It's official. There is water on the moon.
Led by astronomer Casey Honniball of NASA's Goddard Space Flight Center, a team of scientists studied wavelengths that could confirm or deny the presence of water on our satellite.
The 6-micrometer infrared range should detect a line that can only be created by two hydrogen atoms and one oxygen atom – the so-called H-O-H bending vibration.
But in fact, it is difficult to make an unambiguous detection in this band. This requires the use of the Stratospheric Observatory for Infrared Astronomy (SOFIA), a dedicated, one-of-a-kind telescope that sits in an airplane over the bulk of Earth's atmosphere.
“SOFIA is the only observatory capable of such observations,” Honnibull said.
'Modern lunar spacecraft do not have instruments that can measure in the 6 micrometer range, and from the ground, the Earth's atmosphere blocks 6 micrometer light, and therefore this cannot be done from ground-based observatories. SOFIA flies over 99.9% of the Earth's water vapor, which made the discovery possible. '
Using FORCAST, scientists carefully studied latitudes around the South Pole. There they found the line of radiation they had hoped for – that unique signature that could only be created by vibration of the H-O-H bend.
Based on their findings, scientists estimate the water content to be between 100 and 400 ppm.
Of course, there are no liquid lakes on the moon's surface, and any frozen water will sublimate as soon as sunlight hits it. But the Moon can still contain surface water.
“We think the water is in a glass,” Honnibull said.
'When a micrometeorite collides with the Moon, it melts some of the lunar material, which quickly cools and forms glass. If water is already present, formed during or delivered during impact, some of the water can be trapped in the glass structures. '
In a separate article, led by astronomer Paul Hain of the University of Colorado at Boulder, scientists explored another possibility – regions of constant shadow in polar craters. At high latitudes, the high rims of the craters create areas that sunlight never reaches.
In these areas, temperatures never exceed about -163 degrees Celsius (-260 degrees Fahrenheit), creating cold traps in which hidden patches of water ice can lurk.
Using data from NASA's lunar reconnaissance orbiter, Hein and his colleagues estimate that such a permanently shaded surface could be up to 40,000 square kilometers. And 60 percent of them are at the South Pole.
“In cold traps, the temperature is so low that the ice behaves like rock,” Hein said. “If water gets there, it won't go anywhere for a billion years.”
But we need to get a better idea of where the water might be and how much there is. Haynes' team work will help decide where to look; the work of the Honnibal team gives us insight into how to do this. All we need now is telescope time.
“We were given two more hours on SOFIA and we are asking for another 72 hours,” Honniball said. “With more observations, we will be able to characterize the behavior of water on the lunar surface and understand its source, where it is and whether it moves along the surface of our satellite.”
Both articles were published in the journal Nature Astronomy. They can be found here and here.
Sources: Photo: Permanently shaded areas where moon water may exist. (NASA's Goddard Space Flight Center)
