Query - Minimum size for asteroids?

Murazor · Post by **Murazor** » 2006-09-25 05:24am

As the name suggests, I'd want to know if there is a scientific standard for the minimum size a space rock must have in order to be considered an asteroid. Wikipedia's entry hasn't been very helpful in this.

Gil Hamilton · Post by **Gil Hamilton** » 2006-09-25 08:39am

Usually when they are big enough to no longer be space dust and aren't falling to Earth. So tiny.

Post by **Surlethe** » 2006-09-25 11:11am

That's what I thought at first, but wouldn't those be considered meteroids? I think the question boils down to, if one exists, what the distinction between meteroid and asteroid is. I'm not sure of the answer.

Sriad · Post by **Sriad** » 2006-09-25 11:41am

From wikipedia (meteoroid):

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.

Oh, astronomers and their vague definitions...

GrandMasterTerwynn · Post by **GrandMasterTerwynn** » 2006-09-25 11:43am

Presumably, the smallest asteroids are the smallest ones that can be reliably detected and tracked. In general, for most asteroids this size limit would be a diameter of a few hundred meters to a few kilometers. However, among the smallest asteroids to be tracked and formally named is 1991 BA which was all of five to ten meters wide. It was detected, in spite of its miniscule size, because it came as close to 177,000 kilometers (110,625 miles) from Earth.

Gil Hamilton · Post by **Gil Hamilton** » 2006-09-25 02:44pm

Surlethe wrote:That's what I thought at first, but wouldn't those be considered meteroids? I think the question boils down to, if one exists, what the distinction between meteroid and asteroid is. I'm not sure of the answer.

Meteoroids are what they call asteroids that are just too small to be directly observed from Earth and/or haven't hit our atmosphere yet to become meteors. If you were looking at one in space, it would just be a pissant asteroid. Remember, an asteroid is any small rocky celestial body that we aren't giving a special name like "planet" too. They through out terms like "micrometeorite", "meteoroid" etc to distinguish size, but they are all asteroids.

Post by **Surlethe** » 2006-09-25 02:45pm

Gil Hamilton wrote:
Surlethe wrote:That's what I thought at first, but wouldn't those be considered meteroids? I think the question boils down to, if one exists, what the distinction between meteroid and asteroid is. I'm not sure of the answer.
Meteoroids are what they call asteroids that are just too small to be directly observed from Earth and/or haven't hit our atmosphere yet to become meteors. If you were looking at one in space, it would just be a pissant asteroid. Remember, an asteroid is any small rocky celestial body that we aren't giving a special name like "planet" too. They through out terms like "micrometeorite", "meteoroid" etc to distinguish size, but they are all asteroids.

That makes sense. Thanks.

darthkommandant · Post by **darthkommandant** » 2006-09-25 10:31pm

The Book Astronomy The Definitive Guide to the Univers by Duncan John Give a definition of a meteoroid as being a rocky or metallic fragment less 50m in diameter. An asteroid is defined as a fragment of rock or metal greater than 50 km in diameter. This size is determined by the ability for the object to pass through Earths atmosphere.