Seasons on Earth and Mars are caused by the tilt of their rotation axes: over the course of an orbital year, the two hemispheres receive different amounts of sunlight. But the seasons on the two planets differ in duration and climate, because their orbits and atmospheres are not the same.
On Earth, the changing seasons are familiar and relatively regular. On Mars, however, its elongated orbit amplifies the differences between seasons: the planet receives different amounts of heat at different points along its path around the Sun. Comparing the two worlds helps us understand how a planet’s motion and atmospheric properties shape its climate.
| Parameter | Earth | Mars |
|---|---|---|
| Axial tilt | около 23,4° | около 25,2° |
| Length of year | около 365,25 суток | около 687 земных суток |
| Orbital eccentricity | около 0,017 | около 0,093 |
| Length of northern summer | примерно три месяца | около 178 солов |
| Length of northern winter | примерно три месяца | около 154 солов |
- 23,4° Earth’s axial tilt
- 25,2° Mars’s axial tilt
- 687 земных суток approximate length of a Martian year
- 0,093 Mars’s orbital eccentricity
- около 40% how much more solar energy Mars receives at perihelion than at aphelion
What causes the seasons on Earth and Mars?
The seasons on Earth and Mars are determined primarily by the tilt of their rotation axes: as a planet moves along its orbit, this tilt changes the Sun’s height above the horizon and the length of the day. Earth’s axis is tilted about 23.4° from the perpendicular to its orbital plane, while Mars’s is tilted about 25.2°.
Axial tilt sets the seasonal rhythm of sunlight, while the orbit determines how the distance from the Sun changes over the course of a year. That is why summer on both planets does not simply arrive when a planet is significantly closer to the Sun; it comes above all when the relevant hemisphere is tilted toward the Sun and receives longer days.
The Martian year is longer
Earth completes one orbit around the Sun in about 365.25 days, while a Martian year lasts about 687 Earth days. Seasons on Mars arise through the same basic mechanism—axial tilt—but unfold over a longer year; changes in the planet’s distance from the Sun, determined by its orbit, also affect the lighting conditions.
Why are Martian seasons unequal in length?
Perihelion and aphelion
Martian seasons are unequal in length because the planet’s noticeably elongated orbit changes its speed: Mars moves faster when it is near the Sun and more slowly when it is farther away. Earth’s orbital eccentricity is about 0.017, compared with about 0.093 for Mars.
Mars passes perihelion—the closest point in its orbit to the Sun—around the beginning of northern summer; it reaches aphelion, its most distant point, around the beginning of northern winter. Because of the position of these orbital points, northern spring on Mars lasts about 194 sols, while northern autumn lasts about 142; a sol is a Martian solar day.
- Northern summer on Mars: about 178 sols.
- Southern summer on Mars: about 154 sols.
Thus, northern summer lasts longer than southern summer, and spring in the northern hemisphere lasts longer than autumn. On Earth, the difference in eccentricity is much smaller: its orbit is nearly circular, so the effect of distance from the Sun on the length of the seasons is weaker than on Mars.
How do the seasons differ between the hemispheres of the two planets?
The seasons in the hemispheres of Earth and Mars are opposite at the same time: when it is summer in the north, it is winter in the south, and northern spring corresponds to southern autumn. The difference between the planets lies in the length of their seasons and the strength of their seasonal contrasts.
On Earth, each season lasts about three months, so the four seasons are similar in length. The exact dates when they begin depend on how the boundaries between seasons are defined, but the changes in the north and south are synchronized: summer in one hemisphere corresponds to winter in the other.
The hemispheres of Mars also experience opposite seasons at the same time, but its elongated orbit makes some seasons longer than others. A Martian year is almost twice as long as an Earth year, so each Martian season lasts significantly longer than three Earth months; at the same time, Martian seasons differ noticeably in length.
How does Mars’s orbit affect its heating and climate?
Solar energy and polar caps
Mars’s elongated orbit amplifies seasonal contrasts: at perihelion, the planet receives about 40% more solar energy than at aphelion. Southern summer coincides with Mars’s rapid passage through the part of its orbit closest to the Sun, so the southern hemisphere heats up more during this season.
Seasonal heating moves carbon dioxide between the atmosphere and the polar caps. In winter, some CO₂ freezes onto the surface; as temperatures rise, it returns to the atmosphere, changing the amount of gas in the Martian atmosphere over the course of a year.
Dust changes how much sunlight reaches the surface
The orbit does not fully explain Martian weather: dust storms can cover large areas and change how much sunlight reaches the surface. Two factors therefore act at the same time—the seasonal change in sunlight caused by Mars’s position in its orbit, and the movement of dust through the atmosphere.
When can comparing Earth and Martian seasons be misleading?
Comparing Earth and Martian seasons can be misleading if Earth months and dates are applied to Mars: a Martian year lasts about 687 Earth days, and its seasons are tracked using the Martian calendar and sols. Earth’s summer therefore does not coincide with Martian summer, and Earth’s equinoxes and solstices do not serve as a calendar for another planet.
Earth’s and Mars’s axial tilts are similar, but that does not make their weather the same: Mars’s atmosphere is much thinner than Earth’s, and surface water does not participate in a familiar Earth-like water cycle. Similar axial tilts explain seasonal changes in sunlight, but do not guarantee similar temperatures, precipitation, or climates.
Why distance from the Sun is not a universal explanation
The claim that “a planet is closer to the Sun in summer” is incorrect as a general explanation of the seasons: on Earth, the seasonal cycle is driven by axial tilt, not changes in distance from the Sun. Mars’s elongated orbit also affects how pronounced its seasons are, so comparisons should take the Martian year and its passage through perihelion into account rather than tying Martian weather to Earth dates.
Frequently asked questions
Why is summer in Mars’s northern hemisphere longer?
How long is a year on Mars?
Why can’t Earth’s seasons be explained by its distance from the Sun?
What is a sol?
