Ivan V. Nemtchinov

Light Flashes Caused by Leonid Meteoroid Impacts on the Lunar Surface

In November 1999, light flashes were recorded on the Moon at the peak of the Leonid stream activity. It is likely that they were produced by the impacts of the stream particles on the lunar surface. In the present work the impacts of cometary particles are studied by solving a two-dimensional radiative-gasdynamic problem for particles of different sizes and densities; the flux of radiation of postimpact hot gas and plasma is calculated, and the luminous efficiencies are estimated, as are the sizes of the particles which could produce the observed flashes.

Mobilization of dust on the Mars surface by the impact of small cosmic bodies

The Impact of small cosmic bodies on the Martian surface may be the cause of local sand storms. The interaction of the shock waves with the thermal layer (created by the action of thermal radiation to the surface) leads to the formation of a high-velocity jet moving along the surface. A reverse vortex in the precursor facilitates dust lifting. This and other factors lead to the dust rising: outgassing of the surface layer due to heating by the radiation impulse; intrusion of the high-pressure atmospheric gas behind the shock wave into the regolith and dust layer and subsequent blow off in the rarefaction wave; and formation of jets moving along the surface due to interaction of the ballistic wave with the blast wave and due to erosion by high-velocity impulsive winds behind the shock wave of the explosion. The results of preliminary theoretical simulations and laboratory modeling are presented.

Analysis of Satellite Observations of Large Meteoroid Impacts

ABSTRACT: Observations from high altitude (> 20,000 km) space‐based infrared and optical sensors which have detected over 200 bright flashes in the atmosphere since 1972 are interpreted in terms of geographical distribution, lightcurves, aerodynamic interaction of the fragments, and heat transfer and luminosity coefficients. The luminosity efficiency for meteorite explosive disintegration is estimated to be about 2 to 3 times smaller than for energetically equivalent nuclear explosions. Explanations for this difference are offered.

Impacts of Large Planetesimals on the Early Earth

We considered the impacts of very large cosmic bodies (with radii in the range 100–200 to 1000–2000 km) on the early Earth, whose mass, radius and density distribution are close to the current values. The impacts of such bodies were possible during the first hundreds of million years after the formation of the Earth and the Moon. We present and analyze the results of a numerical simulation of the impact of a planetesimal, the size of which is equal to that of the contemporary Moon (1700 km). In three-dimensional computations, the velocity (15 and 30 km/s) and the angle (45°, 60°, and 90°) of the impact are varied. We determined the mass losses and traced the evolution of the shape of the Earths surface, taking into account the self-consistent gravitational forces that arise in the ejected and remaining materials in accordance with the real, time-dependent mass distribution. Shock waves reflected from the core are shown to propagate from the impact site deep into the Earth. The core undergoes strong, gradually damped oscillations. Although motions in the Earths mantle gradually decline, they have enough time to put the Earth in a rotational motion. As a result, a wave travels over the Earths surface, whose amplitude, in the case of an oblique impact, depends on the direction of the wave propagation. The maximum height of this wave is tremendous—it attains several hundred kilometers. Some portion of the ejected material (up to 40% of the impactor mass) falls back onto Earth under the action of gravity. This portion is equivalent to the layer of a condensed material with a thickness on the order of ten kilometers. The appearance of this hot layer should result in a global melting of near-surface layers, which can limit the age of terrestrial rocks by the time of the impact under consideration. For lesser-sized impactors, say, for impactors with radii of about 160 km, the qualitative picture resembles that described above but the amplitude of disturbances is considerably smaller. This amplitude, however, is sufficient to cause a crustal disruption (if such a crust has already formed) and intense volcanic activity.

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.

Atmospheric Disturbances and Radiation Impulses Caused by Large-Meteoroid Impacts on the Surface of Mars. I. Formation and Evolution of Dust Cloud

We consider the mechanisms of the formation of dust ejected from craters produced by large-meteoroid impacts on the Martian surface, as well as the mechanisms of the elevation of dust that already existed on the surface, due to impulsed aeolian processes. Detailed numerical calculations of the dust injection, the shock wave propagation, and the formation and evolution of the dust cloud are carried out for vertical impacts of meteoroids with sizes from 1 m to 100 m. The results of these calculations show that dust raised by a 1-m impactor is sufficient to produce a local dust storm, while the mass of dust formed in impacts of large bodies is comparable to the mass of a regional or even a global dust storm. The impact detection rates for 1-, 5-, 20-, and 100-m-sized meteoroids are estimated to be a few impact events per year, one event in every 5–6 years, one event in every 300–800 years, and one event in every 5000–20 000 years, respectively. In the last case, the thickness of the global layer of precipitated dust and small fragments, which has been formed through impacts over a period of 107–108 years, is comparable to the thickness of the global dust layer on the Martian surface. In the first case, the mass of raised dust is greater than that for typical “dust devils.” The speed of impulsed wind at large distances from the impact site is shown to exceed the critical speed at which the blowing-off of dust from the surface begins. Some factors that may enhance the dust ejection have been previously ignored in numerical calculations. We discuss here the role of these factors. The second part of our study deals with the determination of the impact-induced radiation impulse and the estimation of its effect on the rise of dust.

Atmospheric Disturbances and Radiation Impulses Caused by Large-Meteoroid Impacts on the Surface of Mars. II. Radiation Impulse Characteristics and Parameters of the Warm Layer

This paper presents the results of the calculation of spectral and angular characteristics of radiation emitted by the disturbed region after the vertical impacts on the Martian surface of stony meteoroids with radii R0 from 1 to 100 m at speeds of 11–20 km/s. The time dependences are given for the density of the radiation flux incident on horizontal surface areas located at different distances from the impact point. For small impactors (R0= 1 m), the heating of the surface and surrounding gas by the radiation impulse from the hot region formed after the impact is insignificant even at the crater edge. However, the radiation impulse that heats up the surface is also emitted during the meteoroid flight through the atmosphere. Although this heating is insufficient to initiate evaporation, heat transfer by turbulent diffusion leads to the formation of a layer with temperatures that substantially exceed the initial temperature of the atmosphere. For large impactors (R0 = 100 m), the total specific impulse of the plume radiation gives rise to the emergence of the heated layer with a thickness on the order of several meters within several kilometers of the impact point. The formation of this “warm” layer may lead to the formation of a high-speed jet moving along the Martian surface as well as eddies at the front of the precursor with a subsequent intense rise of dust.