Asteroid Risk Assessment: A Probabilistic Approach.

Following the 2013 Chelyabinsk event, the risks posed by asteroids attracted renewed interest, from both the scientific and policy-making communities. It reminded the world that impacts from near-Earth objects (NEOs), while rare, have the potential to cause great damage to cities and populations. Point estimates of the risk (such as mean numbers of casualties) have been proposed, but because of the low-probability, high-consequence nature of asteroid impacts, these averages provide limited actionable information. While more work is needed to further refine its input distributions (e.g., NEO diameters), the probabilistic model presented in this article allows a more complete evaluation of the risk of NEO impacts because the results are distributions that cover the range of potential casualties. This model is based on a modularized simulation that uses probabilistic inputs to estimate probabilistic risk metrics, including those of rare asteroid impacts. Illustrative results of this analysis are presented for a period of 100 years. As part of this demonstration, we assess the effectiveness of civil defense measures in mitigating the risk of human casualties. We find that they are likely to be beneficial but not a panacea. We also compute the probability-but not the consequences-of an impact with global effects ("cataclysm"). We conclude that there is a continued need for NEO observation, and for analyses of the feasibility and risk-reduction effectiveness of space missions designed to deflect or destroy asteroids that threaten the Earth.

Chelyabinsk airburst, damage assessment, meteorite recovery, and characterization.

The asteroid impact near the Russian city of Chelyabinsk on 15 February 2013 was the largest airburst on Earth since the 1908 Tunguska event, causing a natural disaster in an area with a population exceeding one million. Because it occurred in an era with modern consumer electronics, field sensors, and laboratory techniques, unprecedented measurements were made of the impact event and the meteoroid that caused it. Here, we document the account of what happened, as understood now, using comprehensive data obtained from astronomy, planetary science, geophysics, meteorology, meteoritics, and cosmochemistry and from social science surveys. A good understanding of the Chelyabinsk incident provides an opportunity to calibrate the event, with implications for the study of near-Earth objects and developing hazard mitigation strategies for planetary protection.

Chaotic exchange of solid material between planetary systems: implications for lithopanspermia.

We examined a low-energy mechanism for the transfer of meteoroids between two planetary systems embedded in a star cluster using quasi-parabolic orbits of minimal energy. Using Monte Carlo simulations, we found that the exchange of meteoroids could have been significantly more efficient than previously estimated. Our study is relevant to astrobiology, as it addresses whether life on Earth could have been transferred to other planetary systems in the Solar System's birth cluster and whether life on Earth could have been transferred from beyond the Solar System. In the Solar System, the timescale over which solid material was delivered to the region from where it could be transferred via this mechanism likely extended to several hundred million years (as indicated by the 3.8-4.0 Ga epoch of the Late Heavy Bombardment). This timescale could have overlapped with the lifetime of the Solar birth cluster (∼100-500 Myr). Therefore, we conclude that lithopanspermia is an open possibility if life had an early start. Adopting parameters from the minimum mass solar nebula, considering a range of planetesimal size distributions derived from observations of asteroids and Kuiper Belt objects and theoretical coagulation models, and taking into account Oort Cloud formation models, we discerned that the expected number of bodies with mass>10 kg that could have been transferred between the Sun and its nearest cluster neighbor could be of the order of 10(14) to 3·10(16), with transfer timescales of tens of millions of years. We estimate that of the order of 3·10(8)·l (km) could potentially be life-bearing, where l is the depth of Earth's crust in kilometers that was ejected as the result of the early bombardment.

Discovery of extra-terrestrial life: assessment by scales of its importance and associated risks.

The Rio Scale accepted by the SETI Committee of the International Academy of Astronautics in 2002 is intended for use in evaluating the impact on society of any announcement regarding the discovery of evidence of extra-terrestrial (ET) intelligence. The Rio Scale is mathematically defined using three parameters (class of phenomenon, type of discovery and distance) and a δ factor, the assumed credibility of a claim. This paper proposes a new scale applicable to announcements alleging evidence of ET life within or outside our Solar System. The London Scale for astrobiology has mathematical structure and logic similar to the Rio Scale, and uses four parameters (life form, nature of phenomenon, type of discovery and distance) as well as a credibility factor δ to calculate a London Scale index (LSI) with values ranging from 0 to 10. The level of risk or biohazard associated with a purported discovery is evaluated independently of the LSI value and may be ranked in four categories. The combined information is intended to provide a scalar assessment of the scientific importance, validity and potential risks associated with putative evidence of ET life discovered on Earth, on nearby bodies in the Solar System or in our Galaxy.

Quantitative colorimetric-imaging analysis of nickel in iron meteorites.

