"There are some dents and holes in these wheels, but the rover is still performing well."
As seen in the inset image above, a closeup section of the inner edge of Curiosity's front left wheel not only has obvious denting, there may also be the beginnings of punctures in the aluminum skin. It may seem alarming, but it is an expected consequence of roving on Mars.
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"We will continue to characterize the wheels both on Mars and in the Marsyard, but we don't expect the wear to impact our ability to get to Mt. Sharp," said Heverly.
The top photograph was captured by Curiosity's Mars Hand Lens Imager (MAHLI), a camera mounted on its robotic arm, on sol 275 of the mission to Gale Crater. Periodically, MSL rover drivers command the camera to survey the rover's undercarriage and wheels to look for damage. The famous "self portraits" are used for the same reason - to make sure the rover is fully intact and to monitor dust build-up.
So, when looking closely at the wonderful array of imagery being beamed back from Mars, keep in mind that Curiosity's big wheels were designed to dominate Mars, but don't be surprised if they pick up some battle scars on the way.