Coordenação de Astronomia e Astrofísica - COAA

Descrição do Seminário

High Energy Emissions in Cool Stars, Planetary Habitability and Life

Resumo: Cool stars of class FGKM have differential rotation and convection zones near their surfaces, thus converting fluid mechanical energy into plasma magnetohydrodynamical energy. This energy is amplified by turbulent shear and dissipated at the surface as high-energy photons and high-velocity particles, which then go on to interact with planetary atmospheres. This high-energy emission is strongly modulated by stellar evolution, as cool stars continuously lose angular momentum through magnetized winds, reducing the efficiency of the surface dynamo and subduing the X-ray, UV and particle fluxes as time passes. Our knowledge of planets and exoplanets, including the Earth, is directly driven by their interaction with the parent star, which is the overwhelmingly larger source of energy. Stellar radiation critically affects the composition, thermal properties, evolution and the mere existence of a planetary atmosphere, directly determining habitability and prospects for life. High-energy emissions play a critical role in the habitability of rocky planets in the habitable zones of M dwarfs, owing to the HZ extreme proximity to the star and the stars’ much extended high activity periods. Even for rocky planets protected by strong magnetic fields, particle fluxes may be high enough to depress magnetospheres to the point of fully eroding a planet’s inventory of volatiles. There is evidence that solar magnetic activity was 10,000 times stronger in the infant Sun, a fact of consequence for the early habitability and atmospheric evolution of Venus, Earth and Mars. Also, photochemical reactions driven by photons and particles may alter and/or erode planetary atmospheres, even to the point of building chemical precursors of life. We explore some aspects of this scenario through the case study of the nearby star Kappa Ceti, an analog of the early Sun.

Palestrante: Gustavo Porto de Mello

Instituto: OV/UFRJ

Data: 01/12/2016

Hora: 15:30

Local: Auditório do prédio Emmanuel Liais

Responsável: Luan Ghezzi e Bruna Vajgel

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