¹John Anfinogenov,²Larisa Budaeva,³Dmitry Kuznetsov,
³Yana Anfinogenova

¹The Tungussky Nature Reserve, the Ministry of Natural Resources and Ecology of the Russian Federation
²The National Research Tomsk State University, the Ministry of Education and Science of the Russian Federation
³The National Research Tomsk Polytechnic University, the Ministry of Education and Science of the Russian Federation

The aim of this study was to discover remnants of the 1908 Tunguska meteorite. Field studies identified exotic rocks, furrows, and penetration funnels reported by the first eyewitnesses. Main methods included decoding of aerial survey photographs, systematic survey of epicenter area of the Tunguska explosion, exploratory excavations, reconstruction studies of the exotic rocks, mineralogical and spectral analysis of specimens, and experimental attempt of plasma-induced reproduction of fusion crust. The authors report the discovery of funnel-like structures and of an exotic boulder known as John’s Stone (JS) in the epicentral area. The article provides detailed description of JS, fresh furrows in the permafrost, multiple shear-fractured splinters, splinters with glassy coatings, evidence of high-speed impact of JS in the ground, and clear consistency in the geometry of spacial arrangements of all splinters, furrows, and cleaved pebbles. Pattern of permafrost destruction suggested about high-speed entry and lateral ricochet of JS in the ground with further deceleration and breakage. Calculated landing velocity of JS was at least 547 m/s. John’s Stone is composed of highly silicified gravelite sandstone (98.5% SiO2) with grain size of 0.5 to 1.5 cm. Outer surface of several splinters showed continuous glassy coating similar to shiny fusion crust reminiscent of freshly applied enamel. Plasma-induced heating of John’s Stone specimen led to its explosive disintegration; residue presented with light-colored semi-transparent pumice-like grains and irregularly shaped fused particles. Overall, our data suggest that John’s Stone may be a fragment of the 1908 Tunguska meteorite and may represent a new type of meteorite.

Reference
Anfinogenov J, Budaeva L, Kuznetsov D, Anfinogenova Y (2014) John’s Stone: a possible fragment of the 1908 Tunguska Meteorite. Icarus (in Press)
Link to Article [DOI: 10.1016/j.icarus.2014.09.006]

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¹Melissa J. Dykhuis,²Lawrence Molnar,²Samuel J. Van Kooten,
¹Richard Greenberg

¹Lunar and Planetary Laboratory, University of Arizona, 1629 E. University Blvd., Tucson, AZ 85719, USA
²Calvin College, 3201 Burton St SE, Grand Rapids, MI 49546, USA

The Flora family resides in the densely populated inner main belt, bounded in semimajor axis by the ν6ν6 secular resonance and the Jupiter 3:1 mean motion resonance. The presence of several large families that overlap dynamically with the Floras (e.g., the Vesta, Baptistina, and Nysa-Polana families), and the removal of a significant fraction of Floras via the nearby ν6ν6 resonance complicates the Flora family’s distinction in both proper orbital elements and reflectance properties. Here we use orbital information from the Asteroids Dynamic Site (AstDyS), color information from the Sloan Digital Sky Survey (SDSS), and albedo information from the Wide-field Infrared Survey Explorer (WISE) to obtain the median orbital and reflectance properties of the Floras by sampling the core of the family in multidimensional phase space. We find the median Flora SDSS colors to be a∗a∗ = 0.126 ± 0.007 and i-z=-0.037±0.007i-z=-0.037±0.007; the median Flora albedo is pVpV = 0.291 ± 0.012. These properties allow us to define ranges for the Flora family in orbital and reflectance properties, as required for a detailed dynamical study. We use the young Karin family, for which we have an age determined via direct backward integration of members’ orbits, to calibrate the Yarkovsky drift rates for the Flora family without having to estimate the Floras’ material properties. The size-dependent dispersion of the Flora members in semimajor axis (the “V” plot) then yields an age for the family of View the MathML source950-170+200 My, with the uncertainty dominated by the uncertainty in the material properties of the family members (e.g., density and surface thermal properties). We discuss the effects on our age estimate of two independent processes that both introduce obliquity variations among the family members on short (My) timescales: 1) the capture of Flora members in spin-orbit resonance, and 2) YORP-driven obliquity variation through YORP cycles. Accounting for these effects does not significantly change this age determination.

