Perseverance landed on Mars on February 8, 2021. This was about two Earth years ago. But the wheel of the year turns slowly on Mars. Just a few days ago, Persistence identified one of its-Mars-year anniversary.
A sol, or Martian day, is less than an hour longer than an Earth day. By comparison, a Martian year is almost twice as long as an Earth year – 687 Earth days, or just shy of 669 Sol. This is partly because Mars, being so far away, takes out a large orbit around the Sun. However, Mars’ orbital eccentricity is also quite large, causing its seasons to vary significantly in length.
Right now, it’s springing for Persistence, where it and its companion helicopter Ingenuity hang out in a basin between Jezero Crater. Once it was turned on for the warm season, the rover immediately began caching sample tubes for the upcoming Mars sample return mission. But this time, instead of diligently drilling rock cores, the child is collecting regolith samples from sand dunes.
Winter is the shortest season on Mars, but it still reaches -190F. That’s cold enough to turn Mars’ carbon dioxide atmosphere into dry ice. To keep its electronics from cracking in the bitter cold of Martian’s first winter, mission engineers ran the rover down to reach a uniform temperature. Fortunately, in the Northern Hemisphere (where all our rovers are), spring is the longest season, lasting 194 days.
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 spring and summer, it is surprisingly smooth. Surface temperatures near the Martian equator can reach 70F during warm seasons. The summer months bring their own dangers; Spring is dust storm season on Mars. NASA’s InSight Mars lander recently succumbed to slow-moving dust on its solar panels. Earlier, Chance “died” on Mars after a terrible dust storm that engulfed the entire planet. Still, persistence pays off.
How does persistence keep time on Mars?
We don’t have a single, unified timekeeping standard on Mars. With twice as many days in a year, it is difficult to draw a direct Martian analog to our Gregorian calendar. NASA decided, quite arbitrarily, that recorded time on Mars would begin on April 11, 1955. (There was one really Bad dust storm on Mars that spring.) However, Mars also has sol dates, indexed to the Julian calendar by a real equation. To define seasons, currently, scientists use Lcome, for solar longitude. At 0° of solar longitude, it is the top of the year, so to speak. In L.Acome 90°, the Red Planet has its local equinox in the Northern Hemisphere.
When it comes to setting your clock, Airy Mean Time (AMT) is the beloved Martian analog of Greenwich Mean Time (GMT). We have Greenwich, England; Mars has Airy Crater. But Mars also has solar time and local mean solar time. Honestly, it’s like the USB standard of the time: yes never Be the only one
The Persistence rover project syncs its mission clock to 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° (1.2 km) east, a difference of about 5 seconds in solar time.
On Earth, it is negligible within the same time zone. However, Mars does not use the same time zone as Earth. The LMST changes, depending on the rover’s speed across the Martian surface. At 18.4°N, the rover (or helicopter) moves east-west with a time difference of about one second every 234 m. Perseverance marks its days when it descends near Sol 0 at 15:54 LMST (10:44 AMT).
Happy first Tuesday birthday, little friend.
Persistence hand feature image via NASA/JPL/Caltech.
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