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Science Educators and guest authors exploring our world and the science and technology that connects us.

 

 

SEASONS ACROSS THE UNIVERSE by Patrick King II, Planetarium Educator

It’s the most wonderful time of the year! You know what that means… getting your gift list in order, strapping up your tauntaun for holiday travel, and most importantly, not forgetting to grab a coat because Jack Frost is nipping at your nose.

via GIPHY

Depending on where you live, weather can be great indicator of the time of year. For most of us in the Northern Hemisphere, the crisp, cooler temperatures of fall transition quickly into frigid, cruel winter weather.

But, I may just be biased.

Here on Earth, we have four seasons that all last roughly 90 days each. Have you ever thought about what summer might look like on Saturn, spring on Mars, or if the other planets even have seasons?

The short answer is yes, no and kind of.

via GIPHY

Don’t worry… I’ll explain.

Let’s begin with our own planet. The tilt between Earth’s spin axis and its orbit around the Sun is 23.5 degrees, which means different parts of the planet face the Sun more directly and longer at different times in the year giving us spring, summer, fall and winter. Summer is warmer than winter in both hemispheres, because the Sun’s rays are more direct and provides more hours of sunlight, with the opposite being true during winter. We experience seasons thanks to Earth’s axial tilt from its orbit.

Mercury is the closest planet to the Sun and the only planet in our Solar System without any tilt, so technically… it has no seasons. Being so close to the Sun causes the surface temperature to fluctuate drastically between day and night. Daytime temperatures can reach up to 800 degrees Fahrenheit while Mercurian nights drop as low as -290 degrees F.


This view shows Mercury's north polar region, colored by the maximum biannual surface temperature, which ranges from >400 K (red) to 50 K (purple). As expected for the Solar System's innermost planet, areas of Mercury's surface that are sunlit reach high temperatures, and hence most of this image is colored red!
NASA/Johns Hopkins University Applied Physics Laboratory/Carnegie Institution of Washington

Next, we have Venus whose size and density are similar to our own, but that's where the similarities end. Unlike Mercury, Venus has a tilt. But at 2.6 degrees, it's not enough to cause any real seasonal changes. Venus’s atmosphere is so thick that the temperature doesn’t change much anywhere on the planet, keeping the average surface temperature at around 900 degrees F. That’s hot enough to melt lead, day or night. Imagine a house on fire with all the windows permanently shut and you’ve got yourself a Venusian sauna.

Mars, the red planet, has a 25-degree tilt (remember, axial tilt gives us seasons!) and one of the greatest orbital eccentricities of any planet. Think of orbital eccentricity as a measurement of the orbit’s lopsidedness. There’s a big difference between the point in its orbit nearest the Sun (perihelion) and furthest away (aphelion). Combining the tilt and eccentricity results in the a more dramatic seasonal change than we experience anywhere on Earth. (Even here in Tennessee!)


Two images by NASA's Mars Global Surveyor orbiter taken in 2001 show a dramatic change in the Red Planet's appearance when haze raised by dust-storm activity in the south became globally distributed. The photos were taken about a month apart.
NASA/JPL-Caltech/MSSS

In fact, not all Martian seasons are created equally. During a typical 687-day Martian year, spring in the northern hemisphere lasts almost 6 ½ months. Summer is about is about 6 months. Bringing up the rear, fall and winter are about 5 months each. Each season comes with distinct weather events, like disappearing polar ice caps in summer or planet wide dust storms in winter. *Insert reference to The Martian here.*

Leaving the inner solar system, we have our gas and ice giants. The largest planet, Jupiter, receives about 4% of the solar energy that the Earth does. Its axial tilt is only 3 degrees, so there isn’t any notable change between seasons. The storms we can see swirling in Jupiter’s atmosphere are a result of the heat released from inside the planet’s core.

via GIPHY

Saturn’s axial tilt is 27 degrees, which is very close to Earth’s own 23-degree tilt, meaning… *ding ding* it has seasons! Saturn takes so long to orbit the Sun that its seasons last longer than 7 years each. Being a gas giant this far from the Sun, its seasonal changes aren’t quite the same as they are here on Earth. You wouldn't be able to have a white Christmas on Saturn, but the North Pole does change color in summer.


These two natural color images from NASA's Cassini spacecraft show the changing appearance of Saturn's north polar region between 2012 and 2016.
NASA / JPL-Caltech / Space Science Institute / Hampton University

Next up, we have the wackiest planet in our solar neighborhood: Uranus. The axis of Uranus has a tilt of 98 degrees, which means the planet essentially “rolls” around the Sun on its 84-year orbit. At 1.7 billion miles away from the Sun, it’ll be COLD no matter which 21-year-long Uranian season you look at.


Uranus is seen in this false-color view from NASA's Hubble Space Telescope from August 2003. The brightness of the planet's faint rings and dark moons has been enhanced for visibility.
NASA / Erich Karkoschka / University of Arizona

In some parts of the year, the Sun shines directly on each pole leaving half the planet in an extremely dark winter. Uranus’s atmosphere has a uniform blue hue… except when the Sun hits regions that haven’t received light in decades. This sudden warming can cause massive storms the size of North America with temperatures at a balmy 300 degrees below zero.

Neptune, the last planet in our solar system, has a 28-degree tilt similar to Earth's but doesn’t experience much variation between seasons. Because it’s the furthest planet from the Sun, Neptune receives the smallest amount of energy in the form of sunlight. The planets own mysterious internal heating is responsible for driving the fastest winds seen anywhere in our Solar System, and contributes to weakening the effects of any seasonal variation.

The seasons of planets can vary from almost unnoticeable to planet-wide madness, and it only gets more exciting when you look beyond our Solar System. Scientists predict wild weather on planets orbiting other stars. Exoplanets like Kepler-413b could possibly harbor even more insane weather phenomenon. At the end of the day, I think I appreciate the regularity of the seasons we have on Earth. It definitely beats the primitive glamping on Hoth.

Learn more:

- Patrick King II, Planetarium Educator

Posted by Molly Hornbuckle at 4:00 PM
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