The spokes are difficult to observe
In a NASA press release it says that “the spokes are related to Saturn’s strong magnetic field, with some sort of solar interaction with the magnetic field producing the spokes”is the leading theory, according to Amy Simon, lead scientist of the Opal (Outer Planets Atmospheres Legacy) program.
The electrostatic forces created by interactions could cause dust or ice to float above the ring, forming the spokes. “We are moving towards the Saturn equinox when we expect peak spoke activity, with spokes appearing more frequent and darker over the next few years”explains the scientist.
Previous Hubble images had already suggested that the spokes only appear seasonally – Saturn’s seasons each last about seven years. Enough time to observe, a long time to explore again. To make matters worse, the spokes are only visible for two or three revolutions around the planet before disappearing again.