Автор: Jakob Deller Название: Hyper-Velocity Impacts on Rubble Pile Asteroids ISBN: 3319479849 ISBN-13(EAN): 9783319479842 Издательство: Springer Рейтинг: Цена: 19564.00 р. Наличие на складе: Есть у поставщика Поставка под заказ.
Описание:
The thesis presents a tool to create rubble pile asteroid simulants for use in numerical impact experiments, and provides evidence that the asteroid disruption threshold and the resultant fragment size distribution are sensitive to the distribution of internal voids. This thesis represents an important step towards a deeper understanding of fragmentation processes in the asteroid belt, and provides a tool to infer the interior structure of rubble pile asteroids.
Most small asteroids are 'rubble piles' – re-accumulated fragments of debris from earlier disruptive collisions. The study of fragmentation processes for rubble pile asteroids plays an essential part in understanding their collisional evolution. An important unanswered question is “what is the distribution of void space inside rubble pile asteroids?” As a result from this thesis, numerical impact experiments can now be used to link surface features to the internal structure and therefore help to answer this question.
Applying this model to asteroid ?teins, which was imaged from close range by the Rosetta spacecraft, a large hill-like structure is shown to be most likely primordial, while a catena of pits can be interpreted as evidence for the existence of fracturing of pre-existing internal voids.
Автор: Haywood Название: Radial-velocity Searches for Planets Around Active Stars ISBN: 3319412728 ISBN-13(EAN): 9783319412726 Издательство: Springer Рейтинг: Цена: 14365.00 р. Наличие на складе: Есть у поставщика Поставка под заказ.
Описание: This thesis develops new and powerful methods for identifying planetary signals in the presence of “noise” generated by stellar activity, and explores the physical origin of stellar intrinsic variability, using unique observations of the Sun seen as a star. In particular, it establishes that the intrinsic stellar radial-velocity variations mainly arise from suppression of photospheric convection by magnetic fields. With the advent of powerful telescopes and instruments we are now on the verge of discovering real Earth twins in orbit around other stars. The intrinsic variability of the host stars themselves, however, currently remains the main obstacle to determining the masses of such small planets. The methods developed here combine Gaussian-process regression for modeling the correlated signals arising from evolving active regions on a rotating star, and Bayesian model selection methods for distinguishing genuine planetary signals from false positives produced by stellar magnetic activity.
The findings of this thesis represent a significant step towards determining the masses of potentially habitable planets orbiting Sun-like stars.
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