NASA rover finds a rock with a hole on it on Mars

[Polybius]

Link to tweet

[WhiteTara]

1. The Flintstones proto type wheel?

[Polybius]

2. It certainly doesn't look natural

If I saw this on Earth, I'd have though someone did that to the rock.

[C_U_L8R]

3. There's a flea on the speck on the frog

on the bump on the branch on the log
in the hole on the rock on the plain on Mars

[Chipper Chat]

4. Fossilized donut.?

[live love laugh]

6. Looks like the ones they sell at Stan's donuts in Chicago.

[GreenWave]

5. Holy Rock!

[tavernier]

7. Erosion

https://en.wikipedia.org/wiki/Hole-in-the-Rock_(Papago_Park)

[Johnny2X2X]

8. Water

Generally, this type of rock formation needs running water to form.

[Turbineguy]

9. Fred Flintstone's spare tire.

[Midnight Writer]

11. The entrance to the morlock's tunnel. Or maybe the deros. They look a lot alike.

[Brother Buzz]

12. How big is that thing?

If I was hazard a guess, I'd say it's a remement of an old vent. No clue how it got separated from the rest of the feature.