'The invisible world part 2: The Moon today'

Above: The Fallen Astronaut, a monument on the Moon to all the astronauts and cosmonauts who have lost their lives. Courtesy of NASA

My Dad's a geologist, so I know that the dullest rock has a story to tell -  and the Moon is big rock, with a big, old, story. But it's also more than that: We're uncovering a subtle but complex modern day Moon. A world with mountains of eternal light, valleys of perpetual darkness, gas explosions, buried ice, delicate frosts, unknown mists, mysterious magnetised swirls, tunnels miles wide, and historic monuments....

An active Moon?

For a long time the Moon was assumed to be essentially dead, but we now know a lot of things are happening there... 

Moon quakes:

 
Above: The Moon is occasionally hit by larger meteorites, travelling at incredible speeds, but they don't come down often enough to cause all the quakes that are observed.

When the Apollo missions visited the Moon they left behind science stations that monitored the Moon for seismic activity. These stations were active on the Moon until 1977, when they were closed down by budget cuts. They found  that the Moon often experienced quakes, up to 5.5 on the Richter scale - enough to damage a building if it isn't well constructed. Deep quakes are probably caused by the  tidal gravitational stress the Earth puts the Moon under. But the origin of the shallow quakes is still unknown, and while they don't get as strong as Earth's strongest quakes they can last for up to ten times as long, setting the whole Moon ringing like a bell. 

Above, Buzz Aldrin sets up one of the lunar monitoring stations, proving that you can travel to another world and still wind up having to put together the equivalent of Ikea furniture. Courtesy of NASA

Active volcanoes:

The Moon has volcanoes, but for most of my lifetime it has been taken as 'obvious' that they must have all gone extinct over a billion years ago. When amateur astronomers reported seeing eruptive activity, the consensus from the scientific community was to lump them into the same group of people who believed “the face on Mars” was a sign of intelligent life.

In case that means you, I'm sorry to have to tell you that the scientific community thinks you're nuts. But take heart, it turns out the lunar eruption theorists at least had a point.....

There was one puzzling volcanic region called Ina D which, geologists admitted, might be a result of younger eruptions,  but generally the Moon was dead.... until spacecraft like LRO and Clementine got there, and began taking high resolution images of the surface. It turns out it's quite possible the Moon is still active...

Above: The Ina-D formation, which is thought to be the collapsed vent of a very low sloping volcano, mainly because the idea of an athletes foot that big is just terrifying.. Courtesy of NASA

Scientists studying these images over the last ten years have revealed tell tale signs that there's still some heat and power left in the Moon. There're seventy more features like Ina, where: 

• Lava flows are much less worn down by meteorite impacts. 
• The ground has accumulated few large craters. 
• Rocks are a subtly (but measurably) different colour. 

All of which suggests these rocks were formed within the last ten million years - an eye blink geologically, and so recent it seems almost certain there'll be future eruptions.

Above: The locations of some of the young volcanic formations on the lunar surface. Courtesy of NASA

Above: An exaggerated colour image of the Ina formation and a fresh crater, showing how the younger material is bluer in tone. Courtesy of NASA

While the lava eruptions are geologically young, there's also some evidence that gas eruptions might even be on going today: Areas like Ina show evidence of being swept clear of dust by gas eruptions, maybe even in the last century. And, ever since the invention of the telescope, certain parts of the Moon have shown mysterious glows 'mists' - like something was stirring up the dust.

Above: Schroter Valley, sometimes called 'the most haunted place on the Moon' for all the unexplained lights seen there. Courtesy of ESA 

Lunar weather?

Talking about weather on a world with no atmosphere seems odd, but there are some surprising lunar equivalents of weather on Earth, like...

Moving  dust:
The lunar dust moves around on the lunar surface, driven by static charges rather than the wind - UV light and charged particles from the sun cause static charges to build up on the surface. The lunar dust is pulled between regions of different charge in the same way this kids hair is being pulled towards the balloon...

