High geocentric velocity meteor ablation

Abstract

Interstellar origin meteoroids have now been detected using radar, image intensified video, large aperture radar and space dust impact techniques. Dynamical and radiation production mechanisms will eject some meteoroids from other planetary systems into orbits which will impact Earth with high geocentric velocities. In this paper we numerically model the ablation of high geocentric velocity (71 to 500 km s −1 ) meteors in order to predict the heights, light curves and trail lengths to be expected. We modeled three compositions and structures: asteroidal, cometary and porous cometary. Meteoroid masses ranging from 10 −6 to 10 −13 kg were used in the model. As expected, these high geocentric velocity meteors, when compared to other meteors, ablate higher in the atmosphere. For example a 300 km s −1 cometary structure meteor of mass 10 −9 kg will have a peak luminosity at about 190 km. They will also have significantly longer trail lengths. The same 300 km s −1 , 10 −9 kg cometary meteor would be within 2 mag of its peak brightness for a vertical displacement of 60 km if incident at a zenith angle of 45• . The peak light intensity of these high geocentric velocity meteors changes only slowly with velocity. Although the incident kinetic energy per unit time increases dramatically, this is largely offset by a decrease in the optical luminous efficiency in this velocity regime according to our luminous efficiency model. The 300 km s −1 , 10 −9 kg cometary meteor would have an absolute meteor magnitude at peak luminosity of about +8.5 mag. Our results suggest that at least those high geocentric velocity meteors larger than about 10 −8 kg should be observable with current meteor electro-optical technology although there may be observational biases against their detection. The results of this paper can be used to help optimize a search strategy for these very high geocentric velocity meteors.

Simultaneous optical and radar measurements of meteors using the Poker Flat Incoherent Scatter Radar

“…It can be noted that the absolute speeds of some of the observed meteors are greater than the 72 km/s limit for hyperbolic heliocentric orbits, indicating that they are on hyperbolic orbits (Hill et al, 2005;Rogers et al, 2004). The large proportion of high velocity meteors observed optically is likely due to a selection effect.…”

Spectra and physical properties of Taurid meteoroids

“…The luminosity efficiency factor, τ l , represents the fraction of the meteoroid's kinetic energy, which has been converted into luminosity in the visual range. For the calculation of τ l , we applied the approach described by Hill et al (2005). The method uses a relation between the luminous efficiency factor and universal excitation coefficient ζ defined by Jones & Halliday (2001):…”

Bulk density of small meteoroids

“…The luminous efficiency (cf. Hill et al 2005) used to compute the photometric mass of meteors has been estimated in the panchromatic band, and not the red (Ceplecha et al 2000;Koten et al 2006). To check for errors introduced when using V magnitudes instead of R, we took a sample of meteor spectra from Borovicka et al (2005), and worked out an average correction factor to convert the R-band meteor magnitude to a V-band meteor magnitude.…”

“…From these previous works, we see that estimating the density of a meteoroid is a difficult task, but it is achievable by combining precise observations (both photometric and astrometric measurements) and a complete model of ablation where all the different processes of mass-loss are taken into account (Hill et al 2005;Popova 2004;Borovička et al 2007;Jones & Kaiser 1966). Strictly speaking, this type of analysis should produce a bulk density for meteoroids not as a single and unique value, but instead as a range of possible solutions.…”