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the hydrogen emission from meteors is assumed to originate mainly from the meteoroid composition, making it a potential tracer of h2o molecules and organic compounds. h α line was previously detected in individual fireballs, but its variation in a larger meteor data set and dependence on the dynamical origin and physical properties have not yet been studied. here, we investigate the relative intensity of h α within 304 meteor spectra observed by the amos (all-sky meteor orbit system) network. we demonstrate that h α emission is favoured in faster meteors (vi > > 30 km s-1) which form the high-temperature spectral component. h α was found to be a characteristic spectral feature of cometary meteoroids with ~92 per cent of all meteoroids with detected h α originating from halley-type and long-period orbits. our results suggest that hydrogen is being depleted from meteoroids with lower perihelion distances (q < 0.4 au). no asteroidal meteoroids with detected h emission were found. however, using spectral data from simulated ablation of different meteorite types, we show that h emission from asteroidal materials can occur, and apparently correlates with their water and organic matter content. strongest h emission was detected from carbonaceous chondrites (cm and cv) and achondrites (ureilite and aubrite), while it was lacking in most ordinary chondrites. the detection of h α in asteroidal meteoroids could be used to identify meteoroids of carbonaceous or achondritic composition. overall, our results suggest that h α emission correlates with the emission of other volatiles (na and cn) and presents a suitable tracer of water and organic matter in meteoroids. | hydrogen emission from meteors and meteorites: mapping traces of h2o molecules and organic compounds in small solar system bodies |
the magnetic field of a host star can impact the orbit of a stellar partner, planet, or asteroid if the orbiting body is itself magnetic or electrically conducting. here, we focus on the instantaneous magnetic forces on an orbiting body in the limit where the dipole approximation describes its magnetic properties as well as those of its stellar host. a permanent magnet in orbit about a star will be inexorably drawn toward the stellar host if the magnetic force is comparable to gravity due to the steep radial dependence of the dipole-dipole interaction. while magnetic fields in observed systems are much too weak to drive a merger event, we confirm that they may be high enough in some close compact binaries to cause measurable orbital precession. when the orbiting body is a conductor, the stellar field induces a time-varying magnetic dipole moment that leads to the possibility of eccentricity pumping and resonance trapping. the challenge is that the orbiter must be close to the stellar host, so that magnetic interactions must compete with tidal forces and the effects of intense stellar radiation. | magnetic interactions in orbital dynamics |
on 2022 september 26, the dart spacecraft will impact the surface of dimorphos, the ~160 m size satellite of the binary near-earth asteroid (nea) (65803) didymos. what will be observed on the surfaces of both asteroids and at the dart impact site is largely unknown, beyond the details of didymos revealed by previous arecibo and goldstone radar observations. we present here the expected dart and liciacube observations of the didymos system and discuss the planned mapping strategies. by searching similar geological features and processes identified on other neas, we constrain the impact conditions that dart might encounter at dimorphos, assessing both the asteroid's surface and interior structure. | anticipated geological assessment of the (65803) didymos-dimorphos system, target of the dart-liciacube mission |
shock metamorphism of minerals in meteorites provides insights into the ancient solar system. calcite is an abundant aqueous alteration mineral in carbonaceous chondrites. return samples from the asteroids ryugu and bennu are expected to contain calcite-group minerals. although shock metamorphism in silicates has been well studied, such data for aqueous alteration minerals are limited. here, we investigated the shock effects in calcite with marble using impact experiments at the planetary exploration research center of chiba institute of technology. we produced decaying compressive pulses with a smaller projectile than the target. a metal container facilitates recovery of a sample that retains its pre-impact stratigraphy. we estimated the peak pressure distributions in the samples with the isale shock physics code. the capability of this method to produce shocked grains that have experienced different degrees of metamorphism from a single experiment is an advantage over conventional uniaxial shock recovery experiments. the shocked samples were investigated by polarizing microscopy and x-ray diffraction analysis. we found that more than half of calcite grains exhibit undulatory extinction when peak pressure exceeds 3 gpa. this shock pressure is one order of magnitude higher than the hugoniot elastic limit (hel) of marble, but it is close to the hel of a calcite crystal, suggesting that the undulatory extinction records dislocation-induced plastic deformation in the crystal. finally, we propose a strategy to re-construct the maximum depth of calcite grains in a meteorite parent body, if shocked calcite grains are identified in chondrites and/or return samples from ryugu and bennu. | shock recovery with decaying compressive pulses: shock effects in calcite (caco3) around the hugoniot elastic limit |
the objective of the psyche magnetometry investigation is to test the hypothesis that asteroid (16) psyche formed from the core of a differentiated planetesimal. to address this, the psyche magnetometer will measure the magnetic field around the asteroid to search for evidence of remanent magnetization. paleomagnetic measurements of meteorites and dynamo theory indicate that a diversity of planetesimals once generated dynamo magnetic fields in their metallic cores. likewise, the detection of a strong magnetic moment (>2 ×1014am2) at psyche would likely indicate that the body once generated a core dynamo, implying that it formed by igneous differentiation. the psyche magnetometer consists of two three-axis fluxgate sensor units (sus) mounted 0.7 m apart along a 2.15-m long boom and connected to two electronics units (eus) located within the spacecraft bus. the magnetometer samples at up to 50 hz, has a range of ±80 ,000 nt, and an instrument noise of 39 ptaxis-13 σ integrated over 0.1 to 1 hz. the two pairs of sus and eus provide redundancy and enable gradiometry measurements to suppress noise from flight system magnetic fields. the magnetometer will be powered on soon after launch and acquire data for the full duration of the mission. the ground data system processes the magnetometer measurements to obtain an estimate of psyche's dipole moment. | the psyche magnetometry investigation |
we used laboratory analysis to investigate the effect of mineral albedo, as defined at 750 nm, on the midinfrared emissivity spectra of silicates under lunar environment conditions. optical darkening has long been recognized as an effect of space weathering on the visible-to-near-infrared spectra of the moon. however, space weathering has not been as thoroughly investigated in the mid-infrared. because mid-infrared spectra are strongly influenced by the anisothermality of the lunar surface environment, it is likely that any darkening effects of space weathering would also change the thermal gradient in heavily space weathered lunar regolith. to isolate this variable, we added nanophase carbon to particulate samples of forsterite, augite, and anorthite to achieve a range of albedo samples and measured their midinfrared spectra under lunar environment conditions within the planetary and asteroid regolith spectroscopy environment chamber at stony brook university. we observe a shift in the christiansen feature maximum to longer wavelengths and decreasing spectral contrast with decreasing albedo. these shifts are well correlated with the observation of space weathering effects on the diviner lunar radiometer experiment compositional data, and point to the need for further investigation into the effects of space weathering on the midinfrared spectra of airless bodies. | effects of albedo on the mir emissivity spectra of silicates for lunar comparison |
we present the physical and dynamical properties of the recently discovered active asteroid (248370) 2005qn173 (aka 433p). from our observations, we derived two possible rotation period solutions of 2.7 ± 0.1 and 4.1 ± 0.1 h. the corresponding light-curve amplitudes computed after correcting for the effect of coma are 0.28 and 0.58 mag, respectively. both period solutions are shorter than the critical rotation limit computed for a strengthless triaxial ellipsoid, suggesting that rotation mass shedding should at least partly be responsible for the observed activity. we confirm that the activity level is fading further, but at a very modest rate of only 0.006 mag d-1, still also compatible with sublimation-driven activity. we found that 248370 likely belongs to the themis asteroid family, making it a fourth main-belt comet associated with this group. orbital characteristics of 248370 are also consistent with its origin in the young 288p cluster of asteroids. the 288p cluster is associated with its namesake main-belt comet, providing an exciting possibility for a comparative analysis of intriguing main-belt comets 248370 and 288p. | photometric and dynamic characterization of active asteroid (248370) 2005qn173 |
the focus of this work is the current distribution of asteroids in co-orbital motion with venus, earth and jupiter, under a quasi-coplanar configuration and for a medium-term timescale of the order of 900 years. a co-orbital trajectory is a heliocentric orbit trapped in a 1:1 mean-motion resonance with a given planet. as such, to model it this work considers the restricted three-body problem in the planar circular case with the help of averaging techniques. the domain of each co-orbital regime, that is, the quasi-satellite motion, the horseshoe motion and the tadpole motion, can be neatly defined by means of an integrable model and a simple two-dimensional map, that is invariant with respect to the mass parameter of the planet, and turns out to be a remarkable tool to investigate the distribution of the co-orbitals objects of interest. the study is based on the data corresponding to the ephemerides computed by the jpl horizons system for asteroids with a sufficient low orbital inclination with respect to the sun-planet orbital plane. these objects are cataloged according to their current dynamics, together with the transitions that occur in the given time frame from a given type of co-orbital motion to another. the results provide a general catalog of co-orbital asteroids in the solar system, the first one to our knowledge, and an efficient mean to study transitions. | on the co-orbital asteroids in the solar system: medium-term timescale analysis of the quasi-coplanar objects |
the thermal/impact histories of sixteen eucrite meteorites were investigated: three monomict eucrites (nwa 999, a-87272,87, and stannern), five polymict eucrites (nwa 1000, nwa 1666, nwa 5601, y-980066,100, and y-980255,100), three quench-textured, eucrite melt rocks (y-981646,21, y-981651,105, and mil 0766214), one eucrite dominantly comprised of quench-textured clasts (que 99005,11), three unclassified eucrite breccias (lap 031316,9, lar 06870,5, que 99799,4) and one unbrecciated eucrite (eet 92004,17), included here due to its shock features. we have measured fifteen high-precision new 40ar/39ar plateau ages on plagioclase and matrix for ten of these meteorites with a tight cluster of nine ages obtained from three different polymict breccias. these ages range from 4534 ± 56 ma to 4491 ± 16 ma resulting in a concordant age population (p = 0.16). the fact that such a cluster of ages is recorded in unrelated breccias which are made of a priori unrelated components, leads us to propose that those ages recorded a single heating event on a large scale, and is interpreted here as a high-energy impact event, early in the history of vesta at 4500 ± 4 ma. we propose that the debris was ejected and isolated from subsequent large impacts in a secondary rubble pile asteroid where the energy of the outgoing shock wave from an impact is significantly reduced as it compacts the target material (holsapple et al., 2002, and references therein). the other analyses define a spread of five plateau ages ranging from 3851 ± 21 ma to 3469 ± 35 ma, over ∼380 ma. an additional apparent plateau age of 4288 ± 38 ma, but with a diffusion profile of cumulative 39ar release, along with published u-pb apatite age of ∼4.14 ga, suggests that the data might either define a true continuum (normal background bombardment) from 4.5 ga to 3.47 ga or cluster between ∼3.85 ga and ∼3.47 ga (excavation of a fresh surface at 3.85 ga continuously bombarded until 3.47 ga). both scenarios are compatible with a final ejection age of 3.47 ga when a major impact liberates the bulk of the brecciated meteorites into another secondary rubble pile asteroid, where the brecciated eucrites stayed relatively well protected from subsequent major impacts. based on these results and recent crater counting measurements, we propose that the excavation and bulk ejection were caused by the rheasilvia (ca. 3.47 ga) basin-forming impact. diffusion models on plagioclase crystals with different ar age spectrum signatures, from a single breccia (nwa1666; 4501 ± 7 ma), suggest that either: (1) the formation of the breccia is very young, or (2) different plagioclase crystals have different diffusion characteristics, and/or (3) the porosity caused heterogeneous temperatures during an impact heating event, particularly likely if the 4.5 ga brecciated eucrites were stored in a rubble pile asteroid. many or possibly most large asteroids being re-accumulated rubble piles with potential large porosity (holsapple et al., 2002). scenarios (2) and (3) preclude the usage of multi-grain aliquots to decipher the time-temperature history of most impact breccia using 40ar/39ar thermochronology. | bombardment history of asteroid 4 vesta recorded by brecciated eucrites: large impact event clusters at 4.50 ga and discreet bombardment until 3.47 ga |
we examine data from the murchison widefield array (mwa) in the frequency range 72-102 mhz for a field of view that serendipitously contained the interstellar object ‘oumuamua on 2017 november 28. observations took place with a time resolution of 0.5 s and a frequency resolution of 10 khz. based on the interesting but highly unlikely suggestion that ‘oumuamua is an interstellar spacecraft, due to some unusual orbital and morphological characteristics, we examine our data for signals that might indicate the presence of intelligent life associated with ‘oumuamua. we searched our radio data for (1) impulsive narrowband signals, (2) persistent narrowband signals, and (3) impulsive broadband signals. we found no such signals with nonterrestrial origins and make estimates of the upper limits on equivalent isotropic radiated power (eirp) for these three cases of approximately 7 kw, 840 w, and 100 kw, respectively. these transmitter powers are well within the capabilities of human technologies, and are therefore plausible for alien civilizations. while the chances of positive detection in any given search for extraterrestrial intelligence (seti) experiment are vanishingly small, the characteristics of new generation telescopes such as the mwa (and, in the future, the square kilometre array) make certain classes of seti experiments easy, or even a trivial by-product of astrophysical observations. this means that the future costs of seti experiments are very low, allowing large target lists to partially balance the low probability of a positive detection. | a serendipitous mwa search for narrowband signals from ‘oumuamua |
the winonaites are primitive achondrites which are associated with the iab iron meteorites. textural evidence implies heating to at least the fe, ni-fes cotectic, but previous geochemical studies are ambiguous about the extent of silicate melting in these samples. oxygen isotope evidence indicates that the precursor material may be related to the carbonaceous chondrites. here we analysed a suite of winonaites for modal mineralogy and bulk major- and trace-element chemistry in order to assess the extent of thermal processing as well as constrain the precursor composition of the winonaite-iab parent asteroid. modal mineralogy and geochemical data are presented for eight winonaites. textural analysis reveals that, for our sub-set of samples, all except the most primitive winonaite (northwest africa 1463) reached the fe, ni-fes cotectic. however, only one (tierra blanca) shows geochemical evidence for silicate melting processes. tierra blanca is interpreted as a residue of small-degree silicate melting. our sample of winona shows geochemical evidence for extensive terrestrial weathering. all other winonaites studied here (fortuna, queen alexander range 94535, hammadah al hamra 193, pontlyfni and nwa 1463) have chondritic major-element ratios and flat ci-normalised bulk rare-earth element patterns, suggesting that most of the winonaites did not reach the silicate melting temperature. the majority of winonaites were therefore heated to a narrow temperature range of between ∼1220 (the fe, ni-fes cotectic temperature) and ∼1370 k (the basaltic partial melting temperature). silicate inclusions in the iab irons demonstrate partial melting did occur in some parts of the parent body (ruzicka and hutson, 2010), thereby implying heterogeneous heat distribution within this asteroid. together, this indicates that melting was the result of internal heating by short-lived radionuclides. the brecciated nature of the winonaites suggests that the parent body was later disrupted by a catastrophic impact, which allowed the preservation of the largely unmelted winonaites. despite major-element similarities to both ordinary and enstatite chondrites, trace-element analysis suggests the winonaite parent body had a carbonaceous chondrite-like precursor composition. the parent body of the winonaites was volatile-depleted relative to ci, but enriched compared to the other carbonaceous classes. the closest match are the cm chondrites; however, the specific precursor is not sampled in current meteorite collections. | a geochemical study of the winonaites: evidence for limited partial melting and constraints on the precursor composition |
