1,025 research outputs found
Measuring the Terminal Heights of Bolides to Understand the Atmospheric Flight of Large Asteroidal Fragments
The extent of penetration into the Earth's atmosphere of a meteoroid is defined by the point where its kinetic energy is no longer sufficient to produce luminosity. For most of the cases this is the point where the meteoroid disintegrates in the atmosphere due to ablation process and dynamic pressure during flight. However, some of these bodies have particular physical properties (bigger size, higher bulk strength, etc.) or favorable flight conditions (lower entry velocity or/and a convenient trajectory slope, etc.) that allow them to become a meteorite-dropper and reach the ground. In both cases, we define the end of the luminous path of the trajectory as the terminal height or end height. Thus, the end point shows the amount of deceleration till the final braking. We thus assume that the ability of a fireball to produce meteorites is directly related to its terminal height. Previous studies have discussed the likely relationship between fireball atmospheric flight properties and the terminal height. Most of these studies require the knowledge of a set of properties and physical variables which cannot be determined with sufficient accuracy from ground-based observations. The recently validated dimensionless methodology offers a new approach to this problem. All the unknowns can be reduced to only two parameters which are easily derived from observations. Despite the calculation of the analytic solution of the equations of motion is not trivial, some simplifications are admitted. Here, we describe the best performance range and the errors associated with these simplifications. We discuss how terminal heights depend on two or three variables that are easily retrieved from the recordings, provided at least three trajectory (h, v) points. Additionally, we review the importance of terminal heights, and the way they have been estimated in previous studies. Finally we discuss a new approach for calculating terminal heights.Peer reviewe
Análisis espectroscópico de fragmentos cometarios y asteroidales a su entrada en la atmósfera terrestre.
RESUMEN
En la presente tesis se analiza el origen y composición de la materia interplanetaria a partir de una perspectiva nueva basada en el estudio de los fenómenos luminosos que producen estas partículas a su entrada a la atmósfera terrestre, llamados meteoros. Estas partículas, procedentes mayoritariamente de la degradación de las superficies de cometas y asteroides, cuando se hayan en órbita solar se denominan genéricamente meteoroides. Dependiendo de la geometría del encuentro con la Tierra los meteoroides alcanzan la atmósfera a velocidades comprendidas en el rango de 11 a 73 km/s. A estas velocidades a alturas de entre 120 y 70 km. la densidad atmosférica es suficiente para que las colisiones atómicas sean frecuentes sobre el meteoroide, calentándolo por encima de 1.500 K en un proceso conocido como ablación. Como consecuencia de ese proceso se produce la fase luminosa denominada meteoro que, siendo perfectamente visible a grandes distancias, puede ser estudiada con técnicas fotográficas o vídeo desde la superficie terrestre.
En la primera parte de la tesis se analizan las imágenes en doble estación de 24 meteoros, la mayoría obtenidos durante la tormenta de Leonidas acaecida en 1999. De las imágenes estereoscópicas desde varias estaciones fotográficas ubicadas en la superficie terrestre se realiza la reconstrucción de las trayectorias reales en la atmósfera y la órbita heliocéntrica, calculada la velocidad geocéntrica de los meteoroides. Las órbitas calculadas permiten asociar los meteoros fotografiados a fragmentos procedentes de los cometas 55P/Tempel-Tuttle, 109P/Swift-Tuttle y 3P/Encke, así como también uno de ellos procedente del asteroide Faetón.
