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Every year the Earth’s atmosphere is bombarded by 30,000 tons of micrometeorite dust particles. Those that are collected at the Earth’s surface are similar in chemistry and mineralogy to porous, wet meteorites. These finds only comprise of 2.8 per cent of recovered meteorites, leaving a large difference in the relative abundances in recovered dry meteorites.
The difference has been attributed to ‘filtering’ from the Earth’s atmosphere, with the porous meteorites being to weak to survive the impact with the Earth’s atmosphere. New results published in 1 May Nature by scientists at Kobe University in Japan give another explanation, concerned with the type of asteroid the dust originates from.
Using a specially designed gun to fire projectiles at 4 026 miles per hours at suspended meteorites, scientists were able to recreate collisions between asteroids in space. Comparing wet and dry targets the Japanese scientist Kazushige Tomeoka concluded “The application of shock to the watery meteorite reduced it to minute particles and produces explosive expansion upon release of the pressure, in contrast to the dry meteorite that does not show significant changes.”
The results show that meteorites collected on Earth are a result of events in space. When wet asteroids collide the impact shock at the surface only expels dust in to space. Where as a dry asteroid will not produce dust but will create fragments whose greater size increases the probability of surviving the fall to the Earth’s surface.
Most asteroids roam around the Sun in a belt between Mars and Jupiter. The fragments of their collisions, and the dust are drawn towards the inner solar system and sometimes cross the Earth’s orbit. The relatively fast moving debris frequently slams into the Earth’s atmosphere and burns up on entry, generating streaks of light know as ‘meteors’ or ‘shooting stars’. Debris moving more slowly will be captured by the planets gravity and can survive the fall.
More info: http://www.nature.com/nature/links/030501/030501-4
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