Scientists have used a telescope on a plane to confirm observations of water on the Moon.
Research also shows the Moon’s shady zones that could trap water are widespread, and the water could be used in future lunar missions. NASA will announce these study results when the embargo lifts on Tuesday morning.
The SMC asked experts to comment on the research.
Associate Professor Jan J. Eldridge, Department of Physics, University of Auckland, comments:
“These two studies are quite remarkable and show us, even though life has looked at the Moon since eyes first evolved it still has a lot to surprise us with.
“Evidence for water, ice and hydration has been inconsistent in the past. Here the study by Casey Honniball and colleagues shows the first clear detection of a signal that can only be due to molecular water. Previous studies could not rule out other molecules with an “O-H” bond in their structure. What’s really interesting is this signal is coming from the lunar surface at high latitudes, the water is still there even under sunlight where we might expect the heat to bake the surface dry. The authors suggest it is locked away and protected inside or between grains of lunar soil. This finding suggests getting water from the lunar surface might be a simple as grinding it up to get water. Although a rough calculation suggests you’d need to process 15 tonnes of rock to get a day’s water intake for an average person.
“The second paper by Paul Hayne looks at another site where we expect water to exist and shows that at the poles there might be huge reservoirs of water ice in permanent shadows since they suggest there are many small such shadowed cold traps that lock away the water compared to the large ones. This water is probably more abundant but quite close to the lunar poles.
“Together these papers suggest that the Moon does have a form of hydrological cycle, while it may not be as obvious and significant as that on the Earth, but it is important. If we can tap that cycle it makes a long-term base on the Moon significantly more viable.”
No conflict of interest.
Professor Richard Easther, Head of Department of Physics, University of Auckland, comments:
“These are exciting results which add to our knowledge of the Moon and may help shape plans for human activity on the lunar surface in the coming decade. However, they will probably be seen by many people as significant but ultimately incremental advances, rather than breakthrough news — previous announcements about water on the moon do not appear to have been accompanied by a clear caveat that the identification was ambiguous, even though it was included in technical write-ups. Likewise, the realisation that there could be many more regions where ice is trapped on the moon does not significantly change the total volume of water we expect to find on the moon — small regions may be more numerous than realised, but they are also shallow compared to the larger regions.
“These results also illuminate the hype machine that operates inside science. The media event accompanying the news has been teased on social media and elsewhere as “Nasa to make major announcement about the moon“, but given the buildup, people could be forgiven for thinking that the whole thing is a damp squib.
“Further, the results appear in Nature Astronomy, a journal run by for-profit publisher Springer that positions itself as a pinnacle of scientific publication, and which frequently operates this sort of media circus. However, there is always the risk of scientists being tempted to over-hype their work in order to meet the threshold for inclusion in its pages even though there is nothing to suggest that these particular results are suspect. However, Nature Astronomy also published the recent work claiming the discovery of phosphine in the atmosphere of Venus, with the claim that this chemical was a potential “biosignature” and thus possible evidence for the existence of simple life in the Venusian cloudtops. Much of this excitement has unraveled in recent days, with doubt being cast on both the validity of the identification of phosphine itself, and the interpretation of the results.
“Moreover, while the flying observatory SOFIA is often a welcome visitor to New Zealand skies, it is also a seen as an inefficient part of NASA’s overall portfolio. A telescope carried aloft by a 747 is always going to be expensive to operate, and SOFIA is under pressure to demonstrate results as it was recently the subject of a damning review which slated its cost-effectiveness and impact. Consequently, its managers are likely to be particularly keen to see it produce some good news.
“My own take is that these shenanigans are ultimately bad for science. The whole “news about the moon” has been greeted with a fair bit of private eyerolling from colleagues. A sequence of media-friendly sugar hits about big discoveries that are tentative or over-sold cost risks distorting the public understanding of the way progress in science actually takes place — there are few genuine “eureka moments”, and consensus often swings back and forth several times as new knowledge is verified.
“Just to reiterate — these results look like solid, interesting and important work. But the media fanfare is overcooked.”
No conflict of interest declared.
Alan Gilmore, retired Superintendent of the University of Canterbury’s Mt John Observatory, comments:
“It has long been expected that water ice would be found in craters near the Moon’s poles where the crater floors are always in darkness. The water would have been delivered to the Moon over millennia by comets and icy asteroids colliding with the Moon. Any water vapour released would freeze onto the cold dark surfaces. The new results extend the range of cold places to shaded areas on rough surfaces near the poles. They also suggest that water may be derived from chemical processes on the Moon’s surface where hydroxyl molecules in lunar soils combine with hydrogen from the solar wind.
“Detection of the 6-micron infra-red signature of water ice, observed from the Stratospheric Observatory for Infrared Astronomy (SOFIA) airborne telescope, appears to confirm the presence of large areas of water ice near the Moon’s poles. The ice will be a valuable resource for any long-term human base on the Moon. Putting such a base in a shaded crater near a pole would protect it from the extreme temperature fluctuations between lunar day and night. It would also provide some protection from solar cosmic rays, high energy particles radiated by the Sun. Having water ice nearby, albeit in low concentrations, would be an advantage.”
