John Plane - Cosmic Dust in the Atmospheres of Earth and Mars

John Plane (University of Leeds) - Cosmic Dust in the Atmospheres of Earth and Mars

Abstract:
Cosmic dust particles are produced in the solar system from the sublimation of comets as they orbit close to the sun, and also from collisions between asteroids. Recent advances in interplanetary dust modelling provide much improved estimates of the fluxes of cosmic dust particles into planetary atmospheres throughout the solar system. Combining the dust particle size and velocity distributions with a chemical meteoric ablation model enables the injection rates of individual elements to be predicted as a function of location and time. This information is essential for understanding a variety of atmospheric impacts, including: the formation of layers of metal atoms and ions; meteoric smoke particles and ice cloud nucleation; perturbations to atmospheric gas-phase chemistry; the injection of bio-available phosphorous and organics; and the effects of the surface deposition of micrometeorites and cosmic spherules.

In this seminar I will describe the results of a large study designed to determine the input rate of cosmic dust to the terrestrial atmosphere, using a self-consistent treatment of cosmic dust from the outer solar system to the Earth’s surface. An astronomical model which tracks the evolution of dust from various sources into the inner solar system was combined with a chemical ablation model to determine the rate of injection of metallic vapours into the atmosphere. Constraining these coupled models with observations of IR emission from the Zodiacal Cloud, lidar measurements of the vertical fluxes of Na and Fe in the terrestrial mesosphere, and the rate of accretion of cosmic spherules at the South Pole, indicates that about 30 tonnes of dust enters the Earth’s atmosphere each day. The Leeds Chemical Ablation Model (CABMOD) was tested and developed using a novel Meteoric Ablation Simulator, which measures the evaporation of metals from meteoritic particles that are flash heated to over 2800 K with a time-resolved temperature profile simulating atmospheric entry. More recently, we have used a new instrument to explore the pyrolysis of organic material in meteoritic particles, which may cause cosmic particles to fragment during atmospheric entry and limit the delivery of organics to the planetary surface.

I will then describe how whole atmosphere global chemistry-climate models (e.g. WACCM, Mars PCM) can be used to explore the various impacts in the atmosphere and at the surface referred to above. The Mars PCM - with the chemistry of four metals - will be compared against observations of metallic species by NASA’s MAVEN spacecraft. MAVEN arrived at Mars just in time to observe the effect of a near miss of the planet by the comet Siding Spring, and since then has made continuous measurements of the Mg+ layer centred around 90 km, as well as occasional deep dip measurements between ~130 and 180 km.


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MIST Online Seminar Series: https://www.mist.ac.uk/meetings/mist-...

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Image credit: NASA/JPL