Exposure history of the Torino meteorite

Abstract

Abstract— We determined He, Ne, Ar, 10Be, 26Al, 36Cl, and 14C concentrations, as well as cosmic‐ray track densities and halogen concentrations in different specimens of the H6 chondrite Torino, in order to constrain its exposure history to cosmic radiation. The Torino meteoroid had a radius of ∼20 cm and travelled in interplanetary space for 2.5–10 Ma. Earlier, Torino was part of a larger body. The smallest possible precursor had a radius of 55 cm and a journey through space longer than ∼65 Ma. If the first‐stage exposure took place in a body with a radius of >3 m or in the parent asteroid, then it lasted nearly 300 Ma. The example of Torino shows that it is easy to underestimate first‐stage exposure ages when constructing two‐stage histories.

3He, 20,21,22Ne, 14C, 10Be, 26Al, and 36Cl in magnetic fractions of cosmic dust from Greenland and Antarctica

“…The solar noble gases may suggest that at least some grains were indeed exposed in space as IDPs. In the second approach, we estimate that at least 42% of the sample material is extraterrestrial, by simply comparing the measured amount of 14 C with an expected upper limit of 30 dpm/kg for a meteoroid with a radius of 10 cm (Wieler et al 1996). Lower 14 C production rate estimates would give larger extraterrestrial fractions.…”

Radiocarbon Beyond this World

“…There is also a possibility of implanted of higher-energy (up to 10's of MeV) particles emitted during solar flares (e.g. Wieler et al 1996;Nishiizumi et al 1997). As already mentioned, Begemann et al (1972) first suggested that the very surface layer of lunar samples could be implanted with solar 14 C. Fireman et al (1976Fireman et al ( , 1977 found higher than expected levels of 14 C in the 600-1000 °C temperature fractions of the Apollo 11 soil 10084 and Apollo 17 trench soils 73221, 73241 and 73261, which they interpreted as implanted solar wind 14 C. If implanted from the solar wind and not another source, this result would imply a 14 C/ 1 H ratio in the solar wind of ~5 × 10 −11 .…”

“…Fluxes for SCR are quoted for proton energies >10 MeV and for a 4π solid angle, defined as J 10 , and has units of protons/cm 2 /s. Values of R 0 in the range 70 to 125 MV have been fitted to a variety of radionuclide data from Figure 1 Depth dependence of GCR production of 14 C in meteoroids of different radii (from Wieler et al 1996). The horizontal line is the mean value observed for H6 falls, with the dashed lines showing the range observed.…”

“…Production Rate of 14 C and Interpretation of 14 C Terrestrial Ages Jull et al (1994) and Wieler et al (1996) have discussed the variation in 14 C production rate at different depths in meteorites of different sizes. Recent falls generally show activities of 14 C equivalent to a production rate of 38-58 atoms/min/kg (as shown in Table 3).…”

“…Wieler et al (1996) showed calculations for meteorites of preatmospheric radii from 20 to 45 cm where the saturated activity (or production rate) should vary from about 38 to 52 dpm/kg for an H chondrite. Smaller objects have lower production rates of 14 C. In Figure 1, we have shown the expected production rates for a sample recovered from a given depth for meteorites of H-chondrite composition of different sizes (Wieler et al 1996). Measurements on the Knyahinya L-chondrite (R=45 cm) gave values of 37 at the surface to 58 dpm/ kg at the center of the meteorite.…”