Natasha Artemieva

PLANETARY SCIENCE INSTITUTE INDIVIDUAL ANNUAL REPORT

Calendar Year 2014

I. Report on research

1. Terrestrial impact ejecta layers and climate (CoI in PSI-ATM Exobiology project, PI in a new project submitted to SSW in 2014, not funded). Collaboration with Imperial College, London, GB; University of Edinburgh, GB; University of Muenster, Germany; Oberlin University; American Museum of Natural History, NYC); Museum

K-Pg layer (Chixculub impact) and global fires. Fig.1. Right: Experimental setup to model heat flux. Left: Calculated by the SOVA code (crosses) and modelled in the lab (solid lines) heat fluxes at various distances and various azimuths from the Chicxulub.

A large extraterrestrial body hit the Yucatán Peninsula at the end of the Cretaceous period. Simplified analytical 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. I modelled numerically the Chicxulub impact, its ejecta and radiation fluxes to the surface at various distances and azimuths (Fig. 1). Then my British colleagues reproduced in the laboratory these fluxes 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 a minor part of the end-Cretaceous story. The paper (Belcher et al 2015) has been accepted in 2014 and published in JGR in January 2015.

Impact glasses related to the Bosumtwi crater, Ivory Coast Geochemical analysis of impact melt glasses (tektites, microtektites, suevite glass shards, fallback spherules) from the Bosumtwi crater revealed a major, albeit different, depletion of volatile elements in four groups of glasses. I modelled molten ejecta from the Bosumtwi to figure out pressure-temperature conditions of ejected materials starting from their shock compression within the target and up to final deposition of these ejecta as tektites, microtektites, suevites, and fall-back spherules. Fig. 2. Fraction of melt (black line, right axis) and vapor (grey line, right axis) versus ejection velocity. Melts prevail in ejecta with velocities > 3 km/s; fraction of vapor is not negligible (>0.1) if velocities are higher than 1 km/s. Although fraction of melt decreases with decreasing ejection velocity, the total amount of melt (left axis, black dashed line) increases (as the total mass of ejecta increases quickly at low velocities).

Different types of ballistically emplaced impact melts had different ejection velocities: microtektites had a velocity of 4-6 km/s (to be deposited thousands of km form the crater); tektites were ejected at 2-3- km/s; and shards – below 1 km/s to be deposited near the crater. On average, lower ejection velocity corresponds to lower shock compression and lower vapor content in ejecta (Fig. 2). Thus, we can expect that the most distal ejecta (microtektites) had the highest vapor content, their cooling is compensated by vapor condensation (i.e., was very low), and their flight to destination sites was the longest. On contrary, glassy shards in suevite were ejected in mixture with solid materials; cooling rate was high (no vapor, cold solid particles around), and their flight was short. Tektites are somewhere in between. Thus, we can expect that microtektites are the most pure in and shards are volatile-rich. Geochemical analysis confirmed these modeling results. Fallback ejecta (FBE) differ from the above ejecta types as they were transported non- ballistically, within the ejecta plume. The plume is the hottest and most vapor-rich ejecta. Thus, it seemed obvious to expect that FBE have the highest deficiency in volatiles. However, it’s not the case and according to geochemical analysis FBE are more similar to volatile-rich suevitic shards. Numerical model helped to resolve this controversy (Fig. 4): FBE belongs to the impact plume, in particular, to its slowest part while the fastest part would be deposited outside the crater. Hence, FBE particles should be chemically similar to other types of low-velocity ejecta (suevite), although should be represented by very small (microns in diameter) particles as large particles move ballistically and are able to escape the plume. Fig. 4. An impact plume above the Bosumtwi transient cavity. Two models differ by the amount of volatiles within the target (upper plates – dry rocks, bottom plates – water-saturated porous rocks). Density contours are shown on the left, velocities – on the right, the thick black line in all plates delineate projectile materials. Dense solid-molten materials (shown in black colors) are ejected ballistically, form ejecta curtain, and are always deposited outside the transient cavity. Partially vaporized materials (different shades of grey, see the color scale) are expanded non-ballistically, forming the ejecta plume; small solid and molten particles may be entrained into this expansion; part of these materials will be deposited within the crater.

The MS in preparation.

