Up in the air: Searching the dark for ‘Planet X’
February 7, 2016 · Planet X
We had a great Public Night at our Dark Sky Observatory at Appalachian State at the end of January, on a modestly cold evening with a clear sky and no wind and good astronomical “seeing.”
One of our targets was Uranus, the second-farthest planet in our solar system now that we demoted Pluto. Even at a distance of 2 billion miles from us it appeared as a small disk, distinctly different from the point-like stars.
I got questions about the new “Planet X” that may have been discovered to live in the outer realms of our system, in the region known as the Kuiper Belt. Announced in a publication this month, the planet’s existence is suggested by the alignment of the orbits of several other Kuiper Belt objects. The as-yet-unseen planet has gravitationally shepherded those other objects’ orbits into one quadrant of the solar system. Co-author Michael Brown had previously discovered other such objects. I remember when he found his first one and wanted to name it Xena, after the character in TV shows and graphic novels. The International Astronomical Union, the group that had booted out Pluto, said no, and it ended up named Eris. I once asked Brown if that bothered him; he was actually OK with it.
At this point we only have an idea of the size, shape and alignment of Planet X’s orbit, but we do not know where the planet is in that giant ellipse. It may take several years of tracking its gravitational effects on its neighbors to pinpoint the location, although searches along its orbit may find it first.
Similar mathematical techniques were employed by the late Clyde Tombaugh to predict where to look to discover Pluto in 1930. He discussed his discovery in an interesting talk at Appalachian State about 25 years ago. I got to meet the man who was at that time the only living discoverer of a planet. Can I still count that?
We can expect more discoveries of KB objects, especially when the Large Synoptic Survey Telescope starts observing in 2020. It will likely discover hundreds if not thousands of new members of the solar family. The LSST will have a relatively large field of view, seven times the angular size of the moon, and its 3.2-gigapixel camera will image all of the night sky that can be seen from Chile, every three nights.
So, we are again at a new dawn of discovery, extending our knowledge of our neighborhood. And, the best part is that we will probably discover things unexpected and unimagined!