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Modern ideas about objects approaching the Earth are discussed. This population includes near-Earth asteroids (NEAs), including potentially hazardous asteroids, short-period comets, meteoroid streams, and large sporadic meteoroids. An overview is given of the currently available information on the dynamic and physical properties of NEAs and comets. Almost 5% of the currently known NEAs are extinct cometary nuclei or their fragments. Being outwardly similar with true asteroids, they differ markedly in their dynamic and physical properties. In order to distinguish between these groups of objects, it is necessary to study both their dynamic and physical parameters. Some of the known meteoroid streams are shown to contain, along with the countless small meteoroids, also large extinct fragments of cometary nuclei, which are classified as NEAs. A meteoroid stream and such bodies belonging to it form together an asteroid–meteoroid complex. Observational and theoretical data are presented to confirm the modern understanding of near-Earth objects.

A noted meteoriticist shows how meteorites have helped build our planet and influenced humanity since the start of civilization.

The mesosphere/lower thermosphere (MLT, 80–100 km) region is an important boundary between Earth's atmosphere below and space above and may act as a sensitive indicator for anthropogenic climate change. Existing observational and modeling studies have shown the middle atmosphere and the MLT is cooling and contracting because of increasing greenhouse gas emissions. However, trend analyses are highly sensitive to the time periods covered, their length, and the measurement type and methodology used. We present for the first time the linear and 11‐year solar cycle responses in the meteor ablation altitude distributions observed by 12 meteor radars at different locations. Decreasing altitudes were seen at all latitudes (linear trends varying from −10.97 to −817.95 m dec−1), and a positive correlation with solar activity was seen for most locations. The divergence of responses at high latitudes indicates an important and complex interplay between atmospheric changes and dynamics at varying time scales. Plain Language Summary High up in our atmosphere lies the mesosphere/lower thermosphere region (80–100 km); an important transition zone between the atmosphere below and space above. Existing studies indicate that this region is changing (cooling and contracting) in response to increasing greenhouse gas emissions, quite unlike the net warming we see near the surface. However these trend studies are often highly sensitive to choice and length of time period covered, and the methodology and type of measurements used. Here we present for the first time a self‐consistent methodology applied to 12 different meteor radar station datasets located at a diverse range of latitudes. We looked at changes in the mean peak altitude of individual meteoroid detections, and found decreasing peak altitudes at all locations examined (linear trends varying from −10.97 to −817.95 m decade−1) consistent with a global cooling and contracting of the upper atmosphere. We also examined the response to the 11‐year solar cycle and found a positive correlation with solar activity (i.e., increased meteoroid peak altitudes during solar maximum, and vice versa) for low and mid‐latitude locations. However we found an anti‐correlation at high latitudes suggestive of an important and complex interplay between atmospheric changes and dynamics at varying time scales. Key Points Use of geographically diverse meteor radar peak detection altitudes to assess long‐term and 11‐year solar cycle (SC) trends in mesopause region The altitude of observed peak meteor height has decreased over time at all locations, regardless of latitude and data set Positive correlation at low‐ and mid‐latitude locations with the 11‐year SC, but more complex response at high‐latitudes

The Martian Moons Exploration (MMX) spacecraft is a JAXA mission to Mars and its moons Phobos and Deimos. MMX will be equipped with the Circum-Martian Dust Monitor (CMDM) which is a newly developed light-weight (650g) large area (1m2) dust impact detector. Cometary meteoroid streams (also referred to as trails) exist along the orbits of comets, forming fine structures of the interplanetary dust cloud. The streams consist predominantly of the largest cometary particles (with sizes of approximately 100μm to 1 cm) which are ejected at low speeds and remain very close to the comet orbit for several revolutions around the Sun. The Interplanetary Meteoroid Environment for eXploration (IMEX) dust streams in space model is a new and recently published universal model for cometary meteoroid streams in the inner Solar System. We use IMEX to study the detection conditions of cometary dust stream particles with CMDM during the MMX mission in the time period 2024 to 2028. The model predicts traverses of 12 cometary meteoroid streams with fluxes of 100μm and bigger particles of at least 10-3m-2day-1 during a total time period of approximately 90 days. The highest flux of 0.15m-2day-1 is predicted for comet 114P/Wiseman-Skiff in October 2026. With its large detection area and high sensitivity CMDM will be able to detect cometary meteoroid streams en route to Phobos. Our simulation results for the Mars orbital phase of MMX also predict the occurrence of meteor showers in the Martian atmosphere which may be observable from the Martian surface with cameras on board landers or rovers. Finally, the IMEX model can be used to study the impact hazards imposed by meteoroid impacts onto large-area spacecraft structures that will be particularly necessary for crewed deep space missions.

Advancements in space exploration and sample return technology present a unique opportunity to leverage sample return capsules (SRCs) towards studying atmospheric entry of meteoroids and asteroids. Specifically engineered for the secure transport of valuable extraterrestrial samples from interplanetary space to Earth, SRCs offer unexpected benefits that reach beyond their intended purpose. As SRCs enter the Earth’s atmosphere at hypervelocity, they are analogous to naturally occurring meteoroids and thus, for all intents and purposes, can be considered artificial meteors. Furthermore, SRCs are capable of generating shockwaves upon reaching the lower transitional flow regime, and thus can be detected by strategically positioned geophysical instrumentation. NASA’s OSIRIS-REx (Origins, Spectral Interpretation, Resource Identification, and Security-Regolith Explorer) SRC is one of only a handful of artificial objects to re-enter the Earth’s atmosphere from interplanetary space since the end of the Apollo era and it will provide an unprecedented observational opportunity. This review summarizes past infrasound and seismic observational studies of SRC re-entries since the end of the Apollo era and presents their utility towards the better characterization of meteoroid flight through the atmosphere.

