Natalia A. Artemieva

Microbial rock inhabitants survive hypervelocity impacts on Mars-like host planets: First phase of lithopanspermia experimentally tested

The scenario of lithopanspermia describes the viable transport of microorganisms via meteorites. To test the first step of lithopanspermia, i.e., the impact ejection from a planet, systematic shock recovery experiments within a pressure range observed in martian meteorites (5-50 GPa) were performed with dry layers of microorganisms (spores of Bacillus subtilis, cells of the endolithic cyanobacterium Chroococcidiopsis, and thalli and ascocarps of the lichen Xanthoria elegans) sandwiched between gabbro discs (martian analogue rock). Actual shock pressures were determined by refractive index measurements and Raman spectroscopy, and shock temperature profiles were calculated. Pressure-effect curves were constructed for survival of B. subtilis spores and Chroococcidiopsis cells from the number of colony-forming units, and for vitality of the photobiont and mycobiont of Xanthoria elegans from confocal laser scanning microscopy after live/dead staining (FUN-I). A vital launch window for the transport of rock-colonizing microorganisms from a Mars-like planet was inferred, which encompasses shock pressures in the range of 5 to about 40 GPa for the bacterial endospores and the lichens, and a more limited shock pressure range for the cyanobacterium (from 5-10 GPa). The results support concepts of viable impact ejections from Mars-like planets and the possibility of reseeding early Earth after asteroid cataclysms.

Efficient disruption of small asteroids by Earth's atmosphere

Accurate modelling of the interaction between the atmosphere and an incoming bolide is a complex task, but crucial to determining the fraction of small asteroids that actually hit the Earths surface. Most semi-analytical approaches have simplified the problem by considering the impactor as a strengthless liquid-like object (‘pancake’ models), but recently a more realistic model has been developed that calculates motion, aerodynamic loading and ablation for each separate particle or fragment in a disrupted impactor. Here we report the results of a large number of simulations in which we use both models to develop a statistical picture of atmosphere–bolide interaction for iron and stony objects with initial diameters up to ∼1 km. We show that the separated-fragments model predicts the total atmospheric disruption of much larger stony bodies than previously thought. In addition, our data set of >1,000 simulated impacts, combined with the known pre-atmospheric flux of asteroids with diameters less than 1 km, elucidates the flux of small bolides at the Earths surface. We estimate that bodies >220 m in diameter will impact every 170,000 years.

Starting Conditions for Hydrothermal Systems Underneath Martian Craters: Hydrocode Modeling

