Expert: Philip Stahl - 12/20/2008

Question
QUESTION: Dr. Stahl,
What would the difference in appearance be between an iron meteor that is still in its "original condition" as it orbits around the Sun and an iron meteorite that has gone through the atmosphere, getting heated and having a sort of melted appearance (or a large one crashing into Earth and smaller ones being splashed up and coming back down)?
Wouldn't the one that is still out there in space have a more rough surface than the one that came down 'cause it did not get slightly melted on the surface? What would the surface of the orbiting one be like?
Thanks so much for your time and hope you are enjoying the winter.
Urania

ANSWER: Hello,

Almost certainly the meteorites that have gone through the atmosphere (assuming they are large enough to survive!) would possess outer surfaces smoother than those traveling through space. This would be especially true of the class called "stony-iron" meteorites since during entry into the atmosphere the stony portion would tend to form a smooth "fusion crust". (Most every basic astronomy text features some photos of these, and you may wish to check them out).

I think when you refer to "melted appearance" it is this fusion crust to which you are referring.

A key and interesting feature about iron meteorites are the large, crystalline patterns called 'Widmanstatten figures'. These figures become evident when the polished, smooth surface of an iron meteorite is etched with acid.

Of course, what meteroids in space *really look like* (their surfaces) must await the first space craft that can "snatch" one and retrieve to examine it carefully. All one can do in the meantime is try to extrapolate from the appearance of actual meteorites to what the original (meteoroid) was like.

One guess currently making the rounds is that large (~ 100 km dia.) "parent bodies" gave rise to assorted meteorites and these generally featured a core of metallic debris and a rocky crust. Most astronomers suspect the asteroids are the most probable "parent bodies" for meteoroids.

Thus, whatever photos or images of asteroids you might see, e.g. Gaspra:

http://neo.jpl.nasa.gov/images/gaspra.html

would be very close to what a meteroid would look like out in space before any interaction with Earth- since meteroids likely emerged from asteroid collisions.



---------- FOLLOW-UP ----------

QUESTION: Just wondering if you have ever heard any talk of interest in retrieving a "pristine" meteoroid out there, or if perhaps they don't think it an important pursuit. I can imagine it would be tricky business and dangerous trying to catch one whizzing by.

Answer
Hello,

I think the retrieval option is simply a lower priority (given budgetary limits) right now. Also, close asteroid flybys, studies hold more import in terms of many different parameters than meteoroids right now. The latter, in other words, are simply not worth the effort - or risk for a direct retrievel mission, given the current budgetary realities.