Distribuição de tamanho-freqüência de asteróides e crateras de impacto: estimativas da taxa de impacto
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ArtigoTamanho-Distribuição de Frequência de Asteroides e Crateras de Impacto: Estimativas da Taxa de Impacto
Abstrato
A distribuição de freqüência de tamanho (SFD) de pequenos corpos no Sistema Solar fornece uma visão importante sobre a origem e a evolução desses corpos. Os principais membros da população de pequenos corpos são asteróides e cometas. O caminho direto para determinar o SFD de pequenos corpos são observações ópticas e de radar diretas. No entanto, a longa distância de um telescópio, normalmente baseado na Terra, coloca severas restrições à integridade das observações quando asteróides menores que 10 km no cinturão principal e menores do que 1 km na população de asteroides próximos da Terra (NEA). contado (Ivezic et al. 2001; Stuart 2001). Os cometas SFD de família Júpiter (JF) e cometas de longo período (LP) são conhecidos aproximadamente devido à presença de coma em pequenas distâncias heliocêntricas e relativamente pequenas estatísticas de observações (Tancredi et al. 2000; ver também Cap. 3).
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(Ivanov, 2008)
Referência: Distribuição de tamanho-freqüência de asteróides e crateras de impacto: estimativas da taxa de impacto
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The terrestrial planets, the Earth's Moon, Mars,Venus, Mercury and the asteroids Gaspra and Ida showstriking similarities in their production crater size distribution characteristics. The investigation of hte crater populations in Gaspra and Ida yield information on the crater size distribution in the source region of the bodieslargely responsibe for cratering the inner solar system planets. Comparison of these data especially with the lunar impact record, which is our most reliable data base, confirms the complex shape of the crater size distribution curve (standarddistibution), and lends strong support to the idea of a common population of bodies impacting the inner planets and largely stemming from the asteroid belt. The steepening of the production crater size distribution at sizes D>= 1 km is confirmed to be due to the characteristics of the primary impactor production size distribution and not to an admixture of objects from secondary cratering processes. The impact hazard for craters, or objects, is assessed for the Earth and the other terrestrial planets relative to the lunar case through application of the lunar production size-frequency distribution which is well known for the crater diameter range 10m>D>1000km. current or past impact rates can be calculated for any size of crater or projectile and are given for specific crater sizes and respective projektile sizes as well as for projectile energies. The impact hazard for projectiles, e.g., capableof forming 1-km craters on solid surfacesof the Earth (if the atomsphere were absent)is assessed for the present and results in a production rate of one crater every 1600 yr for the surface area of the whole Earth, or every 6000 yr for the area of the continents; for 100-km craters, e.g. the corresponding number is one event every 27 Myr for the whole Earth.
The well-investigated size-frequency distributions (SFD) for lunar craters can be used to estimate the SFD for projectiles that formed craters both on terrestrial planets and on asteroids. Our results suggest these distributions may have been relative stable over the past 4 G.y. The derived projectile SFD is found to have a shape that is similar to the SFD of main-belt asteroids as compared with the astronomical observations (Spacewatch asteroid data, Palomar-Leiden survey, IRAS data) and in situ images obtained by space missions. This result suggests that asteroids (or, more generally, collisionally evolved bodies) are the main component of the family of impactors striking the terrestrial planets.
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