It’s almost 40 years since the last humans visited the lunar surface during the Apollo 17 mission of December 1972.  

Indeed, the last controlled landing on the moon was just four years later when the Soviet Union’s sample-return mission, Luna 24, touched down in July 1976.

Since then, nothing (although in recent years both the US and India have crashed probes into the lunar surface). 

So it’s high time we returned to the lunar surface, say Ian Crawford at Birkbeck College in London and a few buddies. Today, they outline of the reasons why and say they are more compelling than ever.

For a start, the Moon is a good place to learn about the Earth. Throughout its history, our planet has been hit by a multitude of asteroids and comets that ejected countless billions of Earth rocks into space. Some of this stuff will have landed on the Moon where it almost certainly still sits today, pristine and untouched.

By some estimates there could be as much as 200 kilograms of Earth per square lunar kilometre. That means the best place to study early Earth rock, its chemical composition and perhaps even the prebiotic cocktail that led to the origin of life is on the surface of the Moon.

Then there is the argument that the Moon is the only place that certain types of astronomical observations are possible. Astronomers have studied the universe across the entire electromagnetic spectrum but there is one small corner of the rainbow that is still inaccessible to Earth-based instruments–ultra-low frequency radio waves.

Below about 30 MHz, the ionosphere does a pretty good job of absorbing or reflecting more or less everything the Universe throws at us. Consequently, the cosmos is essentially uncharted at these frequencies.

The far side of the Moon, on the other hand, is the perfect radio-silent place to observe them. Crawford and co suggest starting with a few antennas and slowly adding to the array to create a radio telescope hundred or even thousands of kilometres in diameter. 

And there ought to be plenty to see. This frequency probes the dark ages–the period several million years after the big bang but before the formation of the first stars and galaxies. “It can essentially only be observed through radio emission from atomic hydrogen red-shifted to several tens of MHz,” say Crawford and co.

In addition to these goals, there are the well worn arguments about better understanding the Moon itself and the resources it may hold for future exploration, such as water and other volatiles.

However, Crawford and co are on less sure ground when they argue for a renewed human presence. They say the study of humans on the Moon would give an important insight into effects of low gravity on human health. 

Maybe. A similar argument is often made about humans on the International Space Station but this work has produced little, if any, benefit for the rest of us. (Indeed the presence of humans is what makes the International Space Station profoundly unsuitable for most micro gravity experiments and astronomical observations.) 

Crawford and co also argue that the presence of humans would speed up decision-making processes, allowing research activities that would otherwise be impossible to conduct.

That seems unlikely. The additional operational and bureaucratic overheads required for human presence would make almost any activity impossibly complex, unmanageable and expensive. 

Crawford and co seem to discount the extraordinary progress being made in robotics that will make automated work on the surface of the Moon and anywhere else orders of magnitude more productive and cost effective than a human effort.

Having said all that, the question is when a robotic mission can return. The answer is not any time soon.  There are numerous proposals in the offing and even a Global Exploration Strategy that the world’s space agencies signed up to in 2007.

Nevertheless, firm plans are few and far between. With Europe in economic crisis, NASA slipping into obscurity and the Russian space agency licking its wounds over its recent lost Mars mission, its not hard to imagine another 40 year wait for a return to the lunar surface.

Unless, of course, there are any emerging nations or private enterprises willing to take on the task. Richard Branson versus Elon Musk versus China in a race to the Moon? Now there’s a thought. 

Ref: arxiv.org/abs/1206.0749: Back to the Moon: The Scientific Rationale for Resuming Lunar Surface Exploration