Without seasons, the Earth would be very different – and it’s quite likely we would not be around. If the Earth’s axis was much more tilted than it is, making seasons more extreme, civilization probably could not exist. The same might also be true if our seasons were more erratic (sorry George RR Martin), as might be the case without the Moon. The best guide to how seasons might operate on planets within the habitable zone of other stars is to look at the diversity of our own Solar System, which certainly reveals there are lots of ways things could pan out.
Since most of the world’s population is now experiencing the onset of winter, let’s concentrate on how that season looks on the other planets, if they have it at all.
Mercury
Thomas Hobbes described life before civilization as “nasty, brutish and short.” The same could be said of winter on Mercury. With a year lasting just 88 Earth days, all seasons on Mercury are short. However, the lack of air – let alone oceans – to smooth out heat distributions leads to swings in temperature that make conditions nasty and brutish as well.
On Earth, the seasons are largely a result of the tilt of the Earth’s axis, so one hemisphere gets more sunlight for a while and the other gets less. That’s not the case on Mercury, whose axial tilt is just two degrees.
That doesn’t mean it has no seasons, however. Mercury’s distance from the Sun varies a lot, from 46 million kilometers to 69 million kilometers, so the whole planet is getting more than twice as much radiation at the closest point in the orbit as at the furthest. The true Mercury winter is when the planet is furthest from the Sun. Temperatures at midday at the equator are 150°C (270°F) cooler at this point than when the planet is at the closest part of its orbit.
The biggest swings in temperature aren’t seasonal, however. Mercury’s day is 59 Earth days long. Consequently, there is plenty of time to heat up and cool down, creating wild variations. Even in winter, it gets very hot in the middle of the day (about 270°C/518°F) at the equator, but the night can be bitterly cold, dropping to -173°C (-279°F) even at the equator, and colder still near the poles.
Venus
Hot. It’s just hot, ok? Even in the middle of winter, and the middle of the night, surface temperatures are not thought to drop below 438°C (820°F), so the Yule fire is definitely out. Plus, there is the whole acidic atmosphere thing. This is what you get when you let too much carbon dioxide build up in the atmosphere, and no amount of eggnog should make you forget it.
Mars
Like so many other features of the red planet, Martian winters are more like those of Earth than any other planet. With a year that lasts almost twice as long as Earth’s, winters are around four months long. They also take place against a much colder planetary average.
Nevertheless, winters on Mars are familiar to us in ways that can’t really be said of other worlds. When it’s winter in one hemisphere, the icecap there grows by capturing about a quarter of the atmosphere as dry ice, before giving it up again in spring.
Icy sand dunes during martian winter, captured by the HiRISE camera aboard NASA’s Mars Reconnaissance Orbiter.
Image Credit: NASA/JPL-Caltech/University of Arizona
On Earth, the effects of the seasons are moderated by the oceans, which act as huge heat stores. In its early days, this would have been true of Mars as well, although never to the same extent. Now, however, there is no such buffer, so the temperature range is greater. With a lower average point to move around, Mars can get very cold indeed in winter, with temperatures like -153°C (-243°F) being recorded. It’s probably worse than that, because many of the landers and rovers we’ve put there shut down in winter for lack of sunlight to charge their batteries, so we don’t record the coldest temperatures.
A Martian winter: when even the rovers don’t run.
Jupiter
Jupiter doesn’t really do seasons. Its axial tilt is only 3 degrees, not much more than Mercury’s. Its orbit is also quite close to round, so the amount of sunlight it gets doesn’t vary much. With a rotation period of less than 10 Earth hours, there isn’t even the appearance of seasonality from long nights. Winter is just like every other time of the year, when you’d feel overwhelmed by the crushing force of gravity, not the desire to scream at your annoying relatives.
Saturn
Saturn’s axis is slightly more tilted to its orbit than Earth’s is, at 26.7 degrees. We’re now approaching Saturn’s equinox, but at other times one hemisphere is getting a fair bit more light than the other. However, that doesn’t change temperatures much. For one thing, even in the heat of summer Saturn is too far away to get greatly warmed. For another, its thick atmosphere redistributes a lot of heat. High in Saturn’s atmosphere, however, temperatures can vary between very cold in summer and an absurd –191°C (-312°F) in winter.
Uranus
Uranus has an axial tilt of 97 degrees, which means it is *almost* lying flat, but actually a little bit backward. This makes for very intense seasons in terms of sunlight, with one pole pointing almost directly at the Sun in its summer, and almost directly away in winter. That makes the winters very long and very dark indeed. They’re also cold, but that’s mainly because the whole planet is cold all the time; colder than Neptune despite being closer to the Sun.
We haven’t had good observational data from Uranus (oh quit sniggering) long enough to really measure the difference winter makes, but the side pointed towards the sun does seem to darken as winter sets in.
Neptune
At 28.3 degrees, Neptune’s axial tilt is greater than Earth’s but in the same ballpark. Its orbit is also very circular, so like Earth, the seasons are about one hemisphere or the other getting more light, not a general fall-off from distance. However, it gets only about 0.1 percent as much sunlight as Earth does.
Neptune’s temperatures actually fluctuate much more than thought, and it can get pretty chilly
Image Credit: NASA/JPL
Unlike Uranus, it does get some respectable warmth from its core, but this doesn’t vary by season, so its winter cold isn’t that different from its summer cold, just with less sign of that bright star-like thing
Pluto
Just kidding, still not a planet. However, Pluto is indicative of the class of Trans-Neptunian Objects (TNOs) to which it belongs. These are all so far from the Sun that even with a large axial tilt the hemispheres don’t diverge too much.
On the other hand, Pluto has a much less circular orbit than the real planets, and other large TNOs like Sedna mostly travel paths more elongated still. Consequently, there is quite a big difference in the amount of light received over the whole planet when they are close to the Sun and when further away.
Even though temperatures are ridiculously cold all year round by our standards, in some cases the whole atmosphere freezes in winter, only to recover modestly on approaching the Sun. Often, however, the biggest difference someone marooned on such a world would notice between winter and summer is how bright the Sun appears, while always being thousands of times fainter than from Earth.
All “explainer” articles are confirmed by fact checkers to be correct at time of publishing. Text, images, and links may be edited, removed, or added to at a later date to keep information current.
Source Link: What Does Winter Look Like On Other Worlds?
