Meteoroid Properties from Photographic Records of Meteors and Fireballs

Abstract

Abstract. Statistical criteria based on the single-body theory enabled the distinction of different composition groups of meteoroids in the past. The new single-body model proposed by Ceplecha (1983, 1984) is capable of determining the individual values of ablation coefficients, which has proved to be a better tool for separating meteoroids of different ablation properties. However, a significant fraction of fireballs exhibit a time-dependence of residuals, when the single-body model is applied to their photographic observations. This was recently explained by assuming sudden fragmentation at a point (gross-fragmentation). The proposed gross-fragmentation model was checked in exceptional cases, when splitting of a fireball was directly visible on the photographs. The new fragmentation model was then applied to the best photographic records of Prairie Network fireballs (PN). Least-squares fit of computed to observed distances along a meteoroid trajectory determines uniquely the ablation coefficient, the shape-density coefficient, the position of the gross-fragmentation point and the amount of fragmented material relative to the main body mass. This enabled not only a better classification according to ablation coefficient (composition groups), but also a recognition of different strength categories according to dynamic pressure at the fragmentation point. Except for composition groups (types) I, II, III A, HIB, each meteoroid with precise photographic data on its fireball can be classified as NF (no-fragmenting), IF (with one point of fragmentation) and MF (with many points of fragmentation). The fragmenting meteoroids (IF and MF) can moreover be sorted into several categories (a, 6, c, if, e) according to dynamic pressure at the fragmentation point. Thus the classification became two dimensional, separating meteoroid composition from structure. Values of ablation coefficients and bulk-densities were revised using this model. The amount of fragmented mass relatively to the main body was also determined. Typical sudden fragmentation for almost half of all fragmenting meteoroids is equivalent to stripping away slightly more than half of the mass. Classification from preheating and ablation.When a meteoroid collides with the Earth's atmosphere, most of the mutual kinetic energy is freed in interaction processes. The meteor phenomenon is thus very much dependent on the composition and structure of the meteoroid. Even the preheating is a sensitive indicator of the physical properties of the material from which the meteor body is composed.The beginning heights of the luminous trajectories can thus be used for classification of meteoroids (Ceplecha 1967(Ceplecha , 1968. This was done in the past for bodies in the mass range from 2 χ 10~8 kg to 0.5 kg by recognizing different discrete levels of beginning heights. Four groups denoted A, B, C, and D can be specified. The A group meteors start their luminous trajectory much lower down than the D group meteors. The ratio of the air density at the beginning height between ...

Assessment of Kinetic Energy of Meteoroids Detected by Satellite-Based Light Sensors

“…vestigated meteor events registered by PN and EN systems With the exception of one event (February 1, 1994), we (see, e.g., Ceplecha and McCrosky 1976, Ceplecha et al do not know the initial velocity. The following averaged 1993, Ceplecha 1987Ceplecha , 1994Ceplecha , 1996. The results of our simulavalue of conversion coefficient for H-chondrites can be tions and that of the dynamical trajectory analysis of PN used in these cases bolides by Ceplecha (1996) in most cases do not contradict each other.…”

“…Usually, hazards due to comets and asteroids have been hancement for 5-50-m bodies (Rabinowitz 1993, 1994, Rabinowitz et al 1993, 1994 and obtained rather good analyzed for rather large cosmic bodies, i.e., with the initial kinetic energy more than 3 ϫ 10 5 Mt (Morrison et al 1994). agreement.…”

“…Recently, it efficiency for such meteoroids is smaller than assumed in (16). To decrease the uncertainty by upgrading the Satellite was argued (Rabinowitz 1993, 1994 that the Spacewatch observations (Scotti 1994, Carusi et Network system, a priority task would be to include trajectory tracking. Some other peculiar features of the nearal.…”

The Observation and Characterization of Lunar Meteoroid Impact Phenomena

“…Visiting the discussion of the seven confirmed events of the November 1999 impacts during the peak of activity at the Moon, out of a ZHR equivalent of at least 50,000 over an effective 2-h period of observation, it follows that about 715 h of monitoring would be needed before an impact could be detected during non-storm periods (based on expressions in Sigismondi and Imponente, 2000). Estimates from Ortiz (2000) and Ceplecha (1994) place this number closer to 200 h. Considering the impact events of November 2001, the maximum flux at the Moon was predicted to be only 10% that of 1999, so one would have expected to see only 10% of the impacts that were seen two years before. A more thorough discussion of "equivalent Earth ZHR" as experienced on the Moon, and how these values are derived, can be found in Ortiz et al (2000).…”

Mobilization of dust on the Mars surface by the impact of small cosmic bodies

“…As an example, we should mention the recent discovery of a near-Earth asteroid belt [Rabinowitz et al, 1993;Rabinowitz, 1994]. The near-Earth objects (NEO'S) population in the size range of <100 m determined by the sensitive Spacewatch system has been found to be in excess of the size-frequency distribution obtained by observations of asteroids through telescopes and by detection of bolides by ground-based meteor networks [Ceplecha, 1994] Entry of large meteoroids into the Martian atmosphere could be analyzed using some models of meteoroid fragmentation and fragment diversion [e.g. Passey and Melosh, 1980 [Bronsten, 1983] and the pancake model by Zahnle [1992], it has been obtained [Nemtchinov et al, 1996] that the critical size for meteoroids impacting the Martian atmosphere is about 1 m (for stony bodies).…”