...cause I was just 'bout to post this:

More radiation reading, it keeps getting interesting...

Here's (http://www.lpi.usra.edu/meetings/lpsc2003/pdf/1856.pdf.) the .pdf, but for some reason the server wasn't talking to me. Great. Tried it through this site, but it wouldn't give me the full printable copy. Google it ("Space Weathering: An Ultraviolet Indicator")and read the text version. The article talks about lunar soil samples that display a blue color due to UV radiation effects. I'm in over my head here, but it's fun!

Money Quotes:

"Introduction: We present evidence suggesting
that the spectral slope of airless bodies in the UV-
visible wavelength range can be used as an indicator of
exposure to space weathering. While space weathering
generally produces a reddening of spectra in the visi-
ble-NIR spectral regions, it tends to result in a bluing
of the UV-visible portion of the spectrum, and may in
some cases produce a spectral reversal. The bluing
effect may be detectable with smaller amounts of
weathering than are necessary to detect the longer-
wavelength weathering effects."

"Laboratory ex-
periments have demonstrated the sensitivity of the UV-
visible wavelength region to simulated space weather-
ing processes. The UV-visible wavelength region ex-
periences drastic changes in brightness with very small
amounts of weathering, as manifested by the addition
of SMFe [3][10]. The addition of more SMFe through
weathering flattens out the UV-visible portion of the
spectrum; it becomes relatively blue. These laboratory
results mimic the effects that are seen in lunar samples,
where, shortward of ~400 nm, lunar soil has a bluer
spectral shape compared to pulverized lunar rock [3]
(also shown in Fig. 1). The lunar soil correspondingly
is darker and exhibits attenuated absorption features at
visible-near IR wavelengths, typical of weathering.
Similar results are obtained in irradiation tests [3]:
shortward of ~500 nm, the spectrum of an irradiated
pulverized lunar rock is bluer (not as spectrally steep)
than the unaltered pulverized lunar rock. "

"These examples of the bluing of the UV-visible
portion of the spectrum in response to simulated
weathering are consistent with the UV spectral rever-
sal: a sample that is more weathered will be spectrally
bluer in the UV-visible region than a less weathered
sample, and at some ultraviolet wavelength (likely
composition dependent), the spectral reversal will oc-
cur. The result is that the more weathered sample,
which is darker in the visible, ends up being brighter in
the ultraviolet."

~~~~~~~

Composition, I believe, would be a factor in how a rock responds to radiation. So is time. No we didn't see this effect in other sites with mafic rocks...or did we and it's all been presented as Hue 19 or there was not enough spectral coverage before.