Meteoroid

From Encyclopedia Jr, free information reference for Kids

A meteoroid is a relatively small (sand- to boulder-sized) fragment of debris in the Solar System. When entering a planet's atmosphere, the meteoroid is heated up by ram pressure and partially or completely vaporizes. The gas along the path of the meteoroid becomes ionized and glows. The trail of glowing vapor is called a meteor, or a shooting star. If any portion of the meteoroid survives to reach the ground, it is then referred to as a meteorite.

The current International Astronomical Union (IAU) definition dates back to the XIth General Assembly, held in 1961:

"A solid object moving in interplanetary space, of a size considerably smaller than an asteroid and considerably larger than an atom or molecule."

As a result of the inexorable progress of instrumentation, this definition is now deemed by many as unacceptably vague. The most common definition was proposed in 1995 ^[1] and sets the size limits of meteoroids to between 100 µm and 10 m across. Larger than that, the object is an asteroid; smaller than that, it is interplanetary dust. Oddly enough, because it is thought that an object must be about 50 m across before it can survive atmospheric entry^[2], this means terrestrial meteorites never come from meteoroids.

[edit] References

1. ^ Beech, M., Steel, D. I. (September 1995). "On the Definition of the Term Meteoroid". Quarterly Journal of the Royal Astronomical Society 36 (3): 281–284. Retrieved on 2006-08-31.)
2. ^ Task Force on potentially hazardous Near Earth Objects (September 2000). "Report of the Task Force on potentially hazardous Near Earth Objects" (PDF). Retrieved on 2006-08-31.

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See also astronomical objects and the solar system's list of objects, sorted by radius or mass.