En la segunda parte de la tesis se estudia el campo de la espectroscopia de meteoros. En la tesis se analizan quince espectros pertenecientes a trece brillantes meteoros (bólidos) registrados desde el Observatorio de Ondrejov (República Checa). Primero se determina la sensitividad del espectrógrafo a partir de la cual se calibra la intensidad de las diversas líneas espectrales. Una vez calibrada se ajustan los espectros observados a un espectro sintético construido a partir de fijar unos valores típicos de la densidad de átomos en la columna meteórica, la temperatura y el área radiante. Cambiando esos parámetros ligeramente por el método de los mínimos cuadrados el espectro sintético alcanza valores de intensidad similares al registrado. En ese momento se varían a su vez las abundancias relativas de los diferentes elementos químicos para mejorar la calidad del ajuste de la intensidad de las líneas. De esa manera se obtuvo a lo largo de la trayectoria de cada bólido un espectro sintético en el intervalo comprendido entre 3.800 y 6.500 Å, de donde se dedujeron finalmente las abundancias químicas relativas al Si de diferentes elementos químicos: Na, Mg, Ca, Ti, Cr, Mn, Fe, Co y Ni. El rango de masa de los meteoroides progenitores de los espectros analizados se encuentra a medio camino entre las partículas de polvo interplanetario (IDPs) y los meteoritos condríticos más pequeños. Comparando las abundancias químicas con las características de IDPs, del polvo del cometa 1P/Halley y de meteoritos condríticos se llega a interesantes conclusiones. La presencia de una mayor abundancia en Na puede estar relacionada con la evaporación de este elemento en el medio interplanetario y probablemente también en la atmósfera. Asimismo se ha confirmado el efecto de evaporación incompleta del calcio que abandona el meteoroide sin fundirse, probablemente en forma de polvo refractario. Los resultados sugieren también que las medidas realizadas por la sonda Giotto del polvo del cometa 1P/Halley no pueden considerarse representativas del polvo cometario dado que varias abundancias químicas son diferentes en meteoroides de otros cometas. Probablemente tales diferencias sean debidas a que los espectrómetros de masas detectasen solo partículas pequeñas de masa equivalente a la de los componentes principales de la matriz de las IDPs. Estos componentes principales que suelen ser granos minerales no suelen tener composición condrítica pese a que el conjunto del IDP si puede poseerla.
La espectroscopia de meteoros constituye pues un campo innovador que permite profundizar en esos procesos y determinar las abundancias y anomalías químicas de estos objetos si bien con una precisión mucho menor que la obtenida del análisis in situ en laboratorio. A pesar de ello posee la ventaja de permitir determinar las abundancias químicas dentro de un rango de error aceptable aun cuando las partículas se desintegren por completo en la atmósfera y no puedan ser por tanto recuperadas para su posterior análisis. Resulta importante destacar que un estudio conjunto de espectros de bólidos por esta técnica y de las partículas de polvo interplanetario (IDPs) en el laboratorio puede ser complementaria y aportar valiosa información sobre los procesos degradativos sufridos por la materia interplanetaria. En especial resulta de interés corroborar la íntima relación entre las IDPs y los meteoroides que se desprende de este trabajo. En definitiva, el análisis de espectros meteóricos puede convertirse en una herramienta de gran valor en el estudio de la composición química de la materia interplanetaria que alcanza la Tierra. Este tipo de estudios puede complementar muy bien misiones mucho más costosas de recogida de materia cometaria in situ, como las misiones Stardust o Rosetta de la NASA y la ESA.
Finalmente cabe mencionar que el interés de estos estudios en astrobiología es obvio. La acreción de materia extraterrestre es un campo fundamental para llegar a comprender el origen del carbono prebiótico y otros compuestos volátiles que fueron presumiblemente claves en el origen de la vida en la Tierra. Probablemente no toda la materia orgánica llegase a través de impactos con cometas y primitivos asteroides sino que también la acreción de meteoroides en la atmósfera terrestre haya sido un mecanismo más continuo y benévolo para depositar especies orgánicas y especies volátiles como el agua sobre nuestro planeta. En este contexto la espectroscopia de meteoros es una manera de profundizar en los mecanismos que regulan la entrada de la materia interplanetaria a la Tierra.
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SUMARY
In this thesis is analysed the origin and composition of the interplanetary matter through the study of meteors, the luminous phase produced by these particles during their atmospheric entry. Meteors are perfectly visible to long distances and it can be analysed using photographic techniques from the Earths surface.
In the first part are analysed multiple station images of 24 meteors, the more important part of them obtained during the 1999 Leonid storm. From stereoscopic images taken from several stations we derived the real trajectories of these meteors in the atmosphere and, one time are calculated their velocities, the respective heliocentric orbits. The derived orbits allow to associate the meteoroids to several streams associated to comets 55P/Tempel-Tuttle, 109P/Swift-Tuttle, 3P/Encke and also one from the asteroid Phaeton.
