This lava tube on Earth may look big, but the ones on the moon and Mars may be large enough to fit ... [+] bases or cities.

Lava tubes on the moon and Mars may be large enough to fit city center-sized groups of astronauts living on these other worlds, a new study finds.

Lava tubes are an underground tunnel that happens due to the flow of molten rock during a volcanic explosion. We get lava tubes on Earth as well, but the ones on the moon and Mars are likely much larger allowing huge communities of people to work, live and explore on other worlds.

A typical tube on Earth will be roughly 30 feet to 100 feet (10 to 30 meters) in diameter. But one on Mars could be the height of the Empire State Building, with a diameter 10 times that of Earth. If that sounds big, consider the moon, where its even lower gravity produces a tube up to 1000 times larger than Earths much taller than the massive Burj Khalifa tower in Dubai.

Its an exciting find because these small, cramped spaces on Earth would instead open up into vast caverns of space on other worlds. Rather than imagining future astronauts working shoulder to shoulder all the time, these space explorers could easily stroll through otherworldly boulevards, all sheltered from deadly outside radiation (and in the case of Mars, fierce dust storms).

"These [lava tubes] represent ideal gateways or windows for subsurface exploration, said study lead author Francesco Sauro in a statement. While weve known about these lava tubes for a while, the new study shows just how large they are able to contain the same space as the city center of Padua, Italy in at least one case, Sauro said.

Sauro is well-versed in cave exploration, as he is head of the European Space Agencys Cooperative Adventure for Valuing and Exercising human behavior and performance Skills (CAVES) program that regularly sends astronauts underground in caves to practice for space missions using an isolated, extreme environment. He is also a speleologist at the University of Bologna.

Japan's Kaguya (SELENE) spacecraft was the first to spot these tubes on the moon, according to NASA. Many follow-up studies were performed using NASAs Lunar Reconnaissance Orbiter, which takes high-definition images of the moons surface from pole to pole. The orbiter has spotted dozens of intriguing holes and NASA is considering ways in which future missions could delve inside. It might be too steep for a rover, so the agency is imagining using swarms of flying or climbing vehicles for exploration.

The researchers used data from moon and Mars imagery and compared that with the literature available on Earth from spelunking (cave exploring) and aerial studies of our own lava tubes. The team also created digital terrain models to get an idea of what these lava tubes on Mars and the moon look like inside, and saw vast possibilities for future exploration.

Astronauts practice for space using an analog cave environment in Sardinia. The European Space ... [+] Agency program is called Cooperative Adventure for Valuing and Exercising human behaviour and performance Skills (CAVES) and has sent dozens of astronauts underground.

"What is most important is that, despite the impressive dimension of the lunar tubes, they remain well within the roof stability threshold, stated Matteo Massironi, a planetary geologist at the University of Padua who co-authored the study. The models indicate, he added, that most of the lava tubes remain intact and very stable, meaning there is little chance of an underground collapse. (Besides which, we can assume future moon engineers would be happy to provide some support structure for extra safety.)

So how soon can we climb into one of these tubes to check things out? NASA is planning to land humans on the moon in 2024, accompanied by a suite of private vehicles under the Commercial Lunar Services Program (CLPS). At first these landers and rovers will be focused on supporting human missions, but there is the possibility of adding science payloads for exploring the lava tubes.

The earliest missions to Mars would happen no earlier than the mid-2030s, of course assuming that the funding and the will persist long enough to make an international coalition possible. We can only send spacecraft there every two years, so a feasibility study for lava tube living would likely be very far in the future given the complication of even getting a vehicle in the tube in the first place.

But perhaps we can be encouraged that the newly launched NASA Perseverance rover mission may be carrying a vehicle that would take the first tentative steps to lunar tube exploration on Mars. The Ingenuity helicopter should be the first flying vehicle on the Red Planet, taking flight sometime in 2021. If the test mission goes to plan, Ingenuitys design could be used for many other future Martian flying vehicles, perhaps including some that could explore the lunar tubes from up close.

A study based on the research was published in Earth-Science Reviews.

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Why We Should Build Astronaut Cities In Moon And Mars Lava Tubes - Forbes