MattEU, thanks for posting that Martian dust devil. Nice comparison.
According to NASA:
Color images from MESSENGER's Wide Angle Camera reveal that the irregular depression and bright halo have distinctive color.
If those bright spots and filaments were camera saturation artifacts, they would have mentioned that in conjunction with the color images. Haven't seen the color images anywhere yet...hmmmmm.
I tried to resolve the filaments as surface features, by manipulating the image, but that seems pretty unlikely to be the case, especially since the color images describe a "bright halo
I can't find a link again, but I remember reading somewhere that they think the large white patch is magnesium oxide
from "volcanic vents".
Notice how the larger, white stained region is pretty much centered on a large, circular, flat bottomed crater, and the "irregular depression" with the bright halo's lies right along the rim of it. I'm thinking that a previous discharge created the larger crater and the large white patch of electro-chemically created magnesium oxide. The current image shows a glow discharge eating away at the rim.
Check this out
We have observed for the first time a deposition of MgO microparticles with spherical shape. Experiment has been carried out in a small coaxial electrode system for an impulse discharge, consisting of an inner Mg-rod electrode of 1.7 mm in diameter, and an outer ring electrode, between which a small-diameter glass tube substrate is placed. From the SEM and Raman analyses, we have observed a formation of MgO particles with size less than several 500 nm. Most of the particles are spherical in shape, and distributed on the glass surface near the electrodes. The formation processes of the spherical particles are discussed.
Mercury has a thin silicate crust (glass beads?), and has abundant magnesium as well, upwards of 25% I think. This area in question is probably a much higher concentration of magnesium, probably around 75% (as a top of the head guesstimate).
There is also NaSiO4
(sodium silicate) detected on the surface...Mercury has a cometary sodium
and a surprising amount of OH. Electro-chemical reactions with solar plasma stream protons H+
would pretty much provide all the chemical ingredients to produce MgO, Na vapor, and probably H2
O that pretty much instantly reacts with the free Na vapor in the discharge column/corona, to produce OH and another free hydrogen to add back into the reaction mix.