giant hypervelocity impacts as unable to produce the observed mineralogy. scenarios involving unusually high si abundances are at odds with the normal stellar absorption near-infrared feature strengths for mg, fe, and si. models involving intense space weathering of a thin surface patina via moderate (t < 1300 k) heating and energetic ion sputtering due to a stellar super-flare from the f4v primary are consistent with the observations. the space-weathered patina should be reddened, contain copious amounts of nanophase fe, and should be transient on timescales of decades unless replenished. | hd 145263: spectral observations of silica debris disk formation via extreme space weathering? |
on 2019 august 7, an impact flash lasting ∼1 s was observed on jupiter. the video of this event was analysed to obtain the light curve, and determine the energy release and initial mass. we find that the impactor released a total energy of 96-151 kilotons of tnt, corresponding to an initial mass between 190 and 260 metric tonnes with a diameter between 4 and 10 m. we developed a fragmentation model to simulate the atmospheric breakup of the object and reproduce the light curve. we model three different materials: cometary, stony, and metallic at speeds of 60, 65, and 70 km s-1, respectively, to determine the material make-up of the impacting object. the slower cases are best fitted by a strong, metallic object while the faster cases require a weaker material. | fragmentation modelling of the 2019 august impact on jupiter |
remote investigations of ancient matter in the solar system have traditionally been carried out through observations of long-period (lp) comets, which are less affected by solar irradiation than their short-period counterparts orbiting much closer to the sun. here we summarize the results of our decade-long survey of the distant activity of lp comets. we found that the most important separation in the data set is based on the dynamical nature of the objects. dynamically new comets are characterized by a higher level of activity on average: the most active new comets in our sample can be characterized by afρ values >3-4, higher than those for our most active returning comets. new comets develop more symmetric comae, suggesting a generally isotropic outflow. in contrast to this, the comae of recurrent comets can be less symmetrical, ocassionally exhibiting negative slope parameters, which suggest sudden variations in matter production. the morphological appearance of the observed comets is rather diverse. a surprisingly large fraction of the comets have long, tenuous tails, but the presence of impressive tails does not show a clear correlation with the brightness of the comets. | activity of 50 long-period comets beyond 5.2 au |
the exceptionally favorable close approach of jupiter-family comet 46p/wirtanen in 2018 december enabled characterization of its primary volatile composition with exceptionally high spatial resolution and sensitivities using the ishell spectrograph at the nasa infrared telescope facility on maunakea, h. we sampled emissions from h2o, hcn, c2h2, nh3, c2h6, and ch3oh on ut 2018 december 21 using two instrumental settings that spanned the 2.9-3.6 μm spectral region. we also obtained a sensitive 3σ upper limit for h2co and for the rarely studied molecule hc3n. we report rotational temperatures, production rates, and mixing ratios (relative to h2o as well as to c2h6). we place our results in context by comparing them with other comets observed at near-ir wavelengths. we also compare our results with those obtained using the nirspec-2 spectrograph on keck ii on ut december 17 and 18 and with results obtained from ishell on other dates during the same apparition. within 1-2σ uncertainty, production rates obtained for all molecules in this work were consistent with those obtained using nirspec-2 except h2o, indicating low-level variability on a timescale of days. mixing ratios with respect to h2o in 46p/wirtanen were consistent with corresponding values from nirspec-2 within the uncertainty with the exception of ch3oh, which yielded a higher ratio on december 21. our measurements afforded a high temporal resolution that spanned ∼2/3 of the rotational period of 46p/wirtanen, enabling us to test short-term variability in the production rates of h2o and hcn due to rotational effects. both h2o and hcn production rates showed similar temporal variability, resulting in nearly constant hcn/h2o. | testing short-term variability and sampling of primary volatiles in comet 46p/wirtanen |
six asteroids including two neas, one of which is pha, accessible for observation in september 2012 were investigated using a low-resolution (r ≈ 100) spectrophotometry in the range 0.35-0.90 μm with the aim to study features of their reflectance spectra. a high-altitude position of our terskol observatory (3150 m above sea level) favorable for the near-uv and visible-range observations of celestial objects allowed us to probably detect some new spectral features of the asteroids. two subtle absorption bands centered at 0.53 and 0.74 μm were found in the reflectance spectra of s-type (32) pomona and interpreted as signs of presence of pyroxenes in the asteroid surface matter and its different oxidation. very similar absorption bands centered at 0.38, 0.44 and 0.67-0.71 μm have been registered in the reflectance spectra of (145) adeona, (704) interamnia, and (779) nina of primitive types. we performed laboratory investigations of ground samples of known carbonaceous chondrites, orguel (ci), mighei (cm2), murchison (cm2), boriskino (cm2), and seven samples of low-iron mg serpentines as possible analogs of the primitive asteroids. in the course of this work, we discovered an intense absorption band (up to ∼25%) centered at 0.44 μm in reflectance spectra of the low-fe serpentine samples. as it turned out, the equivalent width of the band has a high correlation with content of fe3+ (octahedral and tetrahedral) in the samples. it may be considered as a confirmation of the previously proposed mechanism of the absorption due to electronic transitions in exchange-coupled pairs (ecp) of fe3+ neighboring cations. it means that the absorption feature can be used as an indicator of ferric iron in oxidized and hydrated low-fe compounds on the surface of asteroids and other atmosphereless celestial bodies. moreover, our measurements showed that the mechanism of light absorption is partially or completely blocked in the case of intermediate to high iron contents. therefore, the method cannot probably be used for quantitative estimation of fe3+ content on the bodies. based on laboratory study of the analog samples, we conclude that spectral characteristics of adeona, interamnia, and nina correspond to a mixture of ci-cm-chondrites and hydrated silicates, oxides and/or hydroxides. spectral signs of sublimation activity on adeona, interamnia, and nina at minimal heliocentric distances are likely discovered in the short-wavelength range (∼0.4-0.6 μm). it is suggested that such cometary-like activity at the highest surface temperatures is a frequent phenomenon for c and close type asteroids including considerable amounts of ices beneath the surface. a usual way of origin of a temporal coma of ice particles around a primitive asteroid is excavated fresh ice at recent impact event(s). the obtained reflectance spectra of two neas, (330825) 2008 xe3 and 2012 qg42, are predominantly featureless and could be attributed to s(c) and s(b)-type bodies, respectively. we discuss reasons why weak spectral features seen in reflectance spectra of the main-belt asteroids are not observed in those of neas. | spectrophotometry of (32) pomona, (145) adeona, (704) interamnia, (779) nina, (330825) 2008 xe3, and 2012 qg42 and laboratory study of possible analog samples |
we have investigated the effect of stellar encounters on the formation and disruption of the oort cloud using the classical impulse approximation. we calculate the evolution of a planetesimal disk into a spherical oort cloud due to the perturbation from passing stars for 10 gyr. we obtain the empirical fits of the e-folding time for the number of oort cloud comets using the standard exponential and kohlrausch formulae as functions of the stellar parameters and the initial semimajor axes of planetesimals. the e-folding time and the evolution timescales of the orbital elements are also analytically derived. in some calculations, the effect of the galactic tide is additionally considered. we also show the radial variations of the e-folding times to the oort cloud. from these timescales, we show that if the initial planetesimal disk has the semimajor axes distribution {dn}/{da}\propto {a}-2, which is produced by planetary scattering, the e-folding time for planetesimals in the oort cloud is ∼10 gyr at any heliocentric distance r. this uniform e-folding time over the oort cloud means that the supply of comets from the inner oort cloud to the outer oort cloud is sufficiently effective to keep the comet distribution as {dn}/{dr}\propto {r}-2. we also show that the final distribution of the semimajor axes in the oort cloud is approximately proportional to {a}-2 for any initial distribution. | effect of stellar encounters on comet cloud formation |
jupiter-family comet 15p/finlay has been reportedly quiet in activity for over a century but has harbored two outbursts during its 2014/2015 perihelion passage. here we present an analysis of these two outbursts using a set of cometary observations. the outbursts took place between 2014 december 15.4-16.0 ut and 2015 january 15.5-16.0 ut as constrained by ground-based and spacecraft observations. we find a characteristic ejection speed of v0 = 300-650 m s-1 for the ejecta of the first outburst and v0 = 550-750 m s-1 for that of the second outburst using a monte carlo dust model. the mass of the ejecta is calculated to be md = (2-3) × 105 kg for the first outburst and md = (4-5) × 105 kg for the second outburst, which corresponds to less than 10-7 of the nucleus mass. the specific energy of the two outbursts is found to be (0.3-2) × 105 j kg-1. we also revisit the long-standing puzzle of the nondetection of the hypothetical finlayid meteor shower by performing a cued search using the 13 yr data from the canadian meteor orbit radar, which does not reveal any positives. earth will pass the 2014/2015 outburst ejecta between 2021 october 6 at 22 hr ut and october 7 at 1 hr ut, with a chance for some significant meteor activity in the radio range, which may provide further clues to the finlayid puzzle. a southerly radiant in the constellation of ara will favor the observers in the southern tip of africa. | bangs and meteors from the quiet comet 15p/finlay |
both centaurs and trans-neptunian objects (tnos) are minor bodies found in the outer solar system. centaurs are a transient population that moves between the orbits of jupiter and neptune, and they probably diffused out of the tnos. tnos move mainly beyond neptune. some of these objects display episodic cometary behaviour; a few percent of them are known to host binary companions. here, we study the light-curves of two centaurs—2060 chiron (1977 ub) and 10199 chariklo (1997 cu26)—and three tnos—38628 huya (2000 eb173), 28978 ixion (2001 kx76), and 90482 orcus (2004 dw)—and the colours of the centaurs and huya. precise, ∼1~%, r-band absolute ccd photometry of these minor bodies acquired between 2006 and 2011 is presented; the new data are used to investigate the rotation rate of these objects. the colours of the centaurs and huya are determined using bvri photometry. the point spread function of the five minor bodies is analysed, searching for signs of a coma or close companions. astrometry is also discussed. a periodogram analysis of the light-curves of these objects gives the following rotational periods: 5.5±0.4~h for chiron, 7.0± 0.6~h for chariklo, 4.45±0.07~h for huya, 12.4±0.3~h for ixion, and 11.9±0.5~h for orcus. the colour indices of chiron are found to be b-v=0.53±0.05, v-r=0.37±0.08, and r-i=0.36±0.15. the values computed for chariklo are v-r=0.62±0.07 and r-i=0.61±0.07. for huya, we find v-r=0.58±0.09 and r-i=0.64±0.20. our rotation periods are similar to and our colour values are consistent with those already published for these objects. we find very low levels of cometary activity (if any) and no sign of close or wide binary companions for these minor bodies. | photometry of centaurs and trans-neptunian objects: 2060 chiron (1977 ub), 10199 chariklo (1997 cu26), 38628 huya (2000 eb173), 28978 ixion (2001 kx76), and 90482 orcus (2004 dw) |
the trojan asteroids, orbiting the sun in jupiter's stable lagrange points, provide a unique perspective on the history of our solar system. as a large population of small bodies, they record important gravitational interactions in the dynamical evolution of the solar system. as primitive bodies, their compositions and physical properties provide windows into the conditions in the solar nebula in the region in which they formed. in the past decade, significant advances have been made in understanding their physical properties, and there has been a revolution in thinking about the origin of trojans. the ice and organics generally presumed to be a significant part of trojan composition have yet to be detected directly, although the low density of the binary system patroclus (and possibly low density of the binary/moonlet system hektor) is consistent with an interior ice component. by contrast, fine-grained silicates that appear to be similar to cometary silicates in composition have been detected, and a color bimodality may indicate distinct compositional groups among the trojans. whereas trojans had traditionally been thought to have formed near 5 au, a new paradigm has developed in which the trojans formed in the proto-kuiper belt, and were scattered inward and captured in the trojan swarms as a result of resonant interactions of the giant planets. whereas the orbital and population distributions of current trojans are consistent with this origin scenario, there are significant differences between current physical properties of trojans and those of kuiper belt objects. these differences may be indicative of surface modification due to the inward migration of objects that became the trojans, but understanding of appropriate modification mechanisms is poor and would benefit from additional laboratory studies. many open questions about this intriguing population remain, and the future promises significant strides in our understanding of trojans. the time is ripe for a spacecraft mission to the trojans, to transform these objects into geologic worlds that can be studied in detail to unravel their complex history. | the complex history of trojan asteroids |
context. surveys in the visible and near-infrared spectral range have revealed the presence of low-albedo asteroids in cometary-like orbits (acos). in contrast to jupiter-family comets (jfcs), acos are inactive, but possess similar orbital parameters.aims: in this work, we discuss why acos are inactive, whereas jfcs show gas-driven dust activity, although both belong to the same class of primitive solar system bodies.methods: we hypothesize that acos and jfcs have formed under the same physical conditions, namely by the gravitational collapse of ensembles of ice and dust aggregates. we use the memory effect of dust-aggregate layers under gravitational compression to discuss under which conditions the gas-driven dust activity of these bodies is possible.results: owing to their smaller sizes, jfcs can sustain gas-driven dust activity much longer than the bigger acos, whose sub-surface regions possess an increased tensile strength, due to gravitational compression of the material. the increased tensile strength leads to the passivation against dust activity after a relatively short time of activity.conclusions: the gravitational-collapse model of the formation of planetesimals, together with the gravitational compression of the sub-surface material simultaneously, explains the inactivity of acos and the gas-driven dust activity of jfcs. their initially larger sizes means that acos possess a higher tensile strength of their sub-surface material, which leads to a faster termination of gas-driven dust activity. most objects with radii larger than 2 km have already lost their activity due to former gravitational compression of their current surface material. | why are jupiter-family comets active and asteroids in cometary-like orbits inactive?. how hydrostatic compression leads to inactivity |