asteroids are the remnants of the process by which planets formed from the protoplanetary disk. laboratory analyses of materials originating from asteroids give us the unique opportunity to reveal the formation history of our solar system about 4.6 billion years ago. to obtain surface regolith in the low-gravity and vacuum environment, a gas-driven sampling strategy has been proposed, but the relation between the collected mass and the gas ejection remains to be explored, which is important for the development of efficient sampling mechanism designs. in this paper, we simulate the gas-particle two-phase flow in the gas-driven sampling process by using the coupled computational fluid dynamics and discrete element method (cfd-dem) method. the results show that the sampling process can be divided into three stages according to the mass of particles that are sampled. initially, the impact ejection of the pressurized gas on the regolith layer dominates, during which the sampling speed increases to a maximum value rapidly. after that, the gas flow transports the ejected particles to the collection chamber. in this stage, the conveyance effect of gas plays a primary role. as grains accumulate near the entrance of the collecting tube, jamming state happens and obstructs the particle flow, making the sampling rate drop to a stable value. by varying the inlet gas velocity, we show that higher gas velocity increases the collected mass rate greatly at the first stage while no significant differences are found after the development of jamming state inside the chamber. the position of the inlets affects the flow field and thus could be used to prevent the unfavorable aggregation of particles near the collecting tube, which facilitates the sampling. the influence of the inlet gas angle is also explored. we find two inward tilting gas inlets could increase the sampling efficiency considerably through striking a balance between ejected mass and ejecting velocity. the results presented in this article are expected to provide important information on the optimal designs of gas-driven sampling devices for future asteroid space mission. | cfd-dem simulation of gas-driven sampling on asteroid regolith: dependence of collected mass on gas ejection |
(16) psyche is the largest m-type asteroid in the main belt and the target of the nasa discovery-class psyche mission. despite gaining considerable interest in the scientific community, psyche's composition and formation remain unconstrained. originally, psyche was considered to be almost entirely composed of metal due to its high radar albedo and spectral similarities to iron meteorites. more recent telescopic observations suggest the additional presence of low-fe pyroxene and exogenic carbonaceous chondrites on the asteroid's surface. to better understand the abundances of these additional materials, we investigated visible near-infrared (0.35-2.5 μm) spectral properties of three-component laboratory mixtures of metal, low-fe pyroxene, and carbonaceous chondrite. we compared the band depths and spectral slopes of these mixtures to the telescopic spectrum of (16) psyche to constrain material abundances. we find that the best matching mixture to psyche consists of 82.5% metal, 7% low-fe pyroxene, and 10.5% carbonaceous chondrite by weight, suggesting that the asteroid is less metallic than originally estimated (∼94%). the relatively high abundance of carbonaceous chondrite material estimated from our laboratory experiments implies the delivery of this exogenic material through low velocity collisions to psyche's surface. assuming that psyche's surface is representative of its bulk material content, our results suggest a porosity of 35% to match recent density estimates. | constraining the regolith composition of asteroid (16) psyche via laboratory visible near-infrared spectroscopy |
on mars, structural loads and the low tensile strength of in-place martian binders make existing solutions for martian structures uneconomical because they are based on the terrestrial sources like inflatable units. here we address this issue by introducing and analyzing three innovative structural forms in accordance with the structural engineering point of view using symmetric optimum parabolic rotated arch shapes and in-place waterless sulfur-based concrete. these forms minimize the tensile stresses under martian structural loads. probable martian structural loads, including gravity, wind, marsquakes, asteroid and meteoroid impact loads and their effects have been investigated and calculated. the proposed models were analyzed under martian structural loads using the implicit finite element method and the results were compared to two concrete structural forms from previous studies. the proposed models could tolerate martian structural loads with complete elastic behavior and would significantly decrease the martian colonization cost due to using martian resources and reduce element importing from earth. | martian buildings: structural forms using in-place sources |
the insoluble organic matter (iom) contained in carbonaceous chondrites has witnessed a diverse suite of processes possibly starting from the evolution of the parent molecular cloud down to the protosolar nebula and finally to asteroidal processes that occurred on the chondrites' parent bodies. laser desorption coupled with ultra-high-resolution mass spectrometry reveals that the iom of the paris meteorite releases a large diversity of molecules. various molecular families ranging from hydrogenated amorphous carbon to chnos aromatic molecules were detected with heteroatoms (nitrogen, oxygen, and sulfur) mainly incorporated within aromatic structures. molecules bearing nitrogen atoms present a significant variation in aromaticity. these unprecedented results allow the proposal that small molecules bearing heteroatoms could be trapped in the large macromolecular network of the iom by hydrophobic interactions. this molecular diversity could originate from different sources, such as the soluble organic matter, the hydrothermal alteration inside the paris's parent body, or even generated during the iom extraction procedure. it has to be noted that some of the molecular diversity may reflect fragmentation and rearrangement of the iom constituents during the laser desorption ionization, although care was taken to minimize such damage. | unprecedented molecular diversity revealed in meteoritic insoluble organic matter: the paris meteorite's case |
active force generation in living organisms, which is mainly involved in actin cytoskeleton and myosin molecular motors, plays a crucial role in various biological processes. although the contractile properties of actomyosin have been extensively investigated, their dynamic contribution to a deformable membrane remains unclear because of the cellular complexities and the difficulties associated with in vitro reconstitution. here, by overcoming these experimental difficulties, we demonstrate the dynamic deformation of a reconstituted lipid interface coupled with self-organized structure of contractile actomyosin. therein, the lipid interface repeatedly oscillates without any remarkable periods. the oscillatory deformation of the interface is caused by the aster-like three-dimensional hierarchical structure of actomyosin inside the droplet, which is revealed that the oscillation occurs stochastically as a poisson process. | non-periodic oscillatory deformation of an actomyosin microdroplet encapsulated within a lipid interface |
lunar dust proved to be troublesome during the apollo missions. the powdery dust got into everything, abrading spacesuit fabric, clogging seals and other critical equipment. even inside the lunar module, apollo astronauts were exposed to this dust after they removed their dust coated spacesuits. the lunar dust is comprised of fine particles, with electric charges imparted by solar winds and ultraviolet radiation. as such, it adheres readily, and easily penetrates through the smallest crevices into mechanisms. while efforts are under way to figure out how to return astronauts to the moon and set up habitats for long duration missions, the issue of lunar dust remains relevant. consequently, nasa has identified dust as a critical environmental challenge to overcome for future planetary surface missions characterized by dusty environments. several concepts were successfully investigated by the international research community for preventing deposition of lunar dust on rigid surfaces (ex: solar cells and thermal radiators). however, applying these technologies for flexible surfaces and specifically to spacesuits has remained an open challenge, due to the complexity of the suit design, geometry, and dynamics. in our research, we developed a spacesuit integrated carbon nanotube dust ejection/removal (spicder) system to protect spacesuits and other flexible surfaces from lunar dust. spicder leverages the efficient electrodynamic dust shield concept developed at nasa for use on solar cells. it is customized for dust mitigation on flexible surfaces, using novel materials and specialized design techniques. the result is a self-cleaning spacesuit that can repel lunar dust. this paper provides an overview of the spicder system and showcases our working prototypes, ranging from coupons to a scaled portion of a lunar spacesuit segment. the design is supported by parametric analysis in ansys maxwell for optimizing spicder integration into the spacesuit outerlayer. the paper emphasizes design considerations for astronaut safety, based on analysis and experimental results. the spicder system can be optimized efficiently for potential missions to mars and asteroids, as well as for earth based applications. | self-cleaning spacesuits for future planetary missions using carbon nanotube technology |
hazards due to near-earth objects (neos) continue to pose a threat to life on earth. while our capability for discovering neos has steadily progressed over the last three decades, physical characterization of a representative population has lagged behind. to test the operational readiness of the global planetary defense capabilities, we conducted a community-led global planetary defense exercise, with support from the nasa's planetary defense coordination office (pdco) and the international asteroid warning network (iawn), to test the operational readiness of global planetary defense capabilities. this campaign focused on the characterization (direct imaging, radar, spectroscopy) of the binary near-earth asteroid (nea) (66391) moshup (formerly known as 1999 kw4) and its moon squannit. we chose a binary system because roughly one in six large neas are binaries. an additional goal was to apply lessons learned from this campaign towards ground-based characterization campaign for binary nea (65803) didymos, the target of the pdco's double asteroid redirection test (dart) and the european space agency's hera missions. spectral observations of moshup from the nasa infrared telescope facility (irtf) show similarities to q-type asteroids. based on its spectral band parameters, the best meteorite analogs for moshup are l chondrites. we did not detect a hydration feature at 3 μm, which suggests that the entire surface is anhydrous. we imaged the binary using the sphere instrument on the very large telescope (vlt) and obtained resolved spectral measurements of moshup similar to those obtained with the nasa irtf. squannit appears to have slightly redder spectral slope than moshup. radar observations arecibo observatory at 2380 mhz indicate a polarization ratio of ~0.4, which is higher than the average values for the s complex asteroids, which includes q types. the visible extent of the components from the radar observations, taken as proxies for their radii, suggest moshup and squannit have diameters of 1500 ± 120 m and 480 ± 60 m, respectively. we constrain the system mass to 2.2 ± 0.5 × 1012 kg with a maximum range for bulk density between ~0.8 g/cm3 for a very low-mass system with spherical shapes up to 2.7 g/cm3 for very high-mass system where moshup has a more ridged-ball shape. we note that the radar-derived parameters presented in the paper are for the purposes of this exercise and do not supersede those in ostro et al. (2006). we assessed the impact risk of a hypothetical impactor based on moshup's physical properties using the probabilistic asteroid impact risk (pair) model. we assessed three impact risk scenarios at different epochs as the state of knowledge of moshup improved. for kilometer-scale impactors like moshup, the risk is driven predominantly by the potential for global climatic effects (95-97% of cases across the epochs) with a few percent driven by local damage and a few tenths of a percent driven by tsunami. | near-earth asteroid (66391) moshup (1999 kw4) observing campaign: results from a global planetary defense characterization exercise |
the south eastern arabian sea (seas) margin represents a tropical eastern boundary upwelling system, which is subjected to intense seasonal hypoxia in the continental shelf, and impingement of oxygen minimum zone (omz) along the continental slope. this paper provides the first comprehensive information on abundance, diversity and distribution patterns of echinoderms, which are highly sensitive to oxygen deficiency and anthropogenic disturbances, in the continental shelf (∼20-250m) of the seas. results are based on depth stratified and seasonally resolved sampling at 241 sites, representing 8 latitudinal grids & 4 depth strata (from inner shelf to shelf edge) using naturalist dredge and smith-mcintyre grab. echinoderms were the numerically dominant group among epifauna (42%), with significant seasonal variations in relative abundance (71% during winter and 17% during summer monsoon). fifty-five species of echinoderms were identified, among which ophiuroids showed highest diversity (24 species) followed by echinoids (11 species) and asteroids (8 species). species richness of echinoderms was higher in the inner and mid shelf (20-80m), while the group was nearly absent in the shelf edge (150-250m). a significant negative correlation was noted between species richness and latitude, and three distinct sub-regions could be delineated based on species diversity and abundance. the observed distribution patterns were found to be determined chiefly by sediment texture and bottom water dissolved oxygen, along with anthropogenic disturbances (bottom trawling). echinoderms showed maximum abundance and species richness in the well-oxygenated sandy sediments of the southern seas, and very low species richness and abundance in relatively silty sediments of the northern seas, which were characterised by high seasonal fluctuations in dissolved oxygen (seasonal hypoxia). the near absence of echinoderms in the shelf edge despite the availability of sandy substrates indicates that this group is more sensitive to the perennially low oxygen conditions prevailing here. | diversity and distribution of echinoderms in the south eastern arabian sea shelf under the influence of seasonal hypoxia |
the asteroid polarimetric database (apd) is a collection of asteroid polarimetry results compiled by d.f. lupishko of karazin kharkiv national university, ukraine. it is intended to include most asteroid polarimetry available through november 15, 2021. | asteroid polametric database (apd) bundle v2.0 |
as we know that the sun is a source of radiation in our solar system, the other planets or asteroids absorb some of the radiations incident on it and some reflected back into the space, these reflected radiations are called albedo. the spacecraft is affected by both radiations i. e direct radiations as well as albedo. in this paper this is investigated how albedo perturbed the libration points and its stability in restricted three-body problem when less massive primary is an ellipsoid? it is found that there exist five libration points, three collinear and two non-collinear, the non-collinear libration points are stable for a critical value of mass parameter μ≤ μc , where μ c= 0.0385208965 …- (0.00891747 + 0.222579 k) α- 0.02206859 σ 1 - 0.04071097 σ 2 but collinear libration points are still unstable. also, an example of sun-earth system is taken in the last as a real application. | a study of libration points in modified cr3bp under albedo effect when smaller primary is an ellipsoid |
the current aim of nasa's journey to mars is a stepwise approach towards landing humans on the red planet, culminating in a sustained presence. there are many recent studies on how this could be achieved in an evolvable and affordable manner. most architectures begin with crewed missions to phobos or mars orbit in the mid-2030's, progress toward short-stay missions on the surface, and then culminate with regular, long-stay missions at a permanent outpost in the 2040's. a common factor of these architectures is that many robotic launches would be required in order to support the crew by prepositioning mission elements and other needed supplies. in this paper, the use of 150 kw reusable solar electric propulsion (sep) tugs as a means to deliver elements both to orbit and the surface is studied. the conceptual sep tugs make use of continued technology developments that were initialized through the asteroid redirect robotic mission (arrm). they would also be used to deliver food and supplies to sustain the crews similar to resupply missions for the international space station. these sep tugs would cycle (with loitering) between staging orbits in cislunar space and mars orbit. the concepts presented here focus on the use of sep for purposes of delivering cargo, and could potentially be complimentary to many human mars architectures presented in the literature. in order to characterize mission design parameters such as dates, masses, and durations, thousands of optimized trajectories were run using low-thrust optimization software. solutions are found for all launch/arrival date pairs for the years 2038-2053. they can be displayed as contour plots called bacon plots - the sep equivalent of porkchop plots. possible mission architecture concepts for a steady-state human presence on mars along with the cargo missions needed to keep it functioning are described and the relevant mission parameters such as launch dates, masses, arrival dates, etc., are given. it was found that the reusable sep tug architecture would be highly beneficial to the logistics of a sustainable mars outpost. | cargo logistics for a notional mars base using solar electric propulsion |
oxygen-isotope ratios of olivine in type i (mgo-rich) and type ii (feo-rich) chondrules and olivine fragments in the matrix from the tagish lake meteorite (ungrouped c2) were measured to understand the characteristics of the formation environment of the tagish lake chondrules. of the 43 samples analyzed, 31 are mgo-rich and 16o-rich (δ17o ∼ -5‰ [=δ17o - 0.52 × δ18o]), which is typical of chondrules in cm, co, and cv chondrites. six samples are feo-rich and 16o-poor (δ17o ∼ -2‰), while three samples are feo-rich chondrules with δ17o ≥ 0‰, the latter being a major component of chondrules and similar to the majority of crystalline silicates recovered from comet wild 2. the correlation between mg# [=mgo/(mgo + feo) mol%] and δ17o values of the samples defines an intermediate trend between those of co-cm chondrite chondrules and comet wild 2 samples. assuming that the cm chondrites, tagish lake meteorite, and comet wild 2 represent c-type asteroids, d-type asteroids, and kuiper belt objects, respectively, the results of this study indicate that type ii chondrules with δ17o ≥ 0‰ formed at a location much farther out than that where the tagish lake meteorite parent body accreted, more than 3.1 million years after the cai formation assuming homogeneous distribution of 26al in the early solar system (tenner et al., 2019). these two aspects, namely the broad range of heliocentric distance and the prolonged period of chondrule formation, are important constraints when considering appropriate mechanisms of chondrule formation in the protoplanetary disk. | oxygen-isotope systematics of chondrules and olivine fragments from tagish lake c2 chondrite: implications of chondrule-forming regions in protoplanetary disk |
