Meteoric Ablation in Planetary Atmospheres

The magnitude of the rate at which cosmic dust enters the Earth’s atmosphere has been highly uncertain, with a daily mass influx ranging between 5 t d-1 and 270 t d-1. In fact, this issue has an important implication because if the upper limit of the estimates is correct, then vertical transport in the middle atmosphere must be faster than is generally assumed. On the other hand, if the lower limit is correct, then our understanding of the cosmic dust evolution in the solar system, and the transport mechanisms from the middle atmosphere to the Earth’s surface will need to be revised. The aim of the work described in this thesis is to estimate a Meteor Input Function (MIF) that allows to understand different atmospheric phenomena in the Mesosphere lower Thermosphere (MLT). For this purpose, the Zodiacal Cloud Model (ZCM) which is contrained by mid-Infrared observations of the zodiacal dust is evaluated. The ZCM is a detailed dynamical model that attempts to explain the origin of cosmic dust and accounts for the directionality, and mass and velocity distribution of Interplanetary Dust Particles (IDPs) in the inner solar system. The thesis is divided into four parts. First, the ZCM – constrained by measurements of the Infrared Astronomical Satellite (IRAS) – is evaluated using the Chemical ABlation MODel developed at the University of Leeds. These results are compared with those obtained from two quite different distributions: the Long Duration Exposure Facility (LDEF) and the incoming flux measured by meteor head echo detections with High- Power and Large-Aperture (HPLA) radars. Second, a newly-developed laboratory Meteor Ablation Simulator (MASI) is used to test the thermodynamic model within CABMOD as well as the use of the Hertz-Knudsen relation to describe the kinetics of evaporation; the Na, Fe, and Ca ablation rate profiles modelled by CABMOD are then refined. Third, the absolute contribution of each cosmic dust population –Jupiter-Family Comets (JFCs), Asteroids (ASTs), and Long-Period Comets (LPCs)– to the global input is estimated accounting for the most recent version of the ZCM constrained by Planck satellite observations, the cosmic flux accretion rate at the bottom of an ice chamber at the Amudsen-Scott base at South Pole, and recent measurements of the vertical fluxes of Na and Fe atoms above 87.5 km in the atmosphere. Finally, the impact of cosmic dust on the atmospheres of Venus, Mars and Titan is examined.