What is the rate of disintegration of the average meteorite (avg. density, speed, etc…), assuming it enters the Earth’s atmosphere straight on? How big would it have to be to arrive at the surface the size of a grain of sand?
Not sure about this one. Maybe these links would be helpful…
International Meteor Organization…
http://www.imo.net/
Ask the Astronomer…
http://itss.raytheon.com/cafe/qadir/ametcom.html
What you want to know about are not meteorites, but meteors. They don’t become meteorites until they reach the Earth’s surface. Before they enter the Earth’s atmosphere they are meteoroids.
Most meteors (about 99% of them) tend to crumble into fragments when they hit the atmosphere. These meteors are composed of dust from the disintigration of comets. I wouldn’t expect any of these to reach the earth’s surface in sizes larger than dust particles.
There are classes of less fragile meteoroids, formed from collisions between bodies in the solar system. These are mostly of asteroid origin, with a few that come from comets, the moon, Mars, etc. The classes are irons (made mostly of iron and nickel), stones (similar to Earth’s rocks) and stony irons (a conglomerate rock with metals imbedded). The rate at which they shrink will depend on the speed, the meteor’s composition, and the cross-sectional area.
Their speed relative to the Earth, before they hit the atmosphere, is anything from 12 km/s to 72 km/s.
Here’s a calculator that will let you toss meteors at various planets and determine the size of the hole it makes:
http://janus.astro.umd.edu/astro/impact.html
Cecil’s has a column What are the chances of a huge meteor smashing us flat? His figures indicate that for every meteor that reaches the earth’s surface, there are about 500,000 that burn up completely.