Dec 18, 2006
The Moon and Its Rilles
Planetary scientists describe it as a
stupendous channel cut by flowing lava. But on closer examination,
Schroeter’s Valley and its many counterparts on the Moon refute all
attempts to categorize them in such terms.
The long, winding channel pictured above is the most prominent
“sinuous rille” on the lunar surface—160 kilometers long and up to
10 kilometers wide—large enough to be clearly visible in Earth-based
telescopes. It is also up to 1300 meters deep—a profound contrast to
any observed effect of flowing lava on Earth.
Long prior to the space age, Schroeter’s Valley was the subject of
many speculations. But crucial details were unknown until the Apollo
lunar exploration missions in the late 60s and early 70s, when
orbiting craft enabled astronauts to take high-resolution pictures
of the lunar surface. The photographs in the composite shown here
were taken from the Endeavour Command Module of Apollo 15.
The seven frames look approximately south, revealing the crater
called “Cobra Head” at the upper left, from which emerges a winding
path that narrows until it disappears on the right. Only the edge of
the crater Herodotus is seen at the top of the composite. (An image
of Herodotus can be seen along with the famous crater Aristarchus in
March 10 Picture of the Day.
Sinuous rilles are defined as long, winding valleys, usually with
steep walls and often emerging from a crater. Of these phenomena,
the Moon presents countless examples at all scales. Two instances
will be seen in the lower portion of our March 10 picture.
speculations based on telescopic observation envisioned “cracks” on
the lunar surface. Then the astronomer William Pickering suggested
flowing water. A series of other speculations followed, most of them
excluded by the findings of the Apollo missions, until planetary
scientists eventually settled on flowing lava as the agent. The
“standard theory” today states that sinuous rilles were created by
lava either flowing across the surface or beneath the ground to form
a “lava tube”, portions of which eventually collapsed.
A considerably larger version of the above picture can be seen
here, and unless you are already certain that such formations
are well understood by planetary scientists, it is worth the look.
The enigmas and contradictions of standard theory lie in details
impossible to deny.
Both the width and length of the Schroeter’s Valley far exceed
anything ever accomplished by lava on Earth. But the reverse should
be expected. On the Earth, the atmosphere is insulating, allowing
lava to retain its heat. In the vacuum of space, heat will be much
more rapidly radiated away. On Earth, as lava flows for long
distances (counted at most in a few tens of kilometers, not
hundreds), the cooling at the surface causes a “roof” to form. It
may then continue to flow as a “tube” beneath the surface. That is
the only way the lava tube can achieve these comparatively modest
In an earlier
Picture of the Day we showed the longest
terrestrial example of a lava tube on Earth, associated with
Barker’s Cave in Australia. It is 35 kilometers long and only about
35 meters in height. The contrast to the much larger lunar rilles
could not be more stark And the only reason the
Barker’s Cave lava tube could achieve its length is that, when the
insulating crust was formed, the lava was able to retain its heat
and continue flowing beneath the surface. No such event occurred in
the case of Schroeter’s Valley: It would be impossible to sustain a
kilometers-wide roof of rock; and there is no evidence of either a
roof or of rubble from a roof’s collapse.
The moon has only about one sixth the gravity of the Earth, and it
is gravity that gives flowing liquid its velocity, its erosive force
and (most emphatically in the case of heated and melted rock) its
ability to cover distance. Yet lunar rilles extend up to 300
kilometers—almost nine times the length of the “record
breaker” on Earth.
The walls of Schröeter’s Valley are both steep and deep. But where
did all of the lava go? A short-lived channel of water might narrow
to a termination point without any overflow or outflow—it could
simply be absorbed into the ground or evaporate into space. But
flowing lava eating away surface material to cut a deep channel
would have to show up somewhere. We should see either breeches in
the deep walls or evidence of abundant outflow. But instead, the
channel simply dwindles until it disappears. In considering the
picture above, it is essential that one realize what planetary
scientists themselves acknowledge: The rille did not create the
maria in which it sits. It cuts through the pre-existing maria. It
is as if the material that once occupied the channel simply
The “flowing lava” seems to have possessed many remarkable features.
Even as it cut so deep (nothing comparable will be seen in any lava
flow on Earth—not even at the much smaller scale of terrestial lava
flows), this rapidly moving, molten rock, could make turns up to 90
degrees without affecting the “bends in the river” in any way.
Neither the extreme sinuosity nor the parallelism of the rille walls
conforms to the behavior of lava erosion.
Consider, for example, the sharply pointed prominence in the most
emphatic change of direction about a third of the way down the rille
from Cobra head. If the lava had the power to create such vertical
cliffs—up to 1300 meters deep—how did that sharp
Curiously, the "flow" of rilles on
other worlds isn't limited to "downhill" like lava and water-carved
channels on Earth. All fluid-erosion theories have chosen to ignore
that the apparent mouth of the “stream” is on high ground,
and the narrowest part of the channel is on lower ground.
The situation should be exactly reversed. As an erosion channel
lengthens, more and more spoil must be carried by the eroding fluid,
and the channel must grow wider to accommodate the load. The
cross-sectional area of any fluid stream must remain constant. Where
it is deep it must be narrow, where it is shallow it must be wide.
However, rilles do not conform to this rule. The famous Hadley's
Rille, amongst others, simply disappears for a short interval, then
reappears. Other rilles travel both up and down across considerable
distances. The most extraordinary example is the
on Venus, which rises and falls
dozens of times, with some
separating its high and low
points along its 6,800 kilometer length.
it is the things barely noticed, or forgotten, that provide the most
telling clues. Within the meandering channel of Schroeter’s Valley
is a much more narrow secondary rille. While planetary scientists
are well aware of this rille-within-a-rille, almost nothing is said
about its defining feature—a chain of small craters running
virtually the entire length of the rille. Yet this feature is not
uncommon. A nearby rille, Rima Prinz I reveals the same
As a rule, the
lunar rilles are much more heavily cratered than the surrounding
maria, yet by their very presence on the maria they must be younger.
Standard dating by “crater count” becomes preposterous. But what is
the meaning of this non-random concentrations of craters along the
link between crater formation and rille formation—though
substantiated on planets and moons throughout the solar
system—becomes highly confused in standard treatments of the
subject. Nevertheless, a unified answer has been available for
decades, and the credibility of science may, in fact, depend on it.
Please visit our
The Electric Sky
and The Electric Universe