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Friday, 20 July 2012

The Valley of Ghosts...

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The Moon has a complex, violent history. And, although it was born from Earth [1], it has always been a very alien world. 

 Image above: The Schroter Valley, as seen from orbit by the crew of Apollo 15. No sniggering, you aren't ten. Unless you are. In which case go for it - but remember: A silly name doesn't make this place any less terrible and fascinating. Image courtesy of NASA.

Nowhere is a better example of this than the Schroter valley [2]*: Carved into the Aristarchus plateau, the one hundred and eighty five kilometre long valley is the longest ‘sinuous rille [3]' on the Moon  Starting at Cobras head, a six kilometre wide hole in crust, the valley snakes through the lunar rock, first north, then north-east, then south, until it crosses the kilometre high drop into Oceanus Procellarum - a sea of crystallised lava..

Off to the east is the ultra bright, 40 kilometre wide Aristarchus crater [4] - for which the plateau is named - and south of there lies a set of smaller valleys: The 121 kilometre long Rimae Aristarchus.

Though the Moon is a smaller world than Earth, Schroter shows that it likes its geology big: In places the valley is ten kilometres wide, a kilometre deep, and has a second, smaller, track carved along it's bed [5].

Take a good look at it. Looks an awful lot like a river, doesn't it?

Video above: A virtual flyover of the two kilometre high Aristarchus plain, built from images by the Hubble Space Telescope. Video courtesy of NASA/Goddard Space Flight Center Scientific Visualization Studio.

That impression isn't wrong - we just have to abandon one preconception: That the river ran with water. Lunar rivers didn't. 

They ran with molten rock. 
Many researchers believe they ran with komatiite [6] - a very hot, very runny lava, not seen on Earth for three billion years. Because of its high temperature, turbulence, and ability to flow komatiite would have eroded the lunar soil much more effectively than regular lava, which tends to build up (more like cold syrup - yum) -  leading to a river like valley, rather than a frozen lava flow.

The smaller channel cut into the base of Schroter is a mystery - the best guess to date is that the komatiite flow slowed to a trickle, dribbling along the bottom of the older channel. It's hard to tell for sure without being able to visit - as the cancelled Apollo eighteen expedition would have done. 
But bizarre geology, with no 'living' counterpart on Earth, isn't the only strange thing about this valley. Schroter has the third highest rate for Transient Lunar Phenomena [7] on the whole Moon. And there's a chance that the whole Aristarchus plain isn't as geologically dead as it seems... 

TLP's are sudden, short lived, changes in the brightness of the lunar surface. Lots of explanations have been put forward, from good old 'you're imagining it' to telescope lens flares, to meteorite impacts. 

Image above: A TLP (the bright spot in the middle), caught on camera by Leon Stuart, in 1953. Image courtesy of Columbia University.
Many scientists are still sceptical about TLPs. But a statistical analysis [8], by Arlin Crotts of the University of  Columbia, suggests that there is reality to many reports. The Apollo missions reported signs of radon gas [9], leaking from the Moons interior - from some of the same locations [10] TLP's are often reported.

To researchers like Crotts that suggests an explanation: Ancient, radon bearing, gas builds up just beneath the Moons surface, until it burbs its way out in a cloud of dust. Voila, one TLP.  
Is the Aristuchus plain where the ghosts of the Moons fiery past are seeping to the surface? It's hard to be sure. There are oddly fresh patches [11] of the Moon, that may well have been shaped by gas [12] eruptions, as little as a million years ago.

Image above: The strange Ina formation, which shows a very young (by which I mean less incredibly old) surface - suggesting it may have been altered by recent geological activity. Image courtesy of NASA.

Until we can get back to the lunar ground [13], to do some close up work on the rocks, places like Schroter and Aristachus will keep their secrets.... it's nice to hear that ESA's lunar lander mission [14] is making progress.

Video above: A run down on the ESA lunar lander mission, the first European attempt to soft land a robot on the Moon. Video courtesy of ESA.

....not to mention the Google Lunar X-prize [15] contestants....

Video above: The announcement for the Google Lunar X-prize contestants. Gist of it is: The Moon is brilliant, lets start exploring it again. Well said. Though my version is quicker. Video courtesy of Google.

...who intend to land there for a pittance. Or perhaps a pittance plus a few million quid.

But the point is this: The Moon might not be the dead place we thought. And it is certainly alive in a lot of peoples hopes....

* Yes, I was once ten as well, I know what it sounds like.Go on, giggle if you have to. People will stare if you're reading this on the train though.....

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