The second part is dedicated to meteor spectroscopy. Fifteen spectra obtained from the Ondrejov Observatory (Czech Republic) have been analysed. Using meteor spectroscopy we obtain information about the meteoroid chemical composition. A simple model was used to determine the physical parameters and chemical abundances in these meteors. This model assumes thermal equilibrium in the meteor head. It is capable to reproduce the main characteristics of all meteor spectra, including the existence of two different components: the main spectrum characterised by a temperature of about 4,500 K and a second spectrum at approximately 10,000 K. Probably the high temperature component is associated to the front wave of the meteoroid whiles the low temperature comes from the meteoroid surroundings. The model was applied to deduce the chemical abundances relative to silicon in thirteen fireballs. The major part of them were produced by cometary fragments as was deduced from the computed heliocentric orbits. We have obtained for these fireballs the abundances of Na, Mg, Ca, Ti, Cr, Mn, Fe, Co and Ni. Comparing these chemical abundances to the characteristics of IDPs, 1P/Halley dust and chondrites we have obtained interesting differences related with meteoroid evolution and heterogeneity
Data Reduction and Control Software for Meteor Observing Stations Based on CCD Video Systems
The SPanish Meteor Network (SPMN) is performing a continuous monitoring of meteor activity over Spain and neighbouring countries. The huge amount of data obtained by the 25 video observing stations that this network is currently operating made it necessary to develop new software packages to accomplish some tasks, such as data reduction and remote operation of autonomous systems based on high-sensitivity CCD video devices. The main characteristics of this software are described here
The effect of aqueous alteration and metamorphism in the survival of presolar silicate grains in chondrites
Relatively small amounts (typically between 2-200 parts per million) of
presolar grains have been preserved in the matrices of chondritic meteorites.
The measured abundances of the different types of grains are highly variable
from one chondrite to another, but are higher in unequilibrated chondrites that
have experienced little or no aqueous alteration and/or metamorphic heating
than in processed meteorites. A general overview of the abundances measured in
presolar grains (particularly the recently identified presolar silicates)
contained in primitive chondrites is presented. Here we will focus on the most
primitive chondrite groups, as typically the highest measured abundances of
presolar grains occur in primitive chondrites that have experienced little
thermal metamorphism. Looking at the most aqueously altered chondrite groups,
we find a clear pattern of decreasing abundance of presolar silicate grains
with increasing level of aqueous alteration. We conclude that the measured
abundances of presolar grains in altered chondrites are strongly biased by
their peculiar histories. Scales quantifying the intensity of aqueous
alteration and shock metamorphism in chondrites could correlate with the
content in presolar silicates. To do this it would be required to infer the
degree of destruction or homogenization of presolar grains in the matrices of
primitive meteorites. To get an unbiased picture of the relative abundance of
presolar grains in the different regions of the protoplanetary disk where first
meteorites consolidated, future dedicated studies of primitive meteorites,
IDPs, and collected materials from sample-return missions (like e.g. the
planned Marco Polo) are urgently required.Comment: 15 pages, 3 figures, published in PASA as part of the Proceedings of
the 2008 Torino Conference "The Origin of the Elements Heavier than Iron
The 2011 October Draconids Outburst. II. Meteoroid Chemical Abundances from Fireball Spectroscopy
On October 8, 2011 the Earth crossed dust trails ejected from comet
21P/Giacobini-Zinner in the late 19th and early 20th Century. This gave rise to
an outburst in the activity of the October Draconid meteor shower, and an
international team was organized to analyze this event. The SPanish Meteor
Network (SPMN) joined this initiative and recorded the October Draconids by
means of low light level CCD cameras. In addition, spectroscopic observations
were carried out. Tens of multi-station meteor trails were recorded, including
an extraordinarily bright October Draconid fireball (absolute mag. -10.5) that
was simultaneously imaged from three SPMN meteor ob-serving stations located in
Andalusia. Its spectrum was obtained, showing a clear evolution in the relative
