The Marian Calendar: Design and Evaluation of a Civil Time Architecture for Mars

Human settlement on Mars will require a civil calendar capable of supporting recurring social and organisational activity across a 668–669-sol year. This preprint treats Martian calendrics as a systems-engineering design problem and presents the Marian Calendar, a requirements-informed architecture evaluated against explicit design objectives for astronomical traceability, structural regularity, recurrence invariance, operational cadence and interplanetary legibility. The calendar combines twelve 55–56-sol months with twenty-four 27–28-sol operational subdivisions, six medium-range planning periods and four equal 167-sol common-year quarters. A nominal seven-sol week with shortened terminal weeks gives invariant valid date–weekday relationships. The civil year is referenced to successive Mars passages through Ls = 15°, selected because around a mid-21st-century reference epoch this places Marian New Year close to the heliocentric direction occupied by Earth at Gregorian New Year. A mnemonic 59-in-100 intercalation rule gives a mean civil year of 668.590000 sols. Evaluation over 2031–2120 using JPL Solar System Dynamics planetary-position formulae gives a descriptive Spearman correlation of ρ = 0.9403 between circular Gregorian–Marian month separation and modelled Earth–Mars one-way light time, with the relationship remaining strong across 41 complete synodic cycles. An independent planetary-ephemeris implementation reproduces the headline correlations to better than 4 × 10⁻⁵ in ρ. Marian makes no claim to priority for its 12-month 56–56–55 arithmetic, which is directly preceded by Levitt’s 1954 proposal. Its contribution is to extend the Levitt–Darian structural lineage into a layered civil operating architecture and to evaluate that architecture against explicit settlement design objectives. Preprint status: This is an author preprint and has not undergone peer review. Supporting computational record: Jonathan Bullock, The Marian Calendar: Computational Data and Reproducibility Package, Zenodo, DOI: 10.5281/zenodo.22686413.