Scholz's star is a star that is believed to have crossed through the Oort Cloud, making it the ONLY known star to do this, and the closest one to us. I believe the orbit is something like every 36 million years, which seems to coincide with past extinction events. There seems to be a pattern with extinction events, if I'm not mistaken, that is close to this orbital period.
There is supposedly some talk about another large planet outside Pluto, but none of this has been confirmed. Hopefully things like this will be answered with the James Webb telescope, slated to launch at the end of 2018. This will be an engineering marvel considering the sheer size and the fact that it needs a Sun Shield to protect its instruments.
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