Meteoritics & Planetary Science, Volume 44, Number 12 (2009)http://hdl.handle.net/10150/6411972024-03-28T16:41:20Z2024-03-28T16:41:20ZA meteorite crater on Earth formed on September 15, 2007: The Carancas hypervelocity impactTancredi, G.Ishitsuka, J.Schultz, P. H.Harris, R. S.Brown, P.ReVelle, D. O.Antier, K.Le Pichon, A.Rosales, D.Vidal, E.Varela, M. E.Sánchez, L.Benavente, S.Bojorquez, J.Cabezas, D.Dalmau, A.http://hdl.handle.net/10150/6566602021-02-16T01:41:54Z2009-01-01T00:00:00ZA meteorite crater on Earth formed on September 15, 2007: The Carancas hypervelocity impact
Tancredi, G.; Ishitsuka, J.; Schultz, P. H.; Harris, R. S.; Brown, P.; ReVelle, D. O.; Antier, K.; Le Pichon, A.; Rosales, D.; Vidal, E.; Varela, M. E.; Sánchez, L.; Benavente, S.; Bojorquez, J.; Cabezas, D.; Dalmau, A.
On September 15, 2007, a bright fireball was observed and a big explosion was heard by many inhabitants near the southern shore of Lake Titicaca. In the community of Carancas (Peru), a 13.5 m crater and several fragments of a stony meteorite were found close to the site of the impact. The Carancas event is the first impact crater whose formation was directly observed by several witnesses as well as the first unambiguous seismic recording of a crater-forming meteorite impact on Earth. We present several lines of evidence that suggest that the Carancas crater was a hypervelocity impact. An event like this should have not occurred according to the accepted picture of stony meteoroids ablating in the Earths atmosphere, therefore it challenges our present models of entry dynamics. We discuss alternatives to explain this particular event. This emphasizes the weakness in the pervasive use of average parameters (such as tensile strength, fragmentation behavior and ablation behavior) in current modeling efforts. This underscores the need to examine a full range of possible values for these parameters when drawing general conclusions from models about impact processes.
2009-01-01T00:00:00ZExperimental study on the collisional disruption of porous gypsum spheresOkamoto, C.Arakawa, M.http://hdl.handle.net/10150/6566582021-02-16T01:40:03Z2009-01-01T00:00:00ZExperimental study on the collisional disruption of porous gypsum spheres
Okamoto, C.; Arakawa, M.
In order to study the catastrophic disruption of porous bodies such as asteroids and planetesimals, we conducted several impact experiments using porous gypsum spheres (porosity: 50%). We investigated the fragment mass and velocity of disrupted gypsum spheres over a wide range of specific energies from 3 x 10^3 J/kg to 5 x 10^4 J/kg. We compared the largest fragment mass (ml/Mt) and the antipodal velocity (Va) of gypsum with those of non-porous materials such as basalt and ice. The results showed that the impact strength of gypsum was notably higher than that of the non-porous bodies; however, the fragment velocity of gypsum was slower than that of the non-porous bodies. This was because the micro-pores dispersed in the gypsum spheres caused a rapid attenuation of shock pressure in them. From these results, we expect that the collisional disruption of porous bodies could be significantly different from that of non-porous bodies.
2009-01-01T00:00:00ZSimultaneous spectroscopic and photometric observations of binary asteroidsPolishook, D.Brosch, N.Prialnik, D.Kaspi, S.http://hdl.handle.net/10150/6566592021-02-16T01:40:33Z2009-01-01T00:00:00ZSimultaneous spectroscopic and photometric observations of binary asteroids
Polishook, D.; Brosch, N.; Prialnik, D.; Kaspi, S.
We present results of visible wavelengths spectroscopic measurements (0.45 to 0.72 microns) of two binary asteroids, obtained with the 1-m telescope at the Wise Observatory on January 2008. The asteroids 90 Antiope and 1509 Esclangona were observed to search for spectroscopic variations correlated with their rotation while presenting different regions of their surface to the viewer. Simultaneous photometric observations were performed with the Wise Observatorys 0.46 m telescope, to investigate the rotational phase behavior and possible eclipse events. 90 Antiope displayed an eclipse event during our observations. We could not measure any slope change of the spectroscopic albedo within the error range of 3%, except for a steady decrease in the total light flux while the eclipse took place. We conclude that the surface compositions of the two components do not differ dramatically, implying a common origin and history. 1509 Esclangona did not show an eclipse, but rather a unique lightcurve with three peaks and a wide and flat minimum, repeating with a period of 3.2524 hours. Careful measurements of the spectral albedo slopes reveal a color variation of 7 to 10 percent on the surface of 1509 Esclangona, which correlates with a specific region in the photometric lightcurve. This result suggests that the different features on the lightcurve are at least partially produced by color variations and could perhaps be explained by the existence of an exposed fresh surface on 1509 Esclangona.
2009-01-01T00:00:00ZComposition of 298 Baptistina: Implications for the K/T impactor linkReddy, V.Emery, J. P.Gaffey, M. J.Bottke, W. F.Cramer, A.Kelley, M. S.http://hdl.handle.net/10150/6566552021-02-16T01:38:05Z2009-01-01T00:00:00ZComposition of 298 Baptistina: Implications for the K/T impactor link
Reddy, V.; Emery, J. P.; Gaffey, M. J.; Bottke, W. F.; Cramer, A.; Kelley, M. S.
Bottke et al. (2007) suggested that the breakup of the Baptistina asteroid family (BAF) 160+30 /-20 Myr ago produced an asteroid shower that increased by a factor of 2-3 the impact flux of kilometer-sized and larger asteroids striking the Earth over the last ~120 Myr. This result led them to propose that the impactor that produced the Cretaceous/Tertiary (K/T) mass extinction event 65 Myr ago also may have come from the BAF. This putative link was based both on collisional/dynamical modeling work and on physical evidence. For the latter, the available broadband color and spectroscopic data on BAF members indicate many are likely to be dark, low albedo asteroids. This is consistent with the carbonaceous chondrite-like nature of a 65 Myr old fossil meteorite (Kyte 1998)and with chromium from K/T boundary sediments with an isotopic signature similar to that from CM2 carbonaceous chondrites. To test elements of this scenario, we obtained near-IR and thermal IR spectroscopic data of asteroid 298 Baptistina using the NASA IRTF in order to determine surface mineralogy and estimate its albedo. We found that the asteroid has moderately strong absorption features due to the presence of olivine and pyroxene, and a moderately high albedo (~20%). These combined properties strongly suggest that the asteroid is more like an S-type rather than Xc-type (Moth-Diniz et al. 2005). This weakens the case for 298 Baptistina being a CM2 carbonaceous chondrite and its link to the K/T impactor. We also observed several bright (V Mag. 16.8) BAF members to determine their composition.
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