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NASA’s SOFIA Discovers Water on Sunlit Surface of Moon
NASA’s Stratospheric Observatory for Infrared Astronomy (SOFIA) has confirmed, for the first time, water on the sunlit surface of the Moon. This discovery indicates that water may be distributed across the lunar surface, and not limited to cold, shadowed places.
Moon’s Clavius Crater with an illustration depicting water trapped in the lunar soil there, along with an image of NASA’s Stratospheric Observatory for Infrared Astronomy (SOFIA) that found sunlit lunar water. Photo: NASA/Daniel Rutter
SOFIA has detected water molecules (H2O) in Clavius Crater, one of the largest craters visible from Earth, located in the Moon’s southern hemisphere.
Previous observations of the Moon’s surface detected some form of hydrogen, but were unable to distinguish between water and its close chemical relative, hydroxyl (OH).
Data from this location reveal water in concentrations of 100 to 412 parts per million – roughly equivalent to a 12-ounce bottle of water – trapped in a cubic meter of soil spread across the lunar surface.
“We had indications that H2O – the familiar water we know – might be present on the sunlit side of the Moon,” said Paul Hertz, director of the Astrophysics Division in the Science Mission Directorate at NASA Headquarters in Washington. “Now we know it is there. This discovery challenges our understanding of the lunar surface and raises intriguing questions about resources relevant for deep space exploration.”
As a comparison, the Sahara desert has 100 times the amount of water than what SOFIA detected in the lunar soil. Despite the small amounts, the discovery raises new questions about how water is created and how it persists on the harsh, airless lunar surface.
SOFIA’s results build on years of previous research examining the presence of water on the Moon. When the Apollo astronauts first returned from the Moon in 1969, it was thought to be completely dry.
Orbital and impactor missions over the past 20 years, such as NASA’s Lunar Crater Observation and Sensing Satellite, confirmed ice in permanently shadowed craters around the Moon’s poles.
Meanwhile, several spacecraft – including the Cassini mission and Deep Impact comet mission, as well as the Indian Space Research Organization’s Chandrayaan-1 mission – and NASA’s ground-based Infrared Telescope Facility, looked broadly across the lunar surface and found evidence of hydration in sunnier regions.
Yet those missions were unable to definitively distinguish the form in which it was present – either H2O or OH.
SOFIA offered a new means of looking at the Moon. Flying at altitudes of up to 45,000 feet, this modified Boeing 747SP jetliner with a 106-inch diameter telescope reaches above 99% of the water vapor in Earth’s atmosphere to get a clearer view of the infrared universe.
Using its Faint Object infraRed CAmera for the SOFIA Telescope (FORCAST), SOFIA was able to pick up the specific wavelength unique to water molecules, at 6.1 microns, and discovered a relatively surprising concentration in sunny Clavius Crater.
“Without a thick atmosphere, water on the sunlit lunar surface should just be lost to space,” said Honniball, who is now a postdoctoral fellow at NASA’s Goddard Space Flight Center in Greenbelt, Maryland. “Yet somehow we’re seeing it. Something is generating the water, and something must be trapping it there.”
Several forces could be at play in the delivery or creation of this water. Micrometeorites raining down on the lunar surface, carrying small amounts of water, could deposit the water on the lunar surface upon impact.
Another possibility is there could be a two-step process whereby the Sun’s solar wind delivers hydrogen to the lunar surface and causes a chemical reaction with oxygen-bearing minerals in the soil to create hydroxyl.
Meanwhile, radiation from the bombardment of micrometeorites could be transforming that hydroxyl into water.
How the water then gets stored – making it possible to accumulate – also raises some intriguing questions. The water could be trapped into tiny beadlike structures in the soil that form out of the high heat created by micrometeorite impacts.
Another possibility is that the water could be hidden between grains of lunar soil and sheltered from the sunlight – potentially making it a bit more accessible than water trapped in beadlike structures. (NASA)
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