Other possibilities for what Curiosity may have found:
* A rock that looks like Jesus
* Lord Lucan
* A black monolith
* A second Curiosity rover
* Unobtanium
* That place where all the missing socks go
But in seriousness, I can see this going the same way as NASA's last "Earth shattering" discovery. "They've found alien life!" -> "They've found bacteria on Earth based on arsenic" -> "They've found bacteria that can use arsenic in exactly the kind of place we'd expect to find them" -> "That paper was quite possibly wrong".