Abstract
The ablation of cosmic dust injects a range of metals into planetary upper atmospheres. In addition, dust particles which survive atmospheric entry can be an important source of organic material at a planetary surface. In this study the contribution of metals and organics from three cosmic dust sources – Jupiter-Family comets (JFCs), the Asteroid belt (AST), and Halley-Type comets (HTCs) – to the atmospheres of Earth, Mars and Venus is estimated by combining a Chemical Ablation Model (CABMOD) with a Zodiacal Cloud Model (ZoDy). ZoDy provides the mass, velocity, and radiant distributions for JFC, AST, and HTC particles. JFCs are shown to be the main mass contributor in all three atmospheres (68% for Venus, 70% Earth, and 52% for Mars), providing a total input mass for Venus, Earth and Mars of 31 ± 18 t d−1, 28 ± 16 t d−1 and 2 ± 1 t d−1, respectively. The mass contribution of AST particles increases with heliocentric distance (6% for Venus, 9% for Earth, and 14% for Mars). A novel multiphase treatment in CABMOD, tested experimentally in a Meteoric Ablation Simulator, is implemented to quantify atmospheric ablation from both the silicate melt and Fe-Ni metal domains. The ratio of Fe:Ni ablation fluxes at Earth, Mars and Venus are predicted to be close to their CI chondritic ratio of 18, in agreement with mass spectrometric measurements of Fe+:Ni+ = 20−8+13 in the terrestrial ionosphere. In contrast, lidar measurements of the neutral atoms at Earth indicate Fe:Ni = 38 ± 11, and observations by the Neutral Gas and Ion Mass Spectrometer on the MAVEN spacecraft at Mars indicate Fe+:Ni+ = 43−10+13. Given the slower average entry velocity of cosmic dust particles at Mars, the accretion rate of unmelted particles in Mars represents 60% of the total input mass, of which a significant fraction of the total unmelted mass (22%) does not reach an organic pyrolysis temperature (~900 K), leading to a flux of intact carbon of 14 kg d−1. This is significantly smaller than previous estimates.
Highlights
Knowing the magnitude of the mass influx of Interplanetary Dust Particles (IDPs) into a solar system body is crucial for understanding the impacts in the atmosphere and at the surface
The metallic layers in the Earth's atmosphere have been studied for decades using ground-based lidar and space-based optical spectroscopy (Plane et al, 2015), the first measurements in another planetary atmosphere were only made very recently: a persistent layer of Mg+ peaking around 90 km was detected in Mars' atmosphere by the Imaging Ultraviolet Spectrograph (IUVS) on board the Mars Atmosphere and Volatile Evolution (MAVEN) spacecraft (Crismani et al, 2017)
The total Chemical Ablation Model (CABMOD) mass flux of 2.1 ± 1.2 t d−1 is 7% of the terrestrial global input of 27.9 ± 16.2 t d−1, and is significantly lower than previous estimates of the Martian mass flux, of around 50% of the terrestrial flux (Adolfsson et al, 1996; Borin et al, 2017). This discrepancy is mainly produced by two factors: first, the ZoDy model is constrained by the measured orbital distribution of meteors (Nesvorný et al, 2010; Nesvorný et al, 2006), which restricts the contribution of the Asteroid belt (AST) meteoroids to the total cosmic dust density in the Zodiacal Cloud, whereas Borin et al (2017) calibrated the flux at Earth by using an updated assessment of the Long Duration Exposure Facility (LDEF); second, as stated above, the ZoDy model considers that long-time evolved particles may be completely destroyed before crossing a planet's orbit, whilst Borin et al (2017) computed the evolution of the particles' trajectories without collisional lifetime limits
Summary
Knowing the magnitude of the mass influx of Interplanetary Dust Particles (IDPs) into a solar system body is crucial for understanding the impacts in the atmosphere and at the surface. We focus on meteoric ablation in the atmospheres of Earth, Mars, and Venus For this purpose, we use the new version of the Chemical Ablation MODel (CABMOD) which has been recently updated with a multiphase treatment to account for the ablation of both bulk silicate and the Fe-Ni metal grains which are normally present in IDPs (Bones et al, 2019). The original version of CABMOD assumed a single monolithic olivine phase and the vapour pressures were estimated directly from the MAGMA thermodynamic module (Fegley and Cameron, 1987; Schaefer and Fegley, 2004); this simplification does not reproduce satisfactorily the Fe evaporation profile observed in laboratory experiments using a Meteoric Ablation Simulator (MASI) (Bones et al, 2019; Gómez-Martín et al, 2017) This is largely because Fe-Ni metal alloy and FeS are commonly found in chondritic meteorites, especially in H-type ordinary chondrites (Jarosewich, 1990), and are thought to play an important role in the formation of the Earth and other planets resulting in core formation in rocky planets and asteroids. Supporting information shows Na, Fe, and Ni ablation profiles for two IDP analogues, comparing MASI experiments and CABMOD simulations
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