in the lightcurve inversion process where asteroid's physical parameters such as rotational period, pole orientation and overall shape are searched, the numerical calculations of the synthetic photometric brightness based on different shape models are frequently implemented. lebedev quadrature is an efficient method to numerically calculate the surface integral on the unit sphere. by transforming the surface integral on the cellinoid shape model to that on the unit sphere, the lightcurve inversion process based on the cellinoid shape model can be remarkably accelerated. furthermore, matlab codes of the lightcurve inversion process based on the cellinoid shape model are available on github for free downloading. the photometric models, i.e., the scattering laws, also play an important role in the lightcurve inversion process, although the shape variations of asteroids dominate the morphologies of the lightcurves. derived from the radiative transfer theory, the hapke model can describe the light reflectance behaviors from the viewpoint of physics, while there are also many empirical models in numerical applications. numerical simulations are implemented for the comparison of the hapke model with the other three numerical models, including the lommel-seeliger, minnaert, and kaasalainen models. the results show that the numerical models with simple function expressions can fit well with the synthetic lightcurves generated based on the hapke model; this good fit implies that they can be adopted in the lightcurve inversion process for asteroids to improve the numerical efficiency and derive similar results to those of the hapke model. | lebedev acceleration and comparison of different photometric models in the inversion of lightcurves for asteroids |
in this study the impact of land-sea breeze circulation and internal boundary layer (ibl) on the atmospheric dispersion of airborne effluent releases at the tropical coastal site kalpakkam is simulated using mesoscale model wrf and lagrangian particle dispersion model flexpart. simulations with wrf are conducted for typical days in different seasons, i.e., 3 may 2011 (summer), 20 sep 2010 and 20 jun 2011 (southwest monsoon). two k-based non-local turbulence closures (ysu, acm) and two tke-based local closures (mynn, myj) in wrf are tested for simulating the sea breeze and ibl. observations from a 50-m meteorological tower, gps sonde, and a doppler sodar are used for validation. simulations indicate that the synoptic flow largely influences the characteristics of the sea breeze at the site. results show that the sea breeze is more predominant with early onset and it is characterized by deep inland penetration, strong horizontal and vertical winds and is associated with formation of a deep ibl relative to monsoon with opposing large-scale flow. the ysu non-local diffusion scheme and the higher order local tke closure (mynn) simulated the sea breeze and ibl characteristics in good agreement with observations. dispersion simulations with a hypothetical tracer release using flexpart showed relatively high ground-level concentrations during ibl formation in the daytime and during stable off-shore flow condition in the morning time. the coupled mesoscale dispersion model could simulate the plume trajectory and buildup of concentrations during sea-breeze time by realistically simulating the winds and mixed-layer characteristics at the coastal site. | simulation of atmospheric dispersion of airborne effluent releases at a tropical coastal site under sea-breeze circulation and internal boundary layer development |
we model radar scattering by planetary surfaces using a ray-optics algorithm that includes fresnelian reflection and refraction, diffuse scattering, and coherent backscattering. we enhance the realism of the ray-optics algorithm by using scattering particles that are geometrically representative of the surfaces and interiors of planetary bodies. the shapes as well as the dielectric properties of the scattering particles have been characterized in laboratory. the results demonstrate the effects of various physical parameters on radar scattering with an emphasis on asteroids. we present the effects of number density, size distribution, and dielectric and geometric properties of scattering particles on the radar reflectivity and circular-polarization ratio of planetary surfaces. we also briefly discuss applications to the galilean moon europa and comets. | radar scattering by planetary surfaces modeled with laboratory-characterized particles |
we study the collapse of pebble clouds with a statistical model to find the internal structure of comet-sized planetesimals. pebble-pebble collisions occur during the collapse, and the outcome of these collisions affects the resulting structure of the planetesimal. we expand our previous models by allowing the individual pebble sub-clouds to contract at different rates and by including the effect of gas drag on the contraction speed and in energy dissipation. our results yield comets that are porous pebble-piles with particle sizes varying with depth. in the surface layers, there is a mixture of primordial pebbles and pebble fragments. the interior, on the other hand, consists only of primordial pebbles with a narrower size distribution, yielding higher porosity there. our results imply that the gas in the protoplanetary disc plays an important role in determining the radial distribution of pebble sizes and porosity inside planetesimals. | radially resolved simulations of collapsing pebble clouds in protoplanetary discs |
multiple-asteroid exploration with low-thrust propulsion requires the design of transfer trajectory and the selection of the visiting sequence, as well as the estimation of the propellant budget. to this end, this paper presents a method to generate transfer trajectories and visiting sequences rapidly using finite fourier series (ffs) and monte-carlo tree search (mcts). the ffs method can generate the transfer trajectory rapidly, which can provide suitable initial approximations, leading to more accurate trajectory optimizations. this study adopts the mcts algorithm for asteroid sequence selection in the multi-asteroid exploration. by comparing with the traversal algorithm, the greedy algorithm and the tree search algorithm with the trimming strategy, the numerical results show that the mcts can be used to obtain a quasi-optimal sequence with higher probability and less computation time. consequently, a method combining ffs and mcts can rapidly acquire the quasi-optimal visiting sequences with a large probability and the suitable initial trajectory for a multi-asteroid exploration mission. this is very important for the rapid feasibility assessment of hundreds of flight scenarios at the preliminary mission design stage. | fast preliminary design of low-thrust trajectories for multi-asteroid exploration |
the tagish lake carbonaceous chondrite exhibits a unique compositional heterogeneity that may be attributed to varying degrees of aqueous alteration within the parent body asteroid. previous analyses of soluble organic compounds from four tagish lake meteorite specimens (tl5b, tl11h, tl11i, tl11v) identified distinct distributions and isotopic compositions that appeared to be linked to their degree of parent body processing (herd et al. 2011; glavin et al. 2012; hilts et al. 2014). in the present study, we build upon these initial observations and evaluate the molecular distribution of amino acids, aldehydes and ketones, monocarboxylic acids, and aliphatic and aromatic hydrocarbons, including compound-specific δ13c compositions, for three additional tagish lake specimens: tl1, tl4, and tl10a. tl1 contains relatively high abundances of soluble organics and appears to be a moderately altered specimen, similar to the previously analyzed tl5b and tl11h lithologies. in contrast, specimens tl4 and tl10a both contain relatively low abundances of all of the soluble organic compound classes measured, similar to tl11i and tl11v. the organic-depleted composition of tl4 appears to have resulted from a relatively low degree of parent body aqueous alteration. in the case of tl10a, some unusual properties (e.g., the lack of detection of intrinsic monocarboxylic acids and aliphatic and aromatic hydrocarbons) suggest that it has experienced extensive alteration and/or a distinct organic-depleted alteration history. collectively, these varying compositions provide valuable new insights into the relationships between asteroidal aqueous alteration and the synthesis and preservation of soluble organic compounds. | new insights into the heterogeneity of the tagish lake meteorite: soluble organic compositions of variously altered specimens |
the current work explores the interactions between asteroid fragments and the associated flow topology to motivate a physically consistent representation of the fragmentation process following a fragmentation event during atmospheric entry. multibody aerodynamic simulations run with computational fluid dynamics (cfd) solvers were used to generate a lookup table of forces detailing the interactions of two spheres. trajectory simulations parsing the resulting database to determine the relative motions of any two spherical fragments were then validated with hypersonic wind tunnel experiments. a following series of fragment interaction simulations yielded categorization of the fragments' final relative states and an estimate of the total time of interaction. the fragment interaction model was nondimensionalized to permit study over a wide range of possible asteroid impacts. the interaction parameters are presented with explicit semi-analytic equations, defining the asteroid fragment-flow interaction model and thereby eliminating the need to perform a separate fragment interaction simulation for each fragmentation event in an atmospheric entry model. finally, a set of illustrative examples demonstrates the efficacy of the model in a variety of fragmentation situations. | interactions between asteroid fragments during atmospheric entry |
in the framework of the near earth objects (neos) observational campaign carried out within the neoshield-2 project, we identify nine new small d-type asteroids with estimated diameter less than 600 m. the link with meteorites for this class of asteroids is weak and the best fit obtained is with the tagish lake meteorite for seven of them. d-type asteroids are believed to contain the most pristine material of the solar system and could have delivered the pre-biotic material to the earth. our results double the known sample of the d-types in the neo population and triple the candidates of this class for a sample-return mission (at very low δv). our finding increases considerably the number of targets for sample-return mission. a sample-return mission to a d-type asteroid will provide a major progress in understanding the early history of the solar system and to investigate the origin of life on the earth. | small d-type asteroids in the neo population: new targets for space missions |
the extension of human space exploration from a low earth orbit to a high earth orbit, then to moon, mars, and possibly asteroids is nasa's biggest challenge for the new millennium. integral to this mission is the effective, sufficient, and reliable supply of cryogenic propellant fluids. therefore, highly energy-efficient thermal-fluid management breakthrough concepts to conserve and minimize the cryogen consumption have become the focus of research and development, especially for the deep space mission to mars. here we introduce such a concept and demonstrate its feasibility in parabolic flights under a simulated space microgravity condition. we show that by coating the inner surface of a cryogenic propellant transfer pipe with low-thermal conductivity microfilms, the quenching efficiency can be increased up to 176% over that of the traditional bare-surface pipe for the thermal management process of chilling down the transfer pipe. to put this into proper perspective, the much higher efficiency translates into a 65% savings in propellant consumption. | an advance in transfer line chilldown heat transfer of cryogenic propellants in microgravity using microfilm coating for enabling deep space exploration |
we develop a simple scaling argument for frictional dissipation in rubble-pile asteroids, parameterized as an effective dissipation factor q. this scaling is combined with a prediction (goldreich, p., sari, r., 2009. tidal evolution of rubble piles. astrophys. j. 691, 54-60) for the tidal response amplitude, parameterized by the love number k2. we compare the combined scaling with k2/q values inferred from asteroid binaries in which the semi-major axis is determined by a balance between tidal dissipation and the binary yorp (or byorp) effect (jacobson, s.a., scheeres, d.j., 2011. long-term stable equilibria for synchronous binary asteroids. astrophys. j. lett. 736, l19). the k2/q scaling matches the inferred values if dissipation is confined to a regolith layer of thickness ∼ 30 m, similar to the available asteroid regolith thickness estimates. the scaling suggests a regolith thickness that is independent of (or decreases slightly with) increasing asteroid radius; this result is consistent with at least one model of regolith generation via impacts. | tidal dissipation in rubble-pile asteroids |
the site selection and certification processes for planetary landers equipped with hazard avoidance capability are reviewed. the prior (large-scale) 'landability' of the target areas determined from orbital remote sensing can be only a few tens of per cent (∼40 % for perseverance, ∼80-90 % for apollo 11 and 60-70 % for subsequent apollo landers) because on-board sensing is able to find safe areas at smaller scales (meters to tens of meters) than the delivery ellipse which may be several to several tens of kilometers across. this contrasts with the 'blind' landings of unguided missions, where safe terrain occupying 95-99 % of the landing ellipse are typically sought. the particulars of apollo 11 and perseverance/ingenuity are discussed, together with the similar chang-e-3 and tianwen-1 moon and mars landers, and the hayabusa-2 and osiris-rex asteroid contacts, since these missions all used on-board terrain-relative navigation to steer relative to hazards either mapped previously or detected in real-time. these missions set the context for the application of these techniques to the dragonfly mission to titan, which has a more austere remote sensing basis on which to select a landing site, but whose rotor propulsion allows substantial divert capability. | planetary landings with terrain sensing and hazard avoidance: a review |
context. meteoroids impacting terrestrial planets at high speed may have different effects. on bodies without atmospheres, such as the moon and mercury, they form impact craters and contribute to the gardening process through which the surface material is constantly mixed. the interaction of high-speed meteoroids with the atmosphere of venus, the earth, and mars, may lead to the deposition in the ionosphere of species such as neutral mg or fe and their ionized atoms, caused by ablation processes during the entry.aims: in this work we estimate and compare the flux and impact speeds onto the planets of the inner solar system by numerically integrating the orbital evolution of putative dust particles of asteroidal and cometary origin.methods: the trajectories of dust particles of different sizes are computed with a numerical code that accounts for the gravitational forces due to all planets, the poynting-robertson drag and the solar wind drag. the flux of dust grains on each planet is estimated by calibrating the outcome of our model with the flux on the earth reported previously.results: we obtain new estimates of the flux and impact velocities for both asteroidal and cometary dust particles on venus and mars. for venus we find that cometary grains enter the planet atmosphere at higher speeds, possibly contributing to the upper layers, while asteroidal grains would be relevant for the lower layers, possibly leading to a compositional gradient. this effect is also present for mars, but it is less marked. we also find that analytical predictions, not taking radiative forces into account, of both flux and average impact speed are reliable for mars but fail for venus because of the complex dynamical evolution of grains in the inner solar system.conclusions: our results on the velocity distributions and fluxes of micrometeoroids on the terrestrial planets can be used to put stringent contraints on models that estimate either the superficial material mixing that is due to meteoroid impacts or the formation of ionospheric layers for planets with an atmosphere. | asteroidal and cometary dust flux in the inner solar system |
we explore the use of spectropolarimetry as a remote sensing tool for asteroids in addition to traditional reflectance measurements. in particular, we are interested in possible relationships between the wavelength-dependent variation of linear polarization and the properties of the surfaces, including albedo and composition. we have obtained optical spectropolarimetric measurements of a dozen asteroids of different albedo and taxonomic classes and of two small regions at the limb of the moon. we found that objects with marginally different relative reflectance spectra (in the optical) may have totally different polarization spectra. this suggests that spectropolarimetry may be used to refine the classification of asteroids. we also found that in some cases the umov law may be violated, that is, in contrast to what is expected from basic physical considerations, the fraction of linear polarization and the reflectance may be positively correlated. in agreement with a few previous studies based on multicolour broad-band polarimetry, we found that the variation of linear polarization with wavelength and with phase-angle is correlated with the albedo and taxonomic class of the objects. finally, we have serendipitously discovered that spinel-rich asteroid (599) luisa, located very close to the watsonia family, is a member of the rare class of barbarian asteroids. we suggest that future modelling attempts of the surface structure of asteroids should be aimed at explaining both reflectance and polarization spectra. | linear spectropolarimetry: a new diagnostic tool for the classification and characterization of asteroids. |
we present hubble space telescope observations of the active asteroid (and geminid stream parent) 3200 phaethon when at its closest approach to earth (separation 0.07 au) in 2017 december. images were recorded within ∼1° of the orbital plane, providing extra sensitivity to low surface brightness caused by scattering from a large-particle trail. we placed an upper limit on the apparent surface brightness of such a trail at 27.2 mag arcsecond-2, corresponding to an in-plane optical depth ≤3 × 10-9. no co-moving sources brighter than absolute magnitude 26.3, corresponding to circular equivalent radius ∼12 m (albedo 0.12 assumed), were detected. phaethon is too hot for near-surface ice to survive. we briefly consider the thermodynamic stability of deeply buried ice, finding that its survival would require either a very small (regolith-like) thermal diffusivity (<10-8 m2 s-1), or the unexpectedly recent injection of phaethon (timescale ≲106 years) into its present orbit, or both. | hubble space telescope observations of 3200 phaethon at closest approach |
