Lunar and Planetary Science XXXV (2004) 1006.pdf
METEORITE ABLATION DERIVED FROM COSMIC RAY TRACK DATA. V.A.Alexeev; Vernadsky Institute of Geochemistry and Analytical Chemistry, Russian Academy of Sciences, 119991, Moscow, Russia ([email protected])
Bhattacharya et al. [1] presented graphically the its mass and shape as well as on the angle of long-term averaged production rates of cosmic ray inclination of trajectory at entering the atmosphere. nuclear tracks (ρ/t) versus the depth (d) in References: meteorites with preatmospheric radii of R = 3-1000 [1] Bhattacharya S.K. et al. (1973) J. Geophys. cm. On the basis of these data, we have found the Res., 78, 34, 8356-8363. generalized type of the equation describing the [2] Re Velle D.O. (1979) J. Atmos. Terr. Phys., 41, value of ρ/t depending on d: lg(ρ/t) = A + BdC (1). 453-473. The values of coefficients for values of R used in
[1] are given in Table. The coefficients for 7 ) t / ρ intermediate values of radii are calculated by the (
method of linear interpolation. The agreement of lg 6 R=5 the data from [1] and those calculated according to R=5 (1) can be seen in Fig. 1. 10 5 10
15 Table. The coefficients A, B, and C in the equation 15
(1) for meteorites with radii R 4 25 25 R, cm А В С 3
5 12.9 -6.67 0.0372 50
2 1000 10 7.62 -1.45 0.250 50 15 7.44 -1.30 0.314 25 7.30 -1.17 0.381 1 1000 50 6.97 -0.799 0.521 0 10203040 d 1000 6.88 -0.715 0.574 Fig. 1. The dependences of the track production rates lg(ρ/t), cm-2 Ma-1, versus the depth d, cm, in We used the equation (1) for the construction of meteorites with preatmospheric radii R, cm. The the nomogram allowing the estimation of the value dashed lines are from [1], the solid lines present the of chondrite ablation (Fig. 2). The value of r/R and calculations according to (1). the ablation of A, % are determined according to N lg(m) and the logarithm of the average value of ρ/t. 16 Here m is the found mass of the meteorite, r is its effective radius, A = (1-r/R) ×100. The average 14
value of ablation for 83 ordinary chondrites is 12 +3.1 found to equal 78.4−3.4% . 10 It is ascertained that the meteorites with the 8 small found mass are drawn towards higher values of ablation (Fig. 3). 6
The possible dependence of the value of ablation 4
upon the velocity of entrance of the meteoroid in 2 the atmosphere is considered (Fig. 4). According to 0 [2], the mass loss for a large meteorite during its 0 0.2 0.4 0.6 0.8 1.0 r/R hypersonic drag interaction with the Earth's 99 95 50 0 A, % atmosphere is approximately given by the 99.9 80 expression: mf = m ×exp(-σ(V 2-V 2)/2)……….(2), 0 0 f Fig. 3. The distributions of the values r/R and A. where mf and m0 are the final and initial masses of the meteorite, σ is the mean parameter of ablation, The summarizing distribution correspond to all V is the out-of-atmosphere geocentric velocity of ordinary chondrites (N=83). The obscured 0 histogram corresponds to the meteorites with the meteorite and Vf is the velocity at which ablation ceases. However, the obtained data testify lgm
Lunar and Planetary Science XXXV (2004) 1006.pdf
lg m 4 R =50 3 40 30 2 20 15 10 1 Pe
5 0 1 SD 0.8 A ,%
0 0.6 25 50 -1 0.4 75 0.3 90 96 -2 0.2 99
-3 0.1 99.9
-4 r/R =0.05
123456lg (ρ /t)
Fig. 2. A nomogram for estimation of the r/R ratio and ablation (A) of ordinary chondrites according to the average value of lg(ρ/t) and lg(m). The points correspond to the H- and L-chondrites (filled and open symbols , respectively), which were found as one specimen. Pe – Peekskill; SD – Suchy Dul
A, % r/R 0 1.0
Br
Pa 50 0.8 PR LC Ku
0.6 Ri 1 80
Ni Dh
0.4 2 95 Ar Pr 3 Pe
99 0.2 In
99.9 4 0 12 14 16 18 20 22 24 V
Fig. 4. The relationship of the values r/R (or ablation A) and the initial atmospheric velocity V, km s-1. 1 – regression line for all the data; 2 – the same without the Peekskill and Innisfree data; 3 – line according to [2]; 4 – calculation according to equation (2). Abbreviations: Ar – Archie; Br – Bruderheim; Dh – Dhajala; In – Innisfree; Ku – Kunashak; LC – Lost City; Ni – Nikolskoe; Pa – Paragould; PR – Peace River; Pe – Peekskill; Pr – Pribram; Ri – Richardton.