in this study, we present high-resolution visible multi-object spectrograph integral field unit spectroscopy (vimos-ifu) of the extremely metal-poor h ii/blue compact dwarf (bcd) galaxy tol 65. the optical appearance of this galaxy shows clearly a cometary morphology with a bright main body and an extended and diffuse stellar tail. we focus on the detection of metallicity gradients or inhomogeneities as expected if the ongoing star formation activity is sustained by the infall/accretion of metal-poor gas. no evidences of significant spatial variations of abundances were found within our uncertainties. however, our findings show a slight anticorrelation between gas metallicity and star formation rate at spaxel scales, in the sense that high star formation is found in regions of low metallicity, but the scatter in this relation indicates that the metals are almost fully diluted. our observations show the presence of extended hα emission in the stellar tail of the galaxy. we estimated that the mass of the ionized gas in the tail m(h ii)tail ∼1.7 × 105 m⊙ corresponds with ∼24 per cent of the total mass of the ionized gas in the galaxy. we found that the hα velocity dispersion of the main body and the tail of the galaxy are comparable with the one found in the neutral gas by previous studies. this suggests that the ionized gas still retains the kinematic memory of its parental cloud and likely a common origin. finally, we suggest that the infall/accretion of cold gas from the outskirts of the galaxy and/or minor merger/interaction may have produced the almost flat abundance gradient and the cometary morphology in tol 65. | on the properties of the interstellar medium in extremely metal-poor blue compact dwarf galaxies. a vimos-ifu study of the cometary galaxy and ly α absorber tol 65 |
metal pollution in white dwarf photospheres originates from the accretion of some combination of planets, moons, asteroids, comets, boulders, pebbles, and dust. when large bodies reside in dynamically stagnant locations - unable themselves to pollute or even closely approach the white dwarf - then smaller reservoirs of impact debris may become a complementary or the primary source of metal pollutants. here, we take a first step towards exploring this possibility by computing limits on the recoil mass that escapes the gravitational pull of the target object following a single impact onto an atmosphere-less surface. by considering vertical impacts only with the full-chain analytical prescription from kurosawa & takada, we provide lower bounds for the ejected mass for basalt, granite, iron, and water-rich target objects across the radii range 100-103 km. our use of the full-chain prescription as opposed to physical experiments or hydrocode simulations allows us to quickly sample a wide range of parameter space appropriate to white dwarf planetary systems. our numerical results could be used in future studies to constrain freshly generated small debris reservoirs around white dwarfs given a particular planetary system architecture, bombardment history, and impact geometries. | generating metal-polluting debris in white dwarf planetary systems from small-impact crater ejecta |
recent observations have suggested that there is water ice present on the surfaces of 24 themis and 1 ceres. we present upper limits on the h2o production rate on these bodies derived using a search for [o i]6300 å emission. for themis, the water production is less than 4.5 × 1027 mol s-1 , while for ceres our derived upper limit is 4.6 × 1028 mol s-1. the derived limits imply a very low fraction of the surface area of each asteroid is active (< 2 ×10-4), though this estimate varies by as much as an order of magnitude depending on thermal properties of the surface. this is much lower than seen for comets, which have active areas of 10-2-10-1. we discuss possible implications for our findings on the nature of water ice on themis and ceres. | observational constraints on water sublimation from 24 themis and 1 ceres |
aims: we aim to determine whether dissociative excitation of cometary neutrals by electron impact is the major source of far-ultraviolet (fuv) emissions at comet 67p/churyumov-gerasimenko in the southern hemisphere at large heliocentric distances, both during quiet conditions and impacts of corotating interaction regions observed in the summer of 2016.methods: we combined multiple datasets from the rosetta mission through a multi-instrument analysis to complete the first forward modelling of fuv emissions in the southern hemisphere of comet 67p and compared modelled brightnesses to observations with the alice fuv imaging spectrograph. we modelled the brightness of oi1356, oi1304, lyman-β, ci1657, and cii1335 emissions, which are associated with the dissociation products of the four major neutral species in the coma: co2, h2o, co, and o2. the suprathermal electron population was probed by the ion and electron sensor of the rosetta plasma consortium and the neutral column density was constrained by several instruments: the rosetta orbiter spectrometer for ion and neutral analysis (rosina), the microwave instrument for the rosetta orbiter and the visual infrared thermal imaging spectrometer.results: the modelled and observed brightnesses of the fuv emission lines agree closely when viewing nadir and dissociative excitation by electron impact is shown to be the dominant source of emissions away from perihelion. the cii1335 emissions are shown to be consistent with the volume mixing ratio of co derived from rosina. when viewing the limb during the impacts of corotating interaction regions, the model reproduces brightnesses of oi1356 and ci1657 well, but resonance scattering in the extended coma may contribute significantly to the observed lyman-β and oi1304 emissions. the correlation between variations in the suprathermal electron flux and the observed fuv line brightnesses when viewing the comet's limb suggests electrons are accelerated on large scales and that they originate in the solar wind. this means that the fuv emissions are auroral in nature. data are only available at the cds via anonymous ftp to cdsarc.u-strasbg.fr (ftp://130.79.128.5) or via http://cdsarc.u-strasbg.fr/viz-bin/cat/j/a+a/647/a119 | multi-instrument analysis of far-ultraviolet aurora in the southern hemisphere of comet 67p/churyumov-gerasimenko |
the composition of solar system surfaces can be inferred through reflectance and emission spectroscopy, by comparing these observations to laboratory measurements and radiative transfer models. while several populations of objects appear to be covered by sub-micrometre sized particles (d < 1 μm) (referred to as hyperfine), there are limited studies on reflectance and emission of particulate surfaces composed of particles smaller than the visible and infrared wavelengths. we have undertaken an effort to determine the reflectance of hyperfine particulate surfaces in conjunction with high-porosity, in order to simulate the physical state of cometary surfaces and their related asteroids (p- and d-types). in this work, we present a technique developed to produce hyperfine particles of astrophysical relevant materials (silicates, sulphides, macromolecular organics). this technique is used to prepare hyperfine powders that were measured in reflectance in the 0.4-2.6 μm range. these powders were then included in water ice particles, sublimated under vacuum, in order to produce a hyperporous sample of hyperfine material (refers as to sublimation residue). when grinded below one micrometre, the four materials studied (olivine, smectite, pyroxene and amorphous silica), show strong decrease of their absorption features together with a blueing of the spectra. this "small grain degeneracy" implies that surfaces covered by hyperfine grains should show only shallow absorption features if any (in the case of moderately absorbing particles as studied here). these two effects, decrease of band depth and spectral blueing, appear magnified when the grains are incorporated in the hyperporous residue. we interpret the distinct behaviour between hyperporous and more compact surfaces by the distancing of individual grains and a decrease in the size of the elemental scatterers. this work implies that hyperfine grains are unabundant at the surfaces of s- or v-type asteroids, and that the blue nature of b-type may be related to a physical effect rather than a compositional effect. | visible and near-infrared reflectance of hyperfine and hyperporous particulate surfaces |
centaurs are small bodies orbiting in the giant planet region that were scattered inward from their source populations beyond neptune. some members of the population display comet-like activity during their transition through the solar system, the source of which is not well understood. the range of heliocentric distances where the active centaurs have been observed and their median lifetime in the region suggest that this activity is driven neither by water-ice sublimation nor entirely by supervolatiles. here we present an observational and thermodynamical study of 13 centaurs discovered in the pan-starrs1 detection database aimed at identifying and characterizing active objects beyond the orbit of jupiter. we find no evidence of activity associated with any of our targets at the time of their observations with the gemini north telescope in 2017 and 2018, or in archival data from 2013 to 2019. upper limits on the possible volatile and dust production rates from our targets are 1-2 orders of magnitude lower than production rates in some known comets and are in agreement with values measured for other inactive centaurs. our numerical integrations show that the orbits of six of our targets evolved interior to r ~ 15 au over the past 100,000 yr, where several possible processes could trigger sublimation and outgassing, but their apparent inactivity indicates that either their dust production is below our detection limit or the objects are dormant. only one centaur in our sample-2014 pq70-experienced a sudden decrease in semimajor axis and perihelion distance attributed to the onset of activity for some previously known inactive centaurs, and therefore it is the most likely candidate for any future outburst. this object should be a target of high interest for any further observational monitoring. | no activity among 13 centaurs discovered in the pan-starrs1 detection database |
the lco outbursting objects key (look) project uses the telescopes of the las cumbres observatory (lco) network to (1) systematically monitor a sample of previously discovered over the whole sky, to assess the evolutionary state of these distant remnants from the early solar system, and (2) use alerts from existing sky surveys to rapidly respond to and characterize detected outburst activity in all small bodies. the data gathered on outbursts helps to characterize each outburst's evolution with time, helps to assess the frequency and magnitude distribution of outbursts in general, and contributes to the understanding of outburst processes and volatile distribution in the solar system. the look project exploits the synergy between current and future wide-field surveys such as ztf, pan-starrs, and lsst, as well as rapid-response telescope networks such as lco, and serves as an excellent test bed for what will be needed for the much larger number of objects coming from rubin observatory. we will describe the look project goals, the planning and target selection (including the use of neoexchange as a target and observation manager or "tom"), and results from the first phase of observations, including the detection of activity and outbursts on the giant comet c/2014 un271 (bernardinelli-bernstein) and the discovery and follow-up of 28 outbursts on 14 comets. within these outburst discoveries, we present a high-cadence light curve of 7p/pons-winnecke with 10 outbursts observed over 90 days, a large outburst on 57p/dutoit-neujmin-delporte, and evidence that comet p/2020 x1 (atlas) was in outburst when discovered. | the lco outbursting objects key project: overview and year 1 status |
the chandra x-ray observatory (chandra) and the x-ray multi-mirror mission (xmm-newton) continue to expand the frontiers of knowledge about high-energy processes in the universe. these groundbreaking observatories lead an x-ray astronomy revolution: revealing the physical processes and extreme conditions involved in producing cosmic x-rays in objects ranging in size from a few kilometres (comets) to millions of light years (clusters of galaxies), and particle densities ranging over 20 orders of magnitude. in probing matter under conditions far outside those accessible from earth, they have a central role in the quest to understand our place in the universe and the fundamental laws that govern our existence. chandra and xmm-newton are also part of a larger picture wherein advances in subarcsecond imaging and high-resolution spectroscopy across a wide range of wavelengths combine to provide a more complete picture of the phenomena under investigation. as these missions mature, deeper observations and larger samples further expand our knowledge, and new phenomena and collaborations with new facilities forge exciting, often unexpected discoveries. this review provides the highlights of a wide range of studies, including auroral activity on jupiter, cosmic-ray acceleration in supernova remnants, colliding neutron stars, missing baryons in low-density hot plasma, and supermassive black holes formed less than a billion years after the big bang. | x-ray astronomy comes of age |
precipitation forecasting is an important scientific challenge that has wide-reaching impacts on society. historically, this challenge has been tackled using numerical weather prediction (nwp) models, grounded on physics-based simulations. recently, many works have proposed an alternative approach, using end-to-end deep learning (dl) models to replace physics-based nwp models. while these dl methods show improved performance and computational efficiency, they exhibit limitations in long-term forecasting and lack the explainability. in this work, we present a hybrid nwp-dl workflow to fill the gap between standalone nwp and dl approaches. under this workflow, the outputs of nwp models are fed into a deep neural network, which post-processes the data to yield a refined precipitation forecast. the deep model is trained with supervision, using automatic weather station (aws) observations as ground-truth labels. this can achieve the best of both worlds, and can even benefit from future improvements in nwp technology. to facilitate study in this direction, we present a novel dataset focused on the korean peninsula, termed komet (korea meteorological dataset), comprised of nwp outputs and aws observations. for the nwp model, the global data assimilation and prediction systems-korea integrated model (gdaps-kim) is utilized. we provide analysis on a comprehensive set of baseline methods aimed at addressing the challenges of komet, including the sparsity of aws observations and class imbalance. to lower the barrier to entry and encourage further study, we also provide an extensive open-source python package for data processing and model development. our benchmark data and code are available at https://github.com/osilab-kaist/komet-benchmark-dataset. | benchmark dataset for precipitation forecasting by post-processing the numerical weather prediction |
