Naturally Occurring Selection Effects on the Terrestrial Accretion of Interplanetary Dust Particles

Abstract

AbstractInterplanetary dust particles deposited in the Earth's atmosphere (IDPs) are an important source of extraterrestrial material. The origin of these particles, whether asteroidal or cometary, is a dispute that can be resolved into two separate questions. What are the fractions of the asteroidal and cometary components of the zodiacal cloud? And what fraction of each component is captured by the Earth? Evidence from the structure of the zodiacal cloud, particularly the dust bands and the Earth's resonant circumsolar ring, indicate that about one third of the cloud is asteroidal while two thirds is cometary. The geometry of capture is such that low eccentricity (e), low inclination (I) particles will be preferentially captured over high e, I particles. Two known abundant sources of low e, I particles are the asteroidal families Themis and Koronis, as witnessed by the associated zodiacal dust bands. We show that capture rates of particles from these two families achieve dominance over every other source. This leads to the result that particles from Themis and Koronis may account for over half of all deposited IDPs and that very few of the IDPs deposited in the Earth's atmosphere are of cometary origin. Furthermore, there are dynamical arguments which suggest that the accretion rate of Themis and Koronis dust particles varies with time. Two perodicities occur, a seasonal variation with a period of six months and a long-term variation with a period near 105 years. The amplitude and period of this long-term variation is supported by measurements of extraterrestrial 3He found in deep-sea sediments.