Cycles refer to a measure of time in the history of the cosmos that are used in a variety of cultures. Dates given in cycles are known as "datecycles", according to text in Captain A.C. Exeter's last log, and consist of 6 numbers, whose significance is currently unclear. The length of a cycle appears to be locally defined, and the unit is used in conjunction with an SI-based set of prefixes.
Length of a cycleEdit
The first use of "cycle", in Metroid Prime, sets the end of Metroid at 09.992.3, and the beginning of Metroid Prime shortly after 11.664.2. According to the Metroid Prime Trilogy art booklet, the span between these games is three years long, indicating that a cycle is approximately a year long.
Based on Metroid Prime 2: Echoes, the Galactic Federation and the Space Pirates seem to use the same system for measuring cycles. The Space Pirate Logs, which start from the beginning of Space Pirate operations on Aether, include the cycle date on which GFMC Task Force Herakles landed on Aether (07.013.6), and this date is very close to the filing of Captain Exeter's report on the planetfall (07.014.2). Additionally, the span of time between the loss of GFMC Task Force Herakles and the start of Samus's mission to Aether is stated to be eight days, and the datecycle span between Herakles's planetfall on Aether and the arrival of Dark Samus is stated by the Space Pirates to be 00.146.3. Given that the middle set of numbers in Tallon IV's datecycles range from "001" to "957", and in Aether's, from "008" to "989", it is likely that the middle set of numbers measure 1/1000 of a cycle. Thus, this set of numbers is roughly equivalent to the "day" of the cycle. Extending this analogy would indicate that the third set of numbers measures 1/10 of a "day", and would be roughly equivalent to the "hour" of the cycle.
If the datecycle is treated similar to a normal decimal number, the initial Space Pirate Data in Metroid Prime 2: Echoes would place the discovery of Phazon on Aether at approximately 00.468.1. However, these dates are inconsistent with those used in Metroid Prime, in which the Space Pirates do not even detect Phazon on Tallon IV until 10.229.2. This suggests that the datecycle may not be a universal system of measurement, but may instead be set so that it starts from an important point in the area's history. The use of Zebesian datecycles on Tallon IV suggests that this method applies to the region's entire solar system. However, such a personal system of measurement makes the shared datecycles in Metroid Prime 2: Echoes somewhat confusing, as it is unlikely that the Galactic Federation and the Space Pirates would use the same local calendars. Given the Space Pirate's propensity for stealth, it is also unlikely that the Galactic Federation bases its datecycles on the Space Pirate calendar, or on the date at which Space Pirate activity is discovered in a region. It is probable, then, that the Space Pirates instead "pirate" their calendar from the Galactic Federation. Metroid Prime 2: Echoes introduces another apparent inconsistency, as its Space Pirate Data logs end with 07.159.9, and thus imply that the Space Pirate's operation on Aether lasted almost seven cycles. This seems to further imply that cycles, as well as datecycles, are somehow defined locally.
While Tallon IV and Zebes are both habitable planets with liquid water, orbiting the same star, and as such would have orbital periods of similar lengths, Aether's status as a rogue planet means that it does not have an analogous solar orbit, so the datecycles used on Aether must be based on some other standard. As Aether would not have a practical length of orbit, it is most probable that its cycle is instead based on its "day", rather than the other way around. Furthermore, the timespan between Metroid Prime and Metroid Prime 2: Echoes is stated to last two years, or approximately 2.0 of Tallon IV's cycles, and the Space Pirate datecycles suggest that their operation on Aether has lasted 6.6918 of its cycles. If the Space Pirates detected Phazon on Aether immediately following its discovery on Tallon IV, then the operation on Aether lasted approximately 3.3194 of Tallon IV's cycles, meaning that Aether's cycle and day would be at most 49.604% of their Zebes and Tallon IV analogues.
The prefixes "centi-" and "deca-" are also used in the Prime series to refer to certain amounts of cycles. In the SI system of measurements, a "centicycle" would be 0.01 cycles, while a "decacycle" would be 10 cycles. This indicates that here, "centi-" is used to mean 100, rather than 1/100, and so a "centicycle" would be 100 cycles.