Discovery of Uranus' Rings

We have discussed before that all the gas planets in the solar system have rings.  Even through a small telescope Saturn has visible rings, but Jupiter, Uranus and Neptune do not. So how did astronomers discover their rings in the first place?

Hubble image of Uranus and its rings

The rings around Uranus were discovered in 1977. Astronomers knew that Uranus was going pass in front of a distant star in the night sky, from Earth's perspective. They pointed their telescopes to towards the planet each night, and expected to see the planet block the light from the star only when the star was directly behind the planet. What they actually observed was the star flickering right before and right after is passed behind the planet. This meant that there must be some unseen object near the planet blocking the starlight! The only plausible explanation was that Uranus has very thin, dim rings that are not visible from telescopes here on Earth. In 1986, Voyager flew by Uranus and imaged the rings for the first time, proving  their existence. Since then, we have discovered rings around Jupiter and Neptune in similar ways.

Ring Around The.... Planets?

Open a new tab in your internet browser (yes, right now). Go to Google and pull up an image of Saturn (I don't care that you know what it looks like, just do it). Remember that picture, and look up a picture of Jupiter, Uranus and Neptune as well. Now if I start singing the song "One of these things is not like the other…" what would your answer be?...... The answer I was going for was Saturn! What's so different about Saturn? Well as you saw from the picture, Saturn has a beautiful ring structure and the other planets don’t….. Wrong! Believe it or not, all of the gas giant planets have rings! (Now if you didn't actually go to Google before, I bet you are now just to see if you can find a wiki page on ringed planets to see if I'm right.) 

 

Saturn's ring structure is very bright and prominent because it is thick and made mostly of ice which reflects light. The rings around Jupiter, Uranus, and Neptune are much thinner and are mostly made of rocks. Pictures of each planets rings are shown above. There's a big black spot over Neptune because Neptune is so bright compared to its rings that the planet's light needed to be blocked out so the rings were visible . Now when someone refers to Saturn as the ringed planet you can say "actually, all the gas giants have rings… but I know which one you mean."

Image credits: NASA/Voyager/J. Rayner/NSFCAM/IRTF