Image tube spectra of pluto and triton from 6800 to 9000 Å

To search for a possible atmosphere on Pluto and Triton, spectra of these objects as well as comparison stars were obtained with a three-stage Varo image tube for the spectral region from 6800 to 9000 Å. Ratio spectra indicate an absorption feature near 8900 Å, although the steeply diminishing response of the image tube at that wavelength casts some doubt on the reality of this feature. The feature appears more definitive in the spectrum of Pluto and less certain in the spectrum of Triton. The absorption was analyzed using our recently determined band-model parameters for methane. Under the assumption of a pressure higher than 0.01 atm an abundance of 3 m-amagat was determined. For pressures limited by the methane abundance itself, an abundance of 50 m-amagat and a pressure of 10^?3 atm was derived (using g = 0.20 g⊕ for both Pluto and Triton). This pressure is close to the pressure that can be expected from the equilibrium vapor pressure of a methane frost. If the absorption at 8900 Å is spurious, our analysis will be applicable as an upper limit for the presence of methane gas on Pluto or Triton.     

Suevite at the Roter Kamm impact crater,Namibia

Abstract— A small area littered with loose decimeter-sized fragments of glass and melt fragment-bearing suevite has been discovered on the western rim of the Roter Kamm impact crater in southern Namibia. The clast population and results of major and trace element chemical analyses are consistent with this breccia having been formed from granitoid basement lithologies only, without contribution from the metasedimentary Gariep and Cenozoic cover sequences. It is assumed that the limited amount of impact melt observed in the Roter Kamm structure could be the result of melt dissipation due to explosive shock-induced devolatilization of the significant marble component of the Gariep supracrustal cover. Preservation of very limited remnants of impact breccia on the rim of the Roter Kamm crater suggests a relatively deep level of erosion of the crater rim.     

A deep drillcore from the Morokweng impact structure, South Africa: petrography, geochemistry, and constraints on the crater size

The Morokweng impact structure in South Africa was formed 145 Ma ago, at the time of the minor mass extinction that marks the Jurassic-Cretaceous boundary. Previous size estimates for the Morokweng impact structure ranged between 70 and 340 km, and those workers favoring a very large size speculated on the role that the Morokweng impact might have played in relation to this mass extinction. Consequently, the actual size of this impact structure has wide-ranging implications. Petrographic and geochemical analyses, combined with SHRIMP U-Pb single zircon chronology, of a >3400 m long drillcore from about 40 km west of the center of the Morokweng impact structure show that this borehole is most likely located outside the impact structure, limiting the maximum crater diameter to <80 km. While the formation of a <80 km impact structure in continental terrane probably did not engender global biological consequences, it is possible that a series of impact events at J/K boundary time could have caused environmental stress on a worldwide scale. The terrestrial impact crater record does list several smaller structures of similar ages to that of the Morokweng structure. The results of this study are also significant for South African Archean geology. Late Archean (2.6-2.8 Ga) granitoids in the crust of the Kaapvaal Craton are much more widespread than previously thought. The overprint of the Namaquan-Kibaran orogenesis at 1.2-0.9 Ga along the western and southern margin of the craton is significant even in the far North West Province of South Africa.