Abstract-Cosmogenic radionuclides, particle tracks and rare gases have been measured in two fragments of the Piplia Kalan eucrite that fell in Rajasthan, India on 1996 June 20. The cosmic-ray exposure age of the meteorite is calculated to be 23 Ma, which is similar to ages of some other eucrites. The track density in feldspars and pyroxenes varies between 0. 2 x lo6 to -4. 5 x lo6 cm-2. The mass ablation of the meteorite, based on the distribution of track density in near-surface samples of the two fragments, is calculated to be -75%, which corresponds to an entry velocity of -17 kmls. The orbital parameters of the eucrite have been computed from the radiant of the meteor trail and the geocentric velocity. The best estimates are a = 2. 47 AU, e = 0. 62 and i = 7. 54", which is similar to the orbital elements of other meteorites, most of which have been inferred to originate within 2. 6 AU of the Sun. The activity of the radionuclide 26A1 agrees with the expected production rate; whereas the shortlived radionuclides 22Na, 54Mn, 46Sc etc. have levels that are consistent with the galactic cosmic-ray fluxes that are expected during the solar minimum period before the time of fall. All the cosmogenic effects ( i e . , radio-and stable-nuclides and particle tracks) are consistent with the meteoroid having had a simple, one-stage exposure history in interplanetary space. Lower radiogenic ages of U, Th-He (0.7 Ga) and K-Ar (3.6 Ga) indicate severe losses of 4He and 40Ar, as observed in most eucrites. A Pu-Xe age, concordant with Angra dos Reis, shows that Piplia belongs to the "old" eucrite group.

No abstract

Abstract-An extremely bright fireball was seen for over 250 km near the eastern coast of India in the evening sky on September 27, 2003. In a rare observation, the fireball was seen by two airline pilots, providing direction of the trail with reasonable accuracy, consistent with ground-based observations. A few fragments of the meteorite were subsequently recovered along the end of the trail in different parts of Kendrapara district (20°30′ N; 86°26′ E) of Orissa. Based on petrography and chemical composition, the meteorite is classified as H5 chondrite. The cosmogenic radionuclides 54 Mn, 22 Na, 60 Co, and 26 Al and tracks have been studied in this stony meteorite. Two of the fragments show an unusually high activity of 60 Co (~160 dpm/kg) indicating a meteoroid radius of 50-150 cm. Assuming that less than 10% (by weight) of the fragments could be recovered because of difficult terrain, an atmospheric mass ablation of >95% is estimated. Based on the observations of the trail and the estimated mass ablation, orbital parameters of the meteoroid have been calculated. The aphelion is found to lie in the asteroidal belt (1.8-2.4 AU), but the inclination of the orbit is large (22°-26°) with respect to the ecliptic. Noble gases have been analysed in two samples of this meteorite. He and Ne are dominantly cosmogenic. Using production rates based on the sample depth derived from 60 Co content, 21 Ne-based exposure age of 4.50 ± 0.45 Ma is derived for Kendrapara. One of the samples, known to be more deeply shielded based on high 60 Co activity, shows the presence of 80 Kr, 82 Kr, and 128 Xe produced by (n, γ) reaction on 79 Br, 81 Br, and 127 I, respectively. The ( 80 Kr/ 82 Kr) n ratio of 3.5 ± 0.9 is consistent with neutrons being mostly thermal. Trapped 84 Kr and 132 Xe are in the expected range for metamorphic grade H5.

No abstract

Abstract-AsteroidCo, and 26 Al) by nondestructive whole rock counting using a sensitive gamma-ray spectrometer. The activities of 60 Co, produced mainly by neutron capture in cobalt, and 26 Al indicate that fragment #15 was located at a depth of 41 ± 14 cm inside the 1.5-2 m radius asteroid. The activity of other radionuclides is also consistent with this shielding depth within the asteroid. The 22 Na ⁄ 26 Al activity ratio is higher than expected for the average cosmic ray flux, probably due to the unusually prolonged solar minimum before the fall.