NASA's Mars Reconnaissance Orbiter launched 12 years ago, and it's still finding parts of the red planet that are stumping scientists.
The space agency recently released this photo of a large hole tucked near Mars' south pole.
The researchers have no answer for how the hole got there.
But scientists have two top guesses. One is that the hole is an impact crater.
NASA has found many of these on the planet. Scientists believe the craters can be used to track the age of different parts of Mars' surface.
The other explanation could be that a bit of Mars' surface collapsed. The newly spotted hole is in an area of the planet with "Swiss cheese terrain" –– a nod to the many shallow pits within the carbon dioxide ice. The idea is that one of these pits may have sunk further.
No matter what caused it, the hole is likely pretty massive. Some estimate it's hundreds of meters across.