Crumbs from the crust of Vesta: Achondritic cosmic spherules from the South Pole water well

Abstract

Abstract-Ten glass cosmic spherules (CS) from the South Pole water well collection were analyzed by electron microprobe. Nine of them have Fe/Mn and Fe/Mg ratios in the range typical of chondrites. One of them (SP37-3), along with up to six other previously analyzed CS, have nonchondritic Fe/Mn and Fe/Mg ratios that agree well with values typical of either (basaltic) howardite, eucrite, and diogenite (HED) meteorites or Martian basalts, but not of lunar samples. SP37-3 also contains an anorthite relic grain. Anorthite has not previously been reported in cosmic spherules, but is well known in HED meteorites. The much greater frequency of HEDs among hand-sized meteorites suggests but does not prove that HED precursors are more likely for the nonchondritic spherules.We estimate that HED-like micrometeorites constitute ~0.5 ± 0.4% of the total population of micrometeorites in the South Pole water well, a fraction that translates to a flux of 1.6 ± 0.3 × 10 −8 g HED micrometeorites/m 2 -y. The ratio of HED-like objects to carbonaceous objects is about 100 times less in micrometeorites than among hand-size specimens. We infer that the comparative mechanical weakness of carbonaceous precursor materials tends to encourage spherule formation.

Ablation and Chemical Alteration of Cosmic Dust Particles During Entry Into the Earth’s Atmosphere

“…The other potential source that has been suggested is fragmentation of large objects that hit the atmosphere (Lal & Jull 2002). This has not been supported by micrometeorite chemical analyses, which are inclined toward the major contributor being carbonaceous chondrites, whereas a majority of meteorites are from ordinary chondrites (Krot et al 2003;Taylor et al 2007). In addition, large cosmic spherules such as glass spherules do not entirely support the concept of fragmentation (Rudraswami et al 2012).…”

3He, 20,21,22Ne, 14C, 10Be, 26Al, and 36Cl in magnetic fractions of cosmic dust from Greenland and Antarctica

“…This preliminary study gives us confidence that we can apply more precise separations and selection of different types of particles (Taylor et al 2007) to future samples of cosmic dust recovered from locations such as Greenland and Antarctic ice.…”

“…We obtained samples of micrometeorite debris from the SPWW, described in detail by Taylor et al (1998Taylor et al ( , 2000Taylor et al ( , 2005Taylor et al ( , 2007. Taylor et al (2000) estimated micrometeorite influx rates from cosmic spherules in SPWW and estimated an accretion rate of 1100 ± 200 tons/yr for particles in the 50-300 μm size range.…”

A unique basaltic micrometeorite expands the inventory of solar system planetary crusts

“…The three oxygen isotopes were measured in multicollection mode (using a Faraday cup for 16 O and two electron multipliers for 17 O on the standards was equal to Ϯ0.28‰, Ϯ0.50‰, and Ϯ 0.36‰, respectively (9 analyses). The two sigma errors given in the text are calculated for each point by adding in quadratic fashion the two sigma internal error (counting statistics) to the two sigma external reproducibility (as determined from the analyses of standards).…”

“…Based purely on their chemistry, 6 totally melted micrometeorites (cosmic spherules) were tentatively linked to the HED meteorites (17) which represent the most common group of achondrites (amounting to Ϸ1.7% of meteorite falls). However, because cosmic spherules are fully melted during atmospheric entry (18), their original textures, mineralogy, and isotopic compositions are compromised or lost, and they cannot provide secure links to the parent bodies from which they come.…”