intensity of emission lines as the fireball penetrated deeper into the
atmosphere. Here we focus on the analysis of this remarkable spectrum, but also
discuss the atmospheric trajectory, atmospheric penetration, and orbital data
computed for this bolide which was probably released during
21P/Giacobini-Zinner return to perihelion in 1907. The spectrum is discussed
together with the tensile strength for the October Draconid meteoroids. The
chemical profile evolution of the main rocky elements for this extremely bright
bolide is compared with the elemental abundances obtained for 5 October
Draconid fireballs also recorded during our spectroscopic campaign but observed
only at a single station. Significant chemical heterogeneity between the small
meteoroids is found as we should expect for cometary aggregates being formed by
diverse dust components.Comment: Manuscript in press in Monthly Notices of the Royal Astronomical
Society. Accepted for publication in MNRAS on April 28th, 2013 Manuscript
Pages: 28 Tables: 5 Figures: 12. Manuscript associated: "The 2011 October
Draconids outburst. I. Orbital elements, meteoroid fluxes and
21P/Giacobini-Zinner delivered mass to Earth" by Trigo-Rodriguez et al. is
also in press in the same journa
The Trajectory, Orbit and Preliminary Fall Data of the JUNE BOOTID Superbolide of July 23, 2008
The results of the atmospheric trajectory, radiant, orbit and preliminary fall data calculations of an extremely bright slow-moving fireball are presented. The fireball had a -20.7 maximum absolute magnitude and the spectacular long-persistence dust trail (Fig 1 and 2) was observed in a widespread region of Tajikistan twenty eight minutes after sunset, precisely at 14h 45m 25s UT on July 23, 2008. The bolide was first recorded at a height of 38.2 km, and attained its maximum brightness at a height of 35.0 km and finished at a height of 19.6 km. These values are very much in line with other well-known fireballs producing meteorites. The first break-up must have occurred under an aerodynamic pressure Pdyn of about 1.5 MPa, similar to those derived from the study of atmospheric break-ups of previously reported meteorite-dropping bolides. Our trajectory, and dynamic results suggest that one might well expect to find meteorites on the ground in this case. The heliocentric orbit of the meteoroid determined from the observations is very similar to the mean orbit of the June Bootid meteor shower, whose parental comet is 7P/Pons-Winnecke (Lindblad et al. 2003). If the parent was indeed a comet, this has implications for the internal structure of comets, and for the survivability of cometary meteorites
Comparing the reflectivity of ungrouped carbonaceous chondrites with that of short period comets like 2P/Encke
Aims. The existence of asteroid complexes produced by the disruption of these
comets suggests that evolved comets could also produce high-strength materials
able to survive as meteorites. We chose as an example comet 2P/Encke, one of
the largest object of the so-called Taurid complex. We compare the reflectance
spectrum of this comet with the laboratory spectra of some Antarctic ungrouped
carbonaceous chondrites to investigate whether some of these meteorites could
be associated with evolved comets. Methods. We compared the spectral behaviour
of 2P/Encke with laboratory spectra of carbonaceous chondrites. Different
specimens of the common carbonaceous chondrite groups do not match the overall
features and slope of comet 2P/Encke. Trying anomalous carbonaceous chondrites,
we found two meteorites, Meteorite Hills 01017 and Grosvenor Mountains 95551,
which could be good proxies for the dark materials forming this short-period
comet. We hypothesise that these two meteorites could be rare surviving
samples, either from the Taurid complex or another compositionally similar
body. In any case, it is difficult to get rid of the effects of terrestrial
weathering in these Antarctic finds, and further studies are needed. Future
sample return from the so-called dormant comets could be also useful to
establish a ground truth on the materials forming evolved short-period comets.
Results. As a natural outcome, we think that identifying good proxies of
2P/Encke-forming materials might have interesting implications for future
sample-return missions to evolved, potentially dormant or extinct comets. To
understand the compositional nature of evolved comets is particularly relevant
in the context of the future mitigation of impact hazard from these dark and
dangerous projectiles.Comment: Accepted for publication in A&A on July 6, 202
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