V. V. Shuvalov

Chelyabinsk airburst, damage assessment, meteorite recovery, and characterization

Deep Impact? On 15 February 2013, the Russian district of Chelyabinsk, with a population of more than 1 million, suffered the impact and atmospheric explosion of a 20-meter-wide asteroid—the largest impact on Earth by an asteroid since 1908. Popova et al. (p. 1069, published online 7 November; see the Perspective by Chapman) provide a comprehensive description of this event and of the body that caused it, including detailed information on the asteroid orbit and atmospheric trajectory, damage assessment, and meteorite recovery and characterization. A detailed study of a recent asteroid impact provides an opportunity to calibrate the damage caused by these rare events. [Also see Perspective by Chapman] 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.

Numerical modeling of Tunguska-like impacts

Abstract A two-dimensional numerical model with radiation and ablation is developed for the study of the impact of rather large (several meters or several tens of meters) meteoroids. This model is applied to consider the vertical impact of a 30 m in radius cometary projectile. Numerical simulations clearly demonstrate the two main stages in the meteoroids evolution. During the first stage the falling body is deformed, flattened and finally transformed into a high velocity debris jet. At the second stage the elongated debris jet is decelerated, and the most of impact energy is released. After the full stop of the jet at an altitude of about 4 km the formation of rarefied entry column is completed. Hot air and vapor in the entry column accelerate upwards and form a ballistic plume. Deceleration of the plume by gravity, fall-back and deceleration of plume material near the 100 km level, lead to the formation of a disk-shaped area of compressed and heated gas. These perturbations, with a scale of about 1000 km , are believed to be responsible for the geomagnetic effect detected by Irkutsk observatory after the Tunguska event.

3D hydrodynamic code sova for multimaterial flows, application to Shoemakerlevy 9 comet impact problem

Summary A totally conservative Eulerian 3D numerical code which conserves mass, momentum and energy both in the source and remap steps is developed. Mass, momentum and kinetic energy are conserved simultaneously during the remapping. The use of special form of linear viscosity makes the code more tolerant to the time step, leaving the second order of accuracy. Multimaterial flows including those contaminated by dust particles may be investigated using this program. The performance of the code is illustrated by modeling the Shoemaker-Levy 9 impact against Jupiter. Penetration of nonuniform fragments with complex structure into the Jovian atmosphere is investigated.

Hydrocode Simulation of the Lockne Marine Target Impact Event

In this study 2D and 3D numerical simulations are used to model the formation of the Lockne crater (centered at 63°00′20″ N, 14°49′30″E) during Middle Ordovician times, about 455 Ma ago. We study a possible mechanism of shallow excavation to explain the concentric structure of the crater, as well as the interaction between basement the ejecta curtain and the water ejecta curtain, to explain the final ejecta distribution on the Earth’s surface. We also consider different angles of trajectory inclination to understand how obliquity can influence the cratering flow in a marine target impact. Comparison between the results of numerical simulations and field studies allows us to estimate a water depth at the time of the impact of about 700–900 m.

Numerical simulation of high-velocity impact ejecta following falls of comets and asteroids onto the Moon

High-velocity comet and asteroid impacts onto the Moon are considered and the material masses ejected after such impacts at velocities above the second-cosmic velocity for the Moon (2.4 km/s) are calculated. Although the results depend on a projectile type and the velocity and angle of an impact, it has been demonstrated that, on average, the lunar mass decreases with time. The Moon has lost about 5 × 1018 kg, that is, about one-hundredth of a percent of its mass, over the last 3.8–3.9 billion years. The ejection of lunar meteorites and lunar dust, rich in 3He, is considered as well. The results of the study are compared to the results of earlier computations and data on lunar meteorites.

