You would be forgiven for thinking that America lost interest in the Moon forty years ago, in December 1972, when Apollo 17 astronaut Gene Cernan left the final footprint on its dusty surface. It’s certainly true that in the 1970s and 80s there was little desire to return to our grey, cratered cosmic neighbour. In fact during the 1980s no-one sent a single spacecraft, robot or orbiter. Thanks to Apollo, American scientists had an enormous pile of lunar rocks to study, Nasa’s attention had switched to the Space Shuttle and the Soviets had run out of money.
But in recent years, there has been a resurgence of interest in studying the Moon in order to tackle some of the many unanswered scientific questions. In the last decade, Europe, Japan, China and India have all sent unmanned orbiters to probe the Moon’s chemical composition, gravitational field and topography. Among other things, they’ve proved the presence of water, discovered potentially useful minerals and uncovered evidence that the Moon may still be geologically active. Now, later this year, the US will be launching its fourth mission since 2009: Ladee.
Ladee (pronounced Lad-ee, rather than Lay-dee) stands for Lunar Atmosphere and Dust Environment Explorer and is designed to build on Apollo science. Looking disconcertingly like an Apollo Command Module smothered in shiny solar panels, this robotic spacecraft will study lunar dust in the Moon’s tenuous atmosphere. “Yes the Moon has an atmosphere,” exclaims Brian Day from Nasa’s Lunar Science Institute. “People are astonished to find that out.
“We uncovered the very beginnings of our understanding of the lunar atmosphere when we visited with Apollo,” Day says, “but we haven’t really revisited the question of how much there is, what it’s made of and how it changes from month to month.”
The mission will also aim to solve another related question that’s unresolved from Apollo: a weird glow that the astronauts saw from lunar orbit. “There were these interesting ‘streamers’ that were seen out the window of the Command Module when it was round the Moon,” says Ladee project scientist Richard Elphic. “Some of the supposition is that these may be pillars of levitated dust, high into the lunar sky. But we don’t know for sure, so we’re trying to understand what role dust might play in the lunar atmosphere.”
Observations made through telescopes on Earth have already given the Ladee science team some idea of what they might find. They know, for instance, that the lunar atmosphere contains argon and helium and they were surprised to also find two metals: sodium and potassium. “Those are just the tip of the iceberg,” says Elphic, “there are probably many other species of chemicals and just as exotic.
The Moon’s thin and fragile atmosphere is technically known as a surface boundary exosphere and what makes this investigation even more interesting is that these types of atmospheres are found around bodies elsewhere in the Solar System. Mercury has one, so do larger asteroids, many of the moons of the gas giants, even the minor planets beyond Neptune. “This may be the most common type of atmosphere in our solar system and we know very little about it,” says Day. “But we happen to have one right next door – how lucky is that? We’re going to take advantage of that and go and explore it.”
The 2m (7ft) long Ladee is equipped with three instruments to sample lunar dust as well as a neat new laser communications system. This will be used to send data back to Earth encoded in beams of light rather than radio waves, massively increasingly bandwidth. If successful, this technology could revolutionise space communications.
The Ladee mission is also significant because it is part of a wider trend of renewed interest in lunar science. Over the last few years there have been a record number of spacecraft in orbit around the Moon at the same time. And unlike the last big push to reach our nearest neighbour, this is not primarily about planting a flag but investigating some fundamental science.
“The Moon is a far more fascinating place than we had previously thought,” says Day. “There’s a lot more going on there than we previously realised. This is not a geologically dead, airless, totally dry world.”
‘Living and breathing’
Lunar scientists are even revisiting theories about the Moon’s formation. Until last year, it was widely accepted that it was formed 4.5 billion years ago from the debris of a collision between a theoretical planet-sized object and the infant Earth. A new theory, from Nasa’s Lunar Science Institute, suggests the Earth and Moon might have resulted from a collision between two massive planets, each five times the size of Mars.
“The Moon was born interesting and it has continued to be interesting over the past four billion years,” says Elphic. “The Moon is still living and breathing.”
Ladee is currently scheduled for launch in August and I wonder whether this ratcheting up of lunar exploration is a step towards returning humans to the Moon. China has certainly made clear its ambitions to land on the Moon and possibly establish a manned settlement but what about the United States?
I always expect diplomatic answers from Nasa employees with this question, particularly as a human mission to the Moon is not currently on the agency’s agenda. But Day says the Moon would be a logical choice for a next small step for mankind. “As we start looking at the further destinations [such as Mars], these are hard places to go to but we can refine our techniques and technologies by going to the Moon.”
Elphic agrees, “Building a base, dealing with the possibilities of in-situ resources that you could use to make fuel or oxygen to breathe, doing this at the Moon makes sense even if your destination is Mars and beyond. Solve all the difficult problems in a place that’s relatively easy to get to and then move on from there.”
As the discoveries from this recent flurry of missions are proving, the Moon would certainly be worth a visit.