Saturn takes nearly 30 years to circle the sun. Most us get to see it orbit twice in a lifetime. If we’re lucky and eat our spinach we might see it loop around a third or even a fourth time. Life is ridiculously short, isn’t it?
Earth takes only a year to complete an orbit because it’s so much closer to the sun and must travel faster to avoid its gravitational grasp. Each year (plus an additional 10-12 days) Earth laps slower Saturn at opposition when the two planets are closest together on the same side of the sun. That happened on July 20th, an occasion NASA used to snap a fresh photo with the Hubble Space Telescope.
Hubble bagged this handsome portrait of Saturn on July 4th when the opulent world was 839 million miles from Earth. It’s currently summer in Saturn’s northern hemisphere, which means that hemisphere is tipped toward the sun. Saturn has seasons because its axis is tilted 26.7°, just 3° more than Earth. Seasons hurry along on Earth, each lasting about 3 months, but on Saturn they linger for more than 7 Earth years apiece because that planet takes so much longer to orbit the sun. During its languorous orbit we see the north face of the rings followed by the south face and then a return to the north face in a repeating 29.5-year cycle.
Hubble found a number of small storms roiling the atmosphere and photographed multiple, parallel bands of clouds called belts that change color slightly from year to year. The ringed planet’s atmosphere is mostly hydrogen and helium with traces of ammonia, methane, water vapor, and hydrocarbons that give it a yellowish-brown color.
A closer look at the north polar region reveals a reddish haze that may be due to heating from increased summer sunlight. Scientists speculate the extra heat may either change the atmospheric circulation or possibly remove ices from haze particles. Saturn’s south pole, currently in the middle of the winter season, is just now appearing from behind the ring plane and appears pale blue in contrast.
A small telescope (above) will show two or three of the planet’s many concentric rings, but Hubble’s sharp view resolves much finely etched, nested ring structure. The rings are mostly made of pieces of ice, with sizes ranging from tiny grains to giant boulders. Just how and when they formed remains one of our solar system’s biggest mysteries. Given how bright — and presumably fresh — they are, they may have formed as recently as when dinosaurs roamed the Earth.
However or whenever they formed they won’t last forever.
“NASA’s Cassini spacecraft measurements of tiny grains raining into Saturn’s atmosphere suggest the rings can only last for 300 million more years, which is one of the arguments for a young age of the ring system,” said photo team member Michael Wong (U-C, Berkeley).
One school of thought holds that the rings formed when comets and asteroids crashed into one or more of the planet’s many moons, breaking them into shards which then fanned out to form the rings. Alternatively, they may be as old as Saturn itself, built from leftover icy debris that orbited the newly-forming planet.
You can see Saturn all summer long just to the left of brilliant Jupiter in the southern sky at nightfall. If you don’t have a telescope you can still detect Saturn’s rings because they give the planet an oblong appearance. Check it out!