Sentence:  For the <WSD>Neptunian</WSD> rings, we again expect that Q_{occ} = 2 for Earth-based occultation data, so long as the mean particle size is substantially larger than the wavelength of observation (2.2μm). [...] In fact, photometric observations suggest that most <WSD>Neptunian</WSD> ring particles are sub-centimeter in size [...], so that we have Q_{occ} \simeq 2. 
Meaning of the word marked with <WSD> tags:  Of or pertaining to the planet Neptune.