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Abstracts 5002-5050.Fm Meteoritics & Planetary Science 38, Nr 7, Supplement, A9–A153 (2003) http://meteoritics.org Abstracts POTENTIAL NEW IMPACT SITES IN PATAGONIA, ARGENTINA, SPIN DYNAMICS OF TERRESTRIAL PLANETS FROM EARTH- SOUTH AMERICA BASED RSDI M. C. L. Rocca. Mendoza 2779–16A, Ciudad de Buenos Aires, Argentina, I. V. Holin. Space Research Institute, Moscow, Russia. E-mail: (1428DKU). E-mail: [email protected] [email protected] Introduction: The southern part of Argentina has a total surface of Introduction: Despite wide Earth-based observations and many 786,112 km2. It is composed of five provinces: Neuquen, Rio Negro, Chubut, spacecraft missions, much remains unknown in spin dynamics of terrestrial Santa Cruz, and Tierra del Fuego. So far, no impact sites have been reported planets and related issues. Through accurate measurement of spin vectors and in this region. As part of an ongoing project to discover meteorite impact their variations with time, we may look deeply into planetary interiors. It has sites, this area was investigated through examination of 76 color LANDSAT not been possible to do so with known Earth-based techniques and spacecraft satellite images (1:250,000; resolution = 250 m) at the Instituto Geografico missions have been the only way to obtain such data. The upcoming Militar (IGM) (Military Geographic Institute) of Buenos Aires. When a Messenger (USA) and BepiColombo (Europe, Japan) orbiting and orbiting/ potential candidate was found, a more detailed study of images was done. landing missions should give obliquity and librations of Mercury closely LANDSAT color images at the scale of 1:100,000 and aerial photographs at related with its internal constitution [1]. In addition, we discuss new Earth- the scale of 1:60,000 (IGM) were then consulted. Sites identified are based opportunities for precision measurement of instantaneous spin described below. The coordinates given are those of the upper left and lower components of planetary mantles offered by the Radar Speckle Displacement right corners of a rectangle enclosing the site. Further evaluation of the Interferometry (RSDI) technique [2–4]. proposed sites is in progress. RSDI and Today’s Radar Facilities: RSDI technique was designed to Neuquen: 1) Meseta de la Barda Negra; 70°00′W, 39°00′S/69°45′W, measure as precisely as possible instantaneous spin components of distant 39°25′S; possible simple crater in black Miocene (14–10 Ma) basalt plateau. bodies by laser or radar. Applied to terrestrial planets, the improvement in Diameter: 1.5 km. Raised rim. Fresh aspect. There are no visible lava flows accuracy can be expected 3 to 4 orders of magnitude with respect to current coming from this crater. The crater has been described as a “salitral” (salty Earth-based techniques [3]. The measuring time can be shortened by 5–7 pan basin) containing blocks, conglomerates, and sands, on the geologic map orders of magnitude (from years to ~1 min). RSDI can measure regular and of the province by SEGEMAR [1]. stochastic variations in spin axis orientation as precisely as in rotation Santa Cruz: 1) Meseta del Lago Buenos Aires; 71°10′W, 47°00′S/ velocity. The limiting accuracy for Mercury, Venus, Mars (better for the 71°30′W, 47°05′S; possible simple crater. Diameter: 1 km, similar to the moon) is a few arcseconds or one part in 100,000 during observation within a Lonar Lake crater, India [2]. The area is composed of basalts of Pliocene age few min (the round trip time is excluded) with existing radar facilities like the 7 to 3 Ma [3]. 3) Estancia Los Mellizos, Ruta Provincial; 39°N; 70°10′W, Goldstone 70 m radar and the Goldstone 70 m—Green Bank 100 m radio 47°15′S/69°50′W, 47°28′S; possible eroded and covered complex structure. interferometer (USA) [2, 4]. This limiting, one-look accuracy roughly At this site, there is a circular feature of ridges and low hills. Diameter: 15 approaches the precision expected from spacecraft missions [1]. Computer km. The DLR’s X-SAR images also show this circular structure. The geology simulation showed that RSDI limits in accuracy can be closely attained in of this entire area is not well known. Apparently, it is composed of degraded reality. Repitition of one-look experiments on Mercury during ~20 days near volcanic and pyroclastic rocks of the Chon Aike Formation of Jurassic age a single inferior conjunction and the use of additional radio interferometers (170–140 Ma) [4]. 