Whenever scientists talk about geology it involved the idea that the globe is locked to its present
spin axis. We have previously discussed some of the evidence that potentially shows that the
crust of the Earth might have shifted a number of times in that past. This idea is frowned
upon by scientists favouring the slow process of continental drift and ice ages to explain these
anomalies. Not that long ago the idea that other planets had tectonic activity was laughed at,
these we thought to be dead worlds with the Earth being the only place we find water and tectonic
plates. Yet as we slowly explored the solar system it revealed a system that was more alive
than we could ever have imagined with moons with oceans of water buried below a thick crust of ice
and moons with volcanoes exploding from the surface. Once we landed on Mars we started to
detect faint rumbles which indicated some sort of tectonic activity deep below the surface.
These planets and moons seemed to be undergoing a similar process to those we see on Earth.
Is it possible to find evidence of a shifting crust on other planets?
Let's dive in and find out...
Finding evidence that one of these might have undergone a crustal displacement would be a shock,
yet it exists and more surprising is that this is over 20 years old!
Let's start by examining the evidence for a shift on Mars. There are a number of different
papers on this concept but the general idea is that about 3 to 3.5 billion years ago
the surface of Mars tilted by 20 to 25 degrees. This was not a simple tilt of the entire globe.
A massive volcanic structure called the Tharsis volcanic dome, which is thought
to be the largest in the Solar system, built up an enormous mass. This mass caused a force
to be exerted on the crust of the planet and caused the outer layers of Mars, the curst,
to rotate around its core. This in part might explain why they have found underground
reservoirs of water ice, which up until that time were considered anomalous, were located
far from the poles of Mars and why the Tharsis dome is now located at the equator.
So before this crustal shift, the poles of Mars were not in the same place they are today.
An interesting find from this is that the rivers beds we see on the surface today
would have been located along a south tropical band on Mars. The idea seems to
be corroborated by many different observations and the original idea stretches back to 1973
and the more recent 2016 paper only strengthens the evidence to support the idea.
So are there any other planets or moons that show crustal slips? Let's start by jumping to Europa,
Jupiter's icy moon. Examining the surface we can see that it is criss-crossed with cracks
at many different angles. Below this ice crust there is thought to be a liquid ocean.
New research has shown that Europa's large global scale circular patterns
formed during a large reorientation of its icy outer shell with respect to its spin axis. Their
findings confirmed that the fractures associated with a true polar wander on Europa cross-cut all
terrains. This means that the true polar wander event is very young and that the ice shell and
all features formed on it have moved more than 70 degrees of latitude from where they first formed.
The idea is that the liquid ocean would allow for the slip of the curst. Europa's crust is thought
to be detached from the rocky core. This raises the question as to whether this liquid ocean would
allow the crust to slip all the time? Does the shape of the crust normally resist this motion,
requiring some sort of deformation when it does slip? Or does the pressure of the crust normally
create enough resistance? Are the cracks we see on the surface created through a similar process
as outlined by Hapgood? We see areas that seem to have been stretched out
and we also see areas of compression and what look like mountain ranges.
Does the sheer number of these corroborate the idea that this is an ongoing mechanic?
The scientists speculate that there was an ice build-up at one of the poles on Europa
which caused the whole crust to move so that the excess ice ended up at the equator.
Let's move further out and examine Saturn's moon Enceladus. It is the sixth-largest moon of Saturn.
It is covered by fresh, clean ice which makes it one of the most reflective bodies in the solar
system. Similar to Europa, Enceladus is thought to have liquid ocean beneath the frozen surface.
It is also thought that this ocean means that the crust is detached from the rocky core.
Again here we find a similar story and evidence of a crustal shift.
By examining the surface details they were able to identify a series of basins along with a pair of
depressions that line up with the equator and pole if it was rotated by about 55 degrees of latitude.
In the left-hand image, we see Enceladus in its old orientations. The chain of basins representing
topographic lows can be seen in blue and purple, running along the equator, with an additional low
region around the original pole. The region that encloses the moon's currently active south polar
terrain, with its long, linear 'tiger stripe' fractures, would have been at middle latitudes
just south of the equator. The map on the right shows the current orientation of Enceladus.
Again on Enceladus, we see similar fault lines
and also areas that appear to have large areas that appear compressed and folded and others
that appear more stretched. There is also a very interesting difference between the northern part
which appears much older compared to the southern half with seems to be much younger?
Jumping back to our moon there is evidence that the surface also underwent a shift
about 3 billion years ago. Using a new study of lunar polar hydrogen from NASA satellite data
they were able to see a shift of the crust. But the shift was
much smaller in comparison to the other examples at just 6 degrees.
A different analysis of the bulges on the surface concluded that the Moon and Mercury had undergone
a reorientation of the surface resulting in a 10 to 30-degree shift of the pole.
The same study also examined Venus but due to the slow spin, it would result in a much
smaller rotational bulge. They had therefore expected that this would mean it would be very
easy to reorient Venus. This is not what they discovered. The largest volcanic features on
Venus are thought to only result in a 10-degree reorientation. Reconstruction of any shifting
of the crust was not possible for Venus due to the uncertainties in Venus' geological record.
So when we examine the solar system we find evidence that the shifting of a planet or
moon's crust is not an unusual event. In some cases the movement are small
but in some cases, the movements seem to be extremely large. The mechanism in the
case of the icy moons of Saturn and Jupiter is thoughts to be excess ice build-up at the poles
in the case of Mars it is thought to be the additional mass created by a large volcano
causing a large enough force to cause the crust to slip and move the bugle closer to the equator.
So why is this an acceptable model for other planets and yet not Earth?
In the case of Mars, we cannot identify any type of plates, and therefore the entire surface is
locked together. As mentioned when I covered Charles Hapgood's model of a crustal movement
it relies on the fact that the entire crust is locked together otherwise the plates would move
and absorb this force and you would end up with additional movement in some plates but not others.
When we look at the icy moons this may be a slightly different story as here they believe
that the ice does act more like plates with boundaries that move relative to each other.
These cracks may instead be the areas of the crust that are undergoing deformation
due to the movement of the whole crust as parts have to stretch and some parts have to compress.
Why would the Earth be any different? Why do we think that Earth is the only planet with plate
movement? There are some recent studies that have suggested that Mars might have had plate movement
in the past but it would only have had a few plates in comparison to the many plates on Earth
and would have moved much slower. In theory, the conditions for plate tectonics to work have
to be just right. The right type of rock, a crust that is not too thin or too thick,
the planet needs to also be just the right size, too much gravity squeezes the plates together.
The temperature of the rocks also needs to be exactly right, not too hot, not too cold,
not too wet, and not too dry. Well, that makes for an awfully narrow list of possibilities
and yet we do see similar features on all the planets and moons, mountains, valleys,
tears, etc. Yet on Earth, these they claim are largely created through plate tectonics,
on the other moons and planets, they have to come up with other mechanisms to account for them.