Found 3 talks width keyword meteors

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Thursday October 25, 2012
Prof. Monica M. Grady
Open University, Milton Keynes, UK

Abstract

Traditionally, astronomers study stars and planets by telescope. But we can also learn about them by using a microscope – through studying meteorites. From meteorites, we can learn about the processes and materials that shaped the Solar System and our planet. Tiny grains within meteorites have come from other stars, giving information about the stellar neighbourhood in which the Sun was born.

Meteorites are fragments of ancient material, natural objects that survive their fall to Earth from space. Some are metallic, but most are made of stone. They are the oldest objects that we have for study. Almost all meteorites are fragments from asteroids, and were formed at the birth of the Solar System, approximately 4570 million years ago. They show a compositional variation that spans a whole range of planetary materials, from completely unmelted and unfractionated stony chondrites to highly fractionated and differentiated iron meteorites. Meteorites, and components within them, carry records of all stages of Solar System history. There are also meteorites from the Moon and from Mars that give us insights to how these bodies have formed and evolved.

In her lecture, Monica will describe how the microscope is another tool that can be employed to trace stellar and planetary processes.


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Friday March 26, 2010
Dr. Josep María Trigo
Instituto de Ciencias del Espacio, Spain

Abstract

Short-lived nuclides (SLNs) were incorporated to the solar nebula at the time of condensation of the first minerals from the vapor phase. The study of the isotopic ratios preserved in primitive meteorites provides clues on the stellar sources that produced these SLN, being supernovae and Asymptotic Giant Branch stars (AGBs) candidates. On the other hand, stellar grains were also preserved in primitive meteorites and Interplanetary Dust Particles (IDPs). Their survival demonstrates that the solar nebula was not so hot as first researchers proposed in the 60s. Interestingly, the available stellar grain abundances in primitive meteorites (chondrites) depend of the physico-chemical processes suffered by their parent bodies: metamorphism, aqueous alteration, etc. An evaluation of the primordial presolar grain abundances in the protoplanetary disk at the time these materials formed would allow a comparison with the derived from theoretical models. For gaining insight on these processes we should study the most primitive meteorites (the chondrites), but also even more pristine materials arrived from comets, particularly these captured in the stratosphere as IDPs, or collected from 81P/Wild 2 comet by Stardust (NASA) spacecraft.

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Thursday June 18, 2009
Dr. Julia de León
Instituto de Astrofísica de Andalucía, Spain

Abstract

Due to their orbits, near-Earth asteroids (NEAs) have been considered the most evident parent bodies of meteorites. Dynamical models show that NEAs come primarily from the inner and central parts of the Main Belt (MB), and they reach their orbits by means of gravitational resonances (mainly ?6 and 3:1). This part of the MB is dominated by spectral types S and Q, also the most common spectral types among the NEA population (~60%), and correspond to objects composed of silicates. Their reflectance spectra show very characteristic absorption bands that can be used to infer their mineralogical composition applying different methods of analysis. Those absorption bands are also present in the spectra of the most abundant class of meteorites (~80%), the ordinary chondrites (OC). In order to better understand the connection between MB asteroids, NEAs and OCs, we undertook a spectroscopic survey of asteroids between 2002 and 2007, using the telescopes and instrument facilities of "El Roque de los Muchachos" Observatory, in the Canary Islands. The survey contains visible and near-infrared spectra (0.5 - 2.5 µm) of a total of 105 asteroids. We have applied a method of mineralogical analysis based on spectral parameters to our sample of NEAs, and also to a sample of 91 MBs and 103 OCs obtained from different databases. We have found some significant compositional differences between NEAs, MBs and OCs. The most remarkable one is that NEAs compositionally differ from the whole set of OCs, and show a more olivine-rich composition, similar to what it is found for LL chondrites (only 8% of the falls). This result suggests that S type NEAs are not the immediate precursors of ordinary chondrites, as it was believed. We consider the size of the objects as the key factor to explain this difference. NEAs are km-sized objects, while meteorites are meter tocm sized objects. Combining the information obtained from the dynamical models and the drift in semimajor axis of the smaller objects due to their thermal intertia (Yarkovsky effect), we set out a possible scenario for the formation and the transport routes of NEAs and meteorites that could explain this compositional difference in a plausible way.

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