context. recent studies have analyzed the dynamical evolution of outer small body populations under the effects of an eccentric inner massive perturber, which result from a planetary scattering event. these investigations suggest that such outer reservoirs are composed of particles on prograde and retrograde orbits, as well as particles whose orbit flips from prograde to retrograde and back again showing a coupling between the inclination i and the ascending node longitude ω (type-f particles).aims: we analyze the role of the general relativity (gr) on the dynamics of outer particles under the influence of an inner eccentric jupiter-mass planet produced by a planetary scattering event. in particular, we are interested in studying how the gr affects the dynamical evolution of the outer type-f particles, which experience an eccentric lidov-kozai mechanism.methods: to do this, we carried out n-body simulations with and without gr effects. such a detailed comparative analysis allows us to strengthen our understanding concerning the gr and eccentric lidov-kozai combined effects on the dynamical evolution of outer particles.results: when the gr is included, the extreme values of ω are obtained for retrograde inclinations, while the minimum and maximum inclinations allowed for type-f particles increase in comparison with that derived without gr effects. according to this, if the gr is included in the simulations, the range of prograde (retrograde) inclinations of the libration region is reduced (increased) with respect to that obtained in absence of gr. we find two new classes of particles when gr effects are included in the simulations. on the one hand, there are particles whose orbital plane flips from prograde to retrograde and back again without experiencing a coupling between i and ω. on the other hand, retrograde particles show a strong coupling between i and ω. we infer that gr may significantly modify the dynamical properties of the outer reservoirs that evolve under the effects of an eccentric inner perturber. | the role of general relativity on icy body reservoirs under the effects of an inner eccentric jupiter |
we present the results of a numerical study to prepare for the remote sensing of asteroid 162173 ryugu (1999 ju3) using the hayabusa2 thermal infrared imager (tir). we simulated the thermal characteristics of the asteroid with a thermophysical model (tpm) using an ideal body with a smooth and spherical surface, and investigated its feasibility to determine the thermophysical properties of the asteroid under two possible spin vectors; (λ_{ecl}, β_{ecl}) = (73°, -62°) and (331°, 20°). each of the simulated snapshots taken at various local times during the 1.5-year proximity phase was analyzed to estimate uncertainties of the diurnal thermal phase delay to infer the thermal inertia of ryugu. the temperature in a pixel was simulated based on the specification of the imager and the observing geometry. moreover, we carried out a regression analysis to estimate albedo and thermal emissivity from the time variation of surface temperature. we also investigated the feasibility of determining thermal phase delay in a first attempt using realistic rough surfaces. we found that precise determination of the thermal phase delay would be difficult in the (331°, 20°) spin type unless the surface was nearly smooth. in contrast, the thermal phase delay is likely to be observable even if the surface topography is moderately rough in the other spin type. from the smooth-surface model, we obtained a less than 20% error of thermal inertia on observation opportunities under the likely range of thermal inertia ≤ 1000 j m^{-2} s^{-1/2} k^{-1}. the error of thermal inertia exceeded 50% under a realistic surface with roughness. | feasibility and accuracy of thermophysical estimation of asteroid 162173 ryugu (1999 ju3) from the hayabusa2 thermal infrared imager |
space capabilities play a crucial role in ensuring human security. one of the threats coming from space is the possible damage to our assets by an asteroid or comet impact. as demonstrated by the object entering the earth's atmosphere over chelyabinsk, russia, in february 2013, the threat of an asteroid or comet impact is a real and global issue demanding development of an international response. addressing such a hazard, by first identifying those objects that pose a threat to enable planning a corresponding mitigation campaign, require international coordination. the united nations member states, especially those with capabilities to engage in a possible planetary defence mission, already share a number of common activities in this field. this paper outlines the progress made in the implementation of recommendations for an international response to the neo impact threat, as agreed under the auspices of the united nations (un) committee on the peaceful uses of outer space (copuos) and welcomed by the un general assembly in its resolution 68/75 of december 2013. the recommendations provide for a coordinated international response to a possible neo threat. they aim at ensuring international information-sharing in discovering, monitoring and physically characterizing potentially hazardous neos with a view that all countries, in particular developing countries with limited capacity in predicting and mitigating a neo impact, are aware of potential threats. they emphasize the need for an effective emergency response and disaster management in the event of a discovered neo impact threat. the international asteroid warning network (iawn) and the space mission planning advisory group (smpag), which are the two entities established in 2014 as a result of the un-endorsed recommendations, are important mechanisms at the global level for strengthening the coordination in the area of planetary defence. the united nations office for outer space affairs (unoosa) acts as secretariat to smpag and works with both iawn and smpag in addressing this global issue. in the event of a credible impact prediction, warnings would be issued by the iawn, the smpag would propose mitigation options and implementation plans for consideration to the member states. the goal is the global protection of the eco-system, of human beings and their properties on earth, and of the civilization of humankind from a devastating asteroid impact. the current paper outlines the work of the iawn and the smpag towards a road-map for planetary defence at the global level, including agreements on initial criteria and thresholds for impact threat response actions, consideration of mitigation mission types and technologies and mapping of threat scenarios to mission types as well as developing a plan for action in case a credible threat is discovered. the paper also reflects on how to convey information about the neo impact warnings and associated impact probabilities to the public and governmental decision-makers as part of the agreed communications guidelines, which are another important pillar in the work of the iawn. | international coordination on planetary defence: the work of the iawn and the smpag |
the fascinating idea of shepherding asteroids for science and resource utilization is being considered as a credible concept in a not too distant future. past studies identified asteroids which could be efficiently injected into manifolds which wind onto periodic orbits around collinear lagrangian points of the sun-earth system. however, the trajectories are unstable, and errors in the capture maneuver would lead to complete mission failure, with potential danger of collision with the earth, if uncontrolled. this paper investigates the controllability of some asteroids along the transfers and the periodic orbits, assuming the use of a solar-electric low-thrust system shepherding the asteroid. firstly, an analytical approach is introduced to estimate the stability of the trajectories from a dynamical point of view; then, a numerical control scheme based on a linear quadratic regulator is proposed, where the gains are optimized for each trajectory through a genetic algorithm. a stochastic simulation with a monte carlo approach is used to account for different perturbed initial conditions and the epistemic uncertainty on the asteroid mass. results show that only a small subset of the considered combinations of trajectories/asteroids are reliably controllable, and therefore controllability must be taken into account in the selection of potential targets. | control of asteroid retrieval trajectories to libration point orbits |
small body missions can significantly benefit from deploying small landing systems onto the surface of the visited object. despite the potential benefit that they may bring, deployments of landers in small body environments may entail significant mission design challenges. this paper thus addresses the potential of ballistic landing opportunities in binary asteroid moons from a mission design perspective, particularly focusing on reliability aspects of the trajectories. two binaries that were previously identified as target bodies in several missions/proposals, didymos and 1996 fg3, are considered in this paper. the dynamics near them are modeled by means of the circular restricted three body problem (cr3bp), which provides a reasonable representation of a standard binary system. natural landing trajectories that allow both minimum-velocity local-vertical touchdown and deployment from a safe distance are investigated. coefficient of restitution values are used as a design parameter to compute the first touchdown speeds that ensure sufficient reliability of landing trajectories. a simple reliability index, which is derived via uncertainty ellipsoid from covariance analysis, is introduced to create a global reliability map across the asteroid surfaces. assuming 3σ deployment errors on the order of 90 m and 2 cm/s, the results show that ballistic landing operations are likely to be successful for larger binary moons if the deployments target near equatorial regions within longitude range 320o-20°. it has also been shown that the deployments to smaller binary moons may require higher accuracy in navigation and deployment systems in their mothership, and/or closer deployment distances. | a comparative reliability analysis of ballistic deployments on binary asteroids |
wd 1145+017 is a unique white dwarf system that has a heavily polluted atmosphere, an infrared excess from a dust disk, numerous broad absorption lines from circumstellar gas, and changing transit features, likely from fragments of an actively disintegrating asteroid. here, we present results from a large photometric and spectroscopic campaign with hubble space telescope, keck, very large telescope (vlt), spitzer, and many other smaller telescopes from 2015 to 2018. somewhat surprisingly the ultraviolet (uv) transit depths are always shallower than those in the optical. we develop a model that can quantitatively explain the observed “bluing” and confirm the previous finding that: (1) the transiting objects, circumstellar gas, and white dwarf are all aligned along our line of sight; (2) the transiting object is blocking a larger fraction of the circumstellar gas than of the white dwarf itself. because most circumstellar lines are concentrated in the uv, the uv flux appears to be less blocked compared to the optical during a transit, leading to a shallower uv transit. this scenario is further supported by the strong anticorrelation between optical transit depth and circumstellar line strength. we have yet to detect any wavelength-dependent transits caused by the transiting material around wd 1145+017. | shallow ultraviolet transits of wd 1145+017 |
we present the first comprehensive thermal and rotational analysis of the second most distant trans-neptunian object (tnos) (225088) 2007 or10. we combined optical light curves provided by the kepler space telescope-k2 extended mission and thermal infrared data provided by the herschel space observatory. we found that (225088) 2007 or10 is likely to be larger and darker than derived by earlier studies: we obtained a diameter of d={1535}-225+75 {{km}} which places (225088) 2007 or10 in the biggest top three tnos. the corresponding visual geometric albedo is {p}v={0.089}-0.009+0.031. the light-curve analysis revealed a slow rotation rate of prot = 44.81 ± 0.37 hr, superseded by very few objects. the most likely light-curve solution is double-peaked with a slight asymmetry; however, we cannot safely rule out the possibility of having a rotation period of prot = 22.40 ± 0.18 hr, which corresponds to a single-peaked solution. due to the size and slow rotation, the shape of the object should be a maclaurin ellipsoid, so the light variation should be caused by surface inhomogeneities. its newly derived larger diameter also implies larger surface gravity and a more likely retention of volatiles—ch4, co, and n2—on the surface. | large size and slow rotation of the trans-neptunian object (225088) 2007 or10 discovered from herschel and k2 observations |
we revisited a mass ejection phenomenon that occurred in asteroid p/2010 a2 in terms of the dynamical properties of the dust particles and large fragments. we constructed a model assuming anisotropic ejection within a solid cone-shaped jet and succeeded in reproducing the time-variant features in archival observational images over ∼3 years from 2010 january to 2012 october. we assumed that the dust particles and fragments were ejected in the same direction from a point where no object had been detected in any observations, and the anisotropic model explains all of the observations including (i) the unique dust cloud morphology, (ii) the trail surface brightness, and (iii) the motions of the fragments. our results suggest that the original body was shattered by an impact with specific energy {q}* ≲ 350 j kg-1, and remnants of slow antipodal ejecta (i.e., anisotropic ejection in our model) were observed as p/2010 a2. the observed quantities are consistent with those obtained through laboratory impact experiments, supporting the idea that the p/2010 a2 event is the first evidence of the impact shattering that occurred in the present main asteroid belt. based in part on data collected at subaru telescope, which is operated by the national astronomical observatory of japan. | anisotropic ejection from active asteroid p/2010 a2: an implication of impact shattering on an asteroid |
asteroids and comets 10-100 m in size that collide with earth disrupt dramatically in the atmosphere with an explosive transfer of energy, caused by extreme air drag. such airbursts produce a strong blastwave that radiates from the meteoroid's trajectory and can cause damage on the surface. an established technique for predicting airburst blastwave damage is to treat the airburst as a static source of energy and to extrapolate empirical results of nuclear explosion tests using an energy-based scaling approach. here we compare this approach to two more complex models using the isale shock physics code. we consider a moving-source airburst model where the meteoroid's energy is partitioned as two-thirds internal energy and one-third kinetic energy at the burst altitude, and a model in which energy is deposited into the atmosphere along the meteoroid's trajectory based on the pancake model of meteoroid disruption. to justify use of the pancake model, we show that it provides a good fit to the inferred energy release of the 2013 chelyabinsk fireball. predicted overpressures from all three models are broadly consistent at radial distances from ground zero that exceed three times the burst height. at smaller radial distances, the moving-source model predicts overpressures two times greater than the static-source model, whereas the cylindrical line-source model based on the pancake model predicts overpressures two times lower than the static-source model. given other uncertainties associated with airblast damage predictions, the static-source approach provides an adequate approximation of the azimuthally averaged airblast for probabilistic hazard assessment. | a numerical assessment of simple airblast models of impact airbursts |
we present a deep imaging and spectroscopic search for emission from (3200) phaethon, a large near-earth asteroid that appears to be the parent of the strong geminid meteoroid stream, using the 4.3 m lowell discovery telescope. observations were conducted on 2017 december 14-18 when phaethon passed only 0.07 au from the earth. we determine the 3σ upper level of dust and cn production rates to be 0.007-0.2 kg s-1 and 2.3 × 1022 molecules s-1 through narrowband imaging. a search in broadband images taken through the sdss r' filter shows no 100 m class fragments in phaethon's vicinity. a deeper but star-contaminated search also shows no sign of fragments down to 15 m. optical spectroscopy of phaethon and comet c/2017 o1 (asassn) as a comparison confirms the absence of cometary emission lines from phaethon and yields 3σ upper levels of cn, c2, and c3 of ∼1024-1025 molecules s-1, 2 orders of magnitude higher than the cn constraint placed by narrowband imaging, due to the much narrower on-sky aperture of the spectrographic slit. we show that narrowband imaging could provide an efficient way to look for weak gas emission from near-extinct bodies near the earth, though these observations require careful interpretation. assuming phaethon's behavior is unchanged, our analysis shows that the destiny+ mission, currently planning to explore phaethon in 2026, may not be able to directly detect a gas coma. | a deep search for emission from "rock comet" (3200) phaethon at 1 au |
space-based telescopes offer unparalleled opportunities for characterizing exoplanets, solar system bodies, and stellar objects. however, observatories in low-earth orbits (e.g., hubble, characterising exoplanets satellite, twinkle, and an ever-increasing number of cubesats) cannot always be continuously pointed at a target due to earth obscuration. for exoplanet observations consisting of transit, or eclipse, spectroscopy, this causes gaps in the light curve, which reduces the information content and can diminish the science return of the observation. terminus, a time-domain simulator, has been developed to model the occurrence of these gaps to predict the potential impact on future observations. the simulator is capable of radiometrically modeling exoplanet observations as well as producing light curves and spectra. here, terminus is baselined on the twinkle mission, but the model can be adapted for any space-based telescope and is especially applicable to those in a low-earth orbit. terminus also has the capability to model observations of other targets such as asteroids or brown dwarfs. | terminus: a versatile simulator for space-based telescopes |
planet nine is a hypothetical planet located well beyond pluto that has been proposed in an attempt to explain the observed clustering in physical space of the perihelia of six extreme trans-neptunian objects or etnos. the predicted approximate values of its orbital elements include a semimajor axis of 700 au, an eccentricity of 0.6, an inclination of 30°, and an argument of perihelion of 150°. searching for this putative planet is already under way. here, we use a monte carlo approach to create a synthetic population of planet nine orbits and study its visibility statistically in terms of various parameters and focusing on the aphelion configuration. our analysis shows that, if planet nine exists and is at aphelion, it might be found projected against one out of the four specific areas in the sky. each area is linked to a particular value of the longitude of the ascending node and two of them are compatible with an apsidal anti-alignment scenario. in addition and after studying the current statistics of etnos, a cautionary note on the robustness of the perihelia clustering is presented. | finding planet nine: a monte carlo approach |
