Curiosity Blog, Sols 4867-4872: Sand Fill In Antofagasta Crater and Finding Our Next Drill Target - NASA Science

On April 17, 2026, NASA’s Mars rover Curiosity arrived at its planned destination: the rim of the Antofagasta crater. This crater is approximately 10 meters, or 33 feet, in diameter. The scientific team had high expectations for this site. They hoped to find a fresh, deep crater with a well-defined rim that had not been significantly eroded by wind or time. Fresh craters are valuable because they expose ancient rock layers from beneath the Martian surface. These exposed layers serve as a geological history book, revealing details about Mars’s distant past. The condition of the crater rim met these expectations. However, the bottom of the crater presented a significant problem.

The crater floor was filled with dark, rippled sand. This sandy material had covered the most scientifically interesting rock layers the team intended to study. The primary goal of visiting the crater was to access rocks that had been protected from harsh space radiation for extended periods. When a crater impact exposes rocks that were previously buried, those rocks can hold crucial clues about the ancient Martian environment. A few rock exposures were visible just above the sand line. These rocks appeared to have been deep enough to have been sheltered from radiation. The main challenge was how to reach them safely. Attempting to drill from the crater rim would have required the rover to tilt at a very steep and awkward angle. In such a position, the rover’s robotic arm would not have been able to accurately deliver a drilled sample to its onboard science instruments.

The team considered an alternative approach. They thought about driving the rover down onto the sandy crater floor to gain a better angle on the exposed rocks. However, this option was deemed too risky. The likelihood of the rover becoming stuck in the loose sand was very high. If Curiosity were to get stuck, it could have permanently ended the mission. The team also examined nearby rock blocks. They wondered if any of these blocks were "ejecta." Ejecta is material thrown out during the formation of a crater. Rocks from deep layers that were ejected could be just as scientifically valuable as the rocks in the crater wall itself.

Unfortunately, all the visible rocks in the crater wall looked very similar to one another. There was no clear way to determine which blocks, if any, came from the deeper layers the team wanted to sample. After carefully weighing these factors, the science and engineering teams made a deliberate decision. They chose not to attempt drilling inside or around the Antofagasta crater. The engineering risks were too great, and the potential scientific return was too uncertain to justify the danger.

Even though no drilling occurred, the area around the crater rim offered many interesting scientific targets. The workspace in front of the rover contained bedrock with noticeable polygonal features. These polygon shapes in the rock typically form from the repeated cycles of drying and wetting mud, or from freezing and thawing processes. Studying these features helps scientists understand the environmental conditions that existed in the past.

The team planned a series of observations from their safe position on the rim. They used the rover’s cameras to take detailed images of the crater and nearby buttes, which are small, flat-topped hills. They used the Alpha Particle X-ray Spectrometer (APXS) to measure the geochemistry, or elemental makeup, of the rocks. The Mars Hand Lens Imager (MAHLI) captured close-up pictures of the rocks containing polygonal patterns. Additionally, the Chemistry and Camera instrument (ChemCam) used its laser to zap rocks and analyze their chemistry from a distance.

The plan also included ongoing monitoring of the present-day Martian environment. Curiosity regularly watches for dust devils, which are small, spinning columns of dust. It also measures atmospheric opacity, which indicates how clear or dusty the air is, and looks for clouds. These observations help scientists understand modern Martian climate and weather patterns. This continuous monitoring provides valuable context for the geological data gathered from rock samples.

With the decision to not drill at Antofagasta finalized, the team immediately began planning the next drilling campaign. Curiosity is currently exploring a region on the slopes of Mount Sharp. This area is known for its layered sulfate rocks. Sulfates are minerals that often form in salty water, indicating that Mars had a wetter past. The rover has been driving up through an area called "Valle Grande."

As it drives, the team has been examining the exposed rock layers in the buttes above them. Based on these observations, scientists have mapped out a sequence of layers. These layers show different styles of sediment deposition and varying levels of "diagenetic" activity. Diagenesis refers to the physical and chemical changes that occur in sediment after it is deposited, eventually turning it into solid rock. By climbing southwards, the rover will encounter these different rock layers one by one.

It had been quite a while since Curiosity drilled into what the team considers "typical" layered sulfate rocks. The last such drill campaign was named "Mineral King" and took place in February and March of 2024. That location was more than 150 meters, or 492 feet, lower in elevation. Since then, the rover has studied distinctive regions like the "boxwork" unit and Gediz Vallis. The boxwork refers to a specific network of ridges found in the rock.

The goal for the next drill campaign was clear. Scientists wanted to measure a representative bedrock sample from the rock layers just above the boxwork-forming unit. This would help them understand how environmental conditions changed as the rover moved up Mount Sharp. On Martian day, or sol, 4870 of the mission, the rover’s workspace presented a promising opportunity. Right in front of the rover was a block of rock that looked both drillable and representative of the surrounding bedrock.

The team named this potential drill target "Atacama." They planned preliminary measurements on it to decide if it was suitable for drilling. These measurements included APXS geochemistry analysis, MAHLI close-up imaging, and ChemCam laser analysis. The team also planned some measurements on the surrounding blocks for context. This ensures that the chosen target is truly representative of the broader area.

If the results from these preliminary checks look good, the next step would be a "preload test." This is an engineering test where the rover presses its drill bit against the rock to see if the rock is stable enough to drill into successfully. Success in this test would lead to a new set of precious drill data from the surface of Mars.

Curiosity’s journey up Mount Sharp is a deliberate climb through Mars’s geological history. Each layer represents a different chapter in the planet’s evolution. The decision at Antofagasta Crater shows the constant balance between scientific curiosity and engineering safety. While the crater itself did not yield a drill target, the process of investigating it provided valuable data about the landscape. It also reinforced the importance of careful planning in space exploration.

The search for the next drill target at "Atacama" exemplifies the mission's systematic approach. The rover does not drill at the first rock it sees. Instead, it uses its full suite of instruments to scout, analyze, and confirm before committing to the complex drilling operation. This method ensures that every drilled sample delivers the maximum possible scientific return. Each successful drill campaign adds a crucial piece to the puzzle of how Mars changed from a warmer, wetter world capable of supporting life to the cold, dry planet we see today.