Crater and Agoudal , Morocco

A relic impact structure was recognized within the strewn field of the Agoudal . The heavily eroded structure has preserved shatter cones in a limestone basement, and remnants of autochthonous and allochthonous . Fragments of iron incorporated into the allochthonous have a chemical composition (Ni = 5.16 wt%, Ir = 0.019 ppm) similar to that of the Agoudal meteorite, supporting a syngenetic origin of the strewn field and the impact structure. The total recovered mass of Agoudal meteorite fragments is estimated at approximately 500 kg. The estimated size of the SE–NW-oriented strewn field is 6×2 km. Model calculations with minimal preatmospheric size show that a similar meteorite strewn field plus one small crater with observed shock effects could be formed by fragmentation of a approximately 1.4 m in diameter with an impact angle of approximately 60° from the horizontal. However, the most probable is an impact of a larger, 3–4 m diameter meteoroid resulting a strewn field with approximately 10 craters, 10–30 m in diameter each, plus numerous meteorite fragments. The calculated scattering area of meteorite shrapnel ejected from these impact craters could completely cover the observed strewn field of the Agoudal meteorite.

Fig. 5. Left: Crater fields produced by iron projectiles with diameters from 2 to 8 m entering the atmosphere with a velocity of 18 km/s at an angle of 45°. The size of each plate is 1 × 1 km. Right: Fragment of the impact breccia with inclusion of oxidized meteorite iron (shown by arrow). The paper was published in M&PS in January 2015.

2. Impact ejecta on the (PI of the LASER project, no cost extension, Co-I in LASER project grunted to University of Austin, Texas).

Volatiles on the Moon In recent decades, several missions have detected signs of water and other volatiles in cold, permanently shadowed craters near the lunar poles. Observations suggest that some of these volatiles could have been delivered by impacts and therefore, understanding the impact delivery mechanism becomes key to explaining the origin and distribution of lunar water. During impact, the constituent ices of a comet nucleus vaporize; a significant part of this vapor remains gravitationally bound to the Moon, transforming the tenuous, collisionless lunar exosphere into a collisionally thick, transient atmosphere. We use numerical simulations to investigate the physical processes governing volatile transport in the transient atmosphere generated after a comet impact, with a focus on how these processes influence the accumulation of water in polar cold traps. We combine two codes in this study: the SOVA code allows to model an impact and initial expansion of ejecta, while the DSMC code allows to model molecular flows within a late- stage rarified plume.

Fig. 6. Schematic depiction of the hybrid SOVA–DSMC approach, showing a two- dimensional cross-section (in the plane of impact) of SOVA and DSMC density contours, 5 s after a 60°, 30 km/s impact. The initial velocity vector is marked, and the comet is drawn approximately to scale. Also indicated is the boundary of the hemispherical interface separating the SOVA and DSMC computational domains. The inset diagram depicts the overlap between SOVA and DSMC cells at the interface, where DSMC molecules are initialized using continuum SOVA data for water vapor (gray). The paper is accepted for publication in Icarus.

Ejection of the NWA5000 The list of lunar consists of 95 names with the total mass of ~75 kg. The spallation theory and numerical simulations allowed to explain the formation of solid high-velocity ejecta and to reconcile the results of numerical models with observations. Presence of a porous regolith layer on the Moon decreases at least tenfold the total mass of solid escape ejecta because of much lower shock pressures required for shock melting. Projectiles smaller than 10-20 m in diameter are able to propel exclusively the regolith (i.e., molten dust with random and unknown inclusions of consolidated breccia or rocks) into space. It means that the contribution of these small cratering events to the flux of lunar meteorites is non-predictable. Larger impact events which are able to excavate underlying megaregolith are statistically unlikely within a short, < 10 kyr, time frame. Thus, one of the biggest (11.5 kg) and the youngest (terrestrial age <10 kyr) lunar meteorite, NWA 5000 (feldsparic breccia) is a real miracle. I tried to model ejection of the NWA 5000 from a relatively small crater excavating lunar regolith with random solid inclusions (potential meteorites). The presence of random non-porous inclusions does not change the excavation flow, i.e., the pressure-velocity distribution within the target is very similar to the pure regolith case. Materials ejected with velocities between 2.4 and 3.2 km/s are considered as candidates for a fast direct delivery to Earth. Most of the regolith ejected at these velocities is shocked above 15-30 GPa and, hence, represents impact melt. Neither the shock compression nor heat exchange with molten/vaporized regolith is able to melt non-porous inclusions. Molten regolithic materials may cover the surface of non-molten ejecta with thin crust, but this crust cannot survive meteorites’ entry into the Earth’s atmosphere.

Fig. 7 Snapshots showing temperature distribution during the ejection of potential lunar meteorites (black squares along a vertical line on the left plate). The maximum shock compression (and, hence, the final physical state) depends on a burial depth within regolith.