we present an in-depth analysis of a time interval when quasi-linear mirror mode structures were detected by magnetic field and plasma measurements as observed by the nasa/mars atmosphere and volatile evolution spacecraft. we employ ion and electron spectrometers in tandem to support the magnetic field measurements and confirm that the signatures are indeed mirror modes. wedged against the magnetic pile-up boundary, the low-frequency signatures last on average ∼10 with corresponding sizes of the order of 15-30 upstream solar wind proton thermal gyroradii, or 10-20 proton gyroradii in the immediate wake of the quasi-perpendicular bow shock. their peak-to-peak amplitudes are of the order of 30-35 nt with respect to the background field, and appear as a mixture of dips and peaks, suggesting that they may have been at different stages in their evolution. situated in a marginally stable plasma with β‖ ∼ 1, we hypothesize that these so-called magnetic bottles, containing a relatively higher energy and denser ion population with respect to the background plasma, are formed upstream of the spacecraft behind the quasi-perpendicular shock. these signatures are very reminiscent of magnetic bottles found at other unmagnetized objects such as venus and comets, also interpreted as mirror modes. our case study constitutes the first unmistakable identification and characterization of mirror modes at mars from the joint points of view of magnetic field, electron and ion measurements. up until now, the lack of high-temporal resolution plasma measurements has prevented such an in-depth study. | making waves: mirror mode structures around mars observed by the maven spacecraft |
high-resolution infrared spectra of comet c/2014 q2 lovejoy were acquired with nirspec at the w. m. keck observatory on two post-perihelion dates (ut 2015 february 2 and 3). h2o was measured simultaneously with co, ch3oh, h2co, ch4, c2h6, c2h4, c2h2, hcn, and nh3 on both dates, and rotational temperatures, production rates, relative abundances, h2o ortho-to-para ratios, and spatial distributions in the coma were determined. the first detection of c2h4 in a comet from ground-based observations is reported. abundances relative to h2o for all species were found to be in the typical range compared with values for other comets in the overall population to date. there is evidence of variability in rotational temperatures and production rates on timescales that are small compared with the rotational period of the comet. spatial distributions of volatiles in the coma suggest complex outgassing behavior. ch3oh, hcn, c2h6, and ch4 spatial distributions in the coma are consistent with direct release from associated ices in the nucleus and are peaked in a more sunward direction compared with co-measured dust. h2o spatial profiles are clearly distinct from these other four species, likely due to a sizable coma contribution from icy grain sublimation. spatial distributions for c2h2, h2co, and nh3 suggest substantial contributions from extended coma sources, providing further evidence for distinct origins and associations for these species in comets. co shows a different spatial distribution compared with other volatiles, consistent with jet activity from discrete nucleus ice sources. | volatile abundances, extended coma sources, and nucleus ice associations in comet c/2014 q2 (lovejoy) |
we present hubble space telescope observations of active asteroid p/2020 o1 taken to examine its development for a year after perihelion. we find that the mass loss peaks at ≲1 kg s-1 in 2020 august and then declines to nearly zero over four months. long-duration mass loss (~180 days) is consistent with a sublimation origin, indicating that this object is likely an ice-bearing main-belt comet. equilibrium sublimation of water ice from an area as small as 1580 m2 can supply the observed mass loss. time-series photometry shows tentative evidence for extremely rapid rotation (double-peaked period <2 hr) of the small nucleus (effective radius ~420 m). ejection velocities of 0.1 mm particles are comparable to the 0.3 m s-1 gravitational escape speed from the nucleus, while larger particles are ejected at speeds less than the escape velocity. these properties are consistent with the sublimation of near-surface ice aided by centripetal acceleration. if water-ice sublimation is confirmed, p/2020 o1 would be an icy asteroid with the smallest semimajor axis (highest temperature), setting new bounds on the distribution of ice in the asteroid belt. | hubble space telescope observations of active asteroid p/2020 o1 (lemmon-panstarrs) |
the parker solar probe (psp) aims to explore the nascent solar wind close to the sun. meanwhile, psp is also expected to encounter small objects like comets and asteroids. in this work, we survey the ephemerides to find the chance of a recent encounter and then model the interaction between released dusty plasmas and solar wind plasmas. on 2019 september 2, a comet-like object, the 322p/solar and heliosphere observatory, just passed its perihelion flying to a heliocentric distance of 0.12 au and swept by psp at a relative distance as close as 0.025 au. we present the dynamics of the dust particles released from 322p, forming a curved dust tail. along the path of psp in the simulated inner heliosphere, the states of plasma and magnetic field are sampled and illustrated, with the magnetic field sequences from simulation results being compared directly with the in situ measurements from psp. through the comparison, we suggest that 322p might be at a deficient activity level releasing limited dusty plasmas on its way to becoming a "rock comet." we also present images of solar wind streamers as recorded by the wide-field imager for solar probe plus, showing an indication of dust bombardment for the images superposed with messy trails. we observe from the large angle and spectrometric coronagraph that 322p was transiting from a dimming region to a relatively bright streamer during its perihelion passage, and perform a simulation to confirm that 322p was flying from relatively faster to slower solar wind streams, modifying the local plasma states of the streams. | the encounter of the parker solar probe and a comet-like object near the sun: model predictions and measurements |
dust transport and deposition behind larger boulders on the comet 67p/churyumov-gerasimenko (67p/c-g) have been observed by the rosetta mission. we present a mechanism for dust-transport vectors based on a homogeneous surface activity model incorporating in detail the topography of 67p/c-g. the combination of gravitation, gas drag, and coriolis force leads to specific dust transfer pathways, which for higher dust velocities fuel the near-nucleus coma. by distributing dust sources homogeneously across the whole cometary surface, we derive a global dust-transport map of 67p/c-g. the transport vectors are in agreement with the reported wind-tail directions in the philae descent area. | prevailing dust-transport directions on comet 67p/churyumov-gerasimenko |
the analysis of photometrical observations of comet 29p/schwassmann-wachmann 1 is presented. the broadband observations were carried out for 15 nights from 2012 to 2019 at the lisnyky observational station of taras shevchenko national university of kyiv. apparent magnitudes and dust productivity level afρ in filter r were calculated. middle and height dust activity of the comet is characterized by parameter afρ which varied from 1246 to 17563 cm during all periods of observation. based on the morphological analysis, four jet-like structures were detected in the coma on almost all dates. using the geometrical model for the jet structure interpretation during all observation sets, we obtained following results: the nucleus rotation period of 57 ± 2 days, the rotational axis orientation, the locations of active regions for four jet-like structures within a narrow belt near the equator. | photometry of comet 29p/schwassmann-wachmann 1 in 2012-2019 |
we measured the degree of linear polarization of comet c/2020 s3 (erasmus) on 2020 november 13, 20, 22, and 23, while the comet was observed at large phase angles, α = 62.6°-66.6°. on the first two epochs, the polarization closely matched what was previously observed in comet c/1989 x1 (austin). on the third epoch, the polarization was found to rise slightly, and on the latest epoch, it rose significantly, exceeding that of comet austin. on the last observation, the polarization of comet erasmus appears to be more consistent with what was previously seen in comet c/1996 b2 (hyakutake) at a similar phase angle. while such short-term transient behaviour has been seen previously, comets austin and hyakutake belong to two different classes in classifications based on the amplitude of their positive polarization pmax and, hence, comet erasmus revealed a transition from the class of low-pmax comets to that of high-pmax comets within only a few days. polarization images and modelling suggest that the transition occurred due to a decrease in the relative abundance of mg-rich silicate particles in the inner coma by 1/3, revealing a qualitative change in emanations of dust particles from the erasmus nucleus. | c/2020 s3 (erasmus): comet with a presumably transient maximum of linear polarization pmax |
in this detailed geochemical, petrological, and microstructural study of felsite clast materials contained in apollo breccia samples 12013, 14321, and 15405, little evidence was found for relatively enriched reservoirs of endogenic lunar volatiles. nanosims measurements have revealed very low volatile abundances (≤ 2-18 ppm hydrogen) in nominally anhydrous minerals (nams) plagioclase, potassic alkali feldspar, and sio2 that make up a majority of these felsic lithologies. yet these mineral assemblages and clast geochemistries on earth would normally yield relatively high volatiles contents in their nams (∼20 to ≥ 80 ppm hydrogen). this difference is particularly notable in felsite 14321,1062 that exhibits extremely low volatile abundances (≤ 2 ppm hydrogen) and a relatively low amount of microstructural evidence for shock metamorphism given that it is a clast of the most evolved (∼74 wt.% sio2) rock-type returned from the moon. if taken at face value, 'wet' felsic magmas (∼1.2-1.7 wt.% water) are implied by the relatively high hydrogen contents of feldspar in felsite clasts in apollo samples 12013 and 15405, but these results are likely misleading. these felsic clasts have microstructural features indicative of significantly higher shock stress than 14321,1062. these crustal lithologies likely obtained no more water from the lunar interior than the magma body producing 14321,1062. rather, we suggest hydrogen was enriched in samples 12013 and 15405 by impact induced exchange, and/or partial assimilation of volatiles added to the surface of the moon by a hydrated impactor (asteroid or comet) or the solar wind. thus, the best estimate for magmatic water contents of felsic lunar magmas comes from 14321,1062 that leads to a calculated magmatic water content of ≤ 0.2 wt.%. this dry felsic magma has a slightly greater, but comparable water content to the ancient mafic magmas implied by the other lithologies that we have studied. based on this and expanding evidence for a significantly dry ancient or early degassed moon it is likely that some recent estimates (100's ppm) of the water abundances in the lunar parental magma ocean have been overestimated. | volatiles in lunar felsite clasts: impact-related delivery of hydrous material to an ancient dry lunar crust |
the emission of [o i] lines in the coma of comet 67p/churyumov-gerasimenko during the rosetta mission have been explained by electron impact dissociation of water rather than the process of photodissociation. this is the direct evidence for the role of electron induced processing has been seen on such a body. analysis of other emission features is handicapped by a lack of detailed knowledge of electron impact cross sections which highlights the need for a broad range of electron scattering data from the molecular systems detected on the comet. in this paper, we present an overview of the needs for electron scattering data relevant for the understanding of observations in coma, the tenuous atmosphere and on the surface of 67p/churyumov-gerasimenko during the rosetta mission. the relevant observations for elucidating the role of electrons come from optical spectra, particle analysis using the ion and electron sensors and mass spectrometry measurements. to model these processes electron impact data should be collated and reviewed in an electron scattering database and an example is given in the beamd, which is a part of a larger consortium of virtual atomic and molecular data centre—vamdc. | rosetta mission: electron scattering cross sections—data needs and coverage in beamdb database |
we report photometric observations with las cumbres observatory 1-m sutherland-lcogt c telescope. the observations from 2021 june 22.174 (utc) indicate that the newly discovered 2014 un271 has cometary activity at heliocentric distance of 20.18 au. the observations were done with a panstarrs w-band filter (equivalent to sdss g'+r'+i') and were calibrated against gaia g-band field stars. | newly discovered object 2014 un271 observed as active at 20.18 au |
we monitor the seasonal erosion and accretion of dust deposits in the imhotep, hatmehit, and ma'at regions of comet 67p/churyumov-gerasimenko with osiris narrow angle camera images. the vertical accuracy of such measurements is 0.2 m and the spatial scale of the images we used is lower than 0.60 m pixel-1. we calculate the height of 21 boulders by applying a tool that allows to measure the shadow length of a boulder projected on the surrounding dust deposit, assuming that any height variation is not due to boulder intrinsic change. any boulder height variation provides a direct measurement about the thickness variation of the surrounding dust layer due to the occurring erosion and/or accretion. the analysis concerns the period from 2014 august, inbound to perihelion, to 2016 september, outbound. we measured the erosion in the ma'at region of 0.6 ± 0.2 m from 2014 september 12 to december 2, and an erosion of 0.4 ± 0.3 m from 2014 december 3 to 2015 february 15. then, we measured a dust deposition of 0.7 ± 0.3 m during the following perihelion phase, until 2016 may-september. this result confirms the link between the erosion of the southern hemisphere and the fallout in the northern regions. the imhotep and hatmehit regions are characterized by a negligible erosion during the inbound orbit, consistent with pebble-made nucleus models predicting no erosion when the temperature of the nucleus surface is ts < 205 k. | long-term measurements of the erosion and accretion of dust deposits on comet 67p/churyumov-gerasimenko with the osiris instrument |
we monitored the comet 67p/churyumov-gerasimenko close to its perihelion in november 2021 with the growth-india telescope. we observed two outbursts of this comet on 2021 october 29.940 and november 17.864 utc, -3.12 days and +15.81 days respectively from the perihelion date. the brightening in the first outburst appears as a compact source, with a radial extent up to 8.″5. the comet brightened by 0.26 ± 0.03 mag in the outburst, with a 27% increase in the effective geometric cross-section and total outburst dust mass of ~5.3 × 105 kg. the second outburst caused a brightening of 0.49 ± 0.08 mag with effective geometric cross-section and total outburst dust mass 2.5 times larger than the first event. these outbursts are up to an order of magnitude larger than the strongest outburst event observed in situ by the rosetta spacecraft in 2015. | outbursts of comet 67p/churyumov-gerasimenko |
aims: the break-up of a dustball meteoroid is investigated numerically based on fluid dynamics simulations of the meteoroid's atmospheric entry flow. both thermal and mechanical break-up mechanisms are implemented, in order to investigate dustball meteoroid disintegration.methods: a three dimensional model of a dustball meteoroid composed of thousands of small spherical grains was used in the atmospheric entry flow simulation, performed with the direct simulation monte carlo (dsmc) method. the dynamics of each meteoroid grain were calculated by means of the discrete element method (dem), which models contact dynamics between grains. by coupling dem with dsmc, the dynamics of a dustball meteoroid were calculated during atmospheric entry. in addition, thermal computations were also carried out taking into account the incoming atmospheric heat flux, thermal radiation, and grain ablation. thus, this methodology is able to compute mechanical as well as thermal dustball meteoroid disintegration.results: to test this novel multi-physics simulation framework, a prototypical dustball meteoroid, namely a draconid meteoroid, was simulated. using typical material properties from the literature, the draconid meteoroid was compressed due to aerodynamic forces to roughly half its size immediately after the start of the simulation at 200 km altitude. later, aerodynamic-induced meteoroid rotation occured until the meteoroid disintegrated mechanically at 120 km altitude. the fact that the meteoroid disintegrated mechanically is directly related to the combination of material properties used in the simulation. | three dimensional atmospheric entry simulation of a high altitude cometary dustball meteoroid |
