Speaker
Description
Meteoroids are interplanetary rocky objects that can reach entry velocities into the Earth atmosphere up to 72 km/s, leading to a high temperature field around the body, ablating the meteoroid material and triggering a chain of chemical and radiative processes. These physico-chemical phenomena result in the formation of a visible plasma flow around the meteoroid head and along its trail, whose extension is in the order of kilometers even for a mm-size meteoroid.
Composition, mass, and trajectory parameters of meteors can be derived by combining observations with the meteor physics equations. The fidelity of these equations, which rely on heuristic coefficients, significantly affects the accuracy of the properties inferred. Our objective is to present a methodology that can be used to compute the luminosity of a meteor entry based on detailed flow simulations.
In the continuum regime, the Navier–Stokes equations are solved using state-of-the-art physico-chemical models for hypersonic flows. It includes accurate boundary conditions to simulate the surface evaporation of the molten material and coupled flow-radiation effects. Such detailed flow simulations allow for the calculation of luminous efficiency, which can be incorporated into the meteor physics equations. Finally, we integrate the radiative transfer equation over a line of sight from the ground to the meteor to derive the luminosity magnitude. We use the developed methodology to simulate the Lost City bolide, obtaining good agreement between numerical results and observations. The computed color index is more prominent than the observations. This is
attributed to a lack of refractory elements such as calcium in the modeled flow that might originate from the vaporization of droplets in the main trail, a phenomenon currently not included in the model.
In the rarefied regime, the Boltzmann kinetic equation is solved by means of a stochastic particle method (Direct Simulation Monte Carlo, or DSMC), including evaporation of the melting meteoroid material and nonequilibrium effects in the gas, in particular ionisation collisions experienced by metals in their encounter with air molecules. A ray-tracing algorithm allows us to extract lines of sight from the DSMC simulation. The radiative transport equation is then solved for an existing observation using NASA’s NEQAIR code along these lines of sight to compute the luminosity reaching a ground observer. The computed total luminosity value is compared to observations by Ceplecha [Bull. Astron. Inst. Czechoslov., 17 (1966)] for a single trajectory point. Preliminary results are encouraging. The radiation emitted by the meteor is assumed to be only due to its vaporized iron material and the populations of electronic energy levels are distributed according to a Boltzmann distribution. The validity of the latter assumption is discussed by means of Quasi-Steady-State detailed chemistry model.
Summary
Meteoroids are interplanetary rocky objects that can reach entry velocities into the Earth atmosphere up to 72 km/s, leading to a high temperature field around the body, ablating the meteoroid material and triggering a chain of chemical and radiative processes. These physico-chemical phenomena result in the formation of a visible plasma flow around the meteoroid head and along its trail, whose extension is in the order of kilometers even for a mm-size meteoroid.
Composition, mass, and trajectory parameters of meteors can be derived by combining observations with the meteor physics equations. The fidelity of these equations, which rely on heuristic coefficients, significantly affects the accuracy of the properties inferred. Our objective is to present a methodology that can be used to compute the luminosity of a meteor entry based on detailed flow simulations.
