NASA's LCROSS approaches the Moon in October.
Credit: NASA
Imagine a dramatic vision of the future: huge processing plants at the Moon's south pole, mining the pristine lunar regolith, piping fresh water to colonies nestling in the lunar landscape. This is a vision often touted by aerospace professionals.
In order to reach out and colonise the Solar System, they argue, we will have to learn new techniques of mineral and water extraction, firstly on our nearest celestial neighbour, the Moon, and then on Mars.
Lunar scientists have just reawakened this vision with the confirmation that the Moon's otherwise dead soils contain significant quantities of water. On 9 October, NASA dropped a two-tonne Centaur rocket into the 100km-wide Cabeus Crater, a permanently shadowed depression near the Moon's South Pole. The impact caused a 1.6-kilometre-high dust plume to form.
Minutes before its own impact, the LCROSS probe's near-infrared spectrometer saw tell-tale signs of water ice and water vapour in the cloud of lunar material. NASA scientists estimate there may have been 100 kg of water detected, from an impact crater no more than 20 to 30 m across.
At the heart of NASA's plans for Solar System exploration is a sustainable human presence on the Moon, to be achieved, ambitiously, by 2020. The LCROSS results were announced in November. At first glance, they imply the Moon has a readily available supply of water. If extraction technology could be developed, it could alleviate the US$20,000 per kg price tag on transporting water to the Moon from Earth.
Unfortunately, the LCROSS results actually don't imply that lunar water is a convenient resource. The data showed that about 100kg of water were contained in the estimated 10 million kg of regolith ejected by the rocket impact. That is actually drier than the driest desert on Earth. By most standards the Moon is totally parched.
But it gets worse. Many leading researchers say it just isn't economical to extract water on the Moon. At least during the first few decades of a permanent Moon base, the cost of producing water there will be much higher than importing it from Earth.
Even so, other scientists suggest that it's the realisation of these technologies that are important, not the timeframe for (or the cost of) their development. We'll need to do this on Mars, they say, so let's get it right on the Moon first.
But that presents us with another conundrum. Mars is very different to the Moon. Only a few months ago, NASA's Mars Reconnaissance Orbiter (MRO) found huge quantities of very pure water ice just below the surface of several mid-latitude craters. It seems that water is much more readily available on Mars than on the Moon.
Mining these huge reserves will be vastly more efficient and economical than squeezing the tiniest bit of moisture out of the lunar regolith. That technology can't be developed on the Moon. So, ultimately, the confirmation of lunar water doesn't justify the belief that humans should return there.
Of course, there is certainly much the Moon can still teach us about the formation and evolution of the Solar System, and the Earth itself. There is, indeed, a lot more science waiting to be done. But you won't find your average lunar scientist advocating manned exploration of the Moon. Most, if not all the science can be done with cheap robotic missions. The LCROSS results are evidence of that.
So, why is NASA fixed on this ambitious goal? If you read between the lines, NASA officials do not defend it on the basis of science alone. Putting people into space, or on the Moon, has a spiritual or emotive value, they say, which justifies the cost. But for many, myself included, this isn't a strong enough motivation. A return to the Moon is pointless, scientifically and technologically.
I'm not alone in expressing this opinion. Even legendary moon-walker Buzz Aldrin has questioned his former employer's vision, pointing out that we'll never launch a mission from the Moon and so have no reason to go back there. Aldrin, and many others, insists the Agency should be looking to Mars.
NASA was also criticised last year by a review committee looking at the Agency's Exploration Technology Development Program. The committee voiced concerns that NASA's current focus is on establishing a human presence on the Moon, whilst the longer-term goal, Mars, is being completely ignored.
Furthermore, the committee concluded that under current financial models, NASA can't afford its ambitious program of lunar development. The Agency needs an additional $3 billion per year to develop its Ares/Orion launch system into a viable system for lunar exploration. In the current financial climate that's about as likely as finding a freshwater lake on the Moon. Consequently, a return to the Moon by 2020 is now looking like a pipe-dream.
Of course, it will cost NASA a lot more than the additional US$3 billion a year to develop a manned mission to Mars. But, if a return to the Moon serves no real purpose, wouldn't that money be better spent on a preliminary study of the requirements for human exploration of Mars?
Since the days of Apollo, Mars has been staring us in the face. It is the next obvious step. Not only does it have vastly more convenient water reserves, but an atmosphere rich in carbon and nitrogen and soils rich in minerals. Mars has the right resources for the establishment of permanent colonies. The Moon is a barren and hostile environment by comparison.
And potentially, Mars can tell us much more about the formation and evolution of the Solar System and about the prevalence or otherwise of life in the Universe. The red planet is where the real challenge lies, scientifically, technologically and politically. And if it's simply glory you want, you get just as much, if not more, by going to Mars and not the Moon.
Alastair Gunn in an astronomer at the Jodrell Bank Observatory in Cheshire, England.
