Volcanoes build caves
The caves in the solar system are as diverse as the planets they are located on.
On cold, icy planets like Pluto, Jupiter’s moon Europa, and Saturn’s moon Enceladus, ice volcanoes and geysers can create caves. Volcanoes emit volatile substances such as water and methane, which quickly evaporate and leave voids in the crater or ice cap.
The Moon, Mars, and Saturn’s moon Titan are not covered in ice, so caves here are formed by processes that we also know from Earth.
Caves have always been composed of liquid materials. For example, most caves on Earth were created by water currents that eroded the soil.
But caves can also form from molten surface material resulting from meteorite impacts or lava flows.
If scientists could access the caves of planets and moons in the solar system, they could find answers to all kinds of questions.
In this way, caves can tell us more about planetary geology over time. Studies of solidified lava can reveal the composition of planetary soil.
For example, the Earth serves as an archive of climate history.
Limestone deposits on stalactites in caves in Majorca show that sea levels were more than 16 meters higher 3.3 million years ago: a warning of what lies ahead if we continue to warm the planet.
Biologists and archaeologists also benefit from cave research, because countless discoveries show that our ancestors took refuge in caves.
Furthermore, caves are attractive to animals, as many species never leave the dark, protected environment.
Life thrives in eternal darkness
Biologists have discovered isolated cave ecosystems teeming with life, even though sunlight never reaches them.
Take, for example, Movil Cave in Romania, discovered in 1986, where life was cut off from the outside world for 5.5 million years.
The pitch-black cave teems with pale yellow leeches, snails, spiders, woodlice and scorpions. In a world without light, where no animal has eyes, colors have no meaning.
Lack of light brings not only challenges but also benefits. The cave provides protection from the elements and the temperature is constant 24 hours a day, all year round.
Caves elsewhere in the solar system have the same benefits. For example, the temperature on the moon ranges from 127°C during the day to -173°C at night, but in caves the temperature is more stable.
in 2022 Researchers from the University of California in the US have discovered that the temperature in a crater on the moon, possibly the entrance to a cave, is a very pleasant 17 degrees Celsius.
It is clear that lunar caves provide stable temperatures and safe environments suitable for exploring and living on the moon.
The same could apply to caves on Mars. Not only does it provide a constant temperature, but it also provides protection against violent sandstorms. On both the Moon and Mars, caves would protect us from the deadly cosmic sun.
Cave exploration in space poses significant technical challenges. First, the robots go out to explore.
But because the terrain in caves is likely to be as rugged as caves on Earth, different robots are needed than the rovers that have so far explored the surfaces of celestial bodies.
In 2019, the European Space Agency requested new ideas for robots to explore caves on the Moon. The University of Manchester in the United Kingdom immediately proposed sending a group of boomerang robots to investigate the hole at Marius Hills.
A group of robots could also play a role on Saturn’s moon Titan. Unlike the Moon and Mars, Titan has a dense atmosphere. In fact, it’s so thick and gravity is so weak that we would fly there if we had wings.
NASA is working on a concept called Shapeshifter, which is an array of up to 12 drones. The quintet drones can fly individually, but they can also form a ball together that can roll over terrain or sail over lakes of liquid methane.
So the robots are equipped for any environment they might encounter in Titan’s caves.
However, a major technical problem remains: how do we stay in touch with robots? Radio waves cannot penetrate cave walls, and without communication researchers cannot send instructions to the robots or receive data from them.
A team of engineers has now also come up with a solution to this problem. The team is led by Wolfgang Fink from the University of Arizona in the United States Communication system It was developed for use by a swarm of small robots in Martian caves.
Fink explained that the system was inspired by the fairy tale Hansel and Gretel.
“If you remember the story, you’ll know that Hansel and Gretel scattered breadcrumbs to help them find their way back.”
In the researchers’ version, the crumbs are electronic devices scattered by thieves as they turn a corner or roll through cave corridors.
The devices act as communication points that receive and transmit radio signals from the rovers. This keeps them in constant contact with the larger “Mother Vehicle” at the cave entrance.
The rovers will have lidar that can scan the caves in 3D. One goal is to determine whether they are suitable for human habitation.
On Mars, lava tunnels are interesting as a permanent base and, in the long term, as a colony. Kilometers of tunnels are sometimes hundreds of meters wide, meaning there is a lot of space.
“Lava tunnels and caves are ideal habitats for astronauts because they don’t have to build anything. They’re naturally protected from harmful cosmic radiation, so all they have to do is decorate them and make them comfortable,” Fink says.
If researchers find a nice place to move to, we’ll see if astronauts will be the first to inhabit a cave on Mars or if they’ll have to share a home with native Martians.