Asteroid Sample Return Mission I: In Search of Eltanin

Details Asteroid Sample Return Mission I: In Search of Eltanin Asteroid Sample Return Mission I: In Search of Eltanin

Sep 1995

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1995metic..30r.531k&link_type=abstract

Meteoritics, vol. 30, no. 5, page 531

Computer Science

Sound

Achondrites, Basaltic, Earth, Impacts, Mesosiderites, Meteorites, Eltanin, Neutron Activitation, Spinel, Strewnfield, Vesicles

Scientific paper

On 20 March 1995, the FS Polarstern departed Punta Arenas, Chile on cruise ANT XII/4, an eight-week oceanographic expedition from the sub-Antarctic eastern Pacific into the Bellingshausen Sea. The main goal of this expedition was a marine geological and geophysical exploration of this poorly studied area of the world ocean. As is typical of such expeditions, the 47-person scientific party also included researchers studying various aspects of the chemical, physical and biological oceanography of the region. However, one scientific objective was not typical - a study of the only known deep-ocean asteroid impact. The strewnfield of this late Pliocene (~2.4 Ma) impact is known to extend across ~600 km of the ocean floor, based on Ir anomalies in four USNS Eltanin piston cores, three of which contained recoverable impact debris [1]. The highest concentrations of impact debris were in core E13-4 (57 degrees 46.2'S, 90 degrees 47.6'W; 4700 m depth). The general plan of the impact study was to initially enter the region from the north, heading toward the E13-4 site and sampling sediments with piston and gravity corers in combination with sediment echosounding and bathymetric mapping. Based on limited data, we anticipated that the impact horizon would be at sediment depths of ~10 m and in a four day pass through the region we would collect it in several localities. A return to the impact region was planned during the seventh week for detailed mapping, coring, and seismic-reflection profiling. As with spacecraft missions, polar research expeditions do not always go according to plan. Our initial entry into the impact region was greeted by a major storm that lasted two days and generated seawaves 10 to 15 m high; conditions that allowed only initial mapping of the impact region, which contains a large, irregular seamount. During our first piston core attempt (1 April), an unexpected mountain of water prematurely triggered and damaged the corer. As we continued we found that the impact deposit was typically buried by more than 20 m of sediment, beyond the reach of our corers. At two sites we probably missed it by <100 cm. On 3 April we left the region empty-handed. On our return to the impact area (30 April), we had a new plan. We now had a working knowledge of the local bathymetry and could correlate late Pliocene to Recent sediments with echo- sounding profiles obtained during the earlier visit. We selected 12 coring sites where it appeared that sediments were thin enough to reach the impact deposit. By the afternoon of the second day we had recovered four cores when the first waves from the next big storm hit!! Four days later the weather finally cleared and we worked day and night, collecting seven piston cores in 36 hours. This left a few days to open some cores, make a short high-resolution seismic profile across the study area, and take a few more cores on our return to Punta Arenas. We recovered eight cores with late Pliocene or older sediments at the base. Five of these were opened and preliminary examination indicates that at least four contain impact debris. We were unsuccessful at collecting new cores at distances >100 km from E13-4. However, we now have 10 sites (including E13-3 and E13-4) that can be used to characterize the composition and distribution of debris within a region ~200 km in diameter. These should greatly improve estimates of the projectile size and models of the impact and its effect on the terrestrial environment. References: [1] Kyte F. T. et al. (1988) Science, 241, 63.

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