A novel instrument to measure differential ablation of meteorite samples and proxies: The Meteoric Ablation Simulator (MASI)

On entering the Earth’s atmosphere, micrometeoroids partially or completely ablate, leaving behind layers of metallic atoms and ions. The relative concentration of the various metal layers is not well explained by current models of ablation. Furthermore, estimates of the total flux of cosmic dust and meteoroids entering the Earth’s atmosphere vary over two orders of magnitude. To better constrain these estimates and to better model the metal layers in the mesosphere, an experimental meteoric Ablation Simulator (MASI) has been developed. Interplanetary Dust Particle (IDP) analogs are subjected to temperature profiles simulating realistic entry heating, to ascertain the differential ablation of relevant metal species. MASI is the first ablation experiment capable of simulating detailed mass, velocity, and entry angle-specific temperature profiles whilst simultaneously tracking the resulting gas-phase ablation products in a time resolved manner. This enables the determination of elemental atmospheric entry yields which consider the mass and size distribution of IDPs. The instrument has also enabled the first direct measurements of differential ablation in a laboratory setting

Injection of meteoric phosphorus into planetary atmospheres

This study explores the delivery of phosphorus to the upper atmospheres of Earth, Mars, and Venus via the ablation of cosmic dust particles. Micron-size meteoritic particles were flash heated to temperatures as high as 2900 ​K in a Meteor Ablation Simulator (MASI), and the ablation of PO and Ca recorded simultaneously by laser induced fluorescence. Apatite grains were also ablated as a reference. The speciation of P in anhydrous chondritic porous Interplanetary Dust Particles was made by K-edge X-ray absorption near edge structure (XANES) spectroscopy, demonstrating that P mainly occurs in phosphate-like domains. A thermodynamic model of P in a silicate melt was then developed for inclusion in the Leeds Chemical Ablation Model (CABMOD). A Regular Solution model used to describe the distribution of P between molten stainless steel and a multicomponent slag is shown to provide the most accurate solution for a chondritic-composition, and reproduces satisfactorily the PO ablation profiles observed in the MASI. Meteoritic P is moderately volatile and ablates before refractory metals such as Ca; its ablation efficiency in the upper atmosphere is similar to Ni and Fe. The speciation of evaporated P depends significantly on the oxygen fugacity, and P should mainly be injected into planetary upper atmospheres as PO2, which will then likely undergo dissociation to PO (and possibly P) through hyperthermal collisions with air molecules. The global P ablation rates are estimated to be 0.017 ​t ​d−1 (tonnes per Earth day), 1.15 ​× ​10−3 ​t ​d−1 and 0.024 ​t ​d−1 for Earth, Mars and Venus, respectively

Characterization of the Extraterrestrial Magnesium Source in the Atmosphere Using a Meteoric Ablation Simulator

Ablation of Mg from meteoroids entering the Earth's atmosphere was studied experimentally using a Meteoric Ablation Simulator: micron‐sized particles of representative meteoritic material were flash heated to simulate atmospheric entry and the ablation rate of Mg with respect to Na measured by fast time‐resolved laser‐induced fluorescence. Over the range of particle diameters and entry velocities studied, Mg ablates 4.3 ± 2.1 times less efficiently than Na and 2.4 ± 0.8 times less efficiently than Fe. The resulting evaporation profiles indicate that Mg mostly ablates around 84 km in the atmosphere, compared with Fe at 88 km and Na at 95 km. The chemical ablation model Chemical Ablation Model predicts satisfactorily the measured peak ablation altitudes and relative ablated fractions of Mg, Na, Fe, and Ca but does not capture the breadth of the ablation profiles, probably due to the inhomogeneity of the minerals present in meteoroids combined with experimental limitations

A Study of the reactions of Al⁺ ions with O₃, N₂, O₂, CO₂ and H₂O: influence on Al⁺ chemistry in planetary ionospheres

The reactions between Al+(31S) and O3, O2, N2, CO2 and H2O were studied using the pulsed laser ablation at 532 nm of an aluminium metal target in a fast flow tube, with mass spectrometric detection of Al+ and AlO+. The rate coefficient for the reaction of Al+ with O3 is k(293 K) = (1.4 ± 0.1) × 10−9 cm3 molecule−1 s−1; the reaction proceeds at the ion–dipole enhanced Langevin capture frequency with a predicted T−0.16 dependence. For the recombination reactions, electronic structure theory calculations were combined with Rice–Ramsperger–Kassel–Markus theory to extrapolate the measured rate coefficients to the temperature and pressure conditions of planetary ionospheres. The following low-pressure limiting rate coefficients were obtained for T = 120–400 K and He bath gas (in cm6 molecule−2 s−1, uncertainty ±σ at 180 K): log10(k, Al+ + N2) = −27.9739 + 0.05036 log10(T) − 0.60987(log10(T))2, σ = 12%; log10(k, Al+ + CO2) = −33.6387 + 7.0522 log10(T) − 2.1467(log10(T))2, σ =13%; log10(k, Al+ + H2O) = −24.7835 + 0.018833 log10(T) − 0.6436(log10(T))2, σ = 27%. The Al+ + O2 reaction was not observed, consistent with a D°(Al+–O2) bond strength of only 12 kJ mol−1. Two reactions of AlO+ were also studied: k(AlO+ + O3, 293 K) = (1.3 ± 0.6) × 10−9 cm3 molecule−1 s−1, with (63 ± 9)% forming Al+ as opposed to OAlO+; and k(AlO+ + H2O, 293 K) = (9 ± 4) × 10−10 cm3 molecule−1 s−1. The chemistry of Al+ in the ionospheres of Earth and Mars is then discussed

Dissociative Recombination of FeO(+) with Electrons: Implications for Plasma Layers in the Ionosphere.