Mars is the most Earth-like of the Solar System s planets, and the first place to look for any sign of present or past extraterrestrial life. Its surface shows many features indicative of the presence of surface and sub-surface water, while impact cratering and volcanism have provided temporary and local surface heat sources throughout Mars geologic history. Impact craters are widely used ubiquitous indicators for the presence of sub-surface water or ice on Mars. In particular, the presence of significant amounts of ground ice or water would cause impact-induced hydrothermal alteration at Martian impact sites. The realization that hydrothermal systems are possible sites for the origin and early evolution of life on Earth has given rise to the hypothesis that hydrothermal systems may have had the same role on Mars. Rough estimates of the heat generated in impact events have been based on scaling relations, or thermal data based on terrestrial impacts on crystalline basements. Preliminary studies also suggest that melt sheets and target uplift are equally important heat sources for the development of a hydrothermal system, while its lifetime depends on the volume and cooling rate of the heat source, as well as the permeability of the host rocks. We present initial results of two-dimensional (2D) and three-dimensional (3D) simulations of impacts on Mars aimed at constraining the initial conditions for modeling the onset and evolution of a hydrothermal system on the red planet. Simulations of the early stages of impact cratering provide an estimate of the amount of shock melting and the pressure-temperature distribution in the target caused by various impacts on the Martian surface. Modeling of the late stage of crater collapse is necessary to characterize the final thermal state of the target, including crater uplift, and distribution of the heated target material (including the melt pool) and hot ejecta around the crater.Introduction: Mars is the most Earth-like of the Solar System’s planets, and the first place to look for any sign of present or past extraterrestrial life. Its surface shows many features indicative of the presence of surface and sub-surface water [1], while impact cratering and volcanism have provided temporary and local surface heat sources throughout Mars geologic history. Impact craters are widely used ubiquitous indicators for the presence of sub-surface water or ice on Mars [2]. In particular, the presence of significant amounts of ground ice or water would cause impactinduced hydrothermal alteration at Martian impact sites [3]. The realization that hydrothermal systems are possible sites for the origin and early evolution of life on Earth [4,5,6] has given rise to the hypothesis that hydrothermal systems may have had the same role on Mars [7,8,9,10]. Rough estimates of the heat generated in impact events have been based on scaling relations [11,12], or thermal data based on terrestrial impacts on crystalline basements [13]. Preliminary studies [14,15] also suggest that melt sheets and target uplift are equally important heat sources for the development of a hydrothermal system, while its lifetime depends on the volume and cooling rate of the heat source, as well as the permeability of the host rocks. We present initial results of two-dimensional (2D) and three-dimensional (3D) simulations of impacts on Mars aimed at constraining the initial conditions for modeling the onset and evolution of a hydrothermal system on the red planet. Simulations of the early stages of impact cratering provide an estimate of the amount of shock melting and the pressure-temperature distribution in the target caused by various impacts on the Martian surface. Modeling of the late stage of crater collapse is necessary to characterize the final thermal state of the target, including crater uplift, and distribution of the heated target material (including the melt pool) and hot ejecta around the crater.

An experimental assessment of the ignition of forest fuels by the thermal pulse generated by the Cretaceous-Palaeogene impact at Chicxulub

A large extraterrestrial body hit the Yucatán Peninsula at the end of the Cretaceous period. Models suggest that a substantial amount of thermal radiation was delivered to the Earth’s surface by the impact, leading to the suggestion that it was capable of igniting extensive wildfires and contributed to the end-Cretaceous extinctions. We have reproduced in the laboratory the most intense impact-induced heat fluxes estimated to have reached different points on the Earth’s surface using a fire propagation apparatus and investigated the ignition potential of forest fuels. The experiments indicate that dry litter can ignite, but live fuels typically do not, suggesting that any ignition caused by impact-induced thermal radiation would have been strongly regional dependent. The intense, but short-lived, pulse downrange and at proximal and intermediate distances from the impact is insufficient to ignite live fuel. However, the less intense but longer-lasting thermal pulse at distal locations may have ignited areas of live fuels. Because plants and ecosystems are generally resistant to single localized fire events, we conclude that any fires ignited by impact-induced thermal radiation cannot be directly responsible for plant extinctions, implying that heat stress is only part of the end-Cretaceous story.

Expansion, radiation and condensation of vapor cloud, created by high-velocity impact onto a target in vacuum

Summary The results of numerical simulations of small meteoroid impacts against the rocky lunar surface are presented which give an estimate of impact luminous efficiency. The obtained values of luminosity can considerably differ from the real ones because of the influence of regolith. Specific features of impacts into the regolith are discussed and a simple model discribing the shock wave structure in the porous target is proposed.

Quantifying the Release of Climate‐Active Gases by Large Meteorite Impacts With a Case Study of Chicxulub

Potentially hazardous asteroids and comets have hit Earth throughout its history, with catastrophic consequences in the case of the Chicxulub impact. Here we reexamine one of the mechanisms that allow an impact to have a global effect—the release of climate-active gases from sedimentary rocks. We use the SOVA hydrocode and model ejected materials for a sufficient time after impact to quantify the volume of gases that reach high enough altitudes (> 25 km) to have global consequences. We vary impact angle, sediment thickness and porosity, water depth, and shock pressure for devolatilization and present the results in a dimensionless form so that the released gases can be estimated for any impact into a sedimentary target. Using new constraints on the Chicxulub impact angle and target composition, we estimate that 325 ± 130 Gt of sulfur and 425 ± 160 Gt CO2 were ejected and produced severe changes to the global climate.

