THE WATERMARKED SURFACE OF MOON
Space
Scientists have recently claimed to have laid their hands on iron-cast evidence signaling the presence of water on the surface of moon — in its bone-dry lunar soil as well as in cold dark craters around the poles. Unsurprisingly, this has turned on the tap a bit more to the prospects for a future lunar settlement, potentially allowing for deep space exploration into the far unknown.
Since 1976, when the Americans and Russians wilted in their scramble to hop on the surface of the moon, the heavenly body next-door has remained largely passé. Apparently, its sunbaked soil coupled with its predominantly rough and pitted surface did not have much to appeal to the inquisitive senses of the scientists and researchers, who then engaged themselves in investigating the worlds of other planets beyond: Mars, Jupiter, Saturn, etc. However, serendipity soon came into play as Clementine, an American satellite dispatched moonwards to test some military sensors, unexpectedly made a startling discovery that redirected the spotlight over the moon. That is — the discovery of water.
In 1994, scientists, using a radio transmitter on Clementine as a makeshift radar, reflected some signals off the lunar surface to a receiving dish on earth. After analysing these echoes, scientists discerned that they emulated similar patterns as if dirty ice rather than rocks sprawled there on the moon’s surface, leading them to speculate that the moon possibly harbors water in the form of ice. Nonetheless, doubt remained: similar patterns could also have been replicated by a dry but rough surface or by ices made of compounds even other than water.
Nevertheless, this finding stirred some excitement among the researchers and made newfound water the talk of the town. Accordingly, scientists flew Lunar Prospector, a spacecraft, over the poles of the moon to hunt for ice less ambiguously by making use of a neutron spectrometer. A neutron spectrometer is a device that counts neutrons that cosmic rays have ejected from the atoms on the moon’s surface, and many of these neutrons collide against more atoms on the surface before finally hurtling away into space at different magnitudes of speed. If they hit heavy atoms, such as those constituting minerals in the rocky lunar soil, called the regolith, they do not lose much of their initial speed. In contrast, if they strike atoms weighing merely as much as themselves, like those of hydrogen, then they tend to slow down significantly. Midway flight, Lunar Prospector picked up shots of slow-speed neutrons, hence revealing hydrogen there. Further, since the regolith is composed of very little hydrogen, scientists finally pronounced that it must be water.
Another piece of evidence came to light in late August 2018, when a team led by Casey Honniball, a researcher at University of Hawaii at Manoa, sought to study the sunlit lunar surface using NASA’s Stratospheric Observatory for Infrared Astronomy (SOFIA). This customized Boeing 747SP jet, equipped with its 2.7-meter telescope onboard, soars above 99 percent of the atmosphere’s obscuring water vapor, facilitating observations in infrared without the use of space-based facilities. The observations, focused on a region at high southern altitudes near the moon’s large crater Clavius, unveiled strong infrared emissions at a wavelength of six microns (micrometers) from the crater and the surrounding landscape — yet again, an exhibition of something that plain H₂O would do.
“We are unaware of any other material reasonable for the Moon that exhibits a single spectral feature at 6 µm other than H2O,” Honniball and her fellow researchers report in their new paper.[1]
Questions remain, however: one about the form in which the water exists. One possibility suggests that it is confined inside tiny glass beads of regolith that emerge from the impact of micrometeorites. The theory behind this is that solar wind continuously deposits hydrogen into the regolith. Some of this hydrogen then reacts with oxygen already present as a part of regolith minerals, leading to the creation of hydroxyl radicals. Eventually, when micrometeorites smash the lunar surface, it brings about the vaporisation of the regolith, hoisting its each individual component into space. Thereby, the hydroxyls combine together to form water molecules that are then encapsulated within drops of rapidly cooling regolith as it falls back to the surface.
Quite conceivably, extracting water from such tiny glass beads would constitute an immensely energy-hungry process, making it almost impracticable to carry out on the moon. A more propitious source would be the ice known to exist in huge cold traps. These cold traps are sunlight-shy places located around the poles where the sun, when visible, appears at a shallow angle and shadows are consequently long. This plunges the temperature of the regions to about -230°C, allowing ice to accumulate in substantial deposits. Although relatively more straightforward, harvesting water from this source still poses some difficulties, particularly inaccessibility and forbiddingly low temperatures.
In addition, another aspect of the discovery that remains to be seen is how much water there really is on the moon. Is it sufficient enough to start caring about it? Honestly, there is considerably more than that. Examining high-resolution images of the moon captured by NASA’s Lunar Reconnaissance Orbiter, a team led by the University of Colorado Boulder planetary scientist Paul Hayne learned that there are more cold traps on the lunar surface than they had conjectured. As expected, most lie around the poles, but a small number of them are also present at lower altitudes where, as well, shadows may maintain low-enough temperatures to stock up ice. This raises the total capacity to store water to roughly 40,000 square kilometers — an extensive region about twice the size of Wales!
Now after taking in such an awful lot of information about water on the moon, you might be actually wondering, “After all, why is lunar water so important?” Well, where there is water, there is life! Surely as eggs are eggs, if the earthlings ever plan on erecting a lunar base, they would require essentials that support life: water and breathable air. Firstly, water itself is a very expensive commodity in space: one million dollars alone is the cost of supplying water to the astronauts each day on International Space Station (ISS)! Next, once water is obtained, deriving oxygen from it should not present a complication — the water can easily be decomposed by electrolysis into its constituent elements, one of which is oxygen. For this purpose, work is already underway and so far The European Space Agency (ESA) has proclaimed that a prototype oxygen-generating plant, utilizing lunar regolith, has been developed at its research centre in Netherlands. Lastly, the oxygen collected at the lunar surface can also be liquified to be used as an efficient and powerful rocket fuel to send exploratory missions from the moon itself further into deep dark space.
Conclusively, once we successfully get our hands on lunar water, we may not be much distant from availing all these advantages. However, the need of the hour flags direct measurements as the most important step to follow from the new findings: that is, actually touching the lunar surface and gathering some elaborate ground-based work. But surely until then, we can rejoice in the excitement of a watermarked surface of moon.
[1] “Water Found in Sunlight and Shadow on the Moon — Scientific American,” accessed February 13, 2021, https://www.scientificamerican.com/article/water-found-in-sunlight-and-shadow-on-the-moon/.
Credits:
- Fig.1 provided by Flickr, https://creativecommons.org/licenses/by/4.0/legalcode
- Fig.2 provided by NASA/Jim Ross on Flickr, https://creativecommons.org/licenses/by/4.0/legalcode
