What time is it on Mars? (And other space time zones)
Earth has a 24-hour day. That's hard-wired into our biology, our clocks, our calendars. But the rest of the solar system doesn't follow our schedule. Mars has its own day length. The International Space Station orbits Earth every 90 minutes, seeing 16 sunrises per actual day. And Pluto's "day" is about 6 of our days. How do scientists and astronauts coordinate time across all of this?
For Earth time conversions, the world clock and time converter handle them. The rest of this post is about everything else.
Mars time
Mars has a slightly longer day than Earth — about 24 hours, 39 minutes, 35 seconds. This difference, called a "Martian sol," means the Martian day rotates a bit slower than Earth's.
For NASA missions to Mars, this matters. Each mission has its own clock that runs in Martian time:
Mars Coordinated Time (MTC): a hypothetical time scale on Mars analogous to UTC.
Mission Local Mean Solar Time (LMST): time at the rover's location, accounting for Mars's tilt and rotation.
For Curiosity rover, scientists in Houston had to live on "Mars time" — meaning they shifted their work day to match Curiosity's "morning" each day. Since each Martian day is 39 minutes longer than Earth's, the team's schedule shifted ~39 minutes later each Earth day. Over weeks, they were out of sync with normal Earth life. The schedule was so disruptive that NASA discontinued strict Mars time after the first 90 days.
ISS time
The International Space Station orbits Earth every ~92 minutes. This means:
- 16 sunrises per actual 24-hour Earth day
- No "morning/noon/evening" in the traditional sense
- Day-night cycles inside the station are essentially arbitrary
The ISS uses UTC for everything operational. Each crew member has their own "morning" routine, but they're all on UTC.
Why UTC? Because the ISS is an international project (US, Russia, Japan, Europe, Canada). Different countries have different "home" times. UTC is neutral.
ISS schedule:
- Wake up: 6 AM UTC
- Work: 8 AM-6 PM UTC
- Dinner: 6 PM UTC
- Sleep: 10 PM UTC
This is "ISS time," consistent regardless of where the station is in orbit.
Why deep space gets even weirder
For missions beyond Earth orbit, time complications multiply:
Communication delay. Mars is 3-22 light-minutes from Earth. Any "what time is it?" question takes that long to round-trip. Real-time coordination is impossible.
Speed-of-light constraints. Anything in motion experiences time differently per relativity. For interstellar speeds, this would be significant. For solar-system speeds, it's measurable but small.
Reference frames. "Now" depends on your reference frame. Time on a moving spacecraft differs slightly from time on Earth.
For typical Mars missions, time on Earth (UTC) is used for command timestamps. Times on Mars are "Mars Solar Time" (referenced to local solar position). Both clocks are correlated to UTC by mission control.
Time on other planets
A planet's "day" depends on its rotation:
| Planet | Day length | Year length |
|--------|-----------|-------------|
| Mercury | 58.6 Earth days | 88 Earth days |
| Venus | 243 Earth days (retrograde) | 225 Earth days |
| Earth | 24 hours | 365.25 days |
| Mars | 24h 39m | 687 Earth days |
| Jupiter | ~9h 55m | 11.86 Earth years |
| Saturn | ~10h 14m | 29.46 Earth years |
| Uranus | ~17h 14m | 84 Earth years |
| Neptune | ~16h 7m | 165 Earth years |
| Pluto | 6.4 Earth days | 248 Earth years |
Day-length differences are why a "day on Venus" is longer than a "year on Venus." Venus rotates so slowly that the planet completes one orbit faster than one rotation.
For mission planning, scientists track time on each body separately. For Mars rovers, "sol-1" is the first Martian day after landing, "sol-2" is the second, etc.
Time at the speed of light
For special-relativistic effects, time moves differently for fast-moving objects. Consequences:
For the ISS: clocks on the ISS run very slightly slower than Earth clocks. The effect is tiny (microseconds per year) but real. GPS satellites have to account for this — without correction, GPS positions would be wrong by hundreds of meters per day.
For interstellar travel (hypothetical): a spacecraft moving at 90% the speed of light would experience time dramatically slower. A 100-Earth-year journey would only feel like ~44 years for the crew. This is the "twin paradox" — the traveling twin returns younger than the stay-at-home twin.
