Laboratory Experiments on Heterogeneous CO2 Ice Nucleation and Growth Rates on Meteor Smoke Particle Analogues in the Martian Mesosphere

Abstract:

CO₂ ice particles with radii of about 100 nm have been detected in the Martian mesosphere region at heights between 80 km and 100 km. Gravity waves propagating upward cause a cooling of this region leading to temporary supersaturated conditions during which heterogeneous nucleation of CO₂ can take place. Large uncertainties in describing the nucleation processes at the extreme conditions of the Martian mesopause region state the need of laboratory measurements.

Sub-3 nanometer radius meteor smoke particle (MSP) analogues are created in a microwave plasma and stored in an electrodynamic trap for examining CO₂ ice nucleation as well as growth rates at low particle temperatures between 60 K and 75 K and CO2 concentrations up to 10¹⁷ m^-3 which are reasonably close to conditions present in the Martian mesosphere. Ice nucleation and growth processes of the particles are examined by analyzing the mass distribution of the particles with a time of flight spectrometer as a function of the residence time under supersaturated conditions.

In this paper, first measurements of CO₂ ice nucleation and growth on iron oxide and silicate particles will be presented. These results are extrapolated to realistic Martian conditions reducing the large uncertainty in dealing with CO2 ice nucleation on MSPs.