– We have assembled data on 13 cases of meteorite falls with accurate tracking data on atmospheric passage. In all cases, we estimate the bulk strength of the object corresponding to its earliest ...observed or inferred fragmentation in the high atmosphere, and can compare these values with measured strengths of meteorites in the taxonomic class for that fall. In all 13 cases, the strength corresponding to earliest observed or inferred fragmentation is much less than the compressive or tensile strength reported for that class of stony meteorites. Bulk strengths upon atmospheric entry of these bodies are shown to be very low, 0.1 to approximately 1 MPa on first breakup, and maximal strength on breakup as 1–10 MPa corresponding to weak and “crumbly” objects, whereas measured average tensile strength of the similar meteorite classes is about 30 MPa. We find a more random relation between bulk sample strength and sample mass than is suggested by a commonly used empirical power law. We estimate bulk strengths on entry being characteristically of the order of 10−1–10−2 times the tensile strengths of recovered samples. We conclude that pre‐entry, meter‐scale interplanetary meteoroids are typically highly fractured or in some cases rubbly in texture, presumably as a result of their parent bodies’ collisional history, and can break up under stresses of a few megapascals. The weakness of some carbonaceous objects may result from very porous primordial accretional structures, more than fractures. These conclusions have implications for future asteroid missions, sample extraction, and asteroid hazard mitigation.
ABSTRACT
Meteor physics can provide new clues about the size, structure, and density of cometary disintegration products, establishing a bridge between different research fields. From meteor ...magnitude data we have estimated the mass distribution of meteoroids from different cometary streams by using the relation between the luminosity and the mass obtained by Verniani. These mass distributions are in the range observed for dust particles released from comets 1P/Halley and 81P/Wild 2 as measured from spacecraft. From the derived mass distributions, we have integrated the incoming mass for the most significant meteor showers. By comparing the mass of the collected interplanetary dust particles (IDPs) with that derived for cometary meteoroids a gap of several orders of magnitude is encountered. The largest examples of fluffy particles are clusters of IDPs no larger than 100 μm in size (or 5 × 10–7 g in mass) while the largest cometary meteoroids are centimeter-sized objects. Such gaps can be explained by the fragmentation in the atmosphere of the original cometary particles. As an application of the mass distribution computations we describe the significance of the disruption of fragile comets in close approaches to Earth as a more efficient (and probably more frequent) way to deliver volatiles than direct impacts. We finally apply our model to quantify the flux of meteoroids from different meteoroid streams, and to describe the main physical processes contributing to the progressive decay of cometary meteoroids in the interplanetary medium.
Abstract
There is an unceasing incoming flux of extraterrestrial materials reaching the Earth atmosphere. Some of these objects produce luminous columns when they ablate during the hypersonic ...encounter with air molecules. A few fireballs occur each year bright enough to be detected from space. The source of these events is still a matter of debate, but it is generally accepted that they are of sporadic origin. We studied the NASA-JPL Center for NEOs Studies (CNEOS) fireball database to infer the dynamic origin of large bolides produced by meter-sized projectiles that impacted our planet. These likely meteorite-dropping events were recorded by the US Government satellite sensors. We estimated the false-positive rate and analyzed the time evolution of multiple orbit dissimilarity criteria concerning potential associations with near-Earth objects and meteoroid streams. We found that at least 16% of the large bolides could be associated with meteoroid streams, about 4% are likely associated with near-Earth asteroids, and 4% may be linked to near-Earth comets. This implies that a significant fraction of meter-sized impactors producing large bolides may have an asteroidal or cometary origin. In addition, we found at least three bolides having hyperbolic orbits with high tensile strength values. Meter-sized meteoroids of interstellar origin could be more common than previously thought, representing about 1% of the flux of large bolides. The inferred bulk physical properties suggest that the interstellar medium could bias these projectiles toward high strength rocks with the ability to survive prolonged exposure to the harsh interstellar space conditions.
Protoplanetary disks are dust-rich structures around young stars. The crystalline and amorphous materials contained within these disks are variably thermally processed and accreted to make bodies of ...a wide range of sizes and compositions, depending on the heliocentric distance of formation. The chondritic meteorites are fragments of relatively small and undifferentiated bodies, and the minerals that they contain carry chemical signatures providing information about the early environment available for planetesimal formation. A current hot topic of debate is the delivery of volatiles to terrestrial planets, understanding that they were built from planetesimals formed under far more reducing conditions than the primordial carbonaceous chondritic bodies. In this review, we describe significant evidence for the accretion of ices and hydrated minerals in the outer protoplanetary disk. In that distant region highly porous and fragile carbon and water-rich transitional asteroids formed, being the parent bodies of the carbonaceous chondrites (CCs). CCs are undifferentiated meteorites that never melted but experienced other physical processes including thermal and aqueous alteration. Recent evidence indicates that few of them have escaped significant alteration, retaining unique features that can be interpreted as evidence of wet accretion. Some examples of carbonaceous chondrite parent body aqueous alteration will be presented. Finally, atomistic interpretations of the first steps leading to water-mediated alteration during the accretion of CCs are provided and discussed. From these new insights into the water retained in CCs we can decipher the pathways of delivery of volatiles to the terrestrial planets.
