Lava tubes under the surface of the Moon and Mars are so large they could host entire planetary bases for future space exploration, planetary scientists claim.
Researchers at the Universities of Bologna and Padua studied the subsurface cavities that lava created billions of years ago under the surface of Mars and the Moon.
These cavities can shield from cosmic radiations, according to the team, who found the celestial bodies held lava tubes up to 1,000 times larger than those on Earth.
Similar tubes found on Earth were measured by the team and used to estimate the size of the ones thought to exist underneath the surface of the other worlds.
The largest of the tubes are found on the Moon and are up to 100ft wide and more than 25 miles long, enough for a base the size of a small town, the team said.
This is an artistic rendering of a possible lava tube. These cavities can shield from cosmic radiation and the Moon holds lava tubes up to 1,000 times larger than those on Earth
The team used data from various interplanetary probes to determine the size and scale of the lava tubes on the Moon and Mars
Tubes found on the Moon are larger than those on Earth or Mars due to the much lower gravity and the impact it had on lava flows in its early development.
Francesco Sauro, of the European Space Agency and Riccardo Pozzobon, a planetary geologist at the University of Padua estimated their scale.
'We can find lava tubes on planet Earth, but also on the subsurface of the Moon and Mars according to the high-resolution pictures of lava tubes' skylights taken by interplanetary probes,' said Sauro.
'Evidence of lava tubes was often inferred by observing linear cavities and sinuous collapse chains where the galleries cracked.'
The way these lava tubes appear on the surface of the Moon and Mars is similar to ones found on the Earth - particularly in Hawaii, Canary Islands and Australia.
These images show the different ways lava tubes are produced on the Earth, Moon and Mars
These tubes have been extensively studied on Earth and the findings have been used to estimate their size, shape and scale on other celestial bodies.
'We measured the size and gathered the morphology of lunar and Martian collapse chains (collapsed lava tubes), using digital terrain models,' said Pozzobon
These were taken from satellite images and laser altimetry devices carried by various interplanetary probes over the years.
'We then compared these data to topographic studies about similar collapse chains on the Earth's surface and to laser scans of the inside of lava tubes in Lanzarote and the Galapagos,' he said.
'These data allowed to establish a restriction to the relationship between collapse chains and subsurface cavities that are still intact'.
Researchers found that Martian and lunar tubes are respectively 100 and 1,000 times wider than those on Earth, which typically have a diameter of up to 98ft.
Lower gravity and its effect on early volcanism helped explain why the tubes on the Moon and Mars are so much larger than on the Earth, the team explained.
Riccardo Pozzobon said tubes this wide can be longer than 25 miles going under the subsurface of the Moon - making it an 'extraordinary target for subsurface exploration and potential settlement'.
These tubes have a wide, protected and stable environment and are big enough that they could contain the entirety of a small town.
'What is most important is that, despite the impressive dimension of the lunar tubes, they remain well within the roof stability threshold because of a lower gravitational attraction', explains Matteo Massironi, from the University of Padua.
'This means that the majority of lava tubes underneath the maria smooth plains are intact,' the planetary geologist explained.
The team used various techniques including 3D modelling to track the path of the lava tubes on the celestial bodies
The authors found that on the Moon the tubes are up to 100ft wide with a length of 25 miles
'The collapse chains we observed might have been caused by asteroids piercing the tube walls. This is what the collapse chains in Marius Hills seem to suggest. From the latter, we can get access to these huge underground cavities'.
Sauro explained that they would provide stable shields from cosmic and solar radiation as well as micrometeorite impacts that happen often on planetary bodies.
A number of projects and design challenges have been happening across the world to create potentially safe designs to help in the colonising of other worlds.
They have used everything from 3D printed materials made from lunar regolith, to beehive like lattice structures design to block meteorites and radiation.
The benefit of the lava tubes, assuming the estimates of their size prove to be correct, would be similar to the human made structures - without the need to build.
They would also have great potential for providing an environment in which temperatures do not vary from day- to night-time.
Researchers examined lava tubes found on Earth to estimate the size and scale of those on the Moon and on Mars
Tubes were found on Mars and the Moon by orbiting satellites and are seen as circles or dents in the surface
'Space agencies are now interested in planetary caves and lava tubes, as they represent a first step towards future explorations of the lunar surface,' said Sauro.
Researchers also point out how this study opens up to a completely new perspective in planetary exploration, which is focusing on the subsurface of Mars and the Moon.
'In autumn 2019, ESA called up universities and industries with a campaign seeking ideas for developing technologies for lunar caves exploration,' said Unibo professor Jo Da Waele, an author of the study.
'They are specifically looking for systems that would land on the lunar surface to operate missions exploring lunar tubes', De Waele explained.
Since 2012, in collaboration with some European universities including Bologna and Padua, ESA has been carrying out two training programmes for astronauts focusing on the exploration of underground systems and planetary geology.
These programmes include lava tubes on the island of Lanzarote and 36 astronauts from five space agencies have received training in cave hiking.
NASA plans to send a manned mission to Mars in the 2030s after first landing on the Moon
Mars has become the next giant leap for mankind's exploration of space.
But before humans get to the red planet, astronauts will take a series of small steps by returning to the moon for a year-long mission.
Details of a the mission in lunar orbit have been unveiled as part of a timeline of events leading to missions to Mars in the 2030s.
Nasa has outlined its four stage plan (pictured) which it hopes will one day allow humans to visit Mars at he Humans to Mars Summit held in Washington DC yesterday. This will entail multiple missions to the moon over coming decades
In May 2017, Greg Williams, deputy associate administrator for policy and plans at Nasa, outlined the space agency's four stage plan that it hopes will one day allow humans to visit Mars, as well as its expected time-frame.
Phase one and two will involve multiple trips to lunar space, to allow for construction of a habitat which will provide a staging area for the journey.
The last piece of delivered hardware would be the actual Deep Space Transport vehicle that would later be used to carry a crew to Mars.
And a year-long simulation of life on Mars will be conducted in 2027.
Phase three and and four will begin after 2030 and will involve sustained crew expeditions to the Martian system and surface of Mars.