Niku, Drac and L91 Perturbed by Planet Nine…or Something Else?

Dr Konstantin Batygin and Dr Mike Brown argue in their latest paper that the retrograde Kuiper Belt Objects Niku and Drac could have once been extended scattered disk objects (1).  If you have been following these blogs during 2016, it will come as no surprise to you to hear that the influence which perturbed them into their anomalous current orbits was Planet Nine, the 10+Earth-mass planet lurking several hundred-plus Astronomical Units away, whose gravitational influence seems to be influencing the objects in and beyond the Kuiper Belt beyond Neptune (2):

“Adopting the same parameters for Planet Nine as those previously invoked to explain the clustering of distant Kuiper belt orbits in physical space, we carry out a series of numerical experiments which elucidate the physical process though which highly inclined Kuiper belt objects with semi-major axes smaller than a < 100 AU are generated. The identified dynamical pathway demonstrates that enigmatic members of the Kuiper belt such as Drac and Niku are derived from the extended scattered disk of the solar system.” (1)

The discovery of the unusual highly inclined Trans-Neptunian Object Niku was announced in August (3), whose unusual orbital path is similar to 2008 KV42, nick-named Drac for its ability to climb walls (4).  The Caltech astronomers, who are currently hunting for the elusive Planet Nine (5), have just published some dynamical calculations to demonstrate a theoretical pathway leading to the currently observed anomalous orbits of these enigmatic objects.  Prior to the speculation about the existence of Planet Nine, it was thought that the two retrograde objects must have originally arisen in the inner Oort Cloud and are following a journey of gentle orbital flux which will eventually turn them into Halley-comet like objects (6).


This would appear to be the case with a new object, unofficially named L91, whose anomalous properties were also described publically for the first time today,  (7).  The distant object, which has a 20,000 year orbit, was first discovered back in 2013 by the Outer Solar System Origins Survey.  Although its size and mass are not yet known, its orbit is truly expansive, and sits almost in the same plane as the planets.

“L91’s elliptical orbit never brings its closer to Earth than about 50 times the Earth–Sun distance (or 50 astronomical units, au). At its farthest, the object is 1,430 au away. That means its orbit is more stretched out, and centred farther from the Sun, than previously discovered worlds such as Sedna and 2012 VP113.

“The location and trajectory of L91 make it “fascinating”, said Michele Bannister, an astronomer at Queen’s University Belfast, UK. L91 may have been tossed into its remote orbit by gravitational interactions with Neptune in the distant past. “This one is right on the hairy edge of everything,” says Nathan Kaib, an astronomer at the University of Oklahoma in Norman.  Bannister and her colleagues think the object may have been banished as far as 2,000AU from the Sun before it began easing its way back towards the star’s gravitational pull. L91’s orbit “is changing in quite a remarkable way”, she said.” (8)

But the Caltech astronomers think otherwise, and consider these three objects to be yet more evidence for the existence of Planet Nine.  There is a healthy scientific debate going on here about the possible perturbing influences that are shepherding these distant scattered objects.  Possibilities include galactic tidal forces, passing stars and undiscovered planets of various sizes lurking unseen in the outer solar system.  As one might imagine, astronomers have different opinions, and often find themselves drawn to particular pet theories.  Sometimes science sees conviction turn to belief.  Currently, in the one corner we have the Caltech team, and in the other the OSSOS team.

An Artist's impression of Planet Nine. Image credit: Caltech/R. Hurt (IPAC)

An Artist’s impression of Planet Nine. Image credit: Caltech/R. Hurt (IPAC)

I’ve been keeping in touch with my ‘man on the ground’ at the American Astronomical Society’s Division for Planetary Science meeting in Pasadena this week about how this lively debate is going!  It seems that the Caltech team have quite a way to go before the convince many of their colleagues in the astrophysics community that Planet Nine is for real.  One of the points they make is that Planet Nine’s effects upon the solar system are many and varied.  The frequent need to bring in a large undiscovered planet to solve various anomalies and solar system riddles is an argument I have often used myself down the years.  Individually, each problem which can be solved by the distant presence of Planet X does not, in itself, provide proof.  But when you start to mesh together multiple anomalies, then a more comprehensive picture emerges which calls for another planet.  the case for Planet X becomes compelling.  Dr Mike Brown put it this way at the conference to assembled science journalists (many of whom might have been expectant of a more exciting announcement!):

“At this stage we have so many lines of evidence that there’s a massive planet out there that, if there’s not a massive planet out there, it has to be that there was one there yesterday and disappeared.” (9)

Two cases in point are two areas of research already described in previous editions of this blog, but which were more publicly aired to journalists at the conference.  The first was the anomaly of the Sun’s tilt (9); the second the apparent integer ratio relationship between the orbits of several extended Kuiper Belt Objects, implying orbital resonances with an as yet unidentified giant planet (10, 11).  In the end, only the amassing data will provide us with the real truth, and as more of these objects are discovered and catalogued (exponentially), that  truth draws rapidly closer.  My bet is one something bigger and further out than Mike Brown’s Planet Nine.  L91 might be one of the first clues pointing to the distant perturbing influence of a highly elliptical planetary object which, at its furthest reach, brushes the very fringes of the inner Oort Cloud – an object I described in these terms over ten years ago (12).

