Thermal Properties of Meteorites as Asteroid Analogs - Br. Robert Macke SJ (24.5.2017)
v stredu 24.5.2017 o 13:10 hod. v posluchárni C
Od: Juraj Tóth
Prednášajúci: Br. Robert Macke SJ (Curator of the Vatican Meteorite Collection)
Názov: Thermal Properties of Meteorites as Asteroid Analogs
Termín: 24.5.2017, 13:10 hod., poslucháreň C
Models of asteroid dynamical behavior and thermal evolution are dependent to a large degree on basic physical properties such as density, porosity, heat capacity, and thermal conductivity. For decades, values for these properties had been assumed based on terrestrial analogs, scant measurements, or in some cases nothing more than the educated guess of the modelers, but there were no actual data covering a statistically significant sample of a variety of different meteorite types until recently. The Vatican meteorite collection has in recent decades served as a test bed for new techniques in simple, non-destructive, and non-contaminating measurements of physical properties. This began in the 1990s with the development of the Archimedean “bead method” for measurement of bulk density, a necessary component of determining meteorite porosity. This technique, along with ideal-gas pycnometry for calculating grain density, has now been applied extensively at meteorite collections around the world. In more recent years, we have developed a technique for the measurement of heat capacity of whole stones (20-80 gm) at low temperature by liquid nitrogen immersion. This, combined with precision measurements of mm3-sized samples by our collaborator at Boston College, has sparked renewed interest in meteorite heat capacities as asteroid analogs. These data are particularly important as components of thermal inertia and thermal diffusivity, factors that are critical for modeling Yarkovsky-type dynamic effects and thermal evolution of asteroids, respectively. Liquid nitrogen immersion provides a breadth of data for many (now more than 100) meteorites at a specific temperature (175 K), while the more limited mm3 data provide the shape of the Cp(T) curve over the range of 5-350 K. Combining the two, we produce Cp(T) models for a statistically significant number of meteorites.