arXiv subjects

Jiri Borovicka

Publications and source records attributed to Jiri Borovicka.

6 recordsLinked to original sources

arXiv2026

Eta-Virginids: another asteroidal meteoroid stream

Eta-Virginids is a less-known meteor shower active in March. We investigated the meteoroids of this shower using fireball data from the European Fireball Network supplemented by video data of faint meteors. We first derived the criteria for assigning meteors to this shower. A fragmentation model was then applied to selected shower fireballs with good deceleration data and light curves. Meteoroid fragmentation strengths and bulk densities were derived and compared with three other showers. We have confirmed the four year periodicity in the activity of eta-Virginids and their presence in the 3:1 mean motion resonance with Jupiter. The orbital period of four years was directly measured for the fireballs. Fainter meteors showed somewhat longer periods but the shower is poor in faint meteors. No member fainter than magnitude +1 was observed instrumentally. The physical properties of meteoroids are different from cometary streams and are similar to the Geminids. The limiting fragmentation strength of 0.5 MPa and typical bulk density of cm-sized meteoroids of 1500 kg/m3 suggest that the parent body is a carbonaceous asteroid. Besides Geminids, eta-Virginids is another stream of asteroidal origin. Some small meteoroids have densities around 2500 kg/m3. Three asteroids of the sizes between 40 - 120 meters have been found to have similar orbits but their relation to eta-Virginids remains uncertain.

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arXiv2020

Physical properties of Taurid meteoroids of various sizes

The origin of the Taurid complex is still debated. In addition to comet 2P/Encke, various asteroids were proposed to be members of the complex and thus possible parent bodies of Taurid meteoroids. Studies of physical properties of Taurid meteoroids can provide constrains on their source. We used a well defined orbital sample of 16 Taurid fireballs with detailed radiometric light curves. The sample represented meteoroids of initial masses from 8 grams to 650 kg (diameters 1 - 70 cm). The semi-empirical fragmentation model was used to study their atmospheric fragmentation and derive strength distribution within the meteoroids. It was found that small meteoroids are stronger than large ones. When considering Taurid material as a whole, the majority has a very low strength of less than 0.01 MPa and a density less than 1000 kg/m3. The low strength material exists mostly as large bodies (>10 cm). If encountered in smaller bodies, it forms only a minor part. Stronger materials up to 0.3 MPa exist in Taurids as well, but the stronger material the rarer it is. Strong material forms small inclusions in large bodies or exists as small (cm-sized) separate bodies. These properties strongly suggest cometary origin of Taurids.

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arXiv2019

The Maribo CM2 meteorite fall - survival of weak material at high entry speed

High entry speed (> 25 km/s) and low density (< 2500 kg/m3) are two factors that lower the chance of a meteoroid to drop meteorites. The 26 g carbonaceous (CM2) meteorite Maribo recovered in Denmark in 2009 was delivered by a superbolide observed by several instruments across northern and central Europe. By reanalyzing the available data, we confirmed the previously reported high entry speed of (28.3 +/- 0.3) km/s and trajectory with slope of 31 degrees to horizontal. In order to understand how such a fragile material survived, we applied three different models of meteoroid atmospheric fragmentation to the detailed bolide light curve obtained by radiometers located in Czech Republic. The Maribo meteoroid was found to be quite inhomogeneous with different parts fragmenting at different dynamic pressures. While 30 - 40% of the (2000 +/- 1000) kg entry mass was destroyed already at 0.02 MPa, another 25 - 40%, according to different models, survived without fragmentation until relatively large dynamic pressures of 3 - 5 MPa. These pressures are only slightly lower than the measured tensile strengths of hydrated carbonaceous chondrite (CC) meteorites and are comparable with usual atmospheric fragmentation pressures of ordinary chondritic (OC) meteoroids. While internal cracks weaken OC meteoroids in comparison with meteorites, this effects seems to be absent in CC, enabling meteorite delivery even at high speeds, though in the form of only small fragments.

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arXiv2015

Are some meteoroids rubble piles?

The possibility that some meteoroids in the size range 1 - 20 meters are rubble piles i.e. assembles of boulders of various sizes held together only by small van der Waals forces, is investigated. Such meteoroids are expected to start disrupting into individual pieces during the atmospheric entry at very low dynamic pressures of ~ 25 Pa, even before the onset of ablation. The heterogeneous bodies as Almahata Sitta (asteroid 2008 TC3) and Benesov are primary candidates for rubble piles. Nevertheless, by analyzing the deceleration, wake, and light curve of the Benesov bolide, we found that the meteoroid disruption started only at a height of 70 km under dynamic pressure of 50 kPa. No evidence for a very early fragmentation was found also for the Chelyabinsk event.

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arXiv2015

On the age and formation mechanism of the core of the Quadrantid meteoroid stream

The Quadrantid meteor shower is among the strongest annual meteor showers, and has drawn the attention of scientists for several decades. The stream is unusual, among others, for several reasons: its very short duration around maximum activity (~12 - 14 hours) as detected by visual, photographic and radar observations, its recent onset (around 1835 AD) and because it had been the only major stream without an obvious parent body until 2003. Ever since, there have been debates as to the age of the stream and the nature of its proposed parent body, asteroid 2003 EH1. In this work, we present results on the most probable age and formation mechanism of the narrow portion of the Quadrantid meteoroid stream. For the first time we use data on eight high precision photographic Quadrantids, equivalent to gram - kilogram size, to constrain the most likely age of the core of the stream. Out of eight high-precision photographic Quadrantids, five pertain directly to the narrow portion of the stream. In addition, we also use data on five high-precision radar Quadrantids, observed within the peak of the shower. We performed backwards numerical integrations of the equations of motion of a large number of 'clones' of both, the eight high-precision photographic and five radar Quadrantid meteors, along with the proposed parent body, 2003 EH1. According to our results, from the backward integrations, the most likely age of the narrow structure of the Quadrantids is between 200 - 300 years. These presumed ejection epochs, corresponding to 1700 - 1800 AD, are then used for forward integrations of large numbers of hypothetical meteoroids, ejected from the parent 2003 EH$_1$, until the present epoch. The aim is to constrain whether the core of the Quadrantid meteoroid stream is consistent with a previously proposed relatively young age (~ 200 years).}

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arXiv2004

Detection of the N2+ First Negative System in a Bright Leonid Fireball

An ultraviolet-visible spectrum between 300 and 450 nm of a cometary meteoroid that originated from 55P/Tempel-Tuttle was investigated, and its new molecules, induced by atmospheric interaction, were discovered. The spectroscopy was carried out using an intensified high-definition TV camera with a slitless reflection grating during the 2001 Leonid meteor shower over Japan. A best-fit calculation mixed with atoms and molecules confirmed the first discovery of N2+ (B-X) bands in the UV meteor spectrum. The N2+ temperature was estimated to be 10,000 K with a low number density of 1.55 x 10^5 cm-3. Such unexpectedly strong ultraviolet emission, in particular for N2+(1,0) at 353.4 nm, is supposed to be formed through the wide dimensions of high-temperature regions caused by a large meteoroid. Spectroscopic observations of reentry capsules will provide us with good opportunities for confirming the discovered N2+.

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