Mars photo credits: MSSS/THEMIS
Lab photos on upper right by Wal Thornhill
Olympus Mons on the planet Mars defies
categorization as a "volcano," but bears a striking similarity to a
Olympus Mons on the planet Mars is taller than
three Mount Everests and about as wide as the entire Hawaiian Island
chain. But it¹s almost as flat as a pancake. Its edge is nearly as
abrupt as a pancake, too, ending in a scarp up to 6 kilometers (almost 4
The huge mound rises amidst several lesser BUT similar mountains in the
regions of the Tharsis Bulge. Planetary scientists call Olympus Mons a
volcano. But when examined in detail, it bears only a superficial
resemblance to some earthly volcanoes.
Olympus Mons has all the characteristics of a
lightning blister. Such raised bell-shaped blisters can be found on the
caps of lightning arrestors after a cloud-to-ground strike. They are
called "fulgamites". The material that forms the elevated fulgamite is
scavenged from the surrounding surface to produce an encircling
depression or moat. Olympus Mons has such a moat, which does not match
the bulge expected from upwelling magma beneath a volcano.
Earthly lightning usually consists of a number of
strokes in quick succession along the same ionized path. So the
discharge that creates a fulgamite is often followed by successive
lesser strokes that may excavate overlapping pits on the top of the
fulgamite. The six overlapping circular craters on the summit of Olympus
Mons display this pattern. The smaller craters center on the walls of
the larger and are cut to different depths, as if with a cookie cutter.
Such a pattern is not volcanic, where the caldera floors are supposed to
be due to collapse or draining of magma from beneath.
A laboratory example of an electric arc scar on a
clay anode surface is shown on the right. At moderate power, the
electric arc rotates (top right) and raises an extensive circular
blister, seen clearly in the middle right image. As the power is
increased, the arc briefly stops moving and burns a small circular
crater, seen as a glowing spot in the top image and at 4 o¹clock in the
bottom image. The tendency for the arc to "stick" to one spot on the
anode creates localized very high temperatures, sufficient to vaporize
some of the anode surface to form smooth circular crater floors and
steep terraced walls exactly as seen in the Olympus Mons calderas.
Do we see any volcano on Earth produce such a
configuration on its summit now? We can find none. Yet the pattern is
repeated more than once on the Martian Tharsis Bulge (row of pictures
below), including the summit of neighboring Ascraeus Mons (lower left),
a striking replica of the Olympus Mons "calderas".
The electrical hypothesis maintains that within
minutes successive strokes from a cosmic lightning bolt lifted the peak
and carved the craters on the summit. It seems likely that the Tharsis
Bulge will also trace to the same period of Martian history, when the
planet must have engaged another charged body at close range. If so,
evidence of such an exchange must be pervasive on the Martian surface,
and all the major features of the planet must be reconsidered from this
new viewpoint. Though geologists have never entertained the electrical
scarring of rocky planets and moons, rapidly accumulating evidence has
the potential to change this situation dramatically.