Poor Uranus. Besides having a name guaranteed to make 12-year-old-boys giggle*, to most people it lacks any sort of interest. It isn’t huge, like Jupiter, or bright, like Venus, or shine with a striking red color, like Mars. It doesn’t have giant glorious rings like Saturn… but it does have rings, and sometimes they can be pretty cool too.
Uranus orbits the Sun once every 84 years (hey, I’m 6 Uranus months old!), and that means that once every 42 years, the Earth and Uranus line up in just the right way that we see those rings edge-on. That’s useful– it can help us measure how thick the rings are, for one. For another, very faint parts of the ring can be seen more easily since the brighter main rings don’t drown them out.
Earth passed through Uranus’s ring plane in mid-August. Since the rings were only discovered in 1977, it’s the first time this event has ever been studied! Several telescopes were trained on the green giant to see what they could see, and that includes Hubble. On August 14, just a week ago, here is what it saw:
How cool is that? The inner and outer rings can both be seen (the outer rings were discovered in 2005 in a Hubble image; humorously they were in an earlier 2003 image but overlooked because they were so faint). The fan shape in the image is scattered light from the planet itself. Oh– note the scale bar, showing 20,000 miles/32,000 km. The Earth, for a sense of scale, is 8000 miles/12,800 km across.
Hubble wasn’t the only ‘scope to gander at the planet. From the Keck 10-meter ‘scopes in Hawaii, here is a long tease of the coy Uranus as it slowly and shyly turned sideways over 7 years:
As Uranus regally orbits the Sun, we slowly get a different view of those rings. Those images were taken in the infrared, and in some of them you can see bright spots on the planet, which are clouds and storms. In the earlier images you can see that there are many rings, like Saturn, but that gets harder to see as our view gets narrower.
Did I mention that Uranus was 2.7 billion kilometers away when these images were taken? Man, that’s a long way off.
In the above Keck image, we’re zoomed in a bit. The rings are labeled (Epsilon is the brightest, and Zeta the closest to the planet surface). What struck me with these images is that in the last one, you can see a bright spot in the rings. That means they aren’t smooth, like Saturn’s! They’re lumpy. Some locations in the rings have more junk in them than others.
Uranus’s rings, like Saturn’s, aren’t solid: they’re made of up of countless chunks of ice. The rings of Uranus are darker than those of Saturn, and I think thicker (at SpaceFest last week, Carolyn Porco noted that Saturn’s rings are literally a few meters thicks, yet hundreds of thousands of kilometers across). As we passed through the ring plane, we saw first the part of the rings where the Sun was shining down on them, and then after we passed through the plane we saw the dark side of the rings. These images are the first time anyone has ever seen this!
Astronomers will use these data to determine better the size, shape, and composition of the rings. Even though the Voyager 2 probe sped past there and took close up images, and we’ve been observing from Earth for years, there are still many mysteries about them. What is the source of the rings? Are there moonlets in the rings, like in Saturn’s, shepherding them and helping to keep them neat and narrow?
Uranus has been the butt of jokes for years (yes, I know, haha, spare me please) but in fact it’s a pretty cool place and worthy of a closer look… at least once every 42 years.
*The only time that I laughed at a Uranus joke (well, besides a few MST3K episodes) was in Futurama, when the professor invented a telescope that allows you to smell astronomical objects (called a smelloscope, natch):
FRY: This is a great, as long as you don’t make me smell Uranus. Heh heh.
LEELA: I don’t get it.
PROFESSOR FARNSWORTH: I’m sorry, Fry, but astronomers renamed Uranus in 2620 to end that stupid joke once and for all.
FRY: Oh. What’s it called now?
PROFESSOR FARNSWORTH: Urectum.
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