Day 12: Earth to Mars, Come In

Thu, 04 Jun 2026 10:00:00 -0500

NASA’s Mars mission control runs on Mars time, not Earth time.

For the first few months of every landed mission (Curiosity, Perseverance, Insight), the scientists shift their work schedules by 39 minutes every day.

They go to sleep 39 minutes later, wake up 39 minutes later, do all their meetings 39 minutes later than yesterday.

After 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.

This 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.

Let’s talk about why time on Mars is hard.

The sol

A Martian solar day is called a sol, and it’s about 24 hours, 39 minutes, 35 seconds.

That’s almost an Earth day. Close enough that NASA’s first instinct in the 1970s was to use Earth time for Mars missions anyway.

Bad idea. Within a single Martian month, your Earth-time schedule drifts nearly a full day out of phase with the local Martian one.

The rover’s morning camera shots happen during your meeting. Its solar panels charge while you’re trying to sleep.

So 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.

They built Mars-time-aware mission scheduling software. They renamed “day” to “sol” so nobody got confused.

It 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.

Mars time shifts your sleep 39 minutes later every day, which is roughly equivalent to flying west across two time zones, every day, forever.

After a few months I can see everyone getting their schedules wrecked.

Each rover has its own time zone

Mars 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.

Curiosity 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.

Curiosity is roughly four hours later in its day than Perseverance, because Gale Crater is 60 degrees east of Jezero.

If you’re a rover and you want to know when the sun will rise tomorrow, you use your LMST, not the other rover’s.

There’s also a coordinated reference: Coordinated Mars Time (MTC), anchored to Airy Crater, which is roughly the Mars equivalent of Greenwich.

Airy 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.

So 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).

The 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.

The Moon is being figured out right now

In 2024, the White House Office of Science and Technology Policy directed NASA to establish Coordinated Lunar Time (LTC) by 2026.

The Artemis program needs it. So does every commercial lunar lander launching this decade: SpaceX, Blue Origin, ispace, Astrobotic.

All of them need to coordinate communications, navigation, and surface operations on the Moon, and they need a shared time standard to do it.

The Moon’s timekeeping problem is harder than Mars’s, for two reasons.

First, the Moon’s day is 29.5 Earth days long (synodic). A lunar “noon” lasts 14 Earth days, and so does the night.

The 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.

Second, 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.

That’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.

LTC is being designed right now. The current proposal is an atomic timescale traceable back to TAI, with relativistic corrections applied at the lunar surface.

It will probably be ready before Artemis 3 lands humans?

Deep space and the light-delay problem

Beyond the Moon and Mars, time becomes a different problem entirely: light delay.

Round-trip to Mars: 6 to 44 minutes, depending on orbital geometry
Round-trip to Jupiter or Saturn: hours
Round-trip to Voyager 1, currently 24 billion kilometers from Earth: about 46 hours

You can’t run NTP to a spacecraft beyond the Moon. The sync protocol assumes round trips of milliseconds, and the universe doesn’t oblige.

The 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.

The 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.

For interplanetary work, physicists use three relativistic coordinate timescales:

TCB (Barycentric Coordinate Time): a clock that lives at the center of mass of the solar system. The natural frame for tracking planets, asteroids, comets.
TCG (Geocentric Coordinate Time): a clock at Earth’s center. The frame for tracking Earth satellites and orbital mechanics close to Earth.
TT (Terrestrial Time): a clock on Earth’s geoid. What UTC is derived from. What humans live in.

TCG drifts about 22 milliseconds per year from TT. TCB drifts nearly half a second per year from both.

Most humans never encounter this.

Anyone doing calculating planetary calculations does.

The deeper point

“The day” is parochial. It works only on the body where it’s defined.

Earth time scales fine on Earth. GPS scales fine in Earth orbit. Mars time scales fine on Mars. None of them scale to each other.

Every body in the solar system has its own “now,” and there’s no single instant that applies everywhere at once.

It’s a consequence of relativity. Time literally runs at different rates at different gravitational potentials and different velocities.

A clock at the solar system barycenter ticks differently than a clock on Earth. There is no “true” rate. There are only frames.

So 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.

The clocks themselves are “easy” but the coordination between them is the not.

The civilian question, what time is it if I want to call my friend on Mars, has no clean answer.

You 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.

And even if there were, you’d still have to handle the light delay.

Tomorrow we come back to Earth, and to the most ubiquitous time format in human history: the number of seconds since midnight, January 1, 1970.

Sources

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