Origin of John’s Stone: A quartzitic boulder from the site of the 1908 Tunguska (Siberia) explosion

The atmospheric fragmentation of the 1908 Tunguska Cosmic Body: reconsidering the possibility of a ground impact

“…Particularly, the yearly thawing results in the production of small circular holes on the terrain, with local small leakage of gas. Such holes were also visible at the lake bottom during many expeditions, as well as the scar of a recent landslide (Gasperini et al, 2012;Gasperini, 2015). This dynamic environment could justify local changes in the shape of the lake and its discrepancies with typical impact crater on solid dry ground.…”

“…The lack of gram-size meteorites makes it impossible to estimate the mechanical strength of the TCB. Little is known about its composition: Longo et al (1994), by analysing microremnants found in the trees' resin, indicated the presence of Fe, Ca, Al, Si, Au, Cu, S, Zn, Cr, Ba, Ti, Ni, C, and O. Anfinogenov et al (2014) suggested that the so-called "John's Stone", a large quarzitic rock found close to the epicentre of the TE, could be a piece of the TCB, but subsequent analyses of the oxygen isotopes made this hypothesis very unlikely (Bonatti et al, 2015;Haack et al, 2016). Studies on the interplanetary dynamics of all possible orbits suggested an asteroidal origin (Sekanina, 1983(Sekanina, , 1998Andreev, 1990;Bronshten, 1999;Farinella et al, 2001;Jopek et al, 2008), while models of atmospheric fragmentation exclude both the ice and the iron body (e.g.…”

“…• Lake Shape: Lake Cheko has a cone-like shape, with ellipsoidal base (∼ 490 × 340 m) and ∼ 50 m depth; it is different from other local thermokarst lake, which in turn are much more shallow. By excluding the shallower parts ( 2 m depth), the lake surface is almost circular with a diameter of ∼ 350 m (Gasperini et al, 2007;Gasperini, 2015).…”

“…Figure 1: Topographic map of the TE region over a Google Earth image. Location of Lake Cheko and approximate position of the airburst epicentre (Longo et al, 2005) are indicated, as well as a likely azimuth of the TCB trajectory (adapted from Gasperini 2015).…”

Challenges of identifying putative planetary-origin meteorites of non-igneous material

“…Detailed study of the structure, mineralogy, and chemistry of John's rock [Bonatti et al 2015] confirms that the rock originated by silica deposition from hydrothermal solutions as was obvious from the very beginning after its discovery. Recent oxygen isotope data suggest that the precipitation of SiO2 could have occurred in equilibrium with hydrothermal water (δ 18 Ow ≈ -16 ‰) at the temperature of about 80°C [Bonatti et al 2015]. High precision triple oxygen isotope data reveal that this rock is inconsistent with the composition of known Martian meteorites [Haack et al 2015, Bonatti et al 2015].…”