Aims. Asteroids have been exposed to impacts since their formation, and as a consequence their surfaces are covered by small particles, pebbles, and boulders. The Japanese JAXA/ISAS Hayabusa mission ...collected micron-sized particles from the regolith of asteroid 25143 Itokawa. The study in terrestrial laboratories of these particles provides a scientific opportunity as their physical properties can be compared with those characteristic of chondritic meteorites that are often considered proxies of the building materials of potentially hazardous asteroids (PHAs). Methods. Here we present the results from a study of the mechanical properties of three of these particles using a precise technique called nanoindentation. The derived results are compared with those obtained via a methodology similar to that used for the Chelyabinsk meteorite. Results. The reduced Young’s modulus values obtained for the Itokawa samples are higher than those measured for the Chelyabinsk chondrite, so these specific particles of asteroid regolith are more compacted than the minerals forming the particular LL chondrite associated with PHAs. This might be a natural consequence of particles surviving long exposure times on the surface of a (near-Earth asteroid) NEA. The Double Asteroid Redirection Test (DART) mission plans to excavate a crater in the surface of the (65803) Didymos satellite. Our results suggest that excavating a crater with a kinetic impactor in an area of significant fine-grained regolith will increase the momentum transfer. As this will facilitate the release of particles carrying target mass in the opposite direction to the movement of the projectile, there is no need to grind up the target during the mechanical excavation phase.
We describe the fall of Annama meteorite occurred in the remote Kola Peninsula (Russia) close to Finnish border on 2014 April 19 (local time). The fireball was instrumentally observed by the Finnish ...Fireball Network. From these observations the strewnfield was computed and two first meteorites were found only a few hundred metres from the predicted landing site on 2014 May 29 and 30, so that the meteorite (an H5 chondrite) experienced only minimal terrestrial alteration. The accuracy of the observations allowed a precise geocentric radiant to be obtained, and the heliocentric orbit for the progenitor meteoroid to be calculated. Backward integrations of the orbits of selected near-Earth asteroids and the Annama meteoroid showed that they rapidly diverged so that the Annama meteorites are unlikely related to them. The only exception seems to be the recently discovered 2014UR116 that shows a plausible dynamic relationship. Instead, analysis of the heliocentric orbit of the meteoroid suggests that the delivery of Annama onto an Earth-crossing Apollo-type orbit occurred via the 3:1 mean motion resonance with Jupiter or the nu6 secular resonance, dynamic mechanisms that are responsible for delivering to Earth most meteorites studied so far.
We show that carbonaceous chondrite meteorites actively and selectively catalyze the formation of relevant prebiotic molecules from formamide in aqueous media. Specific catalytic behaviours are ...observed, depending on the origin and composition of the chondrites and on the type of water present in the system (activity: thermal > seawater > pure). We report the one-pot synthesis of all the natural nucleobases, of aminoacids and of eight carboxylic acids (forming, from pyruvic acid to citric acid, a continuous series encompassing a large part of the extant Krebs cycle). These data shape a general prebiotic scenario consisting of carbonaceous meteorites acting as catalysts and of a volcanic-like environment providing heat, thermal waters and formamide. This scenario also applies to the other solar system locations that experienced rich delivery of carbonaceous materials, and whose physical-chemical conditions could have allowed chemical evolution.
We present laboratory experiments on the formation of macroscopic dust aggregates. The centimeter-sized highly porous bodies are produced by random ballistic deposition from individual ...micrometer-sized dust particles. We find packing densities between 0.07 and 0.15 for uncompressed samples, dependent on the shape and size distribution of the constituent dust grains. Impacts into these bodies are simulated by uniaxial compression experiments. We find that the maximum compression, equivalent to the highest protoplanetary impact velocities of 650 m s super(-1), increases the packing density to 0.20-0.33. Tensile strength measurements with our laboratory samples yield values in the range 200-1100 Pa for slightly compressed samples. We review packing densities and tensile strengths found for primitive solar system bodies, e.g., for comets, primitive meteorites, and meteoroids. We find a consistency between packing densities and tensile strengths of our laboratory samples with those from cometary origin.
Interplanetary dust particles and meteoroids mostly originate from comets and asteroids. Understanding their distribution in the Solar system, their dynamical behavior and their properties, sheds ...light on the current state and the dynamical behavior of the Solar system. Dust particles can endanger Earth-orbiting satellites and deep-space probes, and a good understanding of the spatial density and velocity distribution of dust and meteoroids in the Solar system is important for designing proper spacecraft shielding. The study of interplanetary dust and meteoroids provides clues to the formation of the Solar system. Particles having formed 4.5 billion years ago can survive planetary accretion and those that survived until now did not evolve significantly since then. Meteoroids and interplanetary dust can be observed by measuring the intensity and polarization of the zodiacal light, by observing meteors entering the Earth’s atmosphere, by collecting them in the upper atmosphere, polar ices and snow, and by detecting them with in-situ detectors on space probes.
Abstract
The impact of the Double Asteroid Redirection Test spacecraft into Dimorphos, moon of the asteroid Didymos, changed Dimorphos’s orbit substantially, largely from the ejection of material. We ...present results from 12 Earth-based facilities involved in a world-wide campaign to monitor the brightness and morphology of the ejecta in the first 35 days after impact. After an initial brightening of ∼1.4 mag, we find consistent dimming rates of 0.11–0.12 mag day
−1
in the first week, and 0.08–0.09 mag day
−1
over the entire study period. The system returned to its pre-impact brightness 24.3–25.3 days after impact though the primary ejecta tail remained. The dimming paused briefly eight days after impact, near in time to the appearance of the second tail. This was likely due to a secondary release of material after re-impact of a boulder released in the initial impact, though movement of the primary ejecta through the aperture likely played a role.
PDF
