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[Theme Song]

Let's play "What If?"

What if I told you that the solar system was nestled in the center of a giant fluffy ice cloud? A cloud that was filled with billions maybe trillions of objects? Even though we know this cloud is there, we don't really have any proof because no one's ever really seen it. 

Oh! And what if there was an extra planet hiding out there? 

Welcome to the messed up marvel that is the Oort Cloud: a zone around the solar system that astronomers agree is there even though its existence hasn't been proven by direct observation. We know it's there because, well, it being there answers a lot of important questions. 

It was first theorized in 1950 by Dutch Astronomer, Jan Oort. Not one to shy away from big, seemingly unanswerable questions, Oort was the first person to discover evidence of dark matter, and to calculate exactly where we are in the milky way: 19,200 light years from the center, for your edification. 

So, in 1950 Oort was trying to solve another puzzle: where do all the comets come from? You see, comets burn up as they fly by the sun and melt in the spectacular process that creates those gorgeous tails. After 100 or so trips around the sun, many comets eventually disappear. And yet, fresh comets just keep a'coming... often arriving by a wildly elliptical orbits that suggest they come from far, far away. 

Oort calculated that these long period comets, the ones with the biggest, most extreme orbits, must come from a reservoir of comets in an icy cloud on the edge of the solar system. These comets start off as humble ice balls that hang out in the cloud until a passing star, or the gravitational forces of the Milky Way itself push them toward the inner solar system. 

But how do these ice balls get there in the first place? The prevailing theory is that they're planetesimals: failed, would-be planets that condensed in the disk of gas surrounding the newly formed sun four and a half billion years ago. These icy planetesimals were then scattered by the gravitation of the gas giants, especially Jupiter. 

So, based on what we know so far about comets, their composition and their orbits, we think that the Oort cloud holds anywhere from a few billion to two trillion icy objects made of ammonia, water, and methane. 

And we think the cloud begins around two thousand astronomical units away from us -- one AU is the distance from earth to the sun -- and it could be as much as one light year thick. 

We also know that the Oort cloud continues to supply us with stupendous comets like Hale-Bopp, and it has a few other surprises. 

In the past decade or so, two large objects have been identified which scientists think may be in the inner Oort Cloud. Sedna, discovered in 2003, is an object three quarters the size of Pluto, and now they found another one called VP113. Intriguingly, the nature of these objects' elliptical orbits suggests that they're being disturbed by another massive but as yet unknown body. This potential planet which may be up to ten times the size of Earth seems to be shepherding other inner Oort Cloud objects into similar orbital configurations. 

So, just over 60 years after Jan Oort put pencil to paper, scientists may be looking at the first evidence of the cloud that bears his name.

Now, while you're digesting all that, we'll be around to answer any of your questions as best we can.

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