Wednesday's L.A. Times article by Jia-Rui Chong about JPL workers' wristwatches keeping Martian time prompted me to do a little bit of research about time zones on Mars. I'll eventually propose a patch to the "Theory" file, but thought I'd first submit the following rough draft on this mailing list for comment. ----- Time and time zones on Mars ----- Some people have adjusted their work schedules to fit Mars time. Dozens of special Mars watches were built for Jet Propulsion Laboratory workers who kept Mars time during the Mars Exploration Rovers mission (2004). These timepieces look like normal Seikos and Citizens but use Mars seconds rather than terrestrial seconds. A Mars solar day is called a "sol" and has a mean period equal to about 24 hours 39 minutes 35.244 seconds in terrestrial time. It is divided into a conventional 24-hour clock, so each Mars second equals about 1.02749125 terrestrial seconds. The prime meridian of Mars goes through the center of the crater Airy-0, named in honor of the British astronomer who built the Greenwich telescope that defines Earth's prime meridian. Mean solar time on the Mars prime meridian is called Mars Coordinated Time (MTC). Each landed mission on Mars has adopted a different reference for solar time keeping, so there is no real standard for Mars time zones. For example, the Mars Exploration Rovers mission defined two time zones "Local Solar Time A" and "Local Solar Time B" for its two missions, each zone designed so that its time equals local true solar time at approximately the middle of the nominal mission. Such a "time zone" is not particularly suited for any application other than the mission itself. Many calendars have been proposed for Mars, but none have achieved wide acceptance. Astronomers often use Mars Sol Date (MSD) which is a sequential count of Mars solar days elapsed since about 1873-12-29 12:00 GMT. The tz database does not currently support Mars time, but it is documented here in the hopes that support will be added eventually. Sources: Michael Allison and Robert Schmunk, "Technical Notes on Mars Solar Time as Adopted by the Mars24 Sunclock" <http://www.giss.nasa.gov/tools/mars24/help/notes.html> (2004-01-12). Jia-Rui Chong, "Workdays Fit for a Martian", Los Angeles Times <http://www.latimes.com/la-sci-marstime14jan14,1,3346745.story> (2004-01-14), pp A1, A20-A21.