Atmospheric erosion and radiation impulse induced by impacts

Two effects of Chicxulub-scale impacts are considered: radiation impulse and impact-induced atmospheric erosion. Detailed numerical simulations show that radiation of the Chicxulub impact plume could be responsible for igniting wildfires over 3%–10% of the Earth’s surface, close to the impact point. Atmospheric erosion is calculated based on detailed numerical modeling of all stages of the impact, including the flight through the atmosphere, cratering, and plume evolution. The mass of escaping air is found to be smaller than predicted by previous investigations. Preliminary results of three-dimensional numerical simulations show that oblique impacts are more effective from the viewpoint of atmospheric erosion. Shuvalov, V.V., and Artemieva, N.A., 2002, Atmospheric erosion and radiation impulse induced by impacts, in Koeberl, C., and MacLeod, K.G., eds., Catastrophic Events and Mass Extinctions: Impacts and Beyond: Boulder, Colorado, Geological Society of America Special Paper 356, p. 695–703. *E-mail: shuvalov@idg.chph.ras.ru INTRODUCTION Impacts of large cosmic bodies played a great role in the evolution of the Earth (Melosh, 1989). An individual impact could cause local and global changes in the atmosphere, hydrosphere, and solid Earth, could influence the Earth’s biosphere, and could even lead to mass extinctions (Silver and Schultz, 1982; Sharpton and Ward, 1990; Toon et al., 1997). The time scale of these effects is 10 yr or less; they may be referred to as short term in the history of Earth. Impacts as a whole controlled the formation and evolution of the solid Earth, its hydrosphere, and atmosphere during the period of heavy bombardment 4.5–3.5 b.y. before present and possibly later. These are long-term effects ( 1 m.y.). In this chapter we consider two effects resulting from large impacts: the radiation impulse (short term) and atmospheric erosion (long term). Light impulse and following global wildfires resulting from the Chicxulub-scale impact are considered as a probable reason for global changes in the biosphere (Toon et al., 1997). Radiation is emitted both by the entering impactor and by the hot air-vapor cloud, or plume, expanding through the Earth’s atmosphere just after the impact. Moreover, Schultz and Gault (1982, 1990) and Melosh et al. (1990) proposed that global wildfires would be caused by the radiation generated due to ejecta reentry. The impacts of large cosmic bodies ( 100 m) could substantially influence the evolution of planetary atmospheres (Lange and Ahrens, 1982; Matsui and Abe, 1986; Ahrens et al., 1989; Melosh and Vickery, 1989; Vickery and Melosh, 1990; Zahnle et al., 1992). The growth of the atmospheric mass was defined by the release of volatiles in the impact process. At the same time some portion of atmospheric gas could be accelerated by the shock wave resulting from the expansion of vapor plume and escape from the Earth. The influence of a single impact can be negligible, but a great number of impacts in the history of the Earth are believed to have affected the evolution of the atmosphere. In order to study radiation effects and atmospheric erosion we performed detailed numerical simulations of the main stages of large impacts, including the flight through the atmosphere, cratering, plume expansion, and shock-wave propagation through the ambient air. The SOVA (solid air vapor) multiV.V. Shuvalov and N.A. Artemieva 696 material hydrocode (Shuvalov, 1999a) is used to model the impacts of 10–30-km-diameter cosmic bodies (both comets and asteroids) with velocities ranging from 20 to 50 km/s. SOVA is an Eulerian material response code with some Lagrangian features. It allows a consideration of strong hydrodynamic flows with accurate description of the boundaries between different materials (e.g., soil, gas, water). The code is similar in concept to the CTH hydrocode (McGlaun et al., 1990), which is widely used in the United States. ANEOS (analytical equation of state, Thompson and Lauson, 1972) and Tillotson (1962) equations of state are used to describe the thermodynamical properties of water and solids. Detailed tables of thermodynamical and optical properties of air (Kuznetsov, 1965) and Hchondrite vapor (Kosarev et al., 1996) are applied to calculate the radiation fluxes. The computational grid consists of 30

Radiation emitted during the flight of asteroids and comets through the atmosphere

Abstract The radiation emitted during the flight of a cosmic body through the atmosphere is an important factor in the bodys interaction with a planet. A variety of radiation aspects are considered in this paper. Altitudes of interest here range from the dense atmosphere to above 100 km where nonequilibrium and nonstationary ionic kinetic and molecular dynamics play an important role. Structure, intensity and the spectrum of radiative shock waves generated in the atmospheres of the Earth and Mars are investigated on the basis of the detailed numerical simulations. Ignition of fires, creation of a thin thermal layer at the ground, which essentially changes flow pattern after the impact, and contamination of the atmosphere by soot, aerosols and dust may pose a threat to humanity. These problems are also considered. Registered radiation of 1–10 m bodies can supply the necessary data on their properties and refine size-frequency curves. A relatively simple method to obtain the body characteristics in flight is developed and some observational data are analyzed. In the proposed scenario the body is heavily fragmented and intensely radiates due to an increase of its effective area.

Aerial bursts in the terrestrial atmosphere

Impacts of cosmic bodies (stony and comet-like) are considered that “burn out” (or, more strictly, totally evaporate) in the atmosphere, which do not form craters but cause fires and destruction on the Earth’s surface. The heights of fragmentation, total evaporation, and deceleration of stony and comet-like meteoroids of different sizes, initial velocities, and impact angles are found from numerical simulations. The possible consequences of such falls are considered. The possible parameters of the Tunguska cosmic body are estimated.

Numerical Modeling of Marine Target Impacts

The principles of the numerical modeling of marine impacts of large cosmic bodies are described. Three underwater impact structures, MjØlnir, Lockne, and Eltanin, are considered with the aim of studying the characteristics of the crater formation at varying sea depths; the distinctions between the underwater and continental craters are discussed. The mechanisms for tsunami-wave generation are studied at different ratios of sea depth to impactor size. The calculation results are compared to the experimental data obtained during underwater nuclear explosions.

Numerical simulation of the LCROSS impact experiment

This study presents the results of the numerical modeling of the Lunar Crater Observation and Sensing Satellite (LCROSS) space experiment, which is scheduled for 2009 by NASA. It is demonstrated that a spacecraft with a mass of 2 tons impacting the Moon at a velocity of 2.5 km/s creates an ejecta plume with a size of more than 100 km and a mass exceeding 100 tons. The detailed characteristics of the ejecta are given and their relation to the impactor structure is investigated.