No conflict of interest.
Dr Duncan Steel, space scientist, comments:
“Several spacecraft missions sent to the Moon by the US, Russia, India and China have given us indications that water might persist on the lunar surface, in the form of frost or ice near the surface. This seems surprising because in the vacuum of space water sublimates (transforms directly from solid to vapour) at a very low temperature – below minus 160 degrees Celsius – and so might not be expected to persist when exposed to sunlight on the Moon’s surface.
“Finding water on the Moon in an accessible form would be important for our future exploration and exploitation of Earth’s natural satellite, perhaps involving permanently-crewed scientific outposts. The water itself would be essential for drinking, showering, and growing food; it could be electrically separated to produce oxygen for breathing; and when split into its constituent hydrogen and oxygen it could be used as rocket fuel. Transporting the necessary water from Earth would be hugely expensive, because we are in a gravity well, whereas the gravity of the Moon is only one-sixth as strong.
The information from the previous space probes, however, could be interpreted in more than one way: essentially what was detected was the hydroxyl radical (OH) rather than water itself (hydrogen hydroxide!). That OH could be bound in minerals, might be in some crystalline form, or might indeed be water itself.
One idea was that there could be surface ice hidden from the Sun in craters close to the poles, in particular in the huge Aitken Basin, which lies on the lunar farside near the South Pole. Such locations are termed Permanently Shadowed Regions (PSRs). There being no atmosphere on the Moon, no substantial amount of heat could get to any ice in a PSR, the only mechanism for energy transfer being radiation (sunlight, starlight) because with no air there is no convective or conductive heat transfer. In theory such ice might remain stable for millions of years.
In part due to this interest in the tantalising evidence for ice on the Moon, the Chinese Change’e 4 probe was landed in the Aitken Basin in January 2019.
The two papers now published by US authors look at the question of lunar ice in quite distinct ways. Rather than restricting the possibility of PSRs to large craters, Paul Hayne (University of Colorado) and colleagues investigated the possibility of there being much smaller areas on the lunar surface where there is permanent shadowing, on scales from kilometres down to centimetres. One can think of these as being similar to ice patches experienced on the road in the shadows after a frosty night: where the early Sun has melted and dried the tarmac, all is good… but you come around a corner into a shaded section and the surface is treacherous. It happens that on the Moon there are regions at high latitudes (where the Sun is always low in the sky) that no sunlight warms the surface. It is only now, with the Moon mapped at high resolution by NASA’s Lunar Reconnaissance Orbiter, that scientists have had the data to perform such an analysis.
“The other paper, by Casey Honniball (NASA-Goddard Space Flight Center) and co-workers, involves the direct detection of water molecules on (or in) the lunar surface. Previous observations in the infra-red part of the spectrum had confirmed the hydroxyl (OH) presence, but Honniball and colleagues used a longer wavelength (six microns) at which a water molecule is resonant, knowing that detecting emission at that wavelength would be an unambiguous signal of water. (Whilst we might represent a water molecule as H-O-H, in fact the molecule is not linear, being shaped more like a letter V, and the angle in the V will oscillate at a specific frequency, and therefore emit radiation at a specific wavelength.) To achieve this, they needed a telescope above the large amount of water vapour in the lower atmosphere, and so used SOFIA (the Stratospheric Observatory For Infrared Astronomy). This is a Boeing 747 equipped with a large telescope, and is a joint project of the space agencies of the USA and Germany. Note that most austral winters SOFIA is based for a couple of months at Christchurch International Airport, and flies out over the Pacific and down over the Antarctic Ocean. (In this case the data collected by Honniball and colleagues did not come from an NZ-based flight.)
“Honniball’s team found the signature of water molecules in data collected pointing SOFIA’s telescope close to the lunar South Pole, but not nearer the equator, consistent with the idea that water ice might persist in PSRs. More than that, though, they suggest that in fact rather being located in macroscopic reservoirs (like craters) in fact the ice could be present on a microscopic scale, between the grains of the lunar ‘soil’ which we term regolith. If their figures are correct, then two or three tonnes of regolith (about a cubic metre) might contain a litre of water.
This discovery is linked to something that is astonishingly obvious, and yet few people realise it to be true: at full moon (when the whole nearside of the Moon is illuminated by the Sun), our natural satellite appears to be about nine or ten times brighter than at first or last quarter (when half of the lunar disk appears illuminated). How come? Why is it not just twice as bright, as twice the solar-illuminated area is visible? The answer is that the lunar surface is rough – not like a ball-bearing or even a disco ball – and so the microstructure of the grainy surface makes a big difference to how much sunlight gets scattered to us on Earth. The interpretation of Honniball and her team is that the water is hiding from sunlight as ice between and within the grains.
Duncan has worked in the past for both NASA and the European Space Agency. He expands on these comments in this blog post.
No conflict of interest.