Do Other Planets Experience Seasonal Changes Like Earth?
There are many ways in which planets and stars differ from one another, but none of them seem quite as evident as their respective seasons. A common misconception is that other planets don't experience seasons or at least the same kind of seasonality that life on Earth does. However, thanks to NASA telescopes and continued observations from humans on Earth, we have learned a few things about seasonal change on other worlds -- like Mars!
It's No Secret that Earth Experiences Seasons…
But, it's also pretty well understood that other planets don't. That said, there are a few ways in which variations in our planets' seasons could be apparent to another planet or astronomical body. First and foremost, our planet revolves around the Sun, meaning it follows an elliptical path along a spiral path around the star. It means that from point A to point B, we could traverse anywhere between 100 and 2000 Earth-dilated kilometers. Since the time it takes for light to travel across the entire distance is roughly 8 minutes on Earth, that means that when it comes to seasons, we are speaking of seasonal changes equaling roughly 24 hours per day.
Furthermore, Earth's orbit is not a perfect circle. Bigger bodies of mass cause gravity to have a more significant influence over smaller ones, and Earth's elliptical path means that one side is closer to the Sun than the other for some time. The same season is occurring on both sides of the planet at this point but living on one side or the other could mean a couple of days difference between where you are and, say, the equator.
While this is true of our Moon and most other astronomical bodies, there are some settings where our planet's seasons aren't as dramatic as they are on Earth. For instance, Mars is an excellent example if we look at our planet's seasons from the perspective of another celestial body. Since it is located in the same part of the solar system as Earth, it, too, revolves around the Sun. However, since Mars is further away from the Sun than Earth, it doesn't take nearly as long for a ray of light to reach any given location on Mars as compared to us. Just like the Moon, which orbits Earth in 2 days and 18 hours -- while orbiting the Sun in its own 88 days -- on average, it takes Mars 687 days to make one revolution around the Sun when accounting for its elliptical orbit (much longer though).
Mars's seasonal cycle is much more dramatic than our own, but some things are similar between the two planetary bodies. For instance, there is a great deal of variation in Earth's seasons and day-night cycles as we go from one hemisphere to another. In addition, Mars has a roughly 25-day period where sunlight (or "solstice") falls at the same time and angle through winter and summer in its northern hemisphere, while it only experiences a season change during these 25 days in the southern hemisphere.
While it doesn't exactly have what we would call a "season”, the dwarf planet Pluto can still display some seasonal changes. Due to Pluto's position outside Neptune's orbit, it does not experience any variation in its yearly distance from the Sun. As such, there are no actual seasonal variations for Pluto as well – until you add in its Moon Charon. In fact, during certain times of the year, Charon passes through elliptical orbits that bring it closer to and farther away from Pluto than Earth is from the Sun.
In December 2048, NASA's New Horizons spacecraft will leave the orbit of Pluto and begin to explore the Kuiper Belt, the ring of icy bodies that surrounds our solar system. In the year before it leaves, researchers will continue trying to find any signs of plant or animal life in this mysterious world.
When the New Horizons probe reaches Pluto, it will be able to observe how long specific parts of the planet are in sunlight. So, for instance, if the New Horizons spacecraft is passing over a region of Pluto that is only ever in sunlight during spring, that means that there is a chance of seeing early spring vegetation or animal life on top of the dwarf planet's surface. While it is certainly possible that Earth-like plant and animal life could develop on Pluto or any other planet in our solar system, we won't know for sure until then!
Some Planets Don't Experience Seasons Altogether
Instead, they experience temperature cycles that repeat at different times of the year. These locations include Mercury, Venus, Mars, and Jupiter. An excellent way to think about these cycles is like Earth's seasons: on Mercury, for instance, we can talk about a "year as an egg" or a "year with three summer months." In other words, it has 243 days exactly as Earth does, and during one set of those days, the planet experiences one of two different temperatures: warmer or colder than average. (Earth is a little bit warmer and a little cooler than average in winter. Mercury is colder than average.) Therefore, the planet experiences very hot and cold seasons that have nothing to do with what season it is on Earth.
In general, the temperature of Mercury goes up and down depending on how much sunlight hits it. It is valid for all hot planets right now. When a solar system is created, the amount of light emitted by its star helps determine how much heat a planet receives. If more heat is directed toward the planet from its star, then it will receive more heat than if there is less solar energy reaching the surface. It happens in many ways, but more minor planets generally receive less heat because they’re closer to their stars than more giant planets, think: Saturn vs. Jupiter for instance.
It's also important to note that, like Earth, Venus spins around its axis in the same direction as its rotation. Therefore, the Sun is always directly above Venus and exerts a solid heart on the planet's surface. When the Sun is on one side of the planet, it is in summer, and when it is on the other side of the planet, it is in winter. It differs from our seasons because, for Venus, there are about 225 days with at least 4 hours of sunlight – which corresponds to the spring and fall months.
While we don't have seasons like Earth does, it is still remarkable that we still have seasons in our galaxy. It also means that planets far from the Sun might not possess similar seasonal cycles. Although Earth and Mars are giant planets with similar solar environments, they are different-looking bodies as well (Earth has a tectonic plate system while Mars has pronounced ridges). While these specific features can affect how planets receive energy from their stars, they don't necessarily impact the number of days or seasons in a planet's year – which would be determined by where the planet orbits its star.