answering fundamental questions about the origin and evolution of small planetary bodies hinges on our ability to image their surface and interior structure in detail and at high resolution. the interior structure is not easily accessible without systematic imaging using, e.g., radar transmission and reflection data from multiple viewpoints, as in medical tomography. radar tomography can be performed using methodology adapted from terrestrial exploration seismology. our feasibility study primarily focuses on full wavefield methods that facilitate high quality imaging of small body interiors. we consider the case of a monostatic system (co-located transmitters and receivers) operated in various frequency bands between 5 and 15 mhz, from a spacecraft in slow polar orbit around a spinning comet nucleus. using realistic numerical experiments, we demonstrate that wavefield techniques can generate high resolution tomograms of comets nuclei with arbitrary shape and complex interior properties. | 3d radar wavefield tomography of comet interiors |
by using the rosetta/osiris-nac data set taken in 2014 august, we focus on the neck region, called hapi, located on 67p churyumov-gerasimenko's northern hemisphere. the gravitational potential and slopes of hapi, coupled with the geological unit identification and the boulder size-frequency distributions, support the interpretation that both taluses and gravitational accumulation deposits observable on hapi are the result of multiple cliff collapses that occurred at different times. by contrast, the fine-particle deposits observable in the central part of the study area are made of aggregates coming from the southern hemisphere and deposited during each perihelion passage. both the consolidated terrains on the western part of hapi, as well as the centrally aligned ridge made of boulder-like features, suggest that hapi is in structural continuity with the onion-like structure of the main lobe of 67p. despite the dusty blanket observable on hapi, its terrains are characterized by water-ice-rich components that, once repeatedly and rapidly illuminated, sublimate, hence resulting in the strong jet activity observed in 2014 august. | multidisciplinary analysis of the hapi region located on comet 67p/churyumov-gerasimenko |
on 12 november 2014 at 15:34 utc, after a 7-h descent, the philae lander made contact with the surface of the comet churyumov-gerasimenko (67p/cg) in the centre of the intended landing zone. following the failure of its anchoring systems, it bounced and continued to fly ballistically. a couple of hours later, telemetry transmitted to rosetta showed that philae was stabilized on the surface and working properly although its precise and final location was and still is not known (biele et al, 2015). from the morning of 13 november 2014, consert data enabled an initial estimate to be made of philae's location based on signals propagated through the 67p/cg nucleus. this rough location was then refined through three sets of measurements carried out during periods of direct visibility between rosetta and philae during the philae's first science sequence (fss) on 13 and 14 november. this paper presents these measurements and the estimate of the final position of philae in november 2014. | philae localization from consert/rosetta measurement |
in the paper we examine two selected mechanisms of matter ejection from the cometary nuclei. the first is a calm sublimation from the comet's nucleus and the second is the ejection caused by jets produced by cometary geysers. the classical old model which assumes that cometary particles are crumbs of ice-dust solid matter of spherical shapes, as well as modern model of cometary particles treating them as random ballistic aggregates of spherical monomers are considered. numerical calculations are focused on finding out the maximum sizes of the chunks of matter that can be ejected from comets. | selected mechanisms of matter ejection out of the cometary nuclei |
in this study, to better our understanding of the current state of conservation of cardisoma guanhumi and its habitats, we evaluated the potential spatio-temporal genomic damage of this species across five estuaries in brazil. the experiment was performed over two consecutive years, and the sampling was performed in the winter and summer seasons. two genetic tests - micronucleus test and comet assay - were used to quantify the dna damage. unlike in the summers and in the winter of 2013, in the winter of 2012 a significant increase was noted in the frequency of micronucleated cells and genomic damage index. the occurrence of genomic damage coincided with the arrival of the harsh winter of 2012 as the water sourced from the coastal rivers significantly affected the estuarine species under study. our results confirmed that this species was resilient to the atypical climatic conditions, which facilitated the generation of excessive waste. | spatial-temporal genome damaging in the blue crab cardisoma guanhumi as ecological indicators for monitoring tropical estuaries |
the a2πi state of 12c16o+ has been reinvestigated using high-resolution, emission spectra obtained via fourier-transform spectroscopy of the (0, 1), (0, 2), (1, 0) and (1, 1) bands of the comet-tail (a2πi - x2σ+) system with accuracy of up to 0.005 cm-1. the high temperature (900 k) of the emission discharge inside the hollow-cathode lamp permitted monitoring of high rotational quantum levels in a2πi(v = 0, 1) up to j = 48.5. all these bands together with the x2σ+ - x2σ+(10, 1) and (10, 2) transitions deriving from a complex, spin-orbit, spin-electronic and l-uncoupling a2π(v = 0) ∼ x2σ+(v = 10) interaction as well as the b2σ+ - x2σ+(6, 10) frequency transitions from our previous study were taken into consideration. in total, 1849 spectral lines were included in the comprehensive deperturbation analysis. this fit leads to a much improved description in terms of deperturbed molecular constants and interaction parameters compared to the previous studies of the same energy region in co+. moreover, the ro-vibronic term values of the a2πi(v = 0) level and its perturber x2σ+(v = 10) were determined as well as λ-doubling of a2πi(v = 0,1), γ-doubling of x2σ+(v = 10) and percentage 2π character of these levels were considered in detail. | fourier-transform spectroscopy of the a2πi - x2σ+ system in co+ and deperturbation analysis of the a2πi(v = 0, 1) levels |
the origin of cometary volatiles remains a major open question in planetary science. comets may have either agglomerated from crystalline ices condensed in the protosolar nebula (psn) or from amorphous ice originating from the molecular cloud and interstellar medium. here, based on the recent argon, krypton, and xenon measurements performed by the rosina mass spectrometer on board the european space agency’s rosetta spacecraft in the coma of 67p/churyumov-gerasimenko, we show that these noble gas relative abundances can be explained if the comet’s building blocks formed from a mixture of gas and h2o grains resulting from the annealing of pristine amorphous ice (i.e., originating from the presolar cloud) in the psn. in this scenario, the different volatiles released during the amorphous-to-crystalline ice phase transition would have been subsequently trapped at lower temperatures in stoichiometric hydrate or clathrate hydrate forms by the crystalline water ice generated by the transition. once crystalline water was completely consumed by clathration in the ∼25-80 k temperature range, the volatile species remaining in the gas phase would have formed pure condensates at lower temperatures. the formation of clathrates hydrates and pure condensates to explain the noble gas relative abundances is consistent with a proposed interstellar origin of molecular oxygen detected in 67p/churyumov-gerasimenko, and with the measured molecular nitrogen depletion in comets. | noble gas abundance ratios indicate the agglomeration of 67p/churyumov-gerasimenko from warmed-up ice |
context. main belt comets are a recently identified population of minor bodies with stable asteroid-like orbits but cometary appearances. sublimation of water ice is the most likely mechanism for their recurrent activity (i.e. dust tails and dust comae), although there has been no direct detection of gas. these peculiar objects could hold the key to the origin of water on earth.aims: in this paper we present a search for the gas responsible for lifting dust from p/2012 t1 (pan-starrs), and review previous attempts at such measurements. to date such searches have mainly been indirect, looking for the common cometary gas cn rather than gasses related to water itself.methods: we use the vlt and x-shooter to search for emission from oh in the uv, a direct dissociation product of water.results: we do not detect any emission lines, and place an upper limit on water production rate from p/2012 t1 of 8-9 × 1025 molecules s-1. this is similar to limits derived from observations using the herschel space telescope.conclusions: we conclude that the best current facilities are incapable of detecting water emission at the exceptionally low levels required to produce the observed activity in main belt comets. based on observations collected at the european organisation for astronomical research in the southern hemisphere under eso programme 290.c-5007(a). | x-shooter search for outgassing from main belt comet p/2012 t1 (pan-starrs) |
during five nights between february 3 and 10, 2021, we monitored the degree of linear polarization in comet 29p/schwassmann-wachmann with the broadband r filter. it is the first polarimetric investigation of this comet measured during a period of quiescent activity. we found a nearly constant negative polarization pq ≈ -2.1% at α ≈ 9.5° that is somewhat stronger than in other comets on average; however, it appears similar to that of comet 67p/churyumov-gerasimenko. modeling the polarization in comet 29p/schwassmann-wachmann suggests its coma consists of at least two components, whose chemical composition and size distribution appear similar to that of other comets. further polarimetric measurements are necessary in order to infer the shape of its branch of negative polarization and, hence, better constrain the microphysical properties of its dust. | monitoring the negative polarization in comet 29p/schwassmann-wachmann during quiescence |
asteroids (24) themis and (65) cybele have an absorption feature at 3.1 μm reported to be directly linked to surface water ice. we searched for water vapor escaping from these asteroids with the herschel space observatory heterodyne instrument for the far infrared. while no h2o line emission was detected, we obtain sensitive 3σ water production rate upper limits of q(h2o) < 4.1 × 1026 molecules s-1 for themis and q(h2o) < 7.6 × 1026 molecules s-1 for cybele. using a thermophysical model, we merge data from the subaru/cooled mid-infrared camera and spectrometer and the herschel/spectral and photometric imaging receiver with the contents of a multi-observatory database to derive new radiometric properties for these two asteroids. for themis, we find a thermal inertia ${\rm{\gamma }}={{20}^{+25}}_{-10}$ j m-2 s-1/2 k-1, a diameter ${{192}^{+10}}_{-7}$ km, and a geometric v-band albedo pv = 0.07 ± 0.01. for cybele, we obtain a thermal inertia ${\rm{\gamma }}={{25}^{+28}}_{-19}$ j m-2 s-1/2 k-1, a diameter 282 ± 9 km, and an albedo pv = 0.042 ± 0.005. using all inputs, we estimate that water ice intimately mixed with the asteroids' dark surface material would cover <0.0017% (for themis) and <0.0033% (for cybele) of their surfaces, while an areal mixture with very clean ice (bond albedo 0.8 for themis and 0.7 for cybele) would cover <2.2% (for themis) and <1.5% (for cybele) of their surfaces. while surface (and subsurface) water ice may exist in small localized amounts on both asteroids, it is not the reason for the observed 3.1 μm absorption feature. | low water outgassing from (24) themis and (65) cybele: 3.1 μm near-ir spectral implications |
on the orbiter of the rosetta spacecraft, the cometary secondary ion mass analyser (cosima) will provide new in situ insights about the chemical composition of cometary grains all along 67p/churyumov-gerasimenko (67p/cg) journey until the end of december 2015 nominally. the aim of this paper is to present the pre-calibration which has already been performed as well as the different methods which have been developed in order to facilitate the interpretation of the cosima mass spectra and more especially of their organic content. the first step was to establish a mass spectra library in positive and negative ion mode of targeted molecules and to determine the specific features of each compound and chemical family analyzed. as the exact nature of the refractory cometary organic matter is nowadays unknown, this library is obviously not exhaustive. therefore this library has also been the starting point for the research of indicators, which enable to highlight the presence of compounds containing specific atom or structure. these indicators correspond to the intensity ratio of specific peaks in the mass spectrum. they have allowed us to identify sample containing nitrogen atom, aliphatic chains or those containing polyaromatic hydrocarbons. from these indicators, a preliminary calibration line, from which the n/c ratio could be derived, has also been established. the research of specific mass difference could also be helpful to identify peaks related to quasi-molecular ions in an unknown mass spectrum. the bayesian positive source separation (bpss) technique will also be very helpful for data analysis. this work is the starting point for the analysis of the cometary refractory organic matter. nevertheless, calibration work will continue in order to reach the best possible interpretation of the cosima observations. | cosima calibration for the detection and characterization of the cometary solid organic matter |
all atmosphere-less planetary bodies are covered with a dust layer, the so-called regolith, which determines the optical, mechanical and thermal properties of their surface. these properties depend on the regolith material, the size distribution of the particles it consists of, and the porosity to which these particles are packed. we performed experiments in parabolic flights to determine the gravity dependency of the packing density of regolith for solid-particle sizes of 60 μ m and 1 mm as well as for 100-250 μ m-sized agglomerates of 1.5 μ m-sized solid grains. we utilized g-levels between 0.7 m s-2 and 18 m s-2 and completed our measurements with experiments under normal gravity conditions. based on previous experimental and theoretical literature and supported by our new experiments, we developed an analytical model to calculate the regolith stratification of celestial rocky and icy bodies and estimated the mechanical yields of the regolith under the weight of an astronaut and a spacecraft resting on these objects. | the stratification of regolith on celestial objects |
