Expert: Jayendra Upadhye - 5/16/2008

Question
I came across a question in an astronomy book that I am reading and puzzled for the answer.

The question is: Which of the following is good evidence that the asteroids are not the remains of a shattered planet?

1, No fossils have been found in meteorites.

2, Meteorites appear to have cooled of quickly.

3, Nothing can shatter a planet.

4, Most asteroids have smooth rather than jagged surfaces.

I would think it would be #3, but I read that there was a theory that they came from shattered planets.

I hope you can help.

Thank you.

Sincerely yours,

Mark


Answer
Hi Mark,
Very good question.
1 - No fossils have been found on meteorites:-
   But they have the "ALH(something)" mars meteorite had fossils of
   bacteria or byproducts of bacteria!
   Secondly the statement presumes meteorites come from asteroids!
   Whis is also wrong as proven by the mars meteorite that hit
   Antarctica couple of 10,000s years ago.

2 - Actually a meteorite usually travels @20 - 30 kilometers per
   second.
   At that speed, its surface heats up drastically and most likely
   undergoes ablative cooling. The heat transfer to the center
   involves conduction and specific heat.
   It is a relatively slow process.
   So in case of large meteorites, the inner areas are likely to
   remain relatively cool.
   But "ccoling off quickly" is rather difficult to swallow.

3 - We both disagree with that one.

4 - This is the most strange truth that is difficult to swallow.
   But true it is. Of late probes have landed on an asteroid or two
   and indeed up close we find though irregular, they have a strange
   smoothness about them.

   To me that may be a consequence of two things.
   a) - Localised heating in the vicinity of the cratering makes the
        "pulls in" sharp edges, by simple viscous force.
   b) - very fine dust from the impacts of micrometorites over the
        millenia blankets smaller sharp edges, with a blanket a few
        mm to a few inches thick.
   Most likely, sharp mm level edges persist under this "regolith".

To me,
The most convincing clue whether a metorite is NOT from a shattered planet is the ABSENCE OF STRIATION.
You see, any planet that has had the time to "form" and cool to some hardness, would stratify due to varying densities of its constituents.
A sufficiently large asteroid would then carry with it, a cross section of that stratification. Or atleast areas of large scale non-homogenity (stratification).

But that again would be a function of size and randomness.

Then again the occurance of the Asteroids in the location predicted by  Bode's law clearly points to a planetary origin.

Lastly people go by "relative abundance" of various elements, as found in rocky planets and non-chondrite (carbonaceous) metorites, andfind it is the same! which again points to a planetary origin.

The only meteorites that originated "with but separate from" the planets would be the "carbonacius Chondrites", that are chiefly made of Carbon! Or the ice/dust balls, the larger of which we call comets.
These formed out of the larger outlying areas of the solar accretion disk, and now have their home in the Kuiper belt beyond Pluto / Oort's cloud at the heliopause.

Hope that suffices.
Please do rate the answer.
Jayen