Astronomy

not convince Fred or others of the radial
features’ reality. Instead, I was met with a
seemingly unified resistance.
As James Bryant of McDonald
Observatory would later write in the 2007
Journal of Astronomical History and
Heritage, “[While his] audience knew him
to be honest, competent, free of agenda …
his evidence was very difficult to accept
because it ran contrary to physics. …
Inaction that followed O’Meara’s report
of spokes in 1976 may have been caused
by others’ distrust of the visual method
he used.”
Going it alone
While I understood the reasoning behind
others’ disbelief, further observations of
the features convinced me they were real.
I could not dismiss them as an atmospheric
phenomenon or telescopic illusion.
Over the next four years, I conducted a
systematic observing campaign of the B
ring. I submitted the results to journals for
publication without success. For instance,
in 43 days (January 24 to March 8, 1977),
I observed 29 radial features (or radial
complexes) when Saturn’s rings were tilted
around 17° to our line of sight.
The more I observed them, the more
dissimilar they became to ring A’s azimuthal
variations. On some evenings, I
would monitor the radial shadings for
hours, watching the motion of individual
streaks, which not only rotated in the same
direction as the planet’s cloud tops but also
at a similar rate. I also followed the radial
features through changing ring-angle
phases (from about 17° in 1976 to nearly
edge-on in 1980). During that time, I created
graphs that showed how the prominence
and number of these radial features
diminished dramatically as the rings’
angle decreased.
My systematic observations ended in
1980 when Saturn and its near edge-on
rings went into conjunction with the Sun
— also just before Voyager 2 arrived at
Saturn and obtained credit for the discovery
of Saturn’s radial “spokes” … but not
before I had one last chance to be heard.
Prior to Voyager 2’s arrival at Saturn, I
showed a sample of my Saturn drawings to
Sky & Telescope’s J. Kelly Beatty, who was
leaving for the Jet Propulsion Laboratory
to cover the event. Kelly first showed me
the latest images from the spacecraft, then
I handed him some of my drawings, saying,
“Please call me when Voyager images
these features in ring B,” and pointed out
the radial shadings. Kelly chuckled and
For years, the
author used
Harvard College
Observatory’s
9-inch Alvan Clark
refractor to observe
Saturn. COURTESY STEPHEN
JAMES O’MEARA
said, “Right.”
About a week
later, Kelly saw
the Voyager 2
images of the
spokes appear on
a large screen at
the JPL pressroom.
He said he fell back in his chair,
exclaiming that I had seen the spokes four
years ago. As Mark Washburn records in
Distant Encounters, “The news traveled
quickly, and an hour later [Voyager imaging
team leader] Brad Smith appeared in
the pressroom, asking Beatty, ‘What’s this I
hear about someone seeing spokes?’ ” Like
others, Smith was unconvinced.
Regardless, Kelly did call, and I was
astounded by the news.
Riddle me this
Now that spacecraft have imaged the
spokes, scientists are trying to solve the riddle
of their existence. One theory is that the
ring’s icy dust particles get an electrostatic
charge when they move out of Saturn’s
shadow and into sunlight. (It’s the same
type of electrostatic discharge that causes
static cling when you pull clothes from a
dryer.) The charge levitates the particles
above the ring plane and into Saturn’s magnetic
field, which co-rotates with the planet.
One mystery, however, is that the spokes
can disappear for long periods of time. For
instance, they remained elusive from 1998
to 2005 — even to the Cassini spacecraft
when it arrived in 2004. Cassini did begin
to detect them in 2005, albeit weakly. That
prompted scientists to speculate that spokes
may appear mainly during certain seasons
of the long saturnian year, perhaps in
response to the changing angle at which
sunlight hits the rings. If so, spokes may
have seasons, and may not form at times
when the Sun is between 17° and 24° above
the ring plane. (Interestingly, my pre-Voyager
observations took place when the Sun
was between 16.5° and 3° above the ring
plane, during a theoretical time of maximum
spoke production.)
Other plausible explanations include
asteroids plowing into the rings and whipping
up a cloud of plasma (which then levitates
above the ring plane because of the
magnetic field), and powerful lightning
strokes that surge up from Saturn’s clouds,
wallop the rings, and blast out jets of electrically
charged dust as spokes. This latter theory
holds promise, as spacecraft data also
suggest that spokes happen with about the
same frequency as the planet’s thunderstorms.
Its magnetic field could transport
electron beams from above these storms into
the rings, where they charge the dust.
Whatever the radial features are in
the B ring, they have now succumbed to
a flurry of new amateur sightings and CCD
images — some with telescopes a lot more
modest than the Harvard 9-inch refractor.
When truth shocks us into believing,
the fog of uncertainty lifts, allowing us to
see more clearly with new eyes.
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