the shape of the heliosphere is thought to resemble a long, comet tail, however, recently it has been suggested that the heliosphere is tailless with a two-lobe structure. the latter study was done with a three-dimensional (3d) magnetohydrodynamic code, which treats the ionized and neutral hydrogen atoms as fluids. previous studies that described the neutrals kinetically claim that this removes the two-lobe structure of the heliosphere. in this work, we use the newly developed solar-wind with hydrogen ion exchange and large-scale dynamics (shield) model. shield is a self-consistent kinetic-mhd model of the outer heliosphere that couples the mhd solution for a single plasma fluid from the bats-r-us mhd code to the kinetic solution for neutral hydrogen atoms solved by the adaptive mesh particle simulator, a 3d, direct simulation monte carlo model that solves the boltzmann equation. we use the same boundary conditions as our previous simulations using multi-fluid neutrals to test whether the two-lobe structure of the heliotail is removed with a kinetic treatment of the neutrals. our results show that despite the large difference in the neutral hydrogen solutions, the two-lobe structure remains. these results are contrary to previous kinetic-mhd models. one such model maintains a perfectly ideal heliopause and does not allow for communication between the solar wind and interstellar medium. this indicates that magnetic reconnection or instabilities downtail play a role for the formation of the two-lobe structure. | the impact of kinetic neutrals on the heliotail |
images and low-resolution spectra of the near-earth jupiter family comet (jfc) 249p/linear in the visible range obtained with the instrument osiris in the 10.4 m gran telescopio canarias (gtc) (la palma, spain) on january 3, 4, 6 and february 6, 2016 are presented, together with a series of images obtained with the 0.4m telescope of the great shefford observatory obtained on oct. 22 and 27, and nov. 1 and 24, 2006. the reflectance spectrum of 249p is similar to that of a b-type asteroid. the comet has an absolute (visual) nuclear magnitude hv = 17.0 ± 0.4 , which corresponds to a radius of about 1-1.3 km for a geometric albedo ∼ 0.04 - 0.07 . from the analysis of gtc images using a monte carlo dust tail code we find that the time of maximum dust ejection rate was around 1.6 days before perihelion. the analysis of the dust tails during the 2006 and 2016 perihelion approaches reveals that, during both epochs, the comet repeated the same dust ejection pattern, with a similar short-lived activity period of about 20 days (fwhm) around perihelion and a dust loss rate peaking at 145 ± 50 kg/s. the total dust mass ejected during its last perihelion passage was (2.5 ± 0.9) × 108 kg, almost all this mass being emitted before the first observation of january 3, 2016. the activity onset, duration, and total ejected mass were very similar during the 2006 perihelion passage. this amount of dust mass is very low as compared with that from other active jfcs. the past orbital evolution of 249p and 100 clones were also followed over a time scale of ∼ 5 × 104 yr. the object and more than 60% of the clones remained bound to the near-earth region for the whole computed period, keeping its perihelion distance within the range q ≃ 0.4 - 1.1 au. the combination of photometric and spectroscopic observations and dynamical studies show that the near-earth comet 249p/linear has several peculiar features that clearly differentiate it from typical jfcs. we may be in front of a new class of near-earth jfc whose source region is not the distant trans-neptunian population, but much closer in the asteroid belt. therefore, 249p/linear may be a near-earth counterpart of the so-called main-belt comets or active asteroids. | physical and dynamical properties of the anomalous comet 249p/linear |
context. n2 is rarely found in comets, or when it is present, it is found only in small quantities despite its abundance on the surfaces of different outer solar system objects. a few comets presented n2+ emission lines in their optical spectra. one of them, c/2016 r2, showed an unusually high abundance of this species in 2018, with dozens of bright n2+ emission lines. a robust model of the n2+ fluorescence in comets would permit us to perform a detailed quantitative analysis of this species and enlarge our comprehension of the surprisingly wide range of n2 abundances in comets.aims: the goal of this work is to provide the necessary tools to interpret n2+ spectra. computing production rates for a cometary species necessitates a good knowledge of the number of molecules located along the line of sight of the spectrometer. this in turn requires a good modeling of the emission spectrum with detailed fluorescence efficiencies for the different bands.methods: we developed a model based on available laboratory data and new theoretical results relative to the n2+ to compute the emission spectrum of this species observed in 8.2m very large telescope high-resolution spectra of comet c/2016 r2. because of some significant differences between spectra obtained on the nucleus and at a cometocentric distance of about 6000 km, it became apparent that a classic fluorescence equilibrium spectrum could not be used. a synthetic spectrum based on a monte carlo method and producing spectra at different times from an initial relative population was developed and compared to our observational data.results: our modeling of the cometary n2+ emission spectrum satisfactorily fits our observed spectra of comet c/2016 r2, leading to the first modeling at high resolution. different fluorescence efficiency factors are computed. | n2+ fluorescence spectrum of comet c/2016 r2 (panstarrs) |
comet 21p/giacobini-zinner (hereafter, comet 21p/g-z) is a jupiter-family comet and a parent comet of the october draconids meteor shower. if meteoroids originating from a jupiter-family comet contain complex organic molecules, such as amino acids, they are essential pieces of the puzzle regarding the origin of life on earth. we observed comet 21p/g-z in the mid-infrared wavelength region using the cooled mid-infrared camera and spectrometer (comics) on the 8.2 m subaru telescope on ut 2005 july 5. here, we report the unidentified infrared (uir) emission features of comet 21p/g-z, which are likely due to complex organic molecules (both aliphatic and aromatic hydrocarbons), and the thermal emission from amorphous/crystalline silicates and amorphous carbon grains in its mid-infrared low-resolution spectrum. the uir features at ~8.2 μm, ~8.5 μm, and ~11.2 μm found in the spectrum of comet 21p/g-z could be attributed to polycyclic aromatic hydrocarbons (or hydrogenated amorphous carbons) contaminated by n- or o-atoms, although part of the feature at ~11.2 μm comes from crystalline olivine. the other feature at ~9.2 μm might originate from aliphatic hydrocarbons. comet 21p/g-z is enriched in complex organic molecules. considering that the derived mass fraction of crystalline silicates in comet 21p/g-z is typical of comets, we propose that the comet originated from a circumplanetary disk of giant planets (similar to jupiter and saturn) where was warmer than the typical comet-forming region (5-30 au from the sun) and was suitable for the formation of complex organic molecules. comets from circumplanetary disks might be enriched in complex organic molecules, such as comet 21p/g-z, and may have provided pre-biotic molecules to ancient earth by direct impact or meteor showers. | unidentified infrared emission features in mid-infrared spectrum of comet 21p/giacobini-zinner |
we investigate numerically and analytically size-polydisperse granular mixtures immersed into a molecular gas. we show that the equipartition of granular temperatures of particles of different sizes is established; however, the granular temperatures significantly differ from the temperature of the molecular gas. this result is surprising since, generally, the energy equipartition is strongly violated in driven granular mixtures. qualitatively, the obtained results do not depend on the collision model, being valid for a constant restitution coefficient ɛ , as well as for the ɛ for viscoelastic particles. our findings may be important for astrophysical applications, such as protoplanetary disks, interstellar dust clouds, and comets. | size-polydisperse dust in molecular gas: energy equipartition versus nonequipartition |
aims: we investigate the surface distribution of the source regions of dust jets on comet 67p/churyumov-gerasimenko as a function of time.methods: the dust jet source regions were traced by the comprehensive imaging data set provided by the osiris scientific camera.results: we show in detail how the projected footpoints of the dust jets and hence the outgassing zone would move in consonance with the sunlit belt. furthermore, a number of source regions characterized by repeated jet activity might be the result of local topographical variations or compositional heterogeneities.conclusions: the spatial and temporal variations in source regions of the dust jets are influenced significantly by the seasonal effect. the strong dependence on the solar zenith angle and local time could be related to the gas sublimation process driven by solar insolation on a surface layer of low thermal inertia. | seasonal variations in source regions of the dust jets on comet 67p/churyumov-gerasimenko |
biological effect directed in vivo tests with model organisms are useful in assessing potential health risks associated with chemical contaminations in surface waters. this study examined the applicability of two in vivo test systems viz. plant, allium cepa root based tests and fish, oreochromis niloticus erythrocyte based tests for screening cytogenotoxic potential of raw source water, water treatment waste (effluents) and treated water of drinking water treatment plants (dwtps) using two dwtps associated with a major river in sri lanka. measured physico-chemical parameters of the raw water, effluents and treated water samples complied with the respective sri lankan standards. in the in vivo tests, raw water induced statistically significant root growth retardation, mitodepression and chromosomal abnormalities in the root meristem of the plant and micronuclei/nuclear buds evolution and genetic damage (as reflected by comet scores) in the erythrocytes of the fish compared to the aged tap water controls signifying greater genotoxicity of the source water especially in the dry period. the effluents provoked relatively high cytogenotoxic effects on both test systems but the toxicity in most cases was considerably reduced to the raw water level with the effluent dilution (1:8). in vivo tests indicated reduction of cytogenotoxic potential in the tested drinking water samples. the results support the potential applications of practically feasible in vivo biological test systems such as a. cepa root based tests and the fish erythrocyte based tests as complementary tools for screening cytogenotoxicity potential of the source water and water treatment waste reaching downstream of aquatic ecosystems and for evaluating cytogenotoxicity eliminating efficacy of the dwtps in different seasons in view of human and ecological safety. | cytogenotoxicity screening of source water, wastewater and treated water of drinking water treatment plants using two in vivo test systems: allium cepa root based and nile tilapia erythrocyte based tests |
this paper is a phenomenological description of multispacecraft observations of energetic particles caused by the close flyby of comet c/2013 a1 siding spring with mars on 19 october 2014. this is the first time that cometary energetic particles have been observed at mars. the mars atmosphere and volatile evolution (maven)-solar energetic particle (sep) and the mars odyssey-high energy neutron detector (hend) instruments recorded evidence of precipitating particles, which are likely o+ pickup ions, during the 10 hr that mars was within the region of the comet's coma. o+ pickup ions were also detected several hours after, although whether their origin is the comet or space weather is not conclusive. we discuss the possible origin of those particles and also the cause of an additional shower of energetic particles that hend observed between 22 and 35 hr after the comet's closest approach, which may be related to dust impacts from the comet's dust tail. an o+ pickup ion energy flux simulation is performed with representative solar wind and cometary conditions, together with a simulation of their energy deposition profile in the atmosphere of mars. results indicate that the o+ pickup ion fluxes observed by sep were deposited in the ionosphere around 105 to 120 km altitude, and they are compared with precomet flyby estimations of cometary pickup ions. the comet's flyby deposited a significant fluence of energetic particles into mars' upper atmosphere, at a similar level to a large space weather event. | energetic particle showers over mars from comet c/2013 a1 siding spring |
since its launch in 1990, the hubble space telescope (hst) has served as a platform with unique capabilities for remote observations of comets in the far-ultraviolet region of the spectrum. successive generations of imagers and spectrographs have seen large advances in sensitivity and spectral resolution enabling observations of the diverse properties of a representative number of comets during the past 25 years. to date, four comets have been observed in the far-ultraviolet by the cosmic origins spectrograph (cos), the last spectrograph to be installed in hst, in 2009: 103p/hartley 2, c/2009 p1 (garradd), c/2012 s1 (ison), and c/2014 q2 (lovejoy). cos has unprecedented sensitivity, but limited spatial information in its 2.″5 diameter circular aperture, and our objective was to determine the co production rates from measurements of the co fourth positive system in the spectral range of 1400-1700 å. in the two brightest comets, 19 bands of this system were clearly identified. the water production rates were derived from nearly concurrent observations of the oh (0,0) band at 3085 å by the space telescope imaging spectrograph. the derived co/{{{h}}}2{{o}} production rate ratio ranged from ∼0.3% for hartley 2 to ∼22% for garradd. in addition, strong partially resolved emission features due to multiplets of s i, centered at 1429 å and 1479 å, and of c i at 1561 å and 1657 å, were observed in all four comets. weak emission from several lines of the {{{h}}}2 lyman band system, excited by solar lyα and lyβ pumped fluorescence, were detected in comet lovejoy. | far-ultraviolet spectroscopy of recent comets with the cosmic origins spectrograph on the hubble space telescope |
a recent study by opher et al. suggested the heliosphere has a “croissant” shape, where the heliosheath plasma is confined by the toroidal solar magnetic field. the “croissant” heliosphere is in contrast to the classically accepted view of a comet-like tail. we investigate the effect of the “croissant” heliosphere model on energetic neutral atom (ena) maps. regardless of the existence of a split tail, the confinement of the heliosheath plasma should appear in ena maps. ena maps from the interstellar boundary explorer (ibex) have shown two high latitude lobes with excess ena flux at higher energies in the tail of the heliosphere. these lobes could be a signature of the confinement of the heliosheath plasma, while some have argued they are caused by the fast/slow solar wind profile. here we present ena maps of the “croissant” heliosphere, focusing on understanding the effect of the heliosheath plasma collimation by the solar magnetic field while using a uniform solar wind. we incorporate pick-up ions (puis) into our model based on malama et al. and zank et al. we use the neutral solution from our mhd model to determine the angular variation of the puis, and include the extinction of puis in the heliosheath. in the presence of a uniform solar wind, we find that the collimation in the “croissant” heliosphere does manifest itself into two high latitude lobes of increased ena flux in the downwind direction. | globally distributed energetic neutral atom maps for the “croissant” heliosphere |
