Pantheon Fossae
Ok, one single phenomena it is!! I pick
Mercuries spider crater! ... I propose this is an electrical discharge scar. A planetary sized lightning strike!! ...
Well the appearance of such stretch marks or extensional faults certainly seems consistent with the geology of the region, known as the Caloris Basin. ...
I see
The Man has beat me to the main point, but I would like to expand a bit by presenting a paper not on his list ...
Could Pantheon Fossae be the Result of the Apollodorus Crater-forming Impact within the Caloris Basin, Mercury?; Freed,
et al., 2009; 40th Lunar and Planetary Conference, 2000 (follow the PDF link, it's freely accessible). In this short paper the authors detail the argument that the Apollodorus impact event caused the Pantheon Fossae features. As the paper puts it: "
Specifically, we explore whether the Apollodorus crater-forming impact modified the state of stress within the central Caloris basin floor in a manner that led to the formation of many, if not all, of the graben of Pantheon Fossae." Of course there is no claim that this is definitely the cause of the Pantheon Fossae features, and the authors are quite explicit about the possibility that they are wrong ("
The fact that no other similar sized impacts induced such a complex implies either that no significant extensional pre-stress was present at the time of those impacts, or our scenario linking Apollodorus to Pantheon Fossae is not correct."). However, the geological & geophysical evidence & arguments are presented, and the entire scenario makes physical sense, and is consistent with known geology & geophysics.
So compare this hypothesis to the competing electrical discharge hypothesis championed by
Sol88. Which seems more likely? Which makes more physical sense? I submit that the electrical discharge hypothesis is much inferior, makes less physical sense, and suffers from far more serious problems than does the alternative, more mainstream geological explanation offered by Freed,
et al.
The pictures shown by
Sol88 are not consistent with the graben pattern seen in pantheon Fossae. In both of his pictures, the electrical discharge pattern spreads out along the surface, and forms a "dendritic pattern" with many branches spreading out from the large radial channels. But look at the pictures of Pantheon Fossae and you see little no branching. Instead you see only strong radial features, and they are fairly straight, rather than following the twisty courses seen in the electrical discharge pictures. The pattern is not consistent with the electrical discharge pictures, but is consistent with the well known geology of grabens. This lends confidence to the geological explanation, and takes confidence away from the electrical discharge hypothesis.
Furthermore,
Sol88 "scales up" the phenomenon in size without justification. Despite claims to the contrary, it is not true that you can "scale up" any plasma process without question. One need only look at the Pantheon Fossae pictures to see that the linear features are quite deep, which presents no problem if they are grabens. However, this poses great problems for the electrical discharge hypothesis, because it is now required of the electrical discharge that it carve deep features into basaltic rocks. There is no experimental or observational evidence to support such an extreme claim, and a lot of evidence to oppose it. For one thing, we see that the channel features interpreted as graben are consistently the same width all along the channel. If they were carved by electrical discharge, they should be thick at the base, and grow thinner, as the electric current loses energy due to the work done digging the channel, and due to energy lost to the dendritic branches (both of which features we do see in the
Sol88 pictures, and do not see in the Pantheon Fossae pictures). This is aside from the extraordinary difficulty in explaining where the very considerable amount of energy required to did even one channel in basalt would come from, let alone that required to dig the entire system.
So here are my conclusions:
Why the electrical hypothesis of Sol88 should be rejected
1) The pictorial evidence that
Sol88 presents is not self consistent, as the branching pattern and channel shapes seen in the pictures are significantly inconsistent with those seen in Pantheon Fossae.
2) The lack of channel thinning in the Pantheon Fossae picture implies that the carving current does not lose energy as it does work, which is not physically reasonable.
3) There is no known mechanism whereby any electric current, under any circumstances, could carve a deep channel in basaltic rock. So this must be assumed
a-priori.
4) Even if we ignore (3), there is no physically reasonable explanation for the source of the enormous energy required in an electrical discharge to mechanically carve the channels.
Why the geological explanation should not be rejected
1) The Apollodorus crater is entirely consistent with impact crater shapes, both from physical models, and from laboratory experiments modeling impact features. There is no reason to reject this as an impact feature.
2) The assumption of pre-existing extensional stress in Caloris Basin is consistent with the observed presence of circumferential graben in the outer Caloris Basin, and is consistent with extensional stress in terrestrial basins.
3) The shape and pattern of channels in Caloris Basin is consistent with the geological interpretation that they are grabens.
4) There is no fundamental energy problem; the impact and pre-existing extensional stress provide all of the energy necessary to explain the work done in creating the grabens.
Last word: I do not claim that the explanation in Freed,
et al. is correct, only that it is scientifically preferable, and significantly so, than the electrical alternative offered by
Sol88. The Freed,
et al., explanation is not without problems of its own, most notably the fact that the radial graben pattern from an impact crater is quite rare. There are alternative geological explanations on the table which do not depend on the impact, as referenced by Freed,
et al.