Martian Time

Earthlings are meticulous about tracking time from the moment we get out of bed–to stop that blaring alarm clock–to the moment we get back in–when we reset that hated alarm. But how do we define time on other planets? For most of us, little could matter less, but for scientists involved in missions to Mars, little could matter more.

Astronomers mark the average length of a Martian day as 24 hours 39 minutes and 35 seconds. To set a Mars Local Time for use in exploratory missions, NASA developed a “Mars clock” based on the terrestrial 24 hour system, but with longer seconds, minutes and hours. Notable robots such as the Mars Pathfinder, the Mars Exploration Rovers, and the Phoenix and their mission controllers have operated on Mars time, rather than Earth time. The ever-shifting time gap between Earth and Mars required Earth-based controllers to advance their schedules by forty minutes each day–many calibrated their wristwatches to Mars time.

“You’re always jet-lagged,” Deborah Bass, the Deputy Project Scientist for the NASA Jet Propulsion Laboratory’s Phoenix Scout Mission, told Popular Science. “It’s only a little bit, because an hour–who cares, that’s not so bad. But it starts to take its toll.”

Many of the current rovers run on solar power–meager solar power at that. Rovers have only a four-hour period around local noon before their clocks run down. Scientists controlling the rover’s actions must be hyper-aware of the time on Mars. To make time keeping more complicated, five of the six successfully-landed rovers defined their own time zone. Only the Mars Pathfinder kept “local true solar time” set to the Martian midnight hour. The twin Mars Exploration Rovers, Spirit and Opportunity, used a “hybrid local solar time” to sync the true solar time with mission operations. For us, hybrid time is like using a watch set for Eastern Standard Time in central California–confusing, but it still counts passing minutes.

Though the length of a Martian day is close to a day here on Earth, the length of a year is almost twice as long on Mars. If months are kept to 28 Martian days to roughly align with Earth months, a year would have 24 months. But what would we call those extra months? Would there be a first December followed by a second December? Would we, as some enthusiasts suggest, alternate Earthly calendar months with Zodiac constellations or maybe science fiction authors? Or should months not be evenly spaced, since the orbit of Mars is not even itself? Mars wobbles around the sun in such a way that spring is the longest season at around 193 Martian days, while autumn is the shortest at around 143 Martian days. Do months need to reflect natural seasons and constellation cycles, or in this modern age are human economic and social patterns more important?

Unfortunately, most of us probably won’t stick around long enough to find out how humanity settles this question, but in the mean time it’s fun to think about.