The dissociative recombination (DR) of FeO(+) ions with electrons has been studied in a flowing afterglow reactor. FeO(+) was generated by the pulsed laser ablation of a solid Fe target, and then entrained in an Ar(+) ion/electron plasma where the absolute electron density was measured using a Langmuir probe. A kinetic model describing gas-phase chemistry and diffusion to the reactor walls was fitted to the experimental data, yielding a DR rate coefficient at 298 K of k(FeO(+) + e(-)) = (5.5 ± 1.0) × 10(-7) cm(3) molecule(-1) s(-1), where the quoted uncertainty is at the 2σ level. Fe(+) ions in the lower thermosphere are oxidized by O3 to FeO(+), and this DR reaction is shown to provide a more important route for neutralizing Fe(+) below 110 km than the radiative/dielectronic recombination of Fe(+) with electrons. The experimental system was first validated by measuring two other DR reaction rate coefficients: k(O2(+) + e(-)) = (2.0 ± 0.4) × 10(-7) and k(N2O(+) + e(-)) = (3.3 ± 0.8) × 10(-7) cm(3) molecule(-1) s(-1), which are in good agreement with the recent literature

A study of the reactions of Ni⁺ and NiO⁺ ions relevant to planetary upper atmospheres

The reactions between Ni+(2D) and O3, O2, N2, CO2 and H2O were studied at 294 K using the pulsed laser ablation at 532 nm of a nickel metal target in a fast flow tube, with mass spectrometric detection of Ni+ and NiO+. The rate coefficient for the reaction of Ni+ with O3 is k(294 K) = (9.7 ± 2.1) × 10−10 cm3 molecule−1 s−1; the reaction proceeds at the ion-permanent dipole enhanced Langevin capture rate with a predicted T−0.16 dependence. Electronic structure theory calculations were combined with Rice–Ramsperger–Kassel–Markus theory to extrapolate the measured recombination rate coefficients to the temperature and pressure conditions of planetary upper atmospheres. The following low-pressure limiting rate coefficients were obtained for T = 120–400 K and He bath gas (in cm6 molecule−2 s−1, uncertainty ±σ at 180 K): log10(k, Ni+ + N2) = −27.5009 + 1.0667log10(T) − 0.74741(log10(T))2, σ = 29%; log10(k, Ni+ + O2) = −27.8098 + 1.3065log10(T) − 0.81136(log10(T))2, σ = 32%; log10(k, Ni+ + CO2) = −29.805 + 4.2282log10(T) − 1.4303(log10(T))2, σ = 28%; log10(k, Ni+ + H2O) = −24.318 + 0.20448log10(T) − 0.66676(log10(T))2, σ = 28%). Other rate coefficients measured (at 294 K, in cm3 molecule−1 s−1) were: k(NiO+ + O) = (1.7 ± 1.2) × 10−10; k(NiO+ + CO) = (7.4 ± 1.3) × 10−11; k(NiO+ + O3) = (2.7 ± 1.0) × 10−10 with (29 ± 21)% forming Ni+ as opposed to NiO2+; k(NiO2+ + O3) = (2.9 ± 1.4) × 10−10, with (16 ± 9)% forming NiO+ as opposed to ONiO2+; and k(Ni+·N2 + O) = (7 ± 4) × 10−12. The chemistry of Ni+ and NiO+ in the upper atmospheres of Earth and Mars is then discussed

Ablation of Ni from micrometeoroids in the upper atmosphere: Experimental and computer simulations and implications for Fe ablation

Modelling the ablation of Ni from micrometeoroids upon their entry to the Earth’s atmosphere enables us to better understand not just the Ni layers in the upper atmosphere but also the differential ablation of Fe. A new version of our meteoroid ablation model has been developed that includes a metal phase in addition to the existing silicate phase. The validity of this new model has been verified via laboratory experiments of Ni ablation. Meteoritic particles (powdered terrestrial meteorites) and mineral proxies were flash heated to temperatures as high as 2700 K to simulate atmospheric entry. Slower linear heating ramps were also conducted to allow a more precise study of ablation as a function of temperature. Ni ablates rapidly, shortly after Na, which was used here as a reference. The model reproduces the experimental results generally within experimental error. Disagreement between the model and the data can be explained by the distribution of Ni in small grains in the meteorite samples, in contrast to the model assumptions of one molten metal phase. Small grain sizes are consistent with the Fe–Ni grain size observed in SEM-EDX mapping of the meteorite particles used for this study