If you explore a Planet with a fleet of lower Ranks than recommended, you will have a lower success rate, however, if its Rank is higher than recommended, you will have a higher success rate.
Planets will be divided into four sections (expandable when there are more planets):
Section 1: from Planet 1 to Planet 10: Rank C is recommended.
Section 2: Planet 11 to Planet 20: Rank B is recommended.
Section 3: Planet 21 to Planet 25: Rank A recommended.
Section 4: Planet 26 to Planet 30: Rank S recommended.
Table of success percentages by Fleet Rank and Veterans Guild Success Cap.
Table for Veterans Guild Success Cap.