NASA’s Mars mission control runs on Mars time, not Earth time.
\nFor the first few months of every landed mission (Curiosity, Perseverance, Insight), the scientists shift their work schedules by 39 minutes every day.
\nThey go to sleep 39 minutes later, wake up 39 minutes later, do all their meetings 39 minutes later than yesterday.
\nAfter a few weeks they’re working at 3 AM Earth time. After a month they’re working at noon. After two months they’re back to where they started.
\nThis is what living on Mars time looks like to humans. It is exhausting and demonstrably bad for sleep. They do it anyway because the rovers don’t care about Earth’s schedule.
\nLet’s talk about why time on Mars is hard.
\nA Martian solar day is called a sol, and it’s about 24 hours, 39 minutes, 35 seconds.
\nThat’s almost an Earth day. Close enough that NASA’s first instinct in the 1970s was to use Earth time for Mars missions anyway.
\nBad idea. Within a single Martian month, your Earth-time schedule drifts nearly a full day out of phase with the local Martian one.
\nThe rover’s morning camera shots happen during your meeting. Its solar panels charge while you’re trying to sleep.
\nSo NASA started using Mars time for the human side of mission ops. They built Mars-time wristwatches in the 1990s, actual mechanical watches modified to run 2.7% slower, and gave them to mission controllers.
\nThey built Mars-time-aware mission scheduling software. They renamed “day” to “sol” so nobody got confused.
\nIt worked. It was also brutal on the humans, because human circadian rhythms evolved for Earth’s 24-hour day, not Mars’s 24-hour-39-minute one.
\nMars time shifts your sleep 39 minutes later every day, which is roughly equivalent to flying west across two time zones, every day, forever.
\nAfter a few months I can see everyone getting their schedules wrecked.
\nMars doesn’t have just one time. Each rover gets its own time zone, called Local Mean Solar Time (LMST), based on its specific longitude on Mars.
\nCuriosity is in Gale Crater. Perseverance is in Jezero Crater. They are about 3,700 kilometers apart on Mars, and they keep local solar times that differ by about four hours.
\nCuriosity is roughly four hours later in its day than Perseverance, because Gale Crater is 60 degrees east of Jezero.
\nIf you’re a rover and you want to know when the sun will rise tomorrow, you use your LMST, not the other rover’s.
\nThere’s also a coordinated reference: Coordinated Mars Time (MTC), anchored to Airy Crater, which is roughly the Mars equivalent of Greenwich.
\nAiry is where Mars’s prime meridian sits by IAU convention, and MTC is the mean solar time at that location. Most planetary scientists default to MTC when reporting Mars events without specifying a longitude.
\nSo Mars has its own day (the sol), its own time zones (LMST per location), its own Greenwich (Airy Crater), and its own UTC-analog (MTC).
\nThe whole planet has built up a parallel set of timekeeping conventions, derived from the same basic problem Earth solved: a rotating body needs a way to talk about when things happen.
\nIn 2024, the White House Office of Science and Technology Policy directed NASA to establish Coordinated Lunar Time (LTC) by 2026.
\nThe Artemis program needs it. So does every commercial lunar lander launching this decade: SpaceX, Blue Origin, ispace, Astrobotic.
\nAll of them need to coordinate communications, navigation, and surface operations on the Moon, and they need a shared time standard to do it.
\nThe Moon’s timekeeping problem is harder than Mars’s, for two reasons.
\nFirst, the Moon’s day is 29.5 Earth days long (synodic). A lunar “noon” lasts 14 Earth days, and so does the night.
\nThe whole concept of “day” as a unit of human activity falls apart. Lunar mission ops will likely use Earth-anchored time for everything and ignore the local sun.
\nSecond, relativity matters more than you’d think. Clocks on the Moon run about 58 microseconds per day faster than clocks on Earth’s surface, due to the Moon’s weaker gravity well.
\nThat’s bigger than GPS’s 38 µs/day. If you want a lunar communication network to synchronize with Earth-side networks, you have to bake in the correction the same way GPS did, but more aggressively.
\nLTC is being designed right now. The current proposal is an atomic timescale traceable back to TAI, with relativistic corrections applied at the lunar surface.
\nIt will probably be ready before Artemis 3 lands humans?
\nBeyond the Moon and Mars, time becomes a different problem entirely: light delay.
\nYou can’t run NTP to a spacecraft beyond the Moon. The sync protocol assumes round trips of milliseconds, and the universe doesn’t oblige.
\nThe Deep Space Network (NASA’s array of giant antennas at Goldstone, Madrid, and Canberra) sends time-tagged commands to spacecraft, and spacecraft tag their telemetry with their own onboard atomic clocks.
\nThe clocks have to be reliable for years or decades without correction, because by the time a round trip resolves, you’ve moved on to the next problem.
\nFor interplanetary work, physicists use three relativistic coordinate timescales:
\nTCG drifts about 22 milliseconds per year from TT. TCB drifts nearly half a second per year from both.
\nMost humans never encounter this.
\nAnyone doing calculating planetary calculations does.
\n“The day” is parochial. It works only on the body where it’s defined.
\nEarth time scales fine on Earth. GPS scales fine in Earth orbit. Mars time scales fine on Mars. None of them scale to each other.
\nEvery body in the solar system has its own “now,” and there’s no single instant that applies everywhere at once.
\nIt’s a consequence of relativity. Time literally runs at different rates at different gravitational potentials and different velocities.
\nA clock at the solar system barycenter ticks differently than a clock on Earth. There is no “true” rate. There are only frames.
\nSo how do we coordinate? The standard answer, for spacecraft and astronomers, is to pick a coordinate frame, anchor everything to it, and convert as needed at the destination. TCB for solar-system work. UTC for Earth civilians. GPS for navigation. LTC (coming) for the Moon. MTC for Mars.
\nThe clocks themselves are “easy” but the coordination between them is the not.
\nThe civilian question, what time is it if I want to call my friend on Mars, has no clean answer.
\nYou pick a coordinate frame, you both agree to use it, and you live with the conversion. There’s no “Mars time on your phone” because there’s no Mars infrastructure to sync your phone with.
\nAnd even if there were, you’d still have to handle the light delay.
\nTomorrow we come back to Earth, and to the most ubiquitous time format in human history: the number of seconds since midnight, January 1, 1970.
\nI’d appreciate a follow. You can subscribe with your email below. The emails go out once a week, or you can find me on Mastodon at @logan@llbbl.blog.
\n", "date_published": "2026-06-04T10:00:00-05:00", "url": "https://llbbl.blog/2026/06/04/day-earth-to-mars-come.html", "tags": ["Space","Engineering","Time","30daysoftime","Mars","Nasa"] } ] }