4) Gran Altiplanicie Central; 70°10′W, 48°23′S/70°05′W, would improve uncertainty in obliquity and libration amplitude to less than 1 48°28′S; possible eroded simple crater in upper Miocene (about 11–12 Ma) arcsec—better than expected from space missions. Unfortunately, the only basaltic plateau. Diameter: 1 km [5, 6]. fully steerable powerful transmitting facility in the world, at Goldstone, most Tierra del Fuego: 1) Cerro Taarsh, Estancia San Justo; 68°45′W, probably cannot be widely used because it is exploited heavily in spacecraft 54°00′S/68°30′W, 54°10′S; possible complex structure. Semi-circular area of navigation. Taking all of the above into account, we conclude that accuracy in concentric low ridges. Estimated diameter: 12 km. Probably very eroded. The spin dynamics of terrestrial planets provided by today’s Earth-based radars ridges of the surrounding area run parallel NW to SE. The area is composed approaches the precision of space missions. of marine sedimentary rocks (limestones) of lower Tertiary age. RSDI Looks into the Future: The Goldstone transmitting facility was Acknowledgements: This work was funded by the Planetary Society, constructed several decades ago and is overwhelmed with proposals. A new, California, USA. much more powerful and dedicated radar is needed to facilitate substantial References: [1] Suero T. 1951. SEGEMAR Boletin 76:67. In Spanish. progress in radar astronomy in the 21st century, e.g., an increase in [2] Fredriksson K. et al. 1973. Science 180:862–864. [3] Giacosta R. and transmitting power by 16 times to ~7 MW instead of today’s 450 KW will Franchi M. 2001. Carta y Hoja Geologica 4772-IV Lago Belgrano y Lago improve accuracy by ~4 times, and a single measurement will replace 16 of Posadas, SEGEMAR, 61 pp. In Spanish. [4] Barrio de R., Panza J. L., and today’s measurements. Regular RSDI observations may result in detailed Nullo F. E. 1999. SEGEMAR Anales Nº 29:511–527. In Spanish. [5] Panza J. knowing of spin dynamics of terrestrial planets to tens of milliarcseconds. L. and Marin G. 1998. SEGEMAR Boletín 239:104. In Spanish. [6] Ardolino Reaching this accuracy through missions is not easy. A new radar may work A. et al. 1999. SEGEMAR Anales 29:579–612. In Spanish. for several decades, while its cost is comparable with a single spacecraft mission. Earth-based RSDI may be the best possible way to investigate detailed rotation dynamics of Mercury, Venus, and Mars in in the 21st Century. References: [1] Peale S. J. et al. 2002. Meteoritics & Planetary Science 37:1269. [2] Holin I. V. 2002. Solar System Research 36:206–213. [3] Holin I. V. 2003. Abstract #1109. 34th Lunar and Planetary Science Conference. [4] Holin I. V. Forthcoming. Meteoritics & Planetary Science. A9 © Meteoritical Society, 2003. Printed in USA. A10 66th Meeting of the Meteoritical Society: Abstracts SEM-STUDY OF A MINERAL GRAIN SURFACE IN PALLASITES CARBONACEOUS XENOLITHS FROM THE KRYMKA I. V. Kvasnytsya and V. P. Semenenko. Institute of Environmental CHONDRITE AS PROBABLE COMETARY MATERIAL Geochemistry, NAS of Ukraine, Palladina 34a, Kiev-142, 03180, Ukraine V. P. Semenenko,1, 2 E. K. Jessberger,2 M. Chaussidon,3 I. Weber,2 C. Wies,2 and T. Stephan2. 1Institute of Environmental Geochemistry, NAS of Ukraine, Scanning electron microscopy (SEM) study of chondrites [1, 2, 5] has Kiev-142, 03180 Ukraine. 2Institut für Planetologie, 48149 Muenster, Ger- shown that a surface of mineral grains is very sensitive to physicochemical many. 3CRPG-CNRS, Vandoeuvre-lès-Nancy, France conditions of their origin and evolution. The surface of mineral grains and chondrules exhibits sculptural features, which are classified according to Campins and Swindle [1], using results from the Halley missions [2], their nature as primary and secondary. In contrast to chondrites, SEM data on discussed the expected characteristics of cometary meteoritic material. They the morphological features of minerals from differentiated meteorites are suggested that among any known type of meteoritic material, carbonaceous scanty. xenoliths from the Krymka LL3.1 chondrite [3–6] are the most probable Here, the results of SEM investigation of sculptural features of mineral candidates to be of cometary origin. grains from the pallasites Omolon, Brahin, and Kraçaoyarsk are originally Here we present the results of mineralogical, chemical, and isotopic presented. The studied objects include of 40–50 grains of olivine and 30–35 studies of two Krymka carbonaceous xenoliths. One of them (K1) is known grains of metal from each pallasite and rare grains of chromite and from a previous investigation [5, 6], and the second one (K3) is new. shreibersite. The grains are characterized by a smooth, ribbed, or fine-grained Occurrences of organic material and graphite microcrystals within xenolith surface. K1 allowed us to propose a metamorphic origin of graphite from organic The following primary sculptures are found on a surface of olivine and compounds [6]. metal grains: 1) inclusions of chromite crystals and their imprints (chiefly on The xenoliths resemble each other and correspond chemically to C the metal) and a native copper (on the olivine); pores. Formation of these chondrites. They differ, however, from the Krymka host by low totals of the sculptures results from a self-rectification from Cr and Cu of the metal and bulk composition, higher Fe content, higher FeO/(FeO + MgO) ratio, higher olivine during a slow cooling of a pallasite parent body.
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