New Delhi: A study in Nature Astronomy has reported an underground tunnel or cave on the surface of the Moon for the first time. The tunnel is inside Mare Tranquillitatis Pit (MTP), the deepest-known pit on the Moon.
The study has said that the underground tunnels or caves can protect against the violent solar radiation on the Moon’s surface and are potentially safe, with a possibility for humans to take shelter in them in the future.
Lunar pits — how and when they formed
Formed after volcanic eruptions on the Moon, lunar pits are geological structures that appear as huge depressions with steep walls. They differ from the Moon’s craters, which are flat-bottomed or bowl-shaped and formed when an asteroid or comet strikes.
When the roof of the volcanic cave tubes — tunnels formed under the Moon’s surface by flowing lava during volcanic activity — collapses, exposing their interior, that void is called the lunar pit. The Moon’s surface has more than 200 such pits, with some dubbed ‘skylights’.
Volcanism on the Moon dates back as early as 4.2 billion years ago, with most activity between 3.8 billion and 3 billion years ago. Initially, scientists thought lunar volcanic eruptions ceased one billion years ago. A 2014 study challenged this notion and suggested small-scale lunar volcanic activity over the last 50 million years.
Further, scientists hold that currently, there are no active volcanoes on the Moon’s surface due to the cooling down of the Moon’s interior and the high density of magma inside the Moon’s core.
Contrary to the Earth, volcanism on the Moon lacks plate tectonics. Instead, surface elevation, crustal thickness, and internal lunar composition influence the lunar volcanic eruptions.
Unlike the conical, towering mountain-like structures left behind after volcanoes on the Earth, lunar volcanoes mostly create vast plains. Behind this is the movement of basaltic lava or magma in the deep lunar craters — rather spread out and less explosive owing to a weak gravitational force and the absence of dissolved water on the Moon’s surface.
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Advanced radar captures underground tunnel
Astronomers, led by Lorenzo Bruzzone and Leonardo Carrer from the information engineering and computer science department of the University of Trento, Italy, this year analysed the radar images of the MTP as captured in 2010 by the Lunar Reconnaissance Orbiter (LRO).
Launched in June 2009, the LRO was a NASA spacecraft to map the Moon’s surface in greater detail.
Prior work by Robinson and colleagues had established the existence of pits originating on the Moon’s surface from the collapse of the lava tubes.
The lunar conduits, lunar tunnels, or lunar caves are associated with the lava tubes. Once the molten material flowing in the tunnels cools down and gets drained away, the empty tubes left behind form a long underground tunnel. Scientists have been speculating that these tunnels provide access to the lunar pits. However, direct evidence of the accessibility between the pits and the tunnels/caves was unavailable till now.
Initially, scientists used bottom-looking radar systems to identify the caves/tunnels near the pits. During the latest study, scientists used a side-looking radar imaging system to analyse a cave on the Moon’s sub-surface.
In a statement shared with ThePrint, Lorenzo Bruzzone, one of the lead researchers of the study and professor and head of the remote sensing laboratory at the University of Trento in Italy, said, “During a NASA mission in 2010, the miniature radio-frequency (mini-RF) radar captured a sequence of images of the lunar surface from lunar orbit.”
“After many years, we conducted a fresh analysis of these images using advanced radar signal processing technologies that we recently developed,” he said about the study.
“This analysis revealed that radar reflections from an area in the Sea of Tranquility (specifically, Mare Tranquillitatis Pit) could be linked to an underground tunnel,” he added.
Increased radar brightness, attributed to sub-surface features, that is, the surface, the pit walls, and the overhangs of the MTP, were observed on the west side of the pit. Using the simulation-based analysis, scientists confirmed that the increased radiation from the west side was from a sub-surface cave conduit running tens of metres long.
“This finding marks the first direct evidence, occurring approximately 50 years after initial speculations about lunar caves, of a tunnel or cave accessible beneath the lunar surface,” said Leonardo Carrer, another lead scientist involved with the study and assistant professor of radar and radio localisation at the University of Trento in Italy.
“Detailed data analysis enabled the construction of a model, representing the initial segment of this tunnel, likely a lava tube,” he added.
The scientists estimated that the tunnel was located at a depth of 130-10 metres and measured 30-80 metres in length and around 45 metres in width. The modelling data also predicted the cave’s surface to be either flat or inclined at an angle of 45 degrees and likely accessible.
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How underground tunnels can be future lunar shelters
The Moon’s surface is constantly bombarded with high-energy radiations, namely proton radiations, X-rays, and gamma rays, coming from the Sun and deep space.
Exposure to these radiations can damage human tissues and the central nervous system and even cause cancer. Sudden exposure to intense radiation leads to instant death by radiation poisoning, posing a huge risk to the lives of the crew of manned, lunar missions.
Besides the radiation, the Moon’s surface is also inhabitable due to the extreme temperatures, owing to a lack of atmosphere. At the Moon’s equator, temperatures can vary from highs of 120° Celsius at day to lows of -130° C at night. The situation is more hostile at the two poles.
According to experts, underground tunnels such as the one found in the study, with stable ambient temperatures of 17° Celsius and several metres of thick rock overhead, can offer substantial natural protection from the dangers of radiation and extreme temperatures.
The scientists proposed that the volcanic cave tubes might be quite a common feature under the lunar plains. They also highlighted the MTP and its tunnel as a promising location for establishing a potential lunar base.
They suggested using the methodology of their study to evaluate and characterise other lunar pits and discover more tunnels. Additionally, future exploration of such tunnels could yield new insights about the evolution of lunar volcanism.
NASA’s Artemis-2, which plans to fly a crew of four, including a woman and man of colour, around the Moon in a 10-day mission before returning them home, is scheduled for late November this year.
Muskan Bhatia is an intern with ThePrint.
(Edited by Madhurita Goswami)
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