[workitout]

Like the parent, this seems odd that just now in 2016 we find there might be another planet in our own solar system when planets are being discovered in other solar systems and galaxies all the time.

There's this from the article:

"For the first time in over 150 years, there is solid evidence that the solar system's planetary census is incomplete."

It's our _own_ solar system and we just now found this massive thing?

[lotharbot]

One of the main methods we use for finding planets in other systems is watching for them to cross our view of the star -- basically, looking for a star to slightly dim in a periodic fashion, something akin to an eclipse.

With objects in our own system that don't emit light of their own and are much farther away from the sun than we are, they'll never block the light from the sun. If by sheer luck they happen to pass in front of another star and temporarily block it, it's still difficult to figure out what the object was, how fast it was moving, and so on and therefore difficult to correlate with "something in our own system".

Keep in mind, the solar system is REALLY big. "Planet Nine" is proposed to be some 55+ billion miles away, or about six hundred times as far away from the Sun as Earth is.

[nkrisc]

Well, we've not yet found it. There is just a very good case for it's existence.

Also, it's arguably easier to find planets in other solar systems because from our vantage point we can observe the stars and measures the dips in light as the planet transits the star (from our perspective). We can't do that without our own solar system given we too are orbiting the same star as the planet we would want to detect.

Also, remember this planet has an orbital period of about 10,000 - 20,000 years, according to the article. It would have just barely completed one orbit since humans started farming.