we use seven year's worth of observations from the catalina sky survey and the siding spring survey covering most of the northern and southern hemisphere at galactic latitudes higher than 20° to search for serendipitously imaged moving objects in the outer solar system. these slowly moving objects would appear as stationary transients in these fast cadence asteroids surveys, so we develop methods to discover objects in the outer solar system using individual observations spaced by months, rather than spaced by hours, as is typically done. while we independently discover eight known bright objects in the outer solar system, the faintest having v=19.8+/- 0.1, no new objects are discovered. we find that the survey is nearly 100% efficient at detecting objects beyond 25 au for v≲ 19.1 (v≲ 18.6 in the southern hemisphere) and that the probability that there is one or more remaining outer solar system object of this brightness left to be discovered in the unsurveyed regions of the galactic plane is approximately 32%. | a serendipitous all sky survey for bright objects in the outer solar system |
we have long known that water and hydroxyl are important components in meteorites and asteroids. however, in the time since the publication of asteroids iii, evolution of astronomical instrumentation, laboratory capabilities, and theoretical models have led to great advances in our understanding of h2o/oh on small bodies, and spacecraft observations of the moon and vesta have important implications for our interpretations of the asteroidal population. we begin this chapter with the importance of water/oh in asteroids, after which we will discuss their spectral features throughout the visible and near-infrared (ir). we continue with an overview of the findings in meteorites and asteroids, closing with a discussion of future opportunities, the results from which we can anticipate reading in asteroids v. because this topic is of broad importance to asteroids, we also point to relevant in-depth discussions elsewhere in this volume. | astronomical observations of volatiles on asteroids |
comets can exhibit non-gravitational accelerations caused by recoil forces due to anisotropic mass loss. so might active asteroids. we present an astrometric investigation of 18 active asteroids in search of non-gravitational acceleration. statistically significant (signal-to-noise ratio (s/n) > 3) detections are obtained from three objects: 313p/gibbs, 324p/la sagra, and (3200) phaethon. the strongest and most convincing detection (>7σ in each of three orthogonal components of the acceleration), is for the ∼1 km diameter nucleus of 324p/la sagra. a 4.5σ detection of the transverse component of the acceleration of 313p/gibbs (also ∼1 km in diameter) is likely genuine too, as evidenced by the stability of the solution to the rejection or inclusion of specific astrometric data sets. we also find a 3.4σ radial-component detection for ∼5 km diameter (3200) phaethon, but this detection is more sensitive to the inclusion of specific data sets, suggesting that it is likely spurious in origin. the other 15 active asteroids in our sample all show non-gravitational accelerations consistent with zero. we explore different physical mechanisms, which may give rise to the observed non-gravitational effects, and estimate mass-loss rates from the non-gravitational accelerations. we present a revised momentum-transfer law based on a physically realistic sublimation model for future work on non-gravitational forces, but note that it has little effect on the derived orbital elements. | non-gravitational acceleration of the active asteroids |
the structural coefficient of restitution describes the kinetic energy dissipation upon low-velocity (~0.1 m/s) impact of a small asteroid lander, mascot, against a hard, ideally elastic plane surface. it is a crucial worst-case input for mission analysis for landing macot on a 1km asteroid in 2018. we conducted pendulum tests and describe their analysis and the results. | experimental determination of the structural coefficient of restitution of a bouncing asteroid lander |
in this review presented at the royal society meeting, `cometary science after rosetta', i present an overview of studies of small solar system objects that exhibit properties of both asteroids and comets (with a focus on so-called active asteroids). sometimes referred to as `transition objects', these bodies are perhaps more appropriately described as `continuum objects', to reflect the notion that rather than necessarily representing actual transitional evolutionary states between asteroids and comets, they simply belong to the general population of small solar system bodies that happen to exhibit a continuous range of observational, physical and dynamical properties. continuum objects are intriguing because they possess many of the properties that make classical comets interesting to study (e.g. relatively primitive compositions, ejection of surface and subsurface material into space where it can be more easily studied, and orbital properties that allow us to sample material from distant parts of the solar system that would otherwise be inaccessible), while allowing us to study regions of the solar system that are not sampled by classical comets. this article is part of the themed issue 'cometary science after rosetta'. | asteroid-comet continuum objects in the solar system |
recently published space-based observations of main-belt asteroids with the akari telescope provide a full description of the 3 μm band, related to the presence of oh bearing minerals. here, we use laboratory spectra of carbonaceous chondrites obtained under controlled atmosphere (ci,cm,co,cv,cr tagish lake) to derive spectral metrics related to the water content in the samples. after testing several spectral metrics, we use a combination of band depth at 2.75 μm and 2.80 μm that shows a correlation with [h2o] in the sample determined by tga, though with a high uncertainty (4 wt% h2o). this relation is used to determine water content at the surface of large c-complex main-belt asteroids and discuss the origin of the variability found. on average c-complex main-belt asteroids (mba) have water contents of 4.5 wt% (volume average, (1) ceres excluded), significantly lower than average cm chondrites. the estimated water content for the most hydrated asteroids are lower than those of the most hydrated meteorites, a difference that could be attributed to space-weathering. an anti-correlation is also present between water content and overall spectral slope, which is opposite to expectation from laboratory simulations of space weathering on dark carbonaceous chondrites. this suggests that part of the variability in the surface hydration among the different c-complex asteroids is not due to space-weathering, but to the composition of surface material. when applied to ceres, the hygrometer presented in this work enables us to estimate that at least 1.22 wt% of the hydrogen is present in the form of organics. this richness in organics strengthens the connection between ceres and cometary materials. | "water" abundance at the surface of c-complex main-belt asteroids |
carbonaceous meteorites are fragments of asteroids rich in organic material. in the forming solar nebula, parent bodies may have accreted organic materials resulting from the evolution of icy grains observed in dense molecular clouds. the major issues of this scenario are the secondary processes having occurred on asteroids, which may have modified the accreted matter. here, we explore the evolution of organic analogs of protostellar/protoplanetary disk material once accreted and submitted to aqueous alteration at 150 °c. the evolution of molecular compounds during up to 100 days is monitored by high resolution mass spectrometry. we report significant evolution of the molecular families, with the decreases of h/c and n/c ratios. we find that the post-aqueous products share compositional similarities with the soluble organic matter of the murchison meteorite. these results give a comprehensive scenario of the possible link between carbonaceous meteorites and ices of dense molecular clouds. | exploring the link between molecular cloud ices and chondritic organic matter in laboratory |
we introduce a new method for analyzing sparse photometric data of asteroids and apply it to zwicky transient facility observations of the jupiter trojan asteroids. this method relies on the creation of a likelihood model that includes the probability distribution of rotational brightness variations at an unknown rotation phase. the likelihood model is analyzed via a markov chain monte carlo to quantify the uncertainty in our parameter estimates. using this method, we provide color, phase parameter, absolute magnitude, and amplitude of rotation measurements for 1049 jupiter trojans. we find that phase parameter is correlated with color and the distribution of trojan asteroid rotational amplitudes is indistinguishable from that of main-belt asteroids. | zwicky transient facility observations of trojan asteroids: a thousand colors, rotation amplitudes, and phase functions |
the mission accessible near-earth objects survey aims to physically characterize sub-km near-earth objects (neos). we report the first photometric results from the survey that began in 2013 august. photometric observations were performed using 1-4 m class telescopes around the world. we present rotational periods and light curve amplitudes for 86 sub-km neos, though in some cases only lower limits are provided. our main goal is to obtain light curves for small neos (typically, sub-km objects) and estimate their rotational periods, light curve amplitudes, and shapes. these properties are used for a statistical study to constrain overall properties of the neo population. a weak correlation seems to indicate that smaller objects are more spherical than larger ones. we also report seven neos that are fully characterized (light curve and visible spectra) as the most suitable candidates for a future human or robotic mission. viable mission targets are objects fully characterized, with δv nhats ≤ 12 km s-1, and a rotational period p > 1 hr. assuming a similar rate of object characterization as reported in this paper, approximately 1230 neos need to be characterized in order to find 100 viable mission targets. | the mission accessible near-earth objects survey (manos): first photometric results |
context. centaurs go around the sun between the orbits of jupiter and neptune. only a fraction of the known centaurs have been found to display comet-like features. comet 29p/schwassmann-wachmann 1 is the most remarkable active centaur. it orbits the sun just beyond jupiter in a nearly circular path. only a handful of known objects follow similar trajectories.aims: we present photometric observations of 2020 mk4, a recently found centaur with an orbit not too different from that of 29p, and we perform a preliminary exploration of its dynamical evolution.methods: we analyzed broadband cousins r and sloan g', r', and i' images of 2020 mk4 acquired with the jacobus kapteyn telescope and the iac80 telescope to search for cometary-like activity and to derive its surface colors and size. its orbital evolution was studied using direct n-body simulations.results: centaur 2020 mk4 is neutral-gray in color and has a faint, compact cometary-like coma. the values of its color indexes, (g'− r') = 0.42 ± 0.04 and (r'− i') = 0.17 ± 0.04, are similar to the solar ones. a lower limit for the absolute magnitude of the nucleus is hg = 11.30 ± 0.03 mag which, for an albedo in the range of 0.1-0.04, gives an upper limit for its size in the interval (23, 37) km. its orbital evolution is very chaotic and 2020 mk4 may be ejected from the solar system during the next 200 kyr. comet 29p experienced relatively close flybys with 2020 mk4 in the past, sometimes when they were temporary jovian satellites.conclusions: based on the analysis of visible ccd images of 2020 mk4, we confirm the presence of a coma of material around a central nucleus. its surface colors place this centaur among the most extreme members of the gray group. although the past, present, and future dynamical evolution of 2020 mk4 resembles that of 29p, more data are required to confirm or reject a possible connection between the two objects and perhaps others. based on observations made with the 1 m jacobus kapteyn telescope (jkt) at observatorio del roque de los muchachos in la palma and the 82 cm telescope of the instituto de astrofisica de canarias (iac80) at observatorio del teide in tenerife (canary islands, spain). | the active centaur 2020 mk4 |
an amateur astronomer in the modern world has the opportunity not only to make visual observations for own interest, but can make scientific astronomical observations and new discoveries in astronomy. in my example, as amateur astronomer and only through self-education, i inform about my discoveries: of the possible dwarf nova on the old digitized photographic plates and of new variable stars from sky surveys data by means of data mining; how i discovered (in the images of the sky surveys): astronomical transients, supernovae, planetary nebula candidates and new binary systems in the data of gaia dr2; i describe my discoveries of three novae in the andromeda galaxy. i report about some of my scientific observations using remote telescopes: of superhumps of cataclysmic variable stars; of echo outburst of am cvn star; of maximum brightness of blazars; of optical afterglows of gamma-ray bursts (including grb 221009a); of microlensing events; of rotation of near-earth asteroid 2022 ab. i also describe my photometric follow-up observations of novae (including v1405 cas and v1674 her) and my astrometric observations of solar system objects (including the confirmation of objects posted at the confirmation pages of the minor planet center) including observations of comet 2i/borisov, asteroids 2020 av2 and (65803) didymos. i also describe some of my observations of occultations: of the star by asteroid (159) aemilia, of the star by saturn's moon titan and of uranus by the moon during total lunar eclipse on november 8, 2022; and visual observations of variable stars, meteors and sunspots (including during the transit of venus in 2012). some of my data already used in scientific papers, others were sent to the databases. i share my experience of discovery and research of astronomical objects and in my example, i show that an amateur astronomer can make a real contribution to the science. | the contribution of the modern amateur astronomer to the science of astronomy |
in this paper, gmv as a major aocs (attitude orbit control system)/gnc (guidance, navigation and control) system provider presents its work on the development of a gnc system for a kinetic impact mission. asteroid impacts on earth are a known source of extinction and played an important role in the evolution of life on earth. this comes as no surprise given the high number of objects orbiting in earth's vicinity-asteroid impacts become a question of "when" rather than "if". this comes as no surprise given the high number of objects orbiting in earth's vicinity-asteroid impacts become a question of "when" rather than "if". under this motivation, thousands of potentially hazardous asteroids (phas) are monitored around the globe and naturally the question on the next step rose: what can we do when an incoming asteroid is identified as being on collision course with earth? this is the motivation behind the field of planetary defence. several mitigation strategies are being studied, but most of these have technology readiness levels still far off from the required. the one that comes closest is the kinetic impactor concept, which is the focus of this work. the concept is simple from a theoretical standpoint - a spacecraft (impactor) is sent into a collision course against the hazard neo transferring enough momentum through kinetic energy to slightly change the neo's trajectory and causes it to miss the earth. the main component of kinetic impactors is the gnc, due to the necessity of a fully autonomous system. the major elements are the camera and the guidance, since they will allow detecting the target and modifying its trajectory to have a successful impact, respectively. this study includes the implementation of the required algorithms as well as an analysis of their performance in the impact scenario. the main variables that control the simulations have been examined in order to determine the design limits. the sensitivity analysis illustrates that the errors introduced in the model were chosen conservatively, inasmuch as the impact could be reached introducing higher uncertainties and errors in the systems considered. in general, even with the not excessively complex algorithms employed, the performance of the gnc is good. this study opens the door for the development of a kinetic impactor mission. | kinetic impactor for a short warning asteroid deflection |
aims: the orbit of the outer satellite alexhelios of (216) kleopatra is already constrained by adaptive-optics astrometry obtained with the vlt/sphere instrument. however, there is also a preceding occultation event in 1980 attributed to this satellite. here, we try to link all observations, spanning 1980-2018, because the nominal orbit exhibits an unexplained shift by + 60° in the true longitude.methods: using both a periodogram analysis and an ℓ = 10 multipole model suitable for the motion of mutually interacting moons about the irregular body, we confirmed that it is not possible to adjust the respective osculating period p2. instead, we were forced to use a model with tidal dissipation (and increasing orbital periods) to explain the shift. we also analysed light curves spanning 1977-2021, and searched for the expected spin deceleration of kleopatra.results: according to our best-fit model, the observed period rate is ṗ2 = (1.8 ± 0.1) × 10−8 d d−1 and the corresponding time-lag δt2 = 42 s of tides, for the assumed value of the love number k2 = 0.3. this is the first detection of tidal evolution for moons orbiting 100 km asteroids. the corresponding dissipation factor q is comparable with that of other terrestrial bodies, albeit at a higher loading frequency 2|ω − n|. we also predict a secular evolution of the inner moon, ṗ1 = 5.0 × 10−8, as well as a spin deceleration of kleopatra, ṗ0 = 1.9 × 10−12. in alternative models, with moons captured in the 3:2 mean-motion resonance or more massive moons, the respective values of δt2 are a factor of between two and three lower. future astrometric observations using direct imaging or occultations should allow us to distinguish between these models, which is important for our understanding of the internal structure and mechanical properties of (216) kleopatra. based on observations made with eso telescopes at the la silla paranal observatory under program 199.c-0074 (pi vernazza). | observed tidal evolution of kleopatra's outer satellite |
