The season of vibrant flowers lining the sidewalk on the commute home, their gentle fragrance wafting into the air. Of sunshine that calls for a light jacket instead of a bulky coat. Of the passionate urge to clean everything in sight.
Outside The Atlantic’s Washington, D.C., headquarters, it’s about 43 degrees Fahrenheit (6 degrees Celsius)—not warm enough for open-toed shoes, but still more pleasant than, say, a polar vortex. I’ve been longing for this day, and it got me thinking about spring on other planets, and whether it even exists.
We owe the seasons to Earth’s axis, which stays tilted at about 23 degrees as the Earth loops around the sun. But the orientation of the planet’s hemispheres in relation to the sun changes; different parts of the Earth lean toward or away from the sun at different times of the year, and receive varying amounts of sunlight.
But how do other planets work? To find out, and also to procrastinate my spring cleaning, I reached out to some scientists who spend their days thinking about other worlds.
“Mercury doesn’t really have anything approaching spring, or any season for that matter,” says Paul Byrne, a planetary geologist at North Carolina State University. The planet’s axial tilt, a fraction of a degree, is negligible. “The amount of daylight at a given latitude on Mercury is essentially fixed during the entire year.”
The daylight is relentless and scorching. But the orientation produces a rather cool phenomenon. “It lets Mercury have regions of permanent shadow near its poles that are never sunlit, and lets ice be present in those regions—even on the planet closest to the sun,” says Nancy Chabot, a planetary scientist at the Johns Hopkins University Applied Physics Laboratory.
“It’s one weird little planet,” Byrne adds.
“There is no springtime on Venus, nor any other season—no seasons in hell!” says Allan Treiman, a scientist at the Lunar and Planetary Institute.
It’s difficult to sugarcoat the environment on Venus. Surface temperatures are a sizzling 870 degrees Fahrenheit (470 degrees Celsius), hot enough to melt lead, all year round. Like Mercury’s, Venus’s axis isn’t tilted enough to produce a noticeable difference.
But the real reason the planet doesn’t have any seasons is its atmosphere, which is choked with clouds. “The clouds are so thick that its surface gets nearly no light or heat from the sun. Nearly all the sunlight and heat are absorbed by clouds, which then radiate heat down to the surface—the famous greenhouse effect,” Tremain says. “Venus clouds circulate faster than the surface does, so all the greenhouse heat is spread around the planet, whether it’s day or night.”
That’s not all. “To top everything else off, Venus’ day is longer than her year,” says Vicki Hansen, a scientist at the Planetary Science Institute. (It takes 243 Earth days for Venus to rotate once on its axis, but 225 Earth days for the planet to loop around the sun.) “So if she had spring, it would be hard to say what day it happened.”
Mars’s axis is tilted slightly more than Earth’s—about 25 degrees—which means the planet experiences distinct seasons, too. In fact, like the Northern hemisphere here, the Northern hemisphere on Mars is entering spring now.
“The Northern hemisphere is starting to heat up; the Southern hemisphere cooling off—just like on Earth,” says Don Banfield, a scientist at the Cornell Center for Astrophysics and Planetary Science.
Well, not just like on Earth. Orbits affect seasons, too; the Martian year is twice as long as a terrestrial year, so the seasons stretch out longer. There are seasonal trends, such as summer dust storms, “but without rain and plants, they aren’t quite as obvious,” says Banfield.
“Jupiter does not have a springtime,” says Cheng Li, a scientist at NASA’s Jet Propulsion Laboratory. Like Mercury, Jupiter’s axial tilt is too small to matter.
Saturn does have spring: Its axial tilt is similar to that of Earth and Mars.
“Saturn is warm in the summer and cold in the winter,” says Leigh Fletcher, a planetary scientist at the University of Leicester. “The clouds and chemicals respond to these changes in sunlight. Perhaps the best example is the color of Saturn’s atmosphere, which shifts from blue hues in the winter—relatively clear skies with very few hazes—to golden hues in summer—a more smoggy atmosphere with lots of hazes.”
Saturnian spring also provides the most visibility for a massive, hexagon-shaped storm at the planet’s north pole that has mesmerized scientists for years. Some parts of Saturn can even experience miniature versions of seasons, thanks to its shimmering rings.
“A fixed point in Saturn’s atmosphere would experience additional periods when the rings shade the sun,” says Mike Wong, a planetary scientist at the University of California, Berkeley. “We actually have something like this at my house, because the neighboring building has a billboard on top. From a certain date in November to a certain date in February, our roof is in constant shade because the billboard blocks the sun, so our house gets colder.”
With a 98-degree tilt of its axis, Uranus basically spins on its side. This alignment means the planet experiences the most extreme seasonal contrasts in the solar system.
“The poles get a great deal of illumination from an overhead sun that barely seems to move in the sky during local summer and a great deal of darkness in winter,” says Glenn Orton, a scientist at NASA’s JPL. “As spring begins, the sun is virtually always at the horizon for anyone living at the poles and virtually straight overhead for a Uranian in the low-latitude tropics.” (We should clarify: These are fictional Uranian residents. Alien life hasn’t been discovered there.)
During spring, a giant white cap emerges over the north pole, standing out against the planet’s usual blue hues. Scientists suspect the warming temperatures produce atmospheric changes.
This far out in the solar system—where orbits are vastly longer—seasons stretch out for years. A Uranus spring lasts 21.
Spring on Neptune is twice as long. The planet experiences distinct seasons, but “I don’t think we’ve been able to observe Neptune long enough with enough detail to say for sure how spring in one hemisphere differs from any other season in terms of atmospheric activity,” says Anne Verbiscer, a planetary scientist at the University of Virginia.
“Why yes, it’s springtime on Pluto right now, at least in the northern hemisphere!” says David Grinspoon, a scientist at the Planetary Science Institute. “And it has been since 1990.”
(Please don’t overthink the inclusion of Pluto on this list. Scientists have spent years arguing over the correct categorization of this celestial body. For some of them, the 2006 decision to reclassify Pluto as a dwarf planet is not the final word. We’ll leave the debating to them.)
Pluto’s orbit around the sun is highly elliptical. “The distance to the sun is quite different for the same season in the south versus the north,” Grinspoon says. “This creates asymmetrical and extreme climate behavior where, over the timescale of the seasons—which are many decades long—the atmosphere goes through the magnitude of changes that on other planets we would call climate changes.”
Spring sounds mild compared with colder seasons. Without enough exposure to sunlight, Pluto can get so cold that its atmosphere freezes and falls on the surface. “You can imagine what life would be like if we had that experience on Earth,” says Bob West, a scientist at JPL. “The air we breathe and which sustains all life on the dry land would form crystals of water, oxygen, nitrogen, and carbon dioxide and fall to the ground as snow, leaving a near vacuum where once there was air.”
Wow. A little spring cleaning doesn’t sound so bad now.
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