During project STARDUST, a systematic decade-long search for micrometeorites in Norway, over 5500 specimens were recovered. Among them, a micrometeorite labelled NMM/L2, collected from a rooftop in Oslo, Norway, revealed the presence of a previously unknown Al-Cu intermetallic alloy with Al.sub.4 Cu.sub.9 stoichiometry. This new phase has been approved by the IMA Commission on New Minerals, Nomenclature and Classification as a new mineral species with the name jonlarsenite (IMA 2024-078a). The microspherule (â¼200 µm in diameter) exhibits a scoriaceous morphology and mineralogical features consistent with micrometeorites, including the presence of olivine, oxides, Fe-Ni metal beads, and Ca-rich silicate glass. Jonlarsenite occurs as â¼2 µm grains intimately intergrown with Cu-bearing aluminum and is associated with magnesian olivine, spinel, taenite, and silicate glass. Its extraterrestrial origin is revealed by oxygen isotope compositions and chondritic bulk chemistry, similar to previously reported Al- and Cu-bearing meteoritic materials. Characterisation by electron probe microanalysis (EPMA), STEM energy-dispersive X-ray spectrometry (STEM-EDS), and HR-TEM indicated the mineral to be cubic, space group P-43m, with aâ8.70 à and a calculated density of 6.979 g cm.sup.-3 . The ideal chemical formula is Al.sub.4 Cu.sub.9, with minor Fe substituting for both Al and Cu. Selected area electron diffraction (SAED) and high-angle annular dark-field scanning TEM (HAADF-STEM) imaging showed a perfect match with the known ordered structure of synthetic γ-Al.sub.4 Cu.sub.9 . Due to micrometre-scale grain size, physical properties could not be measured. Jonlarsenite expands the suite of known natural intermetallic Al-Cu(-Fe) phases and highlights the significance of micrometeorites as repositories of exotic materials formed under extreme astrophysical conditions.

The ionization heights of meteor trails are strongly dependent on local atmospheric conditions in the mesosphere and lower thermosphere (MLT)-region. We present here latitudinal difference in ionization heights of meteor trails at two distinct latitudes, Thumba (8.5∘N, 77∘E), India and Eureka (80∘N, 85.8∘W), Canada. There is a large seasonal variation in meteor count at high latitude as compared to low latitude. Similarly, there is a large variation in meteor trail ionization heights at high latitudes, but not at low latitudes. However, it noticed that the trail ionisation heights at low latitude are found to be about 2 km higher. The latitudinal differences are probably related to changes in electron line densities at local MLT-regions. The identification of meteoroid streams in the sporadic background is still a noteworthy problem to pursue. By considering ionisation heights of meteor trails as a simple but robust metric, we identified shower meteors from the background sporadic activity, as the ionization heights of shower meteors are different from the sporadic meteors. We apply this shower detection technique on long-term data set at two different latitudes and compared with existing shower calendars. By using the median height of meteor trails and their corresponding upper and lower quartiles (Uq and Lq) as a metric, we unambiguously identified all northern hemisphere showers with a zenithal hourly rate larger than 20, which are in good agreement with the known showers.

We measure group velocity dispersion of surface waves generated by two meteoroid impacts on Mars close to the lander of the InSight mission. This allows us to probe the crustal structure in the first few kilometers beneath the InSight lander. In combination with body wave arrival times from five impact events, we obtain direct seismic constraints on the seismic velocity of the crust in the vicinity of the InSight landing site. We confirm the existence of a uppermost low‐velocity layer with a mean thickness of ∼1.2 km, interpreted as layered volcanic materials, possibly interstratified with sedimentary and altered materials. Our joint inversion of surface and body waves shows a four‐layer model for the Martian crust, compatible with high‐ and low‐frequency P‐to‐S receiver functions estimated in previous studies. Plain Language Summary The knowledge of the crustal structure of Mars is essential for understanding the formation and evolution of the planet. Thanks to the Very Broadband Seismometer of the InSight mission which landed on the surface of Mars (its operational life lasted almost four terrestrial years), seismic signals generated by meteoroid impacts have been recorded. Five craters have been identified by orbital imaging to be located within a circle of ∼250 km radius around the lander. For two of these meteoroid impacts, we measured surface waves for the first time, which are mostly sensitive to the crustal structure in the first kilometers below the InSight lander. Our surface wave analysis, in combination with other measurements, are compatible with a crustal model in the vicinity of the InSight lander made of four layers, with a shallow low velocity layer ∼1.2 km thick. We verified the compatibility of our results with independent observations from previous studies. Key Points Group velocity dispersion generated by two meteoroid impacts (S0986c and S1034a) near the InSight landing site is measured A shallow low‐velocity crustal layer of ∼1.2 km thickness explains both surface wave and body wave observations A four‐layer crustal model is obtained, compatible with surface waves, body waves, and receiver function measurements

The ecological well-being of the Earth is closely connected with the prevention of asteroid-comet-meteoroid hazard. Asteroids and comets are the parent bodies of many meteoroids. Meteoroids, which are observed as meteors in the Earth’s atmosphere, always collide with the Earth. This means that the orbits of such meteoroids can be a signal for the detection of potentially dangerous larger bodies in such orbits. At the same time, the dynamics of the complex of meteoroid orbits has a complex intricate character. Meteor science is also engaged in unraveling the patterns of orbital paths and paths of interplanetary bodies potentially dangerous for life on Earth. A separate section of meteor science is associated with the chemistry of the influx of meteoric matter. The report is devoted to the analysis of the above problems, as well as related issues, using open databases of meteor data and others, with an emphasis on radio data.