Twists and turns

One of the things I love the most about science is how one thing leads to another.

Someone notices something anomalous, and thinks to ask, "why?"  The answer to that question leads to more "whys" and "hows," and before long it's led you somewhere you never dreamed of, and opened up new vistas for understanding the universe.

Take, for example, the strange phenomenon of lunar swirls.

Swirls near Firsov Crater [Image is in the Public Domain courtesy of NASA/JPL]

Lunar swirls are pretty much what they sound like; undulating curls of light-colored rock and dust, often overlying craters and other topographic features, but seeming not to follow any obvious contour lines.  This is odder than it may appear to be at first.  We see lots of looping, curly stuff on Earth -- cirrus clouds, the twist of hurricanes and tornadoes, the meanders of rivers -- but all of those occur because of some fluid flowing, be it air or water vapor or liquid water.  The Moon has no atmosphere, and never has had flowing water; so what's causing the sinuous shape?

The mystery deepened when lunar sampling missions found out that the light regions had somehow been magnetized.  This at least explained the color difference; the magnetized bits deflected the particles in the solar wind, causing them to hit nearby rocks instead.  This triggered a series of chemical reactions that darkened the rocks' surfaces, while the magnetized parts were spared and stayed light-colored.

But then the question was, how did the light-colored rocks get magnetized in the first place?

It happens easily enough on Earth; a lot of terrestrial rocks have particles of magnetite (iron II, III oxide), and while they're in the molten state the particles are free to move.  They respond like compass needles, aligning with the Earth's magnetic field, and when the lava cools the magnetite crystals are frozen in place, locking in a magnetic signature.  (You probably know that this property is how geologists found out that the Earth's magnetic field periodically flips -- something that was key to proving the plate tectonics model.)

The problem is twofold.  First, magnetite is rare in lunar rocks; and even more difficult to explain -- the Moon has no magnetic field.  So what are these magnetic crystals, and how are they aligning well enough to make the rocks magnetized?

A possible answer was the subject of a paper this week in the Journal of Geophysical Research, describing a study out of Washington University.  A rock called ilmenite, common on the Moon's surface, can form crystalline iron (which is highly magnetic).  As far as how the crystals got aligned, the research team found a process that could cause enough of a magnetic field anomaly to cause it -- if there was a flow of high-titanium magma underground.

"Our analog experiments showed that at lunar conditions, we could create the magnetizable material that we needed," said study co-author Michael Krawczynski. "So, it's plausible that these swirls are caused by subsurface magma...  If you're going to make magnetic anomalies by the methods that we describe, then the underground magma needs to have high titanium.  We have seen hints of this reaction creating iron metal in lunar meteorites and in lunar samples from Apollo.  But all of those samples are surface lava flows, and our study shows cooling underground should significantly enhance these metal-forming reactions."

So a formation on the lunar surface led to an inference about magnetism and the solar wind, and ultimately gave us information about the subsurface geology of the Moon.  I don't know about you, but I love this kind of stuff.  So many of us just look at things and shrug our shoulders, if we notice them at all.  And maybe that's what sets scientists apart; their capacity for seeing what the rest of us miss, and most importantly, wondering why things are the way they are.

It's pretty clear that science isn't just a list of vocabulary -- even though sadly, it's often taught that way.  Science is a verb.  As the brilliant polymath Jules Henri Poincaré put it, "Science is built up with facts as a house is with stones; but a collection of facts is no more a science than a heap of stones is a house."

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