Update 31/10/16

There have been a lot of scientific publications released this month relating to the hunt for ‘Planet Nine’.  What has been lacking is the hoped-for announcement of its discovery.  As yet, there has not been a direct observation of this proposed planet, despite the endeavours of several international teams hungry to have their names written into the history books.  In particular, no announcement from Drs Brown and Batygin, despite several nights spent on the Subaru telescope.  In the war of attrition between rival camps hoping to solve the mysteries of the outer solar system, backers of ‘anything-but-Planet-X’ seem to have edged forward.  My belief is that the object is larger, and more distant than the Caltech astronomers have posited (although they did seem to leave some room open for this possibility in their original paper (2)).  In which case, a substantial, distant Planet X body would be potentially affecting comets within the inner Oort Cloud, perturbing their orbits and periodically sending some our way.  This thinking was used by earlier sub-brown dwarf researchers, who continue to hunt for a massive planet ~ 20,000AU distant in the outer Oort Cloud (13).


Perhaps, though, it is the much closer inner Oort Cloud which should be scrutinised for a similar non-random distribution of comets.  The announcement of the discovery of the distant object L91 by the Canadian Outer Solar System Origins Survey team this month may mark a watershed moment for objects originating from this zone as a result of a distant brush with Planet X (14).  Recent statistical analyses, echoing the previous work of John Matese’s team (15,16), and John Murray (17), may re-vitalise such arguments:

“Further strategies involve examining Planet Nine’s own possible gravitational influence on a variety of other bodies. Astronomers Yuri Medvedev and Dmitri Vavilov at the Institute of Applied Astronomy of the Russian Academy of Sciences looked at 768 comets entering the solar system for the first time, noting five that might have came close to Planet Nine—whose gravity would have altered their paths—sometime in the past.

Their analysis suggests that “maybe Planet Nine made these comets go into the solar system,” Vavilov says. “We think comets could help narrow down Planet Nine’s location. It would help to find other comets.” [Scott] Sheppard [of the Carnegie Institution for Science] says he would “be wary about using comets to help find Planet Nine, since there may be a lot of forces besides Planet Nine that could influence the comets’ orbits. … Still, while I’m skeptical, it could be helpful.” (18)

This latest analysis hopes to further constrain the position of the Planet X body now so keenly sought (19).  Perhaps re-visiting the previous work on non-random patterns of long-period comet orbits might be helpful?  The truth might lie somewhere between Caltech’s Planet Nine and Matese’s Tyche.


Written by Andy Lloyd,  18th – 31st October 2016


1)  Konstantin Batygin & Michael Brown “Generation of Highly Inclined Trans-Neptunian Objects by Planet Nine” 17th October 2016

2)  K. Batygin & M. Brown “Evidence for a Distant Giant Planet in the Solar System” 20th January 2016, The Astronomical Journal, Volume 151, Number 2,

3)  Ying-Tung Chen et al “Discovery of A New Retrograde Trans-Neptunian Object: Hint of A Common Orbital Plane for Low Semi-Major Axis, High Inclination TNOs and Centaurs” 5th August 2016, ApJ Letters,

4)  Ian O’Neill “Kuiper Belt Object Travelling the Wrong Way in a one-way solar system” 5th September 2008

5)  Andy Lloyd, Could Subaru Spot Nibiru? 19th September 2016

6)  Andy Lloyd “Going the Wrong Way Round” 14th August 2016

7)  Adam Mann “New icy world with 20,000-year orbit could point to Planet Nine” 17th October 2016

8)  Alexandra Witze “Astronomers spot distant world in Solar System’s far reaches” 18th October 2016

9)  Alan Yuhas “A possible ninth planet may be the reason for a tilt in our solar system” 19th October 2016 thanks to Lee

10)  PhysOrg “More evidence for ninth planet roaming solar system’s outer fringes” 19th October 2016

11)  Renu Malhotra, Kathryn Volk & Xianyu Wang “Corralling a Distant Planet with Extreme Resonant Kuiper Belt Objects,” 20th June 2016, Astrophysical Journal letters,

12)  Andy Lloyd “Dark Star: The Planet X Evidence” Timeless Voyager Press 2005

13)  Matese and Whitmire “Searching the WISE Preliminary Catalog for Massive Planets in the Oort Cloud” EPSC-DPS Joint Meeting 2011

14)  Alexandra Witze “Astronomers spot distant world in Solar System’s far reaches” 18th October 2016

15)  John Matese et al “Cometary Evidence of a Massive Body in the Outer Oort Clouds” 1999, Icarus. 141 (2): 354

16)  John Matese et al “A Widebinary Solar Companion as a Possible Origin of Sedna-like Objects” 2006, Earth, Moon, and Planets. 97 (3–4): 459–470

17)  John Murray “Arguments for the Presence of a Distant Large Undiscovered Solar System Planet” 1999, Monthly Notices of the Royal Astronomical Society. 309 (1): 31–34

18)  Charles Choi “Closing in on a Giant Ghost Planet: Scientists have shrunk the hunting ground for the mysterious Planet Nine by half” 25th October 2016

19)  Yurii Medvedev & Dmitrii Vavilov “Position of Planet X obtained from motion of near-parabolic comets” October 2016, American Astronomical Society, DPS meeting #48, id.#120.01….4812001M

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