Blade Drop

If you drop a lightsaber blade side down, would it cut through the world? What substance can't it cut?

It was my understanding that the only substance not able to be cut by a lightsaber is another lightsaber. Thus, if you drop one with the blade side down, what would stop it from cutting a hole straight through the planet you are standing on?

There actually are materials that a lightsaber cannot cut through, frik for example.
And you don't have to hold a lightsaber for it to stay on, infact it was up to the person who built it, in many cases the builder included pressure sensors that automatically shut off the blade had the user been disarmed (to prevent collateral damage and friendly fire if the wielder lost his weapon.) but that wasn't always the case.
Also, you have to consider that even though a lightsaber could cut through many things, it wasn't always easy. An example of this is episode 1, when Qui Gon was trying to cut through the blast door's lock. He had to slowly cut through because the metal had a high melting temp.
Lastly, while the lightsaber's blade was very powerful, the handles were often much more fragile. So if the lightsaber encountered a thicker metal, even if it was melting through, the molten metal would likely destroy the handle, stopping the blade.

Ryona Vorpal Rabbit -- Blade drop death animation

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