Exploring the Moon and Mars means not only scouring their surfaces, but also unraveling the mysteries of their subsurface environments. Now, an international team of researchers has developed robotic rovers specifically designed for these subterranean tasks.
The team behind the new robots tested their creations on the Spanish island of Lanzarote, utilizing a vertical shaft that led to an underground cave as a natural laboratory. Working in tandem, the rovers successfully rappelled down the shaft in a real-world demonstration of their prowess, delving into rugged subsurface terrain.
Challenging Extraterrestrial Environments
The next environments scientists have an eye on exploring are rocky landscapes, featuring even more challenging caves and tunnels. To successfully navigate such terrain, robots will need to be capable of much more than navigating the smooth, artificial environments of indoor laboratories. The complex underground exploration competence demonstrated by the robots is a significant step forward for future missions exploring the caves of Mars and the Moon.
A geological feature well known on Earth is the lava tube. These underground tunnels form in the aftermath of volcanic eruptions, the now-empty channels through which subsurface lava flowed during the volcano’s active period. Such tunnels are not limited to Earth; satellite surveys have previously detected lava tubes on both the Moon and Mars.
Lacking the protection offered by Earth’s atmosphere, such underground locations may be the best options for long-term habitation on Mars and the Moon, shielding astronauts against solar storms, cosmic rays, and micrometeorites. “It could be a very good place to find life signatures, and also to place a human habitat,” says co-author Carlos Pérez-del-Pulgar, a roboticist at the University of Malaga in Spain.
Testing Under Realistic Conditions
The team developed a complex strategy for their two rovers to work together, navigating and exploring the Lanzarote lava tubes safely. Their plan began with the two robots stationed at the entrance of the cave, carefully mapping the area surrounding it. Next, one of the rovers released a smaller probe, similar in design to a cubesat, which was dropped into the cave to scan its immediate environment, allowing for the creation of a detailed 3-D map of the cave entrance. With this data in hand, the rovers were able to calculate the optimal route for a safe descent into the lava tube.
During the initial descent, the smaller rover installed itself onto the larger one in preparation for the trek before they began rappelling down the lava-hewn channel. At that point, the smaller robot then separated from the larger to navigate through 235 meters of rough, rocky terrain to perform another mapping scan.
Pushing Robot Design for Space Exploration
While the robots are capable of some autonomous functions, maintaining communication with human operators remains essential for any potential mission. With that in mind, the team sees mitigating communications issues as their greatest present challenge. The robots are designed to explore deep inside caves, yet rock impedes the radio signals necessary for communication. The team continues to explore solutions in this area.
The team’s inspiration stems from the 2021 US Defense Advanced Research Projects Agency (DARPA) Subterranean Challenge. In that DARPA-sponsored competition, teams deployed a variety of robots, including rovers, drones, and even legged designs, into subterranean environments.
Competition and knowledge sharing within the robotics field are major growth drivers, much like individual teams that bring together diverse teams with specialized knowledge.
The paper, “Cooperative Robotic Exploration of a Planetary Skylight Surface and Lava Cave,” appeared in Science Robotics on August 13, 2025.
Ryan Whalen covers science and technology for The Debrief. He holds an MA in History and a Master of Library and Information Science with a certificate in Data Science. He can be contacted at ryan@thedebrief.org, and follow him on Twitter @mdntwvlf.