Spiders Crawl Out Of Their Holes As Mars Celebrates Spring

Photo taken by the Mars Reconnaissance Orbiter on the first day of spring in Mars’ southern hemisphere. Dark material is deposited on top of the ice carried there by escaping gas flowing through the spidery channels carved in the surface. Credit: NASA/JPL/University of Arizona

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.

Oct. 21, 2012 image of the south pole of Mars where sunlight is now defrosting CO2 ice. Alternating layers of dust and ice are exposed along the edge of the polar cap. Credit: NASA/JPL/ASU

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.

Orbits of Mars and Earth seen from above our north pole. Season length varies from 199 Earth days when Mars is farthest from the sun (aphelion) to 147 days when closest (perihelion). Distance varies by 26.5 million miles. Credit: Wikipedia

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.

2 Responses

  1. Giorgio Rizzarelli

    Very interesting facts about season lengths, food for though. Obviously perihelion precession will reverse the effects in a future epoch. I did a research on Wikipedia about the long term variations of seasons and learned there’s more. Eccentricity itself varies on long term, also for Earth, which will someday have a considerable one, so with seasonal effects similar to today’s Mars!
    In addition there’s the well known precession of the equinoxes, and, as you probably know, the axial tilt angle itself changes in time – for Mars it may have been 60° in a past epoch, resulting in an extreme ice age which covered 2/3 of the planet in ice (the famous NASA art pic of the “tennis ball” Mars). Interestingly, such extreme ice ages can’t happen on Earth because our big Moon keeps Earth’s axis quite more stable.
    So a big moon may well be an element making more likely the evolving of durable/intelligent life on a planet (also because, as some say, life evolved from water to dry land through tide pools, which we have thanx the Moon), making a sensible difference in Drake formula. And such a big moon in comparison to its planet is not too common, as our Moon was the result of the accidental collision of Earth with another planet.
    More, Mars has almost no seasonal lag (and extremal day/night thermal excursion) because it has no sea, a bit like Earth deserts.
    I suddenly developed more respect for both our sea and the Moon!

    1. astrobob

      Indeed! It’s the changing eccentricity and tilt of Mars that are connected to long-term climate changes including melting of ice, etc. over the aeons.

Comments are closed.