Getting to know 2015 TG 387, aka "the Goblin," an unconfirmed dwarf planet lurking in the Ort cloud

Originally published at:


The paper estimates a radius of 150 km.

The video depicts the object as round. Yet…

notes that Mimas (r=198.2 km) is “round (smallest body currently known to have an ellipsoidal shape, but not in hydrostatic equilibrium)”.

so, the artist’s depiction-- based on scant evidence, mind you-- is dubious. I’d have thought that mass was the controlling factor, but all we have to go on is a rough estimate of radius, based on albedo.


What sign is it in, and what significance will astrologers assign to it?



It’s probably pretty much a constant for people, and most civilizations.


I was out of the loop on space for a while, and only recently got into dwarf planets when I got a book for my daughter from the library. I didn’t realize Pluto was in such good company now. Now I want to go back to 2006 when everyone was whining about Pluto’s demotion and say “well, you have two choices. cut out one, or memorize all 13. Just how many pizzas did your mom serve, eh, tough guy?”


I remain curious if they will end up discovering the potential/likely large planet (~5x Earth’s mass) that used to be called planet X/10, but with Pluto’s demotion is now called Planet 9. It seems there is a decent amount of consensus that it exists, based on orbit perturbations of some of the outer bodies in the solar system.


I’m sure DrBecky will cover it in an upcoming Night Sky News.

Oh wait, I thought you said astro -blogers.

1 Like



Still waiting for that superjovian and its …interesting colonizers.


Citations please.

Planet X was a theoretical construct of Percevel Lowell based on perturbations in Neptune and Uranus, and Tombaugh’s assignment was to find it. But Pluto turned out to be too small, and the search for yet another planet resumed.

However, it turned out that Lowell was using a inaccurate estimate for Neptune’s mass, and in 1993, scientists redid his calculations using Voyager 2’s data.

No planet X!

The new Planet 9 hypothesis is based on an analysis of Sedna’s orbit.

In summary:

1846: Le Verier predicts position of Neptune, based on irregularities in orbit of Uranus. Berlin Observatory confirms position immediately after receiving prediction
1906: Percivel Lowell proposes a trans neptunian planet based on pertubations in Neptunes orbit.
1930: Clyde Tombaugh finds Lowell’s planet. But it’s too small. The search resumes!
1978: Pluto has a moon. Charon. Scientists use these new observations to calculate a new mass for Pluto. Wow. Pluto is really small.
1989: Voyager 2 visits Neptune.
1993: Scientists use new data to analyze Lowell’s hypothesis. There’s no discrepancy that would necessitate an extra planet.

2003: Sedna discovered. At r=995 km, it’s not a planet.
2005: Eris discovered (r=2326 km). It might be even larger than Pluto (r=2377 km). Ten planets at last! Makemake (r=1430km) discovered. Eleven Planets. Haumea (r=1560 km) discovered. Twelve Planets. This is getting ridiculous.
2006: New Horizons launched
2006: Eris, Pluto, Haumea, Makemake, and a bunch of other objects reclassified as dwarf planets.

2015: New Horizons reaches Pluto. Hey, this thing looks like a Planet! And it’s bigger than Eris! Oh, well, what’s done is done.
2016: New Horizons maneuvers towards Arrokoth.
2016: Planet 9 hypothesis proposed, based on orbits of several Kuiper Belt Objects including 2012 VP113 and Sedna. Several of these objects are now known as Sednoids.

2019: New Horizons visits Arrokoth.

Probably contains errors, but I hope it demonstrates the discontinuity between Planet X and Planet 9. At the time Pluto was demoted, there wasn’t enough data to propose a super earth in the outer solar system.


Every time I read about this stuff, I think about Lovecraft’s The Whisperer in Darkness:

Astronomers, with a hideous appropriateness they little suspect, have named this thing “Pluto”. I feel, beyond question, that it is nothing less than nighted Yuggoth—and I shiver when I try to figure out the real reason why its monstrous denizens wish it to be known in this way at this especial time.