A quantitative analytical imaging approach for determining the nickel content of metallic meteorites is proposed. The approach uses a digital image of a series of standard solutions of the nickel-dimethylglyoxime coloured chelate and a meteorite sample solution subjected to the same treatment as the nickel standards for quantitation. The image is processed with suitable software to assign a colour-dependent numerical value (analytical signal) to each standard. Such a value is directly proportional to the analyte concentration, which facilitates construction of a calibration graph where the value for the unknown sample can be interpolated to calculate the nickel content of the meteorite. The results thus obtained were validated by comparison with the official, ISO-endorsed spectrophotometric method for nickel. The proposed method is fairly simple and inexpensive; in fact, it uses a commercially available digital camera as measuring instrument and the images it provides are processed with highly user-friendly public domain software (specifically, ImageJ, developed by the National Institutes of Health and freely available for download on the Internet). In a scenario dominated by increasingly sophisticated and expensive equipment, the proposed method provides a cost-effective alternative based on simple, robust hardware that is affordable and can be readily accessed worldwide. This can be especially advantageous for countries were available resources for analytical equipment investments are scant. The proposed method is essentially an adaptation of classical chemical analysis to current, straightforward, robust, cost-effective instrumentation.

The asteroid and comet impact hazard: risk assessment and mitigation options.

The impact of extraterrestrial matter onto Earth is a continuous process. On average, some 50,000 tons of dust are delivered to our planet every year. While objects smaller than about 30 m mainly disintegrate in the Earth's atmosphere, larger ones can penetrate through it and cause damage on the ground. When an object of hundreds of meters in diameter impacts an ocean, a tsunami is created that can devastate coastal cities. Further, if a km-sized object hit the Earth it would cause a global catastrophe due to the transport of enormous amounts of dust and vapour into the atmosphere resulting in a change in the Earth's climate. This article gives an overview of the near-Earth asteroid and comet (near-Earth object-NEO) impact hazard and the NEO search programmes which are gathering important data on these objects. It also points out options for impact hazard mitigation by using deflection systems. It further discusses the critical constraints for NEO deflection strategies and systems as well as mitigation and evacuation costs and benefits. Recommendations are given for future activities to solve the NEO impact hazard problem.

Lithopanspermia in star-forming clusters.

This paper considers the lithopanspermia hypothesis in star-forming groups and clusters, where the chances of biological material spreading from one solar system to another is greatly enhanced (relative to action in the field) because of the close proximity of the systems and lower relative velocities. These effects more than compensate for the reduced time spent in such crowded environments. This paper uses approximately 300,000 Monte Carlo scattering calculations to determine the cross sections for rocks to be captured by binaries and provides fitting formulae for other applications. We assess the odds of transfer as a function of the ejection speed v (eject) and number N(.) of members in the birth aggregate. The odds of any given ejected meteoroid being recaptured by another solar system are relatively low, about 1:10(3)-10(6) over the expected range of ejection speeds and cluster sizes. Because the number of ejected rocks (with mass m > 10 kg) per system can be large, N (R) approximately 10(16), virtually all solar systems are likely to share rocky ejecta with all of the other solar systems in their birth cluster. The number of ejected rocks that carry living microorganisms is much smaller and less certain, but we estimate that N (B) approximately 10(7) rocks can be ejected from a biologically active solar system. For typical birth environments, the capture of life-bearing rocks is expected to occur N (bio) asymptotically equal to 10-16,000 times (per cluster), depending on the ejection speeds. Only a small fraction (f (imp) approximately 10(4)) of the captured rocks impact the surfaces of terrestrial planets, so that N (lps) asymptotically equal to 10(3)-1.6 lithopanspermia events are expected per cluster (under favorable conditions). Finally, we discuss the question of internal versus external seeding of clusters and the possibility of Earth seeding young clusters over its biologically active lifetime.

International Academy of Astronautics 5th cosmic study--preparing for a 21st century program of integrated, Lunar and Martian exploration and development (executive summary).

This report is an initial review of plans for a extensive program to survey and develop the Moon and to explore the planet Mars during the 21st century. It presents current typical plans for separate, associated and fully integrated programs of Lunar and Martian research, exploration and development, and concludes that detailed integrated plans must be prepared and be subject to formal criticism. Before responsible politicians approve a new thrust into space they will demand attractive, defensible, and detailed proposals that explain the WHEN, HOW and WHY of each stage of an expanded program of 21st century space research, development and exploration. In particular, the claims of daring, innovative, but untried systems must be compared with the known performance of existing technologies. The time has come to supersede the present haphazard approach to strategic space studies with a formal international structure to plan for future advanced space missions under the aegis of the world's national space agencies, and supported by governments and the corporate sector.

Hydrothermal systems on Mars: an assessment of present evidence.

