picture of the day
The deeply cratered surface of Saturn's
moon Phoebe. Credit: NASA/JPL
Jul 25, 2007
Explaining Phoebe's Giant Spiral
What could have
created the giant logarithmic spiral carved into Saturn's
small but enigmatic moon?
Saturn's outer moon,
Phoebe is very small, only 220 kilometers in diameter.
Its gravity is a mere .05m/s2, compared to the
9m/s2 we experience here on Earth. While the
majority of Saturn's other moons are quite reflective of
visible light, Phoebe is as black as coal, making it one of
darkest objects in the solar system.
Based on data
collected by Cassini,
NASA scientists describe Phoebe as "very strange" and
probably a captured moon, rather than having formed along
with its parent planet. Said Torrence Johnson, a Cassini
team member at JPL: "And what it's told us is that it's a
collection of ice and rock and probably carbonaceous
compounds. We believe this object has many characteristics
in common with things like Pluto and (Neptune's moon) Triton
in the outer solar system. In other words, it's a first look
at one of these denizens of the outer solar system that
we've (seen previously) only from afar."
A number of
huge craters mark Phoebe's surface, making it look very
much like the heavily cratered surfaces of some asteroids.
Just as one must ask why the asteroids were not destroyed by
the impacts, one must ask why
Phoebe was not blown apart by whatever "impact" events
craters. Phoebe's dark surface is also reminiscent of
Wild 2's surface, revealed when the
Stardust probe made its close approach on January 2,
2004. The dark, cratered terrain on both bodies gives them
the appearance of twins, contrary to the expectations of
NASA observers that Wild 2 would have a "snowball"
Images from the
Cassini spacecraft depict a
moon that has features like those found on others we
have mentioned in recent articles. Some look very much like
the craters on
Mars, with similar morphology. The
crater rims have alternating striations, with steep
gullies running down one side and hard edges that appear as
if they were cut into the rock and ice. What appear to be
rounded boulders lie inside some of the craters as well
as in the faces of the crater walls.
closer examination casts doubt on the notion that the
largest crater could have been created by an object smashing
into Phoebe. The alternative--formation by plasma
discharge--is well supported. The most obvious evidence is
the spiral-shaped crater rim and the steeply carved cliffs.
These are not features expected under the impact hypothesis.
The visual evidence is consistent with a huge electric arc
cutting a long
chain of craters into one hemisphere, ending in the
winding curve and the
narrow canyon walls. Of course, the shallow craters, the
overlapping rims and the lack of impact debris are also
important considerations in the theory of electrical
effects, not only on
Phoebe but the rest of Saturn's moons as well.
Wal Thornhill recently wrote:
universe model explains the craters as Phoebe's birthmarks.
It is a model supported by examination of spark-machined
surfaces. Just as stars are observed to do, gas giant
planets may also expel a jet of matter during periods of
electrical instability. Accretion of matter in the jet is
mediated by the electromagnetic pinch effect and
electrostatic deposition. Both of these mechanisms are far
superior to accretion by impacts (tending to shatter and
scatter instead of to accrete). Electrostatic deposition
easily creates the layering seen in all rocky objects to
date. Electrical discharges between the parent and departing
child carve out the circular craters. Because they are not
formed by a sudden mechanical impact, the craters are neat
and do not cause disruption to adjacent craters or fill them
with debris as we see on Phoebe."
By thinking only
in terms of meteor impacts, landslides and other familiar
geological forces, NASA is ignoring the one possibility that
makes all the disparate features we see cohesive: an
electrically dynamic solar system in its formative phases,
when cosmic thunderbolts carved the surfaces of planets and
By Stephen Smith
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