Is There a Planet 9?

All of the 8 planets of the Solar System and most of the minor objects you have learned about so far were discovered long before any of us was born (yes, even your instructors…). You may be part of a privileged few to be alive when a new planet is found in our Solar System! Some astronomers claim that you will likely get to lay eyes on the first images of it very soon, but a growing number of astronomers are highly skeptical that it exists at all.
We have yet to actually observe this cold, dark denizen of our planetary family, but there are a number of pieces of evidence that suggest that it is out there. But to find Planet 9, we need to narrow down where to look, and look carefully. Meanwhile, other researchers have come up with alternative non-Planet-9 explanations for the clues that seem to point to the existence of another planet in our Solar System, and these scientists are making predictions of their own as to what we might see in the dim, dark outer limits of our Solar System. Woo! Weird phenomena. Competing theories to explain them. Predictions for observational tests. Science in action!! :)
This week, we'd like you to do a little research on the scientific debate over the mysterious Planet 9 to learn more about why some scientists think it might be out there, and what it might be like if it is, and why other scientists think you might not need a Planet 9 to explain some of the unexplained observable characteristics of our planetary system. Feel free to take one side of this scientific debate or the other. Or present both arguments, it's up to you!
The articles you select (and you'll likely have to read more than one) can come from any of the previously given Reading Summary websites - those are probably good places to start - or from one of your choosing. Other good places to look for the latest on this object are Scientific American, Astronomy, and National Geographic Magazines. Each of those have recently had great articles on the topic.
Discussion Suggestions

1. What is the evidence for Planet 9's existence (in other words, why do we suspect it's out there?).
2. How are astronomers searching for it?
3. Roughly where "out there" is it believed to be located? Describe its predicted general location with respect to objects or structures you have learned about in the Solar System.
4. Based on the influence it is apparently having on the Solar System, what are Planet 9's inferred properties? eg.: How big is it suspected to be? What is it's temperature? Which object in the Solar System is it predicted to be most like?
5. How do you think this object got to its current predicted location? Knowing what you now know about the Solar System, could it have formed there? Come up with your own hypothesis and discuss - there's no right or wrong answer for this one so give it a shot!
6. Discuss the alternative explanation for the solar system observations that seemed to point to Planet 9. How does this explanation connect to what you have learned about the formation of our Solar System? Are there any drawbacks to this explanation? What does this theory predict we might see with more sensitive telescopes?