The moon in the black sky

‘Moon frost’ spotted near south pole by Nasa orbiter

Image credit: Dreamstime

Data from a Nasa orbiter, the Lunar Reconnaissance Orbiter (LRO), suggests that cold, dark spots near the Moon’s south pole could be home to frost.

The clues were spotted in cold traps: permanently dark and cold areas, such as those hidden on the floor of a deep crater. Under these conditions, water could remain as ice for potentially billions of years.

For more than half a century, scientists have suggested that ice could exist in cold traps on the moon, but it has proved challenging to observe these hidden spots. In the 1990s, Nasa’s Lunar Prospector orbiter identified hydrogen-rich areas near the Moon’s poles, but could not confirm the presence of water.

“What has always been intriguing about the Moon is that we expect to find ice wherever the temperatures are cold enough for ice, but that’s not quite what we see,” said Dr Matt Siegler, an author of the study and researcher at the Planetary Science Institute in Dallas, Texas.

The scientists found evidence of lunar frost by comparing temperature measurements from LRO with brightness measurements from its laser altimeter. Analysing data collected by LRO, they identified bright areas in craters near the Moon’s south pole that were cold enough to feasibly contain ice.

“We found that the coldest places near the Moon’s south pole are also the brightest places – brighter than we would expect from soil alone – and that might indicate the presence of surface frost,” said Elizabeth Fisher of Brown University, lead author of the study.

The icy deposits appear patchy, thin, and possibly mixed with soil, dust and small rocks from the surface: regolith. This is consistent with surface frost, rather than expanses of ice such as a frozen lake.

The researchers’ conclusions are consistent with the 2015 findings of another team, which used LRO data and a different methodology to search for signs of frost.

“These findings demonstrate once again the value of studying the Moon from orbit long-term,” said John Keller, an LRO project scientist at Nasa’s Goddard Space Flight Center. “All of this work begins with comprehensive data sets made up of years’ worth of continuous measurements.”

While the new study adds to the mounting body of evidence that there could be frost in cold traps near the Moon’s south pole, there are no clues so far that there could be frost near the Moon’s north pole as well. As scientists continue to search lunar orbiter data for further clues, they may also begin to ask questions about how old the ice may be and how it first came to be.

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