The team that operates NASA’s Curiosity Mars rover has chosen their fourth rock for drilling. Named the “Bonanza King”, the rock is not in the area they had originally targeted however difficulty driving in the loose sand of the area known as the “Hidden Valley” has forced NASA to change course.

The Curiosity team had originally hoped to find a drilling site in the “Pahrump Hills” by mid-August. However, the ripples of sand on the floor of floor of a valley turned out to be more difficult to drive in than NASA had anticipated after test driving rovers on California sand drones.

The Bonanza King rock is, however, similar to those in the area that they were originally aiming for.

“Geologically speaking, we can tie the Bonanza King rocks to those at Pahrump Hills. Studying them here will give us a head start in understanding how they fit into the bigger picture of Gale Crater and Mount Sharp,” said Curiosity Deputy Project Scientist Ashwin Vasavada of NASA’s Jet Propulsion Laboratory in a statement.

Mount Sharp is Curiosity’s ultimate destination. It offers a stack of layers which should give researchers valuable information about environmental changes on Mars over long periods of time.

The three rocks tested to date have been associated with the floor of the Gale crater, where Curiosity landed in August of 2012. The earlier samples have provided evidence that the Martian environment was once conducive to microbial life. The Bonanza King will, if approved for drilling by engineers, provide evidence of how that environment changed over time.

“This rock has an appearance quite different from the sandstones we’ve been driving through for several months. The landscape is changing, and that’s worth checking out,” said Vasavada

Bonanza King is in one of several patches of slabs about the size of dinner plates on a natural ramp at the northeastern end of the “Hidden Valley”. As Curiosity passed over the rocks, one broke open revealing a bright interior which could indicate mineral veins.

“We considered postponing the first condensed drilling, and we considered other possible drilling targets, but this outcrop on the ramp is too appealing to pass up,” said Vasavada.

As the rover makes its way toward Mount Sharp the NASA team is facing some navigational challenges. Previously, driving over terrain with sharp rocks tore holes in Curiosity’s tires. However, the deep sand of the Hidden Valley proved to slippery to navigate. The team is currently seeking a sandy route where sand ripples do not completely cover the terrain.

“We need to gain a better understanding of the interaction between the wheels and Martian sand ripples, and Hidden Valley is not a good location for experimenting,” said Curiosity Project Manager Jim Erickson of JPL.