Published: 2021-02-07 14:19:00
Updated: 2021-02-07 14:21:14
Posted February 7, 2021 2:19 p.m. EST
Updated February 7, 2021 2:21 p.m. EST
We could all use a reason to celebrate, how about New Year's Day... on Mars?
Today is the Spring Equinox in the northern hemisphere of Mars, where the Viking, Phoenix, Pathfinder, and InSight missions landed.
Scientists studying dust storms using data the Viking missions needed a way to compare conditions from (Martian) year to year. They selected the northern hemisphere's Spring Equinox when the solar longitude, or Mars-Sun angle, of 0° as the beginning of the Martian year.
They selected the equinox on April 11 1955 to begin year one. This encompasses all Mars missions beginning with the Mariner 4 flyby in 1965 (Mars year 6) and the great Martian dust storm in 1956 (Mars year 1)
Mars experiences seasons and temperature variations similar to Earth because Mars' axial tilt (25.19°) is very similar to Earth's (23.44°). The similarities don't stop there.
Mars' elliptical orbit brings it closest to the Sun during northern hemisphere winter months and furthest during summer months. Like Earth, Mars' seasonal temperatures are much more affected by that axial tilt than distance to the Sun.
Spring brings not only a slight increase in Mars' chilly temperatures, but also increasing atmospheric pressure as the northern polar ice cap melts going directly from solid dry ice to gaseous carbon dioxide. This yearly pattern has been observed by every mission since the Viking program in the 1970s.
While several have been proposed, no official calendar exists. Dividing the Mars year into months is even more troublesome than Earth.
While months on Earth roughly align with the Moon's 29.53 day long cycle through its phases, Mars' moons are of a little help in determining a "month" on Mars. Phobos and Deimos in about 8 hours and 30 hours respectively. The 668 sol (687 Earth day) trip around the Sun for Mars also suffers from the same hard to divide evenly problem we see on Earth.
Months 6, 12 and 18, of British astronomer Sir Patrick Moore's calendar has 38 sols (a Martian day, 39 minutes, 35 seconds longer than an Earth day) with 37 sols in the rest of the 18 month calender. Czech astronomer Josef Šurán chose 23 "months" of 28 days followed by a shortened 24th month at the end of the year.
Another celebration opportunity arrives Friday, February 12 Chinese New Year or Lunar New Year on the lunar calendar.
It will be a busy beginning to year 36 with three missions arriving in the coming weeks