Reference
Dykhuis MJ, Molnar L, Van Kooten SJ, Greenberg R (2014) Defining the Flora Family: Orbital Properties, Reflectance Properties and Age. Icarus (in Press)
Link to Article [DOI: 10.1016/j.icarus.2014.09.011]

Copyright Elsevier

¹Richard W. Court, ¹Mark A. Sephton
¹Impacts and Astromaterials Research Centre, Department of Earth Science and Engineering, Imperial College, London, SW7 2AZ, UK

Heating and ablation of micrometeoroids during atmospheric entry yields volatile gases capable of altering atmospheric chemistry, surface climate and habitability. We have subjected powdered samples of the carbonaceous chondrites Orgueil (CI1), ALH 88045 (CM1), Cold Bokkeveld (CM2), Murchison (CM2) and Mokoia (CV3) to stepped pyrolysis-Fourier transform infrared spectroscopy to simulate the atmospheric entry of micrometeoroids and to quantify the yields of water, carbon dioxide and sulphur dioxide at various temperatures, offering insights into the nature of their source phases. We have incorporated these data into the recently-developed E-Belt model of the Late Heavy Bombardment (LHB) to estimate the production of volatiles from infalling micrometeoroids at Earth and Mars around four billion years ago. At the present day, the 4 (±2)×1010 g yr-1 of micrometeoroids arriving at Earth yield around 2.5 (±1.3) ×109 g yr-1 of indigenous water, 4.1 (±2.2) ×109 g yr-1 of total water, 1.9 (±1.0) ×109 g yr-1 of carbon dioxide and about 1.1 (±0.6) ×109 g yr-1 of sulphur dioxide, where “indigenous” water exclude water evolved at the initial pyrolysis step of 250 °C. For Mars, the infall of 6.8×109 g yr-1 of micrometeoroids yields 3.6 (±1.9) ×108 g yr-1 of indigenous water, 6.4 (±3.4) ×108 g yr-1 of total water, 2.4 (±1.3) ×108 g yr-1 of carbon dioxide and 1.5 (±0.8) ×108 g yr-1 of sulphur dioxide. The LHB is associated with micrometeoroidal infall masses of 1.3 (±0.8)×1022 g at Earth and 2.3 (±1.3)×1021 g at Mars. For Earth, this mass is estimated to have produced 8.3 (±4.9)×1020 g of indigenous water, 1.4 (±0.8)×1021 g of total water, 6.3 (±3.7)×1020 g of carbon dioxide and 3.8 (±2.2)×1020 g of sulphur dioxide, with production rates in the peak 50 Myr of the LHB estimated at 5.1 (±3.1) ×1012 g yr-1 of indigenous water, 8.6 (±5.1) ×1012 g yr-1 of total water, 3.9 (±2.3) ×1012 g yr-1 of carbon dioxide and 2.3 (±1.4) ×1012 g yr-1 of sulphur dioxide. For Mars, total 4.1-3.7 Ga production of 1.3 (±0.8) ×1020 g of indigenous water, 2.2 (±1.3) ×1020 g of total water, 9.3 (±5.5) ×1019 g of carbon dioxide and around 5.8 (±3.4) ×1019 g of sulphur dioxide is estimated, with peak 50 Myr rates of 8.2 (±4.8) ×1011 g yr-1 of indigenous water, 1.4 (±0.8) ×1012 g yr-1 of total water, 5.8 (±3.5) ×1011 g yr-1 of carbon dioxide and 3.6 (±2.1) ×1011 g yr-1 of sulphur dioxide. The errors in these estimates for the present-day rates are dominated by ±50% uncertainty in the LDEF figure of 4 (±2)×1010 g yr-1 of micrometeoroids while the errors for the ancient rates are dominated by the similarly large uncertainty regarding the mass ratio of micrometeoroids to asteroids. These errors indicate the need for improved understandings of infall rates and better models of solar system evolution. Current models of climate for early Earth and Mars focus on volcanic outgassing for greenhouse gases and aerosols, but pay less attention to extraterrestrial sources. Our data quantify an additional exogenous source of volatiles that augments the endogenous production.

Reference
Court RW, Sephton MA (2014) New estimates of the production of volatile gases from ablating carbonaceous micrometeoroids at Earth and Mars during an E-belt-type Late Heavy Bombardment. Geochimica et Cosmochimica Acta (in Press)
Link to Article [DOI: 10.1016/j.gca.2014.09.010]

Copyright Elsevier