Are the radial spokes in Saturn's rings reliably visible via ground-based telescopes

Question

In the mid 1970's, Franklin and O'Meara saw persistent "radial spoke-like features" in the rings of Saturn, that should not have existed due to the differential rotation of the rings. A publication on this observation was rejected by a journal apparently on the grounds that the phenomenon was considered to be illusory (c.f Sciparelli/Lowell's Martian canals?).

From "Seeing in the Dark: How Amateur Astronomers Are Discovering the Wonder" By Timothy Ferris.

My question is, how reliably were these features visible from the ground-based telescopes of the day? Could sufficiently strong evidence for the existence been obtained before images from space probes? Was the rejection of the paper reasonable in the historical context in which the paper was submitted?

Answer 1

Bryan (2007) gives a number of reasons why O'Meara's discovery was largely discounted:

• As you stated, the behavior was entirely inconsistent with Keplerian predictions of motion.
• While O'Meara was able to reproduce his findings, no other independent observers could.
• The detections were done entirely visually, rather than with numerical measurements.
• There had been previous observations (i.e. in the 19th century), but in different places in the rings (the A and C rings, not the B ring). These have never been confirmed, and it is still believed that these were actually illusions.

Reliable observations from ground-based telescopes, especially those of amateurs, have arisen within the past decade or so. Since 2007, 67 "candidate" observations have been made of the spokes, many during the 2009 Saturnian equinox (keep in mind that the spokes may be a seasonal phenomenon). One additional factor that made observations difficult was that the spokes seemed to have vanished, even from space probes, in the years after the Voyager observations, making it impossible for ground-based telescopes to see them.