Fig. 3: Examples of Class 1 lineaments in the Bright Plains region imaged by Galileo on orbit E6. The prominent ridge pair running from lower left to upper right is an example of a larger Class 1 feature, which might form as quickly as 30,000 yr according to the calculations in this paper. (The possibly flooded margins suggest that this feature may have been massive enough to promote crustal downwarping and consequent flooding; The central groove shows evidence of fall-back of debris as the crack was worked by diurnal tides.) Numerous smaller examples of Class 1 pairs are also evident in this region, and may have formed even more quickly, or may have been active when there was less diurnal working. Running from the lower right perpendicular to the prominent ridge pair is an example of a small Class 2 structure, with multiple ridges (two on each side in this case), symmetrical about the central groove.