The one-ton robot geologist was set to pull a sample out of a rock that looked like a slab of "pale paving stone," lying on the northeast end of a place called Hidden Valley. But when the rover performed a little pre-drill exercise – hitting the rock a few times to make a little dent – the rock moved.
If Bonanza King isn't totally stable, the exercise could end up damaging the rover's drill. Rather than risk that, Curiosity's handlers are putting aside their own scientific curiosity for now and putting the rover back on track to its ultimate target, Mt. Sharp, a three-mile-high mound in the middle of Gale Crater.
The team hadn't originally planned for Curiosity to end up in Hidden Valley. They were hoping to reach a rock at a site called Pahrump Hills. But when the rover's wheels kept suffering scarring and damage from sharp rocks on the Red Planet's surface, the scientists tried to reroute through the sandy-bottomed Hidden Valley. But those sands turned out to be a slog.
Before leaving Hidden Valley, the researchers decided to try drilling Bonanza King, given that it seemed to resemble the Pahrump Hills outcrop.
"This rock has an appearance quite different from the sandstones we've been driving through for several months," Curiosity's deputy project scientist Ashwin Vasavada said in a statement this month. "The landscape is changing, and that's worth checking out."
The researchers ultimately decided to forgo the shaky target, which would have been the fourth rock drilled on the Martian surface. The rover has already drilled three rocks since landing in Gale Crater in August 2012. Those first two rocks revealed a chemical smorgasbord in Yellowknife Bay showing that Mars could have hosted environments suitable for microbial life.
Now that they've abandoned Bonanza King, the team can focus on the ultimate prize – Mt. Sharp, whose lower layers of clay-rich rock could hold a veritable trove of information on how habitable Mars could have been over time.
And in the meantime the rover will just have to pick its way as carefully as it can – sometimes even driving backward – across the sharp, unforgiving terrain.