You Oort to Know

The Oort cloud is a sphere of ice and rock and lots of other frozen stuff that marks the limit of our Sun's gravitational pull. It is hypothesized that comets come from the Oort cloud, getting knocked out of it in any number of ways, and then getting drawn in towards the Sun (and it is likely Earth's oceans came from Comets - thus, the Oort cloud). It is also HUGE - another lesson, folks: Everything's bigger than you can imagine. The Oort cloud represents the end of our Solar System - our home - and it stretches out to 1 light year in a circle around the sun. For perspective, our nearest stellar neighbor, Proxima Centauri, is 4 light years from the Sun. Here's another picture that might give you a sense of the scale:
As you can see, what we traditionally think of as the Solar System - the planets in their orbits - is really, really small compared to what is actually our Solar System - the Oort Cloud and everything within it. So much bigger, in fact, that there's a growing realization there might be other planetoids, like Pluto, hiding out there, hitherto undetected. One such new plaentoid was found recently, named Sedna:
Read the above picture from upper left (inner solar system) to upper right (outer solar system, with Sedna indicated), down to lower right (Sedna's orbit as compared to Neptune and the Gang) than lower left (Sedna's orbit as compared to the Oort Cloud), each frame encompassing the previous. 

If I've done my job, this should all remind you of something, but if not, check back in in a few days - payoff's a'coming.

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