Water On The Moon: New Findings Promise To Make Lunar Exploration A Tad Bit Easier And More Exciting

Two new findings about the Moon came to the fore on Monday (26 October) that expand our understanding — and create new possibilities for human space exploration — of our closest natural neighbour in space.

Using observations from a telescope on a plane, the American space agency National Aeronautics and Space Administration (NASA) revealed that water is present, beyond the cold, dark, and shadowed craters where water is known to exist, in the sunny parts of the Moon.

Even with respect to the well-known presence of water ice in the large permanently shadowed regions, there’s a new development, courtesy theoretical models and data from NASA’s Lunar Reconnaissance Orbiter — water is said to be present in what are called “micro cold traps” or shallow, hidden pockets at the lunar poles.

Both these studies were published on Monday in the journal Nature Astronomy — “Molecular water detected on the sunlit Moon by SOFIA” and “Micro cold traps on the Moon”.

Water on the Moon

According to NASA, water has been detected in concentrations of 100 to 412 parts per million — something like a 12-ounce (0.3 kg) bottle of water — trapped in a cubic metre of soil.

For Earthly comparison, the space agency says that the Sahara desert, which you would associate as having little to no water, has 100 times more water than detected on the lunar surface.

Now, while a surface reading of this comparison may lead some to undermine the detection, it would be a mistake. This discovery holds the key to unlocking some of the puzzles about the Moon and, as an extension of it, our solar system.

But are we sure that it’s water?

The water molecules detected in the Clavius crater, one of the largest on the Moon, have the precise spectral signature of water.

Earlier observations had detected widespread hydration on the Moon, but it was hard to distinguish between water — two hydrogen atoms and one oxygen atom making up the H20 molecule — and its close chemical relative, hydroxyl, made up of single atoms of hydrogen and oxygen (OH).

No methods were available to mark the two compounds apart at the particular wavelength at which they were observed. The Moon Mineralogy Mapper on Chandrayaan-1, for example, had detected absorption features near 2.8 to 3 micrometres.

The features could have been attributed to hydroxyl — and/or water-bearing materials.

But in SOFIA’s case, the absorption features were detected around the 6 micrometre-mark. This is the water molecule unmistakably. The paper says: “...a fundamental vibration of molecular water produces a spectral signature at 6 µm that is not shared by other hydroxyl compounds.”

Where the water was detected, the Clavius crater, can be seen from Earth without the help of binoculars or a telescope. The crater is the second-largest on the visible near-side and has a diameter of about 230 km, nearly the distance from Delhi to Chandigarh.

Clavius was also home to the fictitious lunar base in the 1968 book and feature-film versions of 2001: A Space Odyssey, created by British science-fiction writer Arthur C Clarke and American filmmaker Stanley Kubrick.

SOFIA’s choice

Previous claims about the detection of water on the Moon have come from ground- and space-based telescopes. There is a twist in this latest claim. The “telescope on a plane” that made the observation is the Stratospheric Observatory for Infrared Astronomy or SOFIA. It is a delightful observatory housed within a modified Boeing 747 jetliner.

Flying at altitudes going up to 45,000 feet, the plane carries within it a reflecting telescope with a diameter of 2.7 m. A door on the side of the plane slides open and the telescope peers into the sky.

This largest airborne observatory in the world is a collaboration between NASA and the German Aerospace Center (DLR).

The advantage of this flying telescope, at least over the ground-based variety, is that it can evade almost all of the water vapour in the Earth’s atmosphere by flying up above it.

What’s that good for? To get a good infrared look at the universe. Infrared light falls on the electromagnetic spectrum, lower in frequency to and placed beside visible light (specifically after red light, hence the name).

This infrared light cannot be seen by the human eye, but can be felt as heat.

Making observations in infrared light gives astronomers a view of the universe hidden from ordinary sight. Using this “superpower”, the SOFIA telescope is typically employed to observe the birth and death of stars, new solar systems, nebulae and dust in galaxies, and supermassive black holes.

But two years ago, it was tasked with something different. The telescope was used to view a more relatable celestial object — the Moon.

A test observation was planned in August 2018. Soon enough, the SOFIA telescope was looking at the Moon for the first time. Initially, scientists were unsure whether they would even obtain reliable data from this experiment, but they went ahead with determination in search of molecular water.

Using the Faint Object Infrared Camera for the SOFIA Telescope instrument, comprising a spectrograph and a mid-infrared camera, scientists made observations of the lunar surface at 6 µm.

The team led by post-doctoral fellow C I Honniball of NASA Goddard Space Flight Center looked at two sunlit locations on the Moon – the high southern latitudes near the Clavius crater and a low-latitude section of Mare Serenitatis.

The idea was to look at one place where the water content was reported to be high and another where little to no water was expected. The observation period for each location was set at 10 minutes.

After data was collected and analysed, all spectral images of the Clavius region were found to exhibit a 6 µm emission band — a distinct marker for the water molecule.

What they were looking at weren’t hydroxyl compounds, as was a possibility in earlier observations made over the years, but water molecules.

To be sure, though, this water isn’t in solid or liquid form but just water molecules far apart.

How did water get there?

Several mechanisms may be contributing to the presence of water on the Moon, the researchers behind the study say.

Micrometeorites crashing into the lunar surface, for instance, may be depositing whatever water they are carrying on their backs to the Moon.

Alternatively, a multi-stage process may be at play: solar winds bring hydrogen to the Moon, the hydrogen reacts with minerals carrying oxygen to create hydroxyl, the hydroxyl turns to water with assistance from radiation by micrometeorite bombardment, and voila, you have water.

Meteorite impacts may be playing a part even in the persistence of water on the Moon. It is suggested that the high heat caused by impacts may have led water to be stored in glass beads in the soil. It is possible also that water may have been locked between grains of lunar soil.

Water in cold traps

A different study led by P O Hayne of the University of Colorado Boulder has found that water on the Moon is not limited to the coldest, darkest, deepest craters around the poles — it can exist in what are called ‘cold traps’. These pockets are just as cold, with temperatures going down to minus 163 degrees Celsius, but not as vast, deep, or treacherous.

The idea behind the study is that since the Moon’s relatively stable axis is tilted only 1.5 degrees, the Sun would trace the same route up and down the lunar sky. This would put certain patches on the Moon near the poles under permanent shadow and in these pockets water may be hiding.

Researchers have found that 0.15 per cent of the lunar surface is permanently shadowed, with roughly 10 per cent of this area distributed in patches smaller than 100 m. Patches in greatest abundance are at the scale of about a centimetre only.

Add up all these pockets, which are understood to number in the thousands of crores, and you get an estimate of water potentially spread across an area slightly larger than the state of Haryana. The volume of water is as yet a mystery because the depth of these water pockets is unknown.

It must be noted at this point that there is no proof yet that water ice exists in all these traps, only that they should. This takes us to the next steps.

There’s water, what’s next?

Now that water is definitely known to exist on the Moon, and certainly more widespread than previously thought, here’s what’s in store: questions of science and deep space exploration.

The presence of water on the Moon can help us tackle questions about the origin of water — on the Moon, on the Earth, and in our solar system.

Already we have moved from thinking about the Moon as a bone-dry object in space until much of the last century to now a potential target for sustainable space exploration where humans can live for short periods of time and get work done.

That’s an incredible evolution in our understanding of the Moon. And to now know that there is the stuff of life there, and probably abundant, gives hope that we can determine water’s journey through the solar system.

After all, we are yet to know for sure where all the water on Earth, let alone the Moon or anywhere else, came from.

What is exciting NASA more, and understandably so, is the promise of human space exploration. This is because the space agency has set its eyes on the Moon and Mars. By this decade, it has plans to send a crew (one woman, one man) to the Moon’s surface (2024) and not long after get a lunar base going there.

NASA hopes to use the Artemis experience with repeated trips to the Moon to make the giant, unprecedented leap to Mars in the 2030s.

For any of this to happen, it would help greatly if there was water already on the Moon since it would be a resource that could be mined and used on site rather than shipped all the way from Earth.

Water is heavy. To take all the water necessary for use to the Moon would rob a mission of other critical payloads required to do proper science. But if water doesn’t have to be packed, there’s more that can be taken along on the lunar journey to make exploration more productive.

Lunar water could be extracted for a variety of purposes. For one, it could be used for drinking. Two, it could be broken down into its components hydrogen and oxygen and the latter could be used for breathing. Survival aside, the hydrogen and oxygen of lunar water could be used as rocket propellants for astronauts to either venture further into the solar system, possibly to Mars, or make a return journey to Earth.

In this regard, the study by Hayne and team in particular provides hope. If water is indeed stored in micro cold traps in the polar regions, these zones would be more accessible to astronauts than, say, large, dark craters where a trek down treacherous depths would become necessary. Perhaps now it could be a matter of arriving at the right place and getting a robot to perform a modest operation if not DIY (“do it yourself”).

Until then, more SOFIA flights are set to collect data from Earth. NASA is also expected to deploy a rover named “Viper” to the Moon’s south pole in 2023 – it will help draw up a water resource map for the Moon. Hopefully, it will shed more light on the dark, possibly water-carrying pockets on the lunar surface.

All this promises to make lunar exploration a tad bit easier and more exciting with prospects of scientific discoveries.