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Abstract:

Hydrogen cyanide (HCN), a key molecule of significant importance in contemporary perspectives on prebiotic chemistry, originates in planetary atmospheres from various processes, such as photochemistry, thermochemistry, and impact chemistry, as well as from delivery by impacts. The resilience of HCN during periods of heavy bombardment, a phenomenon caused by an influx of material on unstable trajectories after accretion, remains relatively understudied. This study extensively investigates the stability of HCN under impact conditions simulated using a laboratory Nd:YAG laser in the ELISE experimental setup. High-resolution infrared spectroscopy was employed to monitor the gas phase composition during these simulations. Impact chemistry was simulated in bulk nitrogen atmospheres with varying mixing ratios of HCN and water vapor. The probed range of compositions spans from ∼0 to 1.8% of HCN and 0 to 2.7% of H₂O in a ∼1 bar nitrogen atmosphere. The primary decomposition products of HCN are CO and CO₂ in the presence of water and unidentified solid phase products in dry conditions. Our experiments revealed a range of initial HCN decomposition rates between 2.43 × 10¹⁵ and 5.17 × 10¹⁷ molec J^-1 of input energy depending on the initial composition. Notably, it is shown that the decomposition process induced by the laser spark simulating the impact plasma is nonlinear, with the duration of the irradiation markedly affecting the decomposition rate. These findings underscore the necessity for careful consideration and allowance for margins when applying these rates to chemical models of molecular synthesis and decomposition in planetary atmospheres.

Abstract:

Recent ground-based observations of Venus have detected a single spectral feature consistent with phosphine (PH₃) in the middle atmosphere, a gas which has been suggested as a biosignature on rocky planets. The presence of PH₃ in the oxidized atmosphere of Venus has not yet been explained by any abiotic process. However, state-of-the-art experimental and theoretical research published in previous works demonstrated a photochemical origin of another potential biosignature-the hydride methane-from carbon dioxide over acidic mineral surfaces on Mars. The production of methane includes formation of the HC · O radical. Our density functional theory (DFT) calculations predict an energetically plausible reaction network leading to PH₃, involving either HC · O or H· radicals. We suggest that, similarly to the photochemical formation of methane over acidic minerals already discussed for Mars, the origin of PH₃ in Venus' atmosphere could be explained by radical chemistry starting with the reaction of ·PO with HC·O, the latter being produced by reduction of CO₂ over acidic dust in upper atmospheric layers of Venus by ultraviolet radiation. HPO, H₂P·O, and H₃P·OH have been identified as key intermediate species in our model pathway for phosphine synthesis.

Abstract:

Abstract A hollow cathode discharge with a CuNi (Cu50Ni50) cathode was operated in an Ar/N$$_2$$ 2 /O$$_2$$ 2 gas mixture. The energy distribution of plasma ions is investigated with the help of energy-resolved mass spectrometry. Formation of singly ionised Ar$$^+$$ + and of Cu$$^+$$ + and Ni$$^+$$ + ions is observed in pure argon. With the addition of N$$_2$$ 2 or O$$_2$$ 2 gas the additional formation of molecular N$$_2^ +$$ 2 + or O$$_2^+$$ 2 + ions is observed. The intensity of these ions is reduced in the Ar+N$$_2$$ 2 +O$$_2$$ 2 gas mixture and molecular NO$$^+$$ + ions become the most abundant ionic species. The formation of neutral NO molecules is confirmed by optical emission spectroscopy. Gas samples collected at the exhaust of the vacuum chamber confirm the formation of NO and, additionally, of NO$$_2$$ 2 molecules. Graphic Abstract Sample taken from the exhaust of the plasma chamber with a liquid-nitrogen-cooled glass container showing solid nitrogen oxide (blue).

Abstract:

Meteor plasmas and impact events are complex, dynamic natural phenomena. Simulating these processes in the laboratory is, however, a challenge. The technique of laser induced dielectric breakdown was first used for this purpose almost 50 years ago. Since then, laser-based experiments have helped to simulate high energy processes in the Tunguska and Chicxulub impact events, heavy bombardment on the early Earth, prebiotic chemical evolution, space weathering of celestial bodies and meteor plasma. This review summarizes the current level of knowledge and outlines possible paths of future development.