The orbit, structure and evolution of the Lyrid meteoroid stream

The orbit and structure of the Lyrid meteor stream based on photographic orbits available in the IAU Meteor database are investigated. Seventeen Lyrids were found in the database and the radiant and orbit of the stream were derived. In the stream three very distinct groups of orbits—short-period, longperiod and extreme (hyperbolic orbits), are separated. The mutual consistence of the groups is investigated by following the orbital evolution of individual meteors. The long-period group has the evolution almost identical with that of the parent comet C/1861 G1 Thatcher. The hyperbolic orbits are most probably the result of erroneous measurements

The Leonid meteor shower 1996-2002: Results from forward-scatter radio observations

Results from the observations of the Leonid meteor shower in 1996-2002 by the BLM (Bologna-Lecce-Modra) forward-scatter radio system for meteor observation carried out along two baselines, Bologna-Lecce (Italy)and Bologna-Modra (Slovakia), are presented and discussed. The activity curves of long-duration echoes (≥ 8 s)and their variations indicate multiple peak activity which are attributed to filamentary structure of the stream. The mass distribution exponents in the period of the shower maximum shows significant changes in individual years, with a high contribution of larger particles chiefly in 1998

The orbit and evolution of the Geminid meteoroid stream

The orbit and radiant of the Geminid meteoroid stream based on an analysis of the current version of the IAU MDC catalogue of photographic meteors are studied and discussed. The mean orbit, shape, size and ephemeris of the radiant are derived. The radiant area of the central part of the stream is more concentrated with the densest part of the size of 2◦ × 2◦. The orbital evolution of the stream is investigated and compared with the evolution of its potential parent asteroid 3200 Phaethon

Geminid meteor shower of 1996-2007: Global activity from forward-scatter observations

Activity and mass distribution of the Geminid meteor shower of 1996-2007 from observations by a forward-scatter radio system operating along Bologna-Modra baseline are analyzed and discussed. Global activity curve for overdense echoes of durations ≥ 1 s and ≥ 8 s depicts two distinct peaks at solar longitudes 261.7◦, 262.3◦ and 261.9◦, 262.3◦, respectively. Larger particles are concentrated more to the centre of the stream and slightly shifted towards the descending branch of the stream activity. The mean mass exponent of the Geminids is 1.73

Microstructure of the Fermo meteorite

Analyses by different electron microscopy methods contribute to draw the overall picture of the microstructure of the Fermo meteorite. Phase composition obtained by Scanning Electron Microscopy (SEM) may provide useful information about the origin of previously reported phases including kamacite, taenite, troilite, enstatite, silicate particles of olivine and pyroxene groups. The morphological aspects of separate micro- and nano-structural constituents revealed by Transmission Electron Microscopy (TEM) may reflect transformations that contribute to reconstruct the events affecting the true history of the cosmic body. Achievements of very fine-grained microstructure of minerals investigated by TEM micrographs and ion milling analysis are approaching current nanotechnology efforts

On the association of the daytime Taurid complex meteor streams with asteroids

The Taurid meteor complex daytime streams Zeta Perseids and Beta Taurids are investigated from the viewpoint of their orbital evolution and relation to the streams of the preperihelion branch of the complex. A search for potential co-parents among NEOs known until mid-June 2005 is made and two candidates for the association with the Zeta Perseids and two for the Beta Taurids are found. The Beta Taurids are shown to be postperihelion continuation of the Northern Taurids and Zeta Perseids are continuation of two complex filaments related to the Southern Taurids

The Lyrid meteor stream: Activity and mass distribution

Observations of the Lyrid meteor shower in 1997-2005 by a forwardscatter radio system for meteor observation operating simultaneously along two baselines, Bologna-Lecce (Italy) and Bologna-Modra (Slovakia), are analysed and discussed. The activity curves of long-duration echoes (≥ 8 s) and their variations indicate a complex structure of the stream. The Earth crosses the stream at a half maximum rate level in about two days. The overall activity peak derived from all observed returns is at solar longitude 32.30o (eq. 2000.0). The mass distribution exponent s and its variations in the period of the shower maximum indicate a relatively stable population of meteoroids in the stream exhibiting filamentary structure

The Quadrantid meteor shower 1997-2004: Activity and mass distribution

Observations of the Quadrantid meteor shower in 1997-2004 by the BLM forward-scatter radio system for meteor observation carried out along two baselines, Bologna-Lecce (Italy) and Bologna-Modra (Slovakia), are analysed from the viewpoint of activity and mass distribution and results are discussed. The activity curves of long-duration echoes (≥8 s) and their variations indicate a filamentary structure of the stream. The width of the stream at a half-maximum rate level is less than half a day (5–11.5 h). The mass distribution exponent s in the period of the shower maximum shows significant changes in individual years, with a high contribution of larger particles in 1997 and small particles in 2001, 2003 and 2004

Tidal disruption of NEAs - a case of P\v{r}\'ibram

This work studies the dynamical evolution of a possible meteor stream along the orbit of the P\v{r}\'{i}bram meteorite, which originated in the tidal disruption of the putative rubble-pile-like parent body during a close approach to the Earth. We assumed the disruption at the time when the ascending or descending node of the parent orbit was close to the Earth's orbit. In the last 5000 years, the P\v{r}\'{i}bram orbit has crossed the Earth orbit twice. It happened about 4200 years and 3300 years ago. In both cases, we modeled the release of particles from the simplified model of rotating asteroid, and traced their individual orbital evolution to the current date. It takes several hundred years to spread released meteoroids along the entire orbit of the parent body. Even today, the stream would be relatively narrow. Considering a model parent body with physical parameters of the asteroid Itokawa, the complete disintegration of the object produced 3.8$\times10^{11}$ meteoroid particles with diameter $\geq$ 1\,cm. The meteor activity observed from the Earth is revealed and justification of follow-up observation during suggested activity of the shower in the first two weeks of April is discussed. The Earth's tidal forces would disintegrate a fraction of NEA population into smaller objects. We evaluate the upper limit of mass of disintegrated asteroids within the mean NEA lifetime and the contribution of disrupted matter to the size distribution of the NEA.Comment: 8 pages, 10 figure