January 5, 2020 – Planet Nine, or Ten?

In my October 8, 2017 article I wrote about the suspected existence of a planet beyond the orbit of Neptune.  It was called planet nine in light of Pluto having been demoted to Dwarf Planet status.  There has been considerable interest in reinstating Pluto as a full-fledged planet so this mystery planet might become planet ten.  Personally, I say Pluto is a planet.  Nevertheless, I will go with planet nine.

Where is planet nine?  In 2017 a couple of groups searching for it thought they had its location identified and hoped to spot it as its location came into their skies.  Well, no luck.  So, the search continued and continues today.  Why is it so elusive?

It’s really far away, way out there, in the Kuiper Belt.  That’s where Pluto resides but Pluto is at the very inner edge of the belt and planet nine is thought to be 3-4 times that distance, at its closest!

Is there evidence for its existence?  Yes, well maybe, in the form of orbital characteristics for other Kuiper Belt objects.

Way back when Neptune was discovered, it was not visible without optical aid. Its existence wasn’t considered until someone noticed that the orbit of Uranus was being perturbed.  It took the predictive power of mathematics (orbital dynamics) to determine where to look for this possible planet beyond Uranus.  Urbain -Jean Joseph Le Verrier and John Couch Adams did the mathematics, then Johann Gottfried Galle used a telescope to spot Neptune.  Pluto was similarly discovered in this way by Clyde Tombaugh, using the calculations of Percival Lowell and W.H. Pickering.

Astronomers peering way out past Neptune have identified around a dozen planetoids and dwarf planets in the Kuiper Belt.  In recent years a couple of groups of astronomers have also been keeping track of these Trans Neptunian Objects (TNOs) and finding new ones.  TNOs are objects that orbit the Sun outside of Neptune’s orbit.  Pluto is the first TNO discovered and is labeled a TNO even though its orbit briefly takes it closer to the Sun than Neptune.  Someone noted a peculiar commonality with the TNOs beyond Pluto.  Once their orbits were determined their closest approachs to the Sun (perihelion) were similar.  That seemed odd.

The astronomers (Konstantin Batygin, Mike Brown, Scott Sheppard, Chad Trujillo, and David Tholen) have been working out hypotheses to explain the perihelion distance coincidences.  The one they all have found most compelling is that a planet of between 5 and 15 Earth masses might be out there acting as a shepherd.  A planet this size in its own orbit around the Sun could be keeping these KBOs orbits stable.

If it’s there it will be found.

Some of the KBO names/nicknames:  Sedna, “Biden”, “The Goblin”, and “Far Out”

What’s in the Sky?

Venus is brilliant in the southwest

January 7; 1 hour after sunset; east:  A bright waxing gibbous Moon is close to Aldebaran in Taurus