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Comment by dm319 | Hacker News Reader

what does the light come from?

The flash is the energy (heat, light) generated by the forces of impact. The asteroid has incredible amounts of energy since it was likely moving very fast compared to the Moon, and it's got to go somewhere.

Layman here. Considering there is no atmosphere on the moon, and stone's conduction properties, does that mean the short flash of light (radiation) was most of the heat energy the impact produced?

You see the part of the spectrum the camera sensor was able to capture. Most of the energy went into displacing/melting the regolith and the shockwave.

There's no shockwave since there's no air on the Moon.

There can be a shockwave along the surface, I suppose, for example.

Could there be a shockwave through the Moon itself?

Possibly, since the regolith is a good conductor.

I meant in the regolith. Can't say if it exceeded the speed of sound in the medium there but given typical impact speeds it probably did. But we can call it a quake if you prefer.

Yes.

There would be no shockwave, just some light and incredible amounts of very localized heat.

Are we sure it didn't just kick up dust into the sunlight?

Looks like the sun might have been just below the horizon.

I thought about this too, but if it were dust, I'm guessing it wouldn't dissipate in 1 second.

Seems like atmospheric intuition.

I'd expect high velocity dust to diffuse rather quickly in near vacuum.

Here's a 2.8km/sec dust cloud from DART for comparison:

https://www.virtualtelescope.eu/wordpress/wp-content/uploads...

If it kicked up dust, would the dust keep going, or would the Moon’s gravity pull it back to the lunar surface quickly? I have no idea.

The moon’s escape velocity is 2.38 km/s (5324 miles/hour), so it just depends on whether or not the material reached escape velocity or not.

Thank you for this! Totally made it click in my head.

In my layman opinion a dust cloud would at very least stick around for much longer than the duration that we see this glowing last. There has to be something else responsible for the flash imo.

It discusses this in the article. The regolith 'Glows' from the kenetic energy transfer, and heat disipation.

The Sun I think.

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