Comment on “John’s stone: A possible fragment of the 1908 Tunguska meteorite” (Anfinogenov et al., 2014, Icarus 243, 139–147)

Haack, Henning; Greenwood, Richard C. and Busemann, Henner (2016). Comment on “John’s stone: A possible fragment of the 1908 Tunguska meteorite” (Anfinogenov et al., 2014, Icarus 243, 139–147). Icarus, 265 pp. 238–240.



Anfinogenov et al. (Anfinogenov et al. [2014]. Icarus 243, 139–147) argue that a highly silicified gravelite sandstone referred to as “John’s stone” could be a fragment of the long-sought-after impactor from the 1908 Tunguska event. We have analyzed the oxygen isotopic composition of two distinct samples of John’s stone both kindly provided by Dr Yana Anfingenova. Both samples had very similar isotopic compositions, such that the average of the two was as follows: δ17O = 6.67 ± 0.15‰; δ18O = 12.78 ± 0.28‰; Δ17O = −0.01 ± 0.01 (errors 1SD). This value is well within the range for samples of terrestrial quartz-bearing sedimentary and metamorphic rocks. John’s stone has an oxygen isotope composition and mineralogy that is unlike any known group of meteorites. If John’s stone is extraterrestrial this would imply that it represents a previously unknown type of meteorite, as suggested by Anfinogenov et al. However, since sandstones can only form on a parent body with liquid water and by inference, also an atmosphere, we argue that there are only two possible parent bodies in the Solar System: the Earth and Mars. Mars can be ruled out for several reasons, including the oxygen isotopic and noble gas composition of John’s stone, which is clearly distinct from martian meteorites. Consistent with the O study, the noble gases do not provide any evidence for an extraterrestrial origin of the samples. The lack of any cosmogenic noble gases (particularly striking in 3He, 21Ne, 38Ar) is consistent with a terrestrial origin or an extraterrestrial origin under large shielding. Based on the combined evidence obtained in this study we infer that John’s stone is a terrestrial rock unrelated to the Tunguska impactor.

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