What, no Nibiru?!

1 Like

The modern “Niburu” is this theory

1 Like

Wait, is this an Oort cloud object? Last I checked, we weren’t 100% sure the Oort cloud even existed, and that if it did, it’d start about twenty times (~2000 AU) as far out as this thing is supposed to be.

To be clear, I’m not an Oort cloud truther; I get that there’s a ton of circumstantial evidence for it. But if we’ve observed any specific thing that makes it up, I missed the memo.

1 Like

I wish I looked that sophisticated when I had this thought. I was on the can reading to my toddler so she wouldn’t tear up the house while I was indisposed.

But seriously, once you find out about Haumea how could you not?

1 Like

It’s on YT. What can ya do.

Here’s the paper:

A New High Perihelion Inner Oort Cloud Object: 2015 TG387. They cite

“Inner Oort Cloud objects (IOCs) or Trans-Plutonian objects (TPOs) have perihelia greater than 50-60 au and are too far from the giant planets to be strongly influenced by them (Gomes et al. 2008).”

Gomes, R., Fernandez, J., Gallardo, T., & Brunini, A. 2008, in The Solar System Beyond Neptune, ed. M. Barucci et al. (Tucson, AZ: Univ. Arizona Press) pp. 259273

and a preprint of that is available here, though thhe text warns non authors to go away. Oh well.

(part V: The Scattered Disk: Origins, Dynamics, and End States (pp. 259–273)), but that refers to

PART II: TRANSNEPTUNIAN OBJECT POPULATIONS Nomenclature in the Outer Solar System (pp. 43–57)
B. Gladman, B. G. Marsden, and C. VanLaerhoven


We will not spend a great deal of time dealing with Oort cloud nomenclature, but feel obligated to put an outer bound on the scattering disk. Although the production mechanism of the Oort cloud and the past galactic environment of the Sun are unclear, since we are basing our definitions on thecurrent dynamics we ask the question: Where does the cur- rent dynamics of a distant object become dominated by ex- ternal influences? Dones et al. (2004) show that a very evi- dent transition in the dynamics begins at a = 2000 AU for TNOs scattered out by the giant planets; for a > 2000 AU the galactic tidal field and passing stars cause appreciable alteration of the perihelia and inclinations. We thus adopt a = 2000 AU as the formal (somewhat arbitrary) beginning of the inner Oort cloud (and thus end of the Kuiper belt). Objectswitha>2000AUbutwithTJ<3.05andq< 7.35 AU would be considered JFCs since their evolution is dominated by Jupiter (see chapter by Duncan et al.).

Note that the definitions above give, for the first time, a formal sharp demarcation of the Kuiper belt, which is bounded on the inner and outer “a” boundaries by the Cen- taurs and Oort cloud, and above in eccentricity by the JFC population (defined by the Tisserand parameter). This definition makes SDOs (see below) part of the Kuiper belt.

The Dones paper is here

edit: enough with trying to play pro astronomer: the press release says:

The new object is on a very elongated orbit and never comes closer to the Sun, a point called perihelion, than about 65 AU. Only 2012 VP113 and Sedna at 80 and 76 AU respectively have more-distant perihelia than 2015 TG387. Though 2015 TG387 has the third-most-distant perihelion, its orbital semi-major axis is larger than 2012 VP113 and Sedna’s, meaning it travels much farther from the Sun than they do. At its furthest point, it reaches all the way out to about 2,300 AU. 2015 TG387 is one of the few known objects that never comes close enough to the Solar System’s giant planets, like Neptune and Jupiter, to have significant gravitational interactions with them.

2300 AU is greater than 2000 AU.


Ah, okay. Those cunning elliptical orbits. Stupid ovals, be more circles!

This topic was automatically closed after 5 days. New replies are no longer allowed.