The poster was presented at LPSC-45 and at theMetCos Meeting. The MS in preparation.

3. The Chelyabinsk (no funding) A deficiency of the total recovered mass (<0.01% of the pre-atmospheric mass) after the fall (february 2013) is probably the single unresolved scientific problem related to this dramatic event. It’s worth to mention that all recently observed large falls produce much less deposits than expected. Seems, ablation process accompanied a meteoroid entry is much more intense in case of large (tens of m) and, hence, most of the meteoroid mass is transformed into tiny ablation particles. These particles form a smoke train behind the entering cosmic body, stay in atmosphere for days, and are finally deposited world-wide. As the first step in our research, we model the smoke train behind the Chelyabinsk and compare modeling results with observations. Fig. 8. Comparison of the modelled wake behind the Chelyabinsk meteoroid (snapshots on the left) with the observed wake (pictures on the right). Colors on the left correspond to the optical thickness of the dusty cloud. A human eye can see an object (a cloud, in particular) if it’s optical thickness is > 0.01. It means that blue-violet doublets of the train consisting of large, cm-sized particles were invisible during the fall. However, exactly these particles were found in the snow shortly after the fall. The smallest particles (red- yellow colors) stayed in the atmosphere for months and have been observed by meteo-satellites. Oral talk at the MetSoc Meeting, posters at the LPSC and at MetSoc Meeting.

II. Publications

3 papers have been accepted (2 were actually published in Jan. 2015): 1. Belcher CM., Hadden RM., Rein G., Morgan JV., Artemieva N., Goldin TJ.,. 2015 An experimental assessment of the ignition of forest fuels by the thermal pulse generated by the Cretaceous–Palaeogene impact at Chicxulub. Journal of Geological Society. January 2015. doi:10.1144/jgs2014-082. 2. Lorenz C., Ivanova M., Artemieva N. et al. 2015. Formation of a small impact structure discovered within the Agoudal meteorite strewn field, Morocco. M&PS 50: 112-134 3. Prem P., Artemieva N. et al. 2015. Transport of water in a transient impact-generated lunar atmosphere. Icarus, accepted in October 2014.

2 papers under revision.

Conference abstracts (7) 1. Huber M., Artemieva N. 2014. Model for upper atmospheric aggregation of ash following hypervelocity impact events. EGU General Assembly 2014, held 27 April - 2 May, 2014 in Vienna, Austria, id.4989 (oral) 2. Artemieva N., Shuvalov V. 2014. The Smoke Train of the Chelyabinsk Meteoroid. 77th Annual Meeting of the , held September 7--12, 2014 in Casablanca, Morocco. LPI Contribution No. 1800, id.5113 (oral). 3. Prem, P.; Artemieva, N. A.; Goldstein, D. B.; Varghese, P. L.; Trafton, L. M.; Stewart, B. D Transport of Water in a Transient Impact-Generated Atmosphere. LPSC-45, Houston, abstract 2742 (oral). 4. Artemieva N. 2014. From the Moon to the Earth Without Jules Verne --- Lunar Meteorites and Lunar Dust Delivery. LPSC-45, Houston, abstract 1659 (poster). 5. Huber M., Artemieva N. 2014. Impact Accretionary Lapilli in Nature and in Numerical Models. LPSC-45, Houston, abstract 1689 (poster). 6. Tagle, R.; Goderis, S.; Fritz, J.; Bartoschewitz, R.; Artemieva, N.; Vanhaecke, F.; Claeys, Ph.An Extraterrestrial Component in Australasian Tektites. LPSC-45, Houston, abstract 2222 (poster). 7. Lukashin, A.; Luther, R.; Artemieva, N.; Shuvalov, V.; Wuennemann, K. 2014. Thermal History of Small Fragments During the Chelyabinsk Meteorite Fall. 77th Annual Meeting of the Meteoritical Society, held September 7--12, 2014 in Casablanca, Morocco. LPI Contribution No. 1800, id.5156 (poster). 8. Artemieva N. 2014. NWA 5000 --- One of a Kind? 77th Annual Meeting of the Meteoritical Society, held September 7--12, 2014 in Casablanca, Morocco. LPI Contribution No. 1800, id.5231 (poster).

III. Service to the Science Community

1. Associate Editor, M&PS 2. Reviewer for Icarus, M&PS, EPSL, Geology, GSA Special Paper, etc. 3. Member of ISSI (International Space Science Institute in Bern, Switzerland) team “Updating The Lunar Chronology And Stratigraphy: New Laboratory And Remote Sensing Data”.