the study of exospheres can help us understand the long-term loss of volatiles from planetary bodies due to interactions of planets, satellites, and small bodies with the interplanetary medium, solar radiation, and internal forces including diffusion and outgassing. recent evidence for water and oh on the moon has spurred interest in processes involving chemistry and sequestration of volatile species at the poles and in voids. in recent years, nasa has sent spacecraft to asteroids including vesta and ceres, and esa sent rosetta to comet 67p/churyumov-gerasimenko and the asteroids lutetia and steins. japan's hayabusa spacecraft returned a sample from asteroid itakowa, and osiris-rex will return a sample from a primitive asteroid, bennu, to earth. in a surface-bounded exosphere, the gases are derived from the surface and thus reflect the composition of the body's regolith, although not in a one-to-one ratio. observation of an escaping exosphere, termed a corona, is challenging. we have therefore embarked on a parametrical study of exospheres as a function of mass of the exospheric species, mass of the primary body and source velocity distribution, specifically thermal (maxwell-boltzmann) and sputtering. the goal is to provide a quick look to determine under what conditions and for what mass of the primary body the species of interest are expected to be bound or escaping and to quickly estimate the observability of exospheric species. this work does not provide a comprehensive model but rather serves as a starting point for further study. these parameters will be useful for mission planning as well as for students beginning a study of planetary exospheres. | exospheric escape: a parametrical study |
context. on 27 april 2015, when comet 67p/churyumov-gerasimenko was at 1.76 au from the sun and moving toward perihelion, the osiris and virtis-m instruments on board the rosetta spacecraft simultaneously observed the evolving dust and gas coma during a complete rotation of the comet.aims: we aim to characterize the spatial distribution of dust, h2o, and co2 gas in the inner coma. to do this, we performed a quantitative analysis of the release of dust and gas and compared the observed h2o production rate with the rate we calculated using a thermophysical model.methods: for this study we selected osiris wac images at 612 nm (dust) and virtis-m image cubes at 612 nm, 2700 nm (h2o emission band), and 4200 nm (co2 emission band). we measured the average signal in a circular annulus to study the spatial variation around the comet, and in a sector of the annulus to study temporal variation in the sunward direction with comet rotation, both at a fixed distance of 3.1 km from the comet center.results: the spatial correlation between dust and water, both coming from the sunlit side of the comet, shows that water is the main driver of dust activity in this time period. the spatial distribution of co2 is not correlated with water and dust. there is no strong temporal correlation between the dust brightness and water production rate as the comet rotates. the dust brightness shows a peak at 0° subsolar longitude, which is not pronounced in the water production. at the same epoch, there is also a maximum in co2 production. an excess of measured water production with respect to the value calculated using a simple thermophysical model is observed when the head lobe and regions of the southern hemisphere with strong seasonal variations are illuminated (subsolar longitude 270°-50°). a drastic decrease in dust production when the water production (both measured and from the model) displays a maximum occurs when typical northern consolidated regions are illuminated and the southern hemisphere regions with strong seasonal variations are instead in shadow (subsolar longitude 50°-90°). possible explanations of these observations are presented and discussed. | diurnal variation of dust and gas production in comet 67p/churyumov-gerasimenko at the inbound equinox as seen by osiris and virtis-m on board rosetta |
we present results from our 47 night imaging campaign of comet 41p/tuttle-giacobini-kresák conducted from lowell observatory between 2017 february 16 and july 2. coma morphology revealed gas jets, whose appearance and motion as a function of time yielded the rotation period and other properties. all narrowband cn images exhibited either one or two jets; one jet appeared as a partial face-on spiral with clockwise rotation, while the second jet evolved from a side-on corkscrew, through face-on, to corkscrew again, with only a slow evolution throughout the apparition due to progressive viewing geometry changes. a total of 78 period determinations were made over a 7 week interval, yielding a smooth and accelerating rotation period starting at 24 hr (march 21 and 22) and passing 48 hr on april 28. while this is by far the fastest rate of change ever measured for a comet nucleus, the torque required is readily within what can exist given likely properties of the nucleus. if the torque remained constant, we estimate that the nucleus could have stopped rotating and/or begun to tumble as soon as only 2 months following perihelion and will certainly reach this stage by early in the next apparition. working backward in time, tuttle-giacobini-kresák would have been rotating near its rotational breakup velocity three to four orbits earlier, suggesting that its extreme 7 mag outburst observed in 2001 might have been caused by a partial fragmentation at that time, as might the pair of 1973 8 mag outbursts if there had been an earlier spin-down and spin-up cycle. | gas jet morphology and the very rapidly increasing rotation period of comet 41p/tuttle-giacobini-kresák |
in 2017 observers of the "churyumov's unified network" from april 15 to 26 registered more than a hundred tracks of daytime lyrid's invasions. the maximum number (18) of daily invasions of lyrids we observed on april 19. tracks had a length of 5 deg. up to 30 deg. some of them were short, thin and rapidly disappearing (less than a minute) traces with thickening at the bottom of the track. others - were visible 10-20 minutes. tracks with a length more 15 were visible more than 20 minutes. the largest trace we observed about 1 hour. on april 25 from 10:20 to 11:30 three observers simultaneously, from different points, registered four tracks of lyrid invasion with length 10-15 deg.; traces were visible for 30-50 minutes. calculations for some dates have made it possible to determine the average altitude of the beginning of appearance of these traces of invasions >34 km. | daytime observations of lyrids in 2017 |
context. solar wind charge-changing reactions are of paramount importance to the physico-chemistry of the atmosphere of a comet, mass-loading the solar wind through an effective conversion of fast light solar wind ions into slow heavy cometary ions.aims: to understand these processes and place them in the context of a solar wind plasma interacting with a neutral atmosphere, numerical or analytical models are necessary. inputs of these models, such as collision cross sections and chemistry, are crucial.methods: book-keeping and fitting of experimentally measured charge-changing and ionization cross sections of hydrogen and helium particles in a water gas are discussed, with emphasis on the low-energy/low-velocity range that is characteristic of solar wind bulk speeds (<20 kev u-1/2000 km s-1).results: we provide polynomial fits for cross sections of charge-changing and ionization reactions, and list the experimental needs for future studies. to take into account the energy distribution of the solar wind, we calculated maxwellian-averaged cross sections and fitted them with bivariate polynomials for solar wind temperatures ranging from 105 to 106 k (12-130 ev).conclusions: single- and double-electron captures by he2+ dominate at typical solar wind speeds. correspondingly, single-electron capture by h+ and single-electron loss by h- dominate at these speeds, resulting in the production of energetic neutral atoms (enas). ionization cross sections all peak at energies above 20 kev and are expected to play a moderate role in the total ion production. however, the effect of solar wind maxwellian temperatures is found to be maximum for cross sections peaking at higher energies, suggesting that local heating at shock structures in cometary and planetary environments may favor processes previously thought to be negligible. this study is the first part in a series of three on charge exchange and ionization processes at comets, with a specific application to comet 67p/churyumov-gerasimenko and the rosetta mission. | solar wind charge exchange in cometary atmospheres. i. charge-changing and ionization cross sections for he and h particles in h2o |
for the last two decades, we have been observing a huge increase in discoveries of long-period comets (lpcs), especially those with large perihelion distances. we collected data for a full sample of lpcs discovered during 1801-2017, including their osculating orbits, discovery moments (to study the discovery distances) and original semimajor axes (to study the number ratio of large-perihelion to small-perihelion lpcs in the function of original 1/a and to construct the precise distribution of original 1/a). to minimize the influence of parabolic comets on these distributions, we determined definitive orbits (which include eccentricities) for more than 20 lpcs previously classified as parabolic comets. we show that the percentage of large-perihelion comets is significantly higher within oort-spike comets than in a group of lpcs with a< 10 000 au; this ratio of large-perihelion to small-perihelion comets for both groups has grown systematically since 1970. the different shape of the oort spike for small-perihelion and large-perihelion lpcs is also discussed. a spectacular decrease of the ratio of large-perihelion to small-perihelion lpcs with the shortening of semimajor axis within the range 5000-100 au is also noticed. analysing discovery circumstances, we found that oort-spike comets are discovered statistically at larger geocentric and heliocentric distances than the remaining lpcs. this difference in the percentage of large-perihelion comets in both groups of lpcs is probably a direct consequence of the well-known comet fading process, due to ageing of the surface during consecutive perihelion passages, and/or reflects different actual q distributions. | discovery statistics and 1/a distribution of long-period comets detected during 1801-2017 |
low-gravity waterworlds (m ≲ 0.1 m ⊕) are of interest for their potential habitability. the weakly bound atmospheres of such worlds have proportionally larger radiative surfaces and are more susceptible to escape. we conduct a unified investigation into these phenomena, combining analytical energy balance and hydrodynamic escape with line-by-line radiative transfer calculations. because outgoing radiation is forced to increase with surface temperature by the expansion of the radiative surface, we find that these worlds do not experience a runaway greenhouse. furthermore, we show that a long-lived liquid water habitable zone is possible for low-gravity waterworlds of sufficient mass. its inner edge is set by the rate of atmospheric escape because a short-lived atmosphere limits the time available for life to evolve. in describing the physics of the parameter space transition from “planet-like” to “comet-like,” our model produces a lower bound for habitability in terms of gravity. these results provide valuable insights in the context of the ongoing hunt for habitable exoplanets and exomoons. | atmospheric evolution on low-gravity waterworlds |
the organization of the orbits of most minor bodies in the solar system seems to follow random patterns, the result of billions of years of chaotic dynamical evolution. much as heterogeneous orbital behaviour is ubiquitous, dynamically coherent pairs and groups of objects are also present everywhere. although first studied among the populations of asteroids and comets that inhabit or traverse the inner solar system, where they are very numerous, at least one asteroid family has been confirmed to exist in the outer solar system and two other candidates have been proposed in the literature. here, we perform a systematic search for statistically significant pairs and groups of dynamically correlated objects through those with semimajor axis greater than 25 au, applying a novel technique that uses the angular separations of orbital poles and perihelia together with the differences in time of perihelion passage to single out pairs of relevant objects. our analysis recovers well-known, dynamically coherent pairs and groups of comets and trans-neptunian objects and uncovers a number of new ones, prime candidates for further spectroscopic study. | dynamically correlated minor bodies in the outer solar system |
the outbursts of comets, sudden large increases in their luminosity, are still very interesting and mysterious signs of activity of this celestial bodies. most of the cometary outbursts are taking place at heliocentric distances where sublimation of water ice plays an important role in the activity of comets. however, the phenomenon is also observed far away from the sun (i.e. ≃5-20 au) where the sublimation of water ice is negligible and the activity of comets is dominated by more volatile chemicals. not only typical comets show `cometary-like' activity but also centaurs. in addition to the long-term changes in brightness related to heliocentric distances and short-periodic variations connected with the rotation of the nucleus, they also exhibit a random variations in luminosity which are similar to the cometary outbursts. paper presents an overview of the most likely hypotheses and models which try to explain this phenomenon. | a review of cometary outbursts at large heliocentric distances |
main-belt asteroid (6478) gault was observed to show cometary features in early 2019. to investigate the cause, we conducted bvr observations at xingming observatory, china, from 2019 january to april. the two tails were formed around 2018 october 26-november 8, and 2018 december 29-2019 january 8, respectively, and consisted of dust grains of ≳20 μm to 3 mm in radius ejected at a speed of 0.15 ± 0.05 m s-1 and following a broken power-law size distribution bending at grain radius ∼70 μm (bulk density 1 g cm-3 assumed). the total mass of dust within a 104 km-radius aperture around gault declined from ∼9 × 106 kg since 2019 january at a rate of 2.28 ± 0.07 kg s-1, but temporarily surged around 2019 march 25, because earth then crossed the orbital plane of gault, near which the ejected dust was mainly distributed. no statistically significant colour or short-term light-curve variation was seen. nonetheless we argue that gault is currently subjected to rotational instability. using the available astrometry, we did not detect any non-gravitational acceleration in the orbital motion of gault. | new active asteroid (6478) gault |
we investigate the centimeter-to-decimeter-scale particle size distribution and dynamics in the coma of comet 73p/schwassmann-wachmann 3 using radar observations obtained shortly after the comet's disintegration in may 2006. we derive the particle size distribution power-law index in the comae of fragments b and c using radar cross sections and circular-polarization ratios observed at s and x bands (2.38 ghz and 8.56 ghz, respectively), and show day-to-day changes in the number of contributing particles. we test three irregular particle morphologies, but find that the particle shape plays a relatively minor role. the power-law indices from 4.0 to 4.8 and major-axis diameters up to about 30 cm provide the best fits to the radar observations, the values depending on the particle shape and the observed radial velocity. a majority of the measured particle velocities exceed the escape velocity of the nuclei. | decimeter-scale particle characterization in the coma of 73p/schwassmann-wachmann 3 using dual-wavelength radar observations |
