DISCOVERIES
The month’s biggest science news. Water on the Moon; ancient marine reptile could float underwater; early Andean hunters were women; secrets of the unsquashable beetle revealed.
Water could be more widespread on the Moon than previously thought. New readings from NASA’s Stratospheric Observatory for Infrared Astronomy (SOFIA) indicate that molecular water (H2O) is present in the Clavius crater, one of the largest craters on the Moon. This discovery is important because water was thought to be present on the Moon only in the permanently shadowed regions near the lunar poles. Although Clavius is in the southern hemisphere at a relatively high latitude, its interior is exposed to sunlight. Since it seems that water can survive at or near the lunar surface here, it implies that water may be much more widely distributed across the lunar surface than previously recognised.
“Without a thick atmosphere, water on the sunlit lunar surface should just be lost to space,” said Dr Casey Honniball of NASA’s Goddard Space Flight Center in >
> Greenbelt, Maryland, and the lead author of the new work. “Yet somehow we’re seeing it. Something is generating the water, and something must be trapping it there.”
But if it’s such a mystery how the water got there, could it mean the NASA researchers have made a mistake in their identification of the molecule? Prof Mahesh Anand, a planetary scientist from The Open University, UK, has studied the discovery and thinks the work is sound. “I think that the researchers have done a very good job in confirming that the spectral signature they are looking at can only be provided by molecular water,” he said.
Even so, the abundance of the water is not high. For comparison, the Sahara Desert possesses 100 times more water than was found in the lunar surface material by SOFIA.
Nevertheless, it is a potentially important discovery because the more water there is on the Moon, the easier it will be to set up a lunar base. The water could be extracted to drink, to make oxygen, and also to make rocket fuel.
Q&A WITH PROF MAHESH ANAND HOW SIGNIFICANT IS THIS FINDING?
Finding the signature for the presence of molecular water in the sunlit portion of the Moon is what makes this more significant than perhaps it would have been, because water has been detected previously on the surface of the Moon.
Finding water on the Moon is not totally unexpected, but what was not known before was whether this water was present as hydroxyl, which is one atom of oxygen attached to an atom of hydrogen, or H2O, which is two hydrogen atoms attached to one oxygen. The latter is molecular water and is what a layperson would understand as water. Molecular water, arguably, has only been detected once before on the Moon, when the LCROSS [Lunar Crater Observation and Sensing Satellite] impactor hit a permanently shaded crater in the southern polar region. So, whatever was there was lifted up in the ejecta plume in which some water ice was detected. But molecular water as such had not been confirmed in the sunlit areas of the Moon, which I think is why this discovery is very exciting.
Scientifically, water or hydroxyl on the Moon could have different origins, which could have quite a different meaning and significance in terms of what its physical status might be, how much is present, and how amenable it might become to future explorers for using it as a resource.
WHY HAS IT TAKEN SO LONG TO FIND WATER?
I think we have to put ourselves back in the early 1970s [the Apollo missions], when humans first visited the Moon and returned to Earth with some lunar samples. Once the Moon’s dust or rock samples were back on Earth, there was a lot of work done to ascertain whether there was any hint of water. There was none, but that was with the technology that was available at that time. We must remember that the Apollo missions did not go in search of water. So in some ways, the right questions weren’t posed at the time. Instead, the question posed was, can humans actually safely land on the Moon and then return to Earth?
There was speculation, even before the Apollo era, that there could be water in the permanently shadowed regions of the Moon. The problem was that none of the Apollo missions, or any subsequent missions until
the 1990s, were equipped with an instrument that could detect anything inside these cold, dark craters. That didn’t happen until the 1990s when two missions, Clementine and Lunar Prospector, were sent to the Moon.
WHERE DID THE LUNAR WATER COME FROM?
Right! Finding water is one thing but the next question is, where did that water come from? Hydrogen occurs in two forms [isotopes]. One is hydrogen as we know it, which has one proton in its nucleus. The other is called deuterium, which contains a proton and a neutron. The Sun gives out almost pure hydrogen in the solar wind, but deuterium-enriched materials exist in the outer Solar System, meaning it could have come from much further out in the Solar System or even beyond.
So imagine a scenario where a comet from far away has collided with the Moon and delivered a lot of water-rich material to the lunar poles. The water from the comet will have a unique hydrogen isotope composition compared to water built from hydrogen from the solar wind or through volcanic eruptions on the Moon itself. It’s like the comet’s own DNA for water. If I were to then go and collect the lunar dust from this polar region, where the comet has contributed some water, and I brought it back into the lab, I could measure the isotopic composition of the water, alongside how much water is present. I will be able to say X per cent of this water is of cometary origin. So, the combination of measuring the amount of water and the isotopic composition will tell us a great deal about where that hydrogen, and so the water, might have come from.
DOES THIS MAKE THE PROSPECT OF HUMAN EXPLORATION OF THE MOON EASIER?
The south polar region is popular right now as a destination because that’s where multiple missions have already indicated the possible presence of water in the permanently shaded craters. But now, if we are also seeing the possibility of some form of water in non-shaded regions, then that means that you improve your chances of actually finding water without risking your life or instruments going down into a hole, which may be less than -200°C. And this is not just about taking someone to the Moon. If you think about it, the inspirational value this has for the next generation of scientists and engineers is tremendous. What it shows is that when you actually look deep enough, and have a curious mind, you make these discoveries that nobody had thought possible.