Mars has seasons because its axis tilts 25.19 degrees, close to Earth's 23.4. A year is long: 686.980 Earth days in the NASA fact sheet, which NASA Science rounds to 687 Earth days, or 669.6 sols. [1] [2]
A sol, the mean solar day, lasts 24 h 39 m 35 s. The sidereal spin is a little shorter, 24 h 37 m 22 s. Rover teams plan by sols, not by Earth midnights. [1]
Why the seasons do not match
Earth's orbit is nearly round, so its seasons are mostly about tilt. Mars adds a noticeable ellipse, eccentricity 0.0935. Perihelion, closest approach to the Sun, falls in late southern spring. Southern summer is therefore shorter and hotter. Northern summer is longer and milder. [1]
That asymmetry drives the dust-storm season and the swing in pressure. Southern summer heats the ground hard, winds rise, and dust storms are more likely. Carbon dioxide frost migrates from one pole to the other and changes the mass of the atmosphere as it goes.
Solar longitude
Missions mark the season with solar longitude, written Ls. Ls = 0 is the northern spring equinox. Ls = 90 is northern summer solstice, Ls = 180 the northern autumn equinox, and Ls = 270 northern winter solstice, which is also southern summer. A paper that says 'Ls 315' is pointing at a date in the Martian year, not a map coordinate.
See also
What links here
References
- NASA Goddard Space Flight Center. Mars Fact Sheet. Rotation, orbit, and obliquity. Updated 19 May 2025. https://nssdc.gsfc.nasa.gov/planetary/factsheet/marsfact.html
- NASA Science. Mars: Facts. Year length in sols. https://science.nasa.gov/mars/facts/