What is Winter Like on Mars?

It’s not only winter in the northern hemisphere here on Earth—it’s also winter in the northern hemisphere of our Red Planet neighbour.

Frost on the martian plains of Utopia Planitia imaged by the Viking 2 lander in May 1979. Image credit: NASA/JPL/Tanya Harrison

At the time of writing this, the solar longitude on Mars is 315°. Solar longitude, written shorthand as Ls (said aloud as “L sub S”), is a way we keep time on Mars. It’s a measure of where Mars is in its orbit around the sun in terms of a 360° ellipse, marking the current season on the Red Planet. Seasons on Mars are quite dynamic with its axial tilt toward the sun of 25°, close to Earth’s current tilt of 23.5°. Changes in season result in changes in weather, surface temperature, and even the distribution of ice on the martian surface. Ls 315° puts us in late winter in the northern hemisphere and late summer in the southern hemisphere.

Martian seasons in terms of solar longitude (Ls). Image credit: NASA/JPL-Caltech

Mars’ polar caps essentially have two components: “Residual” and “seasonal” caps. The residual polar caps are the bulk of the polar cap that persist year after year. The residual northern polar cap remains pretty consistent over time, while the residual southern polar cap is changing quite a bit…but we’ll save the complexities of the southern cap for their own article.