Real interstellar missions are much slower than this, so the effect is small. But future generations may need to deal with it.
Astronomical time
For astronomy specifically, several time scales coexist:
TAI (International Atomic Time): based on atomic clocks. Steady, no leap seconds.
UTC: TAI minus accumulated leap seconds. Used for civilian timekeeping.
TT (Terrestrial Time): a theoretical time scale used for astronomical calculations.
TDB (Barycentric Dynamical Time): time as measured at the solar system's center of mass. Used for astronomical ephemerides.
TCB (Barycentric Coordinate Time): a slight refinement of TDB.
UT1: time aligned with Earth's rotation (slightly different from UTC).
Sidereal time: time relative to the stars rather than the sun. ~23h 56m per day.
For astronomy purposes, the choice of time scale matters. For everyday purposes, all are roughly the same.
Practical relevance
For most people, this is curiosity. A few practical applications:
GPS users: GPS uses GPS time (related to TAI but offset by 18 seconds as of 2024). Your GPS receiver converts to UTC for display.
Scientific researchers: those working with astronomical data, satellites, or interplanetary missions need to use the appropriate time scale.
Software developers in aerospace: must handle multiple time scales correctly.
Science fiction writers: get to play with this stuff for fun.
When humans live on Mars
When (if?) humans establish a permanent presence on Mars, the time question becomes practical:
- A "Martian day" (sol) is 24h 39m
- Living in 24-hour Earth time on Mars would be misaligned with the local sun
- Mars colonies will likely use Martian sols for daily life
- Earth-Mars communication will use UTC for time-stamping
Some proposals already exist for "Mars Coordinated Time" and Martian calendars. None is officially adopted, but mission planning incorporates these concepts.
Mars time conversion
Approximate Mars time conversions:
- 1 Earth day = 24 hours = 1.027 Martian sols
- 1 Martian sol = 24h 39m 35s = 0.974 Earth days
- 1 Earth year = ~669 Martian sols (less than 2 Martian years — Mars takes longer to orbit)
- 1 Martian year = 668.6 Martian sols = 686.97 Earth days
A "second on Mars" (Martian second) is the same length as an Earth second. The day length differs because Mars rotates slower.
ISS time observances
How astronauts handle time:
Christmas/New Year: celebrated on UTC, so the entire international crew shares a moment.
Birthdays: usually celebrated on UTC of the astronaut's home country birthday.
Religious observances: each astronaut handles privately. Muslim astronauts have specific guidance for prayer times in space.
Weekends: 2 days off per week, same as Earth. Workout, leisure, video calls home.
The 90-minute orbit means astronauts see a sunrise/sunset every 45-46 minutes. This is visible in many ISS photos and videos.
What about Pluto?
Pluto has a 6.4 Earth-day rotation period and an 248 Earth-year orbit. If we ever sent a probe to Pluto's surface (we haven't), each "day" would be over a week long. A "year" would mean 248 Earth years.
Time-keeping there would be radically different from Earth.
FAQ
What time is it on Mars right now?
There's no single answer. "Mars Solar Time" depends on which longitude on Mars you're at (just like Earth has time zones). NASA missions use Mission Local Mean Solar Time (LMST) at the spacecraft's location.
How long is a Martian year?
687 Earth days, or about 1.88 Earth years. So a Martian "winter" is about 6 Earth months.
Will humans ever live on a Martian schedule?
Probably yes for any long-term Mars colony. The 24h 39m sol cycles work biologically (close to Earth's 24-hour day).
Does Mars have time zones?
Conceptually yes — different longitudes have different solar noons. NASA and ESA missions have developed coordinate systems for this.
Is space "really" UTC for the ISS?
Yes — the ISS uses UTC for all internal coordination. This is documented in mission protocols.
How accurate are atomic clocks in space?
Very. Optical lattice clocks on Earth are accurate to one part in 10^18. Space clocks (e.g., on GPS satellites) are slightly less accurate but extremely precise (one part in 10^13 or better).
Bottom line
Time in space is more complicated than on Earth. Mars has a 24-hour 39-minute day. The ISS uses UTC. Other planets have radically different day/year lengths. Astronomical time has multiple precise scales (TAI, TT, TDB, etc.) for different purposes. For everyday human use, UTC works for everything.
For Earth-based time conversions, the time converter and world clock handle them.