A Mars Proleptic Calendar and Sol-Date Timing Reference

Michael Allison
Goddard Institute for Space Studies

presented at
the Founding Convention of the Mars Society, August 13-16 1998,
University of Colorado, Boulder, Colorado, USA


A new proposal for a 22 month Mars solar calendar is designed with a view to some preservation of the conventional (Gregorian calendar) context for monthly/seasonal statistics and annual time lines, with a numerical origin preceding the important 19th century observations of Mars dust storms, and an accurately determined reference to archival sol-date chronology. A 22 month division of the Mars tropical orbit (of 668.592 solar days or sols) would permit a cognizant transferal of the familiar names and lengths of the terrestrial months to approximately the same solar season, interspersed with ten new (30/31sol) months for Mars. (e.g. "January, February, Bradbury, Clarke, March, April, May, Hypatia, Huygens, Kepler...," etc.)

The specified (C.E.2000) calibration epoch for the proposed "Mars Proleptic Calendar" (MPC) defines a sequential "Mars Sol-Date" MSD = (MJD.TAI - 51549.0 + k)/1.02749125 + 44796.0, where MJD.TAI is the Modified Julian Date, Temps Atomique International, and k a small (approximately 0.00014d or 12sec) timing correction to the as yet inexactly navigated position of the crater Airy-0 defining the Mars prime meridian. As proposed, MSD44796.0 corresponds to Mars mean solar midnight (cf. Allison, 1997; Geophys. Res. Lett. 24, 1967) at 0 deg longitude ("Airy Mean Time") on "MPC067 Jan1" and C.E. 2000 January6.0-k (TAI) on the terrestrial calendar-clock. 67 Mars years (44796sols) correspond to 126.02 Earth years or 59.02 synodic periods and closely represent a half-day/sol commensurability. The implied Mars Sol-Date "MSD0.0 = MPC000 Jan0.0" therefore originates at C.E.1873 December29.502 (MJD05521.502), at a near coincidence of the Earth and Mars planetocentric solar longitudes, and precedes the earliest recorded occurrence of a regional Martian dust storm in C.E.1877.

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