This phenomena was first picked up by experiments left on the Moon by the Apollo missions, and might be a cause for the mysterious glows seen over the lunar surface by some spacecraft. Lunar dust might even be 'blown' vast distances across the lunar surface by these charges, and dust from meteorite impacts can also pick up charges, forming a tail of levitating dust behind the Moon. The LADEE mission is currently at the Moon, investigating exactly this. 

Above: A quick rundown, courtesy of NASA, of the LADEE mission.

Seasonal frost:

Above: A frost flower, which forms when water vapour freezes onto a growing collection of water ice, without going through the liquid phase. Is it possible the Moon has something similar?

The Moon's poles hold craters and valleys where the sun literally never rises, and where the temperatures are so low that water frost can build up even in the lunar vacuum. But these regions are not entirely lightless - the sunlight can reflect off of surrounding mountains at angles that vary during the year, so the frosts can migrate across the valley floors, following the regions of deepest shadow.

Landslides and gullies:
Some of the best evidence for the Moon as an active, changing, world is simply that the landscape visibly changes between photographs taken a few years apart. Recently, comparisons between younger and older photographs have shown us that landslides are constantly sculpting and reshaping the Moon's slopes in response to impacts and quakes, making the lunar surface a constantly evolving thing.

Mysteries of the Moon;

Lava tubes:

Above: The collapsed roof of a lava tube allows an orbiting spacecraft to peek inside

Lava can carve out - or perhaps more accurately grow - underground tunnels called lava tubes. On the Moon we've had glimpses of these, where the ceilings have collapsed. Some of these are a mile across, giving the Moon a network of titanic underground tunnels - what's in there, we may never know.... 

Above: Since I couldn't arrange a tour of a lunar lava tube, here's Tony Farley taking us through one on Earth. Just imagine everything a lot bigger, and everyone wearing space suits...

Permanently shadowed regions:

Above: A temperature map of the lunar poles, showing regions where the temperature is cold enough to hold ice.

A lot has been written about the permanently shadowed regions at the Moon's poles, but for those who've not heard of them: The Moon has craters at its north and south poles so deep that the Sun never shines directly into them - they're colder than the back side of Pluto, on the far edge of the solar system. For a long time it was theorised that ice and other low temperature materials might have accumulated there, but it was only since the late '90's that solid evidence began to build for ices there. The LCROSS mission revealed not only water ice but organic materials, potentially making the poles a time capsule for the earliest organic chemistry in the solar system, and a laboratory for how organic chemistry behaves at low temperatures.

Thorium anomaly:
There's a patch on the far side of the Moon that just screams 'odd'. It's called the Compton-Belkovich Thorium anomaly. It has a high concentration of the radioactive element thorium, has a quartz rich highly reflective soils,  and seems to have been a volcanic hotspot - one of the last really big volcanic regions on the Moon to stop erupting. With a central caldera it might be the Lunar equivalent of a super volcano like Yellowstone.

Why is the lunar crust thicker on one side?
One really basic mystery on the Moon is that its crust is thicker on one side than the other. A lot of explanations for this have been put forward, including one I mentioned last week -  that there was once a second, smaller Moon. The smaller Moon hit the bigger one at a slow speed, and ended up pancaked over one hemisphere like a huge bug on an even huger windscreen... but we just don't know.

Where does lunar water come from?
When the existence of lunar water came to light it was something of a shock to a lot of scientists, and it's origin still hasn't been nailed down - it seems to be created by a chemical reaction with the lunar rocks, but some could also come from cometary impacts, and there even seems to be some water coming from inside the Moon....

Treasures from the Moon

Some things on the Moon are just plain beautiful, so here are few of the Moons treasures:

Beads of volcanic glass:

Sunrise over Tycho:

The Earthrise:

Lunar swirls:
These mysterious waves of colour seem to be etched into the lunar surface. No-one knows how they form, although they all have magnetic anomalies associated with them.

Above: No, it wasn't a kid with a spray can. That'd be some ambitious graffiti though... Courtesy of NASA.

Next Week: Will the Moon become Earth's Eighth continent?

This view of the Moon rising, from the international space station, hints at what the future might hold... 

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