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A set of 50,000 artificial Earth impacting asteroids was used to obtain, for the first time, information about the dominance of individual impact effects such as wind blast, overpressure shock, thermal radiation, cratering, seismic shaking, ejecta deposition and tsunami for the loss of human life during an impact event for impactor sizes between 15 to 400 m and how the dominance of impact effects changes over size. Information about the dominance of each impact effect can enable disaster managers to plan for the most relevant effects in the event of an asteroid impact. Furthermore, the analysis of average casualty numbers per impactor shows that there is a significant difference in expected loss for airburst and surface impacts and that the average impact over land is an order of magnitude more dangerous than one over water.
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An asteroid impact is a low probability event with potentially devastating consequences. The Asteroid Risk Mitigation Optimization and Research (ARMOR) software tool calculates whether a colliding asteroid experiences an airburst or surface impact and calculates effect severity as well as reach on the global map. To calculate the consequences of an impact in terms of loss of human life, new vulnerability models are derived that connect the severity of seven impact effects (strong winds, overpressure shockwave, thermal radiation, seismic shaking, ejecta deposition, cratering and tsunamis) with lethality to human populations. With the new vulnerability models ARMOR estimates casualties of an impact under consideration of the local population and geography. The presented algorithms and models are employed in two case studies to estimate total casualties as well as the damage contribution of each impact effect. The case studies highlight that aerothermal effects are most harmful except for deep water impacts, where tsunamis are the dominant hazard. Continental shelves serve a protective function against the tsunami hazard caused by impactors on the shelf. Furthermore, the calculation of impact consequences facilitates asteroid risk estimation to better characterize a given threat and the concept of risk as well as its applicability to the asteroid impact scenario are presented.
The most significant periodicities in the terrestrial impact crater record are due to the human-signal: the bias of assigning integer values for the crater ages. This bias seems to have eluded the proponents and opponents of real periodicity in the occurrence of these events, as well as the theorists searching for an extraterrestrial explanation for such periodicity. The human-signal should be seriously considered by scientists in astronomy, geology and paleontology when searching for a connection between terrestrial major comet or asteroid impacts and mass extinctions of species.
The Asteroid Redirect Mission (ARM) proposes to retrieve a near-Earth asteroid and position it in a lunar distant retrograde orbit (DRO) for later study, crewed exploration, and ultimately resource exploitation. During the Caltech Space Challenge, a recent workshop to design a crewed mission to a captured asteroid in a DRO, it became apparent that the asteroids low escape velocity (<1 cm s$^{-1}$) would permit the escape of asteroid particles during any meaningful interaction with astronauts or robotic probes. This Note finds that up to 5% of escaped asteroid fragments will cross Earth-geosynchronous orbits and estimates the risk to satellites from particle escapes or complete disruption of a loosely bound rubble pile.
Switchbacks (rotations of the magnetic field) are observed on the Parker Solar Probe. Their evolution, content, and plasma effects are studied in this paper. The solar wind does not receive a net acceleration from switchbacks that it encountered upstream of the observation point. The typical switchback rotation angle increased with radial distance. Significant Poynting fluxes existed inside, but not outside, switchbacks and they are related to the increased EXB/B2 flow caused by the magnetic field rotating to become more perpendicular to the flow direction. (Outside the switchbacks, the magnetic field and solar wind flow were generally radial.) The solar wind flow inside switchbacks was faster than that outside due to the frozen-in ions moving with the magnetic structure at the Alfven speed. This energy gain results from the divergence of the Poynting flux from outside to inside the switchback, which produces a loss of electromagnetic energy on switchback entry and recovery of that energy on exit, with the lost energy appearing in the plasma flow. Switchbacks contain 0.3-10 Hz waves that may result from currents and the Kelvin-Helmholtz instability that occurs at the switchback boundaries. These waves may combine with lower frequency MHD waves to heat the plasma. The radial decreases of the Poynting flux and solar wind speed inside switchbacks are due to a geometrical effect.
Eruptive events of solar activity often trigger abrupt variations of the geomagnetic field. Through the induction of electric currents, human infrastructures are also affected, namely the equipment of electric power transmission networks. It was shown in past studies that the rate of power-grid anomalies may increase after an exposure to strong geomagnetically induced currents. We search for a rapid response of devices in the Czech electric distribution grid to disturbed days of high geomagnetic activity. Such disturbed days are described either by the cumulative storm-time $Dst$ or $d(textit{SYM-H})/dt$ low-latitude indices mainly influenced by ring current variations, by the cumulative $AE$ high-latitude index measuring substorm-related auroral current variations, or by the cumulative $ap$ mid-latitude index measuring both ring and auroral current variations. We use superposed epoch analysis to identify possible increases of anomaly rates during and after such disturbed days. We show that in the case of abundant series of anomalies on power lines, the anomaly rate increases significantly immediately (within 1 day) after the onset of geomagnetic storms. In the case of transformers, the increase of the anomaly rate is generally delayed by 2--3 days. We also find that transformers and some electric substations seem to be sensitive to a prolonged exposure to substorms, with a delayed increase of anomalies. Overall, we show that in the 5-day period following the commencement of geomagnetic activity there is an approximately 5--10% increase in the recorded anomalies in the Czech power grid and thus this fraction of anomalies is probably related to an exposure to GICs.
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