context. stellar occultation is a powerful technique that allows the determination of some physical parameters of the occulting object. the result depends on the photometric accuracy, the temporal resolution, and the number of chords obtained. space telescopes can achieve high photometric accuracy as they are not affected by atmospheric scintillation.aims: using esa's cheops space telescope, we observed a stellar occultation by the transneptunian object (50000) quaoar. we compare the obtained chord with previous occultations by this object and determine its astrometry with sub-milliarcsecond precision. also, we determine upper limits to the presence of a global methane atmosphere on the occulting body.methods: we predicted and observed a stellar occultation by quaoar using the cheops space telescope. we measured the occultation light curve from this dataset and determined the dis- and reappearance of the star behind the occulting body. furthermore, a ground-based telescope in australia was used to constrain quaoar's limb. combined with results from previous works, these measurements allowed us to obtain a precise position of quaoar at the occultation time.results: we present the results obtained from the first stellar occultation by a transneptunian object using a space telescope orbiting earth; it was the occultation by quaoar observed on 2020 june 11. we used the cheops light curve to obtain a surface pressure upper limit of 85 nbar for the detection of a global methane atmosphere. also, combining this observation with a ground-based observation, we fitted quaoar's limb to determine its astrometric position with an uncertainty below 1.0 mas.conclusions: this observation is the first of its kind, and it shall be considered as a proof of concept of stellar occultation observations of transneptunian objects with space telescopes orbiting earth. moreover, it shows significant prospects for the james webb space telescope. the light curves and the fitted models 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/664/l15 this article uses data from cheops programme ch_pr100021. | a stellar occultation by the transneptunian object (50000) quaoar observed by cheops |
abstract orbital systems are often self-organized and/or characterized by harmonic relations. inspired by music theory, we rewrite the geddes and king-hele (qjras, 24, 10-13, 1983) equations for mirror symmetries among the distances of the planets of the solar system in an elegant and compact form by using the 2/3rd power of the ratios of the semi-major axis lengths of two neighboring planets (eight pairs, including the belt of the asteroids). this metric suggests that the solar system could be characterized by a scaling and mirror-like structure relative to the asteroid belt that relates together the terrestrial and jovian planets. these relations are based on a 9/8 ratio multiplied by powers of 2, which correspond musically to the interval of the pythagorean epogdoon (a major second) and its addition with one or more octaves. extensions of the same model are discussed and found compatible also with the still hypothetical vulcanoid asteroids versus the transneptunian objects. the found relation also suggests that the planetary self-organization of our system could be generated by the 3:1 and 7:3 resonances of jupiter, which are already known to have shaped the asteroid belt. the proposed model predicts the main kirkwood asteroid gaps and the ratio among the planetary orbital parameters with a 99% accuracy, which is three times better than an alternative, recently proposed harmonic-resonance model for the solar system. furthermore, the ratios of neighboring planetary pairs correspond to four musical "consonances" having frequency ratios of 5/4 (major third), 4/3 (perfect fourth), 3/2 (perfect fifth) and 8/5 (minor sixth); the probability of obtaining this result randomly has a p<0.001. musical consonances are "pleasing" tones that harmoniously interrelate when sounded together, which suggests that the orbits of the planets of our solar system could form some kind of gravitationally optimized and coordinated structure. physical modeling indicates that energy non-conserving perturbations could drive a planetary system into a self-organized periodic state with characteristics vaguely similar of those found in our solar system. however, our specific finding suggests that the planetary organization of our solar system could be rather peculiar and based on more complex and unknown dynamical structures. | scaling, mirror symmetries and musical consonances among the distances of the planets of the solar system |
the discovery of activity emanating from asteroid (4015) wilson-harrington in 1950 (harris, 1950) prompted astronomers to realize that comet-like activity, such as comae and tails, is not limited to comets. fewer than 30 of these "active asteroids" have been discovered (chandler et al., 2018) in the last 70 years, yet they promise to hold clues about fundamental physical and chemical processes at play in our solar system (jewitt, 2012; hsieh et al., 2015a). activity is attributed to sublimation for roughly half of these objects, highlighting asteroids as a "volatile reservoir." in this context a volatile reservoir is any dynamical group of bodies in the solar system that is known to harbor volatiles. understanding the past and present volatile distribution in the solar system has broad implications ranging from informing future space exploration pro- grams to helping us understand how planetary systems form with volatiles prerequisite to life as we know it, especially water. notably, the origin of earth's water is essentially unknown, although it is now believed that asteroids account for at least some of the terrestrial volatile budget (alexander, 2017).a second volatile reservoir came to light following the 1977 discovery of centaur (2060) chiron (kowal & gehrels, 1977). centaurs, found between the orbits of jupiter and neptune, are thought to be icy objects originating from the kuiper belt, a circumstellar region between the orbit of neptune (30 au) and about 50 au from the sun (jewitt, 2009). the kuiper belt is roughly 200 times more massive than the asteroid belt. nevertheless, active centaurs are also rare, with fewer than 20 discovered to date (chandler et al., 2020).we set out to increase the number of known active objects in order to (1) enable the study of these active objects as populations, and (2) search for new volatile reservoirs. i proposed to the nsf graduate research fellowship program (grfp) to create a citizen science project designed to carry out an outreach program while searching through millions of images of known asteroids in order to find previously unknown active objects. my proposal was selected for funding, and on 31 august 2022 we successfully launched active asteroids (http://activeasteroids.net), a nasa partner, and discoveries have been abundant ever since.in this dissertation i present (1) hunting for activity in repositories with vetting-enhanced search techniques (harvest), a pipeline that extracts images of known solar system objects for presentation to citizen scientists, (2) our proof-of-concept demonstrating dark energy camera (decam) images are well-suited for activity detection (chandler et al., 2018), (3) how we discovered a potential new recurrent activity mechanism (chandler et al., 2019), (4) a centaur activity discovery plus a novel technique for estimating which species are sublimating (chandler et al., 2020), (5) how our discovery of an additional activity epoch for an active asteroid enabled us to classify the object as a member of the main-belt comet (mbc) (chandler et al., 2021b), a rare (< 10) active asteroid subset that orbits in the asteroid belt that is known for sublimation-driven activity, (6) a dynamical pathway that can explain the presence of some of the active asteroids, and (7) the citizen science project active asteroids, including initial results. | chasing tails: active asteroid, centaur, and quasi-hilda discovery with astroinformatics and citizen science |
to more thoroughly study the effects of radiative forces on the orbits of small, astronomical bodies, we introduce the yarkovsky effect into reboundx, an extensional library for the n-body integrator rebound. two different versions of the yarkovsky effect (the "full version" and the "simple version") are available for use, depending on the needs of the user. we provide demonstrations for both versions of the effect and compare their computational efficiency with another previously implemented radiative force. in addition, we show how this effect can be used in tandem with other features in reboundx by simulating the orbits of asteroids during the asymptotic giant branch phase of a 2 m ⊙ star. this effect is made freely available for use with the latest release of reboundx. | the yarkovsky effect in reboundx |
context. in situ observations of small asteroids, such as itokawa, ryugu, and bennu, show that surfaces covered by boulders and coarse terrain are frequent on such bodies. regolith grain sizes have distributions on approximately mm and cm scales, and the behavior of such large grains in the very low-gravity environments of small body surfaces dictates their morphology and evolution.aims: in order to support the understanding of natural processes (e.g., the recapturing of impact ejecta) or spacecraft-induced interactions (e.g., the fate of a small lander), we aim to experimentally investigate the response of coarse-grained target surfaces to very-low-speed impacts (below 2 m s-1).methods: we present the outcome of 86 low-speed impacts of a cm-sized spherical projectile into a bed of simulated regolith, composed of irregular mm- and cm-sized grains. these impacts were performed under vacuum and microgravity conditions. our results include measurements for the projectile coefficient of restitution and penetration depth, as well as ejecta production, speed, and mass estimation. as part of our data analysis, we compared our data set with impacts performed in similar conditions with fine grain regolith targets to determine the dependence of our measurements on the target grain size.results: we find that impact outcomes include the frequent occurrence of projectile bouncing and tangential rolling on the target surface upon impact. ejecta is produced for impact speeds higher than about 12 cm s-1, and ejecta speeds scale with the projectile to target the grain size ratio and the impact speed. ejected mass estimations indicate that ejecta is increasingly difficult to produce for increasing grain sizes. coefficients of restitution of rebounding projectiles do not display a dependency on the target grain size, unlike their maximum penetration depth, which can be scaled with the projectile to target grain size ratio. finally, we compare our experimental measurements to spacecraft data and numerical work on hayabusa 2's mascot landing on the surface of the asteroid ryugu. | regolith behavior under asteroid-level gravity conditions: low-velocity impacts into mm- and cm-sized grain targets |
first-order variational equations are widely used in n-body simulations to study how nearby trajectories diverge from one another. these allow for efficient and reliable determinations of chaos indicators such as the maximal lyapunov characteristic exponent (mle) and the mean exponential growth factor of nearby orbits (megno). in this paper we lay out the theoretical framework to extend the idea of variational equations to higher order. we explicitly derive the differential equations that govern the evolution of second-order variations in the n-body problem. going to second order opens the door to new applications, including optimization algorithms that require the first and second derivatives of the solution, like the classical newton's method. typically, these methods have faster convergence rates than derivative-free methods. derivatives are also required for riemann manifold langevin and hamiltonian monte carlo methods which provide significantly shorter correlation times than standard methods. such improved optimization methods can be applied to anything from radial-velocity/transit-timing-variation fitting to spacecraft trajectory optimization to asteroid deflection. we provide an implementation of first- and second-order variational equations for the publicly available rebound integrator package. our implementation allows the simultaneous integration of any number of first- and second-order variational equations with the high-accuracy ias15 integrator. we also provide routines to generate consistent and accurate initial conditions without the need for finite differencing. | second-order variational equations for n-body simulations |
a nearly dynamically symmetric rigid body is considered. an approximation of this body by a system of two homogeneous balls is studied, such that the components of the euler-poinsot tensor of the original body and its approximation coincide up to the third order and the moments of inertia of the body are well approximated by the moments of inertia of the system of two balls. asteroids 1620 geographos and 25143 itokawa are considered as examples. | on the approximation of a nearly dynamically symmetric rigid body by two balls |
two primitive near-earth asteroids, (101955) bennu and (162173) ryugu, will be visited by a spacecraft with the aim of returning samples back to earth. since these objects are believed to originate in the inner main belt primitive collisional families (erigone, polana, clarissa, and sulamitis) or in the background of asteroids outside these families, the characterization of these primitive populations will enhance the scientific return of the missions. the main goal of this work is to shed light on the composition of the erigone collisional family by means of visible spectroscopy. asteroid (163) erigone has been classified as a primitive object, and we expect the members of this family to be consistent with the spectral type of the parent body. we have obtained visible spectra (0.5-0.9 μm) for 101 members of the erigone family, using the osiris instrument at the 10.4 m gran telescopio canarias. we found that 87% of the objects have typically primitive visible spectra consistent with that of (163) erigone. in addition, we found that a significant fraction of these objects (~50%) present evidence of aqueous alteration. | compositional study of asteroids in the erigone collisional family using visible spectroscopy at the 10.4 m gtc |
in this study, equilibrium points and periodic orbits in the potential field of asteroids are investigated. we present the linearized equations of motion relative to the equilibrium points and characteristic equations. we find that the distribution of characteristic multipliers of periodic orbits around the equilibrium point and the distribution of eigenvalues of the equilibrium point correspond to each other. the distribution of eigenvalues of the equilibrium point confirms the topology and the stability of periodic orbits around the equilibrium point. | equilibrium points and periodic orbits in the vicinity of asteroids with an application to 216 kleopatra |
the breakup of the l-chondrite parent body (lcpb) in the mid-ordovician is the largest documented asteroid breakup event during the past 3 gyr. it affected earth by a dramatic increase in the flux of l-chondritic material and left prominent traces in both meteorite and sedimentary records. a precise constraint on the timing of the lcpb breakup is important when evaluating the terrestrial biotic and climatic effects of the event, as well as for global stratigraphic correlations. direct dating using heavily shocked l chondrites is hampered by both incomplete initial k-ar degassing and isotopic resetting by later impact events. in order to better constrain the absolute age of this event we carried out high-precision u-pb dating of zircons from three limestone beds recording discrete volcanic ash fallouts within mid-ordovician strata in southern sweden. these strata are rich in fossilized l-chondritic meteorites (1-20 cm large) that arrived on earth shortly after the breakup event. zircons from the ash-bearing layers provide stratigraphically consistent depositional ages that range from 464.22 ± 0.37 ma to 465.01 ± 0.26 ma. combined with recently published 3he profiles that pinpoint the arrival on earth of the first dust from the breakup, and sedimentation rates constrained by cosmogenic 21ne in the fossil meteorites, the lcpb breakup is estimated to have occurred at 465.76 ± 0.30 ma. this provides the presently most precise absolute dating of the lcpb breakup, enabling a robust global stratigraphic correlation of bounding strata. based on our new u-pb data for the ash-bearing beds, the absolute ages for the boundaries of biozones and dapingian-floian stages overlap within error with those given by the 2012 geological timescale and require no modification. | absolute dating of the l-chondrite parent body breakup with high-precision u-pb zircon geochronology from ordovician limestone |
epithelial tissues (epithelia) remove excess cells through extrusion, preventing the accumulation of unnecessary or pathological cells. the extrusion process can be triggered by apoptotic signalling, oncogenic transformation and overcrowding of cells. despite the important linkage of cell extrusion to developmental, homeostatic and pathological processes such as cancer metastasis, its underlying mechanism and connections to the intrinsic mechanics of the epithelium are largely unexplored. we approach this problem by modelling the epithelium as an active nematic liquid crystal (that has a long range directional order), and comparing numerical simulations to strain rate and stress measurements within monolayers of mdck (madin darby canine kidney) cells. here we show that apoptotic cell extrusion is provoked by singularities in cell alignments in the form of comet-shaped topological defects. we find a universal correlation between extrusion sites and positions of nematic defects in the cell orientation field in different epithelium types. the results confirm the active nematic nature of epithelia, and demonstrate that defect-induced isotropic stresses are the primary precursors of mechanotransductive responses in cells, including yap (yes-associated protein) transcription factor activity, caspase-3-mediated cell death, and extrusions. importantly, the defect-driven extrusion mechanism depends on intercellular junctions, because the weakening of cell-cell interactions in an α-catenin knockdown monolayer reduces the defect size and increases both the number of defects and extrusion rates, as is also predicted by our model. we further demonstrate the ability to control extrusion hotspots by geometrically inducing defects through microcontact printing of patterned monolayers. on the basis of these results, we propose a mechanism for apoptotic cell extrusion: spontaneously formed topological defects in epithelia govern cell fate. this will be important in predicting extrusion hotspots and dynamics in vivo, with potential applications to tissue regeneration and the suppression of metastasis. moreover, we anticipate that the analogy between the epithelium and active nematic liquid crystals will trigger further investigations of the link between cellular processes and the material properties of epithelia. | topological defects in epithelia govern cell death and extrusion |
the importance of comets for the origin of life on earth has been advocated for many decades. amino acids are key ingredients in chemistry, leading to life as we know it. many primitive meteorites contain amino acids, and it is generally believed that these are formed by aqueous alterations. in the collector aerogel and foil samples of the stardust mission after the flyby at comet wild 2, the simplest form of amino acids, glycine, has been found together with precursor molecules methylamine and ethylamine. because of contamination issues of the samples, a cometary origin was deduced from the 13c isotopic signature. we report the presence of volatile glycine accompanied by methylamine and ethylamine in the coma of 67p/churyumov-gerasimenko measured by the rosina (rosetta orbiter spectrometer for ion and neutral analysis) mass spectrometer, confirming the stardust results. together with the detection of phosphorus and a multitude of organic molecules, this result demonstrates that comets could have played a crucial role in the emergence of life on earth. | prebiotic chemicals--amino acid and phosphorus--in the coma of comet 67p/churyumov-gerasimenko |