on the night of october 31, 2015 two bright southern taurid fireballs occurred over poland, being one of the most spectacular bolides of this shower in recent years. the first fireball - pf311015a okonek - was detected by six video stations of polish fireball network (pfn) and photographed by several bystanders, allowing for precise determination of the trajectory and orbit of the event. the pf311015a okonek entered earth's atmosphere with the velocity of 33.2 ± 0.1 km s-1 and started to shine at height of 117.88 ± 0.05 km. the maximum brightness of -16.0 ± 0.4 mag was reached at height of 82.5 ± 0.1 km. the trajectory of the fireball ended at height of 60.2 ± 0.2 km with terminal velocity of 30.2 ± 1.0 km s-1. the second fireball - pf311015b ostrowite - was detected by six video stations of pfn. it started with velocity of 33.2 ± 0.1 km s-1 at height of 108.05 ± 0.02 km. the peak brightness of -14.8 ± 0.5 mag was recorded at height of 82.2 ± 0.1 km. the terminal velocity was 31.8 ± 0.5 km s-1 and was observed at height of 57.86 ± 0.03 km. the orbits of both fireballs are similar not only to orbits of southern taurids and comet 2p/encke, but even closer resemblance was noticed for orbits of 2005 ur and 2005 tf50 asteroids. especially the former object is interesting because of its close flyby during spectacular taurid maximum in 2005. we carried out a further search to investigate the possible genetic relationship of okonek and ostrowite fireballs with both asteroids, that are considered to be associated with taurid complex. although, we could not have confirmed unequivocally the relation between fireballs and these objects, we showed that both asteroids could be associated, having the same origin in a disruption process that separates them. | 2015 southern taurid fireballs and asteroids 2005 ur and 2005 tf50 |
given that a strong 14c variation in ad 775 has recently been suggested to be due to the largest solar flare ever recorded in history, it is relevant to investigate whether celestial events observed around that time may have been aurorae, possibly even very strong aurorae, or otherwise related to the 14c variation (e.g. a suggested comet impact with earth's atmosphere). we critically review several celestial observations from ad 757 to the end of the 770s, most of which were previously considered to be true, and in some cases, strong aurorae; we discuss in detail the east asian records and their wording. we conclude that probably none among the events after ad 770 was actually an aurora, including the event in ad 776 jan, which was misdated for ad 774 or 775; the observed white qi phenomenon that happened "above the moon" in the south-east was most probably a halo effect near the full moon - too late in any case to be related to the 14c variation in ad 774/5. there is another report of a similar (or identical) white qi phenomenon "above the moon", reported just before a comet observation and dated to ad 776 jan; the reported comet observed by the chinese was misdated to ad 776, but actually sighted in ad 767. our critical review of east asian reports of aurorae circa ad 775 shows some very likely true chinese auroral displays observed and reported for ad 762; there were also several events prior to ad 771 that may have been aurorae but are questionable. | a review of east asian reports of aurorae and comets circa ad 775 |
topic of this work are comets, small and elusive objects that may hold great secrets about the origin of the solar system and life on earth, being among the most primitive objects. the method of investigation addressed in this work is the visible and infrared spectrophotometry by imaging spectrometers, designed for the observation of remote planetary atmospheres and surfaces, capable to acquire hyperspectral data with high spatial and spectral resolution. the context under which this mission moves its steps is described in the first chapter. in the second chapter the performances of the virts instrument, onboard rosetta spacecraft, are analyzed in detail. in particular the modeling of the signal to noise ratio is the main argument of this chapter. the third chapter shows simulations of possible spectra of the comet's nucleus, which are useful for both a comparison with real spectra, and for a planning of the observations. hapke's radiative transfer model is used to invert acquired data to infer physical properties. the fourth chapter introduces a method for spectral modeling. it includes the information on the instrumental noise, permitting the analysis of the goodness of the models, and an estimation of the error of the retrieved parameters. the fifth chapter presents the spectral analysis of tempel 1 and hartley 2 whose data are coming from deep impact space mission and its extended investigation. the sixth chapter shows the photometric analysis of lutetia asteroid, which was encountered by rosetta during its cruise phase. this work have paved the way to the analysis of the final target of rosetta: comet 67p/churyumov-gerasimenko. the tools presented are currently used by the virtis team to produce works on the comet, that are recommended to the reader. since a complete analysis on the comet is outside the scope of this work, just preliminary results are shown here. | spectrophotometric analysis of cometary nuclei from in situ observations (phd thesis) |
context. the thermal conductivity of highly porous dust aggregates is a key parameter for many subjects in planetary science; it is not yet fully understood, however.aims: we investigate the thermal conductivity of fluffy dust aggregates with filling factors lower than 10-1.methods: we determined the temperature structure and heat flux of the porous dust aggregates calculated through n-body simulations of static compression in the periodic boundary condition.results: we derive an empirical formula for the thermal conductivity through the solid network ksol as a function of the filling factor of dust aggregates φ. the results reveal that ksol is approximately proportional to φ2, and the thermal conductivity through the solid network is significantly lower than previously assumed. in light of these findings, we must reconsider the thermal histories of small planetary bodies. | thermal conductivity of porous aggregates |
many asymptotic giant branch (agb) and supergiant stars exhibit extended detached shells in the far-infrared, resembling rings or arcs. these structures have long been interpreted as the bow shock formed in the interface between the stellar wind and the interstellar medium (ism), the astrosphere. to date, only a few agb stars have been observed showing an extended shell in the ultraviolet (uv): the cometary tail drifting away from o ceti, and a bubble around irc+10216, cit6, and u hya. this paper describes a search of uv extended shells around agb stars using archival galaxy evolution explorer (galex) far-uv images. after inspecting visually 282 galex images, we identified the fourth discovery of a uv bubble around the agb star r dor. the bubble is seen as a 26 arcmin × 29 arcmin ring, corresponding to an actual diameter of 0.41 × 0.46 parsec2. the mass of the thin uv bubble is estimated to be ≃0.003 m⊙. the morphological asymmetry (less than ~20 per cent) and brightness variations of this shell are uncorrelated with the stellar proper motion and thus they can rather be ascribed to inhomogeneities in the ism. archival infrared astronomical satellite 60 and 100 μm images reveal that the bubble is filled with cold (i.e. ${\lesssim} 32$ k) dust. all uv bubbles known to date are limited to be within a distance ${\lesssim} 350$ pc and at high galactic latitudes ($|b| \gtrsim 35^{\circ }$), which suggests that their detection is hampered in most cases by the strong uv interstellar extinction. | a large bubble around the agb star r dor detected in the uv |
the cometary secondary ion mass analyzer (cosima) onboard esa's rosetta orbiter has revealed that dust particles in the coma of comet 67p/churyumov-gerasimenko are aggregates of small grains. we study the morphological, elastic, and electric properties of dust aggregates in the coma of comet 67p/churyumov-gerasimenko using optical microscopic images taken by the cosima instrument. dust aggregates in cosima images are well represented as fractals in harmony with morphological data from midas (micro-imaging dust analysis system) and giada (grain impact analyzer and dust accumulator) onboard rosetta. cosima's images, together with the data from the other rosetta's instruments such as midas and giada do not contradict the so-called rainout growth of 10 μm -sized particles in the solar nebula. the elastic and electric properties of dust aggregates measured by cosima suggest that the surface chemistry of cometary dust is well represented as carbonaceous matter rather than silicates or ices, consistent with the mass spectra, and that organic matter is to some extent carbonized by solar radiation, as inferred from optical and infrared observations of various comets. electrostatic lofting of cometary dust by intense electric fields at the terminator of its parent comet is unlikely, unless the surface chemistry of the dust changes from a dielectric to a conductor. our findings are not in conflict with our current understanding of comet formation and evolution, which begin with the accumulation of condensates in the solar nebula and follow with the formation of a dust mantle in the inner solar system. | the morphological, elastic, and electric properties of dust aggregates in comets: a close look at cosima/rosetta's data on dust in comet 67p/churyumov-gerasimenko |
at discovery time, c/2017 k2 (panstarrs) was the second most distant inbound active comet ever observed. it has been argued that this object is in the process of crossing the inner solar system for the first time, but other authors have concluded that it is dynamically old. we have performed full n-body simulations for 3 myr into the past using the latest public orbit determination for this object and most of them, 67%, are consistent with a bound and dynamically old oort cloud comet, but about 29% of the studied orbits are compatible with an interstellar origin. our independent calculations strongly suggest that c/2017 k2 is not a dynamically new oort cloud comet. | comet c/2017 k2 (panstarrs): dynamically old or new? |
we present an optical and near-infrared (hereafter nir) polarimetric study of a comet c/2013 us10 (catalina) observed on ut 2015 december 17-18 at phase angles of α = 52.°1-53.°1. additionally, we obtained an optical spectrum and multi-band images to examine the influence of gas emission. we find that the observed optical signals are significantly influenced by gas emission; that is, the gas-to-total intensity ratio varies from 5 to 30% in the r c and 3%-18% in the i c bands, depending on the position in the coma. we derive the “gas-free dust polarization degrees” of 13.8% ± 1.0% in the r c and 12.5% ± 1.1% in the i c bands and a gray polarimetric color, i.e., -8.7% ± 9.9% μm-1 in optical and 1.6% ± 0.9% μm-1 in nir. the increments of polarization obtained from the gas correction show that the polarimetric properties of the dust in this low-polarization comet are not different from those in high-polarization comets. in this process, the cometocentric distance dependence of polarization has disappeared. we also find that the r c-band polarization degree of the southeast dust tail, which consists of large dust particles (100 μm-1 mm), is similar to that in the outer coma where small and large ones are mixed. our study confirms that the dichotomy of cometary polarization does not result from the difference of dust properties, but from depolarizing gas contamination. this conclusion can provide a strong support for similarity in origin of comets. | optical and near-infrared polarimetry of non-periodic comet c/2013 us10 (catalina) |
the physical composition and structure of meteoroids gives us insight into the formation processes of their parent asteroids and comets. the strength of and fundamental grain sizes in meteoroids tell us about the environment in which small solar system bodies formed, and the processes which built up these basic planetary building blocks. the structure of meteorites can be studied directly, but the set of objects which survive entry through the atmosphere is biased toward large, strong objects with slow encounter speeds. fragile objects, small objects and objects with high relative speeds are very unlikely to survive impact with the atmosphere. objects between 100 μm and 1 m, which are not strong enough to survive the ablation process, must be studied by radar or optical methods. large meteoroids, which produce bright fireballs, are generally studied by investigating their compressive strength when they fragment, and their strength can also be inferred indirectly from their end heights. fragmentation in faint meteors can be inferred from interference in radar observations, or observed directly with high-resolution optical systems. meteor light curves, begin heights and time-evolving spectra can also be used to infer meteoroid structure. this paper presents a review of the meteor observation methods currently used to infer the structure and fragmentation of meteoroids in the millimeter to meter size range, and the current state of understanding these observations have given us. | meteoroid structure and fragmentation |
carbonaceous chondrite meteorites are some of the oldest solar system planetary materials available for study. the ci group has bulk abundances of elements similar to those of the solar photosphere. of particular interest in carbonaceous chondrite compositions are labile elements, which vaporize and mobilize efficiently during post-accretionary parent-body heating events. thus, they can record low-temperature alteration events throughout asteroid evolution. however, the precise nature of labile-element mobilization in planetary materials is unknown. here we characterize the thermally induced movements of the labile elements s, as, se, te, cd, sb, and hg in carbonaceous chondrites by conducting experimental simulations of volatile-element mobilization during thermal metamorphism. this process results in appreciable loss of some elements at temperatures as low as 500 k. this work builds on previous laboratory heating experiments on primitive meteorites and shows the sensitivity of chondrite compositions to excursions in temperature. elements such as s and hg have the most active response to temperature across different meteorite groups. labile element mobilization in primitive meteorites is essential for quantifying elemental fractionation that occurred on asteroids early in solar system history. this work is relevant to maintaining a pristine sample from asteroid (101955) bennu from the osiris-rex mission and constraining the past orbital history of bennu. additionally, we discuss thermal effects on surface processes of near-earth asteroids, including the thermal history of "rock comets" such as (3200) phaethon. this work is also critical for constraining the concentrations of contaminants in vaporized water extracted from asteroid regolith as part of future in situ resource utilization for sustained robotic and human space exploration. | thermal alteration of labile elements in carbonaceous chondrites |
133p/elst-pizarro is the first recognized main-belt comet, but we still know little about its nucleus. first we use mid-infrared data of spitzer mips, spitzer irs, and the wide-field infrared survey explorer to estimate its effective diameter, ${d}_{\mathrm{eff}}={3.9}_{-0.3}^{+0.4}$ km, geometric albedo, ${p}_{{\rm{v}}}=0.074\pm 0.013$ , and mean bond albedo ${a}_{\mathrm{eff},{\rm{b}}}=0.024\pm 0.004$ . the albedo is used to compute 133p's temperature distribution, which shows significant seasonal variation, especially polar regions, ranging from ∼40 to ∼200 k. based on current activity observations, the maximum water gas production rate is estimated to be $\sim 1.4\times {10}^{23}\,{{\rm{s}}}^{-1}$ , being far weaker than $\sim {10}^{26}\,{{\rm{s}}}^{-1}$ of jfc 67p at a similar heliocentric distance of ∼2.7 au, indicating a thick dust mantle on the surface to lower down the gas production rate. the diameter of the sublimation area may be <∼200 m according to our model prediction. we thus propose that 133p's activity is more likely to be caused by sublimation of a regional near-surface ice patch rather than a homogeneous buried ice layer. such a small near-surface ice patch might be exposed by one impact event, before which 133p may be an extinct comet (or ice-rich asteroid) with an ice layer buried below ∼40 m depth. the proposed ice patch may be located somewhere within latitude -50 ∼ 50° by comparing theoretical variation of sublimation temperature to the constraints from observations. the timescale to form such a thick dust mantle is estimated to be >100 myr, indicating that 133p may be more likely to be a relatively old planetesimals or a member of an old family than a recently formed fragment of some young family. | low-activity main-belt comet 133p/elst-pizarro: new constraints on its albedo, temperature, and active mechanism from a thermophysical perspective |
context. solar orbiter is expected to have flown close to the tail of comet c/2019 y4 (atlas) during the spacecraft's first perihelion in june 2020. models predict a possible crossing of the comet tails by the spacecraft at a distance from the sun of approximately 0.5 au.aims: this study is aimed at identifying possible signatures of the interaction of the solar wind plasma with material released by comet atlas, including the detection of draped magnetic field as well as the presence of cometary pick-up ions and of ion-scale waves excited by associated instabilities. this encounter provides us with the first opportunity of addressing such dynamics in the inner heliosphere and improving our understanding of the plasma interaction between comets and the solar wind.methods: we analysed data from all in situ instruments on board solar orbiter and compared their independent measurements in order to identify and characterize the nature of structures and waves observed in the plasma when the encounter was predicted.results: we identified a magnetic field structure observed at the start of 4 june, associated with a full magnetic reversal, a local deceleration of the flow and large plasma density, and enhanced dust and energetic ions events. the cross-comparison of all these observations support a possible cometary origin for this structure and suggests the presence of magnetic field draping around some low-field and high-density object. inside and around this large scale structure, several ion-scale wave-forms are detected that are consistent with small-scale waves and structures generated by cometary pick-up ion instabilities.conclusions: solar orbiter measurements are consistent with the crossing through a magnetic and plasma structure of cometary origin embedded in the ambient solar wind. we suggest that this corresponds to the magnetotail of one of the fragments of comet atlas or to a portion of the tail that was previously disconnected and advected past the spacecraft by the solar wind. | solar orbiter's encounter with the tail of comet c/2019 y4 (atlas): magnetic field draping and cometary pick-up ion waves |
glass with embedded metal and sulfides (gems) is a major component of chondritic porous interplanetary dust particles. although gems is one of the most primitive components in the solar system, its formation process and conditions have not been constrained. we performed condensation experiments of gases in the system of mg-si-o (mgsio3 composition) and of the s-free ci chondritic composition (si-mg-fe-na-al-ca-ni-o system) in induction thermal plasma equipment. amorphous mg-silicate particles condensed in the experiments of the mg-si-o system, and their grain size distribution depended on the experimental conditions (mainly partial pressure of sio). in the ci chondritic composition experiments, irregularly shaped amorphous silicate particles of less than a few hundred nanometers embedded with multiple fe-ni nanoparticles of ≤20 nm were successfully synthesized. these characteristics are very similar to those of gems, except for the presence of fesi instead of sulfide grains. we propose that the condensation of amorphous silicate grains smaller than a few tens of nanometers and with metallic cores, followed by coagulation, could be the precursor material that forms gems prior to sulfidation. movie is available at https://www.aanda.org | condensation of cometary silicate dust using an induction thermal plasma system. i. enstatite and ci chondritic composition |
equipping a spacecraft with multiple solar-powered electric engines (of the same or different types) compounds the task of optimal trajectory design due to presence of both real-valued inputs (power input to each engine in addition to the direction of thrust vector) and discrete variables (number of active engines). each engine can be switched on/off independently and "optimal" operating power of each engine depends on the available solar power, which depends on the distance from the sun. application of the composite smooth control (csc) framework to a heliocentric fuel-optimal trajectory optimization from the earth to the comet 67p/churyumov-gerasimenko is demonstrated, which presents a new approach to deal with multiple-engine problems. operation of engine clusters with 4, 6, 10 and even 20 engines of the same type can be optimized. moreover, engine clusters with different/mixed electric engines are considered with either 2, 3 or 4 different types of engines. remarkably, the csc framework allows us 1) to reduce the original multi-point boundary-value problem to a two-point boundary-value problem (tpbvp), and 2) to solve the resulting tpbvps using a single-shooting solution scheme and with a random initialization of the missing costates. while the approach we present is a continuous neighbor of the discontinuous extremals, we show that the discontinuous necessary conditions are satisfied in the asymptotic limit. we believe this is the first indirect method to accommodate a multi-mode control of this level of complexity with realistic engine performance curves. the results are interesting and promising for dealing with a large family of such challenging multi-mode optimal control problems. | a novel approach for optimal trajectory design with multiple operation modes of propulsion system, part 2 |
the virtis imaging spectrometer on board rosetta has shown that the nucleus surface of comet 67p/churyumov-gerasimenko (67p/cg) is characterized by a broad absorption band at around 3.2 μm. the feature is ubiquitous across the surface and its attribution to (a) specific material(s) has been challenging. in the present letter, we report an experimental investigation showing that the interaction of hydrogen atoms with mg-rich amorphous silicates determines the formation of hydroxyl groups. the resulting ir spectrum exhibits a broad feature around 3.2 μm similar to that of comet 67p/cg. hapke's radiative transfer model was employed to estimate an upper limit contribution of 65% of hydroxylated silicates to the observed cometary band intensity. the presence of a hydroxylated fraction in silicates on the cometary surface would represent an evolutionary link between primitive objects of the solar system and dust in the interstellar medium (ism), where silicate grains can be hydroxylated after having interacted with hydrogen atoms. this link is consistent with the detection of the aliphatic organics in 67p/cg that also originate in the ism. | hydroxylated mg-rich amorphous silicates: a new component of the 3.2 μm absorption band of comet 67p/churyumov-gerasimenko |
the current composition of giant planet atmospheres provides information on how such planets formed, and on the origin of the solid building blocks that contributed to their formation. noble gas abundances and their isotope ratios are among the most valuable pieces of evidence for tracing the origin of the materials from which the giant planets formed. in this review we first outline the current state of knowledge for heavy element abundances in the giant planets and explain what is currently understood about the reservoirs of icy building blocks that could have contributed to the formation of the ice giants. we then outline how noble gas isotope ratios have provided details on the original sources of noble gases in various materials throughout the solar system. we follow this with a discussion on how noble gases are trapped in ice and rock that later became the building blocks for the giant planets and how the heavy element abundances could have been locally enriched in the protosolar nebula. we then provide a review of the current state of knowledge of noble gas abundances and isotope ratios in various solar system reservoirs, and discuss measurements needed to understand the origin of the ice giants. finally, we outline how formation and interior evolution will influence the noble gas abundances and isotope ratios observed in the ice giants today. measurements that a future atmospheric probe will need to make include (1) the 3he/4he isotope ratio to help constrain the protosolar d/h and 3he/4he; (2) the 20ne/22ne and 21ne/22ne to separate primordial noble gas reservoirs similar to the approach used in studying meteorites; (3) the kr/ar and xe/ar to determine if the building blocks were jupiter-like or similar to 67p/c-g and chondrites; (4) the krypton isotope ratios for the first giant planet observations of these isotopes; and (5) the xenon isotopes for comparison with the wide range of values represented by solar system reservoirs. | tracing the origins of the ice giants through noble gas isotopic composition |
context. the esa rosetta mission has allowed for an extensive in situ study of the comet 67p/churyumov-gerasimenko. in measurements performed by the ram gauge of the comet pressure sensor (cops), observed features are seen to deviate from the nominal ram gauge signal. this effect is attributable to the sublimation of the volatile fraction of cometary icy particles containing volatiles and refractories.aims: the objective of this work is to investigate the volatile content of icy particles that enter the cops ram gauge.methods: we inspected the ram gauge measurements to search for features associated with the sublimation of the volatile component of cometary particles impacting the instrument. all the sublimation features with a high-enough signal-to-noise ratio were modelled by fitting one or more exponential decay functions. the parameters of these fits were used to categorise different compositions of the sublimating component.results: based on features that are attributable to ice sublimation, we infer the detection of 73 icy particles containing volatiles. of these, 25 detections have enough volatile content for an in-depth study. from the values of the exponential decay constants, we classified the 25 inferred icy particles into three types, interpreted as different volatile compositions, which are possibly further complicated by their differing morphologies. the available data do not give any indication as to which molecules compose the different types. nevertheless, we can estimate the total volume of volatiles, which is expressed as the diameter of an equivalent sphere of water (density of 1 g cm-3). this result was found to be on the order of hundreds of nanometres. | detection of volatiles undergoing sublimation from 67p/churyumov-gerasimenko coma particles using rosina/cops. i. the ram gauge |
the recent observations show that comet c/2016 r2 (pan-starrs) has a unique and peculiar composition when compared with several other comets observed at 2.8 au heliocentric distance. assuming solar resonance fluorescence is the only excitation source, the observed ionic emission intensity ratios are used to constrain the corresponding neutral abundances in this comet. we developed a physico-chemical model to study the ion density distribution in the inner coma of this comet by accounting for photon and electron impact ionization of neutrals, charge exchange and proton transfer reactions between ions and neutrals, and electron-ion thermal recombination reactions. our calculations show that co2+ and co+ are the major ions in the inner coma, and close to the surface of nucleus ch3oh+, ch3oh2+, and o2+ are also important ions. by considering various excitation sources, we also studied the emission mechanisms of different excited states of co+, co2+, n2+, and h2o+. we found that the photon and electron impact ionization and excitation of corresponding neutrals significantly contribute to the observed ionic emissions for radial distances smaller than 300 km and at larger distances, solar resonance fluorescence is the major excitation source. our modelled ion emission intensity ratios are consistent with the ground-based observations. based on the modelled emission processes, we suggest that the observed ion emission intensity ratios can be used to derive the neutral composition in the cometary coma only when the ion densities are significantly controlled by photon and photoelectron impact ionization of neutrals rather than by the ion-neutral chemistry. | a physico-chemical model to study the ion density distribution in the inner coma of comet c/2016 r2 (pan-starrs) |
in this work we present the experimental verification of different approaches to calculate the rate of the outgassing of cometary analogues. we investigated both new, and known formulations applicable for the mass flux of water vapor from mixtures of ice agglomerates. for the purpose of the verification we performed experiments using samples composed of different ice agglomerates. we tested both samples made of approximately uniform agglomerates and samples composed of agglomerates of hierarchical structure. the largest agglomerates have diameters about one centimeter. all experiments were performed in vacuum. we have found, that at the temperature above 200 k the pressure of vapor between agglomerates is close to the pressure of the phase equilibrium and exhibits some dependence on the temperature. we propose the appropriate functions. in addition, we present the method of calculating the lifetime of large centimeter sized porous ice-dust particles present in cometary comae. | outgassing of ice agglomerates |
the relation between ice composition in the nucleus of comet 67p/churyumov-gerasimenko on the one hand and relative abundances of volatiles in the coma on the other hand is important for the interpretation of density measurements in the environment of the cometary nucleus. for the 2015 apparition, in situ measurements from the two rosina (rosetta orbiter spectrometer for ion and neutral analysis) sensors cops (comet pressure sensor) and dfms (double focusing mass spectrometer) determined gas densities at the spacecraft position for the 14 gas species h2o, co2, co, h2s, o2, c2h6, ch3oh, h2co, ch4, nh3, hcn, c2h5oh, ocs, and cs2. we derive the spatial distribution of the gas emissions on the complex shape of the nucleus separately for 50 subintervals of the two-year mission time. the most active patches of gas emission are identified on the surface. we retrieve the relation between solar irradiation and observed emissions from these patches. the emission rates are compared to a minimal thermophysical model to infer the surface active fraction of h2o and co2. we obtain characteristic differences in the ice composition close to the surface between the two hemispheres with a reduced abundance of co2 ice on the northern hemisphere (locations with positive latitude). we do not see significant differences for the ice composition on the two lobes of 67p/c-g. | the ice composition close to the surface of comet 67p/churyumov-gerasimenko |
highly periodic structures are often said to convey the beauty of nature. however, most material properties are strongly influenced by the defects they contain. on the mesoscopic scale, molecular self-assembly exemplifies this interplay; thermodynamic principles determine short-range order, but long-range order is mainly impeded by the kinetic history of the material and by thermal fluctuations. for the development of self-assembly technologies, it is imperative to characterise and understand the interplay between self-assembled order and defect-induced disorder. here we used synchrotron-based hard x-ray nanotomography to reveal a pair of extended topological defects within a self-assembled single-diamond network morphology. these defects are morphologically similar to the comet and trefoil patterns of equal and opposite half-integer topological charges observed in liquid crystals and appear to maintain a constant separation across the thickness of the sample, resembling pairs of full vortices in superconductors and other hard condensed matter systems. these results are expected to open new windows to study defect formation in soft condensed matter, particularly in biological systems where most structures are formed by self-assembly. | high-resolution three-dimensional imaging of topological textures in single-diamond networks |
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