NASA Can't Explain What Made This Strange, Deep Hole on Mars (sciencealert.com)

Cool image. Im guessing some more alien conspiracy theories will arise from it.

This looks like it has to be a collapse of some void below.

There's no ejecta around the crater, or any of the other impact signs.

I'm no expert, but that looks like a gas pocket of some sort ruptured, created a cavity and collapsed in on itself. Kind like those methane craters in Siberia.