Other
Scientific paper
Sep 1995
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1995metic..30q.488b&link_type=abstract
Meteoritics, vol. 30, no. 5, page 488
Other
Ages, Terrestrial, Chondrites, Ordinary, Mathematical Modeling, Meteorite Flux, Spectroscopy, Mossbauer, Weathering
Scientific paper
Introduction: Estimates of current meteorite flux come from camera observations [1], however, data from meteorite accumulation sites also provide information. For Roosevelt County (RC) in particular, field data [2], [3] combined with a decay constant yields an estimate of flux. The model: Data from RC showing oxidation over time [4] may be fitted by a function R = a + b In t, where R is the spectral area scaled to the interval (0,1) and t is the age in kiloyears, then for ordinary chondrites (OCs) the values a = 0.23 and b = 0.085 are reasonable. Assuming steady-state, the number,N(sub)o(M), of falls >= M grams per 10^6 km^2 per 1000 years is constant. To account larger falls surviving longer, we assume that fall of mass m(>=M) has a life t(m)=km^L. Then from an initial fall of N(sub)o(M)dt during interval dt a number n(t) dt remain, of age t, where n(t) = No (M) for t <= tau and n(t)=N(sub)o((t/k)^1/L) for t>tau*. Here tau*=kM^L is the nominal erosion time for falls of mass M. Generally a power law is chosen for the flux rate of the form N(sub)o (M) = cM^A where A may be given different values over different mass ranges [1], [2], [5]. Here we fix A . By integrating n(t) over all ages, 0 to infinity, one finds that the total number n(sub)tot and the flux N(sub)o(M) are related by N(sub)o(M) = lambda n(sub)tot, where lambda = (1/tau*)(1 + L/A) is the effective decay constant. Combining weathering data from all three hot desert sites giving frequencies of different values of oxidation, we can estimate tau*, A/L and b. Since t and R are related by t=exp[(R-a)/b], the distribution with R, N(R), is given by N(R)dR=[n(t)(dt/dR)]dR . Fitting the slope of 1n(N(R)) suggests b=0.085+/-0.015 and A/L=-1.57+/-O.1, so giving tau*-=8.4+/-2.9ky (for R*=0.4 and a=0.23), and hence lambda=0.05+/-0.02. For RC, the search area is llkm^2 and the number of falls, of mass >= 10g, is 42 [2]. This suggests the value N(sub)o(lOg)~190+/-75 per 10^6 km^2 per yr . Taking A~-0.5, which is representative [1], gives N(sub)o(20g)~N(sub)o(lOg)/square root of 2~130+/-50 per l0^6 km^2 per yr Discussion: OCs contribute 80% of present flux, so scaling by 1.25 gives an estimate of total flux. Table 1 compares our data and previous estimates [1,2,6]. The main divergence from [1] is for small masses. Allowing that our preliminary model is very basic, there may be other contributing factors: For the camera data events <= 25 g may be lost; and the "strewn field effect" may exaggerate estimates based on small search areas [7]. This work suggests that the flux of meteorites to the Earth has remained largely unchanged over the last 40,000 years. References: [1] Halliday I. et al. (1989) Meteoritics, 24,173-178. [2] Zolensky M. E. et al. (1990) Meteoritics, 25, 11-17. [3] Zolensky M. E. et al. (1992) Meteoritics, 27, 460-462. [4] Bland P. A. et al. (1994) Workshop on Meteorites from Cold and Hot Deserts, LPI, Houston, in press. [5] Jull A. J. T. et al. (1993) Meteoritics, 28,188-195. [6] Huss G. R. (1990) Meteoritics, 25, 41-56. [7] Halliday I. et al. (1991) Meteoritics, 26, 243-249.
Berry Frank J.
Bland Philip A.
Pillinger Colin T.
Smith Bryan T.
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