Perseverance landed on Mars on Feb. 8, 2021. That’s nearly two Earth years ago. But on Mars, the wheel of the year turns slowly. Just a few days ago, Perseverance marked its one-Mars-year anniversary.
A sol, or Martian day, is less than an hour longer than an Earth day. By comparison, a Mars year is almost twice as long as an Earth year — 687 Earth days, or just shy of 669 sols. This is partly because Mars, being farther away, sweeps out a larger orbit around the sun. However, Mars’ orbital eccentricity is also considerably larger, which causes its seasons to vary significantly in length.
Right now, it’s spring for Perseverance, where it and its companion helicopter Ingenuity are hanging out in a basin within the Jezero Crater. Once it powered on for the warm season, the rover immediately started caching sample tubes for the upcoming Mars Sample Return mission. But this time around, Perseverance is scooping up samples of regolith from baby sand dunes, instead of drilling out rock cores.
Winter on Mars is the shortest season, but it still reaches -190F. That’s cold enough to freeze Mars’ whiff of a carbon dioxide atmosphere into dry ice. To guard against its electronics cracking in the extreme cold of its first Martian winter, mission engineers powered the rover down so that it would reach a uniform temperature. Happily, in the northern hemisphere (where all our rovers are), spring is the longest season, lasting 194 sols.
You can use this zoomable widget from NASA to see what the pair have been up to, day by day, since their mission began:
In the spring and summer, it’s surprisingly balmy. Surface temperatures near Mars’ equator can reach 70F in the warm season. The summer months come with their own hazards; spring is dust storm season on Mars. NASA’s InSight Mars lander recently succumbed to the slow buildup of dust on its solar panels. Before that, Opportunity “died” on Mars after a terrible dust storm that encircled the entire planet. Even so, Perseverance is holding up fine.
How Does Perseverance Keep Time on Mars?
We don’t have a single, unified timekeeping standard on Mars. With twice as many days in its year, it’s tough to draw a direct Martian analog to our Gregorian calendar. NASA decided, quite arbitrarily, that Mars recorded time begins on April 11, 1955. (There was a really bad dust storm on Mars that spring.) However, there’s also the Mars Sol Date, which is indexed to the Julian calendar by way of an actual equation. To define seasons, currently, scientists are using LS, for solar longitude. At 0° of solar longitude, it’s the top of the year, so to speak. At LS 90°, the Red Planet’s northern hemisphere has its vernal equinox.
When it comes to setting your watch, Airy Mean Time (AMT) is a favorite Martian analog to Greenwich Mean Time (GMT). We have Greenwich, England; Mars has the Airy Crater. But there’s Mars Solar Time, too, and Local Mean Solar Time. Honestly, it’s like the USB standard of time: There can never be only one.
Did you know Perseverance has a pet rock? The rover captured this image of its pet rock on May 26, 2022 (Sol 449), using its onboard Hazard Avoidance Camera. Image credits: NASA/JPL-Caltech
The Perseverance rover project set its mission clock in sync with Local Mean Solar Time, at the rover’s planned landing longitude of 77.43°E. This corresponds to a mission clock of AMT+05:09:43. The actual landing site was about 0.02° (1.2km) farther east, a difference of perhaps 5 seconds in solar time.
On Earth, that’s trivially within the same time zone. However, Mars doesn’t use time zones as Earth does. The LMST changes, depending on the rover’s motion across the Martian surface. At 18.4°N, there’s about one second of time difference for every 234 meters the rover (or helicopter) moves in the east-west direction. Perseverance marks its days and sols from when it touched down around 15:54 LMST (10:44 AMT) of Sol 0.
Happy first Mars birthday, little dude.
Feature image of Perseverance’s arm via NASA/JPL/Caltech.
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