Oblique impacts

[Xerxes68]

Looking at some tracks that appear as scuffs forming lateral tears in the surface. Can these be true tracks? Being no expert in physics, it does seem to me that if even a microscopic particle travelling at 60k mph hit the aerogel at a very shallow angle its impact would be sufficient to cause it to deflect into the gel and not skid across its surface ducks and drakes fashion. I would be interested in anyone's views on this.

[ZackG]

Yes, I think this is correct. There would certainly be some critical speed for a given particle that would determine whether it reflected off the aerogel or went in. I expect for all practical purposes, for a very fast particle, that angle cannot be distinguished from 90 degrees (i.e. parallel to the surface of the aerogel). However, also remember that particles fragment and the aerogel isn't perfectly flat and a number of other variables. I don't think we have a theoretical reason to exclude either possibility at this point (and probably not ever since I don't think this is a problem that is sitting heavily on the theorists' minds...)

I think more important is the question of how many of these scratches exist... I doubt there are hundreds of particles hitting at just about exactly 90 degrees, and not so many at any other angle. So what the phenomena is caused by is not really clear ... [enter imagination]

[GelDelve]

I expect for all practical purposes, for a very fast particle, that angle cannot be distinguished from 90 degrees (i.e. parallel to the surface of the aerogel).

I've been trying to find in the various sites with Stardust information, here and at NASA and JPL, if the aerogel surface was flush to the top of the tray it was carried in. I know that since the aerogel surface undulates considerable that at least some of the aerogel cannot be even with the top of the tray, but what if it was only placed into the tray so that the highest aerogel surface is 1mm or even 5mm from the top? That might make it almost impossible for a particle to enter at a 90% angle (relative to the direction and speed of the moving space craft). I can't remember for sure who said it, maybe Dr. Butterworth, but it is suspected that particles that enter at rather oblique angles into the aerogel surface are probably not interstellar, since the detected interstellar stream is flowing in a generally parallel course with the space craft when the capture tray was opened and exposed for capture.

I also could not determine what the tray material is. It looks like aluminum or possibly stainless steel. I'm guessing aluminum because of the weight factor. Aluminum is a relatively soft metal. A couple of particles hitting very close to the edge of the aluminum tray could have either deflected a particle at an angle different than it's initial approach or separated some tray material that skimmed the aerogel surface or both.

Just a couple of thoughts I had on this subject!

[fjgiie]

Interesting links if not completely on topic.

http://stardustathome.ssl.berkeley.edu/ ... light=#968
we do not know what angle ipd dust comes from.

http://stardustathome.ssl.berkeley.edu/ ... ight=#6477
nothing but IS no comet dust

http://stardustathome.ssl.berkeley.edu/ ... ight=#1042
4000 now 5000 total

If aluminum, it's probably 6061-T6 or 5052.
http://www.ez.org/aluminum.htm

This only says aluminum - http://stardust.jpl.nasa.gov/mission/capsule.html

[ZackG]

Yes, the tray is made of aluminum. In addition, the portion of the tray that was exposed to space is covered in an aluminum foil that can be peeled off and examined as its own "collector". A particle impacting the aluminum foil makes a small (typically microsopic) crater rather than a track.

A particle really can't enter at exactly 90 degrees because the tiles are contained entirely in their frame, and the aerogel is recessed towards the middle of the tile. A particle can come in pretty close to 90 degrees, though admittedly, that's not likely. If you do math, remember that the size of the collector shrinks when coming in from sharper angles: I.e. looking from the side, the size of the collector is A*cos(90) = zero. It's like looking at a sheet of paper from the side...

So even if we had interplanetary particles coming in from a sharp angle, we should see fewer of them than head on.