The orbit and exposure history of the Piplia Kalan eucrite

Abstract

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.

The Puerto Lápice eucrite

“…This should have increased the activity of the very short lived radionuclides ( 46 Sc and 54 Mn). This situation is quite similar to the Piplia Kalan eucrite as reported by Bhandari et al (1998). Taking the calculations in order to predict the activities for the short-lived radionuclides using the composition of Piplia Kalan as reported in that paper, their activity concentrations are consistent with the expected values calculated on the sun spot numbers as index of GCR activity (Bonino et al 1995).…”

Cosmic-Ray Exposure Ages of Meteorites

“…Determinations of the 38 Ar ages of the eucrites Piplia Kalan and Vissannapeta appear to place both meteorites in the cluster between 20 and 25 Ma (Bhandari et al, 1998;Mahajan et al, 2000).…”

Itawa Bhopji (L3–5) chondrite regolith breccia: Fall, classification, and cosmogenic records

“…Gases extracted by stepwise heating were analyzed for their isotopic composition. The data reported in Table 5 have been corrected for blanks, interferences and instrumental mass discrimination as described in earlier publications Bhandari et al, 1998;Bonino et al, 2001b).…”