In northeastern California lies a series of caves that formed thousands of years ago when volcanoes erupted lava that later solidified, leaving behind tunnels wide enough for humans to walk through. But Earth isn’t the only planet in our solar system with volcanoes — extraterrestrial caves formed all across the solar system.
Take Mars, for instance. Millions of years before life on Earth came to be, volcanoes erupted on the Red Planet, too. Martian volcanoes appear to be dormant right now, but that former activity left behind the largest tunnel network in the solar system. The resulting lava tubes stretch over 820 feet (250 meters) across, more than eight times the width of California’s tunnels. So far, researchers have found tube systems on Mars reaching over 746 miles (1,200 kilometers), enough to cover the continental United States three times over. Plus, scientists think more tunnels are yet to be discovered.
But in order to understand how vast the network is, scientists are pushing at the limits of space exploration. One of these scientists suggests the idea of “dandelion drones.”
At present, our Mars exploration efforts have been pretty heavily based around rovers, like Curiosity and Perseverance. However, as pioneering as these robotic vehicles are, they’re reaching their limitations when it comes to lava tubes.
“The rovers are the size of a school bus,” Mostafa Hassanalian, associated professor at New Mexico Tech, told Space.com. “That’s why they can’t get in.”
The atmosphere of Mars is also unforgiving, meaning winds of up to 60 miles per hour (97 kilometers per hour) can battery these explorers, and have even torn chunks out of Curiosity rover across the years.
What’s a dandelion drone?
Hassanalian’s drones are designed on the idea of biomimicry: the concept that robotics should copy what we observe in nature instead of reinventing what nature already succeeds in doing.
Biomimicry often fails when the design is too large, Hassanalian says, but is most efficient on the microscale. “There’s a reason airplanes don’t flap,” he explained.
For example, the dandelion drone concept begins with another kind of robot Hassanalian and his team designed called the “roly-poly robot,” based on a pillbug, which rolls up into a ball when threatened. The idea is to deploy a pillbug drone through a hole in the roof of a cave, equipping it with a parachute to allow it to drift down to the cave floor. This roly-poly robot will be holding thousands of small drones, or dandelion drones, within.
The pillbug robot will then release all of those thousands of drones in the cave, with the dandelion robots being propelled by Mars’ strong winds for miles upon miles and mapping out the tunnels as they fly.
However, one hurdle will be making sure there is enough wind to carry the dandelion drones. Because nothing human-made has ever entered Martian lava tubes, scientists aren’t exactly sure how strong the winds will be. A lack of wind would pose a problem.
But many researchers think the holes in the cave system ceiling will ventilate the tunnels, making them very windy. Plus, the robot comes equipped with a high-powered fan, in case the wind isn’t strong enough or dies down.
Another complication the team must think about is the fact that sunlight can’t enter the cave, so solar panels — the most common source of powering a spacecraft — won’t work. Instead, Hassanalian has designed the dandelion drones to work with piezoelectricity, made from a flexible polymer which generates an electric charge.
During the design phase, the team also realized that air-propelled seeds in nature are usually white because they reflect more sunlight, keeping them cooler and lighter. They thus plan to paint the dandelion drones white to let them travel further.
Once in the air, the dandelion drones would transmit data via radio signals, collecting readings on humidity, temperature and eventually creating a blueprint of the entire tunnel system.
A race to the tunnels
Hassanalian’s isn’t the only team looking at lava-tube exploration. In a series of tests beginning in 2023, a group of European scientists led by the Space Robotics Laboratory at the University of Malaga dropped robots into lava tubes found on an island in Spain called Lanzarote in order to map out the tunnel system in preparation for a possible future Mars mission.
NASA has also made 72 flights using the Ingenuity Mars Helicopter across the planet’s surface, proving the potential for further exploration. But this drone was designed to fly in the open air, and never got a chance to venture into the lava tubes before ultimately meeting its demise in 2024.
Drone plans developed by NASA suggest the space agency is particularly interested in Arsia Mons, a shield volcano in Mars’ Tharsis region, which includes the largest volcanoes in the solar system, such as Olympus Mons — almost three times as high as Mount Everest.
The Tharsis region alone is the size of the dwarf planet Ceres. When the bulge formed, it added so much mass that Mars is thought to have tilted approximately 20 degrees. The exact reason why is debated by scientists, but theories include a huge collision in early Martian history, or unstable mantle plumes.
The Arsia Mons volcano is of particular interest to NASA because the agency spotted holes in the shield where the volcanic ceiling had collapsed, leaving skylights behind and revealing a vast tunnel network within.
Thermal readings taken from the volcanic holes suggested that the temperature inside wasn’t changing as drastically as the surface, exciting hopes that humans could one day within, and even the idea that life native to Mars had survived inside.
NASA is also eyeing up potential caves on Titan, Saturn’s largest moon, selecting Johns Hopkins’ “Dragonfly” spacecraft to explore the surface.
Humans aren’t supposed to land on the planet until the 2030s at the very earliest. When that day finally comes, drone scouting could prove vital for humanity’s long-term survival on Mars.