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SirLauncelot t1_jajdmou wrote

Reply to comment by Embite in NASA’s DART data validates kinetic impact as planetary defense method | DART altered the orbit of the asteroid moonlet Dimorphos by 33 minutes by mepper

If it bounces off, that means a lot of the energy was reflected back. If it takes greater time to sink into the asteroid, more energy is transferred.

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Embite t1_jajvgby wrote

If shrapnel bounces off the asteroid but doesn't accelerate it that would violate conservation of momentum?

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Ouatcheur t1_jalot2h wrote

Nope. The energy that is trsnsferred from the DART to the asteroid CANNOT be higher than the initial kinetic energy it has initially, no matter the way it penetrates the asteroids.

You don't get energy out of nothing!

But people often ignnore that the total enerrgy before must equal the totlal enerrgy after.

And before it is:

DART + ASTEROID.

And after is is:

now-a-bit-saller-ASTEROID + its-EJECTA

People just tend to ignore the ejecta.

so in their minds it is

DART + ASTEROID(before) = ASTEROID(after)

or even worse it is:

DART + ASTEROID(before) + magicalwaytheimpacthappened = ASTEROID(after).

Like in "Oh it hit the dense core so it transferred MORE energy". Morer energy than what exactly? The DART fully crasthe asteroid, its, so it's gonna give 100% of it's kinetic energy no matter what. No "it transfers more than 100% because it hit something more solid". Duuh huuh huuh.

Sp, always remember the ejecta. And note that the ejecta is mostly ejected in the OTHER direction.

So the *only* way for the kinetic equations to balance out is for the asteroid to move faster once accounting for its ejecta (faster than if there hadn't been any ejecta at all).

The solidity of the "central" core part is irrelevant.

As the DART experiment proved, the amount of ejecta gives a MAJOR effect to the results.

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