Hydrothermal processes have been suggested to explain a number of observations for Mars, including D/H ratios of water extracted from Martian meteorites, as a means for removing CO2 from the Martian atmosphere and sequestering it in the crust as carbonates, and as a possible origin for iron oxide-rich spectral units on the floors of some rifted basins (chasmata). There are numerous examples of Martian channels formed by discharges of subsurface water near potential magmatic heat sources, and hydrothermal processes have also been proposed as a mechanism for aquifer recharge needed to sustain long term erosion of sapping channels. The following geological settings have been identified as targets for ancient hydrothermal systems on Mars: channels located along the margins of impact crater melt sheets and on the slopes of ancient volcanoes; chaotic and fretted terranes where shallow subsurface heat sources are thought to have interacted with ground ice; and the floors of calderas and rifted basins (e.g. chasmata). On Earth, such geological environments are often a locus for hydrothermal mineralization. But we presently lack the mineralogical information needed for a definitive evaluation of hypotheses. A preferred tool for identifying minerals by remote sensing methods on Earth is high spatial resolution, hyperspectral, near-infrared spectroscopy, a technique that has been extensively developed by mineral explorationists. Future efforts to explore Mars for ancient hydrothermal systems would benefit from the application of methods developed by the mining industry to look for similar deposits on Earth. But Earth-based exploration models must be adapted to account for the large differences in the climatic and geological history of Mars. For example, it is likely that the early surface environment of Mars was cool, perhaps consistently below freezing, with the shallow portions of hydrothermal systems being dominated by magma-cryosphere interactions. Given the smaller gravitational field, declining atmospheric pressure, and widespread, permeable megaregolith on Mars, volatile outgassing and magmatic cooling would have been more effective than on Earth. Thus, hydrothermal systems are likely to have had much lower average surface temperatures than comparable geological settings on Earth. The likely predominance of basaltic crust on Mars suggests that hydrothermal fluids and associated deposits should be enriched in Fe, Mg, Si and Ca, with surficial deposits being dominated by lower temperature, mixed iron oxide and carbonate mineralogies.

Influx of cometary volatiles to planetary moons: the atmospheres of 1000 possible Titans.

We use a Monte Carlo model to simulate impact histories of possible Titans, Callistos, and Ganymedes. Comets create or erode satellite atmospheres, depending on their mass and velocity distributions: faster and bigger comets remove atmophiles; slower or smaller comets supply them. Mass distributions and the minimum total mass of comets passing through the Saturn system were derived from the crater records of Rhea and Iapetus. These were then scaled to give a minimum impact history for Titan. From this cometary population, of 1000 initially airless Titans, 16% acquired atmospheres larger than Titan's present atmosphere (9 x 10(21) g), and more than half accumulated atmospheres larger than 10(21) g. In contrasts to the work of Zahnle et al. (1992), we find that, in most trials, Callisto acquires comet-based atmospheres. Atmospheres acquired by Callisto and, especially, Ganymede are sensitive to assumptions regarding energy partitioning into the ejecta plume. If we assume that only the normal velocity component heats the plume, the majority of Ganymedes and half of the Callistos accreted atmospheres smaller than 10(20) g. If all the impactor's velocity heats the plume, Callisto's most likely atmosphere is 10(17) g and Ganymede's is negligible. The true cometary flux was most likely larger than that derived from crater records, which raises the probability that Titan, Ganymede, and Callisto acquired substantial atmospheres. However, other loss processes (e.g., sputtering by ions swept up by the planetary magnetic field, solar UV photolysis of hydrocarbons) are potentially capable of eliminating small atmospheres over the age of the solar system. The dark material on Callisto's surface may be a remnant of an earlier, now vanished atmosphere.

Possible consequences of absence of "Jupiters" in planetary systems.

The formation of the gas giant planets Jupiter and Saturn probably required the growth of massive approximately 15 Earth-mass cores on a time scale shorter than the approximately 10(7) time scale for removal of nebular gas. Relatively minor variations in nebular parameters could preclude the growth of full-size gas giants even in systems in which the terrestrial planet region is similar to our own. Systems containing "failed Jupiters," resembling Uranus and Neptune in their failure to capture much nebular gas, would be expected to contain more densely populated cometary source regions. They will also eject a smaller number of comets into interstellar space. If systems of this kind were the norm, observation of hyperbolic comets would be unexpected. Monte Carlo calculations of the orbital evolution of region of such systems (the Kuiper belt) indicate that throughout Earth history the cometary impact flux in their terrestrial planet regions would be approximately 1000 times greater than in our Solar System. It may be speculated that this could frustrate the evolution of organisms that observe and seek to understand their planetary system. For this reason our observation of these planets in our Solar System may tell us nothing about the probability of similar gas giants occurring in other planetary systems. This situation can be corrected by observation of an unbiased sample of planetary systems.