images from the osiris scientific imaging system onboard rosetta show that the nucleus of 67p/churyumov-gerasimenko consists of two lobes connected by a short neck. the nucleus has a bulk density less than half that of water. activity at a distance from the sun of >3 astronomical units is predominantly from the neck, where jets have been seen consistently. the nucleus rotates about the principal axis of momentum. the surface morphology suggests that the removal of larger volumes of material, possibly via explosive release of subsurface pressure or via creation of overhangs by sublimation, may be a major mass loss process. the shape raises the question of whether the two lobes represent a contact binary formed 4.5 billion years ago, or a single body where a gap has evolved via mass loss. | on the nucleus structure and activity of comet 67p/churyumov-gerasimenko |
we present the first measurement of elliptic (v2) and triangular (v3) flow in high-multiplicity 3he +au collisions at √{sn n }=200 gev . two-particle correlations, where the particles have a large separation in pseudorapidity, are compared in 3he +au and in p +p collisions and indicate that collective effects dominate the second and third fourier components for the correlations observed in the 3he +au system. the collective behavior is quantified in terms of elliptic v2 and triangular v3 anisotropy coefficients measured with respect to their corresponding event planes. the v2 values are comparable to those previously measured in d +au collisions at the same nucleon-nucleon center-of-mass energy. comparisons with various theoretical predictions are made, including to models where the hot spots created by the impact of the three 3he nucleons on the au nucleus expand hydrodynamically to generate the triangular flow. the agreement of these models with data may indicate the formation of low-viscosity quark-gluon plasma even in these small collision systems. | measurements of elliptic and triangular flow in high-multiplicity 3he +au collisions at √{sn n }=200 gev |
the rosetta spacecraft reached comet 67p/churyumov-gerasimenko (hereafter 67p/c-g) in august 2014 at an heliocentric distance of 3.6 a.u. and was then put in orbit around its nucleus to perform detailed observations. among the collected data are the images acquired by the osiris instrument up to the perihelion passage of the comet in august 2015, which allowed us to map the entire nucleus surface at high-resolution in the visible. stereophotoclinometry methods have been used to reconstruct a global high-resolution shape model and to monitor its rotational parameters using data collected up to perihelion. the nucleus has a conspicuous bilobate shape with overall dimensions along its principal axes of (4.34 ± 0.02) × (2.60 ± 0.02) × (2.12 ± 0.06) km. the best-fit ellipsoid dimensions of the individual lobes along their principal axes of inertia are found to be 4.10 × 3.52 × 1.63 km and 2.50 × 2.14 × 1.64 km. their volume amounts to 66% and 27% of the total volume of the nucleus. the two lobes are connected by a "neck" whose volume has been estimated to represent ∼7% of the total volume of the comet. combining the derived volume of 18.8 ± 0.3 km3 with the mass of 9.982 ± 0.003 × 1012 kg determined by the rosetta/rsi experiment, we obtained a bulk density of the nucleus of 532 ± 7 kg m-3 . together with the companion value of 535 ± 35 kg m-3 deduced from the stereophotogrammetry shape model of the nucleus (preusker et al. [2015] astron. astrophys. 583, a33), these constitute the first reliable and most accurate determination of the density of a cometary nucleus to date. the calculated porosity is quite large, ranging approximately from 70% to 75% depending upon the assumed density of the dust grains and the dust-to-ice mass ratio. the nature of the porosity, either micro or macro or both, remains unconstrained. the coordinates of the center of gravity are not compatible with a uniform nucleus density. the direction of the offset between the center of gravity and the center of figure suggests that the big lobe has a slightly higher bulk density compared to the small one. the center of mass position cannot be explained by different, but homogenous densities in the two lobes. the initial rotational period of 12.4041 ± 0.0001 h of the nucleus persisted until october 2014. it then slightly increased to a maximum of 12.4304 h reached on 19 may 2015 and finally dropped to 12.305 h just before perihelion on august 10, 2015. a periodogram analysis of the (ra, dec) direction of the z-axis of the comet obtained in parallel with the shape reconstruction exhibits a highly significant minima at 11.5 ± 0.5 day clearly indicating an excited rotational state with an amplitude of 0.15 ± 0.03°. | the global shape, density and rotation of comet 67p/churyumov-gerasimenko from preperihelion rosetta/osiris observations |
context. the esa rosetta spacecraft (s/c) is tracking comet 67p/churyumov-gerasimenko in close vicinity. this prolonged encounter enables studying the evolution of the volatile coma composition.aims: our work aims at comparing the diversity of the coma of 67p/churyumov-gerasimenko at large heliocentric distance to study the evolution of the comet during its passage around the sun and at trying to classify it relative to other comets.methods: we used the double focussing mass spectrometer (dfms) of the rosina experiment on esa's rosetta mission to determine relative abundances of major and minor volatile species. this study is restricted to species that have previously been detected elsewhere.results: we detect almost all species currently known to be present in cometary coma with rosina dfms. as dfms measured the composition locally, we cannot derive a global abundance, but we compare measurements from the summer and the winter hemisphere with known abundances from other comets. differences between relative abundances between summer and winter hemispheres are large, which points to a possible evolution of the cometary surface. this comet appears to be very rich in co2 and ethane. heavy oxygenated compounds such as ethylene glycol are underabundant at 3 au, probably due to their high sublimation temperatures, but nevertheless, their presence proves that kuiper belt comets also contain complex organic molecules. | inventory of the volatiles on comet 67p/churyumov-gerasimenko from rosetta/rosina |
cometary nuclei consist mostly of dust and water ice. previous observations have found nuclei to be low-density and highly porous bodies, but have only moderately constrained the range of allowed densities because of the measurement uncertainties. here we report the precise mass, bulk density, porosity and internal structure of the nucleus of comet 67p/churyumov-gerasimenko on the basis of its gravity field. the mass and gravity field are derived from measured spacecraft velocity perturbations at fly-by distances between 10 and 100 kilometres. the gravitational point mass is gm = 666.2 ± 0.2 cubic metres per second squared, giving a mass m = (9,982 ± 3) × 109 kilograms. together with the current estimate of the volume of the nucleus, the average bulk density of the nucleus is 533 ± 6 kilograms per cubic metre. the nucleus appears to be a low-density, highly porous (72-74 per cent) dusty body, similar to that of comet 9p/tempel 1. the most likely composition mix has approximately four times more dust than ice by mass and two times more dust than ice by volume. we conclude that the interior of the nucleus is homogeneous and constant in density on a global scale without large voids. the high porosity seems to be an inherent property of the nucleus material. | a homogeneous nucleus for comet 67p/churyumov-gerasimenko from its gravity field |
the sample analysis at mars (sam) instrument on board the mars science laboratory curiosity rover is designed to conduct inorganic and organic chemical analyses of the atmosphere and the surface regolith and rocks to help evaluate the past and present habitability potential of mars at gale crater. central to this task is the development of an inventory of any organic molecules present to elucidate processes associated with their origin, diagenesis, concentration, and long-term preservation. this will guide the future search for biosignatures. here we report the definitive identification of chlorobenzene (150-300 parts per billion by weight (ppbw)) and c2 to c4 dichloroalkanes (up to 70 ppbw) with the sam gas chromatograph mass spectrometer (gcms) and detection of chlorobenzene in the direct evolved gas analysis (ega) mode, in multiple portions of the fines from the cumberland drill hole in the sheepbed mudstone at yellowknife bay. when combined with gcms and ega data from multiple scooped and drilled samples, blank runs, and supporting laboratory analog studies, the elevated levels of chlorobenzene and the dichloroalkanes cannot be solely explained by instrument background sources known to be present in sam. we conclude that these chlorinated hydrocarbons are the reaction products of martian chlorine and organic carbon derived from martian sources (e.g., igneous, hydrothermal, atmospheric, or biological) or exogenous sources such as meteorites, comets, or interplanetary dust particles. | organic molecules in the sheepbed mudstone, gale crater, mars |
the composition of the neutral gas comas of most comets is dominated by h2o, co and co2, typically comprising as much as 95 per cent of the total gas density. in addition, cometary comas have been found to contain a rich array of other molecules, including sulfuric compounds and complex hydrocarbons. molecular oxygen (o2), however, despite its detection on other icy bodies such as the moons of jupiter and saturn, has remained undetected in cometary comas. here we report in situ measurement of o2 in the coma of comet 67p/churyumov-gerasimenko, with local abundances ranging from one per cent to ten per cent relative to h2o and with a mean value of 3.80 +/- 0.85 per cent. our observations indicate that the o2/h2o ratio is isotropic in the coma and does not change systematically with heliocentric distance. this suggests that primordial o2 was incorporated into the nucleus during the comet's formation, which is unexpected given the low upper limits from remote sensing observations. current solar system formation models do not predict conditions that would allow this to occur. | abundant molecular oxygen in the coma of comet 67p/churyumov-gerasimenko |
'oumuamua (1i/2017 u1) is the first known object of interstellar origin to have entered the solar system on an unbound and hyperbolic trajectory with respect to the sun. various physical observations collected during its visit to the solar system showed that it has an unusually elongated shape and a tumbling rotation state and that the physical properties of its surface resemble those of cometary nuclei, even though it showed no evidence of cometary activity. the motion of all celestial bodies is governed mostly by gravity, but the trajectories of comets can also be affected by non-gravitational forces due to cometary outgassing. because non-gravitational accelerations are at least three to four orders of magnitude weaker than gravitational acceleration, the detection of any deviation from a purely gravity-driven trajectory requires high-quality astrometry over a long arc. as a result, non-gravitational effects have been measured on only a limited subset of the small-body population. here we report the detection, at 30σ significance, of non-gravitational acceleration in the motion of 'oumuamua. we analyse imaging data from extensive observations by ground-based and orbiting facilities. this analysis rules out systematic biases and shows that all astrometric data can be described once a non-gravitational component representing a heliocentric radial acceleration proportional to r-2 or r-1 (where r is the heliocentric distance) is included in the model. after ruling out solar-radiation pressure, drag- and friction-like forces, interaction with solar wind for a highly magnetized object, and geometric effects originating from 'oumuamua potentially being composed of several spatially separated bodies or having a pronounced offset between its photocentre and centre of mass, we find comet-like outgassing to be a physically viable explanation, provided that 'oumuamua has thermal properties similar to comets. | non-gravitational acceleration in the trajectory of 1i/2017 u1 ('oumuamua) |
the virtis (visible, infrared and thermal imaging spectrometer) instrument on board the rosetta spacecraft has provided evidence of carbon-bearing compounds on the nucleus of the comet 67p/churyumov-gerasimenko. the very low reflectance of the nucleus (normal albedo of 0.060 ± 0.003 at 0.55 micrometers), the spectral slopes in visible and infrared ranges (5 to 25 and 1.5 to 5% kå-1), and the broad absorption feature in the 2.9-to-3.6-micrometer range present across the entire illuminated surface are compatible with opaque minerals associated with nonvolatile organic macromolecular materials: a complex mixture of various types of carbon-hydrogen and/or oxygen-hydrogen chemical groups, with little contribution of nitrogen-hydrogen groups. in active areas, the changes in spectral slope and absorption feature width may suggest small amounts of water-ice. however, no ice-rich patches are observed, indicating a generally dehydrated nature for the surface currently illuminated by the sun. | the organic-rich surface of comet 67p/churyumov-gerasimenko as seen by virtis/rosetta |
cometary ices are rich in co2, co and organic volatile compounds, but the carbon content of cometary dust was only measured for the oort cloud comet 1p/halley, during its flyby in 1986. the cometary secondary ion mass analyzer (cosima)/rosetta mass spectrometer analysed dust particles with sizes ranging from 50 to 1000 μm, collected over 2 yr, from 67p/churyumov-gerasimenko (67p), a jupiter family comet. here, we report 67p dust composition focusing on the elements c and o. it has a high carbon content (atomic {{c}}/{{si}} = 5.5{{ }}_{ - 1.2}^{ + 1.4} {{on average}} ) close to the solar value and comparable to the 1p/halley data. from cosima measurements, we conclude that 67p particles are made of nearly 50 per cent organic matter in mass, mixed with mineral phases that are mostly anhydrous. the whole composition, rich in carbon and non-hydrated minerals, points to a primitive matter that likely preserved its initial characteristics since the comet accretion in the outer regions of the protoplanetary disc. | carbon-rich dust in comet 67p/churyumov-gerasimenko measured by cosima/rosetta |
as well known, boltzmann-gibbs statistics is the correct way of thermostatistically approaching ergodic systems. on the other hand, nontrivial ergodicity breakdown and strong correlations typically drag the system into out-of-equilibrium states where boltzmann-gibbs statistics fails. for a wide class of such systems, it has been shown in recent years that the correct approach is to use tsallis statistics instead. here we show how the dynamics of the paradigmatic conservative (area-preserving) stan-dard map exhibits, in an exceptionally clear manner, the crossing from one statistics to the other. our results unambiguously illustrate the domains of validity of both boltzmann-gibbs and tsallis statistical distributions. since various important physical systems from particle confinement in magnetic traps to autoionization of molecular rydberg states, through particle dynamics in accelerators and comet dynamics, can be reduced to the standard map, our results are expected to enlighten and enable an improved interpretation of diverse experimental and observational results. | the standard map: from boltzmann-gibbs statistics to tsallis statistics |
we examine the evolution of the water production of comet 67p/churyumov-gerasimenko during the rosetta mission (2014 june-2016 may) based on in situ and remote sensing measurements made by rosetta instruments, earth-based telescopes and through the development of an empirical coma model. the derivation of the empirical model is described and the model is then applied to detrend spacecraft position effects from the rosetta orbiter spectrometer for ion and neutral analysis (rosina) data. the inter-comparison of the instrument data sets shows a high level of consistency and provides insights into the water and dust production. we examine different phases of the orbit, including the early mission (beyond 3.5 au) where the rosina water production does not show the expected increase with decreasing heliocentric distance. a second important phase is the period around the inbound equinox, where the peak water production makes a dramatic transition from northern to southern latitudes. during this transition, the water distribution is complex, but is driven by rotation and active areas in the north and south. finally, we consider the perihelion period, where there may be evidence of time dependence in the water production rate. the peak water production, as measured by rosina, occurs 18-22 d after perihelion at 3.5 ± 0.5 × 1028 water molecules s-1. we show that the water production is highly correlated with ground-based dust measurements, possibly indicating that several dust parameters are constant during the observed period. using estimates of the dust/gas ratio, we use our measured water production rate to calculate a uniform surface loss of 2-4 m during the current perihelion passage. | evolution of water production of 67p/churyumov-gerasimenko: an empirical model and a multi-instrument study |
comets harbor the most pristine material in our solar system in the form of ice, dust, silicates, and refractory organic material with some interstellar heritage. the evolved gas analyzer cometary sampling and composition (cosac) experiment aboard rosetta’s philae lander was designed for in situ analysis of organic molecules on comet 67p/churyumov-gerasimenko. twenty-five minutes after philae’s initial comet touchdown, the cosac mass spectrometer took a spectrum in sniffing mode, which displayed a suite of 16 organic compounds, including many nitrogen-bearing species but no sulfur-bearing species, and four compounds—methyl isocyanate, acetone, propionaldehyde, and acetamide—that had not previously been reported in comets. | organic compounds on comet 67p/churyumov-gerasimenko revealed by cosac mass spectrometry |
we use the gaia dr2 distances of about 700 mid-infrared selected young stellar objects in the benchmark giant molecular cloud orion a to infer its 3d shape and orientation. we find that orion a is not the fairly straight filamentary cloud that we see in (2d) projection, but instead a cometary-like cloud oriented toward the galactic plane, with two distinct components: a denser and enhanced star-forming (bent) head, and a lower density and star-formation quieter ∼75 pc long tail. the true extent of orion a is not the projected ∼40 pc but ∼90 pc, making it by far the largest molecular cloud in the local neighborhood. its aspect ratio (∼30:1) and high column-density fraction (∼45%) make it similar to large-scale milky way filaments ("bones"), despite its distance to the galactic mid-plane being an order of magnitude larger than typically found for these structures. full table b.1 is only available at the cds via anonymous ftp to http://cdsarc.u-strasbg.fr (ftp://130.79.128.5) or via http://cdsarc.u-strasbg.fr/viz-bin/qcat?j/a+a/619/a106 | 3d shape of orion a from gaia dr2 |
