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About Uranus

by Carolyn Porco

What's interesting about my planet?

Well, you have to understand that I consider myself to be one of the most privileged human beings on the face of the earth because I person ally participated in the Voyager (robotic spacecraft: ed) mission to the outer solar system, and I was there for the encounters with Saturn, Uranus and Neptune. And I was a member of the Voyager imaging team for the encounter with Uranus, and then Neptune, so those two planets... I have a personal relationship with them practically, so they are all very exciting to me, so just the thought of studying any of them is... is like going home, almost...

As far as what I find personally exciting about Uranus, Uranus is a very puzzling object. It's tilted relative to its orbit... its axis is tilted some ninety-eight degrees, so it's one of the two or three oddball planets in the solar system that has such an exaggerated tilt, but it's the only large, gaseous planet that falls into that category, so it obviously went through a very catastrophic event. People believe it got hit by an Earth-, Mars- or Earth-sized object, sometime while it was forming, which tilted the planet on its side and caused it to have this bizarre rotation. And all the objects in orbit around it, the rings and the satellites are all in the equatorial plane, so they formed afterwards, obviously, or else they would not find themselves in the place that they do. So that's puzzling: is that really what happened? I mean, I just told you something that we believe to be true, but is that really what happened? Did a large proto-planet actually hit Uranus and cause it to tilt on its side?

If indeed that did happen, then it also has very interesting implications for the composition of the objects that orbit around Uranus because such an event would probably have spewed out materials from the proto-Uranus object, and the material that got spewed out into this disk would have been very different from the material that existed in the outer part of the (proto-planetary: ed) disk, for example, in composition. And that ties into the fact that the Uranian rings and the Uranian satellites are very spectroscopically peculiar compared to the objects that are orbiting around Saturn and Jupiter, for instance. (see the next update for more on HST and its instrumentation: ed.)

...The material, the dark material that we see in the Jovian and the Saturnian systems, that is, in the rings and in the satellites in orbit around those two planets, is very dark but it's red, and we are coming more to the idea that the material in those systems is organic... However the material, the dark material in the Uranian system is sp ectrally gray, that means it has about the same brightness across the visible portion of the spectrum, so it's different. Now, we don't know why it's different. And it may be compositionally different, it may be different because of some process that's going on in the Uranian system and has been going on since Uranus formed, we just donUt know the answer to that...

Planet Advocate Carolyn Porco further writes about The Earth-Uranus Connection


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