By Aoife Hilton for ABC
This is a high-Sun view of the Mare Tranquillitatis pit crater revealing boulders on an otherwise smooth floor. This image from LRO’s Narrow Angle Camera is 400 meters (1,312 feet) wide, north is up. Photo: NASA/Goddard/Arizona State University
New research has indicated that a cave found on the Moon provides ideal conditions for human exploration.
Research published in the journal Nature Astronomy on Monday analysed images that NASA's Lunar Reconnaissance Orbiter (LRO) spacecraft took in 2010 of a pit in the Mare Tranquillitatis.
The site, where Apollo 11 landed in 1969, is visible from Earth.
The Nature Astronomy paper confirmed previous research from Geophysical Research Letters last year, which indicated the pit led to a Moon cave.
The cave extends approximately 100 metres deep and at least 45m wide, the study says.
It has a skylight on the Moon's surface, leading down to vertical and overhanging walls, and a sloping floor that might extend further underground.
Scientists have suspected there may be caves on the Moon for more than 50 years.
They first discovered pits on the Moon in 2009 and wondered if they led to caves, but didn't confirm the theory at the time.
A 'possible option' for a lunar base
This morning, one researcher told ABC Radio National the Moon cave marks a possible site for humanity's next lunar base.
Lorenzo Bruzzone, director of the Remote Sensing Laboratory at the University of Trento in Italy, said the cave's mild temperatures and shield from radiation could help human explorers.
"One of the possible options for building a lunar base is to exploit these cavities because they shield the possible human beings, astronauts, from the radiation that we have on the surface," he told RN Breakfast.
"We have a climate which is much more mild than what we have on the surface, where we have big changes in temperature between the night and the day."
While the lunar surface heats up to about 127C during the day and cools to around -173C at night, the Geophysical Research Letters study estimates the cave consistently hovers at a balmy temperature of 17C.
The study notes the visible overhangs on LRO images of the pits both indicate the presence of the cave itself and shield it, limiting the extreme heat from entering during the day and preventing it from radiating away at night.
A day on the Moon lasts about 15 Earth days.
'Sub-surface' exploration needed
Although the study only confirmed the existence of one Moon cave, it indicated there were others.
Bruzzone said more Moon cave exploration was needed to find the ideal spot for our next lunar base.
"We don't know if this specific cave is the right one for the astronauts," he said.
"We could have a robotic mission that, first of all, goes there and explores the cave to understand what is in the sub-surface."
The study identified more than 200 pits, 16 of which researchers said were probably collapsed lava tubes.
Lava tubes - also found on Earth - form when molten lava flows beneath a field of cooled lava or a crust forms over a river of lava, leaving a long, hollow tunnel.
If the ceiling of a solidified lava tube collapses, it opens a pit that can lead into the rest of the cave-like tube.
Two of the most prominent Moon pits have visible overhangs that clearly lead to caves or voids, and there is strong evidence that another's overhang may also lead to a large cave.
The Moon was home to "a lot" of volcanic activity two to three billion years ago, according to Bruzzone, opening up the possibility of a vast system of caves and tunnel-like lava tubes under the surface.
However, more exploration was needed.
"There is the possibility to explore the sub-surface of the Moon," Bruzzone said.
"These caves can also [reveal] the presence of water, ice or other resources. So it could be interesting not only for humans as possible habitation, but it could be very interesting for taking resources for astronauts."
- ABC