No birds twitter during Martian spring, but ice disappears and the landscape comes alive with spiders. Mars has seasons because its axis it tilted much like Earth’s. During the 6-month-long Martian winter, a significant fraction of its carbon dioxide atmosphere condenses out as ice at the poles. When spring arrives, sunlight vaporizes the ice, turning it directly from solid to gas.
In the photo above, taken on the first day of spring (Sept. 30, 2012 by Earth’s calendar) in Mars’ south polar region, the landscape is covered in ice, but even the slanted rays of the returning sun are enough to tip the scales.
Solar-liberated carbon dioxide gas coming from the bottom surface of the ice builds up pressure and carves channels into the ground on its way up and out into the atmosphere. Dark soils go along for the gassy ride and are deposited on the surface as spidery forms. Spring has sprung!
Martian seasons are about twice as long as our own because the planet’s year – the time it takes to go around the sun – is 687 Earth days. Seasons on our planet are of similar length because Earth’s orbit is nearly circular, so it moves at a near constant speed around the Sun. For the record, when closest to the sun in northern winter, Earth travels a little faster than when farthest in July. The difference is small enough so that season length varies from 89 days in winter to 93 days in summer.
Mars orbit is much more eccentric or oval-shaped than Earth’s with the distance between closest and farthest points varying by 26.5 million miles. This huge difference in distance and orbital speed throws its seasons out of balance.
Aphelion or furthest distance from the sun coincides with the northern hemisphere summer solstice. Summers there are longer and more temperate. When winter comes round, the planet is at perihelion or closest to the sun, making northern winters shorter and less intense.
In contrast, southern summer coincides with Mars’ closest approach to the sun. Compared to the northern hemisphere, southern summers are scorching and brief and followed by long and bitter winters at aphelion. The relatively intense heat during the southern summer is one of the reasons why dust storms are more frequent there than in the north.
Mars’ extremes of climate make Earth appear all that more clement especially when November winds tear at my shingles and rattle the house like they are today.