<P> On January 17, 2013 at 05: 21 PST, a 1 meter - sized comet from the Oort cloud entered Earth atmosphere over California and Nevada . The object had a retrograde orbit with perihelion at 0.98 ± 0.03 AU . It approached from the direction of the constellation Virgo (which was in the south about 50 ° above the horizon at the time), and collided head - on with Earth's atmosphere at 72 ± 6 km / s vapourising more than 100 km above ground over a period of several seconds . </P> <P> When meteoroids intersect with Earth's atmosphere at night, they are likely to become visible as meteors . If meteoroids survive the entry through the atmosphere and reach Earth's surface, they are called meteorites . Meteorites are transformed in structure and chemistry by the heat of entry and force of impact . A noted 4 - meter asteroid, 2008 TC 3, was observed in space on a collision course with Earth on 6 October 2008 and entered Earth's atmosphere the next day, striking a remote area of northern Sudan . It was the first time that a meteoroid had been observed in space and tracked prior to impacting Earth . NASA has produced a map showing the most notable asteroid collisions with Earth and its atmosphere from 1994 to 2013 from data gathered by U.S. government sensors (see below). </P> <P> A meteor, known colloquially as a "shooting star" or "falling star", is the visible passage of a glowing meteoroid, micrometeoroid, comet or asteroid through Earth's atmosphere, after being heated to incandescence by collisions with air molecules in the upper atmosphere, creating a streak of light via its rapid motion and sometimes also by shedding glowing material in its wake . Although a meteor may seem to be a few thousand feet from the Earth, meteors typically occur in the mesosphere at altitudes from 76 to 100 km (47 to 62 mi). The root word meteor comes from the Greek meteōros, meaning "high in the air". </P> <P> Millions of meteors occur in Earth's atmosphere daily . Most meteoroids that cause meteors are about the size of a grain of sand . Meteors may occur in showers, which arise when Earth passes through a stream of debris left by a comet, or as "random" or "sporadic" meteors, not associated with a specific stream of space debris . A number of specific meteors have been observed, largely by members of the public and largely by accident, but with enough detail that orbits of the meteoroids producing the meteors have been calculated . All of the orbits passed through the asteroid belt . The atmospheric velocities of meteors result from the movement of Earth around the Sun at about 30 km / s (18 miles / second), the orbital speeds of meteoroids, and the gravity well of Earth . </P>

In which layer of the atmosphere do meteors burn up before impacting earth