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On 26 October, NASA’s Stratospheric Observatory for Infrared Astronomy (SOFIA) confirmed that water exists on the sunlit surface of the moon. This implies that water may be present, spread across the lunar surface– as opposed to previous supposition of it being present only in the cold, dark regions of the moon.
How SOFIA Works and Discovering Water Molecules
SOFIA is a modified Boeing 747SP aircraft that allows the astronomers to study the solar system and outer space in ways that are normally not possible when using ground-based telescopes. SOFIA’s Faint Object infraRed CAmera for the SOFIA Telescope (FORCAST) allows it to observe the infrared universe. Using FORCAST, SOFIA was able to pick up the specific wavelength unique to water molecules at 6.1 microns on 31 August 2018. The preceding spacecraft had mistakenyl detected them as hydroxyl molecules at approximately 3 microns; hydroxyl ions and molecular water are indistinguishable at that particular wavelength. FORCAST’s observations confirm that the previously-assumed hydrogen molecules are actually water trapped inside the moon’s surface. Another interesting observation is that the sunny Clavius Crater contains a relatively surprising concentration of these molecules.
This illustration depicts the Moon’s Clavius Crater with an illustration of water trapped in the lunar soil there, and an image of SOFIA: the observatory that found sunlit lunar water.
Nature of Water on the Lunar Surface
Water was previously thought to be found only in the cooler and perennially shielded surface of the moon, especially on the Southern Pole. Due to this, it was assumed that, since the lack of atmosphere on the moon provided no thermal regulation, the sunless regions were at subzero temperatures, and that water was trapped in the form of ice. Water on the lunar surface is considered unstable in nature on exposure to the sun, and is prone to quick disintegration, thus narrowing the chances that water could be present in the sunlit regions of the moon with higher temperatures. However, planetary scientists, data from NASA, and thermal modelling indicate that water may be trapped in ice on the sunlit areas as well.
“Without a thick atmosphere, water on the sunlit lunar surface should just be lost to space,” said Casey Honniball, who is a postdoctoral fellow at NASA’s Goddard Space Flight Center, Greenbelt, Maryland. “Yet somehow we’re seeing it. Something is generating the water, and something must be trapping it there.”
Formation and Storage of Water
Honniball led a group that was able to observe water in concentrations of 100- 412 parts per million in the high southern latitudes of the moon, trapped in 1 cubic metre of soil. This water was detected as vapour; according to NASA, several forces could be at play in the formation and deposition of this water.
Some of these speculations include micrometeorite showers on the moon, which could be carrying small amounts of water, depositing it upon impact. Another possibility is that the sun’s solar wind delivers hydrogen to the moon’s surface, which reacts with the oxygen-bearing minerals in lunar soil to create hydroxyl. The radiations from the micrometeorites could be transforming the hydroxyl ions into water.
The storage of water creates intrigue as well: some scientists believe that the micrometeorite bombardments may lead to the formation of miniscule bead-like structures in soil due to high heat on impact. Another consideration is that water could be hidden between grains of lunar soil and sheltered from the sunlight.
The new study, which was published in the Nature Astronomy journal, found evidence that billions of micro-craters could hold a tiny amount of water ice each, which are viewed as tiny shadows across the surface of the moon. "If you were standing on the Moon near one of the poles, you would see a whole 'galaxy' of little shadows speckled across the surface," said lead author Paul Hayne of the Department of Astrophysics at the University of Colorado.
The authors of the study state that this means that approximately 4000 kilometres sqs. of the Moon’s surface has the capacity to hold water. They were able to reconstruct the size and distribution of these micro-craters, using high-resolution images and lunar temperature measurements from NASA’s Lunar Reconnaissance Orbiter (LRO).
What are the New Possibilities?
NASA’s plans for the future include SOFIA’s follow-up flights which will look for water in more sunlit locations, and during different lunar phases to learn more about how the water is formed, stored, and deposited across the moon. The data will add to the work of future moon missions, such as NASA’s Volatiles Investigating Polar Exploration Rover (VIPER), in order to create the first water resource maps of the moon for future human space exploration.
Under NASA’s Artemis program, the agency is eager to learn about the presence of water on the moon, before sending the first woman and next man to the lunar surface in 2024. The purpose of this mission is to establish a sustainable human presence on the moon by the end of the decade. NASA also plans to establish a space station in lunar orbit called Gateway, and hopes that excavated ice from the moon's south pole may one day supply drinking water.
“If we can use the resources at the moon, then we can carry less water and more equipment to help enable new scientific discoveries.”
“Water is a valuable resource, for both scientific purposes and for use by our explorers,” said Jacob Bleacher, chief exploration scientist for NASA’s Human Exploration and Operations Mission Directorate.