HIGH-VELOCITY IMPACT EJECTA: TEKTITES AND MARTIAN METEORITES

Earth retains the poorest record of impact craters through geologic time. Important clues of the occurrence of large impact events through Earth’s geologic history come from the presence of preserved distal ejecta layers. Distal ejecta comprise a small but essential fraction of material ejected in impacts; it was crucial in the recognition of the end-Cretaceous impact event (Alvarez et al. 1980). This chapter discusses specific types of distal ejecta, which are characterized by substantial shock compression, and high ejection velocity, and are best represented by the enigmatic tektites and Martian–lunar meteorites. Tektites are naturally occurring glasses, generally a few centimeters in diameter, currently found in four distinct strewn fields (Table 1). Microtektites (<1 mm in diameter) have been found in deep-sea cores of three of the four strewn fields (Glass 1972). Tektites of a given strewn field are related to each other by their chemistry, age, and petrologic and physical characteristics (see reviews by Glass 1990; Koeberl 1990, 1994). There is numerous evidence that tektites were used by ancient civilizations. However, their scientific study began with Charles Darwin’s description of Australites in Geology of the Voyage of the Beagle (1851). Early hypotheses of their origin (volcanic glass, impact of glassy asteroid, ablation of high-velocity cosmic body in the Earth’s atmosphere, and

Marine Target Impacts

Most cosmic bodies impacting the Earth fall into seas and oceans, which cover more than two-thirds of the Earth’s surface. However, among more than 150 craters discovered on the Earth, only 15–20 found recently were formed as a result of marine target impacts (Ormo and Lindstrom 2000). The deficit of underwater craters is explained by the relative youth of a typical ocean floor (<150–180 Ma), insufficient exploration of the sea/ocean floor, and specific features of the underwater cratering process. Most of the known underwater craters were formed in shallow seas, where the water depth is comparable with an impactor size. Eltanin (Gersonde et al. 1997) is the only presently known impact structure formed due to impact into a deep (∼4 km) ocean. The process of cratering of marine target impacts has been poorly investigated; however, relations obtained for continental craters are commonly used to estimate the parameters of underwater craters. A small number of numerical simulations were performed for the first stage of marine impacts of very large projectiles (∼10 km), which are of interest from the viewpoint of impact-induced mass extinctions of biota (O’Keefe and Ahrens 1982b; Roddy et al. 1987). However, these simulations gave neither the shape of a final crater nor the parameters of generated tsunami waves. Laboratory experiments (Gault and Sonnet 1982) and detailed numerical simulations (Artemieva and Shuvalov 2002) made it possible to determine the critical sea depth at which an underwater crater is formed at the sea floor and where shock-modified material can be found. A number of works (Adushkin and Nemchinov 1994; Hills et al. 1994; Nemtchinov et al. 1996) used the estimates based on nuclear explosion data and the numerical modeling of the impact initial phase to study tsunami generation caused by the impact of a comet into an ocean 4 km in depth.

Effects of Moon's Thermal State on the Impact Basin Ejecta Distribution

We investigate how different temperature gradients of the Moon affect the ejection of lithic and molten materials for impact basin several hundred kilometers in diameter to quantify the thickness and melt content of ejecta blanket as a function of radial distance. We find, by means of numerical modeling, that the ejecta thickness and melt content, similar to the basin formation, is sensitive to the thermal properties of the target. For two similar impact scenarios, the ejecta thickness with radial distance is proportional to a power law, but for a “warm” target, it declines faster than for a “cold” target. In addition, the impact on the warm target produces more molten ejecta than in the case of the cold target. The thermal effects on the ejecta thickness distribution can be testified by the topographic variations around Imbrium and Orientale basins, which were thought to be formed on a warm and cold Moon, respectively. Our study demonstrates that the thermal effect needs to be taken into account to estimate the ejecta thickness distribution for large-scale impact basins on airless planetary surfaces.