For more than a month now, Mars Rover Curiosity has been preparing to test its hammering drill on a Martian rock. The rover team took great pains to scan a low-lying area called “Yellowknife Bay” for the perfect rock specimen.

Today, researchers have announced that the a flat rock with pale veins has been chosen as the target. Curiosity is currently on-route to the rock, which NASA has named “John Klein” in tribute to the former Mars Science Laboratory deputy manager of the same name who died in 2011. If the rock still looks interesting to researchers when the rover gets a closer view, it will become the first Martian rock to be drilled for a sample.

“Drilling into a rock to collect a sample will be this mission’s most challenging activity since the landing,” said Richard Cook, Mars Science Laboratory project manager at NASA’s Jet Propulsion Laboratory (JPL). “It has never been done on Mars. The drill hardware interacts energetically with Martian material we don’t control. We won’t be surprised if some steps in the process don’t go exactly as planned the first time through.”

The rover team is hoping to find evidence of Mars’ watery past inside John Klein. The rock was chosen because of the light-toned veins that were detected using Curiosity’s Chemistry and Camera (ChemCam), indicating elevated levels of calcium, sulfur, and hydrogen.

“These veins are likely composed of hydrated calcium sulfate, such as bassinite or gypsum,” said Nicolas Mangold, ChemCam team member at the Laboratoire de Planétologie et Géodynamique de Nantes. “On Earth, forming veins like these requires water circulating in fractures.”

(Image courtesy NASA/JPL-Caltech/MSSS)