Extraterrestrial microparticles fromantarctic ice cores and the search for

cometary dust

ELBERT A. KING and JERRY WAGSTAFF

Department of GeosciencesUniversity of HoustonHouston, Texas 77004

Our attempt to find and identify cometary dust from antarcticice cores of preindustrial age has been in progress for approx-imately 2 years. We began by characterizing various con-taminants we would encounter by examining surface ice sam-ples with the same analytical techniques, scanning electronmicroscopy, and energy dispersive X-ray analysis we wouldlater apply to preindustrial-age samples. This type of databaseis essential for any type of microparticle work that is attemptingto identify a possibly unique population of particles. Previousattempts to isolate and analyze any type of extraterrestrial parti-cle from individual ice layers have failed, mostly because of thetremendous abundance of terrestrial particles in most sampleintervals. Therefore, we chose to work with a core interval thathas a relatively low total particle content (Mosley-Thompsonand Thompson 1980), one that should contain particulate debrisfrom the great Leonid meteor shower of 1833.

During the course of our layer-by-layer particle imaging andanalysis, we found that the modal analyses of particle types inadjacent or different layers may be quite distinct. For example,one layer may be dominated by volcanic shards and spheres,while the adjacent layer contains mostly carbonate-rich loessgrains. Also, particle morphology and grain size vary consider-

Figure 1. Scanning electron microscope image of a large meteoriticnickel-iron particle showing crude hexahedral cleavage. The nickel-to-Iron ratio is approximately 1:10. The particle is mounted on nu-cleopore filter paper; scale bar = approximately 2 micrometers.

FA-Z

Figure 2. Scanning electron microscope image of a sphere com-posed almost entirely of iron oxide (probably magnetite) with a veryminor amount of sulfur. Probably a meteoritic ablation spherule;scale bar = approximately 1 micrometer.

ably from layer to layer. This offers the potential for building upreference dust lithostratigraphic sections for use in ice stratigra-phy and chronology; however, this would be a very large taskand is beyond the scope of the present work.

Of more immediate interest is the discovery of extraterrestrialmicroparticles in a number of the ice core samples. Initial de-scriptions and analyses of the particles (King and Wagstaff 1982;Wagstaff and King 1981a, 1981b, King and Wagstaff 1980) showthat most are common types of meteoritic material (figures 1 and2). It appears that we are finding particles of extraterrestrialmaterials that are very similar or identical to those now beingcollected in the stratosphere (e.g., Brownlee et al. 1976; CosmicDust Preliminary Examination Team 1982). Thus our prelimin-ary data indicate that there is no major difference between theextraterrestrial materials that were entering the Earth's at-mosphere in 1833 and those encountering the Earth at present.The possibility should be considered that some (many?) parti-cles we have imaged and analyzed are cometary debris, that is,that cometary particles are identical to some common types ofmeteoritic particles. Wood and Mendell (1982) have recentlymade such a proposal on both observational and theoreticalgrounds. If, after collecting data from a large number of extrater-restrial particles from this stratigraphic interval, we still findonly normal meteoritic materials, our data will strongly supporttheir model.

One of the most commonly cited candidates for cometarymaterial is carbonaceous chondrite. In our preparatory studies,we examined grains from gently crushed carbonaceouschondntes and found identical grains in dust samples from theantarctic ice cores (figure 3).

We still must examine enough total grains and extraterrestrialgrains to get statistically significant data. However, this willrequire a substantial amount of time, as in even the most abun-dant sample intervals extraterrestrial grains are only about oneparticle in ten thousand.

This work is supported by National Science Foundation grantDPP 78-20410.

611982 REVIEW

Figure 3. Scanning electron microscope image of a large irregularparticle that is carbon-rich. It contains discrete inclusions of ironsulfide and iron-magnesium silicates 1 to 2 micrometers in diameterembedded in a carbon-rich matrix that appears to be amorphous.Scale bar = approximately 2 micrometers. Similar particles arefound in gently disaggregated carbonaceous chondrites.

References

Brownlee, D. E., Hörz, F, Tomandi, D. A., and Hodge, P. W. 1976. Anatlas of extraterrestrial particles collected with NASA U-2 aircraft. Houston:National Aeronauties and Space Administration.

Cosmic Dust Preliminary Examination Team (CDPET). 1982. Cosmic dustcatalog (Publication 59). Houston: National Aeronautics and SpaceAdministration, Johnson Space Center, Curatorial Branch.

King, E. A., and Wagstaff, J . 1980. Search for cometary dust in theantarctic ice. Antarctic Journal of the U.S., 15(5), 78-79.

King, E. A., and Wagstaff, J . 1982. Micrometeorites from antarctic icecores. Antarctic Journal of the U.S., 16(5), 92-93.

Mosley-Thompson, E., and Thompson, L. G. 1980. 911 years of micro pa r-tide deposition at the South Pole: A climatic interpretation (Contribution73). Columbus: Ohio State University, Institute of Polar Studies.

Wagstaff, J . , and King, E. A. 1981. Micrometeorites and possible come-tary dust from antarctic ice cores. Lunar and Planetary Science, 12(3),1124-1126. (a)

Wagstaff, J . , and King, E. A. 1981. Search for possible cometary dust inantarctic ice cores. International Astronomical Union, Colloquim 61—Comets: Gases, ices, grains, and plasma. Program with abstracts, D.3. (b)

Wood, C. A., and Mendell, W. W. 1982. Comets, asteroids, and mete-ors: A new paradigm of interrelations. Lunar and Planetary Science,13(2), 877-878.

Victoria Land meteorite collections,with RKPA79015 (originally classified as an iron with silicate

1980-1981 inclusions); 15 L6 chondrites from the Allan Hills appear to bepieces of a single meteorite; several of the L6 chondrites fromReckling Peak are paired with RKPA78001; and 13 H6 chondritesfrom Reckling Peak appear to be pieces of a single meteorite.BRIAN MASON Additional pairings are possible on further examination.

Department of Mineral SciencesSmithsonian Institution

Washington, D.C. 20560

During the 1980-81 field season, a U.S. party collected 32meteorite specimens in the Allan Hills (ALH) area, 67 near Reck-ling Peak (RKP), and 1 near Outpost Nunatak (OTT) (Cassidy andAnnexstad 1981).* These specimens have been classified as fol-lows: irons, 2; mesosiderites, 4; eucrites, 3; ureilite, 1;chondrites, 90. The chondrites belong to the following classesand types: carbonaceous—c3, 1; olivine-bronzite—H3, 2; H4, 7;H5, 25; H6, 18; olivine-hypersthene--L3, 3; L4, 2; L5, 3; L6, 22;LL5, 2; LL6, 4; and enstatite—E5, 1. The mesosiderites are paired

Reference

Cassidy, W. A., and Annexstad, J . 0. 1981. Antarctic search for mete-orites, 1980-1981. Antarctic Journal of the U.S., 16(5), 61-62.

*Figures differ slightly from those reported by Cassidy and Annexstad.Their figure of 69 specimens collected near Reckling Peak included Icollected near Outpost Nunatak; in addition, 1 specimen reportedfrom near Reckling Peak and 2 from the Allan Hills were determinednot to be meteorites.

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