The Goblin Points to Presence of Planet X

The announcement of the discovery a new object in the outer solar system may bring us a step closer to the elusive Planet X (more recently dubbed Planet Nine).  This new dwarf object, known as 2015 TG387, is a distant member of the mysterious scattered disk of objects beyond the Kuiper Belt.  This particular object can travel so far away from the Sun during its orbit that it moves through the inner Oort cloud of comets, beyond 2000AU:

The newly discovered object is called 2015 TG387, is probably a small dwarf planet at just 300km across, and is incredibly far away. It is currently lying about two and a half times further away from the Sun than Pluto is.  It often reaches much further away. Its orbit takes it to about 2,300 AU — that is 2,300 times as far away from the sun as we are, and vastly more than the already huge 34 AU that the distant Pluto sits at.(1)

The object’s vast orbit is so vast that it takes about 40,000 years to do one circuit around the Sun.  Yet, its orbit is highly eccentric.  It distance from the Sun varies from 64AU at perihelion to 2037AU at aphelion.  Incredibly, then, it skirts both the Kuiper Belt and the inner Oort cloud, transiting between these quite distinct belts of objects.

As more objects are discovered between the Kuiper Belt and the inner Oort cloud (a torus-shaped disk of comets), the classifications of these objects are becoming more complex.  A significant factor is whether these objects have perihelia within 40AU, which might briefly bring them within the influential scope of the planet Neptune.  Extreme scattered disk objects fall into this category.  Significantly, 2015 TG387 is fully detached from this influence at perihelion, and may be considered to be an inner Oort cloud object. 

Importantly, its properties fit with the Planet Nine clustering of scattered disk objects:

“2015 TG387 continues the longitude clustering trend seen for the inner Oort cloud objects and ETNOs, which might be caused by a massive planet shepherding these objects.” (2)

“If you look at Sedna, and you look at VP113, and you look at a few of the other extreme objects with these very distant orbits, they all are very similar,” [Scott] Sheppard [of the Carnegie Institution’s for Science] says. “They all are clustered on the same part of the sky, they all come to perihelion—their closest approach to the sun—at the same place, and you would expect that to be random across the sky. … That’s why we think there’s a bigger planet out there, because it’s shepherding these objects into these types of orbits.” (3)

In fact, it seems to fit amazingly well in computer simulations involving Planet Nine (as inferred from the clustering of ETNOs).  Indeed, without the shepherding presence of a significant Planet X object, it seems incapable of maintaining long-term orbital stability:

“Amazingly, in most simulations with a Planet X, we found 2015 TG387 librates in its longitude or perihelion, keeping it anti-aligned and thus stable with the eccentric Planet X for the age of the solar system. This longitude of perihelion libration is not seen in the the simulations without a Planet X. This supports the theory that a Planet X exists as 2015 TG387’s orbit was only determined after the basics of the Planet X orbit was realized, yet 2015 TG387 reacts with the planet very similarly to the other known IOCs [Inner Oort Cloud objects] and ETNOs [Extreme Trans-Neptunian Objects].” (2)

Finally, in an almost throw-away line which will most certainly set Sitchinite pulses racing, this:

“In addition, some 2015 TG387 clones obtain retrograde orbits yet still remain stable and anti-aligned with planet X for the age of the solar system, suggesting retrograde ETNOs should exist in most planet X scenarios. We further found that the planet itself might be on a retrograde orbit as 2015 TG387 and other ETNOs were similarly stable as in the prograde planet case.” (2)

2015 TG387 has been unofficially given the name ‘the Goblin’ by its discoverers (3).  As its name implies, it was originally discovered in 2015.  However, because its is so far away, it has taken three years to pin down its orbital path sufficiently accurately to determine its bizarre orbital properties.  It seems that other discoveries of distant outer solar system objects, made in the last few years, are similarly being scrutinised (3).  In the near future, these may offer  further tantalising evidence of the elusive Planet X.


Written by Andy Lloyd,

10th October 2018


1) Andrew Griffin “Scientists find mysterious object hovering at the edge of our solar system” 2 October 2018 with thanks to Lee

2) Sheppard, S., Trujillo, C., Tholen, D. and Kaib, N. “A New High Perihelion Inner Oort Cloud Object” (September 28, 2018)

3)  Jay Bennett “New Discovery Stirs Up Signs of the Elusive Planet 9” 2 October 2018, Read more: with thanks to Lee

Image Credits:  Roberto Molar Candanosa and Scott Sheppard, Carnegie Institution for Science

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