Needs to weigh 350 tons to come through the atmosphere largely unaffected. 100,000 million meteoroids enter Earth’s atmosphere every day, almost all very small and burn up in atmosphere. The meteor will arch into a more vertical trajectory, slow to terminal velocity of about 0.1 km/sec and fall as a meteorite. Light emission from incandescence and ion recombination ceases. If a meteoroid’s size, composition, speed and entry angle allow it to survive the “meteor” phase of entry, it will slow to about 4 km/sec and enter “dark flight” at 20 km to 15 km above earth. Most ionization trails become visible at around 95 kilometres up. The left-over debris is called meteoric dust or just meteor dust. In a couple of seconds most meteors are have been consumed. Less frequently seen are the emission lines of hydrogen (H), Silicon (Si), Manganese (Mn), and Chromium (Cr). The most common emission lines from meteors originate from iron (Fe), oxygen (O), magnesium (Mg), sodium (Na), nitrogen (N), and calcium (Ca). Energy goes into melting and vaporizing stone and metal. This plasma becomes visible at between about 120 km and 75 km above the earth. Ram pressure between the air and the object create a very high temperature plasma at the front of the meteor. Incoming meteoroids enter the earth’s atmosphere at 11 km/sec to 72 km/sec. The kinetic energy of an object of mass m traveling at a speed v is = (½) mv 2, provided v is much less than the speed of light. If the meteoroid is of sufficient size to keep it’s hyper-velocity >12 km/sec through the atmosphere becoming an impactor, it will impact the ground and explode. Meteorite Self Test 73rd Annual Meteoritical Society Meeting (2010) 1.
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