context. the complex shape of comet 67p and its oblique rotation axis cause pronounced seasonal effects. irradiation and hence activity vary strongly.aims: we investigate the insolation of the cometary surface in order to predict the sublimation of water ice. the strongly varying erosion levels are correlated with the topography and morphology of the present cometary surface and its evolution.methods: the insolation as a function of heliocentric distance and diurnal (spin dependent) variation is calculated using >105 facets of a detailed digital terrain model. shading, but also illumination and thermal radiation by facets in the field of view of a specific facet are iteratively taken into account. we use a two-layer model of a thin porous dust cover above an icy surface to calculate the water sublimation, presuming steady state and a uniform surface. our second model, which includes the history of warming and cooling due to thermal inertia, is restricted to a much simpler shape model but allows us to test various distributions of active areas.results: sublimation from a dirty ice surface yields maximum erosion. a thin dust cover of 50 μm yields similar rates at perihelion. only about 6% of the surface needs to be active to match the observed water production rates at perihelion. a dust layer of 1 mm thickness suppresses the activity by a factor of 4 to 5. erosion on the south side can reach more than 10 m per orbit at active spots. the energy input to the concave neck area (hapi) during northern summer is enhanced by about 50% owing to self-illumination. here surface temperatures reach maximum values along the foot of the hathor wall. integrated over the whole orbit this area receives the least energy input. based on the detailed shape model, the simulations identify "hot spots" in depressions and larger pits in good correlation with observed dust activity. three-quarters of the total sublimation is produced while the sub-solar latitude is south, resulting in a distinct dichotomy in activity and morphology.conclusions: the northern areas display a much rougher morphology than what is seen on imhotep, an area at the equator that will be fully illuminated when 67p is closer to the sun. self-illumination in concave regions enhance the energy input and hence erosion. this explains the early activity observed at hapi. cliffs are more prone to erosion than horizontal, often dust covered, areas, which leads to surface planation. local activity can only persist if the forming cliff walls are eroding. comet 67p has two lobes and also two distinct sides. transport of material from the south to the north is probable. the morphology of the imhotep plain should be typical for the terrains of the yet unseen southern hemisphere. | insolation, erosion, and morphology of comet 67p/churyumov-gerasimenko |
the rosetta probe, orbiting jupiter-family comet 67p/churyumov-gerasimenko, has been detecting individual dust particles of mass larger than 10-10 kg by means of the giada dust collector and the osiris wide angle camera and narrow angle camera since 2014 august and will continue until 2016 september. detections of single dust particles allow us to estimate the anisotropic dust flux from 67p, infer the dust loss rate and size distribution at the surface of the sunlit nucleus, and see whether the dust size distribution of 67p evolves in time. the velocity of the rosetta orbiter, relative to 67p, is much lower than the dust velocity measured by giada, thus dust counts when giada is nadir-pointing will directly provide the dust flux. in osiris observations, the dust flux is derived from the measurement of the dust space density close to the spacecraft. under the assumption of radial expansion of the dust, observations in the nadir direction provide the distance of the particles by measuring their trail length, with a parallax baseline determined by the motion of the spacecraft. the dust size distribution at sizes >1 mm observed by osiris is consistent with a differential power index of -4, which was derived from models of 67p’s trail. at sizes <1 mm, the size distribution observed by giada shows a strong time evolution, with a differential power index drifting from -2 beyond 2 au to -3.7 at perihelion, in agreement with the evolution derived from coma and tail models based on ground-based data. the refractory-to-water mass ratio of the nucleus is close to six during the entire inbound orbit and at perihelion. | evolution of the dust size distribution of comet 67p/churyumov-gerasimenko from 2.2 au to perihelion |
measurements of midrapidity charged-particle multiplicity distributions, d nch/d η , and midrapidity transverse-energy distributions, d et/d η , are presented for a variety of collision systems and energies. included are distributions for au +au collisions at √{snn}=200 , 130, 62.4, 39, 27, 19.6, 14.5, and 7.7 gev, cu +cu collisions at √{snn}=200 and 62.4 gev, cu +au collisions at √{snn}=200 gev, u +u collisions at √{snn}=193 gev, d +au collisions at √{snn}=200 gev, 3he+au collisions at √{snn}=200 gev, and p +p collisions at √{snn}=200 gev. centrality-dependent distributions at midrapidity are presented in terms of the number of nucleon participants, npart, and the number of constituent quark participants, nqp. for all a +a collisions down to √{snn}=7.7 gev, it is observed that the midrapidity data are better described by scaling with nqp than scaling with npart. also presented are estimates of the bjorken energy density, ɛbj, and the ratio of d et/d η to d nch/d η , the latter of which is seen to be constant as a function of centrality for all systems. | transverse energy production and charged-particle multiplicity at midrapidity in various systems from √{sn n}=7.7 to 200 gev |
a prevailing theory for the interstellar production of complex organic molecules (coms) involves formation on warm dust-grain surfaces, via the diffusion and reaction of radicals produced through grain-surface photodissociation of stable molecules. however, some gas-phase o-bearing coms, notably acetaldehyde (ch3cho), methyl formate (ch3ocho), and dimethyl ether (ch3och3), are now observed at very low temperatures, challenging the warm scenario. here, we introduce a selection of new nondiffusive mechanisms into an astrochemical model to account for the failure of the standard diffusive picture and to provide a more generalized scenario of com formation on interstellar grains. new generic rate formulations are provided for cases where (i) radicals are formed by reactions occurring close to another reactant, producing an immediate follow-on reaction; (ii) radicals are formed in an excited state, allowing them to overcome activation barriers to react with nearby stable molecules; and (iii) radicals are formed through photodissociation close to a reaction partner, followed by immediate reaction. each process occurs without thermal diffusion of large radicals. the new mechanisms significantly enhance cold com abundances, successfully reproducing key observational results for prestellar core l1544. h abstraction from grain-surface coms, followed by recombination, plays a crucial role in amplifying chemical desorption into the gas phase. the ultraviolet-induced chemistry produces significant com abundances in the bulk ices, which are retained on the grains and may persist to later stages. o2 is also formed strongly in the mantle though photolysis, suggesting cometary o2 could indeed be interstellar. | formation of complex organic molecules in cold interstellar environments through nondiffusive grain-surface and ice-mantle chemistry |
the esa rosetta spacecraft followed comet 67p at a close distance for more than 2 yr. in addition, it deployed the lander philae on to the surface of the comet. the (surface) composition of the comet is of great interest to understand the origin and evolution of comets. by combining measurements made on the comet itself and in the coma, we probe the nature of this surface material and compare it to remote sensing observations. we compare data from the double focusing mass spectrometer (dfms) of the rosina experiment on esa's rosetta mission and previously published data from the two mass spectrometers cosac (cometary sampling and composition) and ptolemy on the lander. the mass spectra of all three instruments show very similar patterns of mainly cho-bearing molecules that sublimate at temperatures of 275 k. the dfms data also show a great variety of ch-, chn-, chs-, cho2- and chno-bearing saturated and unsaturated species. methyl isocyanate, propanal and glycol aldehyde suggested by the earlier analysis of the measured cosac spectrum could not be confirmed. the presence of polyoxymethylene in the ptolemy spectrum was found to be unlikely. however, the signature of the aromatic compound toluene was identified in dfms and ptolemy data. comparison with remote sensing instruments confirms the complex nature of the organics on the surface of 67p, which is much more diverse than anticipated. | organics in comet 67p - a first comparative analysis of mass spectra from rosina-dfms, cosac and ptolemy |
the origin of life is believed to have started with prebiotic molecules reacting along unidentified pathways to produce key molecules such as nucleosides. to date, a single prebiotic pathway to purine nucleosides had been proposed. it is considered to be inefficient due to missing regioselectivity and low yields. we report that the condensation of formamidopyrimidines (fapys) with sugars provides the natural n-9 nucleosides with extreme regioselectivity and in good yields (60%). the fapys are available from formic acid and aminopyrimidines, which are in turn available from prebiotic molecules that were also detected during the rosetta comet mission. this nucleoside formation pathway can be fused to sugar-forming reactions to produce pentosides, providing a plausible scenario of how purine nucleosides may have formed under prebiotic conditions. | a high-yielding, strictly regioselective prebiotic purine nucleoside formation pathway |
context. the elemental depletion of interstellar sulfur from the gas phase has been a recurring challenge for astrochemical models. observations show that sulfur remains relatively non-depleted with respect to its cosmic value throughout the diffuse and translucent stages of an interstellar molecular cloud, but its atomic and molecular gas-phase constituents cannot account for this cosmic value toward lines of sight containing higher-density environments.aims: we have attempted to address this issue by modeling the evolution of an interstellar cloud from its pristine state as a diffuse atomic cloud to a molecular environment of much higher density, using a gas-grain astrochemical code and an enhanced sulfur reaction network.methods: a common gas-grain astrochemical reaction network has been systematically updated and greatly extended based on previous literature and previous sulfur models, with a focus on the grain chemistry and processes. a simple astrochemical model was used to benchmark the resulting network updates, and the results of the model were compared to typical astronomical observations sourced from the literature.results: our new gas-grain astrochemical model is able to reproduce the elemental depletion of sulfur, whereby sulfur can be depleted from the gas-phase by two orders of magnitude, and that this process may occur under dark cloud conditions if the cloud has a chemical age of at least 106 years. the resulting mix of sulfur-bearing species on the grain ranges across all the most common chemical elements (h/c/n/o), not dissimilar to the molecules observed in cometary environments. notably, this mixture is not dominated simply by h2s, unlike all other current astrochemical models.conclusions: despite our relatively simple physical model, most of the known gas-phase s-bearing molecular abundances are accurately reproduced under dense conditions, however they are not expected to be the primary molecular sinks of sulfur. our model predicts that most of the "missing" sulfur is in the form of organo-sulfur species that are trapped on grains. full tables a.1 and b.4 are only available at the cds via anonymous ftp to http://cdsarc.u-strasbg.fr (ftp://130.79.128.5) or via http://cdsarc.u-strasbg.fr/viz-bin/qcat?j/a+a/624/a108 | modeling sulfur depletion in interstellar clouds |
the virtis (visible, infrared and thermal imaging spectrometer) instrument aboard the rosetta spacecraft has performed extensive spectral mapping of the surface of comet 67p/churyumov-gerasimenko in the range 0.3-5 μm. the reflectance spectra collected across the surface display a low reflectance factor over the whole spectral range, two spectral slopes in the visible and near-infrared ranges and a broad absorption band centered at 3.2 μm. the first two of these characteristics are typical of dark small bodies of the solar system and are difficult to interpret in terms of composition. moreover, solar wind irradiation may modify the structure and composition of surface materials and there is no unequivocal interpretation of these spectra devoid of vibrational bands. to circumvent these problems, we consider the composition of cometary grains analyzed in the laboratory to constrain the nature of the cometary materials and consider results on surface rejuvenation and solar wind processing provided by the osiris and rosina instruments, respectively. our results lead to five main conclusions: (i) the low albedo of comet 67p/cg is accounted for by a dark refractory polyaromatic carbonaceous component mixed with opaque minerals. virtis data do not provide direct insights into the nature of these opaque minerals. however, according to the composition of cometary grains analyzed in the laboratory, we infer that they consist of fe-ni alloys and fes sulfides. (ii) a semi-volatile component, consisting of a complex mix of low weight molecular species not volatilized at t∼220 k, is likely a major carrier of the 3.2 μm band. water ice contributes significantly to this feature in the neck region but not in other regions of the comet. cooh in carboxylic acids is the only chemical group that encompasses the broad width of this feature. it appears as a highly plausible candidate along with the nh4+ ion. (iii) photolytic/thermal residues, produced in the laboratory from interstellar ice analogs, are potentially good spectral analogs. (iv) no hydrated minerals were identified and our data support the lack of genetic links with the ci, cr and cm primitive chondrites. this concerns in particular the orgueil chondrite, previously suspected to have been of cometary origin. (v) the comparison between fresh and aged terrains revealed no effect of solar wind irradiation on the 3.2 μm band. this is consistent with the presence of efficient resurfacing processes such as dust transport from the interior to the surface, as revealed by the osiris camera. | refractory and semi-volatile organics at the surface of comet 67p/churyumov-gerasimenko: insights from the virtis/rosetta imaging spectrometer |
observations of cometary nuclei have revealed a very limited amount of surface water ice, which is insufficient to explain the observed water outgassing. this was clearly demonstrated on comet 9p/tempel 1, where the dust jets (driven by volatiles) were only partially correlated with the exposed ice regions. the observations of 67p/churyumov-gerasimenko have revealed that activity has a diurnal variation in intensity arising from changing insolation conditions. it was previously concluded that water vapour was generated in ice-rich subsurface layers with a transport mechanism linked to solar illumination, but that has not hitherto been observed. periodic condensations of water vapour very close to, or on, the surface were suggested to explain short-lived outbursts seen near sunrise on comet 9p/tempel 1. here we report observations of water ice on the surface of comet 67p/churyumov-gerasimenko, appearing and disappearing in a cyclic pattern that follows local illumination conditions, providing a source of localized activity. this water cycle appears to be an important process in the evolution of the comet, leading to cyclical modification of the relative abundance of water ice on its surface. | the diurnal cycle of water ice on comet 67p/churyumov-gerasimenko |
the phenix collaboration presents first measurements of low-momentum (0.4 <pt<3 gev /c ) direct-photon yields from au + au collisions at √{sn n}=39 and 62.4 gev. for both beam energies the direct-photon yields are substantially enhanced with respect to expectations from prompt processes, similar to the yields observed in au + au collisions at √{sn n}=200 . analyzing the photon yield as a function of the experimental observable d nch/d η reveals that the low-momentum (>1 gev /c ) direct-photon yield d nγdir/d η is a smooth function of d nch/d η and can be well described as proportional to (d nch/d η )α with α ≈1.25 . this scaling behavior holds for a wide range of beam energies at the relativistic heavy ion collider and the large hadron collider, for centrality selected samples, as well as for different a +a collision systems. at a given beam energy, the scaling also holds for high pt (>5 gev /c ), but when results from different collision energies are compared, an additional √{sn n}-dependent multiplicative factor is needed to describe the integrated-direct-photon yield. | beam energy and centrality dependence of direct-photon emission from ultrarelativistic heavy-ion collisions |
the european space agency (esa) recently selected comet interceptor as its first `fast' (f-class) mission. it will be developed rapidly to share a launch with another mission and is unique, as it will wait in space for a yet-to-be-discovered comet. | the european space agency's comet interceptor lies in wait |
context. we present an investigation of the surface properties of areas on the nucleus of comet 67p/churyumov-gerasimenko.aims: we aim to show that transport of material from one part of the cometary nucleus to another is a significant mechanism that influences the appearance of the nucleus and the surface thermal properties.methods: we used data from the osiris imaging system onboard the rosetta spacecraft to identify surface features on the nucleus that can be produced by various transport mechanisms. we used simple calculations based on previous works to establish the plausibility of dust transport from one part of the nucleus to another.results: we show by observation and modeling that "airfall" as a consequence of non-escaping large particles emitted from the neck region of the nucleus is a plausible explanation for the smooth thin deposits in the northern hemisphere of the nucleus. the consequences are also discussed. we also present observations of aeolian ripples and ventifacts. we show by numerical modeling that a type of saltation is plausible even under the rarified gas densities seen at the surface of the nucleus. however, interparticle cohesive forces present difficulties for this model, and an alternative mechanism for the initiation of reptation and creep may result from the airfall mechanism. the requirements on gas density and other parameters of this alternative make it a more attractive explanation for the observations. the uncertainties and implications are discussed. | redistribution of particles across the nucleus of comet 67p/churyumov-gerasimenko |
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