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Natasha Artemieva

2008 Research Report

1. Chicxulub plume and K-Pg distal ejecta

Natalia Artemieva has run a suite of numerical simulations of the Chicxulub event to replicate the observational data, with a focus on the distal K-Pg layer and the impact glasses at proximal sites such as Beloc, Haiti. The results partially reproduced the observed ejecta thickness at proximal sites (~1000 km from the impact site), and the modeled ejecta is composed of sediments and silicate basement rocks (so-called Haitian glasses). Models that use a 45° impact angle are able to replicate the total ejecta and iridium volume at distal sites, and the majority of the ejecta is composed of meteorite and target sediments. Sub-vertical impacts generate too little iridium, and oblique impacts of <= 30 degrees generate too much. However, in contrast to observations, models that involve ballistic transport of ejecta lead to ejecta thickness decreasing with increasing distance, and are unable to transport shocked minerals (quartz and zircon) from the Chicxulub basement rocks around the globe. Thus, the K-Pg ejecta are transported non-ballistically with the most plausible mechanism being through re-distribution from a hot, expanding atmosphere during the ejecta re-entry (Fig.1). The results are important for future investigations of the environmental effects of the Chicxulub impact. The MS (Jo Morgan as a co-author is accepted for publication in Icarus).

2. Role of water in impact cratering (terresrial craters Sudbury and Ries, martian craters).

Melt deficiency within impact craters in sedimentary rocks is usually explained by intensive melt dispersion by volatiles and/or water (pore water, bounded water in minerals, surface water -- rivers, lakes, ocean). Seems, it is not the end of the story. Until recently, 2-km-thick Onaping formation in the Sudbury crater (Canada) and tens of m thick Suevite layer in the Ries crater (Germany) were treated as fallback non-ballistic ejecta (i.e. deposits of materials suspended in an impact plume and deposited after the crater formation in a quite environmental conditions). Numerical models show that such non-ballistic plume ejecta do exist, but its thickness can not exceed tens of cm (up to a meter). Natalia Artemieva (in collaboration with Richard Grieve and Dieter Stoeffler) suggested that both formations are the result of hot melt interaction with water, filling an impact crater (oceanic water in the Sudbury, fresh water in the Ries). Natural steam explosions (phreato-magmatic eruptions, PMEs) are common in terrestrial volcanoes where magma interacts with near-surface water. Similar (but not identical) effects, known as "melt-coolant" (or fuel-coolant) interaction, occur in foundries and nuclear power plants. In these cases, explosion efficiency depends on the water/melt ratio and has a maximum for values of 0.1-0.4, depending on the efficiency of water/melt mixing. Water is quite common on Earth -- and seemingly was on Mars as well. The proposed mechanism may help to explain the origin of suevite(s) in other craters and resolve the apparent problem of impact melt deficiency in sediment-target impact structures (as recently noted in the ICDP drilling projects at Chicxulub, Bosumtwi, and Chesapeake Bay). Oral presentation at the LPSC-40.

3. Chondrite formation in planetesimal collisions (together with Lon Hood).

High-velocity planetesimal impacts not only lead to the production of a cloud of heated melt and vapor that expands thermally and/or is jetted rapidly away from the impact point, but also generate a shock wave in the nebula gas that can potentially produce a much larger quantity of partial melt droplets by thermally processing any solid particles in the ambient nebula. Numerical modeling by Natalia Artemieva shows that the most efficient shock waves are generated in a head-on collision of planetesimals of a similar size. An amount of processed nebula is mainly defined by an impact velocity. For a 1000-km-diameter planetesimal this amount is equal to 1029 cm3 at 8 km/s, is twice less at 6 km/s, and totally vanished at 4 km/s (shock waves are too weak to melt solid particles). Paper (first author Lon Hood is accepted in M&PS).

4. Unveiling Tunguska enigma.

Traditionally, there were four main enigmas related with the Tunguska explosion in Russian Siberia in 1908: 1) an absence of impact crater at the epicenter; 2) butterfly shape of the forest fallout; 3) total absence of any extraterrestrial material (meteorites, spherules, Ir-anomalies); 4) "white nights" in Europe, i.e. a lot of dust in the upper atmosphere thousands km away from the impact site. The first two charades were solved many years ago: it was shown that a few tens of meters cosmic bodies are totally disrupted, melted, and decelerated in the Earth's atmosphere, Strong shock waves interacts with the Earth's surface, creates strong "winds" along this surface, and causes "butterfly"-like damage. Natalia Artemieva modeled interaction of shock waves with the surface and received almost a perfect "butterfly" -- see Fig.2. Moreover, it was shown that the resulting fragments and droplets are extremely small and are totally entrained into the atmospheric wake. This wake is hydrodynamically unstable, forms a plume in the atmosphere (similar to Shoemaker-Levy 9 comet on Juputer). Half an hour later, dust is dispersed up to ~1500 km from the impact site while remaining at high altitudes (Fig.3). Further dispersion is defined by local atmospheric flows. Cosmic dust (and water entrained by the plume from lower atmosphere) may reach Europe within the next day or even sooner. This huge cloud may work a giant mirrow (although more work is needed to estimate optical properties of this cloud). Thus, the Tunguska wonders do not exist any more. MS for M&PS in preparation.

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Figure 1: Shock waves in atmosphere and dispersion ejecta as it re-enters the atmosphere. Atmosphere thickness (Y-axis) is 100 km, numbers along the X-axis show distance from the re-entry point in km. Y-scale shows 100 km of the Earth's atmosphere. Colors represent particles of different sizes: yellow -- 1 cm; cyan -- 1 mm; red -- 0.1 mm. Numbers in the upper right corner of each snapshots are time in seconds.

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Figure 2: (from left to right): Map of the forest fallout at the Tunguska site; Modelled wind speed along the surface in m/s: < 25 m/s -- minimal action, > 40 -- substantial damage; telegraph poles at the epicenter (there is no wind at this point as the shock wave arrives exactly vertically).

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Figure 3: Dispersion of the Tunguska fragments and ablation products (in green and yellow) in atmosphere: at zero time (total deceleration of cosmic body); 1 minute later; 3 minutes; in half an hour.

Papers:

Hood, L., Artemieva N. (2008) Antipodal effects of lunar basin-forming impacts: initial 3D simulations and comparisons with observations. Icarus, 193, 485-502.

Horneck G. et al. (2008) Microbial Rock Inhabitants Survive Hypervelocity Impacts on Mars-Like Host Planets: First Phase of Lithopanspermia Experimentally Tested. Astrobiology, 8, 17-44.

Abstracts:

Hood, L. L., Artemieva, N. (2008) Magnetic field, shock, and crustal magnetization effects of lunar basin-forming impacts. American Geophysical Union, Fall Meeting 2008, abstract #GP33B-04.

Hood, L. L., Ciesla, F. J., Artemieva, N. A., Weidenschilling, S. J. (2008) Nebular Shock Waves Generated by Large-Scale Impacts: Possible Sites for Chondrule Formation. LPSC-39, Abstr. 2147.

Bland, P. A., Artemieva, N. A., Collins, G. S., Bottke, W. F., Bussey, D. B. J., Joy, K. H. (2008) Asteroids on the Moon: Projectile Survival During Low Velocity Impact. LPSC-39, Abstr. 2045.

Artemieva, N. A. (2008) Tektites: Model Versus Reality. LPSC-39, Abstr. 1651

Artemieva, N. A., Morgan, J. (2008) Possible Mechanisms of the Chicxulub Distal Ejecta Emplacement. LPSC-39, Abstr. 1581.

Pierazzo, E., Artemieva, N. A., and 10 co-authors (2008) The Impact Hydrocode Benchmark and Validation Project: Results of Validation Tests. LPSC-39, Abstr. 1177.

Kenkmann, T., Artemieva, N. A., Poelchau, M. H. (2008) The Carancas Event on September 15, 2007: Meteorite Fall, Impact Conditions, and Crater Characteristics. LPSC-39, Abstr. 1094.

Artemieva N.A. (2008) Impact Ejecta Modeling: Main Principles and a few Examples. Large Meteorite Impacts and Planetary Evolution IV, South Africa, Abstr. 3082.

Meyer, C., Artemieva, N., Stöffler, D., Reimold, W. U., Wünnemann, K. (2008) Possible Mechanisms of Suevite Deposition in the Ries Crater, Germany: Analysis of Otting Drill Core. Meteorite Impacts and Planetary Evolution IV, South Africa, Abstr. 3066.

Kenkmann, T., Artemieva, N. A., Wünnemann, K., Poelchau, H., Elbeshausen, D., Nunez Del Prado, H. (2008) The Remarkable Meteorite Impact Event on September 15, 2007, Carancas, Peru: What Did We Learn? Meteorite Impacts and Planetary Evolution IV, South Africa, Abstr. 3063.

Milkereit, B., Artemieva, N., Ugalde, H. (2008) Geophysical Signature of the Footwall of Large Meteorite Impact Craters. Meteorite Impacts and Planetary Evolution IV, South Africa, Abstr. 3024.

Morgan, J. V., Artemieva, N. (2008) Chicxulub Distal Ejecta: Modeling Versus Observations. Meteorite Impacts and Planetary Evolution IV, South Africa, Abstr. 3016 (invited).

Research Year: 
2008
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