How can a paint fleck make a window bullseye?

Question

This answer repeats the fact that something as small as a few micrometers in diameter can make a visible bullseye in a window in orbit. I heard it with respect to the space shuttle, and now they have one on the ISS.

But we’re talking about a total energy delivered of about a microjoule, even at orbital speeds!

How can so little energy make such an impact?

I'd guess it's because it's concentrated in such a small area, something is going to happen, and as glass is so brittle, you can't just have it break in a single tiny spot. — user19742, Jun 11 '17 at 21:55
I'm having trouble finding resources worthy of a SE answer, but the reality is that hypersonic impacts are strange. Strange enough that NASA is willing to spend money building huge vacuum chambers and railguns to throw things at those velocities just to see how they behave. When you can transmit energy/momentum faster than it can propagate through the material, you can strike things in very unusual ways. — Cort Ammon, Jun 12 '17 at 00:48
A microjoule? You're about five or six orders of magnitude off. — Tristan, Jun 12 '17 at 01:50
@Tristan a 2-micron diameter piece of iron moving at 8 km/s has 1 microjoule of kinetic energy. Perhaps the object that caused the damage in the linked photo was a bit larger than that, though. — pericynthion, Jun 12 '17 at 02:50
A chip 7 mm in diameter? Definitely not 2 micron. Closer to 3-400 micron. — Tristan, Jun 12 '17 at 03:18
@Organic Marble how is the debris traveling at 8km/s relative to the spacecraft if they're both in orbit. They can still collide but if it were to be with any meaningful velocity it'd have to be in a retrograde orbit — R. Hall, Sep 11 '20 at 05:05
@ReubenFarley-Hall why are you asking me? I have nothing to do with this question. — Organic Marble, Sep 11 '20 at 06:43
-oh sorry about that, the tag, sorry I should have asked @JDlugosz — R. Hall, Sep 11 '20 at 06:51

How can a paint fleck make a window bullseye?

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