For decades, astronomers have speculated that there may be water on the moon. In recent years, this speculation has been confirmed to be an orbiting satellite, and another has found water ice near the lunar south pole. In this part of the moon’s surface (called the Aitken Basin, Antarctica), water ice is sustained due to the many permanently shadowed craters located there.
But until now, scientists still assume that moon water can only be found in a crater in permanent shadow. However, thanks to the Stratospheric Infrared Astronomical Observatory (SOFIA) of the National Aeronautics and Space Administration (NASA), water was observed for the first time under the sun of the moon. This discovery suggests that water may be distributed over the entire surface of the moon, not only in dark corners.
The study describing their findings was recently published in the journal Natural astronomy. The research was led by Casey Honniball, a NASA postdoctoral fellow at the Institute of Geophysics and Planetary Research at the University of Hawaii. Members include the Space Science Institute (SSI), Georgia Institute of Technology, Johns Hopkins University Applied Physics Laboratory (JHUAPL), and NASA Goddard Space Flight Center.
SOFIA is essentially a modified Boeing 747SP aircraft equipped with a 2.7-meter (106-inch) infrared telescope. SOFIA’s service ceiling is 11,600 to 13,700 meters (38,000 to 45,000 feet), can fly through 99% of the Earth’s infrared blocking atmosphere, and use the SOFIA telescope (FORCAST) weak object infrared camera to search for other weak objects.
When Dr. Honnibal and her colleagues used SOFIA to observe the moon, they noticed water molecules (H2O) In the second largest crater visible on earth. This is the Clavius Crater, which is located in the southern hemisphere of the moon and has a diameter of 231 kilometers (143.5 miles) and a depth of 3.5 kilometers (2 miles).
As Paul Hertz, Director of the Astrophysics Department of NASA’s Science Mission Department (SMD), said in a recent NASA statement:
“We have signs that H2O-the familiar water we know-may exist under the sun on the moon. Now we know it is there. This discovery challenges our understanding of the surface of the moon and raises interesting questions about resources related to deep space exploration. “
Although previous observations have detected traces of hydrogen in the crater, it is impossible to determine whether it is due to water or hydroxyl (OH). This chemical substance is formed when molecular oxygen in the moon bonds with hydrogen atoms, which is the result of electrons being absorbed by the charged particles (protons) emitted by the sun (solar wind) to travel in space.
Honnibal and her team used the FORCAST telescope to make this decision because the hydrogen they detected had a specific wavelength (6.1 microns) specific to water molecules. As Honnibal said:
“Before SOFIA’s observation, we knew that there was some kind of hydration. But we didn’t know how many (if any) water molecules actually were-like the water we drink every day-or more like a drain cleaner… …Without a thick atmosphere, the water on the surface of the moon irradiated by the sun will only be lost to space. However, we are seeing it to some extent. Something is producing water, and something must trap it there .”
Data obtained by SOFIA shows that the concentration of water in a cubic meter of soil distributed over the entire surface of the moon ranges from 100 to 412 parts per million. This is equivalent to a bottle of about 350 ml (12 ounces), which is 100 times less water than the Sahara Desert. Despite the small amount of water, this discovery is very important because it raises new questions about the source of lunar water and its persistence.
In addition, this discovery has important implications for lunar exploration, especially in terms of long-term missions and lunar habitats. As part of the Artemis project, NASA is seeking to establish a “sustainable lunar exploration” program, which will include bases around the Antarctic region. The presence of water ice can not only ensure the supply of drinking water, but also can be used to make propellants.
“Water is a precious resource for scientific purposes and for the use of our explorers,” said Jacob Blecher, Chief Exploration Scientist of NASA’s Human Exploration and Operations Mission. “If we can use the resources on the moon, then we can carry less water and more equipment to help make new scientific discoveries.”
This finding is also meaningful because it represents the culmination of decades of research. When Apollo astronauts first landed on the moon, the moon was considered completely dry. Interestingly, the rocks returned from these missions provided the first signs of lunar water, although they were rejected due to pollution at the time.
Another interesting aspect of the latest discovery is that it is not a study that SOFIA missions usually conduct. Usually, SOFIA’s high-altitude observations are guided by cameras that track stars, which allows the controller to stably lock the telescope on its target. These include darker objects (such as red dwarfs and black holes) or distant objects such as star clusters and galaxies.
The moon, which is neither faint nor far away, usually fills the entire field of view that guides the camera. After conducting test observations in August 2018, NASA scientists were convinced that it was worth a try. Naseem Rangwala, SOFIA project scientist at NASA Ames Research Center said:
“Actually, this is SOFIA’s first observation of the moon. We are not even sure whether we will get reliable data, but the problem with lunar water forces us to try. Incredibly, this discovery is actually a test. , And now that we know we can do this, we are planning more flights to make more observations.”
Of course, scientists still need to solve many unanswered questions. For beginners, there is a question whether it is possible to enter the water in the sun-lit part of the moon. There are persistent mysteries about the origin of lunar water (whether it is locally produced or deposited), how it accumulates and persists in sunlit areas, and how it is transported on the moon.
NASA hopes to conduct follow-up observations with SOFIA in the near future to collect more data and (hopefully) answer these questions. In particular, they will look for other sources of water in places exposed to sunlight and during different moon phases. The data will also provide information for future missions such as NASA’s Volatiles Survey Polar Exploration Rover (VIPER) and help create